o Fish and Wildlife Coordination Act Report...This Fish and Wildlife Coordination Act (FWCA) Report...
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Prepared for U.S. Fish and Wildlife Service Denver, Colorado _______________________ Fish and Wildlife Coordination Act Report Moffat Collection System Project _______________________ October 4, 2016 URS Corporation 6200 South Quebec Street Greenwood Village, CO 80111 Prepared by Federal Action Agency U.S. Army Corps of Engineers Project Proponent Denver Water
Transcript of o Fish and Wildlife Coordination Act Report...This Fish and Wildlife Coordination Act (FWCA) Report...
Prepared for
U.S. Fish and Wildlife Service Denver, Colorado
_______________________ o
Fish and Wildlife Coordination Act Report
Moffat Collection System Project
_______________________
October 4, 2016
URS Corporation
6200 South Quebec Street Greenwood Village, CO 80111
Prepared by
Federal Action Agency U.S. Army Corps of
Engineers
Project Proponent
Denver Water
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Contents
1. EXECUTIVE SUMMARY ............................................................................................................... 1
2. INTRODUCTION ............................................................................................................................. 3
2.1 Purpose, Scope, and Authority .................................................................................................. 3 2.2 Relevant Prior Studies, Reports, and Previous Consultation ..................................................... 4
3. DESCRIPTION OF THE STUDY AREA ...................................................................................... 7
3.1 Reservoirs ................................................................................................................................ 13 3.2 Other Facilities ........................................................................................................................ 17 3.3 River Segments........................................................................................................................ 17
3.3.1 Fraser River ................................................................................................................ 18 3.3.2 Williams Fork River ................................................................................................... 19 3.3.3 Colorado River ........................................................................................................... 20 3.3.4 Blue River .................................................................................................................. 21 3.3.5 South Boulder Creek .................................................................................................. 21 3.3.6 North Fork South Platte River .................................................................................... 22 3.3.7 South Platte River ....................................................................................................... 22
4. FISH AND WILDLIFE CONCERNS AND PLANNING OBJECTIVES ................................. 25
4.1 Aquatic Resources ................................................................................................................... 25 4.1.1 Study Area .................................................................................................................. 25 4.1.2 Regulatory Framework ............................................................................................... 25
4.2 Wildlife Resources .................................................................................................................. 26 4.2.1 Study Area .................................................................................................................. 26 4.2.2 Regulatory Framework ............................................................................................... 26
4.3 Vegetation Resources .............................................................................................................. 27 4.3.1 Study Area .................................................................................................................. 27 4.3.2 Regulatory Framework ............................................................................................... 27
5. EVALUATION METHODS .......................................................................................................... 29
5.1 Hydrologic Modeling .............................................................................................................. 29 5.2 Aquatic Resources ................................................................................................................... 34
5.2.1 Habitat Simulation Methods ....................................................................................... 34 5.2.2 Approach to Impact Analysis ..................................................................................... 37
5.3 Wildlife Resources .................................................................................................................. 39 5.4 Vegetation Resources .............................................................................................................. 39
6. FISH AND WILDLIFE RESOURCES – CURRENT CONDITIONS ....................................... 41
6.1 Aquatic Resources ................................................................................................................... 41 6.1.1 Gross Reservoir .......................................................................................................... 41 6.1.2 Other Project Facilities ............................................................................................... 42 6.1.3 Fraser River ................................................................................................................ 42 6.1.4 Williams Fork River ................................................................................................... 49 6.1.5 Colorado River ........................................................................................................... 52 6.1.6 Blue River .................................................................................................................. 53 6.1.7 South Boulder Creek .................................................................................................. 54 6.1.8 North Fork South Platte River .................................................................................... 55 6.1.9 South Platte River ....................................................................................................... 55
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6.2 Wildlife Resources .................................................................................................................. 57 6.2.1 Federally-Listed Threatened and Endangered Species ............................................... 57 6.2.2 State Threatened and Endangered Species and Species of Special Concern ............. 59 6.2.3 USFS Species ............................................................................................................. 61 6.2.4 CNHP Species ............................................................................................................ 62 6.2.5 Big Game .................................................................................................................... 63 6.2.6 Other Wildlife ............................................................................................................ 63 6.2.7 Raptors and Other Migratory Birds ............................................................................ 64 6.2.8 USFS Management Indicator Species and Wildlife Habitats ..................................... 64 6.2.9 Sensitive Areas ........................................................................................................... 64
6.3 Vegetation Resources .............................................................................................................. 65 6.3.1 Federally-Listed Threatened and Endangered Species ............................................... 65 6.3.2 USFS Species ............................................................................................................. 67 6.3.3 CNHP Species ............................................................................................................ 69 6.3.4 Vegetation Cover Types ............................................................................................. 69 6.3.5 Plant Communities of Concern .................................................................................. 74 6.3.6 Noxious Weeds .......................................................................................................... 74
7. FISH AND WILDLIFE RESOURCES – FULL USE OF THE EXISTING SYSTEM
WITH RFFAS.................................................................................................................................. 77
7.1 Aquatic Resource Impacts ....................................................................................................... 77 7.1.1 Depletion of Strategic Water Reserve Strategy .......................................................... 77 7.1.2 Combination Strategy ................................................................................................. 80
7.2 Wildlife Resources Impacts ..................................................................................................... 80 7.3 Vegetation Resource Impacts .................................................................................................. 81
8. DESCRIPTION OF ALTERNATIVES ........................................................................................ 83
8.1 Development of Alternatives ................................................................................................... 83 8.2 Description of Alternatives ..................................................................................................... 84
8.2.1 Proposed Action (Alternative 1a) ............................................................................... 84 8.2.2 Alternative 1c ............................................................................................................. 85 8.2.3 Alternative 8a ............................................................................................................. 86 8.2.4 Alternative 10a ........................................................................................................... 86 8.2.5 Alternative 13a ........................................................................................................... 86 8.2.6 No Action Alternative ................................................................................................ 86
9. PROJECT IMPACTS ................................................................................................................... 101
9.1 Aquatic Resource Effects ...................................................................................................... 101 9.1.1 Gross Reservoir ........................................................................................................ 101 9.1.2 Leyden Gulch Reservoir ........................................................................................... 101 9.1.3 Other Project Facilities ............................................................................................. 102 9.1.4 Fraser River .............................................................................................................. 102 9.1.5 Fraser River Tributaries............................................................................................ 106 9.1.6 Williams Fork River ................................................................................................. 110 9.1.7 Williams Fork River Tributaries .............................................................................. 111 9.1.8 Colorado River ......................................................................................................... 112 9.1.9 Blue River ................................................................................................................ 112 9.1.10 South Boulder Creek ................................................................................................ 113 9.1.11 North Fork South Platte River .................................................................................. 114 9.1.12 South Platte River ..................................................................................................... 115
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9.2 Wildlife Resources Effects .................................................................................................... 115 9.2.1 Federal Threatened and Endangered Species ........................................................... 115 9.2.2 State Threatened and Endangered Species ............................................................... 118 9.2.3 USFS Species ........................................................................................................... 122 9.2.4 CNHP Species .......................................................................................................... 123 9.2.5 Big Game .................................................................................................................. 123 9.2.6 Other Wildlife .......................................................................................................... 126 9.2.7 Raptors and Other Migratory Birds .......................................................................... 126 9.2.8 USFS Management Indicator Species and Wildlife Habitats ................................... 127 9.2.9 Sensitive Areas ......................................................................................................... 128
9.3 Vegetation Resource Effects ................................................................................................. 128 9.3.1 Federally-Listed Threatened and Endangered Species ............................................. 128 9.3.2 USFS and CNHP Species ......................................................................................... 129 9.3.3 Vegetation Cover Types ........................................................................................... 130 9.3.4 Plant Communities of Concern ................................................................................ 130 9.3.5 Noxious Weeds ........................................................................................................ 131
9.4 Cumulative Effects Analysis ................................................................................................. 133 9.4.1 Aquatic Resources .................................................................................................... 134 9.4.2 Wildlife Resources ................................................................................................... 134 9.4.3 Vegetation Resources ............................................................................................... 135
9.5 Evaluation and Comparison of the Alternatives .................................................................... 135
10. RECOMMENDED FISH AND WILDLIFE CONSERVATION MEASURES ...................... 141
10.1 Aquatic Resources Mitigation ............................................................................................... 141 10.2 Wildlife Resources Mitigation .............................................................................................. 142
10.2.1 Endangered Species .................................................................................................. 143 10.3 Vegetation Resources Mitigation .......................................................................................... 144
10.3.1 Revegetation ............................................................................................................. 145 10.3.2 Noxious Weeds ........................................................................................................ 145 10.3.3 Wetlands and Riparian ............................................................................................. 145 10.3.4 Construction Phase Mitigation ................................................................................. 145 10.3.5 Special Status Plants at Gross Reservoir .................................................................. 145
11. REFERENCES .............................................................................................................................. 147
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Tables
Table 1 River Segments Study Area .................................................................................................... 17
Table 2 Moffat Collection System Diversion Points on Fraser River Tributaries................................ 19
Table 3 Modeled Average Annual Streamflow Effects ........................................................................ 31
Table 4 Modeled Average Annual Reservoir Volumes ........................................................................ 33
Table 5 Stream Segments Modeled with PHABSIM Habitat Simulations in the Moffat Study
Area ......................................................................................................................................... 35
Table 6 Periodicity of Fish Species in Streams in the Moffat Project Study Area ............................... 35
Table 7 PHABSIM Habitat Relationships Available for Stream Segments and Trout Species
and Life Stages in the Moffat Collection System Study Area ................................................. 36
Table 8 Summary of Alternative Components ..................................................................................... 84
Table 9 Permanent and Temporary Direct Effects on Terrestrial Wildlife Habitat for Each
Alternative ............................................................................................................................. 124
Table 10 Permanent and Temporary Direct Effects on Plant Species and Plant Communities of
Concern for Each Alternative ................................................................................................ 129
Table 11 Acres of Permanent and Temporary Direct Effects on Vegetation Cover Types for
Each Alternative .................................................................................................................... 132
Table 12 Summary of Direct and Indirect Effects to Fish and Wildlife Resources ............................. 137
Figures
Figure 1 Denver Water’s Collection System ........................................................................................... 8
Figure 2 Overview of Alternative Components ....................................................................................... 9
Figure 3 River Segments Overall Study Area........................................................................................ 11
Figure 4 Gross Reservoir Components .................................................................................................. 15
Figure 5 Proposed Action (Alternative 1a) Components ....................................................................... 89
Figure 6 Alternative 1c Components ..................................................................................................... 91
Figure 7 Alternative 1c Proposed Leyden Gulch Reservoir .................................................................. 93
Figure 8 Alternative 8a Components ..................................................................................................... 95
Figure 9 Alternative 10a Components ................................................................................................... 97
Figure 10 Alternative 13a Components ................................................................................................... 99
Appendix
Appendix A U.S. Fish and Wildlife Service Letter of Approval of Fish and Wildlife Coordination
Act (FWCA) Report and Acknowledgement that the U.S. Army Corps of Engineers
Responsibilities under the FWCA Have Been Met
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Acronyms
% percent
AF acre-feet
AF/yr acre-feet per year
ARNF Arapaho & Roosevelt National Forests
AWTP advanced water treatment plant
B1 outstanding biodiversity significance
B5 general biodiversity significance
BA Biological Assessment
BLM Bureau of Land Management
BMP best management practice
BO Biological Opinion
CDNR Colorado Department of Natural Resources
CDPHE Colorado Department of Public Health and Environment
CEC Chadwick Environmental Consultants
CEQ Council on Environmental Quality
CFR Code of Federal Regulations
cfs cubic feet per second
cm centimeter
CNHP Colorado Natural Heritage Program
Corps U.S. Army Corps of Engineers
CPW Colorado Parks and Wildlife
CR County Road
CRCA Colorado River Cooperative Agreement
C.R.S. Colorado Revised Statute
CWA Clean Water Act
DEIS Draft Environmental Impact Statement
Denver Water City and County of Denver’s Board of Water Commissioners
ECA Environmental Conservation Area
EIS Environmental Impact Statement
EPA U.S. Environmental Protection Agency
ESA Endangered Species Act
FEIS Final Environmental Impact Statement
FERC Federal Energy Regulatory Commission
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fish/ha fish per hectare
fish/mile fish per mile
FWCA Fish and Wildlife Coordination Act
GIS geographic information system
GPS global positioning system
ha hectare
I- Interstate
IFIM Instream Flow Incremental Methodology
IHA Indicators of Hydrologic Alteration
kg/ha kilogram per hectare
LEDPA least environmentally damaging practicable alternative
m meter
m2
square meter
MBTA Migratory Bird Treaty Act of 1918
Metro Robert W. Hite Treatment Facility
MIS Management Indicator Species
MMI Multimetric Index
Moffat Project
or Project Moffat Collection System Project
NDIS Natural Diversity Information System
NEPA National Environmental Policy Act of 1969
NWR National Wildlife Refuge
organisms/m2
organisms per square meter
PACSM Platte and Colorado Simulation Model
PCA Potential Conservation Area
PHABSIM Physical Habitat Simulation
PRRIP Platte River Recovery Implementation Program
RFFA reasonably foreseeable future action
ROW right-of-way
SEO State Engineer’s Office
S1 critically imperiled plant species
S2 imperiled plant species
Service U.S. Fish and Wildlife Service
SH State Highway
SPWRAP South Platte Water Related Activities Program, Inc.
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U.S. United States
U.S.C. U.S. Code
USFS U.S. Forest Service
USGS U.S. Geological Survey
YOY young-of-the-year
WQCD Water Quality Control Division
WTP water treatment plant
WUA weighted usable area
WWTP wastewater treatment plant
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1. Executive Summary
This Fish and Wildlife Coordination Act (FWCA) Report documents an analysis of the potential
consequences to fish and wildlife resources of the proposed Moffat Collection System Project (Moffat
Project or Project). The Project is proposed by the City and County of Denver, acting by and through its
Board of Water Commissioners (Denver Water) to develop 18,000 acre-feet per year (AF/yr) of new,
annual firm yield to the Moffat Treatment Plant and raw water customers upstream of the Moffat
Treatment Plant pursuant to Denver Water’s commitment to its customers. The major Federal action
analyzed in this FWCA Report and the associated Final Environmental Impact Statement (FEIS)
(Corps 2014) is the potential issuance of a Clean Water Act (CWA) Section 404 Permit by the U.S. Army
Corps of Engineers (Corps) for placement of fill material in jurisdictional waters of the United States
(U.S.), including wetlands, for the construction of an enlarged water storage facility.
The basic purpose of the Project is to increase reliability of water supply, reduce vulnerability of the
existing water collection system, increase flexibility within system operations, and to meet firm yield
water service obligations. The proposed Project would address an overall near-term water supply
shortage and the imbalance of water storage and supply between Denver Water’s North and South
systems.
Alternatives were developed based on requirements under the National Environmental Policy Act of 1969
(NEPA) regulations and Section 404 of the CWA. The alternatives analysis was conducted by the Corps,
with review and input from the U.S. Environmental Protection Agency (EPA), the Federal Energy
Regulatory Commission (FERC), the Colorado Department of Natural Resources (CDNR), and the
Colorado Department of Public Health and Environment (CDPHE) as Cooperating Agencies, and from
Grand County as a consulting agency. The alternative screening process used an integrated approach to
ensure that the range of alternatives carried forward for detailed analysis in the Environmental Impact
Statement (EIS) met the Project Purpose and Need, and were practicable and reasonable.
Six alternatives were analyzed in detail as part of the FEIS. Maps of these alternatives are provided in
Section 8.0.
Denver Water’s Proposed Action (Alternative 1a) – expansion of Gross Reservoir (additional
77,000 acre-feet [AF]), including the 5,000-AF Environmental Pool* for mitigation
Alternative 1c – Gross Reservoir expansion (additional 40,700 AF)/New Leyden Gulch Reservoir
(31,300 AF)
Alternative 8a – Gross Reservoir expansion (additional 52,000 AF)/reusable return flows/gravel
pit storage (5,000 AF).
Alternative 10a – Gross Reservoir expansion (additional 52,000 AF)/reusable return
flows/Denver Basin Aquifer storage
Alternative 13a – Gross Reservoir expansion (additional 60,000 AF)/transfer of agricultural water
rights/gravel pit storage (3,625 AF)
No Action – Denver Water would not receive approval from the Corps to implement the Moffat
Project; Denver Water would use a combination of strategies, including using a portion of the
Strategic Water Reserve and imposing more frequent and severe mandatory water use
restrictions.
* Denver Water proposes to create an additional 5,000 AF of storage in Gross Reservoir in order to store water that
would be used in flow releases to enhance aquatic habitat in South Boulder Creek. This additional storage is
identified as the Environmental Pool throughout this document. See Section 8.2.1 for additional details regarding
the Environmental Pool.
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Using information prepared as part of the FEIS, the U.S. Forest Service (USFS) evaluated the effects of
these alternatives. Appendix G-3 of the FEIS contains a Special Status Species Technical Report that was
prepared in response to USFS comments on the Moffat Draft Environmental Impact Statement (DEIS).
The Special Status Species Technical Report contains attachments with the results of the northern leopard
frog (Lithobates pipiens) and rare and sensitive plant species surveys that were conducted at Gross
Reservoir. Aquatic resources could be affected by changes in streamflow storage patterns in reservoirs,
water quality, flooding, channel geomorphology, and/or riparian vegetation. Vegetation and wildlife
species could incur temporary or permanent effects due to construction activities, permanent building and
facilities, reservoir inundation, and/or due to changes in wildlife habitat along streams potentially affected
by altered flow regimes. Effects were evaluated compared to a Full Use of the Existing System with
reasonably foreseeable future actions (RFFAs) scenario, in which the No Action Alternative would likely
be implemented in place of the action alternatives (alternatives 1a, 1c, 8a, 10a, and 13a). The direct and
indirect effects evaluations in the FEIS were used as the basis for evaluation in this FWCA Report.
Most impacts would be similar or the same for the five action alternatives. Impacts to habitat at Gross
Reservoir would be reduced for the alternatives with smaller reservoir sizes. Most biological impacts
would be negligible or minor, but some moderate adverse or beneficial impacts would occur.
Mitigation strategies were proposed in Chapter 5 of the FEIS and in Denver Water’s Conceptual
Mitigation Plan (FEIS Appendix M-1) (Corps 2014). These mitigation strategies included avoidance,
minimization, protection, and compensation. The primary mitigation this report is intended to address is
covered by the December 6, 2013 Colorado River and Platte River depletions Biological Opinion (BO),
the January 29, 2016 BO for the Gross Reservoir Environmental Pool, and the June 17, 2016 BO for the
green lineage cutthroat trout and the Moffat Project that were issued by the U.S. Fish and Wildlife Service
(Service), as well as commitments made by Denver Water in the State-approved Moffat Project Fish and
Wildlife Mitigation Plan. Mitigation will be refined and described in more detail in Denver Water’s Final
Mitigation Plan.
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2. Introduction
In 2003, Denver Water notified the Corps of its intent to apply for a Department of the Army Permit
(CWA Section 404 Individual Permit) to place fill material in jurisdictional waters of the U.S. in order to
develop additional water supply. More specifically, the Moffat Project involves expansion of Gross
Reservoir in Boulder County, Colorado and increased stream diversions in the Colorado and Platte River
Systems. This FWCA Report documents an analysis of the potential consequences to fish and wildlife
resources from Denver Water’s proposed Moffat Project. The primary major Federal action analyzed in
the FWCA Report and associated FEIS is the issuance of a Section 404 Individual Permit. Cooperating
Agencies in the NEPA process include the EPA, FERC, CDNR, and CDPHE; Grand County is a
consulting agency.
2.1 Purpose, Scope, and Authority
The purpose of the Moffat Project is to develop 18,000 AF/yr of new, annual firm yield to the Moffat
Treatment Plant and raw water customers upstream of the Moffat water treatment plant (WTP) pursuant
to Denver Water’s commitment to its customers.
Denver Water’s need for the proposed Moffat Project is based on two major issues:
Timeliness: Water Supply Shortage in the Near-Term Timeframe (prior to 2032). Beginning as
early as 2022, Denver Water predicts its average annual water demand could exceed available
supplies and grow to 34,000 AF/yr by 2032. This shortfall was determined after analyzing
existing supply, projected demand, and savings from system refinements, non-potable reuse,
natural replacement, and cooperative projects with other water providers. Of this near-term
34,000 AF/yr shortfall, Denver Water will rely on 16,000 AF/yr forthcoming from the
implementation of additional conservation efforts. New firm yield must be identified to meet the
remaining shortfall. Denver Water proposes to meet the remaining shortfall with 18,000 AF/yr of
newly-developed supplies.
Location: Need for Water to the Moffat WTP. Approximately 90 percent (%) of the available
reservoir storage and 80% of the available water supplies rely on the South System. This
imbalance in reservoir storage and water supplies between the North and South systems has
created water supply challenges that have resulted in:
o Unreliable water supply for the Moffat WTP and Moffat Collection System raw water
customers
o System-wide vulnerability issues
o Limited operational flexibility of the treated water system
To address the two major issues, Denver Water is pursuing the proposed Moffat Project to provide
18,000 AF/yr of new, firm yield. The proposed Moffat Project would address both the overall near-term
water supply shortage and the imbalance in water storage and supply between the North and South
systems.
This FWCA Report for the Moffat Project was prepared under the authority of and in accordance with the
FWCA (16 U.S. Code [U.S.C.] 661-667e), the Endangered Species Act (ESA) (16 U.S.C. 1531 et seq.),
NEPA, as amended (42 U.S.C. 4321 et seq.), and the Migratory Bird Treaty Act of 1918 (MBTA), as
amended (16 U.S.C. 703 et seq.). This report constitutes the report of the Secretary of the Interior as
required by Section 2(b) of the FWCA. Appendix A contains a September 28, 2016 letter from the
Service approving this FWCA Report prepared for the Moffat Project. In that letter, the Service
acknowledges that the Corps’ responsibilities under the FWCA have been met.
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2.2 Relevant Prior Studies, Reports, and Previous Consultation
A detailed analysis of the alternatives for the full range of environmental effects is disclosed in the FEIS
(Corps 2014). Supporting documentation is provided in Appendix G of the FEIS, including special status
species lists, the Initial 2009 BO, the revised Biological Assessment (BA) (Corps 2013) and associated
2013 BO, and a technical report prepared in response to the USFS comments on the DEIS. Other relevant
reports include the Aquatic Resources Technical Report (GEI 2013) and the BA for greenback cutthroat
trout (Onchorhynchus clarki stomias) (Corps 2015). The Corps prepared a separate Platte River
depletions BA for the Gross Reservoir Environmental Pool and request for consultation, and a final BO
was issued by the Service in 2016 (USFWS 2016a).
The following is a summary of previous consultations for the Moffat Project, as provided in the BA
(Corps 2015):
February 20, 2009 – Corps requested initiation of formal consultation for the Moffat Project and
provided two BAs: one for Federally-listed species in Nebraska, and one for all other Federally-
listed species potentially affected by the Moffat Project.
July 31, 2009 – The Service issued a BO. The Service concurred with the determination of “not
likely to adversely affect” the greenback cutthroat trout. This 2009 BO was subsequently
replaced by a BO issued on December 6, 2013.
October 30, 2009 – Corps issued the DEIS.
February 16, 2010 – The Service submitted a letter commenting on the DEIS recommending
re-initiation of consultation regarding a number of issues, including the Moffat Project effects to
greenback cutthroat trout.
August 14, 2012 – Corps requested re-initiation of formal consultation for the Moffat Project and
provided a Supplemental BA for greenback cutthroat trout and Preble’s meadow jumping mouse
(Zapus hudsonius preblei).
November 20, 2012 – The Service submitted a letter not concurring with the Corps’ effects
determination for greenback cutthroat trout. The Service stated that the Moffat Project will result
in take of greenback cutthroat trout due to increased entrainment at the diversions and therefore
reinitiated formal consultation.
December 20, 2012 – The Service sent an email to the Corps (Scott Franklin) indicating that the
Service would provide two BOs for the Moffat Project: one to address depletions to the Platte and
Colorado rivers and impacts to Preble’s meadow jumping mouse, and a second to address impacts
to greenback cutthroat trout.
August 14, 2013 – Corps submitted a separate revised BA addressing depletions in the Colorado
River and Platte River systems and Preble’s meadow jumping mouse.
December 6, 2013 – The Colorado River and Platte River depletions BO was issued by the
Service, which replaced the 2009 BO.
April 25, 2014 – Corps issued the FEIS.
September 1, 2015 – Corps submitted a Platte River depletions BA for the Gross Reservoir
Environmental Pool. The Applicants are the cities of Boulder and Lafayette.
January 29, 2016 – The Service completed the BO for the Gross Reservoir Environmental Pool.
June 17, 2016 – The Service issued a BO for the green lineage cutthroat trout and the Moffat
Collection System Project, including the continuation of Denver Water’s existing operations and
future operations of the Moffat Project.
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Denver Water’s Conceptual Mitigation Plan for fish and wildlife resources was included in Appendix M
of the FEIS. Appendix M of the FEIS also included Denver Water’s Moffat Collection System Fish and
Wildlife Mitigation Plan and Fish and Wildlife Enhancement Plan, prepared for the Colorado Wildlife
Commission pursuant to Colorado Revised Statute (C.R.S.) 37-60-122.2.
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3. Description of the Study Area
Denver Water’s system is comprised of a water collection system, which stores and distributes raw water
prior to treatment, and a treated water system, which delivers treated water to its customers. The water
collection system is defined as all facilities that divert, collect, store and distribute water prior to
treatment. Denver Water’s raw water collection system is comprised of two major delivery systems,
which are not physically connected (Figure 1).
The North System (the Moffat Collection System) is comprised of the Moffat Tunnel Collection
System and delivers water to the Moffat WTP. The Moffat Tunnel Collection System captures
water from the Fraser River, Williams Fork River, South Boulder Creek, and Ralston Creek.
Major facilities include the William Fork River Collection System, Gumlick Tunnel, Vasquez
Tunnel, Fraser-River Collection System, Cabin-Meadow Creek Collection System, Gross
Reservoir, South Boulder Diversion Canal, and Ralston Reservoir.
The South System, which is comprised of the Roberts Tunnel Collection System and the South
Platte Collection System, delivers water to Foothills and Marston WTPs. The Roberts Tunnel
Collection System is comprised of Dillon Reservoir and the Roberts Tunnel. Major facilities in
the South Platte Collection System include Antero, Elven Mile Canyon, Cheesman, and Strontia
Springs reservoirs; Conduit 26; Platte Canyon Intake Dam; Conduit 20, and Marston and Platte
Canyon reservoirs.
Other components of Denver Water’s collection system include replacement facilities, exchange sources,
a non-potable recycling facility, and hydropower generation at Gross Reservoir. Williams Fork Reservoir
is owned and operated by Denver Water as a replacement facility for Denver Water’s trans-mountain
diversion projects. It provides exchange water to meet downstream senior water rights requirements.
Wolford Mountain Reservoir, owned and operated by the Colorado River Water Conservation District, is
used as a substitution source for Denver Water’s obligation to Green Mountain Reservoir.
The proposed Moffat Project would be located within the South Platte River Basin of Colorado. One or
more Project alternatives include proposed facilities in Adams, Boulder, Denver, and Jefferson counties.
Operation of the alternatives may affect the hydrology of streams in additional counties. Overview maps
of the facilities study area and river segment study area are shown on Figures 2 and 3. The study areas
included the area of potential physical disturbance for each alternative as well as areas that would be
affected by inundation, and changes in flow or water quality. Study areas vary by resource and are
discussed in more detail for each resource in Section 4.
The Moffat Project area is comprised of the following five study areas:
1. Reservoirs
2. Conveyance Systems
3. South Platte River Facilities
4. Denver Basin Aquifer Facilities
5. River Segments
North System Geographic BoundarySouth System Geographic BoundarySouth Platte Collection SystemRoberts Tunnel Collection SystemMoffat Collection SystemWilliams Fork Reservoir WatershedDenver Water Treatment PlantContinental DivideMajor Stream or RiverMajor Canal or TunnelMajor Lake or ReservoirTown
SOURCE: DENVER WATER, JUNE 2003
Figure 1Denver Water’s Collection System
Moffat Collection System Project FEIS
9/4/12
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offa
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Commercial SandQuarries
Haul Route
Gross Reservoir PotentialStorage Increase
(Alt. 1a - 72,000 AF)(Alt. 1c - 40,700 AF)
(Alt. 8a/10a - 52,000 AF)(Alt. 13a - 60,000 AF)
Proposed Leyden Gulch ReservoirPotential Storage
(Alt. 1c - 31,300 AF)
Existing Conduits 16 & 22
Existing Moffat Treatment Plant
Conduit O(Alt. 8a & 13a)
Conduit M(Alt. 10a)
Existing Denver WaterRecycling Plant
AWT Plant(Alt. 10a)
Deep Aquifer Wells(Alt. 10a)
Aquifer DistributionPipelines(Alt. 10a)
Challenger Gravel Pit(Alt. 13a)
North Tower Gravel Pit(Alt. 8a)
South Tower Gravel Pit(Alt. 8a & 13a)
Worthing Gravel Pit(Alt. 8a & 13a)
AWT Plant(Alt. 8a & 13a)
Existing South BoulderDiversion Canal
Gravel Pit Pipeline
Conduits O & M(Alt. 8a, 10a, & 13a)
Existing Ralston Reservoir
South Boulder
Cre
ek
South Boulder Cre
ek
Boulder C reek
Boulder C re
ek
Sou
th P
la
t te
Riv
er
South
PlatteRive
r
BOULDER
ADAMS
WELD
JEFFERSON
GILPIN
DENVER
ARAPAHOE
CLEAR CREEK
BROOMFIELD
ADAMS
Conduit O
Conduit M
Gravel Pit Pipeline
Aquifer Distribution Pipeline
Haul Route
Existing South Boulder Diversion Canal
Existing Conduits 16 & 22
Existing Moffat Treatment Plant
Commercial Sand Quarries
Advanced Water Treatment (AWT) Plant
Denver County Parks
Gravel Pit
Counties
Deep Aquifer Wells
Stream/River
3 0 3Miles
1:200,000
Reference:1:100,000-scale quad maps originally from USGS(1980s) and created with TOPO!, ©2006 NationalGeographic Maps, All Rights Reserved.
9/4/12
Moffat Collection System Project FEIS
Figure 2Overview of
Alternative Components
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Ute Pass(9,568 ft)
Vail Pass(10,603 ft)
Boreas Pass(11,481 ft)
Fremont Pass(11,318 ft) Hoosier Pass
(11,539 ft)
Loveland Pass(11,990 ft)
Berthoud Pass(11,315 ft)
Tennessee Pass(10,424 ft)
Cottonwood Pass(12,126 ft)
Trout Creek Pass(9,487 ft)
Independence Pass(12,093 ft)
Vail
Bond
Grant
Granby
Golden
Fraser
Dillon
Bailey
Wolcott
Hartsel
Deckers
Boulder
Redcliff
Parshall
Longmont
Fairplay
Brighton
Leadville
Kremmling
Winter Park
Palmer Lake
Castle Rock
Buena Vista
Rollinsville
Breckenridge
Idaho Springs
Eldorado Springs
Colorado Springs
PARK COUNTY
GRAND COUNTY
ELB
ERT
CO
UN
TY
EAGLE COUNTY
ADAMS COUNTY
DOUGLAS COUNTY
EL PASO COUNTY
BOULDER COUNTY
JEFFERSON COUNTY
SUMMIT COUNTY
TELLER COUNTY
LAKE COUNTY
CLEAR CREEK COUNTY
GILPIN COUNTY
DENVER COUNTY
BROOMFIELD COUNTY
RO
UTT
CO
UN
TY
CHAFFEE COUNTY
GUNNISON COUNTY
WELD COUNTY
ARAPAHOE COUNTY
High Line Canal
Harold D. Roberts Tunnel
City
Ditc
h
Burlin
gton D
itch
O'Bria
n Can
al
Conduit 16/22
Conduit 15
Hunter
Tun
nel
Conduit 26
Boustead Tunnel
Hom
estake Tunnel
Con
duit
20
Nast Tunnel
Moffat Tunnel
Twin Lakes Tunnel
South Fork Tunnel
Vasq
uez
Tunn
el
High Line Canal
Nev
ada
Ditc
h
Jones Pass Tunnel
Big Lake Ditch
City
Ditc
h
Big Lake Ditch
South Boulder Diversion Canal
Lake Granby
Barr Lake
Turquoise Lake
Taylor Park Reservoir
Spinney Mountain Reservoir
Standley Lake
Green Mountain Reservoir
Aurora Reservoir
Marston Reservoir
Cherry Creek Reservoir
Horse Creek Reservoir
Boulder Reservoir
Twin Lakes Reservoir
Clear Creek Reservoir
Homestake Reservoir
Marshall Reservoir
Rampart Reservoir(Colorado Springs)
Willow Creek Reservoir
Barker Reservoir
Quincy Reservoir
Tarryall Reservoir
Wellington Lake
Monarch Lake
McLellan Reservoir
Boot Lake Reservoir
Jefferson Lake
Clinton Reservoir
Lake George
Meadow Creek Reservoir
Montgomery Reservoir
Sylvan Lake
Rampart Reservoir(Aurora)
Homestake Pipeline
Blue River Pipeline
Blue
Riv
er
Boulder Creek
Bee
be S
eep
Can
al
Lime Creek
Nas
t Tun
nel
SouthPlatteRiver
Lake Fork
Meadow Creek
Guller
Creek
Aurora Aqueduct
Blac
k C
reek
Illinois Gulch
Martin Creek
Iron Creek
Pitk
in C
reek
Columbine Creek
Camp Creek
Wearyman Creek
Echo Creek
Marylan
d Cree
k
Trai
l Cre
ek
Hom
estake Pipeline
Blue
Riv
er P
ipel
ine
Lake Fork
Lake
For
k
Clear Creek
Clear Creek
Eagle River
Cherry Creek
Bear Creek
Bear
Cre
ek
Milk CreekPiney River
Coal Creek
Coal Creek
Fulto
n D
itch
Elk Creek
Elk
Cre
ek
Blue River
Roc
k C
reek
Roc
k C
reek
Big Dry
Creek
Fountain Creek
Wes
t Cre
ek
Deep Creek
Trou
t Cre
ek
Bra
ntne
r Ditc
h
Taylor River
Gore Creek
N. Fork of the South Platte River
East
Plu
m C
reek
Monum
ent Creek
Cros
s Cre
ek
Rule
Cree
k
William
s Fork River
Colorad
o Rive
r
Colorado River
Michigan Creek
South Saint Vrain Creek
Wes
t Plu
m C
reek
Trout Creek
Trout Creek
Trout Creek
Condu
it 27
Cabin Creek
Cabin Creek
Fraser River
Fraser River
Ralston Creek
Ralston Creek
Craig Creek
Trou
bles
ome
Cre
ek
Boulder Creek
Box
Eld
er C
reek
Box Elder Creek
Tenm
ile C
reek
Tenm
ile C
reek
Saint Vrain Creek
East Lake Creek
Geneva Creek
South Boulder Creek
Sout
h Bo
ulde
r Cre
ek
Fourmile Creek
St. L
ouis
Cree
k
Hunter Creek
Jefferson CreekFryingpan River
Fryi
ngpa
n R
iver
Plum Creek
Ranch C
reek
Willow Creek
Willow Creek
Willow Creek
Willow Creek
Brush C
reek
West Clear Creek
Alkali Creek
Vasq
uez
Cre
ek
Squ
aw C
reek
Salt Creek
Sand Creek
Straight Creek
South Platte Supply Canal
Hom
esta
ke C
reek
Hom
esta
ke C
reek
M. Fork of the South Platte River
Lake Creek
Lake
Cre
ek
Fall C
reek
Tarryall Creek
Tarryall Creek
Texas CreekTexas Creek
Brig
hton
Ditc
h
Keyser Creek
East Brush Creek
East Brush Creek
Snake River
Middle Saint Vrain Creek
Buffalo Creek
North Boulder Creek
Denver Hudson Canal
Slate Creek
West Lake C
reek
Crooked Creek
Lime
Cree
k
Lime
Cree
k
Deer Creek
Little Dry Creek
Sheep Creek
French Gulch
Bow
les
Seep
Can
al
North Turkey Creek
Brig
hton
Lat
eral
Peru Creek
Arapaho Creek
Sout
h Pl
atte
Riv
er
Goose Creek
Mar
ten
Cre
ek
Sout
h C
lear
Cre
ek
Strawberry Creek
East Inlet
Chapm
anG
ulch
Hurd Creek
Turkey Creek
Turkey Creek
June
Cre
ek
Swan River
Tenn
esse
e C
reek
Red
Top
Valle
y Di
tch
South Fork Fryingpan River
Black Gore Creek
Ivanhoe Creek
Lincoln Creek
Spru
ce C
reek
Jim Creek
Cottonwood Creek
Ellio
tt Cr
eek
Meado
w Cree
k
Soda Creek
Wurts Ditch
North Rock
Creek
Keystone Gulch
Paradise Creek
Last Chance Creek
South Rock Creek
Boot
h C
reek
S. Fork of the South Platte River
S. Fork of the
South Platte River
Hamilton Creek
Min
ers
Cree
k
Indiana Creek
Twin Creek
Mid
dle
Cre
ek
Bobt
ail C
reek
Bighorn
Cree
k
Darling Creek
West Toll Gate Creek
Resolution Creek
French Creek
Midway Creek
Marcy Gulch
Yoder Gulch
Platteville Lateral
Sout
h Tu
rkey
Cre
ek
South Cottonwood Creek
Pearl Creek
Red
Sand
ston
e Cr
eek
S. Fork of the William
s Fork River
West Monument Creek
North Fork Fryingpan River
Middle Boulder Creek
Leav
enwort
h Cree
k
North Tenmile Creek
Salt Lick Gulch
Reed Creek
Stee
lman
Cre
ek
Littl
e Va
sque
z C
reek
North F
ork Sna
ke R
iver
Cascade Creek
High Line Canal (aban.)
East Fork of Eagle River
West C
ross C
reek Pe
ters
on C
reek
Reeder C
reek
Free
man
Cre
ek
Walden Hollow
East St. Louis Creek
Middle Fork Swan River
West Brush C
reek
Wildcat Creek
East Fork of the Arkansas River
Pole C
reek
Pole Creek
North Fork Swan River
Fancy Creek
Cata
ract
Cre
ek
West St. Louis Creek
Whitney Creek
Moniger Creek
South Barton Gulch
Officers Gulch
Chapman Tunnel
Hel
l Can
yon
Range
r Cree
k
Columbine DitchCarte
r Cre
ek
Box Elder Lateral
N. Fork of Ranch Creek
McQ
uear
y Cr
eek
Ewing D
itch
Sawy
er C
reek
Dribble Creek
Granb
y Pum
p Ca
nal
Vidler Tunnel
North Tarryall Creek
Heimbaugh Creek
Boulder Feeder Canal
Boulder Creek Supply Canal
Hoo
sier
Pas
s Tu
nnel
Boreas Ditch N
o. 2
Coop
er
Cre
ek
Farm
ers
& G
arde
ners
Ditc
h
Ute Creek
Meadow Creek
Sout
h Pl
atte
Rive
r
Sout
h Pl
atte
Rive
r
Meadow Creek
Homestake Pipeline
Ute C
reek
Blue River Pipeline
Bear Creek
Blue R
iver
Beeb
e Se
ep C
analBlue R
iver
3600
2810
2500
2490
2370
1400
2580
2700
2600
14252900
42404250
4500
3300
3750
4650
2200
39505020 4800
13501600
57100
50750
5843558440
51290
56050
50300
50150
50450
5070051200
51540
571805712057140
NODE NUMBER NODE NAME
1350 Windy Gap Diversion1400 Hot Sulphur Springs Div/Dem1425 Colorado River Below Hot Sulphur Springs1600 Wolford Mountain Reservoir2200 St Louis Creek Near Fraser Gage2370 Cozen's Ditch/Vasquez Creek Gage2490 No Fork Ranch and Dribble Creek Diversion2500 Main Ranch Creek Diversion2810 Fraser River Below Crooked Creek2900 Fraser River At Granby Gage3300 Williams Fork River Below Steelman Creek Gage3600 Williams Fork Above Darling Creek Gage3750 Henderson Mill Div (Williams Fork Nr Leal Gage)3950 Williams Fork Reservoir4240 West Portal Roberts Tunnel Diversion4250 Dillon Reservoir4500 Blue River Below Boulder Creek4650 Green Mountain Reservoir4800 Blue River At Mouth5020 Colorado River Near Kremmling Gage
50150 Antero Reservoir50300 Eleven Mile Reservoir50450 Cheesman Reservoir50700 North Fork South Platte Below Geneva Cr Gage50750 North Fork South Platte Above Pine51200 South Platte River At Waterton Gage51290 South Platte Below Chatfield51540 South Platte River At Denver Gage56050 Leyden Gulch Reservoir57100 South Boulder Creek Near Buckeye Mtn57120 South Boulder Creek Native At Pinecliffe Gage57140 Gross Reservoir57180 South Boulder Cr Near Eldorado Springs Gage58435 Downstream Storage58440 South Platte River At Henderson Gage
Selected PACSM Nodes
Town
Major Stream of River
Major Canal or Tunnel
Major Road or Highway
Continental Divide
County Line
Lake or Reservoir
Overall Study Area Segments
Moffat Tunnel
Affected Reservoirs
Graphic not to scale
This Geographic Information Systems (GIS) map is provided 'as is' with no claim by the Denver Water Board as to the completeness, usefulness or accuracy of its content. © 2007 Denver Water
Figure 3River Segments
Overall Study Area
Moffat Collection SystemProject FEIS
9/4/12
Strontia Springs Reservoir
Dillon Reservoir
AnteroReservoir
Elevenmile Canyon Reservoir
Wolford Mountain Reservoir
Williams Fork Reservoir
Cheesman Reservoir
Chatfield Reservoir
Ralston Reservoir
Gross Reservoir
North Fork South Platte RiverNorth Fork South Platte River
South Platte River
South Platte River
South Boulder Creek
Colorado River
Blue River
Williams Fork River
Fraser River
5
12
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13
3.1 Reservoirs
Gross Reservoir. Gross Reservoir, located in Boulder County, is a component of all FEIS action
alternatives. The boundary of the study area is the current FERC-licensed Project boundary modified to
include all proposed facilities (Figure 4). The existing Gross Reservoir Dam spans South Boulder Creek,
impounding its waters and those of Winiger Gulch and Forsythe Canyon, which are small tributaries to
South Boulder Creek. In addition, the reservoir is filled with water delivered to upper South Boulder
Creek by the Moffat Tunnel, having been diverted from the Williams Fork River and Fraser River basins.
Water is released from Gross Reservoir for diversion at the South Boulder Diversion Canal approximately
4.5 miles downstream. The South Boulder Diversion Canal delivers water to Ralston Reservoir. The
existing dam crest elevation is 7,290 feet. At a surface elevation of 7,282 feet (the normal high water
line), storage capacity of the reservoir is 41,811 AF. The reservoir lies in a deeply-incised valley, and
when filled to capacity has a surface area of 418 acres. The drainage area at the dam is 92.8 square miles.
The land surrounding the reservoir is generally forested, with steep slopes (50% and greater in places).
Much of the reservoir is within the Arapaho & Roosevelt National Forests (ARNF). Normal annual
precipitation at Gross Reservoir is 20.5 inches.
Proposed Leyden Gulch Reservoir. The Leyden Gulch site, located in Jefferson County, is a
component of Alternative 1c. The study area was defined to encompass all proposed facilities shown in
Figure 7. The proposed Leyden Gulch Reservoir site is located on Leyden Gulch in the upper watershed
of Leyden Creek. Leyden Creek originates on the east side of the foothills between Coal Creek to the
north and Ralston Creek to the south, and flows east and southeast, joining Ralston Creek, then joining
Clear Creek near the Jefferson/Adams County line. The proposed reservoir site is located approximately
2.5 stream miles from the watershed divide and drains an area of 2.5 square miles. There are no
U.S. Geological Survey (USGS) gages on Leyden Gulch or Leyden Creek. Based on the National
Hydrography Dataset, a small tributary to Leyden Creek located in the northwest portion of the site is
considered perennial. The main reach of Leyden Creek through the site is considered intermittent.
Other Reservoirs. Although Denver Water’s raw water system is not interconnected, the treated water
system is. Thus, Denver Water’s North and South systems operate in an integrated manner. The
proposed operational changes associated with the Moffat Project would result in changes in reservoir
contents and levels in nine other reservoirs, including three on the West Slope (Dillon, Williams Fork,
and Wolford Mountain reservoirs) and six on the East Slope (Antero, Eleven Mile Canyon, Cheesman,
Strontia Springs, Ralston, and Chatfield reservoirs).
14
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Y:\G
IS\P
roje
cts\
Den
ver_
Wat
er_M
offa
t\M
XD
s\A
ltern
ativ
e_m
aps\
Gro
ss_c
ombi
ned\
Gro
ss_c
ombi
ned.
mxd
Relocated DamAccess Road
Stockpile Area
Quarry Access Road
Stockpile Area
Existing Power Plant
Existing Parking Lot
Dam Footprint
Relocated DamAccess Road
PotentialSpoil Area
Benched Quarry Site
Unbenched Quarry Site Potential Spoil AreaSpillway Construction Access Road
Spillway Relocated Access Road
Auxiliary Spillway
ExistingAccess Road
Spillway RelocatedAccess Road
Auxiliary Spillway Channel
ConstructionDisturbance Boundary
Staging Areas
Cha
mbe
rlain
Gul
ch
Retallack Gulch
Winiger Gulch
South Boulder Creek
Nineteen G
ulch
Forsythe Canyon
Advent Gulch
South Boulde r Creek
9/4/12
Moffat Collection System Project FEIS
Gross Reservoir Study AreaAlt. 1a Gross Reservoir - 72,000 AF EnlargementAlt. 13a Gross Reservoir - 60,000 AF EnlargementAlt. 8a and 10a Gross Reservoir - 52,000 AF EnlargementAlt. 1c Gross Reservoir - 40,700 AF EnlargementDam Footprint
Construction DisturbanceExisting Parking Lot
Existing Power Plant
Unbenched Quarry Site
Benched Quarry SiteStockpile Area
Auxiliary Spillway
Auxiliary Spillway ChannelSpoil Area
Staging Area
Access Road
Existing Access Road
Stream/River
1,200 0 1,200Feet
Figure Gross Reservoir
Components
1:14,400
Reference:1:24,000-scale quad maps originally from USGS(1972 & 1994) and created with TOPO!, ©2006 National Geographic Maps, All Rights Reserved.
16
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17
3.2 Other Facilities
Conveyance Systems. The primary conveyance systems that would convey water from a proposed
advanced water treatment plant (AWTP) to the Moffat Collection System include conduits M and O.
Conduit M, located in Adams and Jefferson counties, is a component of Alternative 10a. The pipeline
would convey water approximately 18 miles from the proposed AWTP near the Denver Water Recycling
Plant to the proposed Moffat Collection System delivery point near State Highway (SH) 72. Conduit O,
located in Adams and Jefferson counties, is a component of alternatives 8a and 13a. The pipeline would
convey water approximately 25 miles from the proposed AWTP near the gravel pit storage facilities in
Adams County to the proposed Moffat Collection System delivery point. Approximately 9 miles of the
Conduit O alignment from Wadsworth Boulevard west to the proposed Moffat Collection System
delivery point follows the same alignment as Conduit M.
South Platte River Facilities. The South Platte River Facilities, located in Adams County, are
components of alternatives 8a and 13a. The study area contains four representative gravel pits and their
associated pipeline network and pump stations, an AWTP, and a diversion structure on the South Platte
River. The study area is defined by the associated construction disturbance footprint for each component.
The gravel pit storage facilities are intended to be representative of facilities located along the South
Platte River. The representative gravel pits include the Worthing, South Tower, North Tower, and
Challenger pits. These gravel pits are in various stages of mining and development. For purposes of the
EIS analysis, it is assumed that when Denver Water acquires the gravel pits needed for the Project, they
would be completely mined and reclaimed as water storage facilities (i.e., slurry walls and reclaimed side
slopes would be in place). It is assumed that the gravel pits would be empty and Denver Water would fill
and operate the pits with newly-acquired or existing water rights in accordance with the raw water sources
identified for each alternative.
Denver Basin Aquifer Facilities. The Denver Basin Aquifer Facilities consist of an aquifer storage and
recovery system located in the City and County of Denver. This storage system is a component of
Alternative 10a. The study area includes 27 injection/recovery well facilities on 23 sites in the Denver
Metropolitan area, 35 miles of distribution pipelines, and a proposed AWTP near the Denver Water
Recycling Plant.
3.3 River Segments
In addition to the study area where there would be direct effects related to ground-disturbing activities
associated with the EIS alternatives, fish and wildlife resources within several drainage basins would be
affected by stream flow alterations from the Moffat Project. Denver Water diverts water from Fraser
River and its upper tributaries, Williams Fork River and its upper tributaries, Blue River, South Platte
River and its tributaries, and South Boulder Creek. Denver Water delivers water to storage or treatment
facilities to the South Platte River, North Fork South Platte River, South Boulder Creek, and Vasquez
Creek. Table 1 lists the overall study area segments and Figure 3 shows the locations.
Table 1
River Segments Study Area
River Overall Study Area Segment1
Fraser River Mainstem and upper tributaries downstream to the Colorado River
Williams Fork River Mainstem from the upper tributaries downstream to the Colorado River
Colorado River From confluence with Fraser River to the Kremmling gage
Blue River From Dillon Reservoir downstream to its confluence with the Colorado River
South Boulder Creek East Portal of the Moffat Tunnel to Gross Reservoir, and from Gross Reservoir
to the South Boulder Diversion Canal
18
Table 1
River Segments Study Area
River Overall Study Area Segment1
North Fork South Platte River East Portal of the Roberts Tunnel to the confluence with the South Platte River
South Platte River From downstream of Antero Reservoir to the Henderson gage
Note: 1 Overall study area segments are defined as river segments where water is being diverted (Fraser River and its tributaries, Williams Fork
River and its tributaries, Blue River, South Platte River, and South Boulder Creek), or used by Denver Water to deliver water to its storage or treatment facilities (South Boulder Creek, South Platte River, North Fork South Platte River, and Vasquez Creek, a tributary to the Fraser
River). Diversions from some of these streams may affect downstream flow in the Colorado River, downstream of the confluence with the
Fraser River.
The river segments study area includes the overall river segments and sampling sites along the river
segments that were used for field data collection. The characterization of Current Conditions and analysis
of impacts was conducted for the overall study area; however, more detailed evaluations and field work
were conducted for areas that would experience the greatest flow changes. Within the overall study area,
the characterization of Current Conditions for the flow-related resources focused on those affected river
segments that would experience an average annual flow increase or decrease of greater than 10% as a
result of the Moffat Project, as determined from the Platte and Colorado Simulation Model (PACSM)
results (see FEIS Section 5.1). The purpose of identifying these segments was to focus the selection of
sample sites, data collection, and field work in areas that experience the greatest flow change. Because
the overall study area covers several river basins, it was impractical to collect data on each individual
sub-reach of every affected stream. Several sampling sites (representative river reaches), that experience
the greatest flow changes were therefore identified for detailed data collection and evaluation. The
approach was to select a variety of sampling sites that were examples of or statistically representative of
different resource conditions encountered in the study area. Data for the sampling sites were evaluated
and extrapolated to the overall study area. Using the criterion of a 10% average annual flow change due
to the Moffat Project alternatives, approximately 200 miles of river segments were identified along the
mainstems and tributaries within the overall study area. In addition, the Colorado River below the
Williams Fork River, Blue River below Green Mountain Reservoir, and South Platte River below
Chatfield Reservoir were analyzed due to flow changes caused by RFFAs.
For specific field data collection efforts, representative sites were identified within river segments that
experience average annual flow changes greater than 10% to obtain specific information to further
characterize the riparian habitat and stream channel dynamics. The sites were selected based on a
preliminary level assessment of the stream type and field reconnaissance to evaluate the site
characteristics as representative of the overall study area. Other factors considered in site selection
included a site’s suitability for hydraulic modeling, the quality and type of riparian and wetland
vegetation, land use or disturbance history, as well as accessibility to the site. A multi-disciplinary
approach was followed at the sampling sites so that riparian vegetation sampling was coordinated with
hydraulic analysis and the channel dynamics study.
3.3.1 Fraser River
The Fraser River Basin is located in Grand County, about 40 miles west of Denver. The basin boundary
is formed by the Vasquez Mountains on the west, which separate it from the Williams Fork River Basin,
and by the Continental Divide on the south and east. The river flows northerly from the vicinity of
Berthoud Pass for approximately 30 miles, entering the Colorado River near the Town of Granby,
Colorado. Major tributaries include Vasquez, St. Louis, Ranch, Crooked, and Strawberry creeks. The
USGS reports a drainage area of 297 square miles at the now discontinued gage site, Fraser River at
Granby, near the river’s mouth. Elevations in the basin range from 7,900 to above 13,000 feet. Annual
precipitation ranges from 35.5 inches per year on Berthoud Pass to 20.3 inches per year at the Town of
19
Fraser (WRCC 2010). Stream hydrology reflects snowmelt, which generates most of the Fraser River’s
flows.
