Groundwater Availability in the Carrizo-Wilcox Aquifer in Central Texas: Numerical Simulations of 2000 through 2050 Withdrawal

Between 1951 and 1996, groundwater pumpage from the Carrizo-Wilcox aquifer, one of Texas' major aquifer systems, increased in the area between the Colorado and Brazos Rivers from approximately 10,600 to 37,900 acre-ft/yr, primarily as a result of mining needs. Continued (and possibly greatly accelerated) growth in groundwater demand for a variety of uses is expected through the year 2050. To assess the general availability of groundwater in the Carrizo- Wilcox aquifer between the Colorado and Brazos Rivers, five groundwater-development scenarios were simulated according to a finite-difference numerical model developed for this study. Simulated water-level change was related to the amount of groundwater withdrawal, its concentration in an area, hydrogeologic properties, and model characteristics. Actual locations and future rates of pumping of water wells, needless to say, might differ from what were simulated. Model calibration by means of historical water-level data had a mean absolute error of 32 ft. On the basis of the calibrated model, groundwater in the Carrizo-Wilcox aquifer in the study area is predicted to remain available to meet specified withdrawal scenarios through the year 2050 and additional demands after 2050. Except for near the centers of simulated pumping areas, the aquifer units are forecast to remain fully saturated, and simulated water-level decline reflects mainly a change in artesian or pressure head. Simulated rate of decline of hydraulic head, however, is constant through the year 2050, and continued drawdown should be expected as long as pumping remains well above historical rates. Availability of groundwater is also determined by pumping lift, drilling depth, transportation to point of use, and property access, as well as other criteria.