INVESTIGATING THE WATER RESOURCES OF THE WESTERN EDWARDS-TRINITY AQUIFER, TEXAS

A comprehensive assessment of the hydrogeology of the western Edwards-Trinity Aquifer was undertaken to provide a quantitative water budget analysis. River discharge measurements were used to calculate recharge for the area that contributes to baseflow in the river. This analysis provided the fraction of river discharge that is attributed to baseflow. Recharge values were then correlated with precipitation in the study area. This correlation indicates that recharge becomes negligible when precipitation decreases below about 16-18 inch/year. Knowing the correlation between precipitation and recharge allowed prediction of how recharge in the study area will vary during periods when precipitation is less than the long-term average. Recharge to the Edwards-Trinity Aquifer varied from 2.14 inch/year in the eastern side of the study area where average annual precipitation is as high as 33 inch/year to 0.34 inch/year in the west where average annual precipitation is 15 inch/year. The percentage of precipitation that recharged varied from 7 percent in the east to less than 2 percent in the western side of the study area. This analysis also indicated that groundwater basins in the study area extend farther north than their overlying surface watersheds, evidence of groundwater piracy.