The uppermost diversion in the Fraser River Basin is the Berthoud Canal, a trans-mountain diversion.
Below the Berthoud Canal, and following the mountainous rim of the basin on its southern and eastern
sides, is Denver Water’s Fraser River Diversion Project, which is a component of the existing Moffat
Collection System. Nearly 28 miles of open canals, pipes, and siphons collect flows from numerous
contributing drainages and direct it to the Moffat Tunnel, located near the Fraser mainstem above the Town
of Winter Park. The system includes Meadow Creek Reservoir and the Englewood-Ranch Collection
System, which comprise the upper end of the east side collection system. This portion belongs jointly to the
City of Englewood and Cyprus Climax Metals Company and is operated by Denver Water. At Vasquez
Creek, the system picks up water delivered from the Williams Fork River Basin via the Gumlick and
Vasquez tunnels and the Vasquez Creek channel.
Denver Water’s 32 primary diversion points in the Fraser River Basin, which contribute flows to the Moffat
Tunnel, are shown in Table 2 and Figure 3. For the period from 1975 through 2004, the Moffat Tunnel
conveyed an average of 55,900 AF/yr under the Continental Divide based on the State’s Hydrobase records
for Station 09022500, Moffat Tunnel at East Portal (CDWR 2005). The capacity of the Moffat Tunnel is
1,360 cubic feet per second (cfs). The water is delivered to South Boulder Creek on the East Slope, stored
in Gross Reservoir, and eventually conveyed to the Moffat WTP in Lakewood.
Table 2
Moffat Collection System Diversion Points on Fraser River Tributaries
St. Louis – Vasquez Creek Section Ranch Creek Section
West St. Louis Creek North Fork Ranch Creek
Short Creek Dribble Creek
St. Louis Creek Main Ranch Creek
Iron Creek Middle Fork Ranch Creek
Byers Creek South Fork Ranch Creek
East St. Louis Creek Cub Creek
Fool Creek Buck Creek
King Creek Wolverine Creek
West Elk Creek Englewood-Ranch Creek Extension
East Fork Main Elk Creek Meadow Creek
West Fork Main Elk Creek South Trail Creek
East Elk Creek North Trail Creek
Vasquez Creek Hurd Creek
Little Vasquez Creek Hamilton Creek
Cooper Creek Cabin Creek
Fraser River – Jim Creek Section Little Cabin Creek
Fraser River
Jim Creek
Source: Denver Water, 2003.
3.3.2 Williams Fork River
The Williams Fork River is the next major southside tributary to the Colorado River, below the Fraser
River. It flows generally northwest, forming a relatively narrow basin approximately 8 miles wide by
30 miles long. The Vasquez Mountains form the divide between the Williams Fork River and the Fraser
River to the east, and the Williams Fork Mountains form the western boundary shared by the Blue River
20
Basin. The southern end is delineated by the Continental Divide, which separates the Williams Fork
River Basin from Clear Creek. The basin rim includes peaks rising above 13,000 feet, while the
confluence with the Colorado River lies at approximately 7,540 feet. The Williams Fork River drains
approximately 230 square miles at the USGS gage 09038500, Williams Fork below Williams Fork
Reservoir. Annual precipitation is estimated to be in excess of 40 inches on the high ridges at the
southern end of the basin, but normal annual precipitation at Williams Fork Dam is 14.1 inches.
The Williams Fork River Basin lies almost entirely within the ARNF, and has no population centers.
Henderson Mill, owned by Cyprus Climax Metals Company, is located in the Ute Creek Basin, a tributary
to Williams Fork River, relatively high in the basin. Ore from the Henderson Mine, east of the
Continental Divide near Berthoud Pass, is hauled through a 12-mile tunnel to the mill. Water is used and
reused in the milling process through an elaborate system of pumping stations, pipelines, reservoirs,
tanks, and a single large tailing pond. Historical diversions, taken both from Ute Creek and Williams
Fork River, average approximately 2,200 AF and are entirely consumed. At lower elevations, irrigated
pasture and hay cropping support livestock production. Generally, these activities represent the only
water use within the basin. Major irrigation ditches in the basin include Big Lake Ditch and Lyman
Ditch.
Williams Fork Reservoir, a 96,822-AF reservoir located approximately 3 miles above the Colorado River
confluence, is the largest reservoir in the basin. Denver Water’s headwater diversions are protected by
Williams Fork Reservoir such that when Denver Water’s rights are out of priority with respect to senior
diverters below Williams Fork Reservoir, there are reservoir releases of water to satisfy the senior
diverters. This type of operation, in which water may be diverted out of priority at one point by replacing
a like amount at a downstream point, is called an exchange. Williams Fork Reservoir is operated in part
to exchange water to replace out-of-priority diversions at Denver Water’s Moffat Collection System,
Roberts Tunnel, and Dillon Reservoir.
Denver Water’s collection system in the Williams Fork River headwaters diverts water from McQueary,
Jones, Bobtail, and Steelman creeks, directing flow to the Gumlick Tunnel (Jones Pass Tunnel) for
delivery into Vasquez Creek in the Fraser River Basin above the Moffat Collection System. The
Williams Fork Collection System intercepts a drainage area of approximately 14.2 square miles. The
decreed capacity of the Gumlick Tunnel is 620 cfs and annual diversions averaged 5,100 AF from 1975
through 2005.
3.3.3 Colorado River
The section of the Colorado River from the confluence with the Fraser River downstream to the
Kremmling gage includes approximately 27 river miles. The confluence with the Fraser River is the most
upstream point at which Denver Water diversions have an impact on the Colorado River mainstem. It
ends at Kremmling, where both the Blue River and Muddy Creek join the Colorado River. Over this
reach, the river drops from 7,900 feet in elevation to approximately 7,400 feet. Major tributaries in the
reach include Troublesome Creek, Fraser River, Blue River, Williams Fork River, and Muddy Creek.
The river valley is sparsely populated, with Hot Sulphur Springs, the Grand County seat, being the only
municipality other than Kremmling.
Diversions in this reach of the river are primarily to flood-irrigate pasture grass grown in a relatively
narrow corridor along the river. Major mainstem irrigation ditches include Sheriff Ditch, Ute Bill No. 2
Ditch, Farris South Side Ditch, Sophronia Day Ditch, Kinney Barriger Ditch, Thompson Pump No. 2, and
McElroy Ditches Nos. 1 and 2. Denver Water’s rights on the Fraser River and Williams Fork River are
junior to many of the irrigation rights associated with these ditches. In addition, there are a series of
irrigation water rights, termed Meadow Pumpers that were granted senior status in relation to the water
rights for the Colorado-Big Thompson Project per Senate Document 80. These water rights are primarily
located along the Colorado River mainstem downstream of the confluence with the Williams Fork River
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and upstream of Kremmling. Several irrigators along the Colorado River are experiencing difficulty in
diverting water, particularly in drought years and during late summer and fall months due to low-flow
conditions. This was most evident in 2002 when flows below the confluence with the Williams Fork
River were extremely low, causing some irrigators to stop diverting. Several irrigators have constructed
make-shift cobble dams to raise water levels at their diversion dams to facilitate diversions from the river.
The other major diversion in this reach is the Windy Gap Firming Project, which has a diversion dam just
below the confluence with the Fraser River, and a pumping station with a capacity of 600 cfs. The Windy
Gap Firming Project is owned and operated by the Municipal Subdistrict of the Northern Colorado Water
Conservancy District. The water diverted at Windy Gap is pumped to Granby Reservoir for eventual
delivery to the East Slope via the Adams Tunnel. The historical average annual diversion at Windy Gap
is approximately 10,600 AF (1985 through 2004).
3.3.4 Blue River
The Blue River rises on the north-facing slopes of the Continental Divide near Hoosier Pass, about
9 miles south of Breckenridge, Colorado. The Continental Divide consists of 13,000- and 14,000-foot
peaks and the high ridges between them, and bounds the basin on its southern and southeastern perimeter.
The Blue River flows generally northwest, toward Dillon Reservoir, then on toward the Colorado River,
forming a long valley between the Williams Fork Mountains to the north and east, and the Gore Range to
the south and west. It enters the Colorado River near the Town of Kremmling, at an elevation of
approximately 7,400 feet. The total drainage area of the basin is 680 square miles.
The Blue River above Dillon Reservoir is divided into three major sub-basins. From east to west, they
are the Snake River Basin, the upper Blue River Basin, and the Ten Mile Creek Basin. Dillon Reservoir
covers the confluence of these three streams. In the lower Blue River Basin, tributary streams are shorter
and drain less area as they come off the mountain fronts on either side of the basin. The higher Gore
Range side produces more water than the Williams Fork Mountain side. Precipitation varies with
elevation across the Blue River Basin, ranging from 15.5 inches at Green Mountain Dam in the lower
Blue River, to nearly 24 inches at Climax Mine near Fremont Pass. Stream flows are highly variable by
season across the basin. Most of the annual stream flow results from snowmelt between the months of
May and July, but short-lived thunderstorms in July and August can produce spikes in the runoff in the
late season.
Dillon Reservoir was completed in 1963 and is the largest reservoir in Denver Water’s collection system.
The reservoir has a storage capacity of 254,000 AF impounded by an earth-fill dam that is 231 feet high.
The West Portal of the Roberts Tunnel is located in the Snake River arm of the reservoir. Diversions by
Dillon Reservoir are delivered via the Roberts Tunnel to the North Fork South Platte River approximately
23 miles away, to Denver’s “southern system” for treatment at either the Foothills or Marston WTPs.
Annual diversions through the Roberts Tunnel averaged 62,600 AF from 1975 through 2005.
3.3.5 South Boulder Creek
South Boulder Creek is a tributary of Boulder Creek in the larger St. Vrain Creek Basin and flows into the
South Platte River. Most of the basin is located west and a little south of the City of Boulder. The creek
drains the east side of the Continental Divide from Rollins Pass to James Peak, elevation 13,300 feet, and
joins Boulder Creek on the plains east of Boulder at an elevation of approximately 5,175 feet. The
affected section of South Boulder Creek is from the East Portal of the Moffat Tunnel, where Denver
Water’s diversions from the Fraser River and Williams Fork River flow into the creek, to the South
Boulder Diversion Dam about 3 miles west of Eldorado Springs. At this diversion dam, Denver Water
diverts water to the South Boulder Diversion Canal for delivery to Ralston Reservoir, raw water
customers, and the Moffat WTP. The reach includes Gross Reservoir.
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The section of the basin through which Denver Water’s water is delivered lies mostly in the ARNF. The
population centers in the basin are the towns of Rollinsville and Pinecliffe. There is relatively little water
use within this reach; the Colorado State Engineer’s Office (SEO) database shows a few small storage and
diversion rights, several of which were apparently appropriated originally for ice making. However,
where the stream leaves the foothills below Eldorado Springs, numerous ditches divert from South
Boulder Creek. Major ditches include the Community and South Boulder & Coal Creek Ditch, owned by
Farmers Reservoir and Irrigation Company; Howard Ditch; East Boulder Ditch, and New Dry Creek
Ditch. Generally, the South Boulder Creek ditches were established historically for irrigation, but in
recent decades the municipalities of Louisville, Lafayette, and Boulder have purchased some of this
agricultural water. Louisville and Lafayette each have pipeline diversions near Eldorado Springs.
Releases from Gross Reservoir to the South Boulder Diversion Canal do not exceed 500 cfs, which is the
capacity of the canal. Denver Water attempts to fill Ralston Reservoir by December 15th each year, after
which it typically shuts the diversion canal until mid-March of the following year.
3.3.6 North Fork South Platte River
The North Fork South Platte River rises along the Continental Divide at the northern edge of South Park,
near Kenosha Pass. It flows generally southeast as far as the settlement of Eastbrook, then follows a
winding course through the mountains to its confluence with the South Platte River. In only a few places
is the river valley bottom more than a third of a mile wide. The drainage is generally forested with open
areas on south-facing slopes and the river bottoms. Elevations range from 6,100 to 12,600 feet.
Approximately 12 miles downstream from the Continental Divide is the East Portal of Roberts Tunnel,
which delivers water from Dillon Reservoir in the Blue River Basin. Denver Water operates its system in
a manner to keep the total flow in the North Fork South Platte River below 680 cfs (daily average) at
Grant and below 980 cfs (daily average) above the confluence with the mainstem. The drainage area near
the mouth is 479 square miles. There are no exports out of the North Fork South Platte River Basin and
there is relatively little local use. The SEO’s database shows only three active diversion rights for 2.0 cfs
or more. Population is dispersed in this area, with only small towns at Shawnee, Bailey, and Pine.
3.3.7 South Platte River
The overall study area of this basin extends from Antero Reservoir to Big Dry Creek near the Henderson
gage. This river segment contains six mainstem reservoirs: Antero, Spinney Mountain, Eleven Mile
Canyon, Cheesman, Strontia Springs, and Chatfield. This basin has been subdivided into an upper
segment from Antero Reservoir downstream to the mouth of Waterton Canyon downstream of Strontia
Springs Reservoir, and a lower segment from Waterton Canyon downstream to Henderson.
South Platte River from Antero Reservoir to Waterton Canyon
The headwaters of the South Platte River lie on the east side of the Mosquito Range, among 13,000- and
14,000-foot peaks that form the western perimeter of Colorado’s South Park. South Park is a wide, level
mountain valley approximately 40 miles from north to south and 25 miles from east to west. Three major
streams flow generally southeast across the plain of South Park. From north to south they are Tarryall
Creek, Middle Fork South Platte River, and South Fork South Platte River. Three miles east of the Town
of Hartsel, the Middle Fork joins the South Fork to form the South Platte River, which exits the mountain
valley along its southeast boundary. Tarryall Creek leaves South Park on its eastern edge and joins the
South Platte River more than 30 stream miles below the confluence of the Middle and South forks. The
upper South Platte River Basin lies generally above 8,800 feet. Although the western peaks receive over
30 inches of precipitation annually, normal precipitation at Antero Reservoir on the valley floor is less
than 10 inches. The land and water in South Park were used historically for ranching, but in recent
decades, most of the water once used to irrigate hay and pasture grass has been purchased by the City of
Aurora and Denver Water.
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Antero Reservoir is located on the South Fork South Platte River. This 20,015-AF facility is owned and
operated by Denver Water, and provides carryover storage for long droughts. As such, it does not
fluctuate seasonally; once drawn down, it may take more than one season to fill because of limited
physical supply, high evaporation rates, and junior water rights.
Below the confluence of the South and Middle forks of the South Platte River is Spinney Mountain
Reservoir. It has a capacity of 53,651 AF. The City of Aurora stores South Platte River water in Spinney
Mountain, as well as trans-basin water diverted from the Colorado River and Arkansas River basins and
delivered via the Otero pumping plant and pipeline. Water is delivered from Spinney Mountain Reservoir
to Aurora via the South Platte River channel to Strontia Springs Reservoir, where it is taken into Aurora’s
Rampart Pipeline system.
Eleven Mile Canyon Reservoir is about 3.5 miles below Spinney Mountain Reservoir dam, at the eastern
edge of South Park. This is Denver Water’s largest East Slope reservoir, at 97,779 AF. Its drainage area
is 963 square miles, and the dam crest elevation is 8,600 feet. The reservoir is 6 miles long. Like Antero
Reservoir, Eleven Mile Canyon is operated for long-term drought storage and may require multiple
seasons to fill after being drawn down.
Below Eleven Mile Canyon Reservoir, the river begins a much steeper descent through Eleven Mile
Canyon, then the South Platte River Canyon and Waterton Canyon, where it emerges onto the eastern
plains. Major tributaries in this reach are Tarryall Creek, Goose Creek, and the North Fork South Platte
River. The North Fork South Platte River delivers Denver Water’s imported Blue River water to the
South Platte River, having been brought by the Roberts Tunnel. With the exception of these streams,
which enter from the northwest, the South Platte River drainage is a relatively narrow corridor through
8,000- to 9,000-foot mountains in this reach. It is generally forested and sparsely populated, with the
small towns of Lake George just below Eleven Mile Canyon, and Deckers below Cheesman Reservoir.
Irrigable terrain is absent due to the narrow canyon and stream gradient, and there is no historical
agricultural use along this reach. The river is a prized fly fishing stream and has heavy recreational use in
the spring and summer.
Cheesman Reservoir is located at the confluence of Goose Creek and the South Platte River. It was
Denver Water’s first mountain reservoir, and has a capacity of 79,064 AF. It provides both seasonal and
long-term supply. Because of its senior rights, it is the most quickly filled of Denver Water’s South Platte
reservoirs.
South Platte River from Waterton Canyon to Henderson
The section of the river from the mouth of Waterton Canyon to the USGS gage at Henderson is
commonly referred to as the “metro reach.” It extends over 30 miles, dropping to an elevation of
4,999 feet. At the Henderson gage, the river has a drainage area of 4,768 square miles. This reach is
characterized by large diversions for both municipal and irrigation use, and an urban and suburban setting
that includes wastewater return flows at the Bi-City (Littleton-Englewood) Wastewater Treatment Plant
(WWTP), Metro Wastewater Reclamation District, Robert W. Hite Treatment Facility (“Metro”), and the
Broomfield WWTP. Major tributaries are Deer Creek, Bear Creek, and Clear Creek from the west, and
Cherry Creek from the east.
Chatfield Reservoir, a Corps’ facility, is located at the upper end of the reach. Denver Water has
27,428 AF of capacity to manage its supply in Chatfield Reservoir, which it uses primarily to capture
minimum releases from Strontia Springs Reservoir and the yield of downstream water rights and return
flows that cannot immediately be exchanged to Strontia Springs or other South Platte reservoirs. Denver
Water operates its pool within the reservoir’s conservation pool, which represents less than 5% of the
reservoir’s total capacity, which is primarily for flood control. A State park is located at Chatfield
Reservoir and provides a swimming beach, camping, and boating facilities.
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Major diverters in the southern half of the Metro reach include the City of Englewood, Centennial Water
and Sanitation District, Public Service Company, and Denver Water. Much of this water is used for
irrigation of municipal sites and facilities by Englewood and Denver. Xcel Energy takes delivery of
relatively small amounts of water at its Arapahoe, Cherokee, and Zuni plants in this reach.
There are three major diversions in the northern half of the reach. Gardener’s Ditch and Burlington Ditch
are located on opposite sides of the river, above the Metro WWTP outfall. The river can be dried up for a
distance of about 1.5 miles here. The last diversion is the Fulton Ditch. These three ditches continue to
serve irrigation use, although some of the historical irrigation supply has been transferred to
municipal/augmentation uses. This section of the river is paralleled by numerous gravel mining
operations. Several spent mines have been or will be converted to lined pits used for storage and
regulation of South Platte River water by various entities.
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4. Fish and Wildlife Concerns and Planning Objectives
Fish and wildlife resources considered in this analysis include Federally-listed threatened and endangered
species, State-listed species, other species of concern, migratory birds, and aquatic resources including
fish, and wetland and riparian habitats important for support of wildlife. The following information
provides a summary of the resource issues, the study area for each resource, and the regulatory framework
for the resource.
4.1 Aquatic Resources
Aquatic resources could be affected by changes in streamflow, storage patterns in reservoirs, water
quality, flooding, channel geomorphology, or riparian vegetation. The Moffat Project could potentially
affect fish and invertebrate communities and their habitat in the study area (as defined in Section 4.1.1).
The analysis for this report focused on changes in fish populations and benthic macroinvertebrate habitat
availability and populations.
Several listed threatened or endangered aquatic species occur in the study area, including greenback
cutthroat trout in the Fraser River and Williams Fork River valleys, four endangered fish species
downstream in the upper Colorado River and several endangered or threatened species downstream in the
Platte River system in Nebraska. The endangered and threatened species in the South Platte and upper
Colorado River were assessed in the EIS as part of the river segments study area (i.e., habitats
downstream of the Project area).
4.1.1 Study Area
The study area for aquatic resources effects includes water bodies potentially affected by the Moffat
Project because of modified hydrology or changes to water quality, flood hydrology, channel
geomorphology, or riparian vegetation, and includes the following surface waters:
Reservoirs, including Gross Reservoir and the proposed Leyden Gulch Reservoir.
Surface waters that would be affected by other Project components such as conveyance systems.
River segments that would have changes in flows, including the Fraser River and its tributaries,
upper Williams Fork and its tributaries, Blue River, South Boulder Creek, Colorado River, North
Fork South Platte River, and South Platte River.
4.1.2 Regulatory Framework
The ESA declares that “…all federal departments and agencies shall seek to conserve endangered species
and threatened species and shall utilize their authorities in furtherance of the purpose of this Act.” Under
the ESA, Federal agencies must consult with the Secretary of the Interior, under Section 7 of the ESA,
whenever an action authorized by such an agency is likely to affect a species listed as threatened or
endangered. One of the fish species in the study area, greenback cutthroat trout, is listed as threatened
under the ESA.
Colorado Parks and Wildlife (CPW) has the authority to manage and conserve wildlife resources within
the State of Colorado for hunted, fished, and non-game wildlife. The CPW enforces various fishing
regulations, including regulations concerning the illegal take or use of threatened and endangered species.
Colorado State Statute 33-2-102 states that endangered or threatened species should be protected for the
purpose of maintaining and enhancing their numbers to the extent possible. Two fish species in the study
area are listed by CPW as Colorado special status species. The Iowa darter (Etheostoma exile) is a
Colorado State species of concern that has been collected previously in the South Platte River in the study
area. The Colorado River cutthroat trout (Oncorhynchus clarkii pleuriticus) has been collected in some
streams in the study area and is also a State species of concern.
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The FWCA (U.S.C. Title 16 Section 661-667e) requires that the department or agency involved with a
project shall first consult with the Service and with the agency exercising administration over the wildlife
resources of the State where the construction will occur. With specific regard to the impoundment or
diversion of waters, the goal of the consultation should be to discuss conservation of wildlife by
preventing loss of and damage to the wildlife resources, and to provide for the development and
improvement of these resources in connection with water-resource development. Based on the FWCA,
adequate provisions must be made for the management of wildlife and their habitat within the Moffat
Project study area. The Corps coordinated with the Service and CPW regarding the FWCA and State law
37-60-122.2, including participation in State Wildlife Commission Workshops regarding Project effects
on wildlife and recommended mitigation measures.
4.2 Wildlife Resources
Wildlife resources could be affected by components of the Moffat Project. The resources that are
addressed include Federally-listed threatened and endangered species, Colorado threatened and
endangered species and species of special concern, USFS Region 2 sensitive species, sensitive species
tracked by the Colorado Natural Heritage Program (CNHP), raptors, waterfowl (Anatidae) and
shorebirds, big game, other wildlife and migratory birds, and biologically sensitive areas. USFS
Management Indicator Species (MIS) and key wildlife habitats, such as old growth, were analyzed on
USFS lands.
4.2.1 Study Area
The wildlife study area is located in Boulder, Jefferson, Denver, Adams, Grand, Summit and Park
counties and encompasses areas potentially affected by Project activities, including the proposed and
alternative facilities, which includes reservoirs, water conveyance systems, South Platte River Facilities,
and Denver Basin Aquifer Facilities. The study area was used to assess direct effects on wildlife
resources. The study area also includes wildlife habitat along streams potentially affected by altered flow
regimes. Because wildlife are mobile and can be affected by disturbance outside the Project footprint, the
study area for indirect effects extended to areas that may potentially affect individual species or the
wildlife community as a whole.
4.2.2 Regulatory Framework
Federally-listed threatened and endangered species are protected under the ESA, as amended. Potential
effects from a project on a Federally-listed species or its habitat resulting from a project with a Federal
action require consultation with the Service under Section 7 of the ESA. Modification of designated
critical habitat for a Federally-listed species also requires consultation with the Service.
Migratory birds, including raptors and active nests, are protected under the MBTA. The MBTA prohibits
activities that may harm or harass migratory birds during the nesting and breeding season. Removal of
active nests that results in the loss of eggs or young is also prohibited (16 U.S.C. Sections 703-712).
Executive Order 13186 directs Federal agencies to take certain actions to implement the MBTA
(86 Federal Register 3853).
The Bald and Golden Eagle Protection Act (16 U.S.C. 668-668d) includes several prohibitions not found
in the MBTA, such as molestation or disturbance. In 1962, the MBTA was amended to include the
golden eagle (Aquilla chrysaetos). In 2007, the term “disturb” was defined to mean “to agitate or bother a
bald eagle (Haliaeetus leucocephalus) or golden eagle to a degree that causes injury to an eagle, a
decrease in productivity, or nest abandonment, by substantially interfering with normal breeding, feeding,
or sheltering behavior (72 Federal Register 31332).
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The FWCA requires the Federal action agency to consult with the USFS and CPW on issues related to
conservation of wildlife resources for Federal projects resulting in modifications to waters or channels of
a body of water (16 U.S.C. Sections 661-667e).
As directed by C.R.S. 33 (Title 33, Article 2, C.R.S. [2007]), the Colorado Wildlife Commission issues
regulations and develops management programs implemented by CPW for wildlife species not Federally
listed as threatened or endangered. This includes maintaining a list of State threatened and endangered
species. CPW also maintains a list of species of special concern that are not protected under Colorado
wildlife statutes concerning non-game and endangered species conservation (Title 33, Article 2, C.R.S.
[2007]). Although this Statute prohibits the take, possession, and sale of a State-listed species, it does not
include protection of their habitat.
4.3 Vegetation Resources
The Moffat Project could affect native vegetation communities including sensitive plant communities and
sensitive plant species. Several types of vegetation resources were assessed:
Vegetation Cover Types – mapped and assessed according to indicators such as dominance by
native or introduced species.
Threatened, Endangered, and Candidate species – listed under the ESA.
Sensitive plant species listed by USFS Region 2, ARNF species of local concern, and CNHP.
Plant communities listed as sensitive by the CNHP or USFS.
Noxious weeds – assessed to determine what type of weed control management would be needed
for this Project.
Direct and cumulative effects on vegetation cover types are measured in acres and would consist of
removing vegetation either permanently (by replacing it with some type of structure or inundation by a
new or expanded reservoir), or temporarily during construction. As with vegetation cover types, effects
on plant communities of concern are measured in acres and would consist of permanent and temporary
effects. These effects on plant communities of concern were estimated by comparing them to the total
acreage of known communities. The removal of plants from permanent and temporary impacts would
affect plant species of concern; although, in temporarily affected areas, the plants may re-establish. These
effects were estimated by comparing them to numbers of known individuals. Indirect effects, such as
susceptibility to noxious weed infestation, were qualitatively described for each alternative.
4.3.1 Study Area
The study area for vegetation resources is the area that would be disturbed for construction, operations,
and maintenance of each of the alternatives. The vegetation resources study area is located in Boulder,
Jefferson, Denver, Adams, Grand, Summit, Gilpin, and Park counties, and encompasses areas potentially
affected by Project activities including the proposed and alternative facilities, which include reservoirs,
water conveyance systems, South Platte River Facilities, and Denver Basin Aquifer facilities. The study
area of sensitive species and plant communities also included habitat along streams potentially affected by
altered flow regimes.
4.3.2 Regulatory Framework
Federally-listed threatened and endangered plant species are protected under the ESA, as amended.
Potential effects from a project on a Federally-listed species or its habitat resulting from a project with a
Federal action require consultation with the Service under Section 7 of the ESA.
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The CNHP tracks plant species and plant communities that are critically imperiled (S1) or imperiled (S2)
within Colorado. S1 and S2 species and plant communities are not regulated by a Federal or State entity.
S1 and S2 plant species and communities are assessed because they are potentially vulnerable to effects
from a proposed project.
The USFS and Bureau of Land Management (BLM) maintain lists of sensitive species that they monitor
on lands they manage. Effects on species listed as sensitive by the USFS and BLM were also assessed for
each of the alternatives.
The Colorado Noxious Weed Management Act states that all landowners must manage noxious weeds
that may be damaging to adjacent landowners. Noxious weeds are defined as plant species that are not
native to Colorado and that negatively affect crops, native plant communities, livestock, and/or the
management of natural or agricultural systems. The Colorado Department of Agriculture maintains three
lists of noxious weed species. The State A list contains noxious weed species targeted for eradication
within Colorado. The State B list contains species that the State recommends controlling. The State C
list contains species for which the State, in cooperation with other interested parties, will develop and
implement weed-management plans.
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5. Evaluation Methods
Evaluation methods for determining the effects on fish and wildlife resources are described in this section.
The effects methods for aquatic resources are highly dependent on the hydrologic modeling methods used
in the FEIS; as such, a discussion of the hydrologic modeling methods is included in this section. Only
those results from the hydrologic modeling that are critical to the aquatic resource analyses are discussed
in this document – other hydrologic information can be found in the FEIS.
Impacts may be direct or indirect in nature and may be temporary (short term) or permanent (long term).
A direct impact is a direct result of the Moffat Project, and occurs at the same time and in the same place
as the actions associated with each alternative. An indirect impact is a secondary or subsequent impact of
the Project, and occurs later in time or at a distance from the action. The primary indirect impacts would
result from Project-induced operational flow changes to the streams in the overall study area. Temporary
impacts generally occur during construction activities and are considered short-term disturbances that can
be reclaimed (e.g., construction and placement of pipelines) or would cease upon completion of
construction activities (e.g., construction noise). Permanent impacts are created by construction or
operational changes and are considered long term, sometimes remaining for the life of the Project
(e.g., dams), or that might occur intermittently over the life of the Moffat Project (e.g., reservoir
inundation).
The following impact thresholds are used to determine the change in intensity of impacts resulting from a
Project alternative:
No impact: no discernable effect.
Negligible: effect is at the lowest level of detection and causes very little or no disturbance.
Minor: effect that is slight, but detectable, with some perceptible effects of disturbance.
Moderate: effect is readily apparent and has measurable effects of disturbance.
Major: effect is readily apparent and has substantial effects of disturbance.
5.1 Hydrologic Modeling
The effects on streamflow and reservoir storage for each alternative were determined using Denver
Water’s PACSM, which is a water allocation computer model. PACSM was used to generate hydrologic
output, including stream flows and reservoir data. Denver Water staff developed each of the model
scenarios assessed and executed PACSM. The input, operations, and results of PACSM were reviewed
and verified by the Corps’ third-party contractor. Detailed information on the study period, network
configuration, natural flow hydrology, water rights, physical attribute data, precipitation and evaporation
rates, diversions and demands, and operational rights included in PACSM were independently evaluated.
PACSM is an integrated system of computer programs used to simulate stream flows, reservoir
operations, and water supply availability. PACSM simulates operations of the raw water supply systems
belonging to Denver Water and others, within portions of the South Platte River and Colorado River
basins. The model accounts for inflows, diversions, river gains and losses, reservoir operations, and water
rights implementation using water allocation priorities. The physical system and water rights represented
in the model are administered in accordance with the Prior Appropriation Doctrine and contractual and
operating agreements such as Senate Document 80 and the Blue River Decree. The water supply system
is represented in the model as a system of linked nodes, which correspond to actual physical features such
as diversion structures, reservoirs, instream flow requirements, demands, trans-basin imports, or stream
gages. The model allocates water to a node based on available flow, water rights, diversion or storage
capacity, and water demand. The model uses a daily time step.
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The geographic area currently modeled in PACSM extends from the headwaters of the Colorado River
and its tributaries along the Continental Divide downstream to the 15-mile reach upstream of the
confluence with the Gunnison River, and from the headwaters of the South Platte River, including the
South, Middle, and North forks, downstream to the Kersey gage. PACSM generates output data at
specific locations throughout the study area called nodes. The study period for PACSM extends 45 years
from water years 1947 through 1991, and includes a variety of hydrologic conditions, such as dry, wet,
and average years.
The following hydrologic scenarios were evaluated using PACSM:
Current Conditions (2006).
Full Use of the Existing System with RFFAs.
Action Alternatives with RFFAs.
No Action Alternative with RFFAs.
Current Conditions (2006) – The Current Conditions scenario reflects existing conditions in 2006,
including demands, facilities, agreements, operations, and administration of the Colorado River and South
Platte River basins. Under the Current Conditions (2006) scenario, Denver Water’s existing average
annual demand is 285,000 AF/yr. The purpose of the Current Conditions (2006) scenario is to model
Denver Water’s and other existing water rights and facilities under the hydrologic conditions that existed
throughout the study period (1947 through 1991). In addition, the operations of all existing reservoirs and
diversion facilities are simulated for the entire study period, regardless of when they came on-line.
Full Use of the Existing System with RFFAs – The Full Use of the Existing System with RFFAs
scenario reflects the operation of Denver Water’s existing system at an average annual demand of
345,000 AF/yr. The Full Use of the Existing System with RFFAs is without a Moffat Project on-line.
Denver Water’s projected demands are estimated to begin to exceed system supplies in year 2022. Under
this scenario, Denver Water would maximize the yield of its existing water supplies using its current
facilities and infrastructure. This scenario also includes other RFFAs/projects that are anticipated to
occur between 2006 and 2032.
Action Alternatives with RFFAs – The action alternatives reflect the operation of Denver Water’s
system in year 2032 with a Moffat Project implemented combined with other RFFAs. Denver Water’s
average demand in year 2032 is estimated to be 363,000 AF/yr (i.e., the 379,000 AF/yr average demand
less 16,000 AF/yr demand, which is anticipated to be met by additional conservation measures). Each
action alternative provides 18,000 AF/yr of new, firm yield.
No Action Alternative with RFFAs – The No Action Alternative with RFFAs scenario reflects the
operation of Denver Water’s system in year 2032 at an average demand of 363,000 AF/yr without any
modifications to its existing facilities or water rights. Under the No Action Alternative, Denver Water’s
average annual total supply would be 345,000 AF/yr because an action alternative was not implemented.
The No Action Alternative also includes other RFFAs that would occur between 2006 and 2032.
Modeling of Full Use of the Existing System with RFFAs, action alternatives, and the No Action
Alternative all included RFFAs taken by other agencies (Federal and non-Federal) and Denver Water’s
existing operations that, when combined with the Project alternatives, may result in a cumulative effect on
the environment. Project impacts were assessed by comparing the action alternatives with RFFAs to Full
Use of the Existing System with RFFAs. Cumulative effects were assessed by comparing Full Use of the
Existing System with RFFAs to Current Conditions (2006).
PACSM was used to generate daily output for stream flow, reservoir content, elevation, and surface area.
Appendix H-1 of the FEIS includes hydrologic output comparing Current Conditions (2006) and Full Use
of the Existing System with RFFAs with each of the EIS alternatives. FEIS appendices H-2 and H-3
31
provide similar output comparing Full Use of the Existing System with RFFAs with the Action
Alternatives with RFFAs. Additional hydrological information is provided in FEIS and Appendix H.
Summaries of modeled average annual streamflow for the Project effects analysis are presented in
Table 3, and average annual reservoir storage is presented in Table 4. Hydrologic output for additional
locations is provided in appendices H-1, H-2, and H-3 of the FEIS.
Table 3
Modeled Average Annual Streamflow Effects
Location Existing
Condition
Full Use
of the
Existing
System
with
RFFAs
No
Action
Alter-
native
Proposed
Action
(Alter-
native 1a)
Alter-
native
1c
Alter-
native
8a
Alter-
native
10a
Alter-
native
13a
Modeled Streamflow (cfs) – 45-year Average
Moffat Tunnel Diversion 87.8 91.5 94.7 105.8 105.5 104.2 104.2 105.1
Below Denver Water’s
Diversion from Jim Creek 1.1 1.0 0.8 0.5 0.5 0.5 0.5 0.5
Fraser River near Winter
Park Gage 11.8 11.0 10.3 8.4 8.4 8.5 8.5 8.4
Below Denver Water’s
Diversion from Vasquez
Creek
10.9 10.4 9.8 7.6 7.7 7.9 7.9 7.8
Fraser River below St.
Louis Creek 52.3 42.7 40.6 33.6 33.7 34.5 34.4 34.0
Williams Fork River below
Steelman Creek Gage 13.3 12.1 11.5 9.4 9.5 9.8 9.8 9.6
Colorado River below
Windy Gap Reservoir 214.5 185.8 183.4 174.8 175.0 176.0 176.0 175.3
Dillon Reservoir Outflow 171.7 133.5 119.4 126.9 126.3 127.5 127.5 127.3
Gross Reservoir Outflow 153.1 156.6 159.8 170.5 170.6 169.2 169.2 170.0
North Fork South Platte
River below Geneva Creek
Gage
162.0 198.2 211.8 204.4 204.9 203.7 203.8 204.0
South Platte River at
Waterton Gage 154.5 138.7 133.4 135.0 134.8 135.0 135.0 134.8
Difference in Streamflow (cfs) – Alternatives Compared to Full Use of the Existing System with RFFAs
Moffat Tunnel Diversion NA NA 3.2 14.3 14.0 12.7 12.7 13.6
Below Denver Water’s
Diversion from Jim Creek NA NA -0.2 -0.5 -0.5 -0.5 -0.5 -0.5
Fraser River near Winter
Park Gage NA NA -0.7 -2.6 -2.6 -2.5 -2.5 -2.6
Below Denver Water’s
Diversion from Vasquez
Creek
NA NA -0.6 -2.8 -2.7 -2.5 -2.5 -2.6
Fraser River below St.
Louis Creek NA NA -2.1 -9.1 -9.0 -8.2 -8.3 -8.7
Williams Fork River below
Steelman Creek Gage NA NA -0.6 -2.7 -2.6 -2.3 -2.3 -2.5
32
Table 3
Modeled Average Annual Streamflow Effects
Location Existing
Condition
Full Use
of the
Existing
System
with
RFFAs
No
Action
Alter-
native
Proposed
Action
(Alter-
native 1a)
Alter-
native
1c
Alter-
native
8a
Alter-
native
10a
Alter-
native
13a
Colorado River below
Windy Gap Reservoir NA NA -2.4 -11.0 -10.8 -9.8 -9.8 -10.5
Dillon Reservoir Outflow NA NA -14.1 -6.6 -7.2 -6.0 -6.0 -6.2
Gross Reservoir Outflow NA NA 3.2 13.9 14.0 12.6 12.6 13.3
North Fork South Platte
River below Geneva Creek
Gage
NA NA 13.6 6.2 6.7 5.5 5.6 5.8
South Platte River at
Waterton Gage NA NA -5.3 -3.7 -3.9 -3.7 -3.7 -3.8
Difference in Streamflow (%) – Alternatives Compared to Full Use of the Existing System with RFFAs
Moffat Tunnel Diversion NA NA 3 16 15 14 14 15
Below Denver Water’s
Diversion from Jim Creek NA NA -20 -50 -50 -50 -50 -50
Fraser River near Winter
Park Gage NA NA -7 -24 -24 -23 -23 -24
Below Denver Water’s
Diversion from Vasquez
Creek
NA NA -6 -27 -26 -24 -24 -25
Fraser River below St.
Louis Creek NA NA -5 -21 -21 -19 -19 -20
Williams Fork River below
Steelman Creek Gage NA NA -5 -22 -21 -19 -19 -20
Colorado River below
Windy Gap Reservoir NA NA -1 -6 -6 -5 -5 -6
Dillon Reservoir Outflow NA NA -11 -5 -5 -4 -4 -5
Gross Reservoir Outflow NA NA 2 9 9 8 8 9
North Fork South Platte
River below Geneva Creek
Gage
NA NA 7 3 3 3 3 3
South Platte River at
Waterton Gage NA NA -4 -3 -3 -3 -3 -3
Notes:
% = percent
cfs = cubic feet per second
NA = not applicable
RFFAs = reasonably foreseeable future actions
33
Table 4
Modeled Average Annual Reservoir Volumes
Location Existing
Condition
Full Use
of the
Existing
System
with
RFFAs
No
Action
Alter-
native
Proposed
Action
(Alter-
native 1a)
Alter-
native
1c
Alter-
native
8a
Alter-
native
10a
Alter-
native
13a
Average Reservoir Storage (AF) – 45-year Average
Williams Fork
Reservoir 62,269 65,764 65,775 65,090 67,018 65,279 65,288 65,338
Dillon Reservoir 220,665 201,820 191,801 198,565 198,192 199,091 199,036 199,042
Wolford Mountain
Reservoir 55,796 52,002 51,826 51,859 51,858 51,865 51,867 51,871
Gross Reservoir 27,149 29,473 28,203 87,819 58,390 70,187 70,227 77,300
Antero Reservoir 18,424 18,096 17,410 17,791 17,790 17,804 17,803 17,810
Eleven Mile Canyon
Reservoir 95,396 92,770 91,047 93,102 93,060 93,130 93,117 93,132
Cheesman Reservoir 66,603 66,463 64,665 65,762 65,738 65,741 65,739 65,764
Leyden Gulch
Reservoir NA NA NA NA 28,956 NA NA NA
Gravel Pit and Deep
Aquifer Storage NA NA NA NA NA 3,486 3,973 2.426
Difference in Storage (AF) – Alternatives Compared to Full Use of the Existing System with RFFAs
Williams Fork
Reservoir NA NA 11 -674 -746 -485 -476 -426
Dillon Reservoir NA NA -10,019 -3,255 -3,628 -2,729 2,784 -2,777
Wolford Mountain
Reservoir NA NA -176 -143 -144 -137 -135 -131
Gross Reservoir NA NA -1,270 58,346 28,917 40,714 40,754 47,827
Antero Reservoir NA NA -686 -305 -306 -292 -293 -286
Eleven Mile Canyon
Reservoir NA NA -1,723 332 290 360 347 362
Cheesman Reservoir NA NA -1,798 -701 -725 -722 -724 -699
Leyden Gulch
Reservoir NA NA NA NA NA NA NA NA
Gravel Pit and Deep
Aquifer Storage NA NA NA NA NA NA NA NA
Difference in Storage (%) – Alternatives Compared to Full Use of the Existing System with RFFAs
Williams Fork
Reservoir NA NA 0% -1% -1% -1% -1% -1%
Dillon Reservoir NA NA -5% -2% -2% -1% -1% -1%
Wolford Mountain
Reservoir NA NA 0% 0% 0% 0% 0% 0%
Gross Reservoir NA NA -4% 198% 98% 138% 138% 162%
Antero Reservoir NA NA -4% -2% -2% -2% -2% -2%
Eleven Mile Canyon
Reservoir NA NA -2% 0% 0% 0% 0% 0%
Cheesman Reservoir NA NA -3% -1% -1% -1% -1% -1%
34
Table 4
Modeled Average Annual Reservoir Volumes
Location Existing
Condition
Full Use
of the
Existing
System
with
RFFAs
No
Action
Alter-
native
Proposed
Action
(Alter-
native 1a)
Alter-
native
1c
Alter-
native
8a
Alter-
native
10a
Alter-
native
13a
Leyden Gulch
Reservoir NA NA NA NA NA NA NA NA
Gravel Pit and Deep
Aquifer Storage NA NA NA NA NA NA NA NA
Notes:
% = percent
cfs = cubic feet per second
NA = not applicable
RFFAs = reasonably foreseeable future actions
5.2 Aquatic Resources
The methods used to evaluate effects on fish and benthic invertebrate communities and their habitat are
described in detail in the FEIS. Each of the alternatives involves changes in the hydrologic regime,
including changes to the quantity and timing of flow and reservoir storage. The FEIS evaluated changes
in flow and storage patterns in streams and reservoirs that may affect the quality and amount of habitat
available for fish and invertebrate species composition and abundance parameters in the study area.
Changes in hydrology can also affect water quality, such as temperature, and can affect channel
morphology and sedimentation. Therefore, the evaluations of changes in water quality, channel
dynamics, and riparian vegetation were also considered as part of the effects analysis for aquatic
resources and their habitat. Environmental effects are described in greater detail in the FEIS.
5.2.1 Habitat Simulation Methods
Physical Habitat Simulation (PHABSIM) was used for evaluating the impacts to fish populations.
PHABSIM simulates a relationship between fish habitat availability and flow in streams. Along with
professional judgment, this method was used to evaluate the relative impacts of the Project on the relevant
fish and benthic invertebrate parameters. PHABSIM information was available for every mainstem section
of stream in the study area with changes in average annual flow of greater than 10% and several other
sections of stream in the study area. The output from the PHABSIM simulation provides habitat versus
flow relationships for different species of fish, based on each species’ known habitat preferences. This
relationship indicates potential habitat availability, expressed as square feet of weighted usable area
(WUA) per 1,000 feet of stream (feet2/1,000 feet) available over a range of flows.
PHABSIM information simulates habitat availability for distinct segments of stream (Table 5). The
impacts analysis was organized with respect to the segments of stream established with the available
PHABSIM data. In the Fraser River and Williams Fork River basins, there are tributaries with Denver
Water diversions that were included in the study area; PHABSIM data were not available for most of
these tributaries, but R-2-Cross data were available for two sites on the lower Fraser River. The
R-2-Cross data method does not model fish habitat, but simulates width, depth, and velocity conditions
across a single stream transect over a range of flows. It is used in Colorado to evaluate the suitability of
low flows to maintain habitat conditions for fish and invertebrates.
35
Table 5
Stream Segments Modeled with PHABSIM Habitat Simulations
in the Moffat Study Area
Stream Segment Description
Fraser River
1 Headwaters to Vasquez Creek
2 Vasquez Creek to St. Louis Creek
3 St. Louis Creek to Ranch Creek
4 Ranch Creek to Mouth of Canyon
5 Mouth of Canyon to Colorado River
St. Louis Creek 1 Denver Water Diversion to Fraser River
Vasquez Creek 1 Denver Water Diversion to Fraser River
Little Vasquez Creek 1 Denver Water Diversion to Vasquez Creek
Ranch Creek 1 Denver Water Diversion to Fraser River
Williams Fork River 1 Confluence of Headwater Tributaries to South Fork
Colorado River 1 Windy Gap Reservoir to Williams Fork River
2 Williams Fork River to Blue River
Blue River
1 Dillon Reservoir to Rock Creek
2 Rock Creek to Green Mountain Reservoir
3 Green Mountain Reservoir to Spring Creek
4 Spring Creek to Colorado River
South Boulder Creek
1 Moffat Tunnel to Pinecliffe
2 Pinecliffe to Gross Reservoir
3 Gross Reservoir to South Boulder Diversion Canal
North Fork South Platte River 1 Roberts Tunnel to Buffalo Creek
2 Buffalo Creek to South Platte River
South Platte River 1 Chatfield Reservoir to Littleton
Fish pass through several life stages during their lives from egg to adult. Periodicity refers to the time of the
year when a life stage is present and PHABSIM habitat simulations are appropriate (Table 6). In most of the
streams and stream segments described in this report, brown trout (Salmo trutta) are self-sustaining and are
the dominant species of fish.
Table 6
Periodicity of Fish Species in Streams in the Moffat Project Study Area
Species/Life Stage Adult Spawning Fry Juvenile
Brook trout All year October – November NA NA
Brown trout All year October – November March – September All year
Rainbow trout All year April – May June – September All year
Note:
NA = not applicable
For the adult and juvenile life stages of trout that are present throughout the year, habitat availability in
most streams usually reaches a minimum during extreme flow conditions, either during the low flows in
late winter or during the peak flows of runoff. During low flows, depths may be too shallow to support
fish in much of the stream. Reduced habitat availability at high flows reflects the fact that when the
stream approaches bankfull depth, velocities are high and low-velocity floodplain habitats and side
36
channels may not be available. During high flows, velocity may become too fast for fish to maintain their
preferred position or they may be washed downstream out of their preferred habitat. Reducing habitat
availability during the times of the year that experience minimum habitat would reduce the suitability of
the stream to support fish and would likely result in adverse impacts. Changes in habitat during other
times of the year would have less influence on fish populations.
The fish habitat use criteria used in PHABSIM modeling represent habitat use for trout for the warmer
seasons of the year and usually at low to moderate flows, as is common with many PHABSIM studies.
Habitat use by fish in winter or at high flows in the study streams may be different. Qualitative studies
suggest that trout use a subset of their summer habitat during the winter months. In winter, trout tend to
use deeper habitat with slower velocity and slightly larger substrate and may be more oriented to cover.
Therefore, using summer low-flow habitat criteria for trout in this study may overestimate the habitat
actually used in the winter.
Using the available hydrology data at PACSM nodes corresponding to the stream segments in the study
area, fish habitat availability was simulated with PHABSIM for average years, wet years, and dry years
for each of the species and life stages (Table 7), given the periodicity described in Table 6. Mean daily
flow was used as the time step for each of the three-year types. Average-year hydrology included all
45 years in the hydrologic period from 1947 through 1991; wet-year hydrology was based on the five
wettest years within this period; and dry-year hydrology was based on the five driest years within this
period.
Output from the Indicators of Hydrologic Alteration (IHA) software (TNC 2006) was also used to
evaluate impacts to aquatic resources. IHA estimates changes to many different types of flow
components. IHA parameters evaluated in this report include the frequency, timing, and magnitude of
high flows, small floods, and large floods which can affect aquatic biological resources.
Table 7
PHABSIM Habitat Relationships Available for Stream Segments and
Trout Species and Life Stages in the Moffat Collection System Study Area
Stream Segment PACSM
Node
Brook
Trout Brown Trout Rainbow Trout
A S A S F J A S F J
Fraser River
1 2580 X X X X X X X X
2 2600 X X
3 2720 X X X X X X
4 2810 X X X X X X X X
5 2900 X X X X X X
St. Louis Creek 1 2200 X X
Vasquez Creek 1 2370 X X
Ranch Creek 1 2500 X X
Williams Fork River 1 3600 X X
Colorado River 1 1350 X X X X X X
2 1430 X X X X X X
Blue River
1 4250 X X X X
2 4500 X X X X X X X X
3 4650 X X X X X X
4 4800 X X X X X X
37
Table 7
PHABSIM Habitat Relationships Available for Stream Segments and
Trout Species and Life Stages in the Moffat Collection System Study Area
Stream Segment PACSM
Node
Brook
Trout Brown Trout Rainbow Trout
A S A S F J A S F J
South Boulder Creek
1 57100 X X X X X
2 57120 X X X
3 57140 X X X
North Fork South Platte River 1 50700 X X X X
2 50750 X X X X
South Platte River 1 51290 X X X X
Notes:
Refer to Figure 3 for the locations of PACSM nodes.
A = adult
F = fry
J = juvenile
S = spawning
PACSM = Platte and Colorado Simulation Model
5.2.2 Approach to Impact Analysis
The types of impacts to aquatic biological resources could include beneficial impacts or adverse impacts,
depending on increases or decreases in the status of the aquatic resources for the Project alternatives with
RFFAs in each stream segment and reservoir. Projected changes in flow and modeled habitat known as
WUA were primary components along with professional judgment about potential effects of each change
on the suitability of the water body to maintain fish and invertebrate populations. Projected changes in
water quality, water temperature, channel geomorphology, sediment characteristics, and riparian
vegetation were also incorporated into this analysis using professional judgment.
In the FEIS, the parameters that were the focus of the analysis of fish populations in streams were the
number and density of self-sustaining species. These parameters are widely used in Colorado to describe
fish communities. Self-sustaining species are fish species that maintain populations through natural
reproduction and, as such, are directly affected by changes in habitat availability, water quality,
hydrology, riparian vegetation, channel morphology, and other ecological factors. Stocked fish are also
affected by these changes, but their population levels are controlled to a large extent by management
decisions by agencies such as CPW.
In most of the coldwater streams in the study area, the fish communities consist of one dominant trout
species and several less common species of trout, as well as species of suckers and sculpins. The species
composition is generally stable, and there are limited opportunities for additional native or introduced
species to become established. Therefore, impacts to study area streams with the alternatives probably
would not affect fish species composition very much except in situations of moderate to major changes in
the suitability of the stream to support fish.
Parameters used in the analysis of fish in Gross Reservoir were the number and abundance of species.
Gross Reservoir is stocked with fish to support recreational fishing and contains a mixture of a few
abundant species and many less common species of both self-sustaining and stocked fish. This evaluation
focused on the potential effects of the alternatives on the suitability of Gross Reservoir and the proposed
Leyden Gulch Reservoir site to support self-sustaining and stocked species of fish. Since the fish
community of Gross Reservoir is managed with stocked species, there are more opportunities for
additional species to become established compared to the more stable species composition in coldwater
38
streams. The impacts of the alternatives may affect fish species composition to a larger degree in
reservoirs than in streams.
The parameters used in the total effects analysis (cumulative effects analysis) of benthic invertebrates
were the number of species present, species composition, and the abundance of invertebrates. These
parameters are widely used in Colorado to describe invertebrate communities. Invertebrate communities
in streams typically consist of a few abundant species and many less common species. These benthic
invertebrate community parameters are sensitive to changes in habitat availability and water quality.
There are many opportunities for invertebrate species introductions in streams primarily because many
insects can fly between streams as a method of dispersal. Therefore, changes in the suitability of the
habitat in a stream may affect invertebrate species composition to a greater degree than for fish.
