Trans-Texas Water Program West Central Study Area Phase II Updated Evaluation of Potential Reservoirs in the Guadalupe River Basin

Author HDR Engineering, Inc and Paul Price Associates, Inc, San Antonio River Authority, San Antonio Water System, Edwards Aquifer Authority et al.
Year 1998
Description Phase II of the West Central Texas water plan for the Trans-Texas Water Program, containing updated evaluations of potential reservoirs in the Guadalupe River Basin. Note: This report is included for its historical value but has been replaced by more recent studies.
Report Number Phase II
Publisher HDR Engineering Inc
Location Guadalupe River Basin
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Note:  This report is included for its historical value but has been replaced by more recent studies.

In Phase I of the Trans-Texas Water Program for the West Central Study Area, six potential reservoirs located in the Guadalupe River Basin were evaluated: Cuero Reservoir (G-16), Lindenau Reservoir (G-17) (now referred to as Sandies Creek Reservoir), Guadalupe River Dam No.7 (G-19), Gonzales Reservoir (G-20), Lockhart Reservoir (G-21), and Dilworth Reservoir (G-22)1. The firm yield for each of these reservoirs was estimated using a water availability model in conjunction with a reservoir operation model (G-16 and G-17), adapted from earlier reports by government agencies or consulting firms (G-19, G-20, and G-21), or estimated from the yield of a nearby, similar project (G-22). Some of these potential reservoir projects could not be compared directly because the Phase I yield estimates were not consistent with regards to water rights considerations, period-of-record hydrology, and/or environmental flow requirements. Since the completion of Phase I studies, the Texas Water Development Board, the Texas Natural Resource Conservation Commission, and the Texas Parks and Wildlife Department have recommended new environmental flow requirements to be utilized in water resources planning efforts (Environmental Water Needs Criteria of the Consensus Planning Process, or Consensus Criteria).

The objective of this study is to provide updated evaluations of each of these potential reservoirs in the Guadalupe River Basin, using a consistent methodology so that the firm yield estimates can be compared directly. A seventh project not previously considered in the TransTexas Water Program, Cloptin Crossing Reservoir, is also evaluated herein. The updated evaluations include yields estimated considering (1) upstream and downstream water rights, (2) a consistent period-of-record hydrology, and (3) environmental flow requirements consistent with the Consensus Criteria.

The availability of water to each of the projects was determined using an updated version of the Guadalupe-San Antonio River Basin Modef (GSA Model). The availability of water to each project was evaluated on a standalone basis, independent of the other projects. Implementation of one project could reduce the availability of water to another project; hence. the firm yield estimated for one project cannot be added to that of another project.

The firm yield for each project was evaluated using a single-reservoir firm yield model, SIMDL Y, developed by the Texas Water Development Board and modified for this study. The SIMDL Y model was used to simulate the operation of each reservoir under a uniform demand using inflows estimated by the GSA Model. The SIMDL Y model was modified to enable pass-through flows to satisfy the Consensus Criteria environmental flow requirements, in various combinations with flows passed to meet downstream senior rights and freshwater inflow requirements to the Guadalupe Estuary.

The cost of each project was updated from the Phase I cost estimate to first-quarter 1996 dollars, with additional consideration given to land acquisition and environmental mitigation costs for some projects. The conservation storage capacities, firm yields, total annual costs, and annual unit costs (dollars per acft) are shown in Figure ES-1, along with an objective assessment of the expected effort for permitting and implementation. The firm yields range from 6,339 acft/year for Lockhart Reservoir to 145,448 acft/year for Cuero Reservoir. Annual project costs range from $3,910,000 for Lockhart Reservoir to $53,910,000 for Cuero Reservoir. Annual unit costs range from $320/acft for Gonzales Reservoir to $804/acft for Guadalupe River Dam No.7. The cost for Sandies Creek Reservoir includes facilities for diversion from the Guadalupe River near Cuero and transmission to the reservoir. The costs presented in this report are for raw water at the lake only, and include no additional transmission, treatment, or distribution costs.