Groundwater availability models now available for major Texas aquifers

Major goal achieved with major GAMs
By Dr. Robert E. Mace and Cindy Ridgeway

AUSTIN, TX, Oct. 21, 2004 -- In 2001, the 77th Texas Legislature gave the Texas Water Development Board (TWDB) a challenging task: develop or obtain groundwater availability models (GAMs) for all of the major aquifers of Texas by Oct. 1, 2004. Thanks to the dedication and hard work of TWDB staff, a number of contractors, and numerous stakeholders, we are happy to declare: Mission accomplished!

The Texas Legislature funded the GAM program to develop numerical groundwater flow models to help groundwater conservation districts, regional water planning groups, and others assess current groundwater availability and the effect of pumping and drought on the state's groundwater resources. Unlike previous modeling efforts, new models developed under the GAM program had substantial stakeholder involvement. In some cases, the GAM represented the first modeling work for the area. All of the models, reports, and support data are available at www.twdb.state.tx.us/gam
or by request from the TWDB.

The nine major aquifers required seventeen different models to provide full coverage. TWDB staff developed five of the models: 1) the Hill Country segment of the Trinity aquifer; 2) the northern, and 3) San Antonio segments of the Edwards aquifer; 4) the southern part of the Gulf Coast aquifer; and 5) the Edwards-Trinity (Plateau) and Cenozoic Pecos Alluvium aquifers. TWDB contractors developed eight of the models: 6) the northern and 7) southern part of the Ogallala aquifer; the 8) northern, 9) central, and 10) southern parts of the Carrizo-Wilcox aquifer; 11) the Seymour aquifer; 12) the northern segment of the Trinity aquifer; and 13) the Barton Springs segment of the Edwards aquifer. TWDB staff and a contractor developed a model of 14) the central Gulf Coast aquifer. The TWDB and Harris-Galveston Coastal Subsidence District funded a project for the U.S. Geological Survey to develop a model of 15) the northern part of the Gulf Coast aquifer. El Paso Water Utilities and the U.S. Geological Survey supported the development of models for the 16) Mesilla and 17) Hueco Bolson aquifer. The Edwards Aquifer Authority is developing a new model for the San Antonio segment of the Edwards aquifer that will be available by the end of 2004.

Although the models for the major aquifers are done, the TWDB's work is not completed. Models need to be "living tools" that are updated with new data and refined to better meet stakeholders' needs. In addition, the 77th Texas Legislature also required the TWDB to develop and obtain GAMs for the minor aquifers of the state, a task on which we are already making progress.

Finally, the TWDB supports the models by assisting groundwater conservation districts, regional water planning groups, and other political subdivisions with requests for additional model simulations and interpretation of model results. Although we accomplished a major mission for the GAM program, more work is needed to ensure that Texas has the best possible tools to effectively manage its groundwater resources.

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