An incremental approach to impacts assessment was used, which assumes a greater intensity of impacts
resulting from a greater change in conditions. The type and intensity of impacts were evaluated on a
case-by-case basis for each stream segment and reservoir included in the study area. Differences of less
than 10% are likely within the margin of error of the hydrologic and statistical data and would be unlikely
to result in adverse or beneficial impacts on fish populations. If key WUA metrics decrease or increase
by 10% or less and there are no substantial changes to channel geomorphology, water quality, etc., the
combined effect of a Project alternative and RFFAs was considered to be no impact.
Negligible impacts resulted when differences in WUA metrics were less than 10% and there were slight
changes in other components, such as flow or channel geomorphology. Differences in WUA parameters
of less than 10% would be unlikely to result in adverse or beneficial impacts on aquatic biota, because
natural variability in hydrologic and biological data renders a change of less than 10% undetectable.
Negligible impacts would indicate that fish and invertebrate populations would continue to fluctuate
within normal historic ranges. Negligible impacts also resulted when one or more of the WUA metrics
had differences of 10% or more but were judged to have no detectible effect on fish. This was the case
when the differences resulted in a combination of a small number of favorable or unfavorable changes to
WUA among the different fish species and life stages with no consistent trend.
If a difference in WUA metrics was more than 10%, the change was graded according to professional
judgment. The impact intensity takes into account the magnitude of the change in a WUA metric, the risk
of crossing an ecological threshold and causing a large change in fish or benthic macroinvertebrate
species composition or abundance, and projected changes in water quality, temperature, channel
geomorphology, sediment characteristics, and riparian vegetation. Minor impacts would result in small
changes to aquatic resources. Moderate impacts would result in detectible and readily-apparent changes
outside the current range of natural variability. Major impacts would likely result in a substantial and
readily-apparent change in abundance and species composition of the fish and benthic invertebrate
communities far outside the current range of natural variability.
Some of the aquatic resources within the study area may be near, at, or past ecological thresholds;
however, such ecological thresholds have not been empirically determined for any of the stream segments
within the study area, and it is likely that each stream will have its own threshold level. Therefore, each
stream segment was evaluated to determine if the proposed flow changes would cause the segment to
cross a flow-based threshold or “tipping point.” Two flow-based thresholds were used. The first was
based on a study by Carlisle et al. (2010), where the risk of fish community impairment increased after a
60% reduction in maximum flows. However, there was considerable variability among the individual
streams. The second was based on a study by Baran et al. (1995) that showed that a 60% reduction in
average annual WUA produced threshold effects on fish populations. However, the relationships between
flow changes, habitat availability changes, and changes in fish populations are complex, and a 60%
reduction in average annual flows does not necessarily create an equivalent reduction in habitat. The use
39
of this threshold assumes a 1:1 relationship between percent flow change and percent habitat loss;
because this is most often not the case, and the change/loss is usually less, this threshold is conservative.
5.3 Wildlife Resources
Existing information was reviewed and special concerns related to the Project were identified through
coordination and consultation with the Service, CPW, USFS, and CNHP, and by review of existing
information including CNHP element occurrence data, the CPW Natural Diversity Information System
(NDIS) website of species’ ranges, USFS data, previous studies and reports, and literature searches.
Wildlife habitat was determined by site reconnaissance, vegetation mapping, aerial photography
interpretation, and database review. General field surveys were conducted at new or expanded reservoirs
and aboveground facilities. Several focused surveys were conducted, including:
Preble’s meadow jumping mouse: A habitat evaluation was conducted for Preble’s meadow
jumping mouse at three canyons upstream of the existing Gross Reservoir in 2005. A trapping
survey was conducted at Leyden Gulch Reservoir in 2005, with negative results (the same as the
1997 survey at Leyden Gulch Reservoir).
Northern goshawk (Accipiter gentilis): A survey was conducted at Gross Reservoir in 2010.
Northern leopard frog: A survey was conducted at Gross Reservoir in 2010.
Quantitative evaluation of direct effects was done by digitizing boundaries of habitat to Geographic
Information System (GIS) polygons and then intersecting them with Project facility shapefiles. The direct
effects on large game winter range were calculated as a percentage of the total acreage of each affected
range as mapped by CPW. Other direct impacts were assessed qualitatively. Indirect effects, including
displacement of wildlife outside the Project footprint due to increased noise, construction traffic, and
other human disturbance, were evaluated qualitatively. Potential hydrologic changes of each alternative
and the associated effect on riparian vegetation were used as indicators of indirect effects on riparian
wildlife species.
The above analyses were completed during preparation of the Moffat DEIS from 2005-2012, with some
updates performed between 2012 and 2014 during preparation of the Moffat FEIS. Qualitative analysis
and an impact summary of two additional USFS Region 2 sensitive species, hoary bat (Lasiurus cinereus)
and Lewis’s woodpecker (Melanerpes lewis), was completed in 2016 based on the current USFS
Region 2 sensitive species list, which, at the time of this writing, is the September 24, 2013 list.
5.4 Vegetation Resources
Vegetation cover types were surveyed and mapped in late August and September 2005, and June 2006 at
the reservoir sites and aboveground facilities. In areas of permanent disturbance, the sites were traversed
on foot to identify plant community associations and dominant species. Areas of temporary disturbance,
such as conveyance facilities, were primarily observed by vehicle reconnaissance, but areas of interest
were surveyed on foot. Observations of plant communities were compared with the cover type
classification used by the Colorado NDIS. Vegetation cover types were digitized to GIS polygons and
then intersected with study area shapefiles.
Separate field surveys were conducted in 2005 and 2006 to delineate wetlands and to map riparian
shrubland and woodland at the reservoirs and aboveground facilities. Wetlands were delineated using the
Routine Determination Procedures outlines in the 1987 Corps’ Wetlands Delineation Manual. Wetland
and riparian boundaries were surveyed with a global positioning system (GPS) or mapped in the field and
the boundaries were transferred to ArcGIS computer software for area calculations and map generation.
Wetland and riparian habitats along the river segments were mapped using existing CPW riparian
40
mapping data, combined with detailed field studies at 12 sample sites that were also used for hydraulic
analysis and study of channel dynamics. Plant associations were mapped at the 12 sample sites.
Surveys for Ute ladies’-tresses orchid (Spiranthes diluvialis) and Colorado butterfly plant (Gaura
neomexicana ssp. coloradensis) were conducted at Leyden Gulch Reservoir in August 2005 and 2006. A
previous survey had been conducted in 1997. Surveys for USFS sensitive and local concern plant species
at Gross Reservoir were conducted during the summer of 2010.
Additional information was obtained from field visits, CNHP element occurrence data, USFS data, CPW
riparian habitat mapping, previous studies and reports, and literature searches.
Tables were assembled rating the potential for occurrence of sensitive species at each Project facility,
based on a combination of habitat surveys and species information.
Impacts were assessed quantitatively using GIS analysis where mapped locations were available. Other
impacts were assessed qualitatively. Direct effects include permanent effects, such as construction of
reservoirs, and temporary construction effects, such as disturbance of vegetation during pipeline
construction.
41
6. Fish and Wildlife Resources – Current Conditions
This section describes the current status of fish and wildlife resources within the study area for each
resource.
6.1 Aquatic Resources
The status of the aquatic biological communities in the study area is a result of historical and current
activities and differs from the natural ecosystem that existed prior to settlement. Activities that have
influenced the aquatic ecosystem have caused changes in hydrology, water quality, and channel
morphology. Also, some fish populations are managed for recreational fishing. These activities resulted
in changes in species composition, species distribution, and habitat from pre-settlement conditions. This
section focuses on Current Conditions and does not attempt to document changes from pre-settlement
conditions.
Threatened, endangered, and other special status aquatic species are described under Wildlife Resources
in Section 6.2, along with terrestrial wildlife species.
6.1.1 Gross Reservoir
Gross Reservoir is located on the mainstem of South Boulder Creek, approximately 22 miles upstream of
the confluence with Boulder Creek. Forsythe Canyon and Winiger Gulch are two small tributary streams
to Gross Reservoir and portions of these streams would be inundated with an expanded reservoir.
Gross Reservoir is a steep-sided reservoir, with limited shallow-water areas near the shoreline. At
bankfull (surface elevation of 7,282 feet), the depth of the reservoir is approximately 330 feet, with a
surface area of 418 acres. The elevation of the reservoir fluctuates approximately 48 feet within a year as
drawdowns use stored water. The deep water, small size, and seasonal fluctuation limit the available
habitat for aquatic biological resources in Gross Reservoir. Gross Reservoir is classified as Aquatic Life
Cold 2 for aquatic life uses. It has moderate water clarity, low to moderate levels of chlorophyll-a, and
meets CDPHE Water Quality Control Division (WQCD) standards for temperature, dissolved oxygen,
and pH. Gross Reservoir, like many other Front Range reservoirs in Colorado is on Colorado’s
Monitoring and Evaluation List for aquatic life use because of elevated levels of mercury in fish tissue.
CPW gill net data collected 1982 through 1996 revealed a diverse fish community present in Gross
Reservoir (FEIS Table 3.11-3). Twelve species and two hybrid varieties have been collected over this
period including both coldwater and warmwater fishes. CPW stocks the reservoir annually with a variety
of species. Rainbow trout (Oncorhynchus mykiss) and splake (Salvelinus fontinalis x S. namaycush) are
stocked nearly every year. Kokanee salmon (Oncorhynchus nerka) were stocked in 2001, 2003, and
2004. Greenback cutthroat trout were stocked in 2002 and 2004, and cutthroat/rainbow trout hybrids
were stocked in 2003 and 2004. All of the stocked fish were small, usually less than 4 inches. Longnose
suckers (Catostomus catostomus) and white suckers (Catostomus commersoni) and rainbow trout have
dominated the gill net catch, with the three species combined consistently averaging over 70% of the total
catch. They probably maintain self-sustaining, naturally-reproducing populations in Gross Reservoir.
Several species were represented by only a few individuals and are not maintained in the reservoir by
natural reproduction or stocking by CPW, including brook trout (Salvelinus fontinalis), brown trout,
longnose dace (Rhinichthys cataractae), black bullheads (Ameuirus melas), and channel catfish (Ictalurus
punctatus).
Forsythe Canyon was sampled in 1985 and 2011, and fish were absent. Winiger Gulch was also sampled
in 1985 and 2011, and brook trout, brown trout, and rainbow trout were present both years. Total fish
density was estimated to be 3,647 fish per hectare (fish/ha) in 1985 and 2,200 fish/ha in 2010. In 1985,
most of the fish were small, either young-of-the-year (YOY) or juvenile fish, and in 2011 all fish were
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YOY. All three species inhabit Gross Reservoir and it is likely Forsythe Canyon is used for spawning
and rearing young fish for the reservoir populations of these species. Five other tributaries enter Gross
Reservoir, but they are ephemeral and dry for much of the year and do not support fish.
Benthic macroinvertebrate sampling data are not available for Gross Reservoir.
6.1.2 Other Project Facilities
The proposed Leyden Gulch Reservoir would inundate portions of Leyden Gulch upstream of SH 93.
Leyden Creek is an ephemeral stream in this section and apparently only has water after precipitation
events. During field studies conducted in August 2005, the channel was dry and overgrown with
terrestrial vegetation. There was no aquatic life present. A short, south branch of Leyden Gulch contains
a spring pool near the railroad tracks. This spring allowed a trickle of water to flow in the channel for less
than 50 feet downstream of the spring. These areas provide no habitat for fish, although a limited
community of benthic invertebrates is probably present within the spring.
Conduit M crosses the following streams from west to east: Little Dry Creek (three crossings), Clear
Creek and its tributary (one crossing), and South Platte River (one crossing). The creeks at the crossings
contain communities of warmwater fish and invertebrates. The tributary to Clear Creek is a small stream
that periodically may be dry, and may support a very limited community of warmwater fish and
invertebrates. The first 9 miles of Conduit O (from west to east) overlaps with the Conduit M corridor.
The stream crossings that are unique to Conduit O (i.e., not shared with Conduit M) include a tributary to
Little Dry Creek and a tributary to Niver Creek. These two small streams probably support limited
communities of warmwater fish and invertebrates. Conduit O also crosses the South Platte River similar
to Conduit M, but in a different location.
No sampling data exist for the gravel pit lakes. However, the three pits with water probably contain
communities of benthic macroinvertebrates, phytoplankton, and zooplankton. Fish may also be present.
The gravel pit lakes would be transferred to Denver Water without water stored in them, and apparently
with no existing aquatic resources. The future aquatic communities of the gravel pit lakes would depend
on their operation and management. They would probably be suitable to support warmwater fish,
invertebrates, and other aquatic organisms.
The proposed diversion structure crosses the South Platte River near the Worthing Pit. The South Platte
River in this section contains a warmwater community of fish and invertebrates.
The distribution pipelines for the Denver Basin Aquifer Facilities cross the following waterways: South
Platte River (two crossings), Lakewood Gulch (one crossing), Cherry Creek (three crossings), and Sand
Creek (one crossing). These four waterways are perennial at the locations of the crossings and sustain
communities of many species of warmwater fish and invertebrates.
6.1.3 Fraser River
Fish populations in the mainstem of the Fraser River are typical of a Rocky Mountain alpine coldwater
fishery. Several species of trout, suckers, and sculpins have been collected from this river. Small (5 to
12 centimeters [cm]) rainbow trout were stocked by CPW in the section of the Fraser River downstream
of Tabernash. The Fraser River has a Denver Water diversion in its headwaters, upstream of most
tributaries. Upstream of the diversion, brook trout and cutthroat trout exist, with brook trout dominant.
Downstream of the diversion, brook trout are dominant in the upper reaches, with brown trout and
rainbow trout becoming more dominant in the lower reaches. Cutthroat trout were present downstream of
the diversion in small numbers from 1985 through 2001. Sculpins are abundant throughout (FEIS
Table 3.11-5), and probably include a mix of Paiute sculpins (Cottus beldingii) and mottled sculpins
(Cottus bairdi). This zonation of fish species is common for Colorado mountain streams.
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Fish densities frequently exceed 1,000 fish/ha, but fluctuate considerably between sites and years. The
fish data for the mainstem of the Fraser River indicate that the population is healthy to sustaining and has
not crossed a tipping point. There appears to be no temporal trend in fish abundance. Although there is
considerable fluctuation in density among the years, there is no decreasing or increasing pattern. The
fluctuation between years is likely due, at least in part, to differences in site locations and the number of
sites.
Whirling disease occurs within the Fraser River mainstem. The rate of infection is relatively high in the
lower Fraser River due to suitable habitat for Tubifex worms (Tubifex tubifex).
Benthic invertebrate populations were sampled at seven sites in August 2007 along the Fraser River. The
number of invertebrate taxa ranged from 24 to 38 at the sites. The invertebrate groups present are typical
of Colorado mountain streams. At all sites there were at least several species of sensitive insects
indicating that habitat and flow conditions were suitable to support sensitive species. Macroinvertebrate
communities were also sampled in the Fraser River in 2008 and the results indicated there were a wide
variety macroinvertebrate groups present including sensitive species. These data were evaluated with the
Colorado Macroinvertebrate Multimetric Index (MMI), an index developed for and used by the CDPHE
to determine aquatic life use attainment in streams, and with the USFS MIS, a regionally specific index
developed by Rees (2009). The USFS MIS score indicated that the macroinvertebrate community in the
Fraser River was similar to those found in reference streams. Sampling at two sites in the spring and fall
of 2010 in segments 4 and 5 of the river also found a relatively high density and number of taxa.
The WQCD macroinvertebrate data were available for two segments of the Fraser River in 2007 and
2010. An MMI score was calculated from two sites each in 2007 and 2010, one in Segment 1 and one in
Segment 2. The WQCD had MMI scores that are much lower and contrast with the diverse and abundant
macroinvertebrates collected by other groups during the same time period. The WQCD samples
generally contained high proportions of Chironomidae midges and mites, which result in low MMI
scores. The abundant Ephemeroptera, Plecoptera, Trichoptera, and other insects present in the samples
from the other groups were less abundant in the WQCD samples.
The total amount of average annual and peak flow diverted from the upper Fraser River is over 60%,
which suggests that this river may be approaching an ecological tipping point, at least in the upper
reaches. However, the fish data for the mainstem of the Fraser River indicate that the population is
healthy to sustaining with no trends over time and has not crossed a tipping point. Much of the data for
macroinvertebrates also indicates the presence of a healthy and diverse community although some recent
WQCD samples had low MMI scores, and the upper reaches of the Fraser River are provisionally listed
on the Section 303(d) List for aquatic life. Overall, the available information indicates that the Fraser
River has not crossed an ecological tipping point.
A total of 32 tributaries to the Fraser River would be affected by implementation of the Moffat Project
alternatives. All of the tributaries have existing Denver Water or Englewood diversions and could
potentially be affected by changes in the pattern of flow diversion, except for Trail Creek which has no
diversion but is downstream of diversions on North Trail and South Trail creeks. Denver Water
diversions can act as barriers to the upstream migration of fish. This allows fish populations upstream of
some of the diversions to be isolated from species that are present downstream. In some cases, this allows
native cutthroat trout populations to exist upstream of the diversions without competition from or
hybridization with non-native trout species. The Moffat Project will not affect flows upstream of the
diversions. A number of the diverted streams have no fish present and no macroinvertebrate data
available, including Short, Byers, Fool, West Fork Main Elk, East Elk, Cooper, Dribble, Wolverine, Cub,
North Trail, and South Trail creeks. Information about the remaining creeks is provided below.
Upstream of the diversions, brook trout and Colorado River cutthroat trout are present. Downstream of
the diversions, the Fraser River tributary streams contain mostly brook trout, with cutthroat trout, brown
trout, and mottled sculpin present in a few streams. No fish are stocked in these streams by CPW,
44
although some streams (Iron, Vasquez, and Jim creeks) have been stocked variously with “cutthroat,”
Pike’s Peak cutthroat (Oncorhynchus clarkii stomias), Trapper’s Lake cutthroat, brook trout, and rainbow
trout in the past. Although the status and distribution of native lineages of cutthroat trout are uncertain,
cutthroat trout populations in the following streams are considered to be genetically pure: Iron, Little
Vasquez, the North Fork of Ranch, Hamilton, and Jim creeks. Cutthroat trout populations in Cabin,
Middle Fork of Ranch, the South Fork of Ranch, and Vasquez creeks could contain genetic characteristics
of rainbow trout, other cutthroat trout subspecies, or both.
West St. Louis Creek is a small, narrow stream with a width of less than 2 m. There is no bypass flow
and it is fully diverted at times. Downstream of the diversion there were no fish in fall 2005, and the
channel was nearly dry just downstream of the diversion. Upstream of the diversion, 56 brook trout were
collected in 2010. Average density was estimated to be 2,545 fish/ha, and average biomass was estimated
to be 17.31 kilograms per hectare (kg/ha). Macroinvertebrate sampling in 2005 found a total of
27 different macroinvertebrate species downstream of the diversion, including mostly species tolerant of
low flows such as beetles (Coleoptera), caddisflies (Trichoptera), and midges. There were fewer species
of invertebrates in this stream compared to other streams sampled at this time. West St. Louis Creek
downstream of the diversion has passed an ecological tipping point.
St. Louis Creek has bypass flows of 10 cfs in the summer and 3 cfs the remainder of the year. It has a
moderate slope with an average bankfull width of 11 meters (m). The diversions amount to 36% of the
native flow on average. Fish populations upstream of the Denver Water diversion were sampled in 2003.
Brook trout and cutthroat trout were collected, with brook trout comprising 95% of the population. No
data are available on the genetic lineage of the cutthroat trout in this stream. Total fish density was
estimated at 797 fish/ha. Downstream of the diversion, brook trout and mottled sculpin were collected in
several sample events, with brook trout dominating the populations, which ranged from 646 to
5,231 fish/ha. Fish data are limited for this stream, but they indicate that the fish populations are
generally healthy. Benthic macroinvertebrate data were collected by CWQCD in 1997, 2000, and 2004 at
five sites. The benthic macroinvertebrate communities are healthy and balanced. MMI scores for these
replicates were relatively high indicating attainment of aquatic life use. It does not appear that St. Louis
Creek has passed an ecological tipping point.
Iron Creek is diverted near its confluence with St. Louis Creek with only a short length of stream (a few
hundred meters) between the diversion and its mouth. There is no bypass flow for Iron Creek and it is
fully diverted at times. This stream was sampled upstream of the diversion in 2001, and a single cutthroat
trout was collected. The density of this population is estimated to be between 0 and 50 fish per mile
(fish/mile). The short section downstream of the diversion was dry in 2001 and in 2010. Though this
stream is large enough to support fish, its steep gradient and cold water temperatures may prevent
establishment of fish populations. Iron Creek Lake, a headwater lake, has been stocked by CPW in the
past. Iron Lake was last surveyed in 1969, and a total of 28 cutthroat trout was collected during a 12-hour
gill net set. The genetic status of these fish is untested, but they are currently classified as unaltered.
There is no benthic macroinvertebrate information available for Iron Creek. The high rate of diversion
resulting in a dry channel downstream indicates that Iron Creek is past an ecological tipping point and the
short section of stream now likely supports a less abundant and less diverse community of benthic
macroinvertebrates.
East St. Louis Creek is a steep, small stream approximately 1 m wide. There is no bypass flow for this
stream. At the time of fish sampling in fall 2005, the stream was being fully diverted and was dry for a
short section downstream of the diversion. Flow from groundwater added water to the stream a short
distance downstream allowing sampling for fish and macroinvertebrates. This stream was sampled
upstream of the diversion in 2010, and fish were absent. Macroinvertebrate sampling in 2005 found
similar density and number of taxa to other tributaries. The macroinvertebrate community was abundant
and diverse with a density of 1,994 organisms per square meter (organisms/m2) and 43 different taxa
present. It included many species of stoneflies (Plecoptera), mayflies (Ephemeroptera), and caddisflies,
45
including species that are usually sensitive to degraded water quality and flow conditions. The amount of
flow diverted and the lack of fish indicate that East St. Louis Creek is past an ecological tipping point.
The healthy macroinvertebrate community not far downstream of the diversion indicates that it starts to
recover quickly with groundwater inputs.
King Creek is a small steep, narrow stream about 0.5 m wide. It has no bypass flow and it is fully
diverted at times. King Creek was sampled upstream of the diversion in 2010 and downstream of the
diversion in 2005 and 2010, and no fish were collected. King Creek may be too small to support fish.
Benthic macroinvertebrates were collected in 2005 downstream of the diversion and the results indicate
the presence of a healthy and diverse community. The density was 2,020 organisms/m2 and there were
53 individual taxa collected, more than at most other sites sampled during that period. The
macroinvertebrate community included a wide range of species including numerous species of stoneflies,
mayflies, and caddisflies which are usually considered to be intolerant of degraded water quality and
flows. Although there is a high rate of diversion it is likely that inputs of groundwater not far from the
diversion are sufficient to maintain the macroinvertebrate community, and that King Creek may not yet be
past an ecological tipping point.
West Elk Creek is a small, steep stream and had no fish upstream of the diversion in 2010. Fish
populations were sampled downstream of the Denver Water diversion in 2005 and brook trout was the
only species collected. Total density was 2,400 fish/ha, and biomass was 48 kg/ha. The population
contained multiple age classes which is characteristic of a healthy, sustaining population.
Macroinvertebrate samples had a density of 6,796 organisms/m2, which was higher than most other sites,
and a total of 57 taxa, which was higher than all other sites. The macroinvertebrate community contained
many different species of stoneflies, mayflies, caddisflies, a hellgrammite, beetles, crustaceans, worms,
and clams (Pelecypoda). The presence of a healthy brook trout population and a healthy and diverse
benthic invertebrate community suggest that West Elk Creek likely has not passed an ecological tipping
point.
Main Elk Creek is steep and narrow. At the fish sampling sites, the width was less than 2 m. There is no
bypass flow for this stream, and it may be fully diverted at times. Sampling in 2005 and 2010 found no
fish. At the 2005 sample site downstream of the two forks, macroinvertebrate density and number of taxa
were relatively high compared to other tributaries in 2005. The 42 species included a diverse mix of
stoneflies, mayflies, caddisflies, and midges. These data indicate that Main Elk Creek has sufficient
inflow from groundwater to sustain the invertebrate community a short distance downstream of the
diversions on the two forks of the stream. Two samples have been collected from Elk Creek at a site near
Fraser using CDPHE protocols; the sample collected in 2000 did not meet the threshold for attainment of
aquatic life use, but the sample from 2010 indicated attainment. The absence of fish may be due to the
small, steep habitat. However, this stream is wider than other streams in the area and the absence of fish
suggests that Main Elk Creek may have passed an ecological tipping point.
Vasquez Creek has a moderately steep channel and an average bankfull width of 7 m. There is a bypass
flow of 8 cfs in the summer and 3 cfs the rest of the year at the Denver Water diversion. The native flow
depletion is 57% on average. Stream morphology is typical of mountain streams and predominantly
consists of riffle-pool complexes with runs. Fish populations were sampled upstream of the Denver
Water diversion in 1964 and downstream in 1964, 1978, 1984, 1985, 1992, 1993, 2002, 2007, and 2009
(FEIS Table 3.11-8). At sites between the Denver Water and Grand County diversions, only brook trout,
cutthroat trout, and sculpin were present and densities were variable throughout the study period.
Downstream of the Grand County diversion, species composition has changed slightly over time, with
brown trout, rainbow trout/cutthroat trout hybrids, and white sucker first seen in 2007 and 2009, with
reductions in brook trout. The Vasquez Creek trout population is characterized by low densities but does
not appear to be declining further. Benthic invertebrate population data were collected upstream and
downstream of the diversion in 1985. The data were similar and indicated healthy populations at both
sites in 1985. Vasquez Creek was also sampled in 2000, 2003, 2010, and 2011 using CDPHE protocol;
46
the MMI value for the 2010 and 2011 samples did not meet the attainment threshold for aquatic life, and
Vasquez Creek is provisionally listed on Colorado’s Section 303(d) List for aquatic life impairment. The
samples collected in 2000 and 2003 scored much higher and met the criteria for attainment. The naturally
low density fish populations do not appear to be declining further and Vasquez Creek has likely not
passed an ecological tipping point.
Little Vasquez Creek is a small, steep stream about 1.3 miles between Denver Water’s diversion and
about 3 miles above the diversion. There are no bypass flows, but there is an agreement between Denver
Water and Grand County Water and Sanitation District to bypass at least 0.5 cfs downstream to the Grand
County diversion. The average diversion of native flows under Current Conditions (2006) is 83%. The
diversion on Little Vasquez Creek acts as a barrier to upstream migration and protects an isolated
population of cutthroat trout. Fish were sampled upstream of the diversion in 1996, 1999, and 2006.
Little Vasquez Creek usually contains low densities of fish. These fish are not genetically altered; as a
result, the cutthroat trout in Little Vasquez Creek are considered a “core conservation population” and are
assumed by the Service to be greenback lineage cutthroat trout given the uncertainty in genetics. Fish
populations were sampled downstream of the Denver Water diversion in 1982, 1983, 1985, 1997, and
2006, resulting in variable average fish densities ranging from 36 to 4,046 fish/ha (FEIS Table 3.11-9).
Biomass was not reported for all surveys, but values ranged up to 94 kg/ha. Brook trout and trout were
the only species present during the sampling period, and the proportion of each species in the sample
exhibited large fluctuations over time. Fish populations in Little Vasquez Creek are either healthy or
sustaining downstream of the diversion. Despite the high diversion rate, it is likely that Little Vasquez
Creek downstream of the diversion has not yet crossed an ecological tipping point.
Jim Creek is a small to mid-sized stream with a moderate gradient and an average width of approximately
4 m. There is no bypass flow for this stream and it is apparently fully diverted at times, but there are
inputs of water from groundwater and wetlands not far downstream of the diversion. Upstream of the
Denver Water diversion, fish populations sampled in 2003 contained brook trout and Colorado River
cutthroat trout. Brook trout comprised over 90% of the population both in terms of density and biomass.
Total estimated fish density was 259 fish/ha, and total estimated biomass was 30 kg/ha. Downstream of
the diversion, fish populations were sampled in 1993 and 2005, with brook and rainbow trout collected in
1993, and only brook trout in 2005. Densities ranged from 588 to 1,688 fish/ha, and biomass estimates
ranged from 10.1 to 24.3 kg/ha. Fish densities are also low in Jim Creek upstream of the diversion,
indicating that water diversion is not the only factor affecting populations in this stream. Although a
remnant population of cutthroat trout persists upstream of the Denver Water diversion, it is threatened by
invading brook and rainbow trout. The Denver Water diversion dam on Jim Creek is downstream of the
collection system, so nonnative fish can easily access the upper reaches of the stream. Benthic
macroinvertebrates were sampled downstream of the diversion in 2005. There were 1,686 organisms/m2
and 41 taxa collected. These values are somewhat lower than at other sites sampled during the same
period. However, the invertebrate community contained a wide variety of species, including 16 species of
stoneflies, mayflies, and caddisflies, and many species of midges. Despite the relatively low density and
number of taxa, the community composition does not indicate signs of impairment. The stream does not
appear to have crossed a tipping point.
North Fork Ranch Creek is a small, steep stream. It has no bypass flow and is fully diverted at times. No
fish were present downstream of the diversion during sampling in 2005 because the stream was fully
diverted and dry. No benthic macroinvertebrate sample could be collected in 2005. North Fork Ranch
Creek was sampled near the mouth in 1996, and a population of cutthroat trout was present. Density was
estimated to be 528 fish/ha. Above the diversion, the North Fork Ranch Creek flows through private
land, so data are limited. No fish were captured during a 2000 USFS survey, but USFS land only
encompasses the headwaters of the stream. No data are available for the more productive reaches
downstream of the forest boundary. The North Fork Ranch Creek is estimated to support a low to
moderate density of cutthroat trout (50 to 150 fish/mile), and the genetic status of the population is
47
categorized as unaltered. The severely diverted flows and dry channel for much of the year indicate that
North Fork Ranch Creek downstream of the diversion has passed an ecological tipping point.
Main Ranch Creek has a steep channel with an average bankfull width of approximately 7 m. It has
bypass flows and native flow diversions under Current Conditions (2006) average 30%. Ranch Creek is
Section 303(d) listed for temperature under the CWA, and temperature exceedances were frequent in
Ranch Creek from 2005 through 2009. Upstream of the diversion, a total of 31 brook trout were collected
in 2010. Densities were estimated to be 780 fish/ha, and biomass was estimated to be 20 kg/ha.
Downstream of the diversion, fish populations were sampled in 1978, 1985, 1986, 1993, and 2005. In
1993, brook trout, brown trout, rainbow trout, longnose sucker, mottled sculpin, and speckled dace
(Catostomus commersoni) were collected, with mottled sculpin the dominant species. Total fish density
was 1,615 fish/ha. Biomass estimates were not calculated. In 2005, only brook trout were collected,
amounting to 133 fish/ha and only 2.2 kg/ha. Macroinvertebrate data collected in 2005 downstream of the
diversion indicate the presence of an abundant, diverse, and healthy community. Density was
43,361 organisms/m2, an order of magnitude higher than most other sites. The number of taxa collected was
46, which is higher than many other sites. The sample contained invertebrates from a wide range of groups
including many species of stoneflies, mayflies, caddisflies, and midges, along with a few species of mites
and worms. The abundant and healthy macroinvertebrate community indicates that flow and water quality
are suitable to sustain the healthy populations of invertebrates including numerous sensitive species. This
may likely be due to the bypass flow in this reach.
Middle Fork Ranch Creek is a small, narrow, steep stream with a width of about 2 m. There is no bypass
flow for Middle Fork Ranch Creek. The cutthroat trout population upstream of the Denver Water
diversion on Middle Fork Ranch Creek is protected by a barrier to upstream migration, either by dry
channels downstream of the diversion or by a gradient barrier lower in the watershed. A 2000 USFS
survey resulted in a total population estimate of 99 fish for Middle Fork Ranch Creek from the Denver
Water diversion to the headwaters. Although this reach is approximately 4,000 m long, fish were only
captured within 800 m upstream of the diversion. This stream was flowing downstream of the diversion in
2005, but fish were absent. Fish were captured in low densities in 1979 and 1992 near the confluence with
the South Fork of Ranch Creek. Benthic macroinvertebrates downstream of the diversion were sampled in
2005 and exhibited a healthy and diverse community. The species composition included many sensitive
species such as numerous stoneflies, mayflies, and caddisflies. Density and number of taxa were
6,262 organisms/m2 and 46, respectively, similar to many other streams sampled in 2005. The fish
populations downstream of the diversion appear to be near collapse or collapsed, but a diverse
macroinvertebrate population persists. This indicates that Middle Fork Ranch Creek may be past an
ecological tipping point.
The South Fork Ranch Creek has a moderately steep and narrow channel, no bypass flow, and is fully
diverted at times. It was dry downstream of the diversion during sampling in 2005, precluding the
collection of fish or macroinvertebrate samples. The diversion on South Fork Ranch Creek has not
isolated cutthroat trout from invading nonnative salmonids and sampling in 2003 found both brook trout
and cutthroat trout. The diversion apparently has been recently modified to function as a barrier.
Downstream of the diversion, South Fork Ranch Creek was sampled in 1978, 1983, and 1992 and was dry
in 2005. In 1978, cutthroat trout were sympatric with brook trout, and their densities were estimated to be
296 and 81 fish/ha, respectively. In 1983, a dense (2,690 fish/ha), population of cutthroat trout was
present. In 1992, cutthroat trout were absent, and this reach of South Fork Ranch Creek supported
approximately 1,076 brook trout/mile. The stream was dry and fish were absent downstream of the
diversion in 2005. Macroinvertebrate data are not available. Fish populations in this stream downstream
of the diversion are near collapse or have collapsed.
Buck Creek is a small, steep stream. It has no bypass flow, and it is fully diverted at times. Fish
sampling upstream of the diversion in 1983 indicated no fish were present. However, a 2007 survey
upstream of the diversion resulted in the capture of 46 brook trout and one rainbow trout. The resulting
48
density estimates were 680 brook trout per hectare (ha) and 15 rainbow trout per ha. This stream was
sampled upstream and downstream of the diversion in 2010, but fish were absent. Fish were only present
upstream of the diversion in one of three surveys, and Buck Creek is directly connected with the Moffat
Collection System, which contains fish. It is likely that fish occasionally access this stream from the
Denver Water aqueduct and that Buck Creek does not support self-sustaining fish populations. However,
the high rate of diversion of native flows suggests that Buck Creek has crossed a tipping point
downstream of the diversion.
Meadow Creek is a mid-sized stream almost 9 feet wide just downstream of the Denver Water diversion.
Although there are bypass flows on this stream, the Vail Ditch also diverts from the stream less than a
mile downstream, and at times fully diverts the stream. Meadow Creek Reservoir upstream of the
diversion has predominantly brook trout with a few cutthroat trout and rainbow trout. No data are
available for the genetic lineage of the cutthroat population. Downstream of the diversion, fish
populations were sampled at various locations in 1979, 1981, 1993, 2005, 2006, and 2007. In 1993,
brook trout, brown trout, and mottled sculpin were collected, but in 2005, only brook trout were collected
just downstream of the diversion, amounting to 252 fish/ha and 1.4 kg/ha. Macroinvertebrates were
sampled in 2005 just downstream of the diversion. The density of 4,212 organisms/m2 and the 53 taxa
collected were comparable to the values collected at many other sites in 2005. The presence of healthy
invertebrate populations and the persistence of fish populations at all sampling sites in Meadow Creek
indicate that it is a mildly diverted stream in most sections and has not crossed an ecological tipping
point.
Trail Creek does not have a Denver Water diversion but is just downstream of diversions on North Trail
and South Trail creeks. Trail Creek is a narrow, steep, small stream, just over 2 m wide downstream of
the confluence of the North Trail and South Trail creeks. Fish were absent in 2005 despite the fact that
the sampling site contained flowing water and one deep pool. A moderate density of 2,802 organisms/m2
and relatively high number of taxa of invertebrates (51) were found in 2005. The macroinvertebrate
community included a wide variety of species including many stoneflies, mayflies, and caddisflies. The
bypass flows on the upper streams apparently allow sufficient water to sustain healthy populations of
invertebrates in Trail Creek. It appears from the limited data that Trail Creek is mildly diverted in its
tributaries and has not passed a tipping point.
Hurd Creek is a small, steep stream with a width of 2 to 3 m and a bypass flow of 1 cfs year round.
Sampling in 2005 below the diversion and in 2010 above the diversion found no fish. Hurd Creek
contained a relatively high density and number of taxa of macroinvertebrates in 2005. Density was
3,380 organisms/m2, which is comparable to most other streams. The number of taxa was 50, which is
higher than many streams. Species composition included a wide variety of invertebrates including many
species that are usually sensitive to flow or water quality degradation such as stoneflies, mayflies, and
caddisflies. The lack of fish at sites just upstream and just downstream of the diversion suggests that this
portion of the stream does not have habitat suitable to support fish The macroinvertebrate data indicate
that flow and water quality are sufficient to sustain healthy populations and fish are present at high
density further downstream of the diversion. This indicates that Hurd Creek is not yet past an ecological
tipping point.
Hamilton Creek is a small steep stream with a stream width of over 2 m downstream of the diversion. It
includes about 3 miles between the diversion and the confluence with Hurd Creek, and about 2.5 miles
above the diversion. There is a bypass flow of 1.5 cfs in June through April, and 1 cfs in May through
early June. Downstream of the diversion, only brook trout were present in 2005, with a density of
484 fish/ha, and a total biomass of 14.5 kg/ha. The diversion dam at Hamilton Creek has been modified
to form a barrier to upstream fish passage, which serves to protect an isolated population of green lineage
cutthroat trout above the diversion. Only cutthroat trout were found above the diversion during sampling
in 2000, 2003, and 2009, and the genetic status of this cutthroat trout population is unaltered. This stream
contained a relatively high density of macroinvertebrates at the site downstream of the diversion in 2005
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(10,604 organisms/m2). The number of taxa, 47, was comparable to many other sites. The high density
was the result of high numbers of midges, but there were also many species of more sensitive insects
including stoneflies, mayflies, and caddisflies. Diversions on Hamilton Creek may be sufficient to have
affected the fish populations downstream but not the macroinvertebrate populations. The very limited
data suggest that the fish populations downstream of the diversion are near collapse but the
macroinvertebrate community is healthy. This stream may be approaching a tipping point from a fishery
perspective.
Cabin Creek is larger than and not as steep as many of the other streams in the Englewood-Ranch Gravity
System. The average width of the stream downstream of the diversion is nearly 4 m. Cabin Creek has a
bypass agreement for 2 cfs year-round although there are downstream diversions that can divert this flow.
Only cutthroat trout are present above the diversion. The Denver Water diversion is not a barrier to
upstream fish movement, but brook trout are absent upstream of it. Brook trout invasions have probably
been prevented by an impassable road culvert or a gradient barrier. The genetic status appears to be
altered. Downstream of the diversion, fish populations have been sampled in several years (1979, 1983,
1996, 1999, 2003, and 2005). In every year except 2003, cutthroat trout was the only species collected,
and density estimates ranged from 269 to 3,365 fish/ha. In 2003, the site sampled was located 1 mile
below the USFS road, considerably downstream of the diversion and the sample sites used in other years,
and brook trout dominated the population at that site, comprising 99% of the population and 92% of the
biomass. Brown trout comprised the rest of the population. Benthic macroinvertebrates were sampled
downstream of the diversion in 2005. The community was diverse and abundant with a density of
6,852 organisms/m2 and 52 taxa. The species composition included many species of stoneflies and
caddisflies and 10 species of mayflies along with beetles, midges, mites, and worms. Cabin Creek
supports a sustaining fish population and a relatively high density and number of taxa of invertebrates.
As with several of the streams in the area, diversions in Cabin Creek may be sufficient to affect the fish
populations but not the macroinvertebrate populations. This stream is not yet near a tipping point.
Little Cabin Creek is a small steep stream. It has a bypass agreement for 0.25 cfs year-round and there
are downstream diversions that also divert water from the stream. No fish were present downstream of
the Denver Water diversion in 2005, and no fish were present upstream of the diversion in 2010. CPW
sampled this stream in 1979 and no fish were collected. In 2005, there was water in the channel of Little
Cabin Creek downstream of the diversion and this section supported a community of invertebrates with
relatively high density and number of taxa. A density of 3,769 organisms/m2 and 52 taxa compare well to
most other streams. The species composition included a diverse assemblage including eight stonefly
species, eight caddisfly species, and numerous species of mayflies and true flies. Similar to many of the
other streams in the area, the macroinvertebrate community is healthy but the fish community is limited
or absent. Fish are likely precluded due to the small stream size and the current flow regime supports a
healthy invertebrate community. This suggests that Little Cabin Creek is not yet near an ecological
tipping point.
6.1.4 Williams Fork River
The Project and its alternatives include additional diversions of water from tributaries in the Williams
Fork River Basin. This would result in depletions in average annual flows of greater than 10% in the
mainstem of the Williams Fork River upstream of the South Fork, but less than 10% from South Fork to
the Colorado River.
Williams Fork River upstream of South Fork is a moderate gradient stream with an average bankfull
width of 9 m. The fish populations in the Williams Fork River mainstem upstream of South Fork are
typical of a Rocky Mountain alpine coldwater fishery. Surveys have been conducted periodically since
the 1960s. Fish species composition in the Williams Fork River has been variable over time; species
collected upstream of the South Fork include brook trout, brown trout, cutthroat trout, rainbow trout, and
Paiute sculpin. Rainbow trout were collected in the 1970s, 1990s, and 2000s, but they have never formed
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a large proportion of the total catch. CPW does not stock this section of the river. Brook trout were often
the most numerous trout species, but mottled sculpin formed the highest percentage of the total catch
when they were present. The few cutthroat trout collected may have moved downstream from
populations in tributaries. Paiute sculpins were rare in all collections, and were more abundant at sites
downstream of the South Fork. Total fish density ranged from 822 to 1,367 fish/ha in samples from the
1980s, with brook trout accounting for 90 to 99% of the density. Total fish biomass ranged from 26 to
82 kg/ha with brook trout comprising 86 to 99% of the biomass. Whirling disease has been identified as
present within the Williams Fork River mainstem.
Benthic macroinvertebrate populations were sampled through the entire Williams Fork River mainstem
above South Fork in the fall of 1984 and spring of 1985. At the five sites upstream of the South Fork on
the mainstem, density estimates ranged from 892 to 2,351 organisms/m2, represented by 15 to 32 taxa per
site. A wide range of invertebrate taxa were collected; included in the groups were Ephemeroptera,
Plecoptera, Coleoptera, Trichoptera, Diptera, Turbellaria, Hirudinea, Oligochaeta, and Pelecypoda. These
invertebrate groups are typical groups found in Rocky Mountain streams.
The fish population of the Williams Fork River between the South Fork and Williams Fork Reservoir was
sampled in 1978 and 1984, each with a site near the confluence with the South Fork and a second site just
upstream of the inlet to the reservoir. Brown trout, rainbow trout, and Paiute sculpin were collected at
both sites in both years. Brook trout were dominant in the upper site in 1978 but were absent from the
lower site; in 1984, however, they comprised approximately 30% of the fish collected at both sites. In
both years, reservoir-resident kokanee salmon were collected at the site just upstream of the reservoir.
Cutthroat trout, longnose suckers, and speckled dace have been collected in small numbers at these sites.
Total fish biomass was not measured in 1978, but was 32.5 and 80.7 kg/ha at the two sites in 1984.
In the section of the Williams Fork River downstream of Williams Fork Reservoir, sampling results from
one site in 1985 contained rainbow and brown trout, mottled sculpin, and longnose sucker. Rainbow trout
were the predominant species present and comprised 68% of the density and 50% of the biomass. Brown
trout comprised the bulk of the remainder of the density and biomass. Sculpin and sucker were much less
abundant. Total fish density and biomass at this site in 1985 was 1,529 fish/ha and 74 kg/ha, respectively.
This section of the river was stocked once by CPW in 2000 with approximately 3,000 small (4-inch)
rainbow trout. Williams Fork Reservoir is commonly stocked with kokanee salmon and rainbow trout.
Benthic macroinvertebrate data from 1984 and 1985 are available from three sites on the Williams Fork
River downstream of the South Fork. The data indicate the presence of diverse, healthy communities
including sensitive species.
The fish data for the mainstem indicate that the population is healthy with no trends over time and that it
has not crossed an ecological tipping point. The limited amount of data for macroinvertebrates also
indicates the presence of healthy and diverse communities. Overall, the available information indicates
that the Williams Fork River has not crossed an ecological tipping point.
Denver Water diverts from four tributaries that form the headwaters of the Williams Fork River:
McQueary, Jones, Bobtail, and Steelman creeks. All four streams are narrow and steep, have no bypass
flows, and are fully diverted at times. Flow is added to the channel from groundwater and other inputs
downstream of the diversions in these streams. There are no fish or benthic invertebrate data available for
Jones Creek; however, aquatic biological resources are described in detail for the remaining three
tributaries. Denver Water diversion structures function as barriers to upstream migration of fish in
McQueary and Bobtail creeks, and populations upstream of the barriers are isolated.
The fish populations in these upper tributaries of the Williams Fork River are typical of Rocky Mountain
headwater, coldwater fisheries. Brook trout and cutthroat trout are the species present, dominating these
headwater streams in varying proportions. No fish are stocked in these streams by CPW. The benthic
invertebrate populations of the upper Williams Fork River tributaries are typical of mountain stream
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invertebrate communities. A total of 39 individual taxa were collected in 1984, representing the
taxonomic groups Ephemeroptera, Plecoptera, Trichoptera, Diptera, Coleoptera, Collembola,
Hydracarina, Oligochaeta, and Turbellaria. The number of taxa in the McQueary, Bobtail, and Steelman
creeks was nearly identical, and averaged 26 taxa per stream. The presence of a diverse
macroinvertebrate community, including sensitive species, indicates that water quality is sufficient to
sustain healthy invertebrate assemblages in these streams. Density in the tributaries was lower than at
many other streams in the study area averaging just over 1,000 organisms/m2.
Upstream of the diversion on McQueary Creek, fish populations were sampled in 1978, 1984, 2000, and
2003; only cutthroat trout were collected. No density or biomass estimates were made in 1978, but in
1984, density was 154 fish/ha and biomass was 13.5 kg/ha. A 2003 CPW survey found similarly low
densities. According to a 2000 population survey, McQueary Creek supported a population of cutthroat
trout upstream of the diversion; the population size was estimated to be 453 plus or minus (±) 154 fish.
Downstream of the diversion, fish were absent in 1978, but brook trout were collected in 1984. Density
of brook trout was 476 fish/ha, and total biomass was 20.9 kg/ha. In 2003, cutthroat trout was the only
species collected downstream of the diversion, with a total density of 182 fish/ha. The genetic status of
this population has not been tested, but McQueary Lake was stocked with cutthroat trout from the
Trapper’s Lake hatchery. After 1956, the Colorado River cutthroat trout produced in the Trapper’s Lake
hatchery were intro-gressed with Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri); therefore,
the cutthroat trout in McQueary Creek are hybridized.
Bobtail Creek includes about 1.6 miles of stream between Denver Water’s diversion and about 3 miles
above the diversion. Fish populations upstream of the Denver Water diversion in Bobtail Creek have
been sampled periodically since 1978, when three sites were sampled. In 1984 and 1985, two groups
collected fish population data in this stream; in 1984, Chadwick Environmental Consultants (CEC)
reported a population dominated by cutthroat trout, with brook trout present in small proportions (FEIS
Table 3.11-15). Total density was 186 fish/ha, and total biomass was 11.0 kg/ha. CPW collected
25 brook trout and 4 cutthroat trout in 1984, and 12 cutthroat trout in 1985, but did not estimate total fish
density or biomass. From 1992 to 2003, brook trout dominated the fish populations with at least 57% of
the total density. A 2000 USFS survey produced a population estimate of 791 plus or minus 165 cutthroat
trout, but brook trout outnumbered cutthroat trout by a ratio of 4:3. The most recent cutthroat trout
density estimate for Bobtail Creek is 0 to 50 fish/mile. A brook trout removal was conducted in 2001 to
alleviate competitive pressure on cutthroat trout, but the proportion of brook trout was similar in 2001 and
2003, indicating that the brook trout population quickly rebounded through recolonization, reproduction,
or a combination of the two. Additional brook trout removals were executed in 2011 through 2014, with
several hundred trout removed each year by CPW. The cutthroat trout in Bobtail Creek are not
genetically altered, and this stream supports a core conservation population. Downstream of the
diversion, fish populations were sampled at two sites in 1984 and at one site in 2001. In all years, only
brook trout and cutthroat trout were collected. In 1984, total fish density at one site was 978 fish/ha, with
brook trout comprising 86% of the population; total fish biomass was 58.6 kg/ha. In 2001, total fish
density was 653 fish/ha, with brook trout comprising 86% of the population. The three available density
estimates suggest that the fish population in this stream is sustaining but may be near collapse. This
section of the stream is downstream of the historic Bobtail Mine near the diversion, which may also have
negative effects on fish density because of decreased water quality.
Steelman Creek has about 1.9 miles below the diversion and about 2 miles above the diversion. Upstream
of the Denver Water diversion in Steelman Creek, fish populations were sampled in 1974, 1978, 1984,
2000, 2003, and 2004. In 1974, 1978, and 1984, cutthroat trout was the only species collected at the two
sites, with total density of 492 fish/ha and total biomass of 24.3 kg/ha in 1984 (FEIS Table 3.11-16). By
2000, brook trout began to comprise sizeable proportions of the population. Although a 2000 USFS
survey produced a cutthroat trout population estimate of 908 plus or minus 532 fish, brook trout
outnumbered the native fish by a ratio of 4:1. The most recent cutthroat trout density estimate is 151 to
52
400 fish/mile; these cutthroat trout are 90 to 99% genetically pure; therefore the cutthroat trout in
Steelman Creek constitute a conservation population. In 2011, during brook trout removals by CPW,
there were 85 cutthroat trout returned to the stream and 166 brook trout removed. In 2013, 270 cutthroat
trout were returned to the stream, including many young fish, and 277 brook trout were removed.
Downstream of the diversion, fish populations were sampled in 1978 and 1984. In 1978, two cutthroat
trout and one brook trout were collected. Density and biomass estimates were not reported. In 1984,
brook trout dominated the community comprising 79% of the density. Total density was 792 fish/ha, and
total biomass was 57.1 kg/ha. Both available density estimates suggest that the Steelman Creek trout
population is sustaining but may be near collapse downstream of the diversion.
6.1.5 Colorado River
The Colorado River in the reach between the confluences with the Fraser River and Blue River is
managed for rainbow and brown trout. Other species, including white, longnose, and flannelmouth
suckers (Catostomus latipinnis), longnose dace, mottled sculpin, and mountain whitefish are also
collected (FEIS Table 3.11-17). Fish population sampling has been conducted on this reach of the
Colorado River multiple times a year since this area became a focus for whirling disease research after
Windy Gap Reservoir was implicated as a sink for the causative agent, M. cerebralis. This section of the
river is stocked by CPW with small (6 inches or less) rainbow trout. In the past few years, an average of
nearly 80,000 rainbow trout has been stocked annually.
Fish data are available at a number of sites in the Colorado River between Windy Gap Reservoir and the
Williams Fork River. The current fish community in the Colorado River between Williams Fork River
and Blue River is dominated by brown trout (FEIS Table 3.11-18). From 2001 through 2010, brown trout
comprised 93 to 96% of the fish sampled in a given year. Rainbow trout were the next most abundant
species in most years, accounting from 2 to 5% of the fish sampled. White suckers were the second-most
abundant species in 2003, accounting for 4% of the fish sampled. In 1998, 90% of the fish collected were
brown trout and 9% were rainbow trout. Snake River cutthroat trout, mottled sculpin, longnose dace,
speckled dace, longnose suckers, and white suckers were collected at low abundances in some years.
CPW has stocked this segment with large numbers of 4- to 5-inch rainbow trout in recent years; however,
successful survival and recruitment has been limited.
Brown trout were the dominant trout species in this reach of river from 2001 through 2010. Rainbow
trout were collected at high densities in 2006 and 2007. However, this reach of stream is routinely
stocked with rainbow trout and the high densities observed in these years are likely the result of collecting
the stocked rainbow trout. The rainbow trout densities in the remaining years also probably include fish
stocked by CPW. Brook trout, Snake River cutthroat trout, cutthroat/rainbow hybrid trout, and kokanee
were collected only occasionally and in low numbers from 2001 through 2008, and generally represented
less than 1% of the catch. Although density data were not always available for mottled sculpin and
speckled dace, these species were collected frequently, sometimes at moderate to high abundances.
Longnose suckers and white suckers were also collected frequently, but at low densities. Creek chub
(Semotilus atromaculatus), longnose dace, and johnny darter (Etheostoma nigrum) were collected only
occasionally and at low abundances. Of all the species collected, only mottled sculpin and speckled dace
are native to the Colorado River Basin.
