) Estimates of recharge in two arid basin aquifers, Red Light Draw and Eagle Flats (Texas, USA): a model of spatially variable net infiltration and its implications

Methods of estimating recharge in arid basin aquifers (such as the 1% rule, Maxey-Eakin method, storm-runoff infiltration and others) overlook the potential contribution of direct recharge on the basin floors. In the Trans-Pecos region of West Texas, USA, this has resulted in potential recharge and solute flux to basin aquifers being ignored. Observed trends in groundwater nitrate (NO3-) concentrations and the presence of young (<70 year old) water in the basins indicate that recharge is occurring through the basin floors. A spatially variable net infiltration model (INFIL 3.0.1) was used to estimate the volume and spatial distribution of potential recharge to two basins: Red Light Draw and Eagle Flats. The INFIL model provides insight into the mechanisms by which recharge and solute flux occurs in arid basin systems. This method demonstrated that recharge is widespread; it is not limited to the mountainous areas and mountain-front recharge mechanisms, and up to 15% of total potential recharge in these basins occurs across widespread areas of the basin floors. Models such as this should improve scientific understanding and sustainable management of arid basin aquifers in Texas and elsewhere.