Rury 206PM Room B_Integr Hab Restor & Stormwater Treat
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Transcript of Rury 206PM Room B_Integr Hab Restor & Stormwater Treat
Integrating Habitat Restoration with Urban Stormwater Treatment at
Alewife Reservation, Cambridge, MA
Phil Rury, Duke Bitsko and Wendi Goldsmith
ALEWIFE RESERVATION ALEWIFE RESERVATION STORMWATER WETLAND PROJECTSTORMWATER WETLAND PROJECT
Project Team• Cambridge Dept. Public Works (client)
• MA Dept. of Conservation & Recreation (land owner)
• Engineering and Landscape Design Consultants– Kleinfelder/SEA (engineering & management)– MWH (site hydrology & hydraulic analysis)– Bioengineering Group (ecological design)
• Construction Contractor - P. Gioioso & Sons
Project History• Project is part of the MWRA Long-Term CSO
Control Plan for Alewife Brook Part of Court-ordered Boston Harbor Cleanup
• Designed to meet the goals and objectives of DCR’s Master Plan for Alewife Reservation Project of Cambridge DPW on DCR Land
Bioengineering facilitated collaboration of its clients DPW and DCR for mutual environmental benefit
CSO Control Plan for Alewife Brook
Goals Achieved to Date: Reduced Average Annual
Discharge to Alewife Brook by 48% since 1997
Cambridge closed CSO CAM 400 in March 2011
Stormwater Treatment Wetland is now under Construction
Goals of MWRA, Cambridge and Somerville: Reduce average annual CSO volume to Alewife Brook by 85% and
average frequency of discharge from 63 to 7 times a year Reduce flooding and sewer backup and Close CAM004 CSO
Alewife Stormwater Wetland
Project Location
Project Location15 acre Site between the Little River, Cambridge Park
Drive and Old Alewife Brook at Alewife MBTA StationIncludes 6.5 acres of existing, degraded freshwater wetland
Old Alewife Brook – Receives CSO CAM004 Discharge
Little RiverProject Location
Alewife T-Station
Alewife Reservation Plant DiversityA Richer Native Flora Inhabits Other Reservation Areas
and many more…
Onsite Wildlife Food Plants:
Alewife Reservation Wildlife16 Mammal Species including Beaver, Coyote, Mink, Muskrat, Rabbit, Raccoon, Red Fox, Weasel, White-tailed Deer, Skunk, Squirrel & Woodchuck
90 Bird Species including Grouse, American Woodcock, Raptors, Shorebirds, Song Birds, Turkey, Waterfowl and Waders
Mixture of Upland & Wetland Habitats Fragmented Wetlands – partly filled Altered Hydrology- starved of water Low Native Floristic Diversity Dominated by Invasive Vegetation
Degraded Site Conditions
• Invasive Plants Dominated 70% of Site: Ailanthus, Buckthorns, Honeysuckles, Japanese Knotweed, Multiflora Rose, Oriental Bittersweet & Phragmites
• Homeless Camps and Local Dumping
• Historically Filled Wetlands
Highly Degraded Site
Jungle of Invasive Vegetation
Purpose and ScopeStormwater Detention to Reduce Flows to Alewife Brook During Storms While Incorporating Goals and Objectives of
the DCR Alewife Reservation Master Plan
The stormwater treatment wetland system will improve water quality and:• Serve as a component of the larger CSO separation project• Detain over 10 acre-feet of water during storm events• Create or restore ecological functions/values of freshwater wetlands and
adjacent terrestrial habitats, emphasizing: Restoration of Severely Degraded Uplands and WetlandsFloristic Diversity and a Mosaic of Plant CommunitiesHydrologic, Water Quality and Wildlife Habitat Functions
Design Goals and Objectives
• Attenuate high volume stormwater flows • Enhance the quality of urban stormwater • Meet state and federal regulatory standards• Low maintenance/self-sustaining system• Create a sustainable and natural hydrology• Reduce invasives, promote native flora• Include components of Alewife Master Plan
Pollutant Removal Pathways within a Stormwater Wetland
• Prolong Detention and/or Retention to Settle Most Suspended Sediments
• Physical Filtration• Adsorption to Sediments• Groundwater Recharge• Microbial Breakdown • Plant Uptake
Soil Storage(peat)
Plant Uptake
Volatilizationof NH3 and
Volatile organics
Inflow
N2
DenitrificationNO3
-
Burial
Sedimentation
Plant Storage
CO2 & CH4
Adsorption- NH4
+, metals, P, organics (to clays, Fe / Al hydroxides, organic matter)Precipitation- P (with Fe, Al, Ca)- Metals (with sulfides)Source: K.R.