Long-term research in this segment reflects a shift from a trout population dominated by rainbow trout to
a population dominated by brown trout, as seen in the current population. From 1979 through 1988,
rainbow trout were the dominant trout species; occurring at a density (543/ha) as much as 10 times greater
than the brown trout density (51/ha) in 1988 at the Lone Buck site in the Hot Sulphur Springs State
Wildlife Area. From 1994 through 1998, the trend was reversed at this site, with brown trout occurring at
greater densities than rainbow trout in all but one year. Long-term data are also available for the Paul
Gilbert site within this study segment, and demonstrate the same shift in dominance from rainbow trout in
53
the 1980s to brown trout in the 1990s. Whirling disease is considered the primary factor for the decline in
the rainbow trout population from the levels observed in the 1980s.
There is some evidence that brown trout have also been affected by whirling disease, immediately
downstream from Windy Gap Dam. A large number of brown trout fry had clinical signs of whirling
disease at the Hitching Post Bridge site, 1.6 km downstream from Windy Gap Dam, from 1994 through
1998. Age-1 brown trout were much less abundant at the Hitching Post Bridge site than at a site further
downstream near Parshall in 1999. The current trout population in this segment is dominated by brown
trout and the total trout density remains high and is similar to densities prior to whirling disease. Overall,
based on the high trout densities observed in recent years and its Gold Medal Water status, the current
trout population appears to be sustaining to healthy.
Recent sampling along the Colorado River in 2010 indicated the presence of a wide variety of
invertebrate taxa at sites from Windy Gap Reservoir downstream to the Blue River. Sampling results
from spring and fall 2010 resulted in the collection of 44 to 55 taxa at the sites. At all sites, there were
numerous species of Ephemeroptera, Plecoptera, and Trichoptera and other macroinvertebrate groups.
Additional information regarding macroinvertebrate sampling in the Colorado River is presented in the
Moffat FEIS.
6.1.6 Blue River
Fish populations in Blue River between Dillon Reservoir and Green Mountain Reservoir have been
periodically sampled by CPW since the 1970s (FEIS Tables 3.11-19 and 3.11-20). Fish species collected
over the years include brook trout, cutthroat trout, rainbow trout, and brown trout; cutthroat/rainbow trout
hybrids; kokanee salmon; mottled sculpin; lake trout (Salvelinus namaycush); and longnose, white, and
bluehead suckers (Catostomus discobolus). This section of the Blue River is annually stocked by CPW
and usually with small (15 cm or less) whirling disease resistant rainbow trout. The stocking rate in the
last few years has ranged from approximately 22,000 to over 51,000 fish per year. A small number
(1,624 individuals) of Snake River cutthroat trout were also stocked in this section in 2002. CPW also
annually stocks Dillon and Green Mountain reservoirs with species that may include rainbow trout, Snake
River cutthroat trout, and kokanee salmon in any given year. These fish may also move into the section of
Blue River that is between Dillon and Green Mountain reservoirs. Whirling disease was detected within
the Blue River watershed.
Historically, brown trout dominated the fish communities in most of the Blue River (FEIS Table 3.11-19),
but the relative abundance of rainbow trout has increased in recent years (FEIS Table 3.11-20). Species
composition in the Blue River can also be affected by seasonal migrations. For example, in 2003, when
sampling efforts within the study area were focused near Green Mountain Reservoir, upstream-migrating
kokanee salmon were the most abundant species. Brook trout have generally been collected in small
numbers (i.e., less than or equal to 6 fish/ha). This distribution of brook trout and brown trout is typical in
Rocky Mountain streams.
Based on a compilation of data conducted by Chadwick and Associates in 1985, total fish density estimates
average 479 fish/ha. Biomass estimates demonstrate an excellent fishery, with up to 217.6 kg/ha. Recent
collections confound total density and biomass estimation, since fish species were sampled inconsistently.
For example, at some sites, brown trout were sampled in a two-pass depletion method while other fish
species were sampled only in a single electrofishing pass. Thus, density and biomass estimates for the
Blue River reflect actual catch abundance, rather than density or biomass per ha. As a result of varying
sampling methods, the status and trends of the fish populations in the Blue River are difficult to evaluate.
However, the most recent catch data does not indicate trends and the continued status of the stream as a
Gold Medal Water stream suggests that the fish assemblage is healthy.
Benthic macroinvertebrate populations in the Blue River in the segments upstream of Green Mountain
Reservoir were sampled at one site in spring and fall 1985. Density estimates ranged from 3,785 to
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4,206 organisms/m2, represented by 30 to 32 taxa/site. The taxonomic groups collected included
Ephemeroptera, Plecoptera, Trichoptera, Coleoptera, Diptera, and Turbellaria. These communities are
typical of Rocky Mountain streams.
Fish populations downstream of Green Mountain reservoir are dominated by brown and rainbow trout and
mottled sculpin, but are also composed of several other species, such as kokanee salmon and bluehead and
longnose sucker. These other species are resident in Green Mountain Reservoir and the Colorado River
and may enter the Blue River within this reach. Fish data were available for five locations from 2000
through 2006 (FEIS Table 3.11-21). Nine fish taxa were collected including one unknown warmwater
species and one cutthroat/rainbow trout hybrid over the seven different sampling events. Brown trout were
the dominant species present in four of the seven samples, and rainbow trout were the dominant species in
the remaining three samples. Brown trout comprised between 21 and 91% of the fish sampled at a site,
while rainbow trout comprised between 8 and 47% of the fish sampled at a site. The remaining species
were collected only occasionally and at low abundances. The relatively large proportions of rainbow trout
collected are attributed to stocked fish as this reach is stocked annually with large numbers of rainbow
trout. Snake River cutthroat trout have also been stocked within this reach in the past.
Benthic macroinvertebrate populations in the Blue River in the segments downstream of Green Mountain
Reservoir were sampled at one site in spring and fall 1985. Density estimates ranged from 2,851 to
4,381 organisms/m2, represented by 31 to 36 taxa/site. There was a wide variety of invertebrates collected,
representing the taxonomic groups Ephemeroptera, Plecoptera, Trichoptera, Coleoptera, Diptera, and
Oligochaeta. These communities are typical of Rocky Mountain streams.
6.1.7 South Boulder Creek
Fish populations were sampled in South Boulder Creek periodically since the 1960s by CPW or CEC.
South Boulder Creek in the overall study area contains several species of trout, along with suckers and
longnose dace. In the past, CPW stocked rainbow trout in sections of the stream upstream of Gross
Reservoir; however, no stocking was conducted from 2000 to 2005. Several species of trout are routinely
stocked in Gross Reservoir by CPW. Resident, naturally-reproducing rainbow trout is the dominant fish
species present in South Boulder Creek in the overall study area. Whirling disease has been identified as
present within the South Boulder Creek watershed.
Upstream of Gross Reservoir, resident rainbow trout are the main component of the fishery, with
cutthroat trout, brook trout, and brown trout also present in smaller numbers (FEIS Table 3.11-22). White
and longnose sucker are also present. Total fish density averages 814 fish/ha. Trout species represent the
largest proportion of biomass in this stream, although suckers comprised up to 30.8 kg/ha in one year.
Fish biomass data were only available for the period from 1985 to 1991.
Benthic macroinvertebrate populations were sampled at two sites in the fall of 1984 and spring of 1985 in
the section of South Boulder Creek in the overall study area. Upstream of Gross Reservoir, density
estimates averaged 2,349 organisms/m2, represented by an average of 29 taxa per site (FEIS
Table 3.11-23). A total of 39 taxa were collected, representing the taxonomic groups Ephemeroptera,
Plecoptera, Trichoptera, Coleoptera, Diptera, and Oligochaeta (Chadwick and Associates 1986), the
typical groups for streams in the mountains of Colorado (Ward 1986, 1994; Ward et al. 2002).
In the section of South Boulder Creek downstream of Gross Reservoir and upstream of the South Boulder
Diversion Canal, resident rainbow trout comprise the bulk of the fishery. A few brown trout are also
present, along with longnose sucker, white sucker, and longnose dace (FEIS Table 3.11-24). Total fish
density averages approximately 2,412 fish/ha. Biomass estimates are not available, except for the time
period 1983 to 1985, in which biomass averaged 127 kg/ha.
Benthic macroinvertebrate populations were sampled at two sites in the fall of 1984 and spring of 1985 in
the section of South Boulder Creek in the overall study area. Density estimates averaged
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2,118 organisms/m2, represented by an average of 28 taxa per site (FEIS Table 3.11-23). Taxonomic
groups included the Ephemeroptera, Plecoptera, Trichoptera, Coleoptera, Diptera, and Oligochaeta, the
typical groups for streams in the mountains of Colorado. New Zealand mud snail (Potamopyrgus
antipodarum) populations have been identified in South Boulder Creek; however, the only currently
known population is at the confluence with Boulder Creek, downstream of the study area.
6.1.8 North Fork South Platte River
Fish populations in the North Fork South Platte River have been sampled since the 1960s (FEIS
Table 3.11-25). Fish species collected include brook trout, brown trout, rainbow trout, speckled dace, and
bluehead, longnose, and white sucker. Brown trout have consistently been the dominant species, both in
terms of abundance and biomass. Density estimates have averaged 745 fish/ha. In general, the fish
community in the North Fork South Platte River is typical of a Rocky Mountain foothills coldwater
fishery. Speckled dace and bluehead sucker are confined to the West Slope in Colorado and are
unexpected in the North Fork. However, both species were reported at a site approximately 1 km above
Estabrook in March 1995. Whirling disease was detected within the North Fork South Platte River.
Benthic macroinvertebrate populations were sampled at seven sites in this reach of the North Fork South
Platte River in spring and fall 1984 and spring 1985. Total density estimates ranged from 34 to
3,615 organisms/m2, with an average of 1,377 organisms/m
2. Total number of taxa/site has ranged from
5 to 40 taxa, averaging 25 taxa per site. Both density and number of taxa were lowest in the upper
reaches of the stream. A total of 76 individual taxa were collected, representing the taxonomic groups
Ephemeroptera, Plecoptera, Trichoptera, Coleoptera, Diptera, Oligochaeta, Turbellaria, Hydracarina,
Amphipoda, and Pelecypoda. The groups present in the benthic invertebrate community in the North
Fork South Platte River are typical of a Rocky Mountain Front Range invertebrate community.
6.1.9 South Platte River
There are six mainstem reservoirs on the South Platte River, including Antero, Spinney Mountain, Eleven
Mile Canyon, Cheesman, Strontia Springs, and Chatfield. These reservoirs are stocked with hundreds of
thousands of fish every year by CPW. Fish species stocked in the upper four reservoirs between 2000 and
2005 include brown, cutthroat, and rainbow trout, cutthroat/rainbow trout hybrids, splake, kokanee
salmon, and smallmouth bass (Micropterus dolomieu). Fish species stocked in Chatfield Reservoir
between 2000 and 2005 include cutthroat and rainbow trout, cutthroat/rainbow trout hybrids, channel
catfish, walleye (Sander vibreus), yellow perch (Perca flavescens), black crappie (Pomoxis
nigromaculatus), bluegill (Lepomis macrochirus), largemouth bass (Micropterus salmoides), smallmouth
bass, gizzard shad (Dorosoma cepedianum), and spottail shiner (Notropis hudsonius). Some of these
species may be found in stream segments near reservoirs as they migrate for spawning.
Whirling disease was detected within the South Platte River. New Zealand mud snail populations have
been identified within the upper reach of the South Platte River, particularly within the 7 miles
immediately downstream of Eleven Mile Canyon Reservoir.
Over 30 individual sites have been sampled periodically from 1968 to 2005 within the reaches of the
South Platte River upstream of the North Fork South Platte River. Fish populations in this area are
dominated by trout (brook, brown, and rainbow) and sucker (longnose and white) species. Both longnose
dace and speckled dace have been reported, although longnose dace are native to the river and speckled
dace are native to the western slope. Occasionally, other species, such as northern pike, kokanee salmon,
splake, spottail shiner, three-spined stickleback (Gasterosteus aculeatus), cutthroat/rainbow trout hybrids,
and fathead minnow (Pimephales promelas), are collected. Several of these species are resident in the
reservoirs and are found near the reservoirs during stream spawning. This section of the South Platte
River is classified as Aquatic Life Cold Class 1. Four reaches of this segment of the South Platte River
are considered to be Gold Medal Waters by CPW: (1) from Antero Reservoir to the inlet of Spinney
Mountain Reservoir, (2) between Spinney Mountain Reservoir and Eleven Mile Canyon Reservoir,
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(3) from Cheesman Dam downstream to the upper boundary of the Wigwam Club, and (4) from the lower
Wigwam Club boundary to the Scraggy View picnic ground.
WQCD macroinvertebrate data are available for this segment of the South Platte River. Two samples
were collected in July 2006: one downstream of Antero Reservoir, and one downstream of Cheesman
Reservoir. The sample downstream of Antero Reservoir contained a minimum of 26 taxa, and the sample
downstream of Cheesman Reservoir contained a minimum of 33 taxa.
Two sites were sampled between North Fork South Platte River and Strontia Springs Reservoir in 1978.
Brown and rainbow trout and longnose suckers were collected. Brown trout were the dominant species,
and the number of longnose suckers was not reported. Total density and biomass exceeded 122 fish/ha
and 61.6 kg/ha, respectively, at the two sites. One site was sampled within this reach in the fall of 1984
and the spring of 1985. Total density ranged from 773 to 5,632 organisms/m2, and taxa richness ranged
from 21 to 41 taxa. Taxonomic groups included Ephemeroptera, Plecoptera, Trichoptera, Coleoptera,
Diptera, Turbellaria, and Oligochaeta (Chadwick and Associates 1986). The groups present in the benthic
invertebrate community in this reach of the South Platte River are typical of a Rocky Mountain Front
Range invertebrate community.
In Waterton Canyon, fish populations, which have been sampled periodically since the 1970s, are
comprised primarily of brown and rainbow trout, longnose and white sucker, and longnose dace. Brown
trout have generally been the dominant species. Snake River cutthroat trout were reported once, in 2004.
At the bottom of the canyon near Chatfield Reservoir, the same mix of species is found, along with some
warmwater and reservoir-resident species, such as black bullhead, creek chub, fathead minnow,
largemouth bass, smallmouth bass, and yellow perch. Two sites were sampled for macroinvertebrates
within this reach in the spring and fall of 1985. Total density ranged from 1,377 to 7,970 organisms/m2,
and taxa richness ranged from 23 to 33 taxa. Taxonomic groups included Ephemeroptera, Plecoptera,
Trichoptera, Coleoptera, Diptera, Amphipoda, Gastropoda, Turbellaria, and Oligochaeta. The groups
present in the benthic invertebrate community in this reach of the South Platte River are typical of a
Rocky Mountain Front Range invertebrate community.
Between Chatfield Reservoir and Bear Creek, fish have been sampled numerous times over the years with
a total of 19 species (FEIS Table 3.11-26) collected. This section was stocked by CPW in 2000 and 2005
with a few thousand small (less than 5 inches) brown trout, but this species has only accounted for less
than 1% of the total catch in any sample year. Creek chub, longnose dace, longnose sucker, and white
sucker frequently are the dominant species in this section of the river.
In the coldwater section of the river upstream of Bowles Avenue, the sampling in 2005 resulted in the
collection of one brown trout and numerous other species, including black crappie, carp, creek chub,
fathead minnow, green sunfish (Lepomis cyanellus), Iowa darter, largemouth bass, longnose dace,
longnose sucker, mosquitofish (Gambusia affinis), sand shiner (Notropis stramineus), smallmouth bass,
and white sucker (FEIS Table 3.11-27). Collections in 1979, 1985, and 2003 at various sites within the
reach yielded many of these species, as well as plains topminnow (Fundulus sciadicus), rainbow trout,
yellow perch, johnny darter, and brook stickleback (Culaea inconstans). Many of these warmwater
species, such as the bass, perch, and crappie, probably move downstream from Chatfield Reservoir.
The river at Bowles Avenue (at the junction of the coldwater and warmwater designated sections) has
been sampled in 1979, 1987, and 1990. In the 1979 sampling episode, salmonids were absent, and the
assemblage was comprised of longnose sucker, white sucker, creek chub, fathead minnow, and yellow
perch. In 1987, six brown trout were captured, along with the above mix of species. In 1990, the same
species were present, along with one rainbow trout, one carp, two green sunfish, and 727 longnose dace.
In the warmwater section of the South Platte River between Bowles Avenue and Bear Creek, the species
composition is similar to that of the coldwater section (FEIS Table 3.11-27). Collection in 2005 produced
black crappie, brook stickleback, carp, creek chub, fathead minnow, green sunfish, largemouth bass,
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longnose dace, mosquitofish, smallmouth bass, and white sucker. In 1979, 1986, 1987, 1988, 1990, and
1995, several of these species were collected at various sites within the reach.
Whirling disease was detected within the lower South Platte River.
Benthic macroinvertebrate data from 1986 and 1987 indicate the presence of several classes/orders of
invertebrates, including Ephemeroptera, Plecoptera, Trichoptera, Odonata, Diptera, Isopoda, Amphipoda,
Hydracarina, Gastropoda, Oligochaeta, Hirudinea, and Turbellaria. The invertebrate communities are
typical of the transition zone from the Rocky Mountain foothills to the high plains. Density at the two
sites in the section of the South Platte River was higher than at other streams in the study area, ranging
from near 6,000 organisms/m2 to over 40,000 organisms/m
2. The number of taxa was similar to other
streams, averaging over 23 taxa per sampling site.
In 2005, three sites were sampled for benthic macroinvertebrates within this segment of the South Platte
River. Total densities averaged 6,325 organisms per sample, ranging from 2,085 to 14,081 organisms per
sample. Number of taxa was similar to the samples collected in 1986 and 1987, averaging 28 taxa per
sample, and ranging from 20 to 32 taxa. Taxonomic groups included Ephemeroptera, Plecoptera,
Hemiptera, Trichoptera, Odonata, Diptera, Isopoda, Amphipoda, Hydracarina, Gastropoda, Oligochaeta,
Hirudinea, and Turbellaria, as in 1986 to 1987.
Downstream of the confluence with Bear Creek to the Henderson gage, fish populations are dominated by
warmwater species. Representative species include black crappie, bluegill, common carp (Cyprinus
carpio), creek chub, fathead minnow, green sunfish, Iowa darter, johnny darter, largemouth bass,
mosquitofish, plains killifish, smallmouth bass, and yellow perch.
6.2 Wildlife Resources
Sub-sections 6.2.1 through 6.2.4 address both aquatic and terrestrial endangered, threatened, and other
special status species. This follows the organization of the Moffat Project FEIS, which consolidated the
analysis of special status species in one section. Information on special status plant species is provided in
the vegetation analysis (Section 6.3).
6.2.1 Federally-Listed Threatened and Endangered Species
No Federally-listed species are present at Gross Reservoir. Three areas of potential habitat were
evaluated for suitability with Preble’s meadow jumping mouse in September 2005. Forsythe Gulch and
South Boulder Creek did not have suitable habitat. Winiger Gulch has suitable habitat but is near the
upper elevational range of this species. If Preble’s meadow jumping mouse did inhabit this area prior to
the construction of Gross Reservoir, the species is now likely extinct because the population has been
isolated from known populations downstream for more than 50 years. Fish that were considered to be
greenback cutthroat trout were stocked in Gross Reservoir in 2002 and 2004. Recent genetic studies
suggest that these fish were hybrids of greenback and Colorado River cutthroat trout. The trout were
stocked for fishing and not as part of a recovery action because Gross Reservoir is not a recovery water
for greenback cutthroat trout. None of the cutthroat trout were found during net sampling in 2007. Gross
Reservoir is not considered a recovery water for green lineage cutthroat trout and a number of other fish
species and hybrids are regularly stocked.
No Federally-listed animal species are known to occur at the Leyden Gulch Reservoir site. Trapping
surveys for Preble’s meadow jumping mouse were conducted in 1997 and in 2005 with negative results,
and the Service concurred that a population of Preble’s mountain jumping mouse is unlikely to be present.
This species is present along upper Ralston Creek above Ralston Reservoir, but the reservoir is a barrier
for individuals to move to lower Ralston Creek. Field surveys for Ute ladies’-tresses orchid and Colorado
butterfly plant were also conducted in 2005 with negative results. Because emergent populations of the
Ute ladies’-tresses orchid may vary from year to year, additional presence/absence surveys would be
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conducted if Alternative 1c was selected as the least environmentally damaging practicable alternative
(LEDPA).
There are no known occurrences of Federally-listed animal species at the other Project facilities. Interior
least tern (Sterna antillarum athalassos) and piping plover (Charadrius melodus) may occur rarely during
migration along the South Platte River and at gravel pit lakes, but no breeding habitat occurs in the study
area.
Canada lynx (Lynx canadensis) are known to occur in Grand County and are likely to be present along
portions of the Fraser River and Williams Fork River, and their tributaries. Grand County is not a core
area for Canada lynx, but they have been tracked at a number of locations. According to a map of
satellite locations (Schenk 2009), the highest use density in Grand County occurs west of Winter Park,
including the St. Louis Creek and Vasquez Creek drainages. The Fraser River and its tributaries that are
east of U.S. Highway 40 have low to moderate density, as does the upper Williams Fork River Valley.
Canada lynx may also occur along the Blue River in Summit County, along South Boulder Creek in
Gilpin County, and near the border of Gilpin and Boulder counties; however both areas have low use
density.
South Boulder Creek from Gross Reservoir to the South Boulder Diversion Canal is within the elevation
range for Preble’s meadow jumping mouse. The habitat in this area consists of mature forest with
scattered shrubs, but Preble’s meadow jumping mouse may occur and this area is considered to be
potential habitat. No surveys have been conducted on South Boulder Creek upstream of Eldorado
Canyon; however, Preble’s meadow jumping mouse have been captured downstream of the study area
along South Boulder Creek. A large area of occupied habitat occurs along South Boulder Creek and
irrigation ditches in City of Boulder open space. The portion of the North Fork South Platte River in
Jefferson County is considered within the overall range of Preble’s meadow jumping mouse, and they
have been found at several locations. Occupied habitat occurs along several portions of the South Platte
River between Cheesman Reservoir and Chatfield Reservoir, including a large area on the south end of
Chatfield Reservoir. Except for a few miles below Chatfield Reservoir, all of the lower South Platte
River to the Henderson gage is within the Denver Metropolitan block-cleared zone, where Preble’s
meadow jumping mouse is not expected to occur. Designated critical habitat is present on the South
Platte River on Corps’ property above Chatfield Reservoir, and on two reaches of USFS land between
Deckers and Nighthawk.
Water depletions to West Slope tributaries of the Colorado River may affect four endangered fish species
where they occur downstream in the Colorado River. These species include bonytail chub (Gila elegans),
Colorado pikeminnow (Ptychocheilus lucius), humpback chub (Gila cypha), and razorback sucker
(Xyrauchen texanus). The decline of these fish species throughout the Colorado River Basin is a result of
extensive loss, fragmentation, modification of habitat, and barriers to fish movement associated with dam
construction and operations. Major dams were constructed in the upper Colorado River Basin in the
1960s, including Flaming Gorge Dam on the Green River, Navajo Dam on the San Juan River, the
Aspinall Units on the Gunnison River, and Glen Canyon Dam on the Colorado River. Glen Canyon Dam
almost divides the lower and upper Colorado River Basin and is also a barrier to fish movement.
Water depletions to the South Platte River may affect several endangered species downstream along the
Platte River in Nebraska. Four special status species are known or expected to occur downstream,
including interior least tern, piping plover, whooping crane (Grus Americana), and pallid sturgeon
(Scaphirhynchus albus). In addition, Eskimo curlew (Numenius borealis) formerly occurred, but has not
been observed for many years and may be extinct.
Native cutthroat trout in Little Vasquez Creek and Hamilton Creek in the Fraser River Valley and in
Bobtail and Steelman creeks in the Williams Fork River watershed were assumed to be greenback
cutthroat trout for NEPA analysis and Section 7 consultation. Information regarding the populations in
these creeks is provided in Section 6.1. Until recently, greenback cutthroat trout were considered to
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occupy 58 to 72 streams and lakes in headwater areas in the Arkansas River and South Platte River
drainages in Colorado and parts of southeastern Wyoming. Recent genetic studies have led to uncertainty
in the current range of greenback cutthroat trout. A 2007 study found 47 populations of greenback
lineage cutthroat trout west of the Continental Divide, including four in the river segments study area. A
follow-up study published in 2012 found that the only population of greenback cutthroat trout surviving
today occurs in Bear Creek, a tributary of the Arkansas River west of Colorado Springs, outside of its
native range in the South Platte River watershed. It was likely established by stocking in the 1880s.
According to the 2016 BO (USFWS 2016b), there are currently two distinct lineages of cutthroat trout on
the West Slope of Colorado, one of which is Colorado River cutthroat trout and the other is a newly
identified lineage referred to as green lineage cutthroat trout. Populations of green lineage cutthroat trout
occur on both sides of the Continental Divide, but the origin of these fish is uncertain. The green lineage
trout currently receives interim protection under the ESA because several of its populations were
previously identified as greenback cutthroat trout, a threatened species. The interim protection will
remain in place until the Service conducts a status review to evaluate the need to list the green lineage
cutthroat trout. Colorado River cutthroat trout have been previously evaluated for listing by the Service
and listing was determined to be not warranted
6.2.2 State Threatened and Endangered Species and Species of Special Concern
Four Colorado species of special concern may occur at Gross Reservoir. American peregrine falcon
(Falco peregrinus anatum) may occur during foraging or migration but are unlikely to occur regularly.
There are no prominent cliffs that would be suitable for nesting, and the nearest known nesting sites are
located about 3 miles away. There is no known roosting habitat for Townsend’s big eared bat
(Corynorhinus townsendii), such as caves or mines. However, suitable foraging habitat is present,
including forested and riparian habitat. This species has been documented at several locations in western
Boulder County and has good potential for occurrence. Bald eagles have been observed at Gross
Reservoir on multiple occasions, but are not known to nest or roost in the area and do not occur regularly.
Marginally-suitable habitat for northern leopard frog is present at Gross Reservoir but this species was not
observed during presence/absence surveys in 2010.
Burrowing owl (Athene cunicularia), a Colorado threatened species, has potential habitat in the Leyden
Gulch Reservoir site within several small black-tailed prairie dog (Cynomys ludovicianus) colonies.
Several species of special concern are also known or expected to occur. Both black-tailed prairie dogs
and northern leopard frog were observed during field surveys and are resident. Ferruginous hawk
(Buteo regalis) and American peregrine falcon may forage over the site but do not nest. No suitable
nesting habitat for bald eagle is present but the southern portion of the site, including Ralston Creek, is
used for winter foraging. The east side of SH 93 at Ralston Creek is a winter concentration area. Since
prairie dogs are present at the Leyden Gulch site, bald eagles may occasionally forage there during winter
months.
State-listed species that may occur along the pipeline corridors or at the South Platte River Facilities
include bald eagle, American peregrine falcon, ferruginous hawk, northern leopard frog, black-tailed
prairie dog, swift fox (Vulpes velox), and common garter snake (Thamnophis sp.). Bald eagles are
relatively common along the South Platte River. Black-tailed prairie dogs were documented along
portions of Conduit O and the South Platte River diversion and conveyance facilities. Northern leopard
frog may occur at the South Platte River Facilities. Swift fox may occur along portions of Conduit O.
Common garter snake may occur along portions of Conduit O and at the South Platte River Facilities.
State-listed endangered or threatened species along the river segments include river otter (Lontra
canadensis), boreal toad (Anaxyrus boreas boreas), and common shiner (Luxilus cornutus). State species
of species concern include Colorado River cutthroat trout, bald eagle, northern leopard frog, American
peregrine falcon, and several additional species.
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River otter is a Colorado threatened species and occurs along the Fraser, Williams Fork, Colorado, and
Blue rivers. River otters inhabit high-quality, perennial rivers that support abundant fish or crustaceans
within many habitats ranging from semi-desert shrublands to montane and subalpine forests. Minimum
estimated water flows for river otter are 10 cfs. Other habitat features that may be important include the
presence of ice-free reaches of stream in winter, water depth, stream width, and suitable access to
shoreline. In the Fraser River Valley, river otter overall range includes the entire length of the Fraser
River below Denver Water’s diversion, and winter range occurs downstream of Granby. The Fraser
River tributaries that are diverted by Denver Water are not within the overall range of this species. The
lower Williams Fork River includes areas occupied by river otter; river otter occur upstream to Kinney
Creek and numerous road kill otter are collected along County Road (CR) 3. The focus segment on the
upper Williams Fork River does not appear to be occupied by river otter. The Colorado River segment is
within the overall range of river otters. Two concentration areas are present, including one approximately
0.5-mile reach of the river 2 miles east of the Town of Hot Sulphur Springs, and Windy Gap.
Concentration areas are where otter sightings and signs of otter activity are higher than in the overall
range. Winter range occurs along a large portion of the Colorado River segment. The entire length of the
Blue River is considered to be occupied by river otter.
Boreal toad is listed as endangered by the State of Colorado and have been found at various locations in
the Fraser River and upper Williams Fork River. They have greatly decreased in Colorado in the last
20 years and many former breeding sites have not had activity in recent years. Three of seven known
sites in Grand County are located on tributaries of the Fraser River, including Jim Creek, Upper Vasquez
Creek, and Pole Creek. No breeding activity has been observed at Jim Creek since 1996 and none has
been observed at Vasquez Creek since 2000, although single toads were observed in the Vasquez Creek
area in a couple of years. Monitoring of the Pole Creek site found adults and egg masses every year and
recruitment most years since 1993. CNHP records show recent occurrences along Pole Creek, its
tributary, Skunk Creek, and Crooked Creek. There does not appear to be recent documentation of boreal
toad presence along the Fraser River and its tributaries below the diversions, but there are relatively large
areas of habitat suitable for adult toads and dispersing juveniles (riparian and wetland areas and adjacent
uplands), as well as potential breeding habitat (shallow, abandoned, or active beaver ponds and other
areas of still, shallow warm water). Three known boreal toad sites are located along the Williams Fork
River, including a known breeding site on the upper Williams Fork River downstream of Bobtail,
Steelman, and McQueary creeks, one at McQueary Lake, and an observation of boreal toad at South Fork
in 2007. The upper Williams Fork River site is located in an abandoned beaver pond, and small numbers
of adults and egg masses were observed each year from 2001 through 2007. Tadpoles were observed in
this pond in the fall of 2010. Suitable habitat for adults and dispersing young occurs along most of the
upper Williams Fork River. Boreal toads have also been recorded at the Blue River watershed; however,
known breeding sites occur on tributaries mostly above Dillon Reservoir and not near Blue River, and the
habitat conditions along the river in the study area are only marginally suitable to support the species.
Marginally-suitable boreal toad habitat is present along South Boulder Creek, but the species is not
known to occur there.
Common shiner, a State threatened species, has been reported to occur in the South Platte River between
Chatfield Reservoir and northern Adams County. One common shiner was captured during sampling
surveys in the South Platte River in Denver in 1981, but even then this species was considered extremely
rare in the South Platte River.
Populations of Colorado River cutthroat trout, a Colorado species of special concern, are known to occur
in the Fraser River and Williams Fork River systems. In the Fraser River Valley, core conservation
populations are present in Iron, Hamilton, Jim, Middle Fork Ranch, North Fork Ranch, South Fork
Ranch, and Little Vasquez creeks above the diversions (Hirsch et al. 2006). Conservation populations are
present in Vasquez and Cabin creeks and the Fraser River. Cutthroat trout have also been reported to
occur above Denver Water’s diversion on St. Louis Creek, and downstream of the diversions on Fraser
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River, Vasquez Creek, Little Vasquez Creek, North Fork Ranch, South Fork Ranch, and Cabin Creek.
Populations of Colorado River cutthroat trout are also known to occur on three of the Williams Fork
River tributaries above the diversions, with the population on Bobtail Creek identified as a core
conservation population and the one on Steelman Creek identified as a conservation population.
Cutthroat trout have also been reported downstream of the diversions on Bobtail and Steelman creeks.
Bald eagles occur along the Fraser, Williams Fork, Colorado, Blue, North Fork South Platte, and South
Platte rivers. The lower 4 miles of the Fraser River is winter foraging habitat for bald eagles. The lower
9 miles of the Williams Fork River contains winter range and foraging habitat and about 2 miles of winter
concentration area. The lower 5 miles of the Williams Fork River is also summer foraging habitat, and
nest sites are located near the confluence of the Colorado River and Williams Fork River. No bald eagle
habitats are located within the focus segment on the upper portions of the Williams Fork River. Nearly
all of the Colorado River from Granby to Kremmling is winter and summer foraging habitat. Winter
concentration areas occur at several locations along about 7 miles of the Colorado River, and a number of
roost sites are present. Active bald eagle nests are located between Windy Gap and Hot Sulphur Springs,
and west of the Town of Parshall. Bald eagle summer and winter foraging areas are located along the
entire length of the Blue River. Three active nests and several bald eagle roost sites are located along the
Blue River above Green Mountain Reservoir, and two active nests, roost sites, and about 9 miles of
winter concentration area are located along the Blue River below Green Mountain Reservoir. On the
North Fork South Platte River, the upper 5 miles below Grant is winter foraging habitat, and the lower
10 miles of the North Fork South Platte River in Jefferson County is bald eagle winter range. The entire
South Platte River segment, except for the Denver urban area from about Bowles Avenue to Interstate (I-)
76, is winter foraging habitat for bald eagle. Winter concentration areas are located in eastern Park
County around Lake George (near SH 24), at Eleven Mile Canyon Reservoir, at Cheesman Reservoir, and
from I-76 to the Henderson gage. The portion of the South Platte River north of I-76 is also a summer
foraging area.
Northern leopard frog may occur along all of the river segments. Northern leopard frogs have been
reported recently in wetlands along the Colorado River near Kremmling and are likely to occur in the
focus segment.
American peregrine falcons occur along the Colorado River, South Boulder Creek, North Fork South
Platte River, and South Platte River. They are known to breed and forage along the Colorado River near
the Town of Hot Sulphur Springs. A known American peregrine falcon nesting area is present near Green
Mountain Reservoir. American peregrine falcon may forage along South Boulder Creek both above and
below Gross Reservoir. A known nesting area is located downstream, and another nesting area is located
within several miles of South Boulder Creek above the reservoir. A known American peregrine falcon
nesting area is located along a portion of the North Fork South Platte River, and peregrine falcons may
forage along the river. Known and potential American peregrine falcon nesting areas are located in the
general vicinity of the South Platte River in several locations, and the falcons may forage along the river.
Common garter snake and Iowa darter may occur along the South Platte River downstream of Waterton
Canyon.
6.2.3 USFS Species
Several species of USFS Region 2 Sensitive Species have the potential to occur on ARNF lands at Gross
Reservoir and along the river segments in the Fraser River and Williams Fork River Valleys. In addition
to the summary in the FEIS, a detailed analysis of USFS sensitive species is available in Appendix G-3 of
the FEIS (Report Responding to USFS Comments). A number of USFS Region 2 sensitive species have
been previously addressed as State-listed species, including bald eagle and northern leopard frog.
Northern goshawk was observed on the west side of Gross Reservoir in 2010. No nests were found, and
the study area likely provides suitable foraging and/or post-fledging habitat, at least on Winiger Ridge.
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CPW recommends a seasonal restriction on human activity within 0.5 mile of active nests from March 1
through September 15.
Flammulated owl (Cathartes aura) are likely to occur in the Gross Reservoir study area because the study
area is within the known range and includes typical habitat of mature ponderosa pine (Pinus ponderosa)
and Douglas-fir (Pseudotsuga menziesii). Flammulated owls are neotropical migrants that are on their
breeding range in Colorado from approximately late April/early May through October, and are actively
nesting in May, June, and July.
American three-toed woodpecker (Picoides dorsalis) and olive-sided flycatcher (Contopus cooperi) may
occur in forested and riparian areas around Gross Reservoir. American three-toed woodpeckers occur
primarily in burned areas and in beetle-killed forest for the first several years after tree death. Olive-sided
flycatcher breed mainly in mature spruce-fir and Douglas-fir forests, in forests with snags and forest
openings consisting of natural clearings, stream or lake shores, burned areas, or logged areas with
standing dead trees.
American peregrine falcon and black swift (Cypseloides niger) have the potential to occur at Gross
Reservoir during and after construction but are unlikely to occur regularly. Known American peregrine
falcon nesting locations are approximately 3 miles away from the reservoir. Black swift may be present
on Gross Reservoir during foraging. Nests are located at waterfalls or other ledges with dripping water in
shaded areas, which are not present at Gross Reservoir.
Both fringed myotis (M. thysanodes) and Townsend’s big-eared bat (Corynorhinus townsendii) may
forage at Gross Reservoir. Fringed myotis use caves, mines, and buildings as maternity roosts, solitary
day and night roosts, and hibernacula. They also roost under bridges, in rock crevices, and under bark or
in hollow trees, especially decayed ponderosa pine and Douglas-fir. Hibernacula are usually in caves or
mines with relatively little variation in temperature. Townsend’s big-eared bats typically roost in caves or
mines. Known Townsend’s big-eared bat roosts are located approximately 2 miles from the reservoir site.
American bittern (Botaurus lentiginosus) may occur in marshes along the lower Fraser, Colorado River,
and South Platte River.
6.2.4 CNHP Species
A number of species tracked by CNHP have the potential to occur at Project facilities or along the river
segments, but have not been reported to occur. This section only addresses CNHP tracked species that
have not been previously discussed under other sensitive species categories.
CNHP tracked species at Gross Reservoir include dwarf shrew (Sorex nanus), and three mollusks:
swampy lymphaea (Lymnaea stagnalis), umbilicate sprite (Promenetus umbilicatellus), and banded physa
(Physa utahensis). Dwarf shrew occurs in foothills, montane, and subalpine habitats above 5,000 feet,
and the mollusks may occur in the existing reservoir.
Several species of butterfly may occur at Leyden Gulch, including Moss’s elfin (Callphrys mossii
schryveri), cross-line skipper (Polites origenes), and rhesus skipper (Polites rhesus). The host plants for
these species are stonecrop (Sedum spp), little bluestem (Schizachyrium scoparium) and other grasses,
and blue grama (Bouteloua gracilis), respectively.
CNHP species that may occur at other Project facilities includes Barrow’s goldeneye (Bucephala
islandica), snowy egret (Egretta thula), white-faced ibis (Plegadis chihi), American white pelican
(Pelecanus erythrorhynchos), and arogos skipper (Atrytone arogos) (a butterfly). Barrow’s goldeneye
occurs occasionally in the Denver area during the winter on reservoirs or in the South Platte River.
Snowy egret is a colonial breeder that is likely to be present during the summer and migration season at
reservoirs, South Platte River, and Clear Creek. Pelicans may occur on reservoirs during migration and in
the summer but do not breed in the Denver area. White-faced ibis may occur during migration in wet
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meadows, temporarily-flooded fields, and reservoir shoreline. Arogos skipper may occur along the
western portions of conduits M and O.
Several species may occur along portions of the river segments, including American white pelican,
white-faced ibis, Barrow’s goldeneye and ovenbird along the lower South Platte River; Barrow’s
goldeneye in the Colorado River in winter; and snowy egret along the North Fork South Platte River and
the South Platte River.
6.2.5 Big Game
The primary big game species at Gross Reservoir are mule deer (Odocoileus hemionus) and elk (Cervus
elaphus). Mule deer are common, non-migratory, year-round residents of the Gross Reservoir study area.
No migration corridors, winter concentration, or severe winter range is located in the vicinity of Gross
Reservoir. American elk (Cervus elaphus) severe winter range is present all around the reservoir and a
winter concentration area exists around the northern two-thirds of the reservoir (FEIS Figure 3.9-2). A
migration corridor extends about 9 miles from south of Nederland to Gross Reservoir and includes the
entire shoreline. Mountain lions (Felis concolor) are also present at Gross Reservoir year-round and
primarily prey on deer. Black bear (Ursus americanus) also inhabit the Gross Reservoir study area
especially in montane forest and shrubland, and areas with berry-producing shrubs.
The proposed Leyden Gulch Reservoir study area has summer and winter range for mule deer. Areas
west of the proposed Leyden Gulch site are winter concentration areas for mule deer (FEIS Figure 3.9-1).
Elk occur in the Leyden Gulch site during winter. Mountain lions and black bears also occur in the site.
The western portion of the Leyden Gulch site is within the overall range of black bears, though they are
concentrated along Ralston Creek, west of Ralston Reservoir, and southwest of the site in fall and
summer. The Leyden Gulch Reservoir study area is within the overall range of mountain lions.
The western end of the study area for conduits M and O to Kipling Boulevard is within the overall range
of white-tailed deer, and the first 2 miles is also elk winter range and mule deer habitat winter range.
Areas north of Conduit M (Rocky Flats National Wildlife Refuge [NWR]) are year-round mule deer
habitat. The Clear Creek corridor on Conduit M is within the overall range of white-tailed deer and is a
limited use area for mule deer, and the portion of Conduit M that crosses the South Platte River is within
a mule deer limited use area. The portion of Conduit O along the South Platte River supports mule deer
resident population and migration corridor, and is also within white-tailed deer winter range, overall
range, and is a concentration area.
The South Platte River Facilities pipeline corridor is year-round mule deer range and migration corridor;
white-tailed deer winter range, overall range, and concentration area; and wild turkey (Meleagris
galloparvo) winter range and production area.
6.2.6 Other Wildlife
A variety of carnivores, rabbits and hares, squirrels, small rodents, bats, reptiles, and amphibians occur at
the Project facilities. Detailed information about occurrence of species at the different facilities is
provided in the FEIS. Wildlife species at Gross Reservoir are primarily associated with montane forests
and grasslands. Species at Leyden Gulch are species of foothills grasslands and shrublands. Species at
other Project sites occur mostly in urban and riparian habitats, and species along the river segments are
associated with riparian habitats. Different species occur depending on the elevation of the river segment.
Some species, such as coyote (Canis latrans), red fox (Vulpes vulpes) and raccoon (Procyon lotor) are
likely to occur in all areas. Black-tailed prairie dog occurs in several areas and has been previously
discussed as a State of Colorado species of concern.
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6.2.7 Raptors and Other Migratory Birds
Raptor species known or likely to occur at the Project facilities include bald eagle, osprey (Pandion
haliaetus), Cooper’s hawk (Accipiter cooperii), northern goshawk, red-tailed hawk (Buteo jamaicensis),
American kestrel (Falco sparverius), turkey vulture (Cathartes aura), flammulated owl, great horned owl
(Bubo virginianus), northern pygmy owl (Glaucidium gnoma), and saw-whet owl (Aegolius acadicus).
Northern harrier (Circus cyaneus) and rough-legged hawk (Buteo lagopus) occur in open areas in winter.
Bald eagle, northern goshawk, and flammulated owl are special status species that were discussed in
detail in the previous sections. No raptor nests are currently known to occur and none were observed
during biological field studies conducted in 2005 and 2010. The USFS installed two osprey nesting
platforms in 1993 and nesting has been attempted, although no successful nesting has been observed.
Ospreys from other nearby nesting areas forage at Gross Reservoir. A red-tailed hawk nest was observed
in riparian woodland along Ralston Creek at the Leyden Gulch site during surveys in 2006, and American
kestrels are likely to nest on the site. No raptor nests were observed along Conduit M during field
surveys. A Swainson’s hawk (Buteo swainsoni) nest was near the South Platte River on Conduit O
during the 2006 field survey, and a pair of red-tailed hawk was also observed, suggesting that their nest
was probably located nearby.
The Gross Reservoir study area is within the overall range of wild turkeys. Winter Range for the species
is east of Gross Reservoir. No wild turkeys are expected to occur on the west side of Gross Reservoir in
the winter. The Leyden Gulch site is considered within the overall range of wild turkey. Additionally,
wild turkey winter range is present northwest of and outside of the site.
No nesting sites for colonial water birds were observed in the study area. Great blue heron (Ardea
herodias), snowy egret, black-crowned night heron (Nycticorax nycticorax), and double-crested
cormorant (Phalacrocorax auritus) are common along the South Platte River, Clear Creek, and reservoirs
in the Denver area. They nest at several sites in the Denver Metropolitan area.
The South Platte River corridor is important nesting habitat for waterfowl and supports large numbers of
wintering ducks. The gravel pits are also important for migrating and wintering waterfowl.
A large number of smaller birds were observed or are likely to occur, as described in the FEIS. Nearly all
bird species present in the study area are protected under the MBTA.
6.2.8 USFS Management Indicator Species and Wildlife Habitats
Several USFS MIS are present or likely to be present at Gross Reservoir, including elk, mule deer, hairy
woodpecker (Picoides villosus), mountain bluebird (Sialia cucrucoides), pygmy nuthatch (Sitta
pygmaea), warbling vireo (Vireo gilvus), and Wilson’s warbler (Cardellina pusilla).
The 1997 Revision of the Land and Resource Management Plan (USFS 1997) evaluated several key
elements of biological diversity, including old growth forests, travel corridors for terrestrial wildlife,
habitat effectiveness, and interior forests. Various amounts of these habitats are present at Gross
Reservoir on USFS lands, as described in the FEIS.
6.2.9 Sensitive Areas
CNHP designates Potential Conservation Areas (PCAs) based on habitats and ecological processes upon
which a species or community depends for its continued existence. CNHP ranks PCAs according to their
biodiversity significance, from outstanding biodiversity significance (B1) to general biodiversity
significance (B5).
Two PCAs are present at Gross Reservoir. The Winiger Gulch PCA includes both Winiger Gulch and a
portion of South Boulder Creek above Gross Reservoir. Winiger Gulch includes a good occurrence of
thinleaf alder (Alnus incana)/mesic forb (Betula occidentalis/Maianthemum stellatum) riparian shrubland
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along Winiger Gulch, and good occurrence of foothills riparian shrubland (Betula occidentalis/
Maianthemum stellaum), and an excellent occurrence of Sprengle’s sedge (Carex sprengelii), a CNHP
and USFS sensitive species. The two riparian shrub plant communities and Sprengle’s sedge are
discussed under Section 6.3, Vegetation Resources. The Boulder Foothills PCA is located east and
northeast of the Gross Reservoir study area and overlaps a small portion of the study area (less than
80 acres). It also contains a segment of the South Boulder Creek watershed downstream of Gross
Reservoir. It includes numerous occurrences of multiple CNHP-ranked birds, insects, natural
communities, and plant species. Moist drainages within this area have a long list of plant species that are
primarily associated with eastern North America, including several species also found at Gross Reservoir.
The Boulder County Comprehensive Plan depicts Environmental Conservation Areas (ECAs) –
individual sites that are critical wildlife habitats, rare plant sites, plant communities of special concern,
and wetlands that Boulder County considers important for protection. Two ECAs are present in the
vicinity of the Gross Reservoir study area. The Winiger Ridge ECA includes 3,000 acres of montane
forest bordering the west side of Gross Reservoir. This ECA was designated for high wildlife and
environmental value because it is an important wildlife corridor for seasonal wildlife movement between
higher and lower elevations. The Hawkin Gulch/Walker Ranch/upper Eldorado Canyon ECA includes
9,500 acres forested and grassland habitat and includes South Boulder Creek below Gross Reservoir.
The Rocky Flats PCA overlaps with the northwestern portion of the Leyden Gulch site and was
designated primarily for the presence of xeric tallgrass prairie and Preble’s meadow jumping mouse. No
tallgrass prairie or Preble’s meadow jumping mouse habitat were observed in this portion of the Leyden
Gulch site during site visits in 2006.
Rocky Flats NWR and Rocky Flats PCA are located north of conduits M and O at the western end near
SH 93. The refuge consists of 6,266 acres surrounded by an additional 50,000 acres of Jefferson County
open space. Habitats within the refuge include xeric tallgrass prairies, the Walnut Creek riparian corridor,
wetlands, and mixed grass prairies. Conduit M borders the Two Ponds NWR on the south and within the
City of Arvada. The Two Ponds NWR is a satellite of the Rocky Mountain Arsenal NWR and occupies
72 acres that are managed for wetlands and native wildlife. It contains ponds, wetland, riparian
woodland, and prairie grassland habitats.
The South Platte River PCA (B5) includes the open water and shorelines of the mainstem South Platte
River and the surrounding large lakes and reservoirs, including Ralston Reservoir and Standley Lake.
Mature cottonwood trees along the South Platte River support roosting bald eagles and nesting red-tailed
hawks and Swainson’s hawks, while the open water habitat supports snowy egret, white pelican, and
Preble’s meadow jumping mouse in southern portions of the PCA.
Both the South Platte River and Clear Creek are important wildlife corridors. Two wildlife viewing areas
occur in the Conduit M study corridor, the South Platte River Greenway/Adams County Greenway and
Riverside Cemetery.
6.3 Vegetation Resources
The study area for special status species and riparian/wetland vegetation included both the Project facility
areas and the river segments. The study area for upland vegetation only included the Project facility
areas.
6.3.1 Federally-Listed Threatened and Endangered Species
No Federally-listed plant species are known or potentially present at Gross Reservoir. Two species, Ute
ladies’-tresses orchid and Colorado butterfly plant, may occur at the Leyden Gulch Reservoir site and at
some other Project facilities.
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Ute ladies’-tresses orchids are perennial, terrestrial orchids that flower from mid-July through August.
The plant may remain dormant underground for at least one growing season before leaves emerge
aboveground (USFWS 1995). The species usually occurs in small, scattered populations in moist soils in
mesic or wet meadows near springs, lakes, or perennial streams in the western U.S. Ute ladies’-tresses
orchids are often found in association with floodplain areas where the water table is near the surface
throughout the growing season and into late summer or early fall. The plant is categorized as Facultative
Wet, meaning that populations usually occur in wetlands but are occasionally found in non-wetlands. In
Colorado, Ute ladies’-tresses orchids occur along the eastern slope of the Front Range between 4,300 and
7,400 feet in elevation. A field survey of the northern part of the Leyden Gulch site was conducted on
August 12, 2005, and of the Ralston Creek corridor on August 29, 2006; no Ute ladies’-tresses orchids
were observed. A previous survey conducted in 1997 also concluded no Ute ladies’-tresses orchids were
present within the site. The 1997 survey included portions of Leyden Gulch above the railroad tracks and
east of SH 93, as well as Barbara Gulch, which were not included in the 2005 survey conducted by URS.
Because emergent populations of Ute ladies’-tresses orchid may fluctuate from year to year, assessing
population status and distribution is difficult. Additional presence/absence surveys would be conducted
prior to construction of the Project in accordance with the ESA.
The Colorado butterfly plant is a short-lived perennial herb that grows in sub-irrigated fields and/or
alluvial soils on level or slightly-sloped floodplains and drainage bottoms within mixed grass prairies in
northeast Colorado. It typically grows at elevations of 5,800 to 6,200 feet. The Colorado butterfly plant
occurs in the same habitat as Ute ladies’-tresses orchid. The Leyden Gulch site contains some areas of
suitable habitat for Colorado butterfly plant at some riparian and wetland crossings such as Leyden Gulch
and Ralston Creek. Surveys were conducted on August 12, 2005, along Leyden Gulch and on August 29,
2006, at Ralston Creek to document habitat and/or presence/absence of the species; no Colorado butterfly
plants were found. Additional presence/absence surveys would be conducted prior to construction of the
Project in accordance with the ESA. In 2000, Colorado butterfly plant was listed as threatened due to
population declines from periodic flooding within the riparian habitat for the plant, herbicides, and land
conversion to agricultural uses and urban development. Additionally, the species declines from
competition by dense growths of willows, grasses, and noxious weeds, such as Canada thistle (Cirsium
arvense) and leafy spurge (Euphorbia esula). No critical habitat occurs within the study area, and the
only critical habitat is located along 113 stream-miles in Platte and Larimer counties in Wyoming and
Nebraska, and in Weld County in Colorado.
There are no known occurrences of Ute ladies’-tresses orchid along Conduit M, but suitable habitat may
be present at some riparian and wetland crossings such as Clear Creek. A population of Colorado
butterfly plant was found in 2011 within 0.5 mile of the Conduit M crossing of Clear Creek and suitable
habitat may be present at other stream crossings. Habitat suitability and/or presence/absence surveys
would be documented at Clear Creek and other drainages prior to construction in accordance with the
ESA. The South Platte River is within the Service block-cleared zone for Ute ladies’-tresses orchid and
Colorado butterfly plant, to surveys along the river would not be needed.
The portions of Conduit O crossing and paralleling the South Platte River are within the Service
block-cleared zone for Ute ladies’-tresses orchid and Colorado butterfly plant. The South Platte River
Facilities are also within the block-cleared zone for these species. These species are not expected to be
present and surveys would not be needed prior to construction.
The east portion of South Boulder Creek below Gross Reservoir is within the elevation range of
Ute-ladies’-tresses orchid. However, habitat evaluations conducted in 1998 concluded no potential
habitat was present. As of 2004, further downstream of the potentially affected segment of South Boulder
Creek, 29 known sites were located on South Boulder Creek within City of Boulder Open Space and
Mountain Parks property or private property. Ute ladies’-tresses orchids do not emerge in all 29 of these
sites each year so assessing population status can be difficult. Colorado butterfly plants are not known to
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occur anywhere along South Boulder Creek, although suitable habitat occurs at many of the same
locations occupied by the Ute ladies’-tresses orchid.
