ROLE OF KARST STUDIES IN GROUNDWATER PROTECTION MANAGEMENT OF THE BARTON SPRINGS SEGMENT OF THE EDWARDS AQUIFER IN AUSTIN TEXAS

The City of Austin conducts karst studies to help protect water supplies, Barton Springs, endangered species and rare cave species related to the Edwards Aquifer. Justification to protect the aquifer includes: a federally-designated sole source water supply for an estimated 60,000 people, the 1996 listing of the aquatic Barton Springs salamander as endangered, the 1996 Balcones Canyonlands Conservation Plan which includes protection of rare and endangered karst species in 62 caves, and an iconic spring-fed swimming facility visited by over 500,000 people annually in the heart of Austin. Karst studies, including recharge studies, groundwater tracing, detailed geological mapping, and cave mapping played vital roles in preserving groundwater resources in rapidly urbanizing Austin. Recharge studies include measurements of creek flow loss as well as using site scaled rainfall budget analysis with eddy covariance evapotranspiration tower and flumes measuring runoff into sinkholes. Groundwater flow and groundwater basins have been studied directly using over 40 aquifer-wide groundwater traces as far as 20 miles from the discharge springs. Some traces were conducted from sites where accidental spills could occur to help prepare for actual spills and identify downgradient sites for monitoring. Shorter traces are used to examine transport through soils and source areas to cave drips and streams. These studies revealed the importance of upland karst recharge areas and stream channels farther away from discharge springs, and were used in the decision of which lands should be acquired and preserved. Refinement of previous geologic mapping helps identify areas that are subject to water quality protection regulations. Cleaning out decades old trash from caves improves recharge to the aquifer and mapping caves has resulted in greater understanding of the significance of caves to recharge and rare species. These studies have help foster understanding and protection of this sensitive and critical resource. Examples of projects utilizing these studies include Davis Lane and State Highway 45 Southwest, both adjacent to protected cave preserve sites, proposed large-scale wastewater irrigation sites, as well as proposed urban development near Barton Springs.