Reddy
Stormwater Detained to Elev. 1.0 ft.1-month Storm Event Hydrograph
0123456789
101112
Time (hours)
Flow
(cfs
)
Inflow Outflow
Water Quality ImprovementsWetlands can remove up to 90% of suspended solids,
heavy metals and nutrients from urban stormwaterExpected Removal Efficiencies for Rainfall Events
Contaminant 1-month 3-monthTotal Suspended Solids 65% 75%Lead 75% 80%Zinc 40% 40%
Total Phosphorus 40% 40%Total Nitrogen 25% 30%
COD [Bacterial Indicator] 35% 40%Source: Schueler 1992
• Improve Quality of Urban Stormwater • Flood Storage - No Net Increase of Discharge• Compensatory Aquatic and Wetland Habitats
Connected to Little River as Mitigation • Benefit from Clean Groundwater Inflows fed
by Head from the Fresh Pond Reservoir• Restore and Enhance Degraded Habitats• Aesthetics, Recreation & Education Benefits
Stormwater Wetland Design Criteria
Designed to Benefit from Groundwater Inflows fed
by GW Head from the Fresh Pond Reservoir• Oxbow Excavated into Sand and Gravel with
Ground Water Up to Elevation 3.0 feet• Valved Equalizing Pipe between Oxbow and
Main Basin to Feed Basin during Low Water• Parts of Main Basin are Perched on Clay –
Wetland Designed for Mean GW Elev. of 1.0 ft.
Stormwater Wetland Hydrology
Impounded Oxbow Water Level 1- 2 ft. > River Level
Surface Water Level of Impounded Oxbow Area Exceeds River Level
Top of Piers Set @ Elev. 2.0 ft.
Oxbow Water 1 foot Higher than adjacent Little River on 2/28/2012
Groundwater Influx @ 750 GPM
Diverse Wetland & Upland Habitats
Over 115,000 Wetland and 3,800 Upland Plantings Broadleaf Floodplain, Riparian & Upland Woodlands New Open Water Habitats of Main Basin and Oxbow Concentric Deep, Emergent and High Marsh Zones Scrub/Shrub Wetlands and Wet Meadow
Grading Plan - Forebay & East Basin
Main Outfall to Little River
Flow: Forebay to Vegetated SwaleForebay = 0.27 acres (50 ft. x 170 ft.)Inlet @ Elev. 0.0 ft.Outlet @ Elev. 1.0 ft.
Swale from Forebay Feeds First Pool
Planting Plan- Forebay & East Basin
Upland Peninsula to Divert Flow to West
Swale from Forebay Feeds First Pool
Compensatory Wetland CreationCreated Extra 0.71 acres of Oxbow Habitats connected to Little River to: Replace degraded finger of wetland used for channel creation and floodplain storage volume lost to create berm for the main basin wetland
Assure ground and surface water influx to basin up to surface water elevation of 1.0 foot
Add gravel bottom pond for Alewife spawning
Grading Plan - Oxbow & West Basin
Compensatory Oxbow Wetland Creation
Water Leveling Pipe
Planting Plan - Oxbow & West Basin
Deepest Pool 5.5 ft.