Suitable habitat for Ute ladies’-tresses orchid and Colorado butterfly plant may be present along the South
Platte River segment. However, no individuals of these species are known to occur along the South Platte
River segment potentially affected by the Moffat Project. The lower portion is within the block-cleared
zone.
As discussed for wildlife, water depletions to the South Platte River may affect several endangered
animals species downstream along the Platte River in Nebraska. One listed plant species, western prairie
fringed orchid (Platanthera praeclara), is known from one extant population along the Platte River in
Nebraska.
6.3.2 USFS Species
The Moffat Collection System DEIS analyzed Federally- and State-listed threatened and endangered
species and species of concern. USFS comments on the DEIS provided by the ARNF and Pawnee
National Grassland requested species of interest to the USFS be added to the analysis, including Region 2
sensitive species, ARNF species of local concern, plant communities of local concern, and USFS MIS.
The report contained in Appendix G-3 of the Moffat FEIS addresses the USFS requests for more
information on species of concern to ARNF, and provided a basis for completing the analysis of special
status species in the FEIS. It was intended to assist with the information needs of the USFS.
In addition, the USFS requested surveys for sensitive and locally rare plants at Gross Reservoir. In
response to the request for surveys, the Corps coordinated with the ARNF botanist and wildlife biologist
and conducted surveys in the summer of 2010. Survey reports are provided in the attachments to the
report included as Appendix G-3 of the Moffat FEIS and the results of the surveys are discussed in the
body of that report.
A previous survey was conducted by Rick Brune in 2001 for Denver Water’s Recreation Management
Plan and power line relocation associated with the FERC relicensing. All of the observed species are
associated with riparian areas and adjacent lower slopes along Forsythe Creek, Winiger Creek, and other
drainages. One species (dwarf raspberry [(Rubus arcticus var. acaulis, Cylactis arctica ssp. acaulis)]) is a
USFS Region 2 sensitive species, and the other species are ARNF plant species of local concern.
Wild sarsaparilla (Aralia nudicaulis). This species was reported to be present at several locations
in 2001, with more than 3,200 plants observed. During surveys conducted in 2010, wild
sarsaparilla was found to be a regular component of riparian habitat and shaded mesic areas in the
Gross Reservoir study area. More than 5,000 individuals were observed in 2010 in five
populations located in Winiger Gulch, Forsythe Canyon, along the South Platte River, and along
two unnamed drainages on the south side of the reservoir.
Dewey sedge (Carex deweyana). Surveys in 2001 found about 50 of this species in Forsythe
Canyon and a few plants in one of the drainages on the south side of Gross Reservoir. Surveys in
2010 confirmed the presence of this species at those locations and additional locations, and about
260 individuals in four populations in Forsythe Canyon, Winiger Gulch, and two drainages on the
south side of Gross Reservoir.
Sprengel’s sedge (Carex sprengelii). CNHP found this species during surveys in 2007, near the
junction of Winiger Gulch and its south fork. This population was re-located in 2010 along with
additional occurrences in other portions of Winiger Gulch and in Forsythe Canyon. An estimated
650 individuals of this species were observed. Sprengel’s sedge was most common in open areas
in the valley bottom. The largest numbers were found at the confluence of Winiger Gulch and its
south fork, at the site where they were originally reported by CNHP.
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Enchantress’ nightshade (Circaea alpina). More than 900 individuals of this species were
observed in Winiger Gulch and one of the tributaries on the south side of the reservoir. This is
likely an underestimate because of the diminutive size of the plant. In Gross Reservoir, C. alpina
occurs on unvegetated, heavily shaded stream banks that grow to the edge of the water. Due to
the dense shade it prefers, the species was always observed with little or no other associated
herbaceous vegetation.
Tall blue lettuce (Lactuca biennis). One individual of this species was found in Forsythe Canyon
in 2001. About 150 plants of this species were found at several locations along Forsythe Canyon
and Winiger Gulch. It is a tall herbaceous plant and grows in areas of dense herbaceous
vegetation in relatively unshaded areas on mesic terraces.
Maryland sanicle (Sanicula marilandica). Several plants of this species were found in 2001 in
one of the drainages on the south side of Gross Reservoir. About 32 individuals of this species
were found in the same drainage again in 2011. They occurred in areas of moderate shade along
the edges of the creek. It appears that none of this population is located on USFS land.
Dwarf raspberry. An occurrence of this species was found in Forsythe Canyon in 2001. It
included approximately 10 plants. This population was not re-located in 2010; however, the
survey was conducted later in the season when the species may have been dormant. The location
that was searched, based on a GPS point, was a mesic riparian area with mineral soils, and not
typical of the habitats in which this species generally occurs.
False melic (Schizachne purpurascens). This species was found during surveys of the Gross
Reservoir area in 2001, with about 20 to 30 individuals at a location in Forsythe Canyon. It was
found in three additional locations in 2010, but the number of individuals observed at those
locations was not recorded. This species appears to be a regular though uncommon constituent of
riparian areas, and was also observed in aspen communities on the north side of Gross reservoir.
This species was observed in lower Forsythe Canyon, in one of the drainages on the south side of
Gross Reservoir, and along the north shore of the reservoir.
Wood lily (Lilium philadelphicum). This species was mentioned as present, but not affected by
activities at Gross Reservoir. The location of the population is not known and is likely not within
the Gross Reservoir study area. Wood lily was not observed during the 2010 survey.
Ferns. All fern species except brittle bladderfern (Cystopteris fragilis) are considered to be plant
species of local concern for the ARNF. Six species of ferns were found during surveys at Gross
Reservoir in 2010, including forked spleenwort (Asplenium septentrionale), brittle bladderfern,
male fern (Dryopteris felix–mas), Rocky Mountain polypody (Polypodium saximontanum),
western brackenfern (Pteridium aquilinum), and Oregon cliff fern (Woodsia oregana ssp.
cathcartiana). The numbers of individuals were not recorded.
Four USFS Region 2 sensitive species may occur along the Fraser River and Williams Fork River. Lesser
panicled sedge (Carex diandra), dwarf raspberry, autumn willow (Salix serissima) and lesser bladderwort
(Utricularia minor) occur in fens. Habitats where they could occur include montane and subalpine fens
(lesser panicled sedge), swampy conifer forest (dwarf raspberry), willow carrs and streambanks (autumn
willow), and freshwater marshes (lesser bladderwort).
Four species of local concern to the ARNF may occur along the Fraser River and Williams Fork River.
Least moonwort (Botrychium simplex) habitat is forest seeps and streamside meadows in the subalpine;
mud sedge (Carex limosa) and sphagnum moss (Sphagnum spp.) occur in montane or subalpine fens; and
buckbean (Menyanthes trifoliata) occurs in upper montane and subalpine ponds.
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6.3.3 CNHP Species
Several of the USFS species discussed above are also tracked by CNHP. This section only addresses
CNHP-tracked species that have not been previously discussed.
Dwarf wild indigo (Amorpha nana), a species of prairies and grasslands, may be present but was not
observed at Leyden Gulch Reservoir. There are no CNHP-tracked plant species potentially present along
the Conveyance facilities or South Platte River Facilities. Three species may occur along portions of the
North Fork South Platte River and South Platte River. Park milkvetch (Astragalus leptaleus) occurs in
montane meadows and grassy stream banks, American current (Ribes americanum) occurs in lowland
riparian areas, and Rocky Mountain bulrush occurs in drawdown areas along pond margins.
6.3.4 Vegetation Cover Types
The following is a summary of the vegetation cover types found in the study area. More detailed
information, including plant list, are provided in the Moffat Project FEIS in Appendix G and Sections 3.7,
4.6.7, and 5.7.
Gross Reservoir
The Gross Reservoir study area is characterized by conifer forests, rangelands, riparian areas, and
mountainous terrain. Upland vegetative communities in the Gross Reservoir study area include grass/forb
mixed and disturbed rangelands, coniferous forest land, talus slopes and rock outcrops, disturbed soil, and
standing water. Small areas of riparian vegetation are present, some of which have been identified as
sensitive plant communities.
Two types of grass/forb rangelands occur at Gross Reservoir grass/forb mix and disturbed rangelands.
The grass/forb mix community occurs primarily on the eastern shore of the reservoir, though small
patches of this community frequently intermingle with the ponderosa pine community. Shrubs, forbs, and
grasses occur in nearly equal proportions. Clumps of wax currant (Ribes cereum) and Fendler’s
ceanothus (Ceanothus fendleri) intermingle with forbs and grasses. Common herbaceous species include
hairy false golden aster (Heterotheca villosa), fringed sage (Artemisia frigida), sulphur buckwheat
(Erigonum umbellatum), common yarrow (Achillea millefolium), Colorado wildrye (Leymus ambiguus),
cheatgrass (Bromus tectorum), Porter’s brome (Bromus porteri), and mountain muhly (Muhlenbergia
montana). Common noxious weed species in the rangeland areas at Gross Reservoir include common
mullein (Verbascum thapsus), cheatgrass, and musk thistle (Carduus nutans). Disturbed rangelands occur
on the western portion of the Gross Reservoir study area where a prescribed burn was conducted several
years ago in a ponderosa pine community and a grass/forb community. Native plants such as those listed
above are common, but invasive species such as cheatgrass, common mullein, and musk thistle are a
significant contribution to the relative cover in some locations.
There are two types of coniferous forest lands at Gross Reservoir, ponderosa pine and ponderosa
pine/Douglas-fir mix. The ponderosa pine communities are typically found on dry (xeric) slopes that
have southern, eastern, or western aspects. Based on field observations, these areas have a 10 to 30% tree
canopy cover and an average basal area of 53 square feet per acre. Within this community type,
ponderosa pine is the dominant tree but Douglas-fir and Rocky Mountain juniper (Juniperus scopulorum)
also occur. Shrubs are common in the understory, including wax currant, Fendler’s ceanothus,
skunkbrush sumac (Rhus trilobata), Woods’ rose (Rosa woodsii), common juniper (Juniperus communis),
and yucca (Yucca glauca). Forbs make up the largest portion of the understory cover. The ponderosa
pine/Douglas-fir mix communities have dense canopies of mixed conifer trees which suppress understory
species, and are typically found on moderately moist (mesic) slopes that have northern or western aspects.
Based on field observations, tree canopy cover is greater than 30% and the average basal area is 65 square
feet per acre. Ponderosa pine and Douglas fir are the dominant trees and occur in nearly equal
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proportions. Common shrub species include wax currant, chokecherry (Prunus virginiana), kinnikkinnik
(Arctostaphylos uva-ursi), and common juniper (Juniperus communis).
The reservoir shoreline vegetation includes small, scattered patches of riparian woodland, shrubland, and
emergent wetlands. Shoreline woodlands are comprised of widely-spaced plains cottonwood (Populus
deltoides) and narrowleaf cottonwood (Populus angustifolia), with pockets of thinleaf alder. Shoreline
riparian shrub mostly consists of very small pockets of sandbar willow (Salix exigua). Reservoir
shoreline emergent wetlands are dominated by creeping bentgrass (Agrostis stolonifera), woolly sedge
(Carex pellita), fowl mannagrass (Glyceria striata), reed canarygrass (Phalaris arundinacea), and
panicled bulrush (Scirpus microcarpus). Riparian vegetation also occurs along Winiger Gulch and
Forsythe Canyon on the west side of the reservoir, along several unnamed drainages on the south side of
the reservoir, and along some portions of South Boulder Creek above and below the reservoir. Riparian
woodlands associated with drainages are commonly dominated by plains and narrowleaf cottonwood,
very tall thinleaf alder, and water birch (Betula occidentalis). Several conifer species are also present,
including Douglas-fir, lodgepole pine (Pinus contorta), blue spruce (Picea pungens), and Engelmann
spruce (Picea engelmanni). Wet riparian shrublands are dominated by thinleaf alder, water birch,
Missouri River willow (Salix eriocephala), sandbar willow, and park willow (Salix monticola). Moist
riparian shrublands along drainages are diverse, with a mix of various willows, serviceberry (Amelanchier
alnifolia), water birch, red osier dogwood (Cornus sericea), cliffbush (Jamesia americana), ninebark
(Physocarpus monogyrus), chokecherry, various gooseberries (Ribes spp.), Woods’ rose, and roundleaf
snowberry (Symphoricarpos rotundifolius), along with patches of dense herbaceous vegetation. Emergent
wetlands associated with the drainages are commonly dominated by giant angelica (Angelica ampla),
common spikerush (Eleocharis palustris), field horsetail (Equisetum arvense), fowl mannagrass, and
American speedwell (Veronica americana).
Other cover types includes barren areas on talus slopes and rock outcrops, disturbed soil where human
activities result in vegetative cover of less than 10%, and standing water in the reservoir. The existing
reservoir surface at its current capacity is approximately 418 acres. As the reservoir is drawn down,
previously-inundated areas become exposed that are generally devoid of vegetation. These areas support
annual vegetation periodically, particularly following periods of prolonged drawdown.
Leyden Gulch Reservoir
Dominant upland vegetative communities in the proposed reservoir area include grass/forb rangelands,
snowberry/shrub mix, and disturbed soil.
Grass/forb mix communities occur throughout the Leyden Gulch site. Common forb species include
fringed sage, curlycup gumweed (Grindelia squarrosa), yellow sweetclover (Melilotus officinalis), white
sagebrush (Artemisia ludoviciana), dotted gayfeather (Liatris punctata), and prairie coneflower (Ratibida
columnifera). Common grass species include needle-and-thread grass (Hesperostipa comata), blue
grama, sideoats grama (Bouteloua curtipendula), Japanese brome (Bromus japonicus), prairie Junegrass
(Koeleria macrantha), smooth brome (Bromus inermis), and purple threeawn (Aristida purpurea).
Noxious weeds are especially common in the valley of the proposed reservoir, but are much less evident
in grasslands in the southern half of the site. Part of the eastern portion of the site is dominated by diffuse
knapweed (Centaurea diffusa).
Disturbed rangelands occur in several locations at the Leyden Gulch site and are dominated by weedy
species. The western site is disturbed from cattle grazing and congregation, and only three species make
a significant contribution to the relative cover in one of the western areas: pepperweed (Lepidium sp.),
field bindweed (Convolvulus arvensis), and musk thistle. The eastern disturbed rangeland occurs outside
of a fenced area and is dominated by yellow sweetclover.
The snowberry/shrub mix is mostly found on steep north-facing slopes along Leyden Gulch and its
tributaries, and on the west side of the hogback that parallels SH 93. In these areas, skunkbrush sumac or
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western snowberry (Symphoricarpos occidentalis) contributed more than 50% of the relative cover, but
understory composition was similar to the grass/forb mix community discussed above. Skunkbush sumac
was visually dominant in most areas and was the only shrub present in some areas.
Forested riparian areas occur in the southern end of the site along Ralston Creek and in the emergency
spillway, and in small areas along Leyden Gulch and one of its tributaries. Common species include
lanceleaf cottonwood (Populus acuminata), plains cottonwood, peachleaf willow (Salix amygdaloides),
Russian olive (Elaeagnus angustifolia), sandbar willow, and crack willow (Salix fragilis). Understory
vegetation is a diverse mix of grass and forbs. Shrub riparian vegetation occurs in limited areas including
a tributary of Leyden Gulch, the South Boulder Diversion Canal, and small portions of Ralston Creek,
and is usually dominated by sandbar willow. Herbaceous riparian areas are associated with Leyden Gulch
and its tributaries, and include areas of groundwater discharge. The wetlands are dominated by redtop
grass (Agrostis gigantea), Nebraska sedge (Carex nebrascensis), common spikerush, foxtail barley
(Hordeum jubatum), Baltic rush (Juncus balticus), annual rabbitsfoot grass (Polypogon monspeliensis),
common threesquare (Scirpus pungens), cloaked bulrush (Scirpus pallidus), and broadleaf cattail (Typha
latifolia), and various sedges and rushes.
Other cover types include talus slopes and rock outcrop at the hogback on the east side of SH 93, areas of
disturbed soil, residential, and water.
Conveyance Systems
Conduit M includes grass/forb rangeland, and irrigated and dryland agriculture. The western 3 miles of
Conduit M is primarily grass/forb rangeland. Species are characteristic of disturbed rangeland and consist
of broom snakeweed (Gutierrezia sarothrae), cactus (Cactaceae), yucca, cheatgrass, Russian thistle
(Salsola tragus), and tall tumble mustard (Sisymbrium altissimum). Forb species include fringed sage,
curlycup gumweed, yellow sweetclover, white sagebrush, dotted gayfeather, and prairie coneflower.
Common grass species include needle-and-thread grass, blue grama, sideoats grama, Japanese brome,
prairie junegrass, smooth brome, purple threeawn, and cheatgrass.
Dryland cropland and irrigated cropland occur in several areas, especially in the western portion of
Conduit M near Indiana Street and near Clear Creek. This type includes both active and fallow
agricultural areas. Active cropland includes cultivated areas and pastures and hay meadows. The
pastures and hay meadows are typically dominated by non-native grass species, especially smooth brome,
and weedy species such as field bindweed.
The majority of Conduit M goes through an urban area dominated by residential and commercial land
uses. The eastern/southern terminus of Conduit M goes through areas characterized by high density
commercial and residential development. Disturbed soil occurs along road edges and on vacant land.
Typical species in disturbed areas include weedy annuals such as kochia thistle (Kochia scoparia) and
Russian thistle, and weeds such as field bindweed.
Riparian vegetation occurs along several creeks and canals and ditches, including the South Platte River,
Little Dry Creek, lower Clear Creek Canal, and Clear Creek. Riparian woodlands and shrublands are
dominated by plains cottonwood, peachleaf willow, sandbar willow, Woods’ rose, Siberian elm (Ulmus
pumila), and Russian olive. Herbaceous riparian consists of emergent wetlands dominated by broadleaf
cattail, softstem bulrush (Schoenoplectus tabernaemontani), common reed (Phragmites australis), Baltic
rush, reed canarygrass, woolly sedge, and common threesquare. Noxious weeds are often abundant in
urban riparian areas and often include Canada thistle, cheatgrass, common teasel (Dipsacus fullonum),
hoary cress (Cardaria draba), leafy spurge, perennial pepperweed, poison hemlock (Conium maculatum),
quackgrass (Elytrigia repens), Russian olive, salt cedar (Tamarix parviflora, T. ramosissimum), and
Scotch thistle (Onopordum acanthium).
Surface water is present in one pond on the south side of Clear Creek, and in Clear Creek, the South Platte
River, and in several canals and ditches.
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The western third of Conduit O has the same alignment as Conduit M. The central third of Conduit O
goes across mostly urban areas, and the eastern third extends northeast down the South Platte River
Valley. The vegetation types are the same as those described for Conduit M.
South Platte River Facilities
Vegetation and land cover types present at and adjacent to the gravel pits include standing water, running
water in the South Platte River, disturbed soil, disturbed rangeland, forested riparian, shrub riparian, and
herbaceous riparian. The Worthing and Challenger pits were active gravel pits in 2006 and contained
disturbed soil resulting from mining and stockpile operation. In 2006, the North Tower and South Tower
pits contained standing water. The South Platte River and riparian woodland are adjacent to portions of
the Worthing, North Tower, and South Tower pits. These woodlands are dominated by plains
cottonwood, peachleaf willow, and Siberian elm, and typically have an open canopy. The understory
consists mostly of sand dropseed (Sporobolus cryptandrus) and weed species. Grasslands that probably
developed from abandoned cropland occur adjacent to the Worthing, North Tower, and South Tower pits,
and are dominated by species such as sand dropseed, rubber rabbitbrush (Chrysothamnus nauseosus),
cheatgrass, field bindweed, prickly lettuce (Lactuca serriola), ragweed (Ambrosia psilostachya),
Canadian horseweed (Conyza canadensis), puncturevine (Tribulus terrestris), and curly dock (Rumex
crispus). The Worthing Pit is also bordered by disturbed soil (other active gravel pits), and the
Challenger Pit is bordered by gravel operations and cropland.
The diversion facilities are comprised of the diversion in the South Platte River and its banks, and a short
conveyance pipeline to the Worthing Pit. Vegetation types include riparian herbaceous (along the South
Platte River), riparian woodland, and disturbed rangeland.
Vegetation types present along the gravel pit pipeline and laterals include irrigated cropland, disturbed
rangeland, riparian shrub, herbaceous riparian, residential, standing water, running water, and disturbed
soil. These communities and the noxious weeds in them are similar to the descriptions provided
previously in this section.
The proposed AWTP would be located adjacent to the Worthing Pit. The gravel pit site is dominated by
disturbed soil resulting from mining operations. It also contains standing water, and small herbaceous
and shrub wetlands on the edge of the pond, dominated by sandbar willow and cattail.
Denver Basin Aquifer Facilities
Some of the injection/recovery well site locations would be located in Denver parks that primarily consist
of residential cover types. Some of the well site locations have standing water nearby in the form of
ponds and lakes. The residential classification includes parks and golf courses with planted trees and
lawns. The Denver International Airport nursery site is highly disturbed, and the Lakewood Gulch area
contains disturbed rangeland and riparian shrub.
Pipelines would follow streets and urban utility corridors, but would cross riparian woodlands at several
stream crossings, including the South Platte River (two locations), Cherry Creek (three locations), and
Sand Creek. Species composition and noxious weeds are generally the same as the riparian areas
described above for Conduit M.
The proposed AWTP would be located near the existing Denver Water Recycling Plant, which is sparsely
vegetated disturbed soil in an industrial area.
River Segments
Riparian vegetation along the river segments was analyzed by two methods, including a summary of
existing CPW riparian mapping, and detailed studies at 12 sites that were also studied for hydraulic
analysis and channel dynamics. Detailed results from the field studies of the 12 sites are provided in
Section 5.7 of the FEIS.
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The affected river segments in the Fraser River Basin include the mainstem Fraser River downstream of
Denver Water’s diversion points to its confluence with the Colorado River below Granby, and 33 diverted
tributaries. A total of 4,915 acres of riparian habitat were mapped according to CPW riparian vegetation
types along all Fraser River segments. Approximately 75% of the riparian vegetation is located in the
valley reach below the Fraser River Canyon, and approximately 25% is in the upper Fraser River and its
tributaries. The main riparian types in the upper reaches are riparian evergreen, riparian shrub, and
riparian herbaceous, while the main type in the valley reach is riparian herbaceous, with riparian shrub in
about 10% of the mapped area. Four sample sites were used, three in the upper Fraser Valley and one in
the Fraser River Canyon. The sites in the Upper Fraser Valley were on the Fraser River at the Idlewild
Campground (FR1), on St. Louis Creek (FR3), and on Ranch Creek (FR4). Various subalpine
fir-Englemann spruce evergreen forest associations and tall willow shrub communities dominate in these
upper Fraser Valley sites, while a mix of tall and short willow and shrubby cinquefoil shrublands
dominate the Fraser Canyon Site (FR2).
The Williams Fork River Basin includes approximately 30 miles from its confluence with the Colorado
River upstream to its headwaters in the Vasquez Mountains and Williams Fork Mountains. The
characterization of existing riparian and wetland acres focused on the 12.3-mile river segment in the
upper Williams Fork and four diverted tributaries: Steelman, Bobtail, Jones, and McQueary creeks. The
mapping of CPW riparian vegetation categories along the upper Williams Fork River segment covers
approximately 336 acres, mostly riparian evergreen and riparian shrub, with a smaller component of
riparian herbaceous. Two samples were located along the upper Williams Fork River. The upper site,
WF2, was mostly subalpine fir-Engelmann spruce evergreen riparian forest associations, while the lower
site, WF1, was a mix of subalpine fir-Engelmann spruce evergreen riparian forest and tall Drummond’s
willow (Salix drummondiana) shrubland.
Characterization of existing riparian and wetland acres focused on the 15.5-mile Colorado River segment
that extends from the confluence with the Fraser River to its confluence with the Williams Fork River.
CPW riparian vegetation mapping along the river segment covers approximately 1,446 acres, most of
which is riparian herbaceous, riparian deciduous tree, and riparian shrub. One sample site was located in
the segment. Dominant vegetation was narrowleaf cottonwood, thinleaf alder shrubland, and reed
canarygrass herbaceous vegetation.
Analysis of riparian and wetland areas along the Blue River focused on the 21.8-mile reach from Dillon
Reservoir downstream to Green Mountain Reservoir. CPW riparian vegetation mapping covers
approximately 891 acres, most of which is riparian herbaceous, riparian deciduous tree, and riparian
shrub. One sample site was located on this segment. The dominant riparian types at BR-1 were blue
spruce/thinleaf alder forest and thinleaf alder-mixed willow shrubland.
Riparian studies on South Boulder Creek focused on the 22 miles from the outlet of Moffat Tunnel to
Eldorado Springs near Denver Water’s South Boulder Diversion Canal. CPW riparian mapping covers
298 acres and is a mixture of all four mapping categories. Two sample sites were located along this
segment. SBC1 was located above Gross Reservoir and was dominated by thinleaf alder-Drummond’s
willow and Drummond’s willow/mesic forb shrubland. SBC3 is located below Gross Reservoir and is
dominated by redtop herbaceous vegetation, with river birch shrubland and blue spruce forest also
present.
The North Fork South Platte River segment is 39.7 miles from the outlet of the Roberts Tunnel near Grant
to the confluence with the South Platte River. CPW mapping covers 1,141 acres, most of which is
riparian herbaceous and riparian shrub. Two sample sites were used on this segment. The upper site
(NF1) had a mix of narrowleaf cottonwood forest, willow and chokecherry scrublands and redtop
herbaceous vegetation. The lower site (NF2) was mostly sandbar willow shrubland and pasture-meadow.
The South Platte River extends from Antero Reservoir to Adams County. About 30 miles are located in
South Park, including two large reservoirs, Spinney and Eleven Mile Canyon. Riparian vegetation
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occupies about 1,937 acres of the river valley between the reservoirs. Nearly all of the riparian area is
riparian herbaceous, and the remainder is riparian shrub. In addition, there are hundreds of acres of
sparsely-vegetated salt flats below Antero Reservoir. From Eleven Mile Canyon Reservoir to the mouth
of Waterton Canyon, the South Platte River passes through mountainous terrain, and riparian vegetation
is limited and generally dominated by shrubs. Only about 375 acres of riparian occurs along about
60 miles of river valley, of which 90% is riparian shrub. The South Platte River emerges from the
mountains at Waterton Canyon, flows for several miles to Chatfield Reservoir, and then goes north
through the Denver Metropolitan area. Above and below Chatfield Reservoir, there are larger patches of
riparian woodland and shrubland associated with the South Platte River, and canals and ponds. Riparian
vegetation in the Denver urban area is limited and is generally dominated by a mix of native and
non-native tree species. More developed areas of riparian woodland occur along the South Platte River
north of Denver, along with numerous reservoirs and gravel pit ponds north of I-270. Overall, the
approximately 43 miles of the South Platte River from Waterton Canyon to Henderson has about
825 acres of riparian vegetation, including 415 acres of riparian deciduous tree, riparian shrub, and
riparian herbaceous.
6.3.5 Plant Communities of Concern
Two globally-rare plant communities occur within the study area; they are also listed as plant
communities of local concern by the ARNF. The foothills riparian shrub river birch/mesic forb
community occurs along South Boulder Creek above Gross Reservoir and along much of Forsythe Gulch,
and the thinleaf alder/mesic forb occurs on Winiger Gulch upstream of the reservoir. South Boulder
Creek above Gross Reservoir and Winiger Gulch are part of the Winiger Gulch PCA, which is described
in Section 3.9, Wildlife of the FEIS. A mix of these communities was also observed along two of the
drainages on the south side of the reservoir during surveys in 2010.
According to data provided by the USFS, about 13.8 acres of old growth ponderosa pine forest is present
in the western portion of the study area. The USFS also identified blue spruce as a plant community of
local concern that may occur in the study area. Blue spruce trees are present in Forsythe Canyon, but
specific blue spruce community types have not been identified.
The northern portion of the Leyden Gulch site is within the Rocky Flats PCA, which contains a globally-
rare plant community, big bluestem–little bluestem (Andropogon gerardii – Schizachryrium scoparium)
Western Great Plains Herbaceous Vegetation (xeric tallgrass prairie). No tallgrass prairie species were
observed during 2005 and 2006 field surveys in the portion of the PCA that overlaps with the Leyden
Gulch site. Xeric tallgrass prairie remnants do occur in nearby areas, but this community is not present in
the Leyden Gulch site.
6.3.6 Noxious Weeds
Noxious weeds were noted during vegetation surveys. A total of 19 State- and county-listed weeds were
observed at one or more facilities, and several additional species were not observed but are expected to be
present. Some of the species that were found are described below; more complete information is
provided in the Moffat Project FEIS.
Canada thistle is a noxious weed that was found throughout the study area mostly along drainages
and other mesic areas. Canada thistle is on the State B list.
Dalmatian toadflax (Linaria dalmatica) was observed at both Gross Reservoir and the proposed
Leyden Gulch Reservoir site and is on the State B list.
Diffuse knapweed was common at the Leyden Gulch site and was also observed at the South
Platte River Facilities. It is on the State B list.
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Field bindweed is widespread throughout the study area, especially in disturbed areas. This
noxious weed is on the State C list.
Leafy spurge was observed at the South Platte River Facilities and conduits M and O. It is on the
State B list.
Musk thistle was observed at Gross Reservoir and Leyden Gulch and is expected in other study
areas. It is listed on the State B list.
Purple loosestrife (Lythrum salicaria) was the only State A list species observed, and was found
at the South Platte River Facilities.
Saltcedar was observed at the South Platte River Facilities and Denver Basin Aquifer facilities.
This noxious weed is listed on the State B list.
Scotch thistle was common at the Leyden Gulch site and South Platte River Facilities. It is on the
State B list.
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7. Fish and Wildlife Resources – Full Use of the Existing System with
RFFAs
The No Action Alternative provides the basis against which the effects of all action alternatives are
compared. A complete description of the No Action Alternative is presented in Section 8.2.1.
Under the No Action Alternative, Denver Water would continue to operate its existing system, with full
utilization of the system projected to occur by the year 2022. At that time, the amount of available water
supply is projected to equal the customer demand on the system, while maintaining a 30,000-AF Strategic
Water Reserve (i.e., Safety Factor). While the action alternatives would meet an additional 18,000 AF/yr
of demand beyond 2022, the No Action Alternative would have to rely on some combination of utilizing
the Strategic Water Reserve and imposing more frequent mandatory restrictions to meet additional
demands during drought sequences. Two strategies were analyzed in the FEIS, Depletion of the Strategic
Water Reserve with no customer watering restrictions, and a combination strategy involving both
Depletion of the Strategic Water Reserve and watering restrictions.
7.1 Aquatic Resource Impacts
7.1.1 Depletion of Strategic Water Reserve Strategy
The hydrology for the No Action Alternative would be much different compared to all other alternatives.
Diversions from the Fraser River and Williams Fork River tributaries would be much less than for the
action alternatives and, therefore, less water would be delivered to South Boulder Creek than under the
other alternatives and Gross Reservoir would not be enlarged. The differences between the No Action
Alternative and the other alternatives would not result in substantial differences in channel morphology
impacts except in South Boulder Creek where the lower flows would have an insignificant impact
compared to the increased erosion that would occur under the other alternatives. For water quality, the
No Action Alternative would have similar impacts to the other alternatives. The impacts of changes in
hydrology for the No Action Alternative on fish and invertebrates are discussed below for Gross
Reservoir and the river segments. The impacts of the No Action Alternative compared to Full Use of the
Existing System with RFFAs would have the same tipping point consequences as described for the
Proposed Action in Section 9.1. As explained for the Proposed Action, in almost all cases, there would
be no changes that would be sufficient to cause a stream to cross an ecological tipping point.
Gross Reservoir
Gross Reservoir would not be enlarged with the No Action Alternative. Reservoir volume would
generally be lower, by up to 11% in some months. The reservoir would also be drawn down to the
minimum pool approximately 50% more often than under Current Conditions. Water quality impacts
may include a slight increase in phosphorus levels leading to slightly higher productivity than for the
other alternatives, which could be beneficial to the reservoir fishery. However, the lower volume of the
reservoir indicates there would be a minor adverse impact to the fish and invertebrate community of
Gross Reservoir with the No Action Alternative compared to Full Use of the Existing System with
RFFAs.
Fraser River
The No Action Alternative would divert more water from the Fraser River Basin tributaries in average
and wet years compared to Full Use of the Existing System with RFFAs. In general, flow depletions with
the No Action Alternative would be approximately half that with the other alternatives and only slightly
more than Full Use of the Existing System with RFFAs. The flow reductions in the Fraser River would
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range from 2% at Granby (PACSM Node 2900) up to 7% downstream of the Denver Water diversion on
the Fraser River (PACSM Node 2120) compared to Full Use of the Existing System with RFFAs.
The differences in flow between the No Action Alternative and Full Use of the Existing System with
RFFAs would result in minimal differences in habitat availability.
In segments 1 through 5 of the Fraser River, the changes in habitat availability for the life stages of brook,
brown, and rainbow trout would all be 1% or less most of the time. These minimal changes in habitat
availability would have a negligible impact on aquatic resources for the No Action Alternative, somewhat
different than the pattern of adverse and beneficial impacts for the Proposed Action. However, under
certain conditions, bypass flows may not be met below diversions in the Fraser River Basin. This could
further reduce flows compared to existing and Full Use of the Existing System with RFFAs of low habitat
availability for fish and invertebrates. If bypass flows are not met, there would be additional adverse impact
to aquatic resources in the upper Fraser River.
Fraser River Tributaries
Reductions in flow in Fraser River tributaries between the No Action Alternative and Full Use of the
Existing System with RFFAs would be 33 to 50% as much as would be diverted with the Proposed
Action. Compared to Full Use of the Existing System with RFFAs, the No Action Alternative would
divert approximately twice the water in average and wet years. In dry years, there would be no additional
diversions compared to Full Use of the Existing System with RFFAs. The differences would not affect
the low winter flows that are now present in many of these streams.
In many of the Fraser River tributaries, the increased diversions with the No Action Alternative are less
than with the Proposed Action compared to Full Use of the Existing System with RFFAs and would not
be high enough to result in the minor impact predicted for the Proposed Action. These streams would
have a negligible impact to aquatic resources with the No Action Alternative. This includes the St. Louis
Creek tributaries, King Creek, Main Elk Creek and tributaries, Cooper Creek, Middle Fork and South
Fork Ranch Creek, Wolverine Creek, Cub Creek, and Buck Creek.
In St. Louis Creek, the No Action Alternative would have reductions in flow due to additional diversions
of 3% on an average annual basis compared to Full Use of the Existing System with RFFAs. Habitat
availability for brook trout would change by 3% or less for median, dry, and wet years. As a result,
habitat availability changes under the No Action Alternative would be similar to the Proposed Action.
The No Action Alternative would have negligible impacts on fish and invertebrates in St. Louis Creek.
In Vasquez Creek, the additional diversions with the No Action Alternative would be 5% on average
compared to Full Use of the Existing System with RFFAs, much less than the additional diversion with
the Proposed Action. Changes in habitat availability for brook trout would be negligible for the No
Action Alternative. The No Action Alternative would have a negligible impact to aquatic resources
compared to the moderate adverse impact for the Proposed Action.
In Jim Creek and Little Vasquez Creek, the changes in flow under the No Action Alternative would be
less than for the Proposed Action, but would still be sufficient to result in a minor adverse impact. The
impact would be similar to the impact for the Proposed Action.
In North Fork Ranch, Main Ranch, and Dribble creeks, the additional diversions under the No Action
Alternative would be 8% or less compared to Current Conditions (2006), less than would be diverted for
the Proposed Action. The No Action Alternative would have a negligible impact.
For the streams in the Englewood Ranch Gravity System, the additional diversions would be similar to
the No Action Alternative and the Proposed Action. For both, there would be negligible impacts to
aquatic resources.
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Williams Fork River
Changes in Williams Fork River flows under the No Action Alternative would be minimal, usually 3% or
less in all months, and about half that of the Proposed Action. Changes in the minimum habitat
availability for brook trout would be less than 1% for life stages in all year types. The No Action
Alternative would have a negligible impact on the fish and invertebrate communities in the Williams Fork
River, similar to the Proposed Action.
Williams Fork River Tributaries
Under the No Action Alternative, more water would be diverted from the Williams Fork River tributaries
in some months in average and wet years. However, the proposed flow changes would be approximately
half that for the action alternatives in average and wet years. No additional flow reductions would occur
in dry years. Under the No Action Alternative, approximately 5% more water would be diverted on an
average annual basis, but more in the runoff months, especially in May. The No Action Alternative
would have a minor adverse impact on fish and invertebrates in the tributaries, similar to the Proposed
Action.
Colorado River
Reductions in flow under the No Action Alternative in the two segments of the Colorado River would
only be slightly less than the reductions with the Proposed Action. Fish habitat availability for the two
alternatives would be very similar. The No Action Alternative would have a negligible impact on fish
and invertebrates in the Colorado River, similar to the Proposed Action.
Blue River
Monthly reductions in Blue River flows under the No Action Alternative would be slightly higher than for
the Proposed Action. The changes in flow would not result in changes in habitat availability for brown and
rainbow trout compared to the Proposed Action. Therefore, the No Action Alternative would have
negligible impacts in the Blue River, similar to the Proposed Action.
South Boulder Creek
In all three segments of South Boulder Creek, the flows under the No Action Alternative would be similar
to Full Use of the Existing System with RFFAs. The increases in average annual flows would be 3% or
less in segments 1 and 2 upstream of Gross Reservoir, and only 2% downstream of Gross Reservoir in
Segment 3. Monthly flows would vary by a greater magnitude; increases would be high in some winter
months in Segment 3. The differences in flow would result in differences in channel morphology in
South Boulder Creek. The changes in bank erosion under the Proposed Action would not occur under the
No Action Alternative.
Changes in trout habitat availability from Full Use of the Existing Systems with RFFAs would usually be
less than 5% for all life stages of trout in segments 1, 2, and 3 of South Boulder Creek. The No Action
Alternative would have a negligible impact on the fish and invertebrate communities in segments 1, 2,
and 3 of South Boulder Creek. This would be different than the minor adverse impacts in segments 1 and
2 and the moderate beneficial impact in Segment 3 under the Proposed Action.
North Fork South Platte River
Under the No Action Alternative, the increases in flow in the North Fork South Platte River would be only
slightly larger than for the Proposed Action, resulting in a minimal effect on habitat availability, channel
morphology, and water quality. The No Action Alternative would have minor adverse impacts to aquatic
resources, similar to the impacts under the Proposed Action.
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South Platte River
Similar to the North Fork South Platte River, under the No Action Alternative, the increases in flow in the
South Platte River would only be slightly larger than for the Proposed Action. This would have a minimal
effect on habitat availability, channel morphology, and water quality.
7.1.2 Combination Strategy
The No Action Alternative would require Denver Water to use a combination of strategies to meet the
need for additional water supply, including using a portion of its Strategic Water Reserve and imposing
mandatory restrictions to help reduce demand during drought periods (referred to as Combination
Strategy here). There would be no significant differences to aquatic biological resources under the No
Action Alternative with the Combination Strategy. In dry years, flow changes would be similar under
either No Action strategy. Under the Combination Strategy, imposing restrictions would generally have
the impact of reserving more water in storage; therefore, storage contents in Denver Water’s reservoirs
could be higher in dry years. Whether storage contents are higher depends on several factors. The
amount and location of water reserved in storage would vary depending on the severity and duration of
restrictions imposed, on storage conditions in Denver Water’s North and South systems, and on
hydrologic conditions. Since storage contents could be higher with restrictions, Denver Water’s
diversions into storage after a drought could be less and stream flows could increase for a short duration
after Denver Water’s reservoirs refill. However, this would not occur if a reservoir is drained even with
restrictions in place. Conversely, with greater restrictions, during a drought stream flows would be less in
some streams as Denver Water would decrease its releases from storage and divert additional water if
bypass flows are reduced. Decreases in stream flow because less water would be released from storage to
meet demand would apply to South Boulder Creek below Gross Reservoir, the North Fork South Platte
River, and South Platte River. Decreases in stream flow because bypass flows are reduced would apply
to several locations in the Fraser River Basin, the Blue River below Dillon Reservoir, along the South
Platte River below Eleven Mile Canyon Reservoir and Cheesman Reservoir, and at the Old Last Chance
Ditch diversion. Changes in streamflow between the two No Action Alternative strategies are not
expected to be significant. If bypass flows are not met, there would be a minor adverse impact to aquatic
resources in the affected streams.
7.2 Wildlife Resources Impacts
The No Action Alternative would not result in any direct effects to habitat because no ground-disturbing
Project components would be implemented. Changes in operation of the existing system would result in
changes in stream flows, which would result in only minor changes in the extent and type of riparian
habitat (FEIS Section 5.8.6). Therefore, similar to the Proposed Action, implementation of the No Action
Alternative would not have a noticeable effect on wildlife habitat or species.
Under the No Action Alternative, there would be no direct or indirect impacts to special status species
from construction of new facilities, but changes in operation of the existing system would result in
changes in stream flow in areas occupied by special status species. The impacts associated with these
flow changes are discussed below. Because there would be no Federal action, the No Action Alternative
would not require nor involve consultation with the Service regarding these impacts.
As previously described, four Federally-listed endangered fish species occur downstream in the Colorado
River. Flow reductions in the Colorado River resulting from the No Action Alternative would be very
similar to those described for the Proposed Action. In average and wet years there would be a reduction
of 2% in annual flows at the Kremmling gage on the Colorado River (FEIS Appendix H, Table H-3.33),
mostly occurring in June and July in average years and in June in wet years. There would be no changes
in dry years. Flow reductions would fall under the existing Recovery Agreement that Denver Water
signed with the Service in 2000 under the Upper Colorado River Recovery Program.
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Several Federally-listed species occur downstream in the Platte River in Nebraska. The No Action
Alternative would result in an average annual increase of 1% in flows at the Henderson gage (FEIS
Appendix H, Table H-3.48). Flows would remain the same or increase slightly in every month except
June, when they would decrease by about 1%. The largest increases would be 3 to 5% in January,
February, and March.
Preble’s meadow jumping mouse and Ute ladies’-tresses orchid occur along South Boulder Creek
downstream of the South Boulder Diversion Canal. Under the No Action Alternative, average annual
flows would decrease by 1% compared to Full Use of the Existing System with RFFAs (FEIS
Appendix H, Table H-3.40). The flow reduction would occur primarily in May and June, when flows are
highest. In wet years, flows would decrease by 2 to 3% in May and June. There would be no reductions
in flows in dry years. Similar to the Proposed Action, the smaller changes in flows under the No Action
Alternative are unlikely to adversely affect habitats used by these species along South Boulder Creek.
Preble’s meadow jumping mouse occur along the South Platte River from below Cheesman Reservoir to
Chatfield Reservoir. Changes in the outflow of Cheesman Reservoir (FEIS Appendix H, Table H-3.44)
would be minor, including small increases in winter (1 to 3% from October to February) and decreases in
summer (-1% in June, July, and August). Dry years would have flow increases in the summer months
(8 to 14% increases from May to September). Wet years would show no change on an annual basis but
slightly decreased flows from October through December and slightly increased flows from January
through March. These changes are unlikely to adversely affect riparian habitats used by Preble’s meadow
jumping mouse, and may have minor beneficial impacts because of increases in dry years during the
warmer months. Changes at the Waterton gage (FEIS Appendix H, Table H-3.45) would be similar to but
slightly larger than the Proposed Action, a decrease of 4% in annual flows in average years, 2% in wet
years, and 1% in dry years. Decreases would occur most of the year. Similar to the Proposed Action,
these small changes are unlikely to result in adverse changes to riparian habitat occupied by Preble’s
meadow jumping mouse in the area between Waterton Canyon and Chatfield Reservoir.
7.3 Vegetation Resource Impacts
There would be no direct vegetation impacts as a result of the No Action Alternative.
Indirect impacts to vegetation resources would occur at Gross Reservoir as a result of more frequent and
prolonged drawdowns. The area between the normal water elevation and the minimum drawdown level
would remain barren of vegetation but would be increasingly susceptible to noxious weed infestations.
Indirect impacts would not affect Federally-listed threatened and endangered species, USFS species,
CNHP species, cover types, or plant communities of concern.
With the exception of mandatory restrictions imposed during stage 3 and 4 drought periods, vegetation
resources in the vicinity of Project components and throughout the greater Denver Water service area
would remain largely unchanged under the No Action Alternative. In both stage 3 and 4 droughts, lawn
watering would be prohibited. Non-native lawn species and ornamental landscaping would be impacted
by the mandatory restrictions. Trees, shrubs, and high-use public turf areas would be limited to watering
once per week. This would result in temporary stresses to irrigation-dependent vegetation, however,
these areas would likely recover once restrictions were removed. Under Stage 4 drought restrictions, all
outdoor watering is prohibited, including trees, shrubs, and high-use public turf areas. Mortality,
although impossible to quantify, is likely in some irrigation-dependent areas under Stage 4.
Indirect impacts would also occur along the river segments from changes in the amount and timing of
surface flows. Under the Depletion of Strategic Water Reserve Strategy Alternative, Denver Water would
continue to operate its existing system at Full Use of the Existing System with RFFAs but under a higher
demand. In addition, the No Action Alternative would use a combination of depleting the 30,000-AF
Strategic Water Reserve and more frequent mandatory restrictions on use during droughts. Stream flows
would change compared to Full Use of the Existing System with RFFAs because of operational changes
82
including increased use of Blue River and South Platte River supplies and the Strategic Water Reserve,
especially during droughts. Hydrologic impacts would be less than the action alternatives in the Fraser
River and Williams Fork River basins and greater in the Blue River Basin. Flows in South Boulder Creek
above and below Gross Reservoir would be less on average than the action alternatives, while flows in the
North Fork South Platte River would increase on average due to additional Roberts Tunnel imports from
the Blue River Basin.
Modeled changes in the wetland area affected by changes in 2-year flows associated with this alternative
are presented in FEIS Table 5.8-13. Changes from Full Use of the Existing System with RFFAs would be
higher than the Proposed Action at the sampling site on the Blue River (BR1), but the same or less at all
other sampling sites. The largest changes would occur at sampling site BR1, where changes in the area
affected under the No Action Alternative would be twice as much as changes in the affected area under
the Proposed Action. The 2-year flow elevation would decrease by 5.6 inches under the No Action
Alternative compared to Full Use of the Existing System with RFFAs, and the width of the inundated area
would be reduced by 4.6 feet, a reduction of less than 5% of the channel width at Full Use of the Existing
System with RFFAs. Changes at other sampling sites would be less than 2 inches in flow elevation and
1 foot in channel width. Changes would be minor along the Blue River (site BR1), and would be
negligible or none at the other sites. Changes in flow are unlikely to adversely affect riparian and wetland
habitats along the South Platte River, because flow changes would generally be small on both an annual
average and monthly basis.
Changes in flow elevations and channel widths due to changes in the 5-year and 10-year flows under the
No Action Alternative are presented in FEIS Table 5.8-14, for locations where changes are different than
for the Proposed Action. About half of the sampling sites would have changes that are the same as the
Proposed Action. Changes in 5-year and 10-year flows under the No Action Alternative would be less
than under the Proposed Action and other action alternatives, and would result in changes in flow
elevations of less than 2 inches and changes in channel width of less than 2 feet at all sites. Effects on
riparian and wetland vegetation would be negligible.
For the Fraser River and Williams Fork River tributaries, the percent change in flows from Full Use of the
Existing System with RFFAs under the No Action Alternative would be the same or slightly less than the
Proposed Action.
No additional impacts on riparian vegetation would result from implementing the Combination Strategy.
During a drought, stream flows could decrease in some streams because less water would be released
from storage.
83
8. Description of Alternatives
The Corps evaluated six alternatives in detail as part of the FEIS. In its selection of alternatives, the
Corps used an integrated approach so that the alternatives met both NEPA and Section 404(b)(1)
requirements. NEPA regulations require that all reasonable alternatives be considered so that the
Proposed Action is well conceived and thoroughly evaluated (40 Code of Federal Regulations [CFR]
1502.14a). Reasonable alternatives, as defined by the Council on Environmental Quality (CEQ), include
“those that are practical or feasible from the technical and economic standpoint and using common sense,
rather than simply desirable from the standpoint of the applicant” (46 CFR 18027, Forty Most Asked
Questions Concerning CEQ’s NEPA Regulations). The Corps’ Section 404(b)(1) guidelines define
practicable alternatives as “available and capable of being done after taking into consideration cost,
existing technology, and logistics in light of the overall project purposes” (40 CFR 231.10[a]).
Alternatives must satisfy the Section 404(b)(1) guidelines as well as a public interest review (33 CFR
320.4[a]).
8.1 Development of Alternatives
The identification, verification, evaluation, and screening of the alternatives were conducted by the Corps,
with review and input from EPA and FERC as Cooperating Agencies, and from Grand County as a
Consulting Agency. The overall screening approach was performed in two phases – Screen 1 and
Screen 2.
Screen 1 progressed from a broad range of 303 potential water supply and infrastructure components to
34 well-defined Project alternatives using numerous evaluation criteria related to Purpose and Need,
existing technology, logistics, costs, and environmental consequences. Screen 1a started with a broad
range of 303 potential water supply sources and infrastructure components which were evaluated to
determine whether they met the Purpose and Need and for fatal flaws. In Screen 1b, the remaining
42 water supply sources and infrastructure components were used to formulate possible Project
alternatives by matching a potential water source with water storage and conveyance components that
would meet the Project Purpose and Need. The 29 remaining potential storage sites were screened to help
configure the LEDPA. The storage components and water sources were combined to formulate
34 alternatives carried forward. In Screen 1c, the 34 alternatives were screened on the basis of rough
order of magnitude costs; those not considered practicable from a cost perspective were eliminated.
Fourteen alternatives were carried forward to Screen 2.
Screen 2 involved a more in-depth analysis of the Project alternatives using criteria focused on
environmental impacts to the aquatic environment and other natural ecosystems. The results of Screen 2
were a set of five alternatives carried forward for further analysis in the EIS. After the alternatives
screening process was completed, components of the five alternatives were further refined and revised as
Denver Water developed additional detail based on further investigations and engineering studies.
The five action alternatives represent a reasonable range of alternatives that encompass a variety of
potential water supplies and storage sites. Each action alternative was configured to increase the firm
yield of Denver Water’s system by 18,000 AF/year, consistent with the Project Purpose and Need
statement. The five alternatives include three potential sources of increased water supply (additional
Moffat Collection System supplies, reuseable water, and transfer of South Platte River agricultural water
rights), and four potential storage components, including Gross Reservoir, Leyden Gulch Reservoir,
gravel pit storage, and Denver Basin aquifers. An AWTP was included with the three alternatives that
included reusable and agricultural water because the existing Moffat WTP would have trouble complying
with regulatory drinking water requirements for finished water quality using raw water from these water
sources.
84
8.2 Description of Alternatives
Six alternatives were selected by the Corps for detailed evaluation and are depicted in Figures 5 through
10. The alternatives include Denver Water’s Proposed Action, four other action alternatives, and the No
Action Alternative. A summary of the components of the alternatives is provided in Table 8.
Table 8
Summary of Alternative Components
Component
Proposed
Action
(Alternative
1a)
Alternative
1c
Alternative
8a
Alternative
10a
Alternative
13a No Action
Water
Source(s)
Moffat
Collection
System
Moffat
Collection
System
Moffat
Collection
System
Unused reusable
water in the
South Platte
River
Moffat
Collection
System
Unused reusable
water in the
Denver Water
Recycling Plant
Moffat Collection
System
New agricultural
water rights
converted to
municipal/
industrial use
Moffat
Collection
System
Strategic Water
Reserve
Blue River and
South Platte
Rivera
Additional
Storage
Capacity at
Gross
Reservoir
77,000 AFb 40,700 AF 52.000 AF 52,000 AF 60,000 AF __
Other Storage
Component __
New Leyden
Gulch
Reservoir
(31,300 AF)
Gravel Pit
Storage
(5,000 AF)
Denver Basin
Aquifer
Injection/
Extraction Wells
(20,000 AF)
Gravel Pit Storage
(3,625 AF) __
Treatment
Facilities __ __
AWTP
(13.6 mgd)
Dechlorination
Facility
AWTP
(13.6 mgd)
AWTP
(10.8 mgd)
Dechlorination
Facility
__
Pipelines __
Minor
relocation of
South
Boulder
Creek
Diversion
Canal
Conduit 0
(25 miles,
3 pump stations)
Gravel Pit
pipelines
(1.4 miles)
Conduit M
(18 miles,
3 pump stations)
Aquifer
distribution
pipelines
(36 miles)
Conduit O
(25 miles, 3 pump
stations)
Gravel Pit
pipelines (5 miles,
pump stations)
__
Other
Facilities __ __
South Platte
River diversion
and 750-foot
pipeline
27 injection/
recovery well
sites
South Platte River
diversion and
750-foot pipeline
__
Notes: aAll action alternatives collect water from the Blue River, South Platte River, and South Boulder Creek. bIncludes 5,000-AF Environmental Pool for cities of Boulder and Lafayette.
