CONCEPTS OF GROUND-WATER RECHARGE IN THE TRANS-PECOS REGION, TEXAS

Typically recharge to ground-water systems in the arid southwest increases with elevation as a result of increase precipitation and decrease in evaporation. This may be the case for Basin and Range topography where mountain ranges receive winter accumulations of snow, but different processes occur in arid lands (Trans-Pecos Region) lacking snow-pack accumulation. Precipitation in the Trans-Pecos region ranges from 20 to 50 centimeters per year, mostly occurring as spring and summer thunderstorms. Average daily evaporation is typically greater than precipitation, year round, and ranges from 170 to 260 centimeters per year. Typically, researchers have assumed the recharge in the Tran-Pecos Region is approximately one percent of the annual precipitation, although results of this study suggests recharge, locally, can be less than one percent to over 5 percent of the annual precipitation depending on hydrogeologic and watershed characteristics. In the Trans-Pecos Region, the rate of recharge does not necessarily increase with elevation, and is more directly related to watershed characteristics, surficial geology, and feasibility of surface water to enter the ground-water system. Age-dating of ground water, water-level data, and ground-water quality data can be combined with results of watershed analysis to provide reasonable estimates of rates and distribution of ground-water recharge.