Abstract

Recharge is important for evaluating groundwater sustainability, and efficiently managing water supplies. In arid areas, especially in areas where the amount of aquifer production outweighs aquifer replenishment, it can be extremely important to quantify recharge and to spatially identify recharge distribution. Field sampling with a Guelph Permeameter helped identify specific recharge areas and the use of the Soil Water Assessment Tool (SWAT) provided meaningful recharge rates for an arid basin in southwest Texas. SWAT modeling for Wild Horse Basin generated an annual amount of recharge into the basin aquifer that was subsequently used in two transient MODFLOW simulations, one with the recharge distributed according to the sediment unit location (distributed zonation), and one with the recharge concentrated in cells adjacent to the front of the mountain chains surrounding the basin (mountain-front zonation). When comparing the results of the two recharge distributions on individual well hydrographs to historic data, mountain-front recharge appeared to improve model calibration efforts. This study indicates that recharge in arid basins cannot be determined solely by calibrating numerical models because it is so small that other simulation errors overwhelm reasonable differences. However, the location of the distribution of recharge appeared significant when calibrating individual well hydrographs. A deterministic analytical model like SWAT is a good way to estimate recharge in arid basins and create meaningful input parameters for numerical models like MODFLOW. MODFLOW was in turn able to evaluate the SWAT recharge estimations for Wild Horse Basin with Calibration and sensitivity analyses.