___ = not applicable
AF = acre-feet AWTP = advanced water treatment plant
mgd = millions gallons per day
8.2.1 Proposed Action (Alternative 1a)
Denver Water’s preferred alternative is to enlarge its existing 41,811-AF Gross Dam and Reservoir,
which is located in Boulder County, Colorado, approximately 35 miles northwest of Denver and 6 miles
southwest of the Boulder (Figure 2). The proposed Moffat Project is to expand the existing reservoir by
85
77,000 AF to a total storage capacity of 118,811 AF. This would be accomplished by raising the existing
concrete gravity arch dam by 131 feet, from 340 to 471 feet. This includes 5,000 AF of storage for water
provided by the cities of Boulder and Lafayette (Environmental Pool), which would be released for
environmental flows to enhance habitat in South Boulder Creek. The surface area of the reservoir would
be expanded from approximately 418 to 842 acres, which would inundate approximately 424 acres of
surrounding shoreline. The dam would have a new spillway over the dam raise and auxiliary spillway
south of the dam. Existing roads and recreation facilities would be relocated. Details of the Project
components at Gross Reservoir are provided in Figure 4.
Denver Water is proposing to create an additional 5,000 AF of storage (Environmental Pool) in Gross
Reservoir, as mitigation, to support environmental flow releases for enhancement of aquatic habitat
downstream in South Boulder Creek. This additional storage would be filled with water provided by the
cities of Boulder and Lafayette. None of Denver Water’s existing or future water supply would be stored
in this 5,000-AF Environmental Pool. To enable storage of additional water, Denver Water proposes to
raise the dam an additional 6 feet beyond the proposed 125-foot raise necessary for increasing the storage
of water, to a total height of 131 feet. The reservoir elevation during storage of the Environmental Pool
would be 7,406 feet. The storage and release of water in the Environmental Pool would be managed
under an Intergovernmental Agreement between Denver Water, Boulder, and Lafayette. Refer to
Appendices H-22 and M-2 of the Moffat FEIS for additional information on the Environmental Pool.
Using existing collection infrastructure, water from the Fraser River, Williams Fork River, and South
Boulder Creek would be diverted and delivered during average to wet years via the Moffat Tunnel and
South Boulder Creek to Gross Reservoir. In order to firm this water supply and provide 18,000 AF/yr of
new firm yield, an additional 72,000 AF of storage capacity is necessary. An additional 5,000 AF of
storage would be used as an Environmental Pool by the cities of Boulder and Lafayette, bringing the total
reservoir size to 77,000 AF. Existing facilities, including the South Boulder Diversion Canal, Ralston
Reservoir, and conduits 16 and 22, would be used to deliver water from the enlarged Gross Reservoir to
the Moffat WTP and raw water customers (Figure 5). To meet future demands, in most years, Denver
Water would continue to rely on supplies from the North and South systems. In a drought or emergency,
Denver Water would rely on the additional water it would have previously stored in the Moffat Collection
System to provide the additional 18,000 AF of yield.
The increased storage of Gross Reservoir would affect Denver Water’s operation of its entire system,
including a load shift of water treatment from the South System to the North System, including the
amount of water in storage, the timing and amount of reusable effluent, and the potential for Denver
Water to exchange water up the South Platte River.
8.2.2 Alternative 1c
Alternative 1c would combine additional Moffat Collection System supplies and two reservoir storage
facilities to provide 18,000 AF/yr of new firm yield. The existing Gross Reservoir would be expanded by
40,700 AF and a new off-stream reservoir would be constructed in Leyden Gulch to provide an additional
31,300 AF of active storage capacity. Using existing Denver Water collection infrastructure, water from
the Fraser River and Williams Fork River basins and South Boulder Creek would be diverted during
average and wet years using existing collection infrastructure, and be delivered to the enlarged Gross
Reservoir and then delivered via the South Boulder Diversion Canal to the new Leyden Gulch Reservoir
(Figure 6). Releases from Leyden Gulch Reservoir would be conveyed via conduits 16 and 22 to either
Ralston Reservoir or directly to the Moffat WTP. Details of the Project components at Gross Reservoir
are provided in Figure 4 and at Leyden Gulch Reservoir in Figure 7. Changes to Denver Water’s system
operations would be the same as for the Proposed Action, except that Moffat Collection System water
would be stored at Leyden Gulch Reservoir.
86
8.2.3 Alternative 8a
Alternative 8a would combine storage of Moffat Collection System supplies in an expanded Gross
Reservoir with reusable return flows. Reusable return flows include water imported from the Blue River,
the Meadow-Cabin Creek Basin in the Fraser River Basin, and fully-consumable agricultural water.
Approximately 13,000 AF/yr would be provided by the expansion of Gross Reservoir, while 5,000 AF/yr
of new firm yield would be provided by reusable flows. A new diversion structure and gravel pit storage
facilities (5,000 AF) would be constructed along the South Platte River. Reusable return flows would be
diverted from the South Platte River, when available, to fill the new gravel pit storage facilities. Water
would be recovered from the gravel pits when needed, treated at a new AWTP, and conveyed via new
pipelines to the Moffat Collection System (Figure 8). Conduit O, the new pipeline, would be 36-inch
diameter pipe and 25 miles long, and would require three pump stations. The water stored in the gravel
pits would generally be used for supply in dry years.
8.2.4 Alternative 10a
Alternative 10a would combine storage of Moffat Collection System supplies in an expanded Gross
Reservoir with deep aquifer storage of reusable return flows. Approximately 13,000 AF/yr of new firm
yield would be provided by the enlargement of Gross Reservoir, while 5,000 AF/year would be provided
by reusable return flows and deep aquifer storage and recovery. When available, reusable return flows
would be treated at a new AWTP and conveyed via a new pipeline distribution system to an
injection/recovery well field in the city of Denver (Figure 9). The water would be injected into the
Denver Basin deep aquifers for storage, and would be recovered when needed and conveyed through new
pipelines to the Moffat Collection System. A total of 27 well facilities with 81 individual wells would be
necessary. The Denver Basin distribution pipeline would be 12 to 48 inches in diameter and
approximately 36 miles long. Conduit M would deliver water from the new AWTP to the Moffat Collect
System delivery point at the South Boulder Diversion Canal, and would be 36 inches in diameter and
about 18.5 miles long. Pipelines would be buried in city streets and urban utility corridors. Water stored
in the Denver Basin aquifers would generally be used in dry years.
8.2.5 Alternative 13a
Alternative 13a would combine storage of Moffat Collection System supplies in an expanded Gross
Reservoir with purchase and transfer of existing South Platte River agricultural water rights.
Approximately 15,000 AF/yr would be provided by the enlargement of Gross Reservoir, and 3,000 AF/yr
by transferred South Platte River agricultural water rights and gravel pit storage. Senior water rights
owned by ditch companies diverting from the South Platte River downstream of Denver would be
purchased and converted to municipal/industrial use. Gravel pit storage would be needed to firm the
agricultural water rights supply, provide operational storage, and meet winter return flow obligations
associated with historical use of the water rights. A new diversion would divert water to the gravel pit
storage facility (Figure 10). Approximately 5 miles of 30-inch diameter pipe would connect the gravel
pits. Conduit O would connect the AWTP and the Moffat Collection System and would be 30-inch
diameter and 25 miles long. Water stored in the gravel pits would generally be used in dry years and in
delayed return flows.
8.2.6 No Action Alternative
In the event that a Section 404 Permit is not issued, Denver Water would continue to develop and
implement its conservation, non-potable recycling, system refinement and cooperative action projects.
Even with full implementation of these projects, demand is expected to exceed supply in the near future.
Denver Water would use a combination of strategies, including using a portion of its Strategic Water
Reserve and imposing more frequent and severe mandatory restrictions to help reduce demand during
drought periods. Under the Strategic Water Reserve Strategy, the Strategic Water Reserve would be used
87
to meet the demand for up to 15,000 AF/yr of water supply. Because there is no Strategic Water Reserve
in Denver Water’s North System, there would still be periodic raw and treated water shortages. Under the
Mandatory Restrictions Strategy, Denver Water would impose mandatory restrictions and curtailment of
deliveries to fixed water contracts based on the drought stage and reservoir storage trigger level. Refer to
Section 7.1.1 and Section 7.1.2 for a more detailed discussion of the No Action Alternative strategies.
88
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EnlargedGross Reservoir
Existing South BoulderDiversion Structure
ExistingSouth Boulder
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Existing Conduits 16 & 22
Existing Moffat Treatment Plant
ExistingMoffat Tunnel
South Boulder Creek
Sout
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ExistingEast Portal
Gross Reservoir Study Area
Gross Reservoir - 72,000 AFEnlargementExisting South Boulder Diversion CanalExisting Conduits 16 & 22
Existing Moffat Treatment Plant
Existing Moffat Tunnel
Stream/River
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1:158,400
Reference:1:100,000-scale quad maps originally from USGS(1980s) and created with TOPO!, ©2006 NationalGeographic Maps, All Rights Reserved.
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Moffat Collection System Project FEIS
Figure Proposed Action(Alternative 1a)
Components
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ExistingMoffat Tunnel
EnlargedGross Reservoir
Proposed Leyden Gulch Reservoir
Existing South BoulderDiversion Structure
ExistingSouth Boulder
Diversion Canal
Existing Conduits 16 & 22
Existing Moffat Treatment Plant
Existing RalstonReservoir
South Boulder Creek
Sout
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ExistingEast Portal
Study AreaExisting South Boulder Diversion CanalExisting Conduits 16 & 22
Existing Moffat Treatment Plant
Existing Moffat Tunnel
Stream/River
2.5 0 2.5Miles
1:158,400
Reference:1:100,000-scale quad maps originally from USGS(1980s) and created with TOPO!, ©2006 NationalGeographic Maps, All Rights Reserved.
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Moffat Collection System Project FEIS
Figure 6Alternative 1cComponents
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Diversion Structure
Diversion Structure Access Road
South Boulder DiversionCanal Discharge to Leyden
Gulch Reservoir
North Crest Access Road
South Boulder DiversionCanal Pipeline
Dam FootprintInlet Tower
Inlet
Leyden GulchReservoir
South BoulderDiversion
CanalDischarge
Bridge Over Outlet Tunnel
Emergency Outlet
Crest Access Road
Access Road to North Tunnel Portal
Access Road to South Tunnel Portal
Staging Area
ExistingConduits 16 & 22
Potential SH 93 Realignment
Cut and Cover Pipeline
Cut and Cover Pipeline
Existing RalstonReservoir
Staging andSpoil Areas
Big Dry Creek
Leyden Gulch
Ralson Creek
Leyden Gulch
Ralston Creek
Ralston CreekRalston Creek
Leyden Gulch Site Study AreaLeyden Gulch Reservoir -31,300 AFLeyden Gulch ReservoirDam FootprintConstruction DisturbanceExisting SH 93
Potential SH 93 Realignment
Bridge Over Outlet Tunnel
Diversion Structure
Staging and Spoil AreasPipeline Tunnel
Cut and Cover PipelineSouth Boulder Diversion CanalDischarge to Leyden GulchReservoirSouth Boulder DiversionCanal PipelineExisting South BoulderDiversion CanalExisting Conduits 16 & 22
Access Road
Existing Conduit
Stream/River
2,000 0 2,000Feet
1:24,000
Reference:1:24,000-scale quad maps originally from USGS (1994)and created with TOPO!, ©2006 National GeographicMaps, All Rights Reserved.
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Figure 7Alternative 1c - ProposedLeyden Gulch Reservoir
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Pl atte
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EnlargedGross Reservoir
ExistingSouth Boulder
Diversion CanalDechlorination Facility
Conduit O
AWT Plant
Existing Conduits 16 & 22
Existing Moffat Treatment Plant
Worthing Gravel Pit
South Tower Gravel Pit
North Tower Gravel Pit
Gravel Pit Pipeline
Existing RalstonReservoir
Sout
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Gross Reservoir Study Area
Gross Reservoir - 60,000 AFEnlargementConduit O
Gravel Pit Pipeline
Exiting South Boulder Diversion CanalExisting Conduits 16 & 22
Existing Moffat Treatment Plant
Advanced Water Treatment (AWT) PlantGravel Pit
Existing Moffat Tunnel
Stream/River
2.5 0 2.5Miles
1:158,400
Reference:1:100,000-scale quad maps originally from USGS(1980s) and created with TOPO!, ©2006 NationalGeographic Maps, All Rights Reserved.
Existing Moffat Tunnel
Existing East Portal
South Boulder Creek
Inse
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Moffat Collection System Project FEIS
Figure Alternative 8aComponents
Inset of Upper Reach of South Boulder Creek(same scale)
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EnlargedGross Reservoir
ExistingSouth Boulder
Diversion CanalConduit M
Existing Conduits 16 & 22
Existing Denver Water Recycling Plant
AWT Plant
Existing Moffat Treatment Plant
Deep Aquifer Well
Sout
hPl
atte
River
AquiferDistribution
Pipeline
Existing RalstonReservoir
Sout
h Bo
ulde
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ek
Gross Reservoir Study Area
Gross Reservoir - 52,000 AFEnlargementConduit M
Existing South Boulder Diversion CanalExisting Conduits 16 & 22
Aquifer Distribution Pipeline
Existing Moffat Treatment Plant
Existing Denver Water Recycling Plant
Advanced Water Treatment (AWT) Plant
Denver County ParksDeep Aquifer Well
Existing Moffat Tunnel
Stream/River
2.5 0 2.5Miles
1:158,400
Reference:1:100,000-scale quad maps originally from USGS(1980s) and created with TOPO!, ©2006 NationalGeographic Maps, All Rights Reserved.
Existing East Portal
Existing Moffat Tunnel
South Boulder Creek
Inse
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Moffat Collection System Project FEIS
Figure Alternative 10a
Components
Inset of Upper Reach of South Boulder Creek(same scale)
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AWT Plant
Worthing Gravel Pit
South Tower Gravel Pit
Challenger Gravel Pit
Gravel Pit Pipeline
Dechlorination Facility
Conduit O
Existing Conduits 16 & 22
Existing Moffat Treatment Plant
EnlargedGross Reservoir
ExistingSouth Boulder
Diversion Canal
Existing RalstonReservoir
Inse
t
Sout
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South
Pl atte
Rive r
Gross Reservoir Study AreaGross Reservoir - 60,000 AFEnlargementConduit O
Gravel Pit PipelineExisting South Boulder Diversion CanalExisting Conduits 16 & 22
Existing Moffat Treatment Plant
Advanced Water Treatment (AWT) Plant
Gravel Pit
Existing Moffat Tunnel
Stream/River
1:158,400
Reference:1:100,000-scale quad maps originally from USGS(1980s) and created with TOPO!, ©2006 NationalGeographic Maps, All Rights Reserved.
Existing East Portal
Existing Moffat Tunnel South Boulder Creek
2.5 0 2.5Miles
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Moffat Collection System Project FEIS
Figure 1Alternative 13aComponents
Inset of Upper Reach of South Boulder Creek(same scale)
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101
9. Project Impacts
Sections 9.1 through 9.3 present a summary of the direct and indirect effects for each action alternative.
Impacts to the river segments would be similar under all action alternatives. A qualitative description of
the cumulative effects analysis for each resource is presented in Section 9.4.
9.1 Aquatic Resource Effects
Impacts from Project facilities and from changes in flows in the river segments are discussed below. In
most stream sections there would be no changes to most water quality parameters or riparian vegetation
that would affect aquatic biological resources in the study area. In river segments where there would be
changes, they are discussed as appropriate. Reductions in flows with the Proposed Action are not
expected to have long-term changes to channel morphology in most of the river segments in the study
area. There may be temporary increases in sediment accumulation in isolated locations and some impacts
to bank erosion or vegetative encroachment; such impacts are discussed as appropriate.
9.1.1 Gross Reservoir
The final surface area of the enlarged reservoir, including the Environmental Pool for mitigation, would
be approximately 842 acres, over twice that of the existing reservoir with the Proposed Action. The water
quality of the enlarged reservoir would be suitable for supporting fish with minimal changes from Current
Conditions (2006). One change to the limnology of Gross Reservoir would be the changes in water
quality associated with decaying organic matter that would be inundated with the expansion of the
reservoir. Although this effect would be minimized by removal of vegetation before inundation,
phosphorus and chlorophyll a concentrations are expected to increase for a short time after inundation
before returning to pre-Project levels. The increased productivity could cause a temporary increase in fish
densities, as was observed in a reservoir in Washington (Stables et al. 1990). When nutrient and
dissolved oxygen levels stabilize after the inundation of new habitat, the increased volume of the reservoir
may support larger fish populations. This would be a moderate beneficial impact to the reservoir fishery,
since the enlarged reservoir would support more fish than the existing reservoir and may provide
opportunities for additional species of fish to become established.
Forsythe Canyon and Winiger Gulch are two small tributary streams to Gross Reservoir and portions of
these streams would be inundated with an expanded reservoir. There would be a moderate adverse
impact to the fish and/or macroinvertebrate communities in these streams. Approximately 5,000 feet of
South Boulder Creek would also be inundated with the expanded reservoir and would transform this
section of stream habitat into reservoir habitat. This would represent a major adverse impact to this
section of stream, but a moderate beneficial impact to the reservoir.
Construction activities during enlargement would not substantially affect the normal operation of the
reservoir. The fish and invertebrate communities in the reservoir would continue to function as normal.
The other action alternatives also include enlargement of Gross Reservoir, but the amount of enlargement
would be less. Under Alternative 1c, the final surface area of the reservoir would be approximately
650 acres, 53% larger than the existing reservoir. With alternatives 8a and 10a, the final surface area of
the reservoir would be approximately 712 acres, 70% larger than the existing reservoir. Under
Alternative 13a, the reservoir would be approximately 754 acres. All of the action alternatives would
have a moderate beneficial impact to the reservoir fishery.
9.1.2 Leyden Gulch Reservoir
With Alternative 1c, Leyden Gulch Reservoir would be created. This would represent a gain of
approximately 331 acres of reservoir habitat available for fish, invertebrates, and other aquatic organisms.
This would represent a minor beneficial impact under Alternative 1c compared to Current Conditions.
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However, under Alternative 1c, the public would not have access to the reservoir. This indicates that the
reservoir fishery would not be managed and would probably include only a few fish species, with no
recreational fishery. The creation of the reservoir would inundate portions of Leyden Gulch. This stream
is ephemeral in this section and does not support aquatic life. A small spring pool on a south branch of
Leyden Gulch would also be inundated by the new reservoir. This pool supports a limited community of
aquatic organisms. The inundation of this pool would represent a minor adverse impact under
Alternative 1c.
9.1.3 Other Project Facilities
Alternative 8a would include approximately 5,000 AF of storage capacity in reclaimed gravel pits
adjacent to the South Platte River. The pits would typically fill with reusable effluent from November
through April, when unused reusable effluent is available. Filling and operation of the gravel pit
reservoirs would provide aquatic resources with approximately 5,000 AF of open water habitat. This
habitat would likely be colonized by aquatic invertebrates and fish over time. This would represent a
moderate beneficial impact. Alternative 13a also includes gravel pit storage; the beneficial impacts from
gravel pit storage would be similar to those described under Alternative 8a, except that only 3,625 AF of
open water habitat would be created under Alternative 13a.
Under alternatives 8a, 10a, and 13a, the diversion structure for filling the gravel pit reservoirs would
include a buried pipe connected from the South Platte River to a gravel pit. Direct minor adverse impacts
on aquatic resources from construction of the diversion would include temporary disturbance in the South
Platte River for the duration of construction.
Also under alternative 8a and 13a, Conduit O would cross several streams, including the South Platte
River, that contain communities of warmwater fish and invertebrates. Stream crossings would be open
cut per Denver Water’s standard practice. Each crossing would be completed in approximately
20 working days, depending on weather and other conditions. Therefore, direct minor adverse impacts on
aquatic resources from construction would include temporary disturbance for the duration of construction.
Under Alternative 10a, the proposed distribution pipelines would cross four streams, including the South
Platte River, that contain communities of warmwater fish and invertebrates. The alignment for Conduit
M is the same for Conduit O between the Moffat Collection System delivery point and the intersection of
80th Avenue and Pierce Street. Streams that would be crossed include Little Dry Creek, Clear Creek, and
the South Platte River. The temporary, direct minor adverse impacts of construction activities on Conduit
M under Alternative 10a on aquatic biological resources in these streams would be the same as described
for Conduit O under Alternative 8a.
Under Alternative 13a, the gravel pit pipeline would extend 5 miles to the northern Challenger Pit and
would cross the South Platte River at Bridge Street. There would be temporary, direct minor adverse
impacts during construction at the crossing.
9.1.4 Fraser River
Impacts to the Fraser River would be the same for all action alternatives. Flow changes would result in
minor adverse impacts in segments 1 and 2 (headwaters to St. Louis Creek), moderate beneficial impact
in Segment 3 (St. Louis Creek to Ranch Creek), and negligible impacts in segments 4 and 5 (Ranch Creek
to Colorado River).
Hydrology data were available at five locations as input for Instream Flow Incremental Methodology
(IFIM) habitat simulation: PACSM Node 2120 (Fraser River at Denver Water Diversion) in IFIM
Segment 1, Node 2600 (Fraser River below Vasquez Creek) in IFIM Segment 2, nodes 2700 (Fraser
River below St. Louis and 2720 (Fraser River below Fraser WWTP) in Segment 3, Node 2810 (Fraser
River below Crooked Creek) in IFIM Segment 4, and Node 2900 (Fraser River at Granby) in Segment 5.
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Reductions in flow could affect water temperatures in the Fraser River. Historically, there have been only
two days of daily maximum temperature exceedances in the segments from Fraser to Granby. The
correlation with flow and water temperature is negative but weak, and variation in water temperature at
low flows is extremely high; air temperature is much more likely to affect water temperatures in this
stream than flow volume. Changes in water temperature would be minor or minimal and are not likely to
adversely affect trout populations. A recent analysis (Miller Ecological Consultants 2015) also found few
Project-related changes. This study used a dynamic water temperature model to evaluate temperature
changes in the Fraser River and its tributaries, including Vasquez, Ranch, and St. Louis creeks. The few
additional exceedances of the temperature standard would occur during the shoulder months of May and
October and would be within the optimum temperature range for trout. There would be no additional
exceedances during the warmer months. There would be no long-term increase in sediment deposition
with the Proposed Action. Flow reductions would likely result in localized sediment deposition;
however, remaining flows are predicted to be high enough to mobilize sediment at a frequency that
changes in channel morphology are not anticipated. Flushing of fine sediments and bed mobilization
would continue with the Proposed Action throughout the length of the Fraser River. Therefore, there
would be no increase in habitat for the T. tubifex that carry whirling disease. Water temperatures are
expected to be similar to Current Conditions on most days. Adequate flows and the similarity in base
flows in late summer and in the sediment transport capabilities of the Fraser River indicate that the
Proposed Action would have no effect on Didymo (Didymosphenia geminata). The Proposed Action
would not change the current system of diversions and canals and would not introduce new pathways for
nuisance species distribution.
Segment 1, Headwaters to Vasquez Creek
In average years, Segment 1 flow reductions would be 37% in May, 43% in June, and 15% in July; flow
reductions in the remaining months would not exceed 4%. In dry years, there would be no further
reductions. In wet years, reductions would only occur from May through July and range from 3% in July
to 12% in May. The action alternatives would not increase the frequency and duration of dry years in the
Fraser River compared to Full Use of the Existing System with RFFAs.
IHA analysis shows that the Proposed Action would result in a minimal (less than 1%) reduction of the
90-day minimum flow. Spring snowmelt runoff would be similar to Current Conditions (2006) with
respect to frequency, timing, and duration because natural high flows are already diverted under Current
Conditions (2006) and with Full Use of the Existing System with RFFAs. However, the magnitude of the
peak flow would be reduced by 19%. IHA small flood and large flood parameters look at floods that
occur less frequently than once every two years. The characteristics of small and large floods in
Segment 1 of the Fraser River would not change appreciably because they have already been altered by
diversion and do not occur every year under Current Conditions (2006). However, large flood frequency
would be reduced by approximately 18% compared to Full Use of the Existing System with RFFAs.
In Segment 1, brook trout adult habitat is most limited during peak runoff in median and wet years and
during late summer, fall, and winter in dry years. Reductions in minimum and average annual habitat
availability never exceed 3% in any year type. The largest change in habitat availability is a 21% increase
during the spring runoff period in median and wet years, which may represent a reduction in stressful
habitat conditions for brook trout. There would be minimal changes in spawning habitat availability.
Adult and juvenile brown trout habitat availability is highest during spring runoff and most limited in
winter. Changes in minimum and average habitat availability for all life stages never exceed 2%. Adult
and juvenile rainbow trout habitat availability is lowest during winter and early spring and highest during
peak runoff, similar to brown trout. In all three year types, reductions in minimum habitat availability for
all life stages never exceed 1%, and reductions in average habitat availability for most life stages never
exceed 4%. Average spawning habitat availability would be reduced by 15% in median years.
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Changes in sediment transport are expected to be insignificant. There may be changes in short-term
sediment cycling that allow sediment to temporarily accumulate but sediment would be removed by
periodic high flows, and no long-term change in channel morphology is expected. Very limited
exceedances of water quality standards for copper and zinc already occur in the upper Fraser River and
there are likely to be further occurrences in the future. Projected habitat availability and temperature
changes in this segment of the Fraser River as a result of the Proposed Action would not be sufficient to
affect trout populations in Segment 1. Also, long-term aggradation is not expected, so spawning habitat
would not become permanently embedded. However, the short-term accumulations of sediment and the
likely changes in benthic macroinvertebrate species composition indicate that the Proposed Action would
have a minor adverse impact on aquatic resources in Segment 1 of the Fraser River. This segment of the
Fraser River has not crossed ecological tipping points that would affect the suitability to maintain fish and
invertebrate populations and likely would not cross a tipping point with the Proposed Action.
Segment 2, Vasquez Creek to St. Louis Creek
Reductions in monthly flow in May through July would range from 23% to 38%, reducing flows up to
46 cfs. Wet year reductions would be 35% in May, 24% in June, and 6% or less the remainder of the
year. There would be no reductions in dry years.
The habitat relationship for adult brook trout for Segment 2 of the Fraser River indicates that the low
flows of winter result in relatively low habitat availability. The reductions in flow with the Proposed
Action would result in no reductions in minimum or average habitat availability in median, dry, and wet
years greater than 3%, and no changes in dry years.
There would be temporary changes in short-term sediment cycling, but sediment would continue to be
removed by periodic high flows, and no long-term aggradation is expected. Because sedimentation
appears to be concentrated near diversions and is not pervasive throughout Segment 2, spawning habitat
should not be affected. There would be no temperature changes in this segment of the Fraser River as a
result of the Proposed Action sufficient to affect trout populations. There may be changes in
macroinvertebrate species composition as rheophilic species are reduced and replaced by species that
prefer lower current velocity. The minimal changes in brook trout habitat availability would result in no
change in populations in Segment 2 of the Fraser River. A minor adverse impact to aquatic resources is
expected as a result of changes to the macroinvertebrate community. However, the impact is not expected
to preclude the maintenance of fish and invertebrate populations and this segment would not be degraded
past a tipping point.
Segment 3, St. Louis Creek to Ranch Creek
In Segment 3 of the Fraser River, flows reductions would be 9% to 31% lower than Full Use of the
Existing System with RFFAs in May through August of average years. During the rest of the year, there
would be no changes greater than 6%. In dry years, there would be no flow reductions and in wet years,
reductions during the wet months would range from 2% to 22% of flows with Full Use of the Existing
System with RFFAs. IHA analysis shows that the Proposed Action would result in no change in the
90-day minimum flow and a few days of zero flow modeled in some years. Although the largest amount
of water would be withdrawn during peak flows, the Fraser River would still have runoff flows, though
reduced, in June and July. Small and large floods would remain unaffected with respect to timing and
magnitude of peak flow, but the duration of large floods would decrease by 28%.
In Segment 3, minimum habitat availability for brown trout and rainbow trout occurs during peak runoff
in median and wet years and during low flows in dry years. The juvenile life stage of both species has a
similar pattern of habitat availability as adults. Peak runoff flows would be reduced and minimum habitat
availability would increase by 57% and 58% for adult brown and rainbow trout, respectively, in median
years. For juvenile brown and rainbow trout, minimum habitat availability would increase by 92% and
79%, respectively, in median years. Average annual habitat availability would not change by more than
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4% for any life stage of brown or rainbow trout. Habitat availability would remain largely unaffected
during low flows. The large increases in juvenile and adult minimum habitat availability would occur in
median years because habitat minima occur during peak runoff. This may represent a reduction in
stressful conditions for these life stages. In dry and wet years, changes in habitat availability for all life
stages of brown and rainbow trout would be 4% or less, and there would be no changes in dry years. The
reductions in peak flows would increase habitat availability for fish and invertebrates and would cause a
moderate beneficial impact to aquatic resources in Segment 3 of the Fraser River.
Segment 4, Ranch Creek to Mouth of Canyon
In Segment 4, flow reductions in average years would be 19% in June and 14% in July. During the rest of
the year, flow reductions would be less than 5% and usually less than 2%. In wet years, flow reductions
would be greatest in June (11%, up to 114 cfs), but they would be 4% or less during summer low flows.
IHA analysis of the Fraser River below Crooked Creek (PACSM Node 2810) shows that the Proposed
Action would result in no reduction of 90-day minimum flows. The spring snowmelt runoff would be
similar to Current Conditions (2006) with respect to timing and duration. The frequency, timing, and
duration of small floods would not change substantially. Large flood peaks would be reduced in
magnitude (18%) and duration (11%), but timing would not change significantly.
Minimum habitat availability for brown trout would not be changed by more than 1%, and average annual
habitat availability would not be changed by more than 3% for any life stage in median, dry, or wet years.
Habitat availability during low flows would not be affected. Minimum habitat availability for rainbow
trout would not be changed by more than 5% under the Proposed Action for most life stages. However,
an increase in minimum fry (54%) and juvenile (14%) rainbow trout habitat would occur in median years
because the minimum habitat availability for both of these life stages currently occurs during peak runoff.
Changes in average annual habitat availability for all year types would be 5% or less for all rainbow trout
life stages except spawning. Reductions in average annual spawning habitat would be 11% in median
years. However, the prevalence of whirling disease has essentially prevented rainbow trout reproduction
in the Fraser River. Efforts to establish whirling disease resistant Hofer-strain rainbow trout populations
could be negatively affected by this reduction in spawning habitat.
For almost all life stages of brown and rainbow trout there would be minimal changes in habitat
availability in this segment of the Fraser River. Exceedances of temperature standards have not occurred
in this segment and changes are expected to be minimal. Changes to sedimentation and channel
morphology are not expected. The result of the Proposed Action would be a negligible impact to aquatic
resources compared to Full Use of the Existing System with RFFAs, and density changes to fish
populations are not expected.
Segment 5, Mouth of Canyon to Colorado River
In Segment 5, average year flow reductions would be 17% and 14% in June and July, respectively;
reductions would be 6% or less in the other months. In dry years, there would be no reductions and in
wet years, depletions would be 10% in June and would be no more than 7% in the other months.
Seasonal changes in habitat availability for brown trout in Segment 5 of the Fraser River indicate that
habitat is most limited at low flows in median and dry years and during spring runoff flows in wet years.
Habitat simulations for brown trout indicate minimal changes in minimum and average annual habitat
availability of 1% or less for all life stages in median, dry, and wet years. Habitat availability during low
flows would remain unaltered.
WUA output for rainbow trout also indicates that habitat availability changes seasonally: adult habitat
was most limited at low flows in all year types, and juvenile habitat was most limited during spring runoff
in all year types. The Proposed Action would not result in minimum habitat availability changes greater
than 3% for any life stage in any year type. Average annual habitat would not change by more than 1%
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for any life stage or year type under the Proposed Action. Habitat during low flows would not be
reduced.
Low winter flows usually occur in January and are generally above 30 cfs in median and wet years. In
dry years, low flows under Full Use of the Existing System with RFFAs and the Proposed Action would
be approximately 23 cfs. These flows are similar to the recommended minimum flows based on
R-2-Cross data (20 cfs and 30 cfs at two sites) and would not change substantially with the Proposed
Action.
The small reductions in peak flows with the Proposed Action would have little effect on fish habitat
availability in Segment 5 of the Fraser River. Temperature changes are expected to be minimal and
would not affect trout populations in Segment 5. Also, long-term sedimentation is not expected, so
spawning habitat would not become permanently embedded. Therefore, the Proposed Action is expected
to have a negligible impact to aquatic resources in Segment 5 of the Fraser River.
9.1.5 Fraser River Tributaries
Denver Water has 31 primary diversion points in the Fraser River Basin. In PACSM, several of the
smaller tributaries are combined and modeled jointly because the tributaries are located in close
proximity, diversions are of similar magnitude and timing, and there is little or no gage data to model
them separately. Additional Moffat Tunnel diversions would occur in average and wet years and would
be highly concentrated in May, June, and July. There would be virtually no additional diversions from
late summer through early spring except in infrequent, very wet years. Diversions would increase in
33 years out of the 45 study years. There would be no additional diversions in dry years and below
average years when Denver Water already diverts the maximum amount physically and legally available.
The Proposed Action and alternatives would result in more days when flows would be reduced to
minimum summer bypass requirements, and tributaries without bypass requirements would be dried up
for longer periods. During winter months, most tributaries that do not have bypass requirements are
already dried up because diversion headgates are set in November or December and are not changed until
April of the following year.
St. Louis Creek Tributaries
The PACSM Node (2180) for the St. Louis Creek tributaries (FEIS Appendix Table H-1.41) includes the
hydrology data for West St. Louis Creek, Short Creek, Iron Creek, Byers Creek, East St. Louis Creek, and
Fool Creek. The action alternatives would have a minor adverse effect to the aquatic organisms in these
streams.
The Proposed Action and other action alternatives would divert 42% more water from these streams in
average years, and 16% more water in wet years on an average annual basis. The additional diversions
would extend the period of no flow by one to two weeks on average. IHA analysis of PACSM Node
2180 shows that small and large floods would remain largely unaffected except for decreases in duration.
High flow, small flood, and large flood durations would be reduced by 25% to 63%.
All of these tributary streams are currently severely diverted and are often dry below the diversions. The
hydrology data for these streams indicate that water passes the diversions only during the high flow
months in most years, May through July. The Proposed Action would not change flow conditions during
the critical winter months in the St. Louis Creek tributaries, but would reduce the flows that pass the
diversions in wet months and extend the period when water does not pass the diversion. Impacts would
be minor because any organisms that persist downstream of these diversions are tolerant of very low
flows and because proposed changes are small in relation to historic diversions.
Because most of the flows have already been diverted from these six St. Louis Creek tributaries, further
threshold effects are unlikely and these streams are already past the tipping point. The relatively small
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increase in the number of zero flow days could lead to a decrease in macroinvertebrate densities and may
further restrict the presence of rheophilic species.
St. Louis Creek
The action alternatives would have a minor adverse effect on the section of St. Louis Creek just
downstream of the diversion, and a negligible impact in the lower section. Downstream of the Denver
Water diversion (PACSM Node 2170), there would be 16% less water in average years and 10% less in
wet years. There would be no reduction in minimum flows, likely because of the bypass flow in this
stream. The frequency of high flows would not change, but the magnitude would increase slightly, and
the duration would decrease by 20%. The small and large flood peaks would not experience appreciable
decreases in magnitude, but the durations would decrease by 71% and 27%, respectively. Because of the
lower spring flows, there may be changes to the macroinvertebrate community with fewer rheophilic
species. Also, the lower flows would further limit the water past the diversion that carries
macroinvertebrates from upstream and available for colonization downstream, slightly decreasing
connectivity to upstream populations. In the lower section of St. Louis Creek, flows would be decreased
13% in average years and 9% in wet years.
PHABSIM habitat simulations were available for one site on lower St. Louis Creek. Changes in
minimum and average habitat availability for brook trout would not exceed 1% under the Proposed
Action in any year. Water quality and water temperatures are not expected to change under the Proposed
Action. The current sediment regime is also expected to be maintained. Flow-related threshold effects
are also not likely under the Proposed Action.
King Creek
Flow reductions in King Creek (PACSM Node 2220) would have a minor adverse effect. Average annual
flows downstream of the diversion would be reduced by 43% in average years, and 17% in wet years with
the additional diversions occurring throughout the year. This tributary currently has no bypass flow
requirements, and greater than 90% of the stream’s native flow is diverted for eight months of the year.
This stream does not support fish but does support macroinvertebrates. The reductions in flow with the
Proposed Action would not change winter flows but would reduce the flows that pass the diversion during
wet months and extend the period when water does not pass the diversion by approximately two weeks on
average. Small and large floods would both decrease in duration by 54% and 44%, respectively, but not
in magnitude. King Creek is already severely diverted and may be near a tipping point. No flow-based
threshold effects are expected. However, a slightly longer no-flow period could lead to decreases in
macroinvertebrate densities and slight changes in species composition.
Elk Creek and Tributaries
PACSM Node 2300 includes West Elk Creek, West Fork Main Elk Creek, Main Elk Creek, and East Elk
Creek. Reductions in flows would result in minor adverse impacts to aquatic organisms. The additional
diversions would reduce flows by 28% in average years, and 16% in wet years on an average annual basis
with no additional diversions in dry years. These four streams have no bypass flows and flows that pass
the diversion would occur approximately one week less. IHA analysis of Elk Creek and its tributaries
shows that the frequency of small and large floods would not change. Small floods and large floods
would decrease in duration by 62% to 87%, respectively. Three of these tributaries are severely diverted
and past tipping points: West Fork Main Elk, Main Elk, and East Elk creeks. As a result, no flow-based
threshold effects are expected for these three tributaries. West Elk Creek contained populations of fish
and invertebrates downstream of the diversion. This stream is mildly diverted and is not likely past an
ecological tipping point, but the reductions in flow in this stream may be sufficient to cross an ecological
tipping point.
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Vasquez Creek
Reduced flows would have a minor adverse effect on aquatic resources in Vasquez Creek. Below the
Denver Water diversion (PACSM Node 2280), proposed flow reductions would be 27% in average years
and 16% in wet years. There is a seasonal bypass flow requirement of 8 cfs in summer and 3 cfs in winter
downstream of the diversion. The number of days when the flow would be reduced to the minimum
bypass would increase by one to two weeks on average. Farther downstream at PACSM Node 2370,
annual flows would be 32% lower in average years and 17% lower in wet years. There would be no
reduction in minimum flows, likely due to the bypass flow. The high flow peak frequency would
decrease from 1 to 0 per year (i.e., peak flows that meet the high flow threshold would not occur
annually). The durations of high flows, small floods, and large floods would be reduced by 13% to 68%.
There would be minimal changes to minimum or average habitat availability for brook trout in any year
type because low winter flows would not change with the Proposed Action. No long-term changes in
sedimentation or channel morphology are expected. Changes in temperature or other water quality
parameters are also not expected. Lower runoff flows could tend to provide more favorable habitat for
invertebrates in average and wet years. However, the large magnitude of flow changes, especially in the
lower reaches of Vasquez Creek, would change the species composition of the benthic invertebrate
community and may be low enough to exclude some rheophilic species. The decrease in wetted area
associated with the increased diversions would probably lead to smaller macroinvertebrate populations.
This stream is very close to the 60% thresholds of Carlisle et al. (2010) and Baran et al. (1995), and
would cross those thresholds with Full Use of the Existing System with RFFAs and the Proposed Action.
The stream would still maintain populations of fish and invertebrates but would likely cross an ecological
tipping point with Full Use of the Existing System with RFFAs. The Proposed Action would further
diminish the aquatic community.
Little Vasquez Creek
Reductions in flow would have a minor adverse effect on aquatic resources. Average annual flow would
be 61% lower in average years and 38% lower in wet years. This stream has no bypass flow requirement
although there is a 0.5-cfs bypass agreement. There is very low flow downstream of the diversion
through the winter with Current Conditions (2006) but this stream supports fish and invertebrates
downstream of the diversion. The action alternatives would reduce the flows that pass the diversion in
wet months, and extend the period when little flow passes the diversion by one to two weeks on average.
An increase in the number of low flow days could cause further declines in fish densities downstream of
the diversion. Flow-based threshold effects are possible on Little Vasquez Creek because it is already
near a tipping point.
Cooper Creek
Additional diversions during wet months would have a minor adverse impact. Additional diversions on
Cooper Creek would result in 31% lower flow in average years and 3% lower flow in wet years at
PACSM Node 2380 on an average annual basis. The diversions would mostly reduce flows during runoff
and extend the period with no flow past the diversion by a few days to one week on average. There is no
bypass flow for this stream and it is fully diverted most of the time with low or no flow through the
stressful winter period. Because Cooper Creek has little remaining native flow and does not support fish,
flow-based threshold effects are not likely under the Proposed Action. Cooper Creek is likely already
past an ecological tipping point. Reductions in macroinvertebrate densities and changes in species
composition are possible, given that the number of zero flow days would increase slightly.
Jim Creek
The action alternatives would have minor adverse effects on aquatic resources. The additional diversions
would result in 51% less water in average years and 30% less water in wet years (PACSM Node 2160) on
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an average annual basis. There is no bypass flow for Jim Creek and it is fully diverted much of the year
and this would be extended by a few more days. There are inputs of water a short distance downstream of
the diversion, and Jim Creek supports fish downstream of the diversion and likely has not crossed a
tipping point. The action alternatives would not change the magnitude but would decrease the duration of
high flows and large floods by 11% and 17%, respectively. The additional diversions in wet months and
the extension of the time of full diversion would have a minor adverse impact on aquatic resources.
Flow-based threshold effects are unlikely in Jim Creek, given that it is 100% diverted much of the year
and there are inputs of groundwater a short distance downstream of the diversion. However, an increase
in zero flow days could cause a decrease in fish and macroinvertebrate densities.
North Fork Ranch and Dribble Creek
The action alternatives would have minor adverse effects on aquatic resources on the North Fork Ranch
Creek and Dribble Creek (PACSM Node 2490). The action alternatives would result in 24% lower flow
in average years and 10% lower flow in wet years on an average annual basis. These two streams have no
bypass flows, are fully diverted for much of the year, and are past ecological tipping points. North Fork
Ranch Creek supports fish and macroinvertebrates farther downstream of the diversion because of inputs
of groundwater. The magnitude and timing of small and large floods would not change under the
Proposed Action, but the duration of both would decrease by 41% and 62%, respectively. Additional
diversions during the wet months would extend the dry period by approximately a week on average and
up to several weeks in some years. Reductions in flow of this magnitude would have a minor adverse
impact on the fish and invertebrate communities in North Fork Ranch Creek and on macroinvertebrates in
Dribble Creek. Fish densities would likely not change appreciably, but an increase in the number of zero
flow days may cause a decrease in macroinvertebrate densities.
Main Ranch Creek
The action alternatives would have minor adverse effects on aquatic resources. At Ranch Creek (PACSM
Node 2500) downstream of the Denver Water diversion, there would be 14% less water in average years
and 7% less water in wet years. IHA analysis results show that minimum flows would not be affected by
the Proposed Action, due to the bypass flow requirement. High flow peaks would continue to occur
under the Proposed Action; the timing, magnitude, frequency, and duration would remain similar. The
duration would decrease for small and large floods by 32% and 61%, respectively, but the magnitude and
timing would remain unaffected. Minimum habitat availability for adult brook trout occurs in March and
April at the lowest flows of the year, and availability is highest during spring runoff in median, wet, and
dry years. There would be no appreciable changes in minimum or average habitat availability for adult or
spawning brook trout in median, dry, or wet years and minimum habitat availability in winter would not
change.
Long-term sediment dynamics are not expected to change. Additional sediment deposition may occur in
localized areas but deposition is expected to be limited in duration. Ranch Creek commonly has
exceedances of temperature criteria in late summer at low flows. Late summer low flows are not
expected to change appreciably and high water temperatures would not change appreciably. Temperature
modeling by Miller Ecological Consultants (2015) found that additional exceedances of the daily
maximum temperature standard would occur in May but would be within the optimum temperature range
for trout Main Ranch Creek consistently supports fish in the lower sections due to inputs of groundwater
and has not crossed a tipping point.
Middle Fork and South Fork Ranch Creek
The action alternatives would have minor adverse effects on aquatic resources. The additional diversions
with the Proposed Action would result in 37% lower flows in average years and 15% lower flows in wet
years (PACSM Node 2520) on an average annual basis. These streams are fully diverted at times and
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there are no bypass requirements. These streams have very low or no flow through the winter, which
probably represents the most stressful period for aquatic organisms. IHA analysis of PACSM Node 2520
shows that decreases in minimum flow characteristics would not be affected, given the extent of current
diversions, but zero flow days would increase slightly. The magnitude, duration, and timing of the high
flow peak would not be affected by the Proposed Action. However, the duration of small and large floods
would decrease by 46% and 73%, respectively. The reduced flows in wet months and the extension of the
period when the streams are fully diverted by one to two weeks on average would have a minor adverse
impact. Flow-based threshold effects are not expected because these streams are already severely
diverted and past tipping points. A minor decrease in macroinvertebrate densities is possible.
Wolverine Creek
There is no PACSM node for Wolverine Creek. We assume that more water would be diverted during the
wet months similar to nearby streams. This very small stream has no bypass flow and is fully diverted
much of the year with low or no flow through the winter. The additional diversions during the wet
months with the Proposed Action would have a minor adverse impact compared to Full Use of the
Existing System with RFFAs. Flow-based threshold effects are not anticipated as a result of the Proposed
Action because this stream is already severely diverted and past a tipping point. Minor decreases in
macroinvertebrate densities may occur as a result of a small increase in the number of zero flow days.
Cub and Buck Creeks
Additional diversions on Cub Creek and Buck Creek (PACSM Node 2540) would reduce flows by 31%
in average years and 27% in wet years on an average annual basis primarily in May, June, and July with
no additional diversions in dry years (FEIS Appendix Table H-3.4). These two small streams have no
bypass flow and are fully diverted much of the year; diversions would be extended for about a week on
average, with low or no flow through the winter. The additional diversions during the wet months with
the Proposed Action would have a minor adverse impact compared to Full Use of the Existing System
with RFFAs. Flow-based threshold effects are not anticipated as a result of the Proposed Action because
these streams are already severely diverted and past tipping points. Minor decreases in macroinvertebrate
densities may occur as a result of a small increase in the number of zero flow days.
Englewood Ranch Gravity System
The Englewood Ranch Gravity System includes diversions on Meadow, South Trail, North Trail, Hurd,
Hamilton, Cabin, and Little Cabin creeks. The diversions on South and North Trail creeks also affect
flows in Trail Creek. PACSM Node 2480 (FEIS Appendix Table H-3.18) models flow in these streams.
With the Proposed Action, changes in average annual flow would be 3% in average years and wet years
on an average annual basis with no additional diversions in dry years. The additional diversions would
occur during spring runoff. The small changes in flow with the Proposed Action would have a negligible
impact on fish and invertebrates in these streams. Current diversions on these streams do not approach
any flow-based thresholds for population-level effects, and diversions under the Proposed Action are not
sufficient to cross these thresholds. Therefore, no flow-based threshold effects are expected for these
streams under the Proposed Action.
9.1.6 Williams Fork River
The Williams Fork River upstream of the South Fork was evaluated with PHABSIM habitat simulation.
Hydrology data from the Williams Fork above Darling Creek gage (PACSM Node 3600) were used to
simulate habitat for adult and spawning life stages of brook trout. The hydrology data for the Proposed
Action indicate average annual flow reductions of 2% in average and dry years, and 2% in wet years with
no reductions in dry years. Peak flow in an average year would be reduced by 14 cfs (7%). The
additional diversions would occur from May through August, and relative reductions would be largest in
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July. The Proposed Action would not increase the frequency and duration of dry years in the Williams
Fork River and tributaries. IHA analysis of flow at PACSM Node 3600 showed that 90-day minimum
flows would decrease by 2%. Changes to high-flow, small-flood, and large-flood IHA parameters would
also be minimal. Downstream of South Fork, reductions in flow with the Proposed Action would be
minimal in the Williams Fork River. Near the Leal gage (PACSM Node 3750), average annual flow
reductions would be 3% or less in all year types. Most of the additional diversions would occur during
runoff flow months. Reductions of this magnitude would have a negligible impact on aquatic resources in
this section of the Williams Fork River.
The pattern of habitat availability for adult brook trout in Segment 1 of the Williams Fork River indicates
minimum habitat during runoff in median, wet, and dry years. The reductions in runoff flows with the
Proposed Action may decrease stressful conditions for brook trout, but minimum and average adult brook
trout habitat availability would experience minimal changes (1% or less) under the Proposed Action.
Changes in spawning habitat would also be small. Minimum and average spawning habitat availability
would decrease by 3% in median years, and no changes are expected in dry or wet years.
For aquatic resources, the small differences in flow for the Proposed Action would have a negligible
impact compared to Full Use of the Existing System with RFFAs. Because the current flow depletions
from this stream do not approach either of the flow-based thresholds, and because additional proposed
diversions are small, no flow-related threshold effects are expected with the Proposed Action.
9.1.7 Williams Fork River Tributaries
The Proposed Action would include additional diversions of water from McQueary, Jones, Bobtail, and
Steelman creeks, which form the headwaters of the Williams Fork River (PACSM nodes 3100, 3150,
3200, and 3250). For these four streams, the additional diversions would be up to 30% in average years
and up to 10% in wet years (FEIS Appendix H, Tables H-3.25 through H-3.28). There would be no
additional diversions in dry years. There would be increased frequency of dry years compared to Full Use
of the Existing System with RFFAs by approximately 2 years over the 45-year period of record. There
are no bypass flows in these streams and they are already fully diverted for much of the year. The
additional diversions would extend the period of no flow past the diversions by approximately one month
in these four streams.
IHA analysis results for Bobtail Creek (PACSM Node 3150) show that 90-day minimum flows would not
be reduced. High flow pulses would decrease in frequency and duration under the Proposed Action by up
to 23%. Small and large floods would not change with respect to magnitude or timing, but durations
would decrease by 41% and 50%, respectively. Similar flow changes may occur in the other three
tributaries.
Downstream of the Denver Water diversions on McQueary, Bobtail, and Steelman creeks, brook trout are
the dominant fish species. Data were not available for Jones Creek, but this stream may also contain
brook trout. Habitat simulation data are not available for these streams. R-2-Cross data for Bobtail Creek
indicate that flows less than 1 cfs would not be sufficient to fully maintain fish and invertebrates and this
is probably true for the other tributaries. The low flows in winter in all four streams at a point
downstream of their diversions are less than 1 cfs with Current Conditions (2006) and would be reduced
with Full Use of the Existing System with RFFAs, during probably the most stressful period for the
aquatic resources of these tributaries. However, similar to the Fraser River tributaries, these streams
resume flow downstream of the diversions from groundwater, tributaries, and wetlands during times when
they are fully diverted.
The flow reductions during runoff would have a minor adverse impact on the fish and invertebrate
populations in these creeks. Although there would be no change in the critical winter flows as there is
already no flow past the diversion in winter, the Proposed Action would reduce the flow passing the
diversions in wet months and extend the period when these streams are fully diverted. Because all of
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these streams are already severely diverted, no flow-based threshold effects are expected. The increase in
zero flow days could reduce fish and macroinvertebrate populations downstream of the diversions.
9.1.8 Colorado River
Hydrology data for two segments of the Colorado River were used to model habitat availability for brown
and rainbow trout. Hydrology data from Colorado River at Windy Gap Reservoir (PACSM Node 1350),
Colorado River upstream of Hot Sulphur Springs (PACSM Node 1400), and Colorado River downstream
of Hot Sulphur Springs (PACSM Node 1425) were used in Segment 1 (Windy Gap Reservoir to Williams
Fork River). Hydrology data for the Colorado River at the Williams Fork confluence (PACSM
Node 1430) and the Colorado River at Kremmling (PACSM Node 5020) were used in Segment 2
(Williams Fork to Blue River) (FEIS Appendix H, Tables H-3.31 through H-3.33).
The Proposed Action and other action alternatives would have negligible impacts on aquatic resources. In
Segment 1, there would be average annual flow reductions of 6% in average years, 4% in wet years, and
no reductions in dry years. Flow reductions in Segment 2 would be 3% to 4% in average and wet years in
Segment 2, with no change in dry years.
In Segment 1, habitat availability time series analyses indicate that there would be minimal changes in
WUA for brown trout under the Proposed Action. Minimum habitat availability changes would usually
be less than 1% and would not exceed 3% in almost all cases. Changes in average WUA would not be
more than 5% in any year type for any life stage. Similarly, most changes to rainbow trout WUA would
be 3% or less. The increased frequency of dry years would result in a variety of increases and decreases
in trout habitat availability based on the relationships of the three study sites in Segment 1. In many
cases, habitat availability for juvenile brown and rainbow trout would be higher with the reduced runoff
flows in dry years, while lower flows would reduce average and minimum habitat availability for adult
trout. In Segment 2, time series analyses of trout habitat availability indicate that most changes in habitat
availability would be minimal, and generally less than 2%.
