Environmental Flows

Bruce A. Moulton

Chief Engineer’s Office

Texas Commission on Environmental Quality

Texas Estuaries:

Case Study

• Named for river sources, not bays.

• 7 along 370 linear miles of coast.

• About 1 million acres in total.

Nueces Watershed History

• La Fruta Dam (old Lake Corpus Christi)– Built in 1935; storage capacity of ~55,000 acre-ft

• Wesley Seale Dam (Lake Corpus Christi)– Built in 1958; storage capacity of ~300,000 acre-ft

(257,260)

• Choke Canyon Dam– Built in 1982; storage capacity of ~700,000 acre-ft

(695,271)

Background

• Choke Canyon Water Right Permit issued: October 12, 1976

“Following completion and filling of Choke Canyon Dam and reservoir, scheduled releases shall be made from the reservoir system at Lake Corpus Christi Dam together with return flows to the estuaries for the proper ecological environment and health of related living resources therein.

Background (cont.)

Water provided to the estuaries from the reservoir system under this paragraph shall be released in such quantities and in accordance with such operational procedures as may be ordered by the Commission. Permittees shall provide not less than 151,000 acre-feet of water per annum for the estuaries by a combination of releases and spills from the reservoir system at the Lake Corpus Christi Dam and return flows to Nueces and Corpus Christi Bays and other receiving estuaries.”

Nueces River

Frio River

Atascosa River

Wesley Seale Dam

Choke Canyon Dam

Nueces Delta

Nueces River Watershed

Corpus Christi Bay

NuecesBay

Oso Bay

RedfishBay

NuecesRiver

CorpusChristi

Gulfof

Mexico

AransasBay

LagunaMadre

Nueces River DeltaAransas

PassNueces Estuary

Nueces Delta and Estuary

T E X A S

2

KilometersN

0 1

Highway 77

IH 37

MoPacRailroad

Upper NuecesBay

South Lake

MoPacRailroad

IH 37

Nueces R.

Nueces R.

Nueces R.

Rincon Bayou

Rincon Bayou

Extreme Annual VariabilityNueces Estuary

1940 1950 1960 1970 1980 1990 2000

Inflo

w B

alan

ce (

ac-f

t/y)

-1000000

0

1000000

2000000

3000000

Effects on Estuary Inflow

• Average annual freshwater inflow into the Nueces Estuary has declined over the period of record.

0

100000

200000

300000

400000

500000

600000

700000

1940-1958 1958-1982 1982-1999

Estimated average annual freshwater inflowfrom the Nueces River (acre-ft)

La Fruta LCC CC-LCC

1940-1958 1958-1982 1982-1997

2.32.0

0.8

0

1

2

3

4

1940-1958 1958-1982 1982-1997

Flooding Frequency(Average number of flood events per

year)

Management History• Physical construction of Choke Canyon

reservoir completed (1982).

• Coalition About Restoration of Estuaries letter to TNRCC in 1989 questioning compliance with permit conditions.

• 1990- TAC established and the first Commission Order issued requiring reservoir releases.

1992– Interim Agreed Order

• Implemented the Interim Reservoir System Operational Plan for freshwater inflows.

• Called for the Creation of an Estuarine Advisory Council (Nueces Estuary Advisory Council)

Established to: “…consider such additional information and related issues and to formulate recommendations for the Commission’s review and action…”

NEAC Goals

• Preserve the ecological environment and health of related natural resources in the Nueces River Basin and Nueces Estuary

• Maintain and preserve (protect) a supply of water to meet the demands of identified beneficial uses in the Nueces River Basin and Corpus Christi area.

NEAC Goals (cont.)

• Minimize the release of stored waters consistent with the preservation of a healthy Nueces River Basin and Nueces Estuarine system.

• Protect the economic interests of all citizens that are dependent upon the Choke Canyon/Lake Corpus Christi reservoir system and the Nueces Estuary.

1995-Final Agreed Order• KEY change from 1992 Order included a

switch to the “Pass-Thru” approach (rather than releases from storage) and implementation of drought-contingency measures

• Continued the NEAC…to monitor implementation of the Order and to prepare recommendations, as needed, relating to any future changes to the Order

Current NEAC Membership

• TCEQ• CBBEP• CC Area Econ. Dev.

Corp.• GLO• Port of CC• City of CC• Coastal Cons. Assoc.

• Nueces River Auth.• UTMSI• San Patricio MWD• TWDB• TAMU—CC• City of Three Rivers• S. TX Water Auth.• Sierra Club

NEAC Membership (cont.)

