RECHARGE TO ARID AND SEMI-ARID GROUNDWATER BASINS

Populations in the south-central United States more than doubled in past 50 years and are expected to increase by an additional 50 percent in the next 50 years. This growth will add additional stress on water resources which, in many cases, are already stressed. These expanding urban populations need to identify additional water resources where existing water resources are expected to be insufficient to meet the increasing demands. Growing urban areas are increasingly targeting environments typically classified as arid and semi-arid for additional water resources even though the water resources of these areas are limited.

To assist in this planning process, recharge and the water budget of groundwater basins in semi-arid environments are estimated by using physical and chemical field measurements. Analysis of these measurements for some areas in central and west Texas indicates that (i) groundwater basins are not necessarily coincident with surface watershed boundaries and (ii) recharge rates become negligible when precipitation is less than some minimum threshold. These results suggest that groundwater resources in arid and semi-arid environments may not be reliable during periods of prolonged drought especially for karst aquifers with high transmissive properties, but limited storage capacity.