Water and Drought Management Plans for the Lower Colorado River Authority

 The Lower Colorado River Authority (LCRA) was established to manage the waters of the lower Colorado River. The district managed by the LCRA is shown in Figure 1.

Figure 1. LCRA Service Area- Highland Lakes


The main functions of the LCRA are: to control floods, to store and distribute the waters of the Colorado River and its tributaries, to provide beneficial uses for the water, and to function as a conservation and reclamation district.

The water policy of the LCRA is stated in the Water Management Plan for the Lower Colorado River Basin. This plan describes the conflicts in the demands for water, and the policies of the LCRA to meet these competing demands during normal operating conditions (other than drought or flood conditions). The key elements of the water management plan are:

During periods of drought, the LCRA operates under the drought management plan. It directs how interruptible water supplies will be curtailed so that firm stored water demands can be fully met throughout the drought. The curtailment policy for interruptible water supplies is presented in Figure 2.

For most periods, the competing water demands (irrigation, instream flows/ bay and estuary needs, and recreation and tourism) can be met. However, problems arise during periods of drought. Irrigation operations have a historical claim to the waters of the Colorado River, and are given priority for the use of interruptible stored water, during periods of drought or otherwise. This priority has been protested by the Sierra Club, which believes that priority should be given to maintaining instream flows in the Colorado River for the benefit of the freshwater ecology and the Matagorda Bay ecosystem. This issue has been pending before the Texas Natural Resource Conservation Commission since 1993 and is currently unresolved.


Figure 2. Conceptual Lakes Management Policy


Irrigation Demands for Rice Production

Rice producers have historic claims to the waters of the Colorado River. The four main rice producers in this region, which are Gulf Coast, Lakeside, Garwood Irrigation Company, and Pierre Ranch, have water rights that are senior in time and superior to LCRA's right to store water in the Highland Lakes (the City of Austin also has senior water rights). For those places with water rights senior to those of LCRA, any inflows to the Highland Lakes that can be diverted for use by these rights must be passed through the Lakes for use downstream. The major water rights holders for water in the lower Colorado River basin are presented in Table 1.


Table 1. Major Water Rights Holders in the Lower Colorado River Basin

Major Water Rights Holders

Amount of Water Right




City of Austin


Gulf Coast






Pierre Ranch




HL&P/LCRA (South Texas Project)




Source: LCRA (1993)


When legislation creating LCRA was first proposed in the Texas Legislature in 1933, promises were made to the rice producers that water stored in the Highland Lakes would be available to serve their needs when the natural flow of the river diminished in dry years. These promises were repeated when LCRA purchased Gulf Coast in 1959 and Lakeside in 1983. Therefore, LCRA currently has a legal obligation to meet the water demands of the irrigation districts.

Also, Texas has one of the largest rice production industries in the country, and the areas served by the Colorado River produce approximately half of the rice produced in the state. The rice production industry generates billions of dollars annually both in domestic and foreign sales of rice. For comparison, the rice production statistics of Texas and the four other largest rice producing states are presented in Table 2.


Table 2. U.S. Rice Production Statistics (1996)





(x 1000)


(1000 cwt)

























Source: USA Rice Federation (1997)


The water supply for the irrigation districts is interruptible, in that the water is supplied by contract and is subject to curtailment during shortages, as discussed above. This is distinguished from firm water supplies, which must remain constant even during a repetition of the critical drought. Firm water supplies are typically supplied to municipalities.

Currently, the vast majority of LCRA's commitments for interruptible water are for the downstream irrigation districts. The annual surface water demand for the irrigation operations is approximately 500,000 acre-feet of water. These irrigation operations pump water from the Colorado River as it is available. During periods of low inflows, the rice farmers request that LCRA release water from storage to make up the deficit. LCRA provides water to the irrigation districts at the rate of 5.25 acre-feet of water per acre irrigated. The amount of water that each irrigation operation may use is presented in Table 3.


