ABSTRACT

Groundwater tracing in the Barton Springs Edwards Aquifer is providing new insight on groundwater flow directions and travel rates from major contributing watersheds.

Results demonstrate that the western portion of the Recharge Zone in Barton and Williamson Creeks contributes flow to Cold Springs and other unidentified springs on the Colorado River. Remaining portions of the Recharge Zone within these watersheds generally support the Main outlet of Barton Springs and Upper Barton Springs. Groundwater recharging in the Slaughter, Bear, Little Bear, and Onion watersheds flows east towards a potentiometric trough that runs parallel east of the Recharge Zone and then travels northeast to Barton Springs. The three major preferential groundwater-flow paths appear to be strongly influenced by geological fault trends.

Groundwater flow rates vary with proximity and connection to major preferential groundwater-flow paths and groundwater-flow conditions. Under moderate and high groundwater-flow conditions, where Barton Springs flows more than 35 cubic feet per second, groundwater generally travels about 4 to 7 miles per day along the major groundwater-flow paths, but only about 1 mile per day from the western side of the Recharge Zone to the eastern side. During low groundwater-flow, groundwater moves at rates of about 1 mile per day to 0.6 mile per day across the aquifer.

Rapid travel rates suggest that Barton Springs is closer hydraulically to more distant watersheds than was previously believed. Results provide information to improve wellhead protection, anticipate the fate of hazardous material spills, assist in developing monitoring strategies, prioritize purchases of water quality/ quantity protection lands, and evaluate sites for recharge enhancement.