There would also be minimal changes in sediment cycles or channel morphology. Because water
temperatures are already of concern in segments 1 and 2 of the Colorado River, the effects would be
moderate. There have been a small number of exceedances for the standards at multiple sites in both
segments 1 and 2 between 2005 and 2010. Temperature exceedances only occurred on hot days when
flows were 125 cfs or less, but the number of days during which flows are 125 cfs of less would be
expected to increase with the action alternatives. There would be a net decrease in the number of
exceedances because of releases of water from Granby Reservoir for compliance with the Upper Colorado
River Recovery Program, although there would be an increase in July, the hottest month (Miller
Ecological Consultants 2015).
Because the current average annual flow depletions from this stream are estimated to be 66%, Segment 1
of the Colorado River is near a flow-based tipping point. The minimal changes to habitat availability,
channel morphology, and water temperatures indicate that the Proposed Action would not cause this
segment of the Colorado River to cross a tipping point.
9.1.9 Blue River
Four PHABSIM segments were evaluated on the Blue River. Hydrology data from the Dillon Reservoir
Outlet (PACSM Node 4250) in Segment 1, the Blue River below Boulder Creek (PACSM Node 4500) in
Segment 2, the Blue River below Green Mountain Reservoir (PACSM Node 4650) in Segment 3, and
Blue River at Mouth (PACSM Node 4800) in Segment 4 were used for evaluation of flow changes and
PHABSIM habitat simulation. Habitat data were available for all life stages of brown trout in all four
segments of the Blue River. Habitat data were available for all life stages of rainbow trout in segments 2
through 4.
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The action alternatives would have a negligible impact on aquatic resources in all four segments. The
Proposed Action and other action alternatives would result in an annual average of 3% to 5% less water in
average and wet years above Green Mountain Reservoir, and 2% less water in average and wet years
between Green Mountain Reservoir and the Colorado River (FEIS Appendix H, Tables H-3.36 and H-3.37).
The action alternatives would also increase the frequency and duration of dry years in Segment 1 (Dillon
Reservoir to Rock Creek).
There would be no appreciable changes in brown trout or rainbow trout habitat availability. Time series
analyses for all life stages of brown and rainbow trout indicate minimal changes. Changes in minimum and
average habitat availability would mostly be 3% or less. In Segment 1, the greater frequency of dry years
would increase habitat availability by reducing flows during the spring runoff period. For adult, fry and
juvenile brown trout, minimum habitat availability would be approximately 80% to 100% higher compared
to median years, and up to 126% compared to wet years.
There would be insignificant changes in sedimentation and channel morphology and negligible changes to
water quality parameters. However, in years when Dillon Reservoir is full and spills, relatively warm water
from the top of the reservoir enters the Blue River and raises the temperature to levels that may result in
better growth of trout, but the frequency of this happening would remain about the same as under Full Use
of the Existing System with RFFAs. The Blue River is not near an ecological tipping point and these
changes would not cause it to approach a tipping point threshold.
9.1.10 South Boulder Creek
PHABSIM habitat simulation data were available for three segments of South Boulder Creek. Segments
1 and 2 include the stream between the Moffat Tunnel and Gross Reservoir, and Segment 3 is
downstream of the reservoir. Hydrology data were available near Rollinsville (PACSM Node 57100) for
Segment 1, at the Pinecliffe gage (PACSM Node 57120) for Segment 2, and downstream of Gross
Reservoir (PACSM Node 57140) for Segment 3. Flow changes upstream of Gross Reservoir would have
minor adverse impacts, while flow changes downstream of Gross Reservoir would have minor beneficial
impacts.
Upstream of Gross Reservoir in segments 1 and 2, the Proposed Action would result in higher mean
monthly flows during the spring runoff period but little change in other months. In average years, the
average annual flows would be 11% higher at Rollinsville and 10% higher at Pinecliffe, and mean
monthly flows in June and July would be as much as 22% higher in average years. Average annual flows
would not change in dry years. In wet years, flows would be 18% and 14% higher on an annual basis in
segments 1 and 2, respectively (FEIS Appendix H, Table H-3.38). High flows would occur more often
under the Proposed Action. The 5- and 10-year floods would be expected to occur every 4 and 7 years,
respectively. As a result, bank erosion could increase, and further stabilization could become necessary.
No changes to water quality would occur that could affect aquatic resources.
With the higher mean monthly flows during runoff in Segment 1 under the Proposed Action, brook trout
minimum adult WUA would decrease by 13% in wet years; all other changes in minimum habitat
availability would be 4% or less. Decreases in average habitat availability would be 3% or less for all life
stages in all year types. For rainbow trout in Segment 1, reductions to minimum habitat availability
would be 13% for adults and 18% for fry in wet years, but changes in minimum WUA would be 3% or
less for all other life stages, regardless of year type. Changes in average WUA would be negligible for all
life stages in all year types. In Segment 2, changes in minimum and average WUA would be 3% or less
for all life stages in all year types.
These flow changes would result in mostly minimal changes in trout habitat availability. However, there
would be increased bank instability which could alter habitat and the increases in runoff flows could have
an effect on benthic invertebrate populations, including reduced density or a shift towards individuals that
live in fast-moving water.
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Downstream of Gross Reservoir, annual flows would increase by 9% in average years, 17% in dry years,
and 14% in wet years (FEIS Appendix H, Table H-3.39). The existing and Full Use of the Existing
System with RFFAs hydrographs have flows that are highest in spring, but they are extremely low in
winter. With the Proposed Action, flows in average, dry, and wet years would be substantially different.
Flows would increase from November through February; the greatest increases (nearly 800% to 900%)
would occur in January and February. Flows during runoff would be up to 23% lower. Winter flows
would increase under the action alternatives, but highest runoff flows would be reduced by 13%. The
5-year and 10-year floods would not be expected to occur under the Proposed Action. These changes
may decrease bank instability in Segment 3 of South Boulder Creek and reduce the need for further bank
stabilization efforts. No changes to water quality would occur that could affect aquatic resources.
With Full Use of the Existing System with RFFAs, the minimum habitat availability for rainbow trout
adults and juveniles occurs in the late winter and during spring runoff. With the action alternatives, there
would be increases in minimum habitat availability up to 126%. For adults, increases would be 31% in
median years and 126% in dry years. Fry minimum habitat availability would increase by 48% in median
years. Juvenile minimum habitat availability would also increase; predicted increases range from 11%
(wet years) to 53% (dry years). Average habitat availability would also increase for some life stages in all
year types. In median years, adult average habitat availability would increase by 17%. Adult WUA
would increase by 22% in dry years and by 14% in wet years. Changes for other life stages in dry and
wet years would be 7% or less.
The increases in winter flows would result in large increases in rainbow trout habitat availability. The
small decreases in spring runoff flows would decrease conditions that may be stressful to early life stages
of this species. The higher winter flows would likely alleviate winter low flow habitat limitations.
Higher winter flows and reduced peak flows would also provide more uniform flow conditions for
benthic invertebrates. With less dramatic drying of the stream in winter months, Segment 3 of South
Boulder Creek may support a higher density of macroinvertebrates or a more species-rich community
including more rheophilic species.
9.1.11 North Fork South Platte River
There are two segments on the North Fork South Platte River with PHABSIMs. In Segment 1, Roberts
Tunnel to Buffalo Creek, hydrology data from the North Fork South Platte River below Geneva Creek
gage (PACSM Node 50700) were used for habitat simulation. In Segment 2, Buffalo Creek to South
Plate River, data from the North Fork South Platte River above Pine (PACSM Node 50750) were used.
In both segments, flow changes would have minor adverse effects to aquatic resources. In Segment 1, the
average annual flow between Full Use of the Existing System with RFFAs and the Proposed Action
would increase by 3% in average years and 1% in dry years, and would decrease by 3% in wet years
(FEIS Appendix H, Table H-3.41). Mean monthly flows would decrease in winter by as much as 37%
(January and February of wet years), and would increase during spring runoff by as much as 29% (May of
average years). Annual flow changes would be similar in Segment 2, while decreases and increases in
monthly flows would be similar but smaller in magnitude.
Habitat simulation data were available for all four life stages of brown trout in Segment 1. With Full Use
of the Existing System with RFFAs, minimum habitat availability occurs during runoff in June for adult,
fry, and juvenile brown trout. Changes in minimum habitat availability would be 9% or less in median
and wet years. Reductions in habitat availability would occur for all life stages in dry years: minimum
WUA reductions would range from 10% to 15% depending on life stage. Average habitat availability
would be less affected. Reductions in average habitat availability would be 6% or less in all year types.
In Segment 2, lowest habitat availability also occurs during high flows. Minimum habitat availability
would decrease for all four life stages of brown trout. Predicted minimum habitat availability decreases
by 18% for spawning in median years, and by 12% for juveniles and 24% for spawning in dry years. In
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wet years, only spawning habitat would be appreciably reduced; losses would be 36%. Average habitat
availability would not change by more than 9% for most life stages except for reductions of 10% for fry
in median years and spawning in wet years.
Although water quality may change due to changes in flow from the Roberts Tunnel, these changes would
generally not lead to exceedances of aquatic life water quality standards. There could be increases in
copper concentrations, which already have standard exceedances sometimes. Increased flows are
expected to increase bank instability, and further bank armoring may be required to stabilize affected
areas.
9.1.12 South Platte River
There would be no impact to aquatic resources to the river or the reservoirs in segments 1 through 3, from
Antero Reservoir to the confluence with the North Fork South Platte River.
In segments 4 and 5, from the North Fork to Chatfield Reservoir, impacts would be negligible. At the
Waterton gage (PACSM Node 51200) there would be a decrease in average annual flow of only 3% in
average years. In dry and wet years, the changes in annual flow would be 2% or less but changes in some
of the individual months would almost always be less than 10% (FEIS Appendix H, Table H-3.45).
PHABSIM habitat simulations are available for life stages of brown and rainbow trout for Segment 5 of
the South Plate River. The Proposed Action would result in minimal changes in habitat availability for
most life stages of brown and rainbow trout. Most of the changes would be 7% or less except for
increases in rainbow trout spawning habitat of 31% and 39% in median and dry years, respectively.
There would be no changes in water quality or channel morphology that would affect aquatic resources in
this segment.
Segment 6, Chatfield Reservoir to Bear Creek, would have a minor beneficial impact because of
increased winter flows in dry years. Changes in mean annual flows would be 3% or less in all years, with
little change flows in all months. Under Current Conditions (2006), flows in this segment of the river are
commonly very low throughout the winter. Minimum habitat availability for adult rainbow trout and
likely for most fish species occurs during the low flow winter period. In dry years, adult and juvenile
rainbow trout minimum habitat availability would increase by over 100%, but spawning habitat
availability would decrease by 27%. In wet years, adult and spawning habitat availability would decrease
by 34% and 12%, respectively. In median years, changes would be 1% or less for fry, juveniles, and
adults. The changes in average habitat availability mostly would be 7% or less. Trout populations are
maintained by stocking juvenile and adult fish in this segment, and changes in spawning or fry WUA
would have negligible effects to the limited trout population. There would be negligible effects to the
existing fish assemblage, which consists mainly of species tolerant to flashy flows and poor water quality.
There would be no water quality changes that would affect fish and invertebrates, and likely no changes
to channel morphology due to the channelization along almost all of length of this segment.
9.2 Wildlife Resources Effects
9.2.1 Federal Threatened and Endangered Species
Construction of Gross Reservoir and other facilities is unlikely to directly affect Federal threatened or
endangered species for all action alternatives. At Gross Reservoir, greenback cutthroat trout have been
stocked in the past but are not currently known to occur, and Preble’s meadow jumping mouse is not
known or expected to occur. The proposed Leyden Gulch Reservoir site study area has potential habitat
for Preble’s meadow jumping mouse at Ralston Creek; however, due to habitat fragmentation from
known occupied habitat above Ralston Dam, the study area is unlikely to support a population of Preble’s
meadow jumping mouse. Implementation of Alternative 1c is unlikely to adversely affect Preble’s
meadow jumping mouse or habitat, but Ralston Creek should be surveyed prior to construction to ensure
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Preble’s meadow jumping mouse have not colonized the site. Operation of Denver Water’s system would
involve changes in flows on the Colorado, South Platte, and other rivers that would affect listed species.
Effects of operation are described below and would be similar for all alternatives. Changes in flows
would adversely affect greenback cutthroat trout in several Fraser River and Williams Fork River
tributaries, endangered fish species in the Colorado River, and endangered species along the Platte River
in Nebraska. Impacts to Colorado River and Platte River species would be mitigated by following the
requirements of the Upper Colorado River Recovery Program and the Platte River Recovery
Implementation Program (PRRIP) and conservation measures have been developed for greenback
cutthroat trout. Project-related flow changes are unlikely to adversely affect other Federally-listed
species.
Colorado River Endangered Species
Four Federally-listed endangered fish species (Colorado pikeminnow, razorback sucker, bonytail chub,
and humpback chub) occur downstream of the study area in the Colorado River. Critical habitat for
endangered Colorado River fish extends from Rifle downstream to Lake Powell. Depletions adversely
affect the listed species by reducing peak spring and base flows that limit access to and the extent of
off-channel waters such as backwaters, eddies, and oxbows, which are necessary as rearing areas for
young fish.
Under all of the action alternatives, changes in flow in the Fraser, Williams Fork, Colorado, and Blue
rivers would adversely affect endangered Colorado River fish by causing water depletions in the upper
Colorado River system. Depletions of any amount are considered by the Service to be an adverse impact.
Under the Proposed Action, average annual diversions from the upper Colorado River would increase by
10,285 AF/yr through the Moffat Tunnel, which includes water diverted from the Fraser River and from
the Williams Fork River through the Gumlick Tunnel, and 4,836 AF/yr through the Roberts Tunnel,
which diverts water from the Blue River. These additional diversions translate into a decrease in flow of
15,121 AF/yr (or 25) on average in the Colorado River near Kremmling gage. Decreases in flow in the
Colorado River would be a result of Denver Water’s increased diversions through the Moffat Tunnel and
Roberts Tunnel.
Consultation with the Service is required under Section 7 of the ESA prior to authorization of any Federal
action that may adversely modify critical habitat, which includes alteration of flow volume or timing
(i.e., depletion). In its BO for the Proposed Action (USFWS 2013), the Service concurred that the new
depletions associated with the Proposed Action would be “likely to adversely affect” the endangered fish
species. In 1999, the Service issued a Programmatic BO with specific elements to implement the
Recovery Implementation Program for Endangered Fish Species in the Upper Colorado River Basin
Recovery Program. In 2000, Denver Water signed a Recovery Agreement with the Service, which
governs consultations under Section 7 of the ESA regarding depletions associated with Denver Water’s
facilities. In the BO, the Service determined that proposed depletions to the Colorado River from
implementing the Proposed Action would be covered under Denver Water’s Recovery Agreement.
Mitigation would be done through payment of a one-time fee to cover the costs of acquisition of water
rights and other recovery actions to offset the depletion effect, and would be included as a stipulation in
the Section 404 Permit.
Platte River Endangered and Threatened Species in Nebraska
Several endangered or threatened species occur downstream in the Platte River in Nebraska, including
whooping crane (Grus Americana), interior least tern, piping plover, pallid sturgeon, Eskimo curlew, and
western prairie fringed orchid. Similar to the Colorado River, depletions to the Platte River system are
considered by the Service to have an adverse impact on endangered species, and specifically on the four
target species: whooping crane, interior least tern, piping plover, and pallid sturgeon. Under the Proposed
Action, average annual flows on the South Platte River at the Henderson gage would increase by 2%, as
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shown in FEIS Appendix H, Table H-3.48. The increase in flows would be due primarily to Denver
Water’s and the City of Arvada’s additional effluent returns at the Metro WWTP, and additional return
flows accruing to the river due to outdoor water usage. Increases in flow would be greatest during the
winter months from October through April. During those months, Denver Water’s additional direct
diversions from the South Platte River are considered minimal and there would be less demand for
reusable effluent.
During the summer months, flow would decrease on average by up to 1%. Denver Water’s additional
direct diversions and exchanges upstream would exceed the additional return flows to the South Platte
River during these months. The monthly average changes in flow range from a 9% increase in December
to a 1% decrease in May and June. The average annual depletion from the South Platte River Basin
would be 3,460 AF, including 2,789 AF of new diversions and 561 AF of additional reservoir
evaporation. Thus, for the Proposed Action, the Service determined that the depletions in the South Platte
River would be “likely to adversely affect” the whooping crane, interior least tern, pallid sturgeon, piping
plover, and western prairie fringed orchid in the central and lower Platte River in Nebraska.
In 2007, the Service issued a Programmatic BO and began implementing the PRRIP to address
water-related activities affecting flow volume and timing in the central Platte River in Nebraska. Denver
Water is a member of the South Platte Water Related Activities Program, Inc. (SPWRAP), which
provides continued Programmatic coverage under the PRRIP for Denver Water’s existing and future
South Platte River Basin water depletions. In the BO (USFWS 2013), the Service determined that the
proposed depletions to the South Platte River from implementing the Proposed Action would be covered
by Denver Water’s continued participation and membership in SPWRAP. Denver Water’s annual
assessments to SPWRAP help to support the water user and State of Colorado obligations under the
PRRIP.
Preble’s Meadow Jumping Mouse
Populations of Preble’s meadow jumping mouse are present downstream from Gross Reservoir along
South Boulder Creek, along the South Platte River between Waterton Canyon and Cheesman Reservoir,
and along a portion of the North Fork South Platte River. Changes in flows in these rivers are unlikely to
adversely affect Preble’s meadow jumping mouse or its habitat, because flows would not change in dry
years and changes would be relatively small in average and wet years. In the BO, the Service concurred
with the determination of “not likely to adversely affect.”
Greenback Cutthroat Trout
The Moffat Project would have a minor adverse impact on green lineage cutthroat trout in Little Vasquez,
Hamilton, Steelman, and Bobtail creeks above the diversions due to increased entrainment. Average
annual diversions would increase by 8% in Little Vasquez Creek, 13% in Hamilton Creek, 18% in
Steelman Creek, and 20% in Bobtail Creek. There would be no change in diversions in dry years.
Increases in diversions in wet years would be larger than in average years. Changes in flows would not
affect the core conservation populations above the diversions. Populations of cutthroat trout below the
diversions have unknown genetics but likely include greenback lineage cutthroat trout from above the
diversion. Denver Water’s diversions on these four creeks are effective barriers to upstream movement of
fish, so that cutthroat trout that move downstream of the diversions cannot return to the isolated
headwater population. Changes in flows below the diversions have the potential to affect individual fish,
but would not affect the conservation populations.
The diversions do not include screens to prevent entrainment, and entrainment is likely to occur. The
Project alternatives do not include any physical modifications to the diversion structures or operations
with the exception of increased water diversions in average and wet years. The diversion structures were
therefore not analyzed in the EIS. The risk of entrainment from operation of the Moffat Collection
System is expected to increase compared to Current Conditions (2006) because of the increased water
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diversions. The Moffat Project alternatives would continue to isolate the populations of green lineage
cutthroat trout located above the diversions. The core conservation populations in Little Vasquez,
Hamilton, and Bobtail creeks, as well as the conservation population in Steelman Creek have sustained as
isolated populations for decades despite the functioning diversions and the likelihood of entrainment.
The Corps assumes that the Moffat Project would cause take of green lineage cutthroat trout, and that the
increased risk of entrainment represents an adverse effect. Diversion of water from green lineage
cutthroat trout streams is estimated to result in a loss of 301 fish per year due to entrainment under current
conditions, based on an estimate of approximately 10% of the population becoming entrained. The
increased number of fish entrained is likely to be less than 10 fish from each stream each year, resulting in
an estimated 40 additional fish entrained per year, for a total of 341 fish per year entrained per year with
the project.
Because the action alternatives would involve increased entrainment, they would adversely affect green
lineage cutthroat trout, which is receiving interim protection as greenback cutthroat trout, a listed
threatened species. A BA (Corps 2015) was prepared to address this species and a separate BO was
issued by the Service on June 17, 2016 (USFWS 2016b). Conservation measures included in that BO are
provided in Section 10.2.
Canada Lynx
Canada lynx may regularly use riparian areas along some of the tributaries of the Fraser River including
Vasquez and St. Louis creeks, and may occasionally use riparian areas along some of the other river
segments including the Fraser River, Williams Fork River and its tributaries, Blue River, and the western
portion of South Boulder Creek. The action alternatives would have negligible to minor effects on
riparian habitats in these areas, and primarily involve changes in vegetation composition (see FEIS
Section 5.8). These changes are unlikely to change habitat suitability or habitat use by Canada lynx.
Canada lynx primarily use forested areas and have large home ranges. Small and localized changes in
riparian habitat would be unlikely to affect habitat or overall habitat use. In addition, the Proposed Action
would not involve any construction, clearing of vegetation, or change of human use activity in Canada
lynx habitat. The Service concurred with the determination of “no effect” for this species.
9.2.2 State Threatened and Endangered Species
Construction of the dam and enlargement of Gross Reservoir would have negligible to minor impacts to
State-listed species. Impacts would be similar for all alternatives:
Bald eagles do not nest at Gross Reservoir and there would be no effects to nesting bald eagles.
During construction, disturbance from equipment operation and earth-moving activities may
temporarily disturb foraging bald eagles and may affect availability of prey species.
American peregrine falcons are unlikely to occur regularly. Construction may have temporary,
minor indirect impacts on these birds due to noise and disturbance associated with earth-moving
and construction activity. Construction would not impact peregrine falcon nesting because
known nesting locations are approximately 3 miles away from the reservoir.
Impacts to Townsend’s big-eared bat would be limited since this species forages at night.
However, individuals at day roosts located near construction activity may be displaced to other
areas. Known Townsend’s big-eared bat roosts are located approximately 2 miles from the
reservoir site; therefore, construction and operation would not impact roosting individuals.
Northern leopard frog is unlikely to occur in drainages and inlets along the reservoir, and was not
found in 2010 surveys. Vegetation clearing and inundation of the expanded reservoir would
remove marginally-suitable habitat in these areas.
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Impacts from construction of Leyden Gulch Reservoir would only occur under Alternative 1c, and would
be minor.
Construction would eliminate suitable nesting habitat for burrowing owls in the black-tailed
prairie dog colonies. Burrowing owls have not been documented in this area, but no
presence/absence surveys were conducted for the Project. Surveys would be required to
determine if burrowing owls occur at Leyden Gulch during the nesting season (April 1 to
September 30). If present, earth-moving and vegetation-clearing activities occurring during the
burrowing owl nesting season would cause owls to flush from the nest or equipment could crush
eggs, young, and adult burrowing owls, and rising water levels may flood nests during reservoir
filling.
Construction of Leyden Gulch Reservoir would not adversely impact bald eagles, although
construction activities may result in avoidance of the area by bald eagles. Following inundation,
bald eagles would lose a small prey base of prairie dogs at Leyden Gulch, but are likely to have
increased availability of waterfowl and fish.
Approximately 7 acres of existing black-tailed prairie dog colonies would be removed during
construction. Besides the mortality of prairie dogs, the proposed reservoir would eliminate
foraging habitat for ferruginous hawk.
Northern leopard frog is known to occur. Impacts to northern leopard frog include direct loss of
habitat as well as mortality to individual frogs (Anura) by crushing or burial during earth-moving
activities for construction of the dam, pipeline, or access roads.
Impacts form the South Platte River Facilities would only occur under alternatives 8a and 13a and would
be negligible to minor, as described below.
If burrowing owls occur where prairie dogs are present along the gravel pit pipeline corridor,
impacts would consist of temporary disturbance to nesting individuals during pipeline
construction. If construction occurs during the burrowing owl breeding season (March 15
through July 31), heavy equipment operation and earth moving may cause nest abandonment or
mortality from crushing or burial if a nest is located near the construction right-of-way (ROW).
Construction may disturb or displace foraging bald eagles, especially if construction occurs
during winter months. The South Platte River corridor adjacent to the proposed gravel pits is
used by bald eagles for foraging year-round and is a winter concentration area. Operation of the
gravel pit reservoirs would benefit bald eagles by creating open water habitat and an increased
prey base of waterfowl and potentially fish. The Project would have no impact on nesting bald
eagles or communal roosts.
Construction and operation of the facilities would have no impacts on peregrine falcons as the
species occurs in the area during foraging and other habitats are available.
Northern leopard frog and common garter snake may be affected where the gravel pit pipeline
crosses riparian and wetland areas. Small terrestrial species including northern leopard frog,
common garter snake, and black-tailed prairie dogs would be directly impacted by ground
disturbance for construction of pipelines and pump stations. Heavy equipment and earth moving
may kill individual animals by crushing or burial.
Impacts from construction of conduits M and O would occur under alternatives 8, 10a, and 13a, and
would be negligible to minor, as described below.
Impacts to burrowing owl would consist of temporary disturbance during construction activity.
Areas of potential habitat for burrowing owls occur near Conduit O in prairie dog colonies,
including the western terminus of the pipeline in the vicinity of SHs 72 and 93 (also Conduit M),
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the vicinity of the South Platte River crossing, and south of the gravel pits. If construction occurs
during the burrowing owl breeding season (March 15 through July 31), heavy equipment
operation and earth moving may cause nest abandonment or mortality from crushing or burial if a
nest is located near the construction ROW.
Impacts to bald eagles may include temporary disturbance during construction activities.
Important bald eagle habitat occurs at Standley Lake, north of conduits M and O, and along the
South Platte River. Bald eagles may occasionally fly over the conduit during foraging or
migrating, but construction would not affect bald eagles occurring near Standley Lake. Heavy
equipment use and earth moving for construction of Conduit O at the South Platte River would
cause temporary and direct impacts to bald eagles from disturbance. Impacts to bald eagles from
construction of Conduit O would be limited to avoidance of the area during construction activity.
Disturbance to ferruginous hawk from construction activity would cause temporary displacement
for the duration of the disturbance.
Since construction would occur within the existing roadway, no black-tailed prairie dog colonies
would be removed; impacts would be limited to temporary disturbance to individuals located
adjacent to the construction activity.
Swift fox may occur in habitats crossed by Conduit O east of the South Platte River; construction
of the conduit may cause individuals to avoid the area for the duration of construction.
Impacts to common garter snake include crushing from heavy equipment and earthmoving where
the snake may be present along roadsides at riparian crossings and wetlands.
Impacts from construction of the Denver Basin Aquifer Facilities would only occur under Alternative 10a
and would be negligible to minor. Habitat for northern leopard frog and common garter snake is present
in the Denver Basin aquifer storage site area. Construction of the AWTP and aquifer distribution
pipelines where they cross Sand Creek, Clear Creek, South Platte River, and Cherry Creek may eliminate
habitat and crush or bury individual northern leopard frog or common garter snake, if present, in the
construction footprint. Construction or operation of the AWTP would not affect bald eagle because the
AWTP would be constructed adjacent to the South Platte River in a highly-industrialized area.
Transfer of agricultural water rights would only occur under Alternative 13a. Some State-listed species,
such as common garter snake and northern leopard frog, would lose potential habitat in ditches, ponds,
and wetlands. Black-tailed prairie dogs are likely to increase, providing more nesting habitat for
burrowing owls and foraging habitat for ferruginous hawks. Impacts would be moderate.
Impacts from changes in flows along the river segments would be the same for all alternatives. Changes
in flows would have no effect or negligible effects to State-listed species.
River otters occur along the Fraser, Colorado, and Blue rivers, but the tributaries of the Fraser
River and the Upper Williams Fork River are not part of their overall range. Flow changes would
have minor or negligible impacts on riparian habitats along these rivers (FEIS Section 5.8),
negligible to beneficial impacts to fish in the Fraser River, and no effect to the fish community in
the Colorado River and Blue River (FEIS Section 5.11). Changes in water levels would not affect
access to dens in winter because flow changes during winter months would be relatively small.
In addition, river otters choose dens opportunistically and often use beaver bank dens, dams, and
lodges, and are highly mobile (Boyle 2006). Based on these considerations, impacts would be
negligible and would not affect distribution or abundance of river otter.
Boreal toads are known to occur along the Upper Williams Fork River and may occur along the
Fraser River and its main tributaries, including Vasquez Creek. They are unlikely to occur along
the Blue River and South Boulder Creek upstream of Gross Reservoir, where habitat is
marginally suitable and there are no known breeding sites. The Project would not directly or
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indirectly affect known breeding sites. Boreal toads breed in ponds, and most commonly in
beaver ponds. The Upper Williams Fork River boreal toad breeding site is located near the
Williams Fork River, but is supported by groundwater and surface flow from a side drainage and
is located several feet higher in elevation than the Williams Fork River. The Jim Creek and
Vasquez Creek breeding sites in the Fraser River Valley also appear to be supported by
groundwater and have no recent breeding records. The McQueary Lake breeding site in the
William Fork River Valley and the Pole Creek breeding site in the Fraser River Valley are located
far upstream on tributaries. The Project is unlikely to adversely affect availability of summer
habitat and hibernacula. Flow changes are expected to have minor or negligible impacts on
riparian habitats. Boreal toads use a wide variety of habitats during the summer and are not
restricted to streamside areas. Large areas of both upland and riparian habitats in the Fraser River
and Williams Fork River valleys are potential summer habitat, and small changes in streamside
riparian habitats are unlikely to adversely affect their population or distribution. The Project
would not involve any construction activity in their habitat and would not cause direct effects or
transmission of disease.
Common shiner may occur in the South Platte River, but there are no recent records of this
species in the portion of the South Platte River in the study area, and it is unlikely to be affected
by flow changes.
American peregrine falcon nests along or near several of the river segments and is likely to forage
along the rivers. Flow changes are unlikely to change the availability of prey or foraging
conditions.
Bald eagle nests, roost sites, and/or foraging areas are located along the Fraser, Colorado, Blue,
North Fork South Platte, and South Platte rivers. Flow changes are expected to have minor or
negligible impacts on riparian habitats and fish populations, and are unlikely to change the
availability of prey or foraging conditions.
Greater sandhill crane (Grus Canadensis tabida) may occur on migration along the North Fork
South Platte River and the South Platte River. Migrants occur on mudflats around reservoirs, in
moist meadows, and in agricultural lands. The Proposed Action would have no effect on these
habitats.
Northern leopard frog has the potential to occur along all of the river segments but is more likely
to occur in ponds and wetlands than in the rivers themselves. Predatory fish in the rivers are
likely to strongly limit use of this habitat. Flow changes in the rivers under the Proposed Action
would affect relatively narrow areas along the river banks and are not expected to affect
availability of pond habitat.
Common garter snakes occur along the lower South Platte River. Flow changes under the
Proposed Action are expected to have a negligible effect on riparian habitat and would be
unlikely to change the availability of prey or foraging conditions.
Iowa darter occurs in Eleven Mile Canyon Reservoir, which is located along the South Platte
River. This reservoir is drawn upon in multi-year droughts, and reservoir operation and contents
under the Proposed Action would be similar to Current Conditions (2006). The Proposed Action
is unlikely to affect this species.
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9.2.3 USFS Species
Several USFS Region 2 sensitive species may be affected by construction of Gross Reservoir, and effects
would be similar across all action alternatives.
Northern goshawk was observed on the west side of the reservoir in 2010. No nests were found, and the
study area likely provides suitable foraging and/or post-fledging habitat, at least on Winiger Ridge.
Disturbance to nesting goshawks would be avoided or minimized by avoidance of construction activity
during the nesting season, or surveys to identify active nests and use of buffer zones and seasonal
restrictions on activity in the vicinity of a goshawk nest. CPW recommends a seasonal restriction on
human activity within 0.5 mile of active nests from March 1 through September 15. Construction
activities could temporarily displace individuals during operation of heavy equipment and removal of
timber, and inundation of the reservoir would result in a loss of foraging habitat. The Proposed Action
would result in the loss of about 473 acres of forested habitat, which may affect the availability of prey.
Displacement during construction and loss of habitat from inundation may have minor to moderate effects
to one pair of northern goshawk, but it not likely to affect regional populations.
Flammulated owl is likely to occur in the Gross Reservoir study area because the study area is within the
known range and includes typical habitat. Tree clearing and other construction activities have the
potential to disturb and displace flammulated owls, although they are reported to be tolerant of human
activity. Tree clearing would be avoided between March 1 and July 31, which generally covers the
nesting period, although some young may fledge in early August. Surveys for flammulated owls would
be conducted prior to tree clearing if clearing is scheduled to occur between May 10 and August 10, and
seasonal buffer zones would be established around nests. Flammulated owls are neotropical migrants that
are on their breeding range in Colorado from about late April/early May through October, and actively
nest in May, June, and July. Clearing and inundation would result in the loss of 473 acres of forest, about
half of which consists of suitable mature ponderosa pine and Douglas-fir forest. The Project would affect
only 1 acre of old growth forest that is preferred by this species. Removal of trees followed by inundation
would have negligible to moderate effects to flammulated owls in and near the construction area, but
would not be likely to affect regional populations.
American three-toed woodpecker and olive-sided flycatcher may occur in forested and riparian areas
around the reservoir. Construction could temporarily displace individuals during operation of heavy
equipment, and inundation of the reservoir would result in a loss of potential habitat. As with other
migratory bird species, impacts to nesting birds would be minimized by avoidance of tree clearing
between March 1 and July 31, which encompasses the breeding season. Pre-construction surveys for
nests of these and other migratory bird species would be conducted if tree clearing were scheduled
between March 1 and July 31. Disturbance and removal of habitat would affect individual woodpeckers
and flycatchers, but would have negligible effects on regional populations.
Other USFS sensitive species at Gross Reservoir are addressed above as State-listed species, including
bald eagle and northern leopard frog. Impacts would be negligible.
USFS sensitive species along the river segments are mostly addressed above as State-listed species,
including river otter and boreal toad. American bittern may occur in marshes along the lower Fraser,
Colorado, and South Platte rivers. Operation of the Project is unlikely to affect marsh habitat, which
typically is associated with impoundments or areas of high groundwater. Impacts to these species would
be negligible.
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9.2.4 CNHP Species
Four species may occur at Gross Reservoir, although their presence has not been documented. Impacts to
dwarf shrew would be similar for all action alternatives and would primarily be loss of habitat and
possible crushing of individuals during construction, if the species is present. Three species of mollusk
(swampy lymphaea, umbilicate sprite, and banded physa) are unlikely to be adversely affected by the
action alternatives because water quality and conditions in Gross Reservoir are not expected to have an
impact on habitat for these species.
Three species of rare butterflies may occur at Leyden Gulch Reservoir, although their presence has not
been documented. Under Alternative 1c, construction of the reservoir would result in loss of suitable
habitat for Moss’s elfin, Cross-line skipper, and Rhesus skipper. Suitable habitat for these species occurs
in areas adjacent to the reservoir site so the Project is not expected to impact the viability of populations
of these species.
Five species may occur at the South Platte River Facilities and along the conduits and could be affected
by alternatives 8a, 10a, and 13a. Operation of the gravel pit storage ponds under alternatives 8a and 13a
would be beneficial to white pelicans and Barrow’s goldeneye through creation of open water habitat.
Snowy egrets and white-faced ibis would also benefit from creation of shoreline habitat at the gravel pits,
though both species would also incur direct and temporary impacts from temporary loss of habitat from
construction of the diversion pipeline south of Worthing Pit. Construction of conduits M and O could
result in temporary displacement of Barrow’s goldeneye, snowy egret, and white-faced ibis from
construction activity for the duration of the disturbance. Arogos skipper may occur near Conduit M
(Alternative 10a) but would not incur any impacts as construction would occur in the existing road ROW.
Several species may occur along portions of the river segments. Changes in water flows are unlikely to
adversely affect habitat, availability of prey, or foraging conditions for American white pelican,
white-faced ibis, Barrow’s goldeneye, snowy egret, or ovenbird (Seiurus).
9.2.5 Big Game
Impacts to big game habitat are summarized in Table 9. All of the action alternatives would affect crucial
elk habitat at Gross Reservoir, including severe winter range, winter concentration areas, and migration
corridors. The amount of habitat affected would vary by alternative and the proposed reservoir size, with
the Proposed Action having the greatest impact and Alternative 1c the least. Severe winter range and
winter concentration areas are separate categories that overlap in some areas and cannot be added together
to derive a total area of elk impact. Elk migration corridors and severe winter range are separate
categories, but all of the construction and operation impacts would occur in both habitats. Impacts to elk
severe winter range and winter concentration areas would be less than 1% across the entire herd unit, a
minor impact. About 7% of the migration corridor would be lost due to the Proposed Action, a moderate
impact. Permanent loss of portions of the migration corridor would likely cause changes in elk migration
patterns, as described below.
Enlargement of Gross Reservoir would also affect non-crucial habitat for mule deer, mountain lion, and
black bear. Mule deer herds inhabiting the Gross Reservoir area are not likely to be adversely effected by
the reservoir enlargement because no crucial seasonal habitats are present, and the affected area
represents a very small part of the habitat available to the data analysis units No. 27 herd. The Proposed
Action would affect about 544 acres of summer range, which would have a minor effect on the mule deer
herd. Impacts to mountain lion and black bear habitat would be minimal because the impacted area
represents only a small portion of the typical home range occupied by individuals of these species. In
addition, mountain lions prey mostly on mule deer and their prey base is not expected to be reduced.
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Table 9
Permanent and Temporary Direct Effects on Terrestrial Wildlife Habitat for Each Alternative
Resource No Action Alternative
Proposed Action
(Alternative 1a) Alternative 1c Alternative 8a Alternative 10a Alternative 13a
P T P T P T P T P T P T
Migratory Birds and General Wildlife
Number of raptor nests potentially affected 0 0 0 0 0 1 0 2 0 0 0 2
Migratory bird and wildlife habitat (acres disturbed) 0 0 465.1 89.3 690.5 281.1 370.4 117.8 382.1 123.2 4320.1 114.4
Total (permanent + temporary acres disturbed) 0 554.4 971.6 488.2 505.3 4,434.5
Big Game Seasonal Ranges (Acres disturbed)
Elk severe winter range and migration corridor 0 0 465.1 89.3 301.5 104.7 363.0 97.9 363 97.9 412.7 93.4
Elk winter concentration area 0 0 369.0 52.1 167.5 62.3 203.2 58.2 293.2 58.2 235.5 55.2
Elk winter range (non-crucial 0 0 0 0 383.0 172.0 0 0 0 0 0 0
Mule deer summer and winter range 0 0 465.1 89.3 684.5 276.7 363.0 97.9 363.0 97.9 412.7 93.4
Mule deer limited use 0 0 0 0 0 0 0 0 0 3.6 0 0
Mule deer resident and migration 0 0 0 0 0 0 1.7 6.1 0 0 1.7 7.2
White-tailed deer winter and concentration area 0 0 0 0 0 0 1.7 6.1 0 0 1.7 7.2
White-tailed deer overall range 0 0 0 0 0 0 0 0 0 1.8 0 0
Turkey winter and production 0 0 0 0 0 0 1.6 3.8 0 0 1.6 3.8
Sensitive Areas
Winiger Gulch PCA 0 0 71.8 0 42.0 0 53.1 0 53.1 0 61.6 0
Rocky Flats PCA 0 0 0 0 0 2.6 0 0 0 0 0 0
South Platte River PCA 0 0 0 0 0 0 5.6 9.6 6.1 9.4 5.1 9.4
Winiger Ridge ECA 0 0 234.4 0 144.2 0 180.6 0 180.6 0 211.8 0
South Platte River Greenway 0 0 0 0 0 0 0.1 1.4 0.3 2.4 0.1 2.4
Source: Corps, 2014.
Notes:
ECA = Environmental Conservation Area
P = permanent
PCA = Potential Conservation Area
T = temporary
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Year-round construction activities at the dam and nearby areas would displace big game from the eastern
side of the reservoir. Operation of the quarry would contribute to displacement although Denver Water
would use confined charge blasting to reduce noise. The distance that animals move to avoid human
disturbance is dependent on the species and/or individual, topography, vegetation cover, and intensity of
the disturbance. The amount of displacement is difficult to estimate, but is likely to be 0.25 to 0.50 mile
or more, involving hundreds of acres adjacent to the construction areas on the east side of the reservoir
and areas along the western shore facing the dam and quarry. Displacement is not likely to affect use of
most of the Winiger Ridge area. Construction would occur year-round, including the winter when the
area would normally be used as elk winter range, concentration area, and severe winter range. This
displacement would occur each winter during the construction period for four years. During operation,
big game is unlikely to exhibit any changes in behavior from Current Conditions (2006).
The only construction activities on the western, northern, and southern sides of the reservoir would be
clearing and disposal of woody vegetation from the new reservoir footprint. This activity would also
displace big game, but would occur mostly during the summer and fall. Clearing and disposal of trees is
expected to take 6 to 8 months and is unlikely to affect wintering elk. Activities in the dam area are
unlikely to cause displacement of big game from the west side of the reservoir because of the distance
from construction disturbance.
Gross Reservoir is near the eastern end of a migration corridor that extends from elk summer
concentration areas west of Nederland to winter concentration areas around and north of the reservoir.
About 7.0% of the migration corridor would be lost due to the Proposed Action, of which about 1.1%
would be temporary impact. Permanent loss of portions of the migration corridor would likely cause
changes in elk migration patterns, and would be a moderate impact. The migration corridor extends
around the reservoir, including the north and south shores. Construction activities on the east side of the
reservoir could affect movement of elk near the reservoir and displace them to adjacent areas, but
movement on the west side of the reservoir and most of the corridor is unlikely to be affected. During
operation, the expanded reservoir would back up water in South Boulder Creek and other tributaries and
would create greater obstacles for movement. Under the Proposed Action, approximately 2,495 feet of
South Boulder Creek and approximately 2,160 feet of Winiger Gulch would be inundated. Inundation of
these streams is likely to result in changes in movement for elk and deer. Inundation of South Boulder
Creek above the reservoir could affect movement of elk and deer near Pinecliffe, because the canyon
between the enlarged reservoir and Pinecliffe is narrow and steep and may be difficult to cross. The new
reservoir arms would be relatively narrow and big game may continue to cross them, especially in the
spring when the reservoir would be at a lower elevation. Loss of habitat and potential change of use
patterns may force elk and deer to adjacent private lands, which could increase the CPW obligations for
game damage compensation. Management of nuisance wildlife issues and public safety is a CPW
priority. Hunting is a primary tool for managing herd size, but closure of areas in Boulder County near
Gross Reservoir to hunting makes it more difficult to achieve adequate harvest of big game.
Other short-term, direct impacts to big game would occur from potential collisions with haul trucks and
other vehicles along access routes including CR 77 South, and SHs 72, 93, and 128 due to the increase in
traffic from construction. The increase in traffic on CR 77 South may result in an increase in collisions
with big game and other wildlife, but is not likely to adversely affect local populations. Portions of
SHs 72 and 93 that are potential haul routes for construction of the Gross Reservoir expansion are
frequently crossed by mule deer. These areas are used year-round by mule deer. Although they are a
safety concern, collisions would have a negligible effect on big game populations.
At Leyden Gulch Reservoir (Alternative 1c), construction of the reservoir would permanently remove
approximately 383 acres of habitat for the dam and reservoir, and would temporarily affect 172 acres of
big game habitat. Mule deer occur in the Leyden Gulch study area during both summer and winter, while
elk are present during winter. Wintering elk and deer would experience more stress from habitat loss,
because resources are more limited. However, creation of Leyden Gulch Reservoir would not measurably
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affect big game populations as no critical habitats would be affected. After reservoir construction and
filling, the 31,300-AF reservoir would prevent these animals from directly moving east-west, although
this area is not considered an important migratory corridor. Animals would be required to travel around
the reservoir. In addition, the reservoir may be hazardous to big game that try to cross thin ice or try to
cross over the ice when predators such as coyotes or mountain lions are present. Black bear primarily use
the Ralston Creek corridor. Black bear would be temporarily displaced from this area during construction
activity and would likely return to the area post construction. Mountain lions would likely avoid the area
during construction. Conflicts between humans and these animals would likely increase during
operations due to the increased human presence in the area for reservoir operation and maintenance.
The Platte River Facilities and conduits M and O would affect relatively small areas of mule deer limited
use, resident and migration habitat; white-tailed deer winter, concentration, and overall habitat; and turkey
production habitat.
9.2.6 Other Wildlife
Direct impacts to small- and medium-sized mammals include habitat loss and mortality from
ground-disturbing construction activity. Small-bodied animals in the immediate area of construction
activity would likely be killed by crushing or burial during construction. More mobile species, including
medium-sized animals, could avoid the construction zones but would be temporarily displaced by
construction. Temporary displacement could result in increased mortality from vehicle collisions and
increased resource competition.
At Gross Reservoir, the increased water level up the fingers at Winiger Gulch and South Boulder Creek
would create a barrier to movement for these species, especially smaller-sized mammals that would have
to travel long distances to move around the water. The indirect impacts of the enlarged reservoir to small-
and medium-sized mammals would be fragmentation of habitat. Numerous bats inhabit the mixed conifer
and ponderosa pine woodlands in the Gross Reservoir study area. The primary impacts to these species
would be loss of roosting trees around the perimeter of the reservoir and disturbance to roosting bats
during construction and vegetation-clearing activities. The enlarged reservoir would create additional
open water foraging habitat for some bat species.
9.2.7 Raptors and Other Migratory Birds
The alternatives would have limited effects to known raptor nests. An osprey nesting platform is present
at Gross Reservoir. It has never been used for nesting and is unlikely to be affected by any of the
alternatives. Raptor nests occur at Leyden Gulch Reservoir and along Conduit O. They are not in the
area of direct effect but nesting raptors could be affected by construction activities if construction
occurred during the nesting season. A summary of raptor nests by alternative is provided in Table 9.
Construction activities at Gross Reservoir Dam and other facility construction would occur primarily
between May and September, which would likely result in impacts to migratory birds. In Denver Water’s
Moffat Collection System Project Fish and Wildlife Mitigation Plan, which has been approved by the
Colorado Wildlife Commission, Denver Water has committed to the use of pre-construction surveys to
identify active nests in the Project footprint and timing of activities to avoid the breeding season. A
summary of acres of habitat affected is provided in Table 9.
Under all action alternatives, operation of the enlarged Gross Reservoir would benefit waterfowl due to
the increased surface area of the reservoir. Under the Proposed Action, the reservoir expansion would
provide an additional 400 acres of open water habitat, depending on water level. Shorebirds, such as
spotted sandpiper (Actitis macularia), may utilize the shoreline for foraging. Nesting habitat along the
shoreline for waterfowl and other birds would be limited due to the fluctuating water levels.
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Under Alternative 1c, operation of Leyden Gulch Reservoir would be beneficial to waterfowl, shorebirds,
and other water birds. The reservoir would provide an average of 332 acres of open water habitat,
depending on water level. For waterfowl, the reservoir would provide resting and loafing areas and
potential foraging habitat. Although the reservoir would not be stocked with fish, some rainbow trout,
brown trout, and other species may enter the reservoir through the South Boulder Diversion Canal. These
fish would provide a food source for piscivorous birds such as cormorants and herons (Ardeidae).
Herbaceous vegetation is likely to become established along the shoreline since water elevations would
generally remain stable during summer months. Over the long term, cottonwood, willow, and herbaceous
wetland vegetation may become established in some areas around the reservoir. Therefore, nesting
habitat for waterfowl would develop along the shoreline in wetland vegetation. The shoreline would also
be used by shorebirds, primarily those in migration.
Under alternatives 8a and 10a, operation of the gravel pit reservoirs would provide a beneficial impact to
migratory birds and wildlife because open water habitat would be created for waterfowl, shorebirds, and
migratory birds, as well as for amphibians and reptiles. Areas that become vegetated along the shoreline
may provide nesting habitat for mallards (Anas platyrhynchos), geese (Anserini), and red-winged
blackbirds (Agelaius phoeniceus).
Implementation of Alternative 13a is expected to result in the loss of about 8 acres of surface waters from
the transfer of agricultural water rights and cessation of irrigation. Species adapted to aquatic habitat and
riparian environments are likely to decrease, such as red-winged blackbird, raccoon, ring-necked pheasant
(Phasianus colchicus), waterfowl, garter snakes, turtles (Testudines), and frogs.
Changes in stream flows along the river segments could potentially affect food availability or cover for
riparian wildlife species. Changes in habitat quality are likely to be small and patchy and relatively subtle
in most places. These changes are not likely to affect overall distribution or populations of bird, mammal,
reptile, and amphibian species.
9.2.8 USFS Management Indicator Species and Wildlife Habitats
Construction and operation of Gross Reservoir would have negligible to moderate impacts to USFS MIS.
Impacts to elk would be moderate and impacts to deer would be minor. Impacts to pygmy nuthatch, hairy
woodpecker, and mountain bluebird reduce the local populations and would be moderate locally but
would have a minor effect on regional populations. Impacts to golden-crowned kinglet (Regulus
satrapa), warbling vireo, and Wilson’s warbler would be negligible. There would be no impacts to
Rocky Mountain bighorn sheep (Ovis canadensis) or boreal toad in the Gross Reservoir area.
Two USFS MIS occur along the Fraser River and Williams Fork River and their tributaries, Wilson’s
warbler and boreal toad. Boreal toad is a special status species that would have negligible effects from
the action alternatives. The action alternatives would have negligible to minor impacts to riparian
vegetation along the Fraser River and Williams Fork River, and their tributaries. These changes may
affect Wilson’s warbler locally, but are not likely to result in adverse effects to overall distribution or
population.
Impacts to USFS wildlife habitats at Gross Reservoir are summarized in FEIS Table 5.9-3. In forested
habitats (forested corridors, interior forest, inventoried, and developing old growth), both permanent and
temporary impacts would result in the removal of habitat and would be considered a long-term impact.
Project impacts would affect the local availability of several types of habitat but would have a minor
effect over a larger area. Impacts would be proportional to the area of reservoir expansion and would be
greatest under the Proposed Action and least under Alternative 1c.
128
9.2.9 Sensitive Areas
All of the action alternatives would affect PCAs identified by CNHP and ECAs identified by Boulder
County. These areas would be directly impacted by vegetation removal and inundation around the
perimeter of the reservoir. These sites are those considered important for protection by CNHP and
Boulder County. Under the Proposed Action, direct impacts to the Winiger Gulch PCA include
inundation of 71.8 acres (3.8% of the total PCA) and the Winiger Ridge ECA would lose 243.4 acres
(7%) to inundation. Impacts of the other alternatives would be less, as shown in Table 9.
For Alternative 1c, The CNHP-designated Rocky Flats PCA overlaps the northern portion of the Leyden
Gulch study area. A 2.5-acre (less than 1%) portion of the PCA would be temporarily impacted for a
41-acre construction staging and spoil area located north of the reservoir. This area would be used to
store the excavated material from the reservoir pool area prior to the dam construction, and earth-moving
equipment would enter and exit the area. The staging area would be restored to its approximate existing
condition before construction following the completion of the reservoir. This would primarily impact
habitat for migratory birds until revegetation is completed.
Under alternatives 8a and 13a, most of the South Platte River Facilities would be located in the South
Platte River PCA, and the diversion dam and outlet structure would be located in the South Platte River
Greenway. Construction would involve both temporary and permanent impacts within these areas.
Because much of the habitat is already disturbed and the South Platte River Facilities would occupy only
a small part of the PCA and Greenway, construction of these facilities would not adversely affect the
viability of the PCA or South Platte River Greenway. The crossing of Conduit O over the South Platte
River would be located in both the South Platte River PCA and South Platte River Greenway. A small
area of habitat would be temporarily affected during construction. Because of the small area and
temporary impacts, construction of the crossing would not adversely affect these areas.
Under Alternative 10a, the crossing of Conduit M over the South Platte River would be located in both
the South Platte River PCA and South Platte River Greenway, and one of the pump stations would be
located in the PCA. A small area of habitat would be temporarily affected during construction. Because
much of the habitat is already disturbed and these facilities would occupy only a small part of the PCA
and South Platte River Greenway, construction of these facilities would not adversely affect the viability
of the PCA or South Platte River Greenway.
9.3 Vegetation Resource Effects
9.3.1 Federally-Listed Threatened and Endangered Species
All of the action alternatives are unlikely to adversely affect Federally-listed plant species, including Ute
ladies-tresses orchid and Colorado butterfly plant. Construction and operation would have no effects for
Gross Reservoir (all alternatives), Denver Basin Aquifer Facilities (Alternative 10a), and agricultural
water transfer (Alternative 13a); and are unlikely to have adverse effects at Leyden Gulch Reservoir
(Alternative 1c), conduits O and M (alternative 8a, 10a, and 13a), and South Platte River Facilities
(alternatives 8a and 13a). Surveys would be conducted at Leyden Gulch Reservoir, Clear Creek, and
other areas of suitable habitat outside the Block Clearance Zone prior to construction to determine the
presence or absence of these plants, and to avoid impacts if present if an alternative with these areas is
selected. Flow changes are unlikely to adversely affect Ute ladies’-tresses orchid populations
downstream of the South Boulder Diversion Canal diversion point on South Boulder Creek.
