THE EDWARDS AQUIFER

The Edwards Aquifer supplies water for over 2 million people, agriculture, and industry; it is in one of the fastest growing regions of the USA. The general aspects of the aquifer have been recognized for over a century - losing streams are the largest source of recharge; most discharge is to a few major springs; and the Edwards Limestone (and equivalent formations) host the aquifer. However, models of the aquifer, its recharge and discharge, and aquifer boundaries have had to be revised substantially as new data have become available. Direct measurements of evapotranspiration and precipitation in recharge areas show that direct recharge is significant. Losing stream recharge is concentrated in limited sites and stream loss calculation is more complex than formerly assumed. Discharge at Cold Springs, at Los Moras Springs, and to Leona River alluvium has been found to be important. Groundwater divides shift and may disappear during droughts. Pumping and tracer tests have demonstrate that the underlying Glen Rose and, in some places, the overlying Buda Limestone and Austin Chalk are part of the aquifer. Additional recharge from the Trinity Aquifer, small ungauged creeks that flow over the recharge area, and urbanization must be considered. Models required for groundwater management must account for our evolving understanding of the Edwards Aquifer system. These models must also be able to address future issues of increasing water demands, the effects of climate change and urbanization, new legal constraints, the requirements of aquifer ecosystems, new sources and types of contamination, and new water technologies.