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TRANS-TEXAS WATER PROGRAM SOUTHEAST AREA System Operation of Surface Water Supply Sources in the Houston Area April 1998 Sabine River Authority of Texas Lower Neches Valley Authority San Jacinto River Authority City of Houston Brazos River Authority Texas Water Development Board Preface This document is a product of the Trans-Texas Water Program: Southeast Area. The program's mission is to propose economically and environmentally beneficial methods to meet water needs in Texas for the long tenn. The program's four planning areas are the Southeast Area. which includes the Houston-Galveston metropolitan area. the South-Central Area (including Corpus Christi). the West­ Central Area (including San Antonio). and the North-Central Area (including Austin). The Southeast Area of the Trans-Texas Water Program draws perspectivesfonn many organizations and citizens. The Policy Management Committee and its Southeast Area subcommittee guide the program; the Southeast Area Technical Advisory Committee serves as program advisor. Local sponsors are the Sabine River Authority of Texas. the Lower Neches Valley Authority. the San Jacinto River Authority. the City of Houston and the Brazos River Authority. The Texas Water Development Board is the lead Texas agency for the Trans-Texas Water Program. The Board. along with the Texas Natural Resource Conservation Commission. the Texas Parks & Wildlife Department and the Texas General Land Office. set goals and policies for the program pertaining to water resources management and are members of the Policy Management Committee. Brown & Root and Freese & Nichols are consulting engineers for the Trans-Texas Water Program: Southeast Area. Blackburn & Carter and Ekistics provide technical support. This document was written l1y: Freese and Nichols, Inc. Thomas C. Gooch, P.E. Jon S. Albright Thomas C. Gooch, P.E. Trans-Texas Water Program Page; Contents Contents Executive Summary . • . • . • . .• i 1. Introduction . • . • . • . • . •. 1-1 2. Existing Facilities •...........•...........................•.......•....•. 2-1 3. Hydrologic Data .•.....••....•...........•............•..•....•...•..... 3-1 4. Prior Rights Downstream from Lake Livingston ...........•...........•..... 4-1 s. Return Flows ...........•..•..•......•...........•....•...•...•...•....• 5-1 6. The Computer Model .....•....•............•.....•.......••...........•• 6-1 7. Lake Houston and Lake Conroe .....................•....•....•..•...•..•. 7-1 8. Lake Livingston and the Wallisville Salt Water Barrier. • . • . • . .. 8-1 9. Four-Reservoir System Operation ........•...........•.......•....•...•... 9-1 10. Realistic Operating Conditions ....•......•.....•.....•.........•..•...... 10-1 11. Water Rights for System Operation •......•................•.......•...... 11-1 12. Environmental Review of Proposed System Operations. • . .. 12-1 13. Dredging to Control Loss of Yield Due to Siltation. .•. .•. • . .•. •. .•. 13-1 14. Summary of Findings .......•....•...................•...•...•........•. 14-1 Appendix A References AppendixB Area and Capacity Data AppendixC Runoff Data AppendixD Net Evaporation Data AppendixE Operation Studies AppendixF Comments Pageii Southeast Area System Operation ofSurface Water Supply Sources in the Houston Area Figures Figure 2-1: Lake Conroe, Lake Houston, and Lake Livingston System Operation ......• 2-1 Figure 5-1: Lake Houston Return Flow (Five-Year Running Average) ....•.......•.... 5-2 Figure 5-2: Upper Trinity Annual Return Flows .........•......................... 5-2 Figure 5-3: Upper Basin Annual Return Flow (Five-Year Running Average) ...•...•... 5-3 Figure 6-1: Operation Model Schematic .................•.....•...•..•...•.•.•... 6-1 Figure 7-1: Effect of Minimum Lake Houston Content on System Yield for Conroe and Lake Livingston ..........•.......•................•...... 7-3 Figure 7-2: Effect of Local Demand at Lake Conroe on System Yield for Lake Conroe and Lake Houston. • . • . • . • .. 7-3 Figure 12-1: Lake Conroe Elevations ..............•.......•...........•...•...•• 12-3 Figure 12-2: Lake Houston Elevations. • . • . • . • . • . • . •• 12-3 Trans-Texas Water Program Page iii Contents Tables Table 2.1: Key Data for the Dams and Reservoirs .........•..••.•......•••...•.•.•. 2-2 Table 2.2: Summary of Water Rights Associated with the Four ..........•.•......•..• 2-2 Reservoirs (Acre-Feet/Y ear) Table 4.1: Lake Livingston "Fixed Right" Obligations ••..•.••••..•.•••.•.•••.•••••• 4-2 Table 5.1: Minimum Recorded Daily Average Flows in the Trinity River Near Crockett, Water Years 1990 through 1996 .••••••........•.•••.••••• 5-4 Table 7.1: San Jacinto River Basin Runoff and Spills During the Critical Drought with Independent Lake Operation (Amounts in Acre-Feet) .••.•••••. 