SPRINGFLOW TRENDS IN THE EDWARDS AQUIFER - LONG TERM URBANIZATION EFFECTS

The extent of groundwater recharge and the natural and urban pathways by which recharge occur differ between groundwater systems and make recharge difficult to understand and quantify. However, quantifying recharge is crucial for determining sustainability and establishing reasonable water-use metrics. The karstic Edwards Aquifer is the primary water source for much of central Texas, supplying water to nearly two million urban residents. This study of the Barton, Comal, and San Marcos spring systems, which are the natural discharge from the aquifer, estimates recharge and shows the effects of urbanization by relating precipitation, springflow, and pumping data over time periods of up to 80 years, dependent on available data for each spring system. Cumulative springflows were normalized against cumulative precipitation at nearby weather stations. The individual spring analyses are related with a correlation coefficient found using cross correlation. The relationship between springflow and precipitation over time shows distinctly different trends for each spring system that correlate to water usage along different parts of the Edwards Aquifer and urbanization over aquifer recharge and contributing zones. Comal Springs, near San Antonio, show decreasing relative springflow over time due to extensive pumping. Barton Springs, near Austin, show an overall increase in springflow despite increased pumping. San Marcos Springs first show a decrease in springflow that is less substantial than for Comal Springs, but which later reverses.