Evaluating the Hydrologic Connection of the Blanco River and Barton Springs using Discharge and Geochemical Data

Barton Springs issues from the karstic Edwards Aquifer in drought-prone central Texas. The Edwards Aquifer provides public water supply and springflow for endangered species and recreation. Delineating source areas and flow paths in karst aquifers is important for understanding water availability. Historic data and recent dye-trace studies indicate that the Blanco River is the hydrologic divide between the Barton Springs and San Antonio segments of the Edwards Aquifer during dry hydrologic conditions, contributing recharge to both segments and their associated springs, such as Barton and San Marcos Springs. This study evaluated historical discharge and geochemical data to characterize and quantify the hydrologic connection between recharge from the Blanco River and Barton Springs, the main discharge point for the Barton Springs segment. Hydrologic data, including stream discharge, spring discharge, and stream recharge estimates (1987 through 2012) during extremely dry hydrologic time periods, when it is inferred that there was no recharge occurring internally within the Barton Springs watershed, were identified and evaluated. A hydrologic connection is considered to exist when estimated recharge from the Blanco River increases and there is a time-lagged increase in discharge and gage height at Barton Springs. Sixteen events with increased recharge from the Blanco River with an associated, time-lagged increased in discharge at Barton Springs were identified. The average increase in recharge from the Blanco River for these 16 events was 2.7 ft3 /s (range 0.2 to 13.8 cfs), while the average increase in discharge at Barton Springs was 1.4 ft3 /s (range 1-2 cfs). The data indicate that the increase in Barton Springs discharge is likely attributable to Blanco River recharge for 4 of the 16 events, and potentially attributable for another 6 events. The 6 remaining events of increased discharge at Barton Springs are within instrument uncertainty and cannot be attributed with confidence to an increase in recharge from th