EVALUATION OF STATISTICALLY-DESIGNED SURVEY METHODS FOR DETERMINING KARST FEATURE DENSITY IN A PORTION OF THE EDWARDS AQUIFER RECHARGE ZONE

Karst inventories provide essential information and data that are used in understanding and evaluating an area’s hydrogeologic connection to local and regional flow systems, as well as its environmental and ecological sensitivity. As urban development expands in karst regions, such as the Edwards Plateau in central Texas, USA, the vulnerability of karstic groundwater systems to development-related impacts and contaminants is rapidly increasing. Identifying and classifying karst features during geological assessments, as mandated by the State of Texas to protect the Edwards Aquifer recharge zone, requires full-coverage visual surveys that are potentially subjective, depending on the experience of each person performing a survey. Additionally, access to land in the recharge zone is often limited prior to a development being planned and approved. In light of this, it would be useful for planning, water conservation, and management purposes to have independent methods for identifying and prioritizing the most sensitive recharge areas for visual surveys when time and resources are limited as well as provide a means for assessing the accuracy of surveys.

The overarching question motivating this research is: can relationships be identified between predictor variables and karst feature density that would allow estimation of density without physical surveys? Relationships between independent factors (e.g., surface geology, soil depth, and distance to the nearest flow path) and karst feature density are well-documented in many regions, but the degree to which they affect karst feature density and distribution in the Edwards Aquifer has not been quantified. Utilizing the 17 km², undisturbed Freeman Center of Texas State University in San Marcos, Texas, the specific objective of this study is to quantify potential correlations between karst feature density and surface geology and a variety of soil and geomorphic factors on the recharge zone for the Edwards Aquifer.

Although statistical analyses are ongoing, preliminary results have been inconclusive on whether any geologic or geomorphic variables are significant in explaining the variability in karst feature density.