Table 3. Conservation Base Acreage or Other Priority Allocation of Interruptible Water



Gulf Coast



Acres x Duty


25,000 x 5.25 = 131,250

50,000 x 5.25 = 262,500

32,000 x 5.25 = 168,000

25,000 with 55,000

Conservation Base or other Priority Allocation

26,000 x 5.25 = 136,500

50,000 x 5.25 = 262,500

32,000 x 5.25 = 168,000

10,476 x 5.25 = 55,000

% of Demand Satisfied by Run-of-River Rights





% of Demand Satisfied by Stored Interruptible Water





Source: LCRA (1993)


Water Demands for Colorado River and Bays and Estuaries

Texas has a complex system of bays and estuaries along its coast that are fed by the freshwater inflows from the rivers of Texas and the surrounding coastal drainage areas. The Texas Parks and Wildlife Department (TPWD) have released recent studies. The following is a quote from a news release about the studies:

The flow of the Colorado River sustains the human community and the river and its banks are also the home for a diverse freshwater ecology. The river then flows into Matagorda Bay where a delicate estuarine ecology is sustained by the zone where the freshwater and the nutrients it contains mix with the brackish sea water. Virtually all finfish and shellfish species in the Gulf of Mexico live at some point in their life cycle in an estuary.

The LCRA conducted a study to determine the freshwater inflow needs of the Matagorda Bay estuarine system. The study is not yet completed but models have been developed and there is now a much better understanding of the effects of variations in the inflows on the estuarine ecology.

Matagorda Bay receives freshwater inflows from three sources: the Colorado River, the Lavaca River, and from the coastal basin surrounding the bay. The flow from the rivers is considered to be at least partially controllable and inflows from the basin are considered to be uncontrollable. Large portions of the river watersheds are not controlled by reservoirs. The relationship between freshwater inflows, the salinity of the estuary and the productivity of the species in the estuary were determined by the study.

For our model the most important flow variables were:


Figure 3. Harvest Performance with Variation in Annual Freshwater Inflow (LCRA, 1997)


This target inflow is distributed through the year as follows:


Table 4. Target Inflows into Matagorda Bay


Colorado River Inflows

(1000 acre-feet)



























Source: LCRA (1997)


Project Objectives and Scope

The purpose of this project was to evaluate the effect of giving priority to maintaining instream flows and meeting bay and estuary needs, as opposed to meeting irrigation demands. In order to achieve these objectives the following steps were taken:


GAMS Model

A GAMS model was developed to determine the effect of prioritizing instream flows vs. irrigation demands. The model was used to determine the amount of water that could be supplied for Austin (firm demand), irrigation (interruptible demand), and flow requirements for streams, bays, and estuaries (firm and interruptible demands). The amount of water that could be supplied was also based on two sets of inflow conditions, which were normal flow conditions (1941-1945), and drought conditions (1947-1951). The model was evaluated for a period of 60 months.

Daily inflow data from 1941-1965 was obtained from the LCRA, which includes the drought of record (1947-1956). Flow data was supplied for flows into Lake Buchanan, Lake LBJ, and Lake Travis. Flow data was also provided for lateral inflow above Lake Travis, lateral inflow between Lake Travis and Austin, lateral inflow between Austin and Smithville, and lateral inflow between Smithville and Columbus. No data was available below Columbus. These daily values were converted into monthly values, and the lateral inflows between Austin and Smithville and Smithville and Columbus were combined into one inflow, representing the lateral inflow below Lake Travis.

Monthly and yearly demands for Austin and irrigation were determined from the Water Management Plan; monthly and yearly demands for stream, bay, and estuary needs were determined from the Water Management Plan and from a draft report by the LCRA for the estimation of freshwater inflow needs into Matagorda Bay. These demands were assumed constant for the 60-month period.

For each flow condition, the objective was to minimize the water deficit for all demands, which can be expressed as:


TD = yearly downstream demand for instream flows and bays and estuaries (1,033,100 acre-feet)

FD(t) = monthly distribution for downstream demand (instream flows/ bay and estuary needs)

RD(t) = releases supplied to downstream

WD = weighting factor for downstream demand

TA = yearly demand for Austin (296,000 acre-feet)

FA(t) = monthly demand distribution for Austin

RA(t) = releases supplied to Austin

WA = weighting factor for Austin demand

TI = yearly demand for irrigation (500,000 acre-feet)

FI(t) = monthly demand distribution for irrigation

RI(t) = releases supplied to irrigation

WI = weighting factor for irrigation demand.