• TPWD

• City of Mathis

• Coastal Bend Bays Foundation

• Private Citizens

• Save Lake Corpus Christi

Matters to be considered:

• The effectiveness of the inflow requirements contained in the Agreed Order on Nueces Estuary and any recommended changes;

• The effect of the releases from the Reservoir System upon the aquatic and wildlife habitat and other beneficial and recreational uses of Choke Canyon Reservoir and Lake Corpus Christi;

Matters (cont.)

• The development and implementation of a short and long-term regional water management plan for the Coastal Bend area;

• The salinity level to be applied for relief measures contained in the Agreed Order;

Matters (cont.)

• The feasibility of discharge at locations where the increased biological productivity justifies an inflow credit computed by multiplying the amount of discharge by a number greater than one; and

• Any other matters pertinent to the conditions contained in the Agreed Order

Agreed Order

• The City of Corpus Christi, as Operator of the Reservoir System, shall provide not less than 151, 000 acft of water per annum for the estuaries

>70% storage capacity—138,000 acft target>40% but less than 70%--97,000 acft target>30% but less than 40%-- 1,200 acft target*<30%-- Total suspension of Pass-thrus*

* Implementation of Lawn Watering Restrictions

Target f.w. Inflow Regime (acft) for the Nueces Estuary

MONTH >70% >40-<70% >30-<40% <30%

January 2,500 2,500 1,200 0

February 2,500 2,500 1,200 0

March 3,500 3,500 1,200 0

April 3,500 3,500 1,200 0

May 25,500 23,500 1.200 0

June 25,500 23,000 1,200 0

July 6,500 4,500 1,200 0

August 6,500 5,000 1,200 0

September 28,500 11,500 1,200 0

October 20,000 9,000 1,200 0

November 9,000 4,000 1,200 0

December 4,500 4,500 1,200 0

TOTAL 138,000 97,000 14,400 0

Public Reactio

n

Rincon BayouDemonstration Project

Restoring Freshwater

to the upper Nueces Estuary

U.S. Bureau of Reclamation

Rincon Bayou Demonstratio

n Project• To increase the

opportunity for freshwater flow events into upper Nueces Delta via Rincon Bayou

• Restore estuarine conditions, increase productivity

Rincon Overflow Channel

Nueces Overflow Channel

Project Features

• Nueces Overflow Channel– 40-ft wide, 900-ft

long– Increase the

opportunity for freshwater flow events into the upper delta.

Project Features

• Rincon Overflow Channel– 100-ft wide, 2000-ft

long– Distributes

freshwater within the upper delta.

Hydrography

• Increased freshwater/ decreased average salinity value from over 50 ppt to about 25 ppt.

• Restored duration and timing, but not volume.

Vegetation Communitie

s• Decreased soil salinity

stimulated annual seed reproduction.

• Increases in vegetation percent cover and decreases in bare area after freshwater flow events.

Benthic Communitie

s• An inverse relationship

was observed between salinity and– The number of

individual benthic animals, and

– The number of species of benthic animals.

• The function of the delta as nursery habitat was improved.

Conclusions - Ecology

• The “reverse estuary” condition largely corrected.

• A significant degree of estuarine function was restored to the delta.

River

Delta

Bay Gulf0-1

21-28

15-30 30-36

Partially Restored

Salinity Gradient

1940-1958 1958-1982 1982-1997

2.32.0

0.8

3.3

0

1

2

3

4

1940-1958 1958-1982 1982-1997

Flooding Frequency(Average number of flood events per

year)

With overflow channel

Synthesis of Results

ATTRIBUTE BEFORE

the Demonstration

AFTER

the Demonstration

Geomorphology Dead-end Flow-through with free exchange

Salinity gradient Higher in the upper delta than in the bay

Lower in the upper delta than in the bay

Nutrient cycling Recycled nitrogen New and recycled nitrogen

Primary production Low in marsh Higher in marsh

Secondary production Constrained by dry conditions

Increased by flow events

Habitat utilization Constrained by dry conditions

Increased during spring and fall

• Research indicated the Nueces Delta would benefit more if releases trigger “pulsed” flow events into the upper delta, especially during the spring and fall.

• Potential water resource development tool if water released has greater environmental value.

Integration with Release

Schedule

A Permanent Diversion Project

• Filled in Fall 2000.

• Rebuilt by City of Corpus Christi Fall 2001 for rule changes.

• Conservation groups trying to buy land.

• New monitoring program.

• Ecological credits?

Management History – Cont.

• 2001 order amended to increase firm yield by 3,000 ac-ft/y and change drought plan in exchange for diversion of river water to delta (Rincon Bayou) for environmental purposes.

• Levels automatically trigger drought plan and relief from releases.

• Less water, but more environmental benefit.

• Public still not happy.

“Adaptive Managemen

t”• The Nueces Delta is

an ideal place to determine how to most effectively balance human need for freshwater resources with environmental needs.