B. J. Hibbs

Reanalysis of Anecdotal Models of Recharge in Southwestern Alluvial Basins

The identification of recharge areas in arid and semi-arid basin environments presents challenges to the hydrogeological interpreter. This is due to the spatial and temporal variability of recharge in desert environments. Quantifying recharge amounts is even more difficult, due to the complexity and uncertainty of parameters used in the evaluation of recharge processes. Understanding recharge in desert systems is key; not only because there is a need to estimate natural quantities of recharge for sustainability purposes, but also due to the common practice of siting waste disposal sites and landfills on desert basin floors where it is often assumed that recharge is negligible. Many anecdotal models of recharge in desert basins are used; for the purposes of formulating rules for aquifer development, for developing policy regarding waste disposal, and for setting model boundary conditions in digital models. Frequently these anecdotal models are slightly to highly inaccurate. The purpose of this paper is to present our experiences during the last 25 years in evaluating recharge in the basin and range systems across the Southwestern United States, with particular focus on desert basins in Trans-Pecos Texas and Eastern New Mexico. Herein we present multi-year studies using environmental isotopes for groundwater age dating and mixing analysis, hydrogeological evaluation using threedimensional well control data, and application of quantitative models. Our results establish the importance of using complementary and multiple techniques to evaluate and quantify recharge in desert basins, while disproving several accepted models of recharge in some important southwestern aquifer systems.