Groundwater Availability Models
By Ric Jensen
People who manage groundwater now have a better idea of the amount of water stored in aquifers throughout much of Texas, thanks to an ongoing computer modeling effort led by the Texas Water Development Board (TWDB).
In 2001, the Texas Legislature passed legislation to enable TWDB to develop and implement the groundwater availability modeling (GAM) program as part of Senate Bill 1 (SB1) planning activities. The Legislature required TWDB to complete GAM modeling for the nine major aquifers of Texas by October 2004. In addition, SB1 mandates that groundwater conservation districts must use GAM data to develop groundwater management plans.
Through the GAM program, TWDB is developing and testing state-of-the-art groundwater models that will help users better understand groundwater processes.
The goal is to provide timely and reliable data about groundwater quantity in specific aquifers that can be used to accurately estimate aquifer storage and the effects of long-term pumping on water yields. GAM methods can also help evaluate the merits of proposed groundwater management strategies.
In basic terms, a GAM model represents factors that influence the volume of water in an aquifer, including geology, hydrology, recharge rates, the volume of water pumped and interactions between ground and surface water. Steps involved in creating a GAM include developing the concept of flow for the aquifer; collecting and inputting data on aquifer characteristics, pumping and water levels; and testing the model to see that results can be accurately calibrated and verified. The model can then be applied to assess current conditions and to examine how future water use can affect aquifer levels.
TWDB is working with GAMs for several regions of Texas. The Board is now developing GAM tools for parts of the Trinity Aquifer, the Gulf Coast aquifer and the Edwards-Trinity Aquifer. Portions of the Ogallala Aquifer, the Barton Springs portion of the Edwards Aquifer and the Gulf Coast Aquifer are being modeled as part of SB1 studies. The United States Geological Survey is developing a GAM for the Hueco Bolson Aquifer in El Paso and part of the Gulf Coast Aquifer, while the Edwards Aquifer Authority is creating a GAM for the Edwards Aquifer.
Scientists at universities throughout Texas are studying, evaluating and applying GAM models. Some examples are shown below:
- David Maidment and graduate students at the Center for Water Research at the University of Texas are developing a groundwater data model for the ArcGIS geographic information system that will represent data simulated by GAMs.
- Researcher Zhuping Sheng of the Texas Agricultural Experiment Station in El Paso is assisting in efforts to model the Hueco Bolson aquifer and Far West Texas Bolson and Igneous aquifers.
- Researcher Alan Dutton of the Bureau of Economic Geology at the University of Texas is working with the Panhandle Regional Water Planning Group, Freese and Nichols, Inc. and TWDB to develop GAM tools for the northern part of Ogallala Aquifer.
- Rick Hay, a researcher at Texas A&M University-Corpus Christi, recently participated in efforts to estimate water availability in the Gulf Coast Aquifer. He is now working to incorporate recharge data into a GAM for the region.
- Kevin Urbanczyk, a researcher at Sul Ross State University in Alpine, is developing GAM simulations for the Bolson and Igneous aquifers in Far West Texas.
For more information visit the TWDB Web site, http://www.twdb.state.tx.us/gam.