The five Highland Lakes (Lake Buchanan, Inks Lake, Lake LBJ, Lake Marble Falls, and Lake Travis) were assumed to start full, and only Lakes Travis and Buchanan supplied stored water (the other lakes were constant level lakes). Flow balances for each lake during each period were governed by the following equation:


ST(t + 1, L) = storage of lake at next time period

ST(t, L) = storage of lake at time t

Q(t, I) = lateral inflow into lake at time t

R(t, L) = release from lake at time t.

Flow balance constraints were also placed on the system in order to meet water demands. The constraint equations were:


R(t, L5) = release from Travis Lake

RX(t) = excess release from lakes required to meet irrigation and other downstream demands

Q(t, I4) = lateral inflow below Lake Travis

and the other parameters are as previously defined. The two constraint equations shown above were not made into hard constraints (equal) in order to obtain feasible solutions.

Furthermore, bounds were placed on storage capacities of the lakes. Maximum storage capacities for the lakes were set as the actual maximum storage capacity of each lake. For normal operating conditions, the minimum storage of Lake Buchanan and Lake Travis were set as, respectively, 560,000 acre-feet and 840,000 acre-feet (for a total of 1,400,000 acre-feet). A minimum storage of 1,400,000 acre-feet is required so that no curtailment of interruptible water occurs, according to the Water Management Plan. For drought conditions, the minimum storage capacities of Lake Buchanan and Lake Travis were set at, respectively, 130,000 acre-feet and 195,000 acre-feet, for a total of 325,000 acre-feet. A minimum storage of 325,000 acre-feet is required for any interruptible water to be supplied, as described in the Water Management Plan.

Three scenarios were investigated using the GAMS model:


Model Results

 Normal Inflow Conditions

For the normal flow conditions, all of the Austin and irrigation demands were met for all periods. The instream flow/ bay and estuary demands were met for 16 months, and for the remaining time, only the critical inflow was supplied. The supply and demand curve for the normal inflow conditions is shown in Figure 4.



Drought Conditions - Meet Irrigation Demands

For the first drought condition, the irrigation demands were met, but the instream/ bay and estuary flow requirements were seldom above the critical value. The firm demands of Austin were met for all periods. The results of this condition are shown in Figure 5.



Drought Conditions - Meet Instream/ Bay and Estuary Demands

For the second drought condition, the instream/ bay and estuary flow requirements were met for the first 23 months, but afterwards, only the critical flow was supplied. No water was available to meet the irrigation demand. Again, Austin's demands were met for all periods. These results are shown in Figure 6.



Releases from Buchanan and Travis Lakes

In the initial periods, the releases from Lake Travis supply all of the downstream demands, while Lake Buchanan releases only enough to remain at or below its maximum level. After Lake Travis reaches its minimum lake storage level, the downstream demands are met by releases from Lake Buchanan. These trends are shown in Figures 7 and 8. The maximum releases are during the summer months (low river flows).



Water Storage in Buchanan and Travis Lakes

The storage of Lake Travis drops in the initial periods, since the downstream water demand is met by Lake Travis. After Lake Travis reaches its minimum storage, the demands are met by Lake Buchanan and its storage begins to drop. These trends are shown in Figures 9 and 10.





 Inflow Data

.GAMS Model

 Rice Irrigation vs. Instream/ Bay and Estuary Demands


Copy of the GAMS file used for modeling: model.html


Lower Colorado River Authority, Water Management Plan for the Lower Colorado River Authority, June 29, 1993.

Lower Colorado River Authority (Q. Martin), "Drop by Drop: The Life Cycle of the Lower Colorado River", LCRA Corporate Communications, 1997.

Lower Colorado River Authority, "Estimation of Freshwater Inflow Needs", Draft Report, 1997.

USA Rice Federation, "U.S. Rice Production Statistics - 1996", http://www.usarice.com/domestic/recipes/stats.htm , 1997.




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