Gravel Bottom Pools 3.5 ft. Deep with River
at Elev. 1.0 ft.
Mosaic of Native Plant CommunitiesPlanting Zones along Moisture Gradient Ephemeral, Infrequent Inundation to Elev. 1.0 ft.Permanent Pools > 3’ deepDeep Marsh 1’- 3’ deepShallow Marsh 0 - 1’ deepScrub/Shrub & RiparianWet MeadowUpland/Peninsula/Island Meadow and Woodlands
Over 100 native species of live plantings and seed mixes were chosen for each plant community to
include many plant species already thriving on site
WETLAND HABITAT ACREAGES & SEED MIXES
Three Wetland
Seed Mixes Prescribed to Include Many Species to be Installed as
Live Plantings
High Marsh Mix: 23 Native Species
of 16 Genera
Construction Ecological OversightMADEP Wetland Permit & Water Quality Certification
require Oversight by a Resident Wetland ScientistAssure Compliance with All Permit ConditionsReview Contractor Submittals & Assure Conformance to Grading, Hydrologic, Soil & Planting Specifications Inspect and Accept Live Plantings and Seed Mixes Provide Bi-weekly Inspection Reports to MADEP
AGONY: FELLING LARGE NATIVE TREES!
ECSTASY: ERADICATING INVASIVE VEGETATION!
Soil Stripping for Disposal or Recovery
for Onsite Reuse:Strip > 6 inches Deep to Dispose of Invasive Roots and Seed BankRecover/Reuse Deeper Upland & Hydric Soils
Nice Surprise: Buried Hydric Soils!
Top 6-inches for Disposal
Deeper Topsoil for Reuse
Planting Soils Tested vs. Specs. @ 1 Sample per 1,000 CY
Subgrade Clay Sample for Soluble Salts
Dewatering via French Drains into:
Bag Filters, Floc Blocks, Filter Fabric and Straw Bales for Removal of Silt and Clay Colloids
Floristic Impact Mitigation• Preconstruction Rare Plant Reconnaissance
Botanist verified absence of state-listed Gentiana Andrewsii
Resident Ecologist Oversaw Invasive
Vegetation Removal and Stripping of Topsoil for Disposal
Identified Upland & Hydric Soils for Reuse
Oversees Dewatering & Erosion Controls
Fish & Wildlife Impact Minimization Construction timed to avoid migratory bird/fish breeding seasons Ecologist monitored for wildlife before/during clearing/grubbing Silt fences included numerous wildlife escape openings
American Woodcock and other sensitive birds nesting at the Reservation migrate south in October and
return in May
Wildlife Impact MitigationPreconstruction Site Reconnaissance for Resident Wildlife: Conferred with Wildlife
Relocation Experts Inspected site for
burrows, dens, nest sitesProvided “gaps” in silt &
construction fencingDaily site monitoring to
detect any fauna at risk
Wetland EstablishmentPost-construction Monitoring to:• Verify Establishment & Health of Vegetation• Replace Installed Plantings as needed • Assure Removal of Invasive Plant Species • Document Success for Certificate of Compliance• Guide Long-term Maintenance of Stormwater
Treatment Wetland by the City of Cambridge
Operation and Maintenance The City of Cambridge is committed to the
Continued, Long-term Maintenance of the Alewife Stormwater Wetland and
Compensatory Oxbow Wetland Habitats
Wetland design is fully integrated with the DCR’s Alewife Reservation and Greenway Master Plan to provide:
Water Quality Improvement Enhancements of Fish and Wildlife Habitat Improved Site Amenities Educational and Recreational Uses
Self-sustaining Wetland Ecosystem offers a Low Maintenance Solution!!
Alewife Reservation Project Benefits
Boardwalk with Overlooks onto Open Water and Wetlands will Support
Outdoor Education
Education and Recreation
Questions?