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 Watershed
Atascosa River
Frio River
Choke Canyon
Dam
Wesley Seale
Dam
Nueces River
Nueces Delta
Nueces Delta and Estuary
Aransas
Bay
Aransas
Pass
Nueces River Delta
Nueces Estuary
Nueces
River
Nueces
Bay
Redfish
Bay
Corpus Christi Bay
Corpus
Christi
TE XAS
Gulf
of
Mexico
Oso Bay
Laguna
Madre
Highway 77
IH 37
MoPac
Railroad
Rincon Bayou
Rincon Bayou
Nueces R.
South Lake
Upper Nueces
Bay
Nueces R.
Nueces R.
MoPac
Railroad
IH 37
N
Kilometers
0
1
2
Extreme Annual Variability
Nueces Estuary
Inflow Balance (ac-ft/y)
3000000
2000000
1000000
0
-1000000
1940
1950
1960
1970
1980
1990
2000
Effects on
Estuary Inflow
• Average annual
freshwater inflow
into the Nueces
Estuary has declined
over the period of
record.
La Fruta
LCC
CC-LCC
700000
600000
500000
400000
300000
200000
100000
0
1940-1958 1958-1982 1982-1999
Estimated average annual freshwater inflow
from the Nueces River (acre-ft)
Flooding Frequency
(Average number of flood events per year)
4
3
2.3
2.0
2
0.8
1
0
1940-1958
1958-1982
1982-1997
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
138,000
97,000
14,400
0
TOTAL
Public
Reaction
Rincon Bayou
Demonstration
Project
Restoring Freshwater
to the upper Nueces Estuary
U.S. Bureau of Reclamation
Rincon Bayou
Demonstration
Project
• To increase the
opportunity for
freshwater flow
events into upper
Nueces Delta via
Rincon Bayou
• Restore estuarine
conditions, increase
productivity
Nueces
Overflow
Channel
Rincon
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
Communities
• Decreased soil salinity
stimulated annual seed
reproduction.
• Increases in vegetation
percent cover and
decreases in bare area
after freshwater flow
events.
Benthic
Communities
• 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.
Partially Restored
Salinity Gradient
Delta
21-28
River
Bay
Gulf
0-1
15-30
30-36
Flooding Frequency
(Average number of flood events per year)
4
3.3
3
2.3
2.0
2
0.8
1
0
1940-1958
1958-1982
1982-1997
 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
Increased during spring
and fall
Constrained by dry
conditions
Integration with
Release Schedule
• 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.
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
Management”
• The Nueces Delta is
an ideal place to
determine how to
most effectively
balance human need
for freshwater
resources with
environmental
needs.