7-4 Table 7.2: Effect of the Minimum Lake Houston Water Level on System Yield for Lake Conroe and Lake Houston •.•.•••....•.•.•••.••••.•••.•••• 7-5 Table 7.3: Impact ofthe Local Demand at Lake Conroe on the System Yield for Lake Conroe and Lake Houston •.....••••.••.••••.••.•••.•••••• 7-5 Table 9.1: Comparative Yields of the Four-Reservoir System and the Combined Two-Reservoir Systems .•.•..••.••.••.••••••.•...•...••••.••. 9-2 Table 13.1: Key parameters of Siltation Rates and Related Decreases in Firm Yield at Lake Conroe and Lake Livingston ..........•..••••..•.•.••.•.•...•• 13-2 Table 14.1: Summary of Firm Yields with Operation at Permitted Diversion Rates (Acre-Feet/Year) ••...........•....••.••...••••••••••• 14-3 Page iv Southeast Area 1. Introduction In cases where a surface water system has more obtained without encountering unacceptable than one source of supply, it is often possible to secondary impacts. To an extent, that is true in coordinate operation of the overall system in a the San Jacinto River Basin, where part of the way that will produce more yield than could be theoretically available yield could only be obtained if the various sources were each operated obtained by drawing Lake Houston down to independently. One of the tasks of Phase 2 of the undesirable levels and keeping it that way for Trans-Texas Water Program investigations is to extended periods of time. analyze the potential gain from coordinated system operation of Lake Houston, Lake Conroe, In this study, the potential yields and system Lake Livingston and the Wallisville salt water operation gains will be examined in two ways. barrier. First, they will be evaluated assuming that maximum system yield is the primary goal and System operation is basically a familiar concept in that all other considerations are secondary. Then, the Houston area. Lake Houston and Lake Conroe they will be analyzed a second time, based on a set have now been functioning to some degree as a of assumptions reflecting some of the more system for more than 20 years, and the value of important practical limitations on factors such as that mode of operation is well established. It has rates of withdrawal and minimum lake levels. also been generally understood that Lake Livingston and the Wallisville barrier will function as a system when construction of the barrier is finished. The goals of this study are (a) to review the system operation methods that are applicable in this instance, (b) to explain briefly why they lead to increased yields, and (c) to evaluate how much yield can potentially be gained by their effective use. One common feature of system operation is that it often involves alternately taking larger amounts cf water from each source than would normally be taken if they were operating individually. This sometimes leads to greater capital costs for diversion, transmission and treatment facilities, and it can also cause greater fluctuations in lake levels. In some cases, there may be practical limits 10 the amounts of increased use that can be Trans-Texas Water Program Page 1-1 2. Existing Facilities The existing surface water supply reservoirs The water rights for these projects are summarized involved in this study consist of Lake Houston, in Table 2.2. The combined sum of the rights is Lake Conroe and Lake Livingston. Although it 1,668,600 acre-feet per year. Approximately 70.4 will contribute no additional conservation storage percent of the total appropriations belong to the as such, the Wallisville salt water barrier will also City of Houston, which has the right to divert be an important element when it is placed in 1,175,467 acre-feet per year and holds some of the operation. Figure 2-1 is a map showing the rights at each of the impoundments. The Trinity locations of the system components. Table 2.1 is River Authority owns rights amounting to 403,200 a summary of key characteristics of the three acre-feet per year, or 24.2 percent of the total. storage reservoirs and the barrier. The San Jacinto River Authority owns run-of-the­ river rights to 88,333 acre-feet per year, or 5.3 Lake Houston was built in 1954. Lake Livingstcn percent. Riceland Properties and Roy A. Seabers was completed in 1969, and Lake Conroe in 1973. own a small senior run-of-the-river right (1,600 The Wallisville barrier is expected to begin acre-feet per year, or 0.1 percent). operation in 1997. The City of Houston owns and operates Lake Houston. Lake Livingston was developed by Houston in cooperation with the Trinity River Authority, which operates that facility. The San Jacinto River Authority operates Lake Conroe. The Wallisville structure will be (I) numbers in parentheses indicate references operated by the U. S. Army Corps of Engineers. listed in Appendix A. The area and capacity information

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