Groundwater Availability Model for the Central Part of the Carrizo-Wilcox Aquifer in Texas

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A quasi-three-dimensional, numerical model of the occurrence and movement of groundwater in the central part of the Carrizo-Wilcox aquifer in Texas was developed to help estimate groundwater availability and water levels in response to potential droughts and future pumping, including new well fields. Formations of the Paleocene-Eocene-age Wilcox Group, along with the overlying Carrizo Formation, make up a major aquifer system in Texas. This model is one of three overlapping models of the Carrizo-Wilcox aquifer in Texas developed as part of a Texas Groundwater Availability Modeling (GAM) program. Groundwater withdrawal from the central part of the Carrizo-Wilcox aquifer accounted for approximately 36 percent of all pumping from the aquifer in 2000. The model is based on data on geological structure and depositional setting of the aquifer, hydrological properties, water-use survey estimates of historical and future groundwater withdrawals, and base flow of rivers and streams. New insights into how the downdip circulation of freshwater is affected by fault zones and a deep-basin geopressured zone are based on maps of total dissolved solids and equivalent water levels from the outcrop to depths of more than 10,000 ft. In addition, results of field studies using "environmental" tracers yielded regional estimates of recharge rates that broadly match estimates from previous models.


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