129
9.3.2 USFS and CNHP Species
None of the action alternatives would directly affect USFS Region 2 sensitive species, but all of the
alternatives would directly affect ARNF plant species of local concern at Gross Reservoir. Table 10
presents a summary of the permanent and temporary direct effects on ARNF plant species of local
concern. In addition to the species shown in Table 10, all of the alternatives would also directly affect
false melic and five species of ferns, but numbers of individual affects are not known. In Table 10,
individual plants in the inundation area are considered to be permanently affected, while those in the tree-
clearing area are shown as temporary impacts. Because of differences in the footprint of Gross Reservoir,
the Proposed Action would have the greatest impacts and Alternative 1c would have the least. Impacts
would be similar across all action alternatives for wild sarsaparilla, Enchantress’s nightshade, and tall
blue lettuce.
Table 10
Permanent and Temporary Direct Effects on Plant Species and Plant Communities
of Concern for Each Alternative
Resource
No Action
Alternative
Proposed
Action
(Alternative
1a)
Alternative
1c
Alternative
8a
Alternative
10a
Alternative
13a
P T P T P T P T P T P T
ARNF Plant Species of Local Concern (number of individuals affected)
Wild sarsaparilla 0 0 4,122 20 3,937 55 3,992 0 3,922 0 4,022 100
Dewey sedge 0 0 156 30 46 0 59 7 59 7 81 46
Sprengel’s sedge 0 0 593 31 37 21 457 81 457 81 652 66
Enchantress’s
nightshade 0 0 706 0 700 0 700 0 700 0 700 0
Tall blue lettuce 0 0 115 0 115 0 115 0 115 0 115 0
Maryland sanicle 0 0 17 0 0 0 7 0 7 0 7 0
Plant Communities of Concern (acres affected)
River birch/mesic
forb and thinleaf
alder/mesic forb
0 0 4.9 0 3.8 0 4.3 0 4.3 0 4.6 0
Existing old growth 0 0 1.2 0 0.1 0 0.5 0 0.5 0 0.8 0
Source: Corps, 2014.
Notes:
ARNF = Arapaho & Roosevelt National Forests
P = permanent
T = temporary
Flow changes along the river segments would have negligible or no effect to populations of USFS
Region 2 sensitive species, ARNF plant species of local concern, and CNHP species:
Three USFS Region 2 sensitive species (lesser panicled sedge, dwarf raspberry, and autumn
willow) and three ARNF plant species of local concern (least moonwort, mud sedge, and
sphagnum) are species that primarily occur in fens and peatlands in montane and subalpine areas,
and may occur along the river segments in the Fraser River and Williams Fork River valleys.
Changes in stream flows resulting from the Proposed Action would have no or negligible impacts
to habitats of these plants, which are primarily supported by groundwater.
Buckbean (ARNF species of local concern) and lesser bladderwort (USFS Region 2 sensitive
species) occur in montane and subalpine ponds. Changes in stream flows under the Proposed
Action are expected to have no impacts to ponds.
130
Park milkvetch (CNHP) may occur in sedge meadows and grassy stream banks along montane
portions of the North Fork South Platte River and South Platte River. Operation of the Proposed
Action is expected to have negligible effects on riparian habitats along these rivers, and impacts
to this species, if present, would also be negligible.
American current (CNHP) occurs in lowland riparian areas along the South Platte River.
Operation of the Proposed Action is expected to have negligible effects on riparian habitats along
the South Platte River, and impacts to this species, if present, would also be negligible.
Rocky Mountain bulrush (CNHP) may occur in ponds along the South Platte River. Changes in
stream flows under the Proposed Action are expected to have no impacts to ponds.
9.3.3 Vegetation Cover Types
Table 11 presents a summary of the temporary and permanent effects on vegetation cover types.
Alternative 13a would have the largest permanent impacts because of conversion of agricultural land.
Alternatives 8a and 10a would have the smallest permanent impacts. Most of the impacts at Gross
Reservoir would occur in the new inundation area (between 7,282 and 7,406 feet) and would occur from
site preparation. All trees and wood would be removed from the inundation area and from the shoreline
at an elevation of 7,410 feet. Various methods may be used to remove the trees, as described in FEIS
Section 2.3.2.1. Trees and associated slash and debris would be removed for sale or disposal, and the area
would be cleared prior to inundation. A portion of the cleared area would also be used for borrow
material. Post-construction restoration of the cleared area above the inundation line would include
re-vegetating with a mix of native grass, forb, and shrub species. At Leyden Gulch Reservoir, permanent
impacts would mostly result from the construction of the dam and clearing of the reservoir area, and
temporary impacts would mostly be caused by construction of the dam and inlet/outlet works, and use of
staging and spoil areas. Because the affected vegetation types are common in the region, losses of
vegetation at the two reservoir sites are considered a moderate impact.
Impacts from the South Platte River Facilities, conduits M and O, and the Denver Basin Aquifer Facilities
would affect much smaller areas than the reservoirs, and are considered to be minor. Transfer of
agricultural water rights (Alternative 13A) would have a large area (3,900 acres), but most of the land is
expected to remain in agricultural use.
Changes in stream flows associated with the action alternatives may cause indirect changes to riparian
vegetation along the river segments. The area covered by 2-year flows would decrease in the Fraser River
and its tributaries, Colorado River, Blue River, and South Boulder Creek below Gross Reservoir; and
would increase in South Boulder Creek above Gross Reservoir and North Fork South Platte River.
Decreases in the 2-year flow could result in a gradual narrowing of the stream banks, which would
decrease flows that would support wetlands within the banks. However, sediment deposition may be
temporary and may be removed by longer-term floods. Impacts would be confined to a wetland fringe
where it currently exists along the edge of the channel. Herbaceous wetland vegetation affected by less
frequent or prolonged flooding would likely change in composition and become more mesic. Changes
would be minor along the Fraser River, St. Louis Creek, Blue River, and South Boulder Creek below
Gross Reservoir, and negligible at other sites. The action alternatives would have no or negligible
impacts to fens in the Fraser River and Williams Fork River valleys.
9.3.4 Plant Communities of Concern
The increased inundation area would affect two globally-rare plant communities that are tracked by the
CNHP and are ARNF plant communities of local concern: river birch/mesic forb foothills riparian shrub
and thinleaf alder/mesic forb riparian shrubland. Impacts to these two communities are considered
moderate because they would cause a local loss of biodiversity but would not substantially affect their
overall distribution or abundance. Increased inundation would also affect small areas of old growth
131
ponderosa pine mapped by ARNF, which is also an ARNF plant community of local concern. Impacts of
the Gross Reservoir expansion would cause a loss of about 0.1% of old growth ponderosa pine on the
ARNF, a minor impact.
9.3.5 Noxious Weeds
All action alternatives would have a similar likelihood of spreading noxious weeds because construction
activities are likely to spread noxious weeds. Weed control, during and after construction, would
minimize the spread of noxious weeds.
132
Table 11
Acres of Permanent and Temporary Direct Effects on Vegetation Cover Types for Each Alternative
Resource No Action Alternative
Proposed Action
(Alternative 1a) Alternative 1c Alternative 8a Alternative 10a Alternative 13a
P T P T P T P T P T P T
Grasslands
Disturbed rangeland 0 0 21.4 0 24.9 0 16.8 5.7 21.3 7.2 20.3 5.7
Grass/forb rangeland 0 0 11.5 2.1 370 145.6 9.4 6.5 8.6 3.8 10.8 7.5
Emergent wetlands 0 0 0.9 0.1 7.0 14.8 0.9 0.2 0.9 0.2 77.9 0.2
Subtotal 0 0 33.8 2.2 401.9 160.4 27.1 12.4 30.8 11.2 109 13.4
Shrublands
Snowberry/shrub mix 0 0 0 0 2.1 4.6 0 0 0 0 0 0
Riparian shrub 0 0 4.4 0 3.4 0 3.8 0 3.8 0.5 4.2 0.1
Subtotal 0 0 4.4 0 5.5 4.6 3.8 0 3.8 0.5 4.2 0.1
Woodlands
Ponderosa pine woodland/forest 0 0 167.9 7.4 108.1 10.8 132.1 8.6 132.1 8.6 148.9 7.9
Ponderosa pine/Douglas-fir 0 0 249 42.4 159.5 54.1 191.7 49.7 191.7 49.7 219.3 45.9
Riparian woodland 0 0 0.7 0 0.6 8.7 0.7 0 0.7 0 0.7 0
Subtotal 0 0 417.6 49.8 268.2 73.6 324.5 58.3 324.5 58.3 368.9 53.8
Other Types
Agricultural lands 0 0 0 0 0 0 0 0 0 0 3816 0
Residential 0 0 0 0 0.1 0.3 0 0 9.8 8.8 0 0
Disturbed areas 0 0 8.9 3.6 14.3 7.2 14.6 13.4 12.8 10.7 14.6 13.4
Waterbodies 0 0 0 33.7 0.1 35 0 33.7 0 33.7 7 33.7
Talus slope/rock outcrop 0 0 0.4 0 0.4 0 0.4 0 0.4 0 0.4 0
Subtotal 0 0 9.3 37.3 14.9 42.5 15 47.1 23 53.2 3838 47.1
Total 0 0 465.1 89.3 690.5 281.1 370.4 117.8 382.1 123.2 4320.1 114.4
Source: Corps, 2014.
Notes:
P = permanent
T = temporary
133
9.4 Cumulative Effects Analysis
The cumulative effects analysis (referred to as the total effects analysis in the Moffat FEIS; see Chapter 4
of the FEIS) for this Project evaluated past and present water- and land-based actions that continue to
influence existing environmental conditions. The cumulative effects analysis also included reasonably
foreseeable water-based or land-based actions that, when combined with one of the action alternatives,
may result in a cumulative effect on the environment.
Cumulative effects analyses were conducted for past, present, and reasonably foreseeable future
land-based and water-based actions. Geographically, cumulative effects resulting from water-based
actions are likely to occur on both the East and West slopes, thus, cumulative effects were evaluated
within the local operational and socio-political boundaries of these activities. The effects of land-based
actions are limited to the Front Range (East Slope) since no Project-related ground-disturbing activities
would occur on the West Slope. Land-based actions were identified by reviewing various city and county
comprehensive plans, recreation management plans, proposed transportation improvement project plans,
regional population statistics, and land parcel database searches.
Future Water-Based Actions
Several water-based actions on the East and West slopes were considered in the evaluation of cumulative
hydrologic effects:
East Slope
Seaman Water Supply Project
Halligan Water Supply Project
Northern Integrated Supply Project
Denver Water Reuse Project
Aurora Prairie Waters Project
Rueter-Hess Reservoir Project
Dry Creek Reservoir Project
Chatfield Reservoir Reallocation Project
Augmentation of lower South Platte Wells Project
East Cherry Creek Valley Project
Cache la Poudre Flood Reduction/Ecosystem Restoration Project
Water Infrastructure and Supply Efficiency Project
West Slope
Windy Gap Firming Project
Urban Growth in Grand and Summit Counties
Reduction of Xcel Energy’s Shoshone Power Plant Call
Changes in Releases from Williams Fork and Wolford Mountain Reservoirs to Meet Service
Flow Recommendations for Endangered Fish in the 15-Mile Reach
Wolford Mountain Reservoir Contract Demand
Expiration of Denver Water’s Contract with Big Lake Ditch in 2013
Colorado Springs Utilities’ Substitution and Power Interference Agreements at Green Mountain
Reservoir
10,825 Water Supply Alternatives
134
Colorado River Cooperative Agreement (CRCA)
Fish and Wildlife Enhancement Plan
Water-based actions refer to proposed water storage and diversion, water rights changes, and Section 404
activities on Colorado’s East and West slopes.
Future Land-Based Actions
Future land-based actions considered for the cumulative effects analysis included construction of
residential, commercial, and industrial structures; construction and expansion of city, county, State, and
Federal roads and highways; and gravel mining.
9.4.1 Aquatic Resources
The enlargement of Gross Reservoir and the construction of Leyden Gulch Reservoir would provide
additional fish habitat creating a beneficial cumulative impact. None to negligible cumulative impacts to
fish, benthic invertebrates, and their habitats are anticipated to occur for most East Slope stream
segments. Exceptions include minor adverse impacts to fish and invertebrates in South Boulder Creek
upstream of Gross Reservoir from increased flows, and moderate adverse impacts in the North Fork South
Platte River which could have increased flows and increased concentrations of copper. An increase in
winter flows in South Boulder Creek below Gross Reservoir and more favorable winter flows in the
South Platte River would have a beneficial cumulative impact to fish and invertebrates. Reductions in
high flows in the upper sections of the Fraser River upstream of St. Louis Creek would have a cumulative
adverse impact to fish and invertebrates. There would be cumulative adverse impacts to fish and
invertebrates in most of the tributaries of the Fraser River and Williams Fork River due to increased
diversions. There would be negligible cumulative impacts to fish and invertebrates in the mainstem of the
Williams Fork River and Colorado River and much of the Blue River. There would be an adverse
cumulative impact in the upper section of the Blue River. The effects of the reduction in the Shoshone
Call would tend to occur 1 out of every 6 or 7 years, usually in dry years, and usually in the spring. The
exact consequences to cumulative hydrology are difficult to predict. However, slight, infrequent
reductions in flows during the spring, when there is usually sufficient water to sustain fish and
invertebrates, would likely have no additional cumulative effect on aquatic resources as a result of the
Project.
9.4.2 Wildlife Resources
Cumulative impacts to wildlife in the Gross Reservoir area would result almost entirely from expansion
of Gross Reservoir, and there are no other RFFAs that would result in more than minor permanent loss of
habitat at Gross Reservoir. There would also be moderate cumulative effects to wildlife in the Front
Range/Weld County area from the loss of aquatic and mesic habitats associated with the transfer of
agricultural water rights under Alternative 13a. Minor cumulative effects to wildlife may occur in other
portions of the study area.
Construction activities at Gross Reservoir would not have adverse effects to Federally-listed species and
therefore would not contribute to cumulative effects resulting from past actions. Construction at Gross
Reservoir may affect individuals or habitat of USFS sensitive wildlife species including northern
goshawk and flammulated owl, but the Proposed Action would not cause a trend to Federal listing or loss
of viability rangewide. Various projects and activities may affect habitat for Colorado River endangered
fish species, including Full Use of the Existing System with RFFAs. These additional depletions have
either already been addressed by previous Section 7 consultations. All projects involving depletions to
habitats for Federally-listed species along the Platte River in Nebraska will need to comply with the
provisions of the PRRIP, which addresses cumulative impacts. Increased diversions in tributaries from
135
Little Vasquez and Hamilton creeks in the Fraser River Basin and from Bobtail and Steelman creeks in
the Williams Fork River Basin would adversely affect greenback cutthroat trout through increased
entrainment. Continued human population growth and development may result in cumulative effects to
other endangered species including Preble’s meadow jumping mouse and Ute ladies’-tresses orchid, but
protective policies are in place for these species and their habitats.
9.4.3 Vegetation Resources
Other than the expansion of Gross Reservoir, there is expected to be a limited amount of loss or
modification of vegetation in the Gross Reservoir area, and the area is expected to continue to be mostly
natural vegetation. The Leyden Gulch Reservoir site is within the expected growth corridor of the
northwest Denver Metropolitan area, and most of the cumulative impacts would be the result of
vegetation losses in future development footprints. The area around the South Platte River Facilities has
already been developed and disturbed and is expected to remain in this condition. Agricultural water
rights transfers, along with other ongoing development activities, would result in the conversion of
irrigated cropland to fallow fields or impermeable surfaces.
Impacts to riparian and wetland resources in the Gross Reservoir area would be the same as those
described for the action alternatives, because no other major development actions are planned. For the
river segments, most of the total environmental effects in the Fraser Valley and on South Boulder Creek
would be caused by the active alternatives, while most of the cumulative changes to flows in the Colorado
River and Blue River would occur from other actions including Full Use of the Existing System with
RFFAs and local growth in water use. Full use of the Existing System with RFFAs would also contribute
to cumulative effects for the Fraser River and its tributaries.
Cumulative effects to riparian and wetland areas are expected to be minor in the other geographic areas
affected by Moffat Project alternatives, except for the Front Range/Weld County area where past, present,
and future agricultural water right transfers would cause moderate to major cumulative effects.
Construction activities at Gross Reservoir would not have adverse effects to Federally-listed species and
therefore would not contribute to cumulative effects resulting from past actions. Construction would
destroy a large portion of local populations of several ARNF plant species of local concern at Gross
Reservoir and may affect their long-term viability on the ARNF, but are unlikely to affect overall
occurrence in Colorado. Continued human population growth and development may result in cumulative
effects to endangered species including Ute ladies’-tresses orchid, but protective policies are in place that
for these species and their habitats.
9.5 Evaluation and Comparison of the Alternatives
Table 12 summarizes and compares the direct and indirect effects to fish and wildlife resources for each
of the alternatives.
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Table 12
Summary of Direct and Indirect Effects to Fish and Wildlife Resources
Type of Impact and Facility No Action Alternative Effects of Action Alternatives Compared to Current Conditions
Proposed Action (Alternative 1a) Alternative 1c Alternative 8a Alternative 10a Alternative 13a
Aquatic Resources
Temporary construction impacts to fish
and invertebrates from dam and pipeline
construction:
1) Gross Reservoir
2) Leyden Gulch Reservoir
3) South Platte River Facilities
4) Conduit O
5) Denver Basin Aquifer Facilities
6) Conduit M
7) Agricultural Water Transfer
1) NA
2) NA
3) NA
4) NA
5) NA
6) NA
7) NA
1) Disruption of normal reservoir
operations would have a negligible
impact on fish and invertebrates in
Gross Reservoir
2) NA
3) NA
4) NA
5) NA
6) NA
7) NA
1) Similar but smaller impacts than
the Proposed Action
2) No impact – no existing
reservoir
3) NA
4) NA
5) NA
6) NA
7) NA
1) Similar but smaller impacts
than the Proposed Action
2) NA
3) Diversion construction would
have a minor adverse impact
on aquatic resources of the
South Platte River
4) Pipeline construction would
have a minor adverse impact
at stream crossings
5) NA
6) NA
7) NA
1) Similar but smaller impacts
than the Proposed Action
2) NA
3) NA
4) NA
5) Pipeline construction would
have a minor adverse
impact at stream crossings
6) Same as Alternative 8a,
Conduit O
7) NA
1) Similar but smaller impacts
than the Proposed Action
2) NA
3) Diversion and gravel pit
pipeline construction would
have a minor adverse
impact on aquatic resources
in the South Platte River
4) Same as Alternative 8a
5) NA
6) NA
7) No impact - no dam or
pipeline construction
Permanent impacts from reservoir
enlargement/creation:
1) Gross Reservoir
2) Leyden Gulch Reservoir
3) Gravel Pit Reservoirs
1) NA
2) NA
3) NA
1) Additional reservoir habitat would
provide moderate beneficial impact to
fish and invertebrates
2) NA
3) NA
1) Similar to Proposed Action but
smaller beneficial impacts
2) New reservoir habitat (331
acres) would be a minor
beneficial impact; inundation of
a small spring pool would be a
minor adverse impact
3) NA
1) Similar to Proposed Action
but smaller beneficial impacts
2) NA
3) Additional 5,000-AF
reservoir would be a
moderate beneficial impact
1) Similar to Proposed Action
but smaller beneficial
impacts
2) NA
3) NA
1) Similar to Proposed Action
but smaller beneficial
impacts
2) NA
3) Additional 3,625-AF
reservoir would be
beneficial to fish and
invertebrates
Impacts to fish and macro- invertebrates
from changes in river flows:
1) Fraser River
2) Williams Fork River
3) Colorado River
4) Blue River
5) South Boulder Creek
6) North Fork South Platte River
7) South Platte River
1) Negligible adverse effects in the Fraser
River and most tributaries; minor in
Jim and Little Vasquez creeks;
additional adverse impacts could occur
under certain conditions when bypass
flows are not met
2) Negligible impacts in Williams Fork
River but minor impacts in tributaries
3) Negligible impacts
4) Negligible impacts
5) Negligible impacts
6) Minor adverse impacts
7) Negligible impacts upstream of
Chatfield Reservoir, minor beneficial
impacts between Chatfield Reservoir
and Bear Creek
1) Adverse to beneficial impacts in the
different segments of the Fraser River;
minor adverse effects in most tributary
streams; negligible impacts in lower St.
Louis Creek and Englewood Ranch
Gravity System
2) Negligible impacts in Williams Fork,
minor impacts in McQueary, Jones,
Bobtail and Steelman creeks
3) Negligible impacts
4) Negligible impacts
5) Minor adverse impacts upstream of
Gross Reservoir, minor beneficial
impacts below it
6) Minor adverse impacts
7) Negligible impacts upstream of
Chatfield Reservoir; minor beneficial
impacts between Chatfield Reservoir
and Bear Creek
Same as Proposed Action Same as Proposed Action
Same as Proposed Action
Same as Proposed Action
138
Table 12
Summary of Direct and Indirect Effects to Fish and Wildlife Resources
Type of Impact and Facility No Action Alternative Effects of Action Alternatives Compared to Current Conditions
Proposed Action (Alternative 1a) Alternative 1c Alternative 8a Alternative 10a Alternative 13a
Wildlife
Impacts to Federally-listed species from
construction and reservoir filling:
1) Gross Reservoir
2) Leyden Gulch Reservoir
3) Other Facilities
NA 1) Not likely to adversely affect greenback
cutthroat trout
2) Not likely to adversely affect Preble’s
meadow jumping mouse or Ute ladies’-
tresses orchid
3) Not likely to affect listed species
1) Same as Proposed Action
2) NA
3) Not likely to affect listed
species
1) Same as Proposed Action
2) NA
3) Not likely to affect listed
species
1) Same as Proposed Action
2) NA
3) Not likely to affect listed
species
1) Same as Proposed Actions
2) NA
3) Not likely to affect listed
species
Impacts to Federally-listed species from
increased diversions and flow changes:
1) West Slope – Fraser, Williams Fork,
Colorado, and Blue rivers
2) East Slope – South Boulder Creek,
North Fork South Platte River, and
South Platte River
1) Flow reductions in Colorado River
system are covered in existing
Recovery Agreement for the Upper
Colorado River Recovery Program
2) Flow changes in Platte River system
covered under existing SPWRAP; not
likely to adversely affect Preble’s
meadow jumping mouse and Ute
ladies’-tresses orchid
1) Likely to adversely affect endangered
Colorado River system fish; likely to
adversely affect greenback cutthroat
trout
2) Likely to adversely affect Platte River
system threatened and endangered
species in Nebraska; not likely to
adversely affect Preble’s meadow
jumping mouse and Ute ladies’-tresses
orchid
Same as Proposed Action Same as Proposed Action Same as Proposed Action Same as Proposed Action
Impacts to State-listed and special
concern species:
1) Gross Reservoir
2) Leyden Gulch Reservoir
3) Other Facilities
4) River Segments
1) NA
2) NA
3) NA
4) No to negligible impacts
1) Negligible to minor impacts to bald
eagle, American peregrine falcon,
Townsend’s big-eared bat, and northern
leopard frog
2) NA
3) NA
4) No to negligible impacts to river otter,
boreal toad, common shiner, and other
species
1) Same as Proposed Action
2) Minor impacts to northern
leopard frog, black-tailed prairie
dog, and possibly burrowing
owls
3) NA
4) Same as Proposed Action
1) Same as Proposed Action
2) NA
3) Negligible to minor impacts
to burrowing owls, bald
eagles, and other species
4) Same as Proposed Action
1) Same as Proposed Action
2) NA
3) Same as Alternative 8a
4) Same as Proposed Action
1) Same as Proposed Action
2) NA
3) Same as Alternative 8a
4) Same as Proposed Action
Impacts to USFS Region 2 Sensitive
Wildlife Species:
1) Gross Reservoir
2) Other Facilities
3) River Segments
1) NA
2) NA
3) Negligible impacts
1) Minor to moderate impacts to one pair
of northern goshawk, negligible to
moderate impacts to flammulated owls,
and negligible impacts to other species
2) No USFS lands
3) Negligible impacts
1) Same as Proposed Action
2) No USFS lands
3) Negligible impacts
1) Same as Proposed Action
2) No USFS lands
3) Negligible impacts
1) Same as Proposed Action
2) No USFS lands
3) Negligible impacts
1) Same as Proposed Action
2) NA
3) Negligible impacts
Impacts to CNHP Species:
1) Gross Reservoir
2) Leyden Gulch Reservoir
3) South Platte River Facilities
4) River Segments
1) NA
2) NA
3) NA
4) No impact
1) Not documented to occur; no impact
2) NA
3) NA
4) No impact
1) Same as Proposed Action
2) Not documented to occur; loss
of suitable habitat for three
butterfly species
3) NA
4) No impact
1) Same as Proposed Action
2) NA
3) Minor long-term beneficial
and temporary adverse
impacts to four aquatic bird
species
4) No impact
1) Same as Proposed Action
2) NA
3) Same as Alternative 8a
4) No impact
1) Same as Proposed Action
2) NA
3) Same as Alternative 8a
4) No impact
Impacts to Big Game Seasonal Ranges:
1) Gross Reservoir
2) Leyden Gulch Reservoir
3) Other Facilities
Note: Acres by habitat type are provided
in Table 9.
1) NA
2) NA
3) NA
1) Moderate impact to elk migration
corridor; minor impact from loss of elk
severe winter range, elk winter
concentration area, and mule deer
summer range
2) NA
3) NA
1) Similar to Proposed Action but
smaller area affected
2) Minor impacts from loss of
mule deer summer and winter
range
3) NA
1) Similar to Proposed Action
but smaller area affected
2) NA
3) Negligible impacts to white-
tailed deer, mule deer, and
turkey
1) Same as Alternative 8a
2) NA
3) Negligible impacts to white-
tailed deer overall range
1) Similar to Proposed Action
but smaller area affected
2) NA
3) Same as Alternative 8a
139
Table 12
Summary of Direct and Indirect Effects to Fish and Wildlife Resources
Type of Impact and Facility No Action Alternative Effects of Action Alternatives Compared to Current Conditions
Proposed Action (Alternative 1a) Alternative 1c Alternative 8a Alternative 10a Alternative 13a
Impacts to USFS Management Indicator
Species:
1) Gross Reservoir
2) Other Facilities
3) River Segments
1) NA
2) NA
3) Negligible or no effect
1) Moderate impacts to elk; minor impacts
to mule deer, pygmy nuthatch, hairy
woodpecker, and mountain bluebird;
negligible impacts to golden-crowned
kinglet, warbling vireo, and Wilson’s
warbler
2) No USFS lands
3) Negligible or no effect
1) Same as Proposed Action but
smaller impacts
2) No USFS lands
3) Same as Proposed Action
1) Same as Proposed Action
but smaller impacts
2) No USFS lands
3) Same as Proposed Action
1) Same as Proposed Action
but smaller impacts
2) No USFS lands
3) Same as Proposed Action
1) Same as Proposed Action
but smaller impacts
2) No USFS lands
3) Same as Proposed Action
Impacts to USFS Wildlife Habitats:
1) Gross Reservoir
2) Other Facilities
1) NA
2) NA
1) Loss of inventoried old growth and old
growth development areas may conflict
with ARNF Forest Plan; minor impacts
to other types
2) No USFS lands
1) Same as Proposed Action but
smaller impacts
2) No USFS lands
1) Same as Proposed Action
but smaller impacts
2) No USFS lands
1) Same as Proposed Action
but smaller impacts
2) No USFS lands
1) Same as Proposed Action
but smaller impacts
2) No USFS lands
Impacts to Sensitive Areas:
1) Gross Reservoir
2) Leyden Gulch Reservoir
3) Other Facilities
4) River Segments
Note: Acres by sensitive area are
provided in Table 9.
1) NA
2) NA
3) NA
4) No or negligible impacts
1) Permanent loss of 4% of Winiger
Gulch PCA and 7% of Winiger Ridge
ECA
2) NA
3) NA
4) No or negligible impacts
1) Permanent loss of 2% of
Winiger Gulch PCA and 4% of
Winiger Ridge ECA
2) Temporary disturbance to less
than 1% of Rocky Flats PCA
3) NA
4) Same as Proposed Action
1) Permanent loss of 3% of
Winiger Gulch PCA and 5%
of Winiger Ridge ECA
2) NA
3) Temporary disturbance to
South Platte River PCA
4) Same as Proposed Action
1) Same as Alternative 8a
2) NA
3) Same as Alternative 8a
4) Same as Proposed Action
1) Permanent loss of 4% of
Winiger Gulch PCA and
6% of Winiger Ridge ECA
2) NA
3) Same as Alternative 8a
4) Same as Proposed Action
Impacts to Raptors and Other Migratory
Birds:
1) Gross Reservoir
2) Leyden Gulch Reservoir
3) Other Facilities
1) NA
2) NA
3) NA
1) Permanent loss of habitat for forest
birds; new water surface is beneficial
impact for water birds
2) NA
3) NA
1) Same as Proposed Action but
smaller impacts
2) Permanent loss of habitat, one
raptor nest affected, and
beneficial impact for water
birds
3) NA
1) Same as Proposed Action
but smaller impacts
2) NA
3) One raptor nest affected, and
beneficial impact for water
birds
1) Same as Proposed Action
but smaller impacts
2) NA
3) Temporary loss of habitat
1) Same as Proposed Action
but smaller impacts
2) NA
3) Same as Alternative 8a
Vegetation
Federally-listed Threatened and
Endangered Plant Species
No impacts Not likely to adversely affect Ute ladies’-
tresses orchid and Colorado butterfly plant
Same as Proposed Action Same as Proposed Action Same as Proposed Action Same as Proposed Action
Impacts to USFS and CNHP Species:
1) Gross Reservoir
2) Other Facilities
3) River Segments
No or negligible impact
1) No effect to USFS Region 2 sensitive
species; may affect the long-term
viability on the ARNF of several
species of local concern to the USFS,
including wild sarsaparilla, Dewey
sedge, Sprengel’s sedge, Enchantress’
nightshade, tall blue lettuce, and
Maryland sanicle
2) No impact
3) No or negligible impact
1) Same as Proposed Action,
except lower impact to Dewey
sedge and no impact to
Maryland sanicle
2) No impact
3) No or negligible impact
1) Same as Proposed Action,
except lower impact to
Dewey sedge and Maryland
sanicle
2) No impact
3) No or negligible impact
Same as Alternative 8a
1) Same as Proposed Action,
except lower impact to
Maryland sanicle
2) No impact
3) No or negligible impact
140
Table 12
Summary of Direct and Indirect Effects to Fish and Wildlife Resources
Type of Impact and Facility No Action Alternative Effects of Action Alternatives Compared to Current Conditions
Proposed Action (Alternative 1a) Alternative 1c Alternative 8a Alternative 10a Alternative 13a
Acres of Vegetation Loss:
1) Gross Reservoir
2) Leyden Gulch Reservoir
3) South Platte River Facilities
4) Conduit O
5) Denver Basin Aquifer Facilities
6) Conduit M
7) Agricultural Water Transfer
Note: Impacts by vegetation type are
provided in Table 11.
No impacts Moderate impacts at Gross Reservoir
1) 456 acres permanent, 52 acres
temporary
2) NA
3) NA
4) NA
5) NA
6) NA
7) NA
Moderate impacts at Gross
Reservoir and Leyden Gulch
Reservoir
1) 293 acres permanent, 67 acres
temporary
2) 383 acres permanent, 172 acres
temporary
3) NA
4) NA
5) NA
6) NA
7) NA
Moderate impacts at Gross
Reservoir and minor elsewhere
1) 354 acres permanent, 61
acres temporary
2) NA
3) 6 acres permanent, 11 acres
temporary
4) 2 acres permanent, 9 acres
temporary
5) NA
6) NA
7) NA
Moderate impacts at Gross
Reservoir, minor to moderate
for Denver Basin Aquifer
facilities, and minor elsewhere
1) 354 acres permanent, 61
acres temporary
2) NA
3) NA
4) NA
5) 18 acres permanent, 21
acres temporary
6) 2 acres permanent, 12 acres
temporary
7) NA
Moderate impacts at Gross
Reservoir and minor elsewhere
1) 404 acres permanent,
56 acres temporary
2) NA
3) 6 acres permanent, 12 acres
temporary
4) 2 acres permanent, 12 acres
temporary
5) NA
6) NA
7) 3,816 acres, mostly
irrigated cropland
Impacts to Plant Communities of
Concern:
1) Gross Reservoir
2) Other facilities
Note: Acres of impact by type are
provided in Table 10.
No impacts 1) Moderate impacts to river birch/mesic
forb and thinleaf alder/mesic forb, and
negligible impacts to old growth
ponderosa pine
2) NA
1) Same as Proposed Action but
smaller impacts
2) No impacts
1) Same as Proposed Action but
smaller impacts
2) No impacts
1) Same as Proposed Action
but smaller impacts
2) No impacts
1) Same as Proposed Action
but smaller impacts
2) No impacts
Impacts to Wetland/Riparian From Flow
Changes:
1) Fraser River and Tributaries
2) Williams Fork River and Tributaries
3) Blue River
4) Colorado River
5) South Boulder Creek
6) North Fork South Platte River
7) South Platte River
1) Negligible impacts
2) Negligible impacts
3) Minor impacts
4) Negligible impacts
5) Negligible impacts
6) Negligible impacts
7) Negligible impacts
1) Minor impacts to wetland and riparian
areas, and no impacts to fens
2) Negligible or no impacts to wetlands
and riparian, and no impacts to fens
3) Negligible impacts
4) Minor impacts to wetlands/riparian
areas
5) Minor impacts to wetlands/riparian
areas
6) Negligible impacts
7) Negligible impacts
Same as Proposed Action Same as Proposed Action Same as Proposed Action Same as Proposed Action
Notes:
NA = facility is not included in alternative
% = percent
ARNF = Arapaho & Roosevelt National Forests
CNHP = Colorado Natural Heritage Program
ECA = Environmental Conservation Area
PCA = Potential Conservation Area
SPWRAP = South Platte Water Related Activities Program
USFS = U.S. Forest Service
141
10. Recommended Fish and Wildlife Conservation Measures
The Chapter 5 of the FEIS includes general mitigation and monitoring recommendations at the end of
each resource impact analysis discussion. The FEIS mitigation measures and Denver Water’s Final
Mitigation Plan will be evaluated by the Corps for inclusion in the Record of Decision and/or the
subsequent Section 404 Permit.
FEIS Appendix M-1 contains Denver Water’s Conceptual Mitigation Plan, and Appendix M-2 contains
the Corps’ evaluation of the operation of the Environmental Pool. The mitigation strategies included in
the FEIS included avoidance, minimization, protection, and compensation. The primary mitigation this
report is intended to address is covered by the December 6, 2013 Colorado River and Platte River
depletions BO, the January 29, 2016 BO for the Gross Reservoir Environmental Pool, and the June 17,
2016 BO for the green lineage cutthroat trout and the Moffat Project that were issued by the Service, as
well as commitments made by Denver Water in the State-approved Moffat Project Fish and Wildlife
Mitigation Plan. Mitigation will be refined and described in more detail in Denver Water’s Final
Mitigation Plan. The Corps will evaluate all proposed compensatory mitigation in its ROD to determine
if it complies with applicable laws, adequately offsets the loss of aquatic resources, and mitigates
significant effects to public interest factors. If a Section 404 Permit is issued, all compensatory mitigation
required by the Corps will be supported by legally enforceable permit conditions. As part of Section 7
consultation, the Corps and Denver Water developed conservation measures for protection, enhancement,
and recovery of green lineage cutthroat trout in the Fraser River and Williams Fork River basins. Details
of these conservation measures were presented in the BA (Corps 2015) and the BO issued by the Service
for the Moffat Project and green lineage cutthroat trout (USFWS 2016b).
Denver Water has also developed three mitigation and enhancement agreements separately from the
NEPA process, which are included in FEIS Appendix M. Pursuant to C.R.S. 37-60-122.2, Denver Water
prepared a Fish and Wildlife Mitigation Plan (Appendix M-3 of the FEIS) to mitigate potential impacts of
the Moffat Project on the State’s fish and wildlife resources. Denver Water also prepared a Fish and
Wildlife Enhancement Plan (Appendix M-4 of the FEIS) to enhance fish and wildlife resources beyond
the levels that currently exist or that would exist with the Moffat Project. In June 2011, the Colorado
Wildlife Commission unanimously approved the Fish and Wildlife Mitigation Plan and authorized CPW
to enter into an Intergovernmental Agreement with Denver Water to implement the Fish and Wildlife
Enhancement Plan. In July 2011, the Colorado Water Conservation Board adopted the Fish and Wildlife
Mitigation Plan. The Fish and Wildlife Mitigation Plan is the official State position on mitigation of
impacts to fish and wildlife resources. To summarize:
Moffat Project, Fish and Wildlife Mitigation Plan (Appendix M-3 of the FEIS), prepared for the
Colorado Wildlife Commission, by Denver Water, June 9, 2011.
Moffat Project, Fish and Wildlife Enhancement Plan (Appendix M-4 of the FEIS), prepared for
the Colorado Wildlife Commission, by Denver Water in Partnership with the Municipal
Subdistrict, Northern Colorado Water Conservancy District, June 9, 2011. The Fish and Wildlife
Enhancement Plan is a voluntary effort by Denver Water to improve existing conditions in the
Colorado River and is not based on Moffat Project impacts identified in the FEIS.
CRCA (Appendix M-5 of the FEIS), September 26, 2013. The CRCA is a voluntary effort by
Denver Water to improve existing conditions in the Colorado River and is not based on Moffat
Project impacts identified in the FEIS.
10.1 Aquatic Resources Mitigation
Appendix M of the FEIS contains conceptual mitigation proposed by Denver Water to address the
impacts identified in the FEIS, and Denver Water’s Fish and Wildlife Mitigation Plan (Denver Water
142
2011), previously approved by the Colorado Wildlife Commission. Both of these plans were prepared for
the Proposed Action, but could be applied to all alternatives because aquatic impacts would be similar.
Aquatic resource mitigation measures included in the FEIS and Denver Water’s Conceptual Mitigation
Plan included the following:
Fraser River and Williams Fork River:
o Denver Water will implement several conservation measures for protection,
enhancement, and recovery of green lineage cutthroat trout that are presented in detail in
the BO issued by the Service for the Moffat Project and green lineage cutthroat trout
(USFWS 2016b) and summarized in Section 10.2.1.
o Denver Water will monitor stream temperatures on Ranch Creek and the Fraser River.
When threshold temperatures are exceeded between July 15 and August 31, Denver
Water will bypass up to 250 AF of diversions from the Fraser River collection system.
o Denver Water will provide up to $750,000 for stream habitat restoration in the Fraser
River and Williams Fork River and tributaries, and will work with CPW and other
participants in a cooperative effort to design and implement stream restoration projects.
Colorado River: Denver Water will work with other parties to install, monitor, and maintain two
temperature monitoring stations on the Colorado River. When threshold temperatures are
exceeded between July 15 and August 31, Denver Water will bypass up to 250 AF of diversions
from the Fraser River collection system.
Gross Reservoir: Denver Water will plant native woody riparian vegetation (see Section 10.3),
will remove as much organic material from the reservoir as possible before filling, and will
monitor metals levels in fish for 5 years after filling.
South Boulder Creek: In a collaborative effort with the cities of Boulder and Lafayette, Denver
Water will compensate for impacts to aquatic habitat by creation of a 5,000-AF Environmental
Pool within Gross Reservoir. Approximately 17 miles of South Boulder Creek would benefit
from the Environmental Pool. The Environmental Pool will be filled with water rights owned and
provided by the cities of Boulder and Lafayette, and released for environmental flows during
winter. Denver Water will also continue monitoring stream bank stability.
North Fork South Platte River: Denver Water will provide up to $1.5 million for aquatic
habitat improvements and will monitor five locations for channel instability. Improvements will
be developed in coordination with the Corps, CPW, USFS, and landowners.
For alternatives 8a, 10a, and 13a, minimization may include careful construction of South Platte River
diversions so they are not barriers to the upstream migration of fish.
The primary mitigation this report is intended to address is covered by the December 6, 2013 Colorado
River and Platte River depletions BO, the January 29, 2016 BO for the Gross Reservoir Environmental
Pool, and the June 17, 2016 BO for the green lineage cutthroat trout and the Moffat Project that were
issued by the Service, as well as commitments made by Denver Water in the State-approved Moffat
Project Fish and Wildlife Mitigation Plan. Mitigation will be refined and described in more detail in
Denver Water’s Final Mitigation Plan.
10.2 Wildlife Resources Mitigation
Denver Water prepared the Moffat Collection System Project Fish and Wildlife Mitigation Plan, which
has been approved by the Colorado Wildlife Commission and is provided in Appendix M of the FEIS.
Mitigation relevant to wildlife and endangered fish and wildlife species includes continued participation
in the Upper Colorado Endangered Fish Recovery Program, continued participation in the PRRIP,
143
compliance with the BO issued by the Service, compliance with the MBTA, use of CPW’s Best
Management Practices (BMPs) for wildlife, implementation of revegetation, forest management and weed
control per the FERC license amendment application, and development of woody riparian plant
communities around Gross Reservoir.
10.2.1 Endangered Species
The Corps initiated Section 7 consultation in 2009, for which the Service issued a BO on July 31, 2009.
Consultation was reinitiated in 2013 to address all of Denver Water’s depletions and new information on
Preble’s meadow jumping mouse in the Fraser River and Williams Fork River systems. A Final BO
addressing the new information was issued in December 2013, replacing the 2009 BO (Appendix G-2 in
the Moffat Project FEIS). The Corps submitted a BA and re-initiated consultation for green lineage
cutthroat trout on December 1, 2015. On June 17, 2016, the Service issued a BO (USFWS 2016b) that
outlines two conservation measures that Denver Water will implement to mitigate for adverse impacts to
green lineage cutthroat trout resulting from Current Conditions (2006), Full Use of the Existing System
with RFFAs, and the Moffat Project in the Fraser River and Williams Fork River basins. The Section 404
permit would require compliance with mandatory terms and conditions to implement the reasonable and
prudent measures that are associated with “incidental take” that are specified in the various BOs. The
Section 404 authorization would be conditional upon Denver Water’s compliance with all of the
mandatory terms and conditions associated with incidental take in the BOs, with the terms and conditions
incorporated by reference in the permit, if one is issued. The conservation measures excerpted from the
BO are presented below:
Conservation Measure 1 - Protection, Enhancement, and Recovery of Green Lineage Cutthroat
Trout in the Upper Williams Fork River Basin. For the upper Williams Fork River Basin, Denver
Water will construct one fish migration barrier below each of its existing diversion structures on
Steelman, Bobtail, and McQueary creeks. These three fish barriers will provide protection to the existing
green lineage cutthroat trout populations on Bobtail and Steelman creeks, which are presently vulnerable
to invasion by brook trout, and will also allow for the establishment of a new protected population on
McQueary Creek. In all, approximately 9 miles of stream habitat will be permanently protected in the
headwaters of Steelman (2.6 miles), Bobtail (3.7 miles), and McQueary (2.6 miles) creeks for green
lineage cutthroat trout populations.
Conservation Measure 2 - Protection of Green Lineage Cutthroat Trout in the Fraser River Basin.
For the Fraser River Basin, Denver Water will ensure that its existing diversion structures and operation
practices on Hamilton and Little Vasquez creeks continue to safeguard existing green lineage cutthroat
trout populations in the headwaters by providing effective barriers to fish passage. This action will
permanently protect approximately 10 miles of stream habitat for green lineage cutthroat trout (7.1 miles
on Little Vasquez Creek and 2.7 miles on Hamilton Creek). Additionally, Denver Water will serve in a
coordinating role for developing and implementing and will actively participate in a cooperative recovery
program for green lineage cutthroat trout in St. Louis Creek with the Service, USFS, CPW, and possibly
others. This cooperative recovery program in St. Louis Creek would permanently protect up to
approximately 15 miles of new green lineage cutthroat trout habitat.
More detailed information pertaining to Conservation Measure 1 and Conservation Measure 2 is
presented in the BO issued by the Service for the Moffat Project and green lineage cutthroat trout
(USFWS 2016b).
Raptors and other Migratory Birds
To comply with the MBTA, Denver Water has committed to use of pre-construction surveys to identify
and avoid active nests in the Project footprint and timing of construction activities to avoid the breeding
season. If practicable, trees in the construction footprint would be cleared prior to March 1 or after
144
July 31 to prevent raptors (and other birds) from nesting on site, and avoid take of or disturbance to active
nests during the breeding season. If clearing during the breeding season cannot be avoided, compliance
would occur by surveys and avoidance of active nests until young are fledged. Surveys would be
conducted during an appropriate season and may need to be conducted at multiple times to address all
species, including owls. If an active nest is located, protective buffer zones would be established around
active nests during construction to avoid disturbance while nesting. Buffer zones and seasonal
restrictions for raptors would be based on CPW recommendations (CDOW 2008) and on consultation
with CPW.
Other Mitigation Measures
During construction, vehicle operation would be limited to designated construction areas, and the
limits of the construction area would be fenced where they are adjacent to sensitive habitats
including prairie dog towns, riparian areas, wetlands, and upland trees and shrubs.
Silt fencing, erosion logs, temporary berms, and other BMPs would be used to prevent
degradation of habitats adjacent to the construction area by transport of eroded sediment.
Temporarily-disturbed areas would be seeded with an appropriate mixture of native grasses and
forbs, and shrubs would be planted where appropriate.
Open cut streams would be restored equal to or better than pre-construction conditions. To
control erosion, bioengineering or the use of plants to control erosion would be preferred instead
of riprap or other unnatural bank stabilization techniques. Banks would be planted with native
plant species.
Alternatives 8a, 10a, and 13a include gravel pit reservoirs that would be located within the
17-mile reach covered by the South Platte River Heritage Corridor Plan. FEIS Section 5.9.7
includes guidelines and considerations for enhancement of wildlife habitat in the gravel pit
reservoirs and adjoining riparian and upland habitats.
Alternatives 1c, 8a, 10a, and 13a include potential impacts to prairie dog towns. Direct impacts
should be avoided if possible. If avoidance is not feasible, prairie dogs should be relocated to
adjacent areas of suitable habitat. If relocation is not feasible, impacted black-tailed prairie dogs
should be humanely removed from burrows that would be directly affected by the Project, and
donated for feeding of captive black-footed ferrets or raptors.
Burrowing owl impacts would be avoided by implementing the procedures included in CPW’s
Recommended Survey Protocol and Actions to Protect Nesting Burrowing Owls (CDOW 2007)
summarized in FEIS Section 5.10.7.
To mitigate for impacts to common garter snakes in areas where BMPs would control erosion
near streams and in riparian habitat, coconut-straw erosion blankets with a biodegradable thread
would be used rather than turf reinforcement mats, which can harm snakes.
10.3 Vegetation Resources Mitigation
Denver Water’s Moffat Collection System Project Fish and Wildlife Mitigation Plan includes a
commitment to the implementation of revegetation, forest management, and weed control per the FERC
license amendment application, development of woody riparian plant communities around Gross
Reservoir, and mitigation of wetlands in accordance with Corps’ requirements, either by purchase of
sufficient credits from an approved mitigation bank, or creation of mitigation wetlands within the South
Boulder Creek watershed.
145
10.3.1 Revegetation
A revegetation plan would be developed prior to construction for all areas that would be temporarily
disturbed during construction of the Moffat Project. The plan would be in compliance with the ARNF
revegetation policy for lands administered by the USFS. Additional recommendations for planning and
implementation are provided in FEIS Section 5.7.7. For Alternative 13a, lands affected by agricultural
water rights transfer should be seeded with grasses to limit expansion of noxious weeds, where the
transfer would result in cessation of agricultural activity or prolonged fallow periods.
10.3.2 Noxious Weeds
A weed management plan would be prepared to control noxious weeds and to prevent degradation of
habitats. All equipment would be cleaned prior to entering a site in order to remove soil and plant parts
that may contain weed seeds. Only certified weed-free mulch and bales would be used. All seed used
would be free of noxious weeds. Native topsoil would be salvaged from areas of temporary disturbance
and permanent impacts at the construction sites, and would be reused in order to enhance revegetation
efforts. Topsoil would not be salvaged from areas infested with noxious weeds. Additional
recommendations are provided in FEIS Section 5.7.7.
10.3.3 Wetlands and Riparian
All impacted wetlands and other water features would be mitigated in accordance with current Corps’
mitigation policies, and the conditions of the Section 404 Permit. Mitigation plans would be developed in
coordination with the Corps and other appropriate agencies during the Section 404 permitting process.
The Corps would determine the appropriate level of mitigation based upon the wetland functions lost or
adversely affected as a result of impacts to aquatic resources. In general, a 1:1 replacement of functions is
required, using on- or off-site mitigation.
If Alternative 1c were permitted, impacted wetlands at Leyden Gulch Reservoir from construction
disturbance associated with the access road, emergency outlet, and the pipeline tunnel would be identified
for further minimization and avoidance during final design.
Denver Water proposes to mitigate direct impacts to riparian habitat at Gross Reservoir by planting native
woody riparian vegetation in suitable areas around the reservoir. Denver Water will prepare a riparian
vegetation establishment plan for review by CPW, the Corps, and the USFS, that would establish a
schedule, and identify planting areas, type and quantity of plant materials, success criteria, and monitoring
methods.
10.3.4 Construction Phase Mitigation
FEIS sections 5.7.7 and 5.8.7 include recommendations for construction phase mitigations, including use
of erosion control BMPs, fencing or marking of construction areas to limit disturbance, removal of trees
in a manner that does not lead to additional spread of mountain pine beetle, and avoidance of construction
in areas of flowing water.
10.3.5 Special Status Plants at Gross Reservoir
Locations of USFS special status plants should be marked in the field prior to clearing operations, with a
buffer zone of at least 10 feet. No ground-disturbing activities should occur within the marked
populations or buffer zones. Hand cutting of trees may be preferential in some locations. FEIS
Section 5.10.7 provides recommendations from the ARNF botanist for each individual species, including
transplanting of impacted plants or collection and distribution of seed, and collection of herbarium
voucher specimens for all affected species.
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11. References
Baran, P., M. Delacoste, F. Dauba, J.M. Lascaux, A. Belaud, and S. Lek. 1995. Effects of Reduced Flow
on Brown Trout (Salmo trutta L.) Populations Downstream Dams in French Pyrenees. Regulated
Rivers: Research and Management 10:347-361.
Boyle, Steve. 2006. North American River Otter (Lontra canadensis): A Technical Conservation
Assessment. Prepared for the USDA Forest Service, Rocky Mountain Region, Species
Conservation Project. BIO-Logic Environmental, Montrose, Colorado.
Carlisle, D.M., D.M. Wolock, and M.R. Meador. 2010. Alteration of Streamflow Magnitudes and
Potential Ecological Consequences: A Multiregional Assessment. Frontiers in Ecology and the
Environment. DOI: 10.1890/100053.
Chadwick and Associates. 1986. Aquatic Baseline, Metropolitan Denver Water Supply Systemwide/
Site-Specific Environmental Impact Statement. Prepared for Denver Water, Denver, Colorado.
Colorado Division of Water Resources (CDWR). 2005. Hydrobase Dataset. Accessed at:
www.dwr.state.co.us.
Colorado Division of Wildlife (CDOW). 2007. Recommended Survey Protocol and Actions to Protect
Nesting Burrowing Owls.
Colorado Division of Wildlife (CDOW). 2008. Recommended Buffer Zones and Seasonal Restrictions
for Colorado Raptors. February.
Denver Board of Water Commissioners (Denver Water). 2003. Operating Information for Denver
Water’s Moffat Collection System. September.
Denver Board of Water Commissioners (Denver Water). 2011. Moffat Collection System Project, Fish
and Wildlife Mitigation Plan. Prepared for the Colorado Wildlife Commission. June 9, 2011.
GEI Consultants, Inc. (GEI). 2013. Aquatic Resources Technical Report for the Moffat Collection
System Project Final Environmental Impact Statement.
Hirsch, C.L., S.E. Albeke, and T.P. Nesler. 2006. Range-Wide Status of Colorado River Cutthroat Trout
(Oncohynchus clarkia pleuriticus): 2005. Colorado River Cutthroat Trout Conservation Team
Report. March.
Miller Ecological Consultants, Inc. 2015. Fraser River Dynamic Water Temperature Model, Moffat
Collection System Project, Section 401 Certification Review.
Rees, D.E. 2009. Summary Report: Benthic Macroinvertebrate Biomonitoring Program. Prepared for
the Northern Colorado Water Conservancy District, Berthoud, Colorado. 86 pages.
Schenk, T.M. 2009. Post-Release Monitoring of Lynx Reintroduced to Colorado, July 1, 2008-
August 31, 2009. Colorado Division of Wildlife, Wildlife Research Report.
Stables, T.B., G.L. Thomas, S.L. Thiesfeld, and G.B. Pauley. 1990. Effects of Reservoir Enlargement
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Appendix A
U.S. Fish and Wildlife Service Letter of Approval of Fish and Wildlife Coordination Act (FWCA) Report and Acknowledgement that the U.S. Army Corps of Engineers
Responsibilities under the FWCA Have Been Met
