RECHARGE ESTIMATION IN THE TRANS-PECOS BOLSON AQUIFERS, TEXAS

In the water-stressed region of Trans-Pecos, West Texas, quantifying recharge to the basin aquifers is important for the long term sustainability of these resources and the communities who are dependent upon them. Previous research has attempted to estimate recharge in the Trans-Pecos region using the Maxey-Eakin and modified Maxey-Eakin methods, storm runoff and redistributed runoff models- these result in a range of estimated recharge between ~10,500 ac-ft/yr (12.95 million cubic meters/yr) and ~135,500 ac-ft/yr (167 million cubic meters/yr). Field data from the region contradicts assumptions made in these methods; in arid regions it is assumed that recharge occurs only in the mountains and along the mountain fronts and not on the basin floors, however our research has detected CFCs in basin groundwater and decadal scale changes in water chemistry that indicate the presence of young (<70 year old) recharge. In light of these observations we chose a different approach to estimating recharge in these basins. INFIL 3.0, a USGS computer program, uses temporally and spatially distributed data provided by the user to calculate daily net infiltration beneath the root zone. Collecting data from 1950 to 2010, we use INFIL 3.0 to estimate recharge to the basin aquifers. Preliminary findings indicate that recharge estimates using the INFIL model are higher than those utilized in the current groundwater availability models (25,367 ac-ft/yr (~31.3 million cubic meters/yr)). We compare our results using INFIL model to the estimates made with the other methods and discuss the benefits and drawbacks to the use of each for estimating recharge in the Trans-Pecos region.