Flow Systems of the Edwards Aquifer Barton Springs Segment Interpreted from Tracing and Associated Field Studies

Dye tracing and field studies conducted from 1996 to 2002 by the Barton Springs/ Edwards Aquifer Conservation District and City of Austin have delineated the groundwater basins and flow routes of the Barton Springs segment of the Edwards aquifer. The methodologies used included: 1) detection of injected tracers at springs and wells; 2) evaluation of potentiometric troughs and mounds; 3) distinguishing groundwater basins by their discharge sites; 4) offset dye arrival times and peaks at different spring discharge outlets; 5) spring water chemistry as an indication of source area; 6) geological structure and hydrostratigraphic unit influences on groundwater flow; and 7) observations of groundwater flow routes from within caves. These approaches and their analysis have refined the understanding of the Barton Springs flow system. Three groundwater basins have been delineated (Cold, Sunset Valley, Manchaca) in the Barton Springs segment, each with a network of flow routes. Most of the flow within the Barton Springs segment occurs along the preferential flow routes, which are strongly influenced by faulting. Groundwater flow in the Manchaca basin follows two principal flow routes, the Manchaca flow route and the Saline-Line flow route. Groundwater flow within the Sunset Valley groundwater basin converges along the Sunset Valley flow route. The Cold Springs groundwater basin discharges to Cold and other springs along the Colorado River. The four major Barton Springs outlets (Main, Eliza, Old Mill, and Upper) have distinctive concentrations of chloride and sulfate that reflect different water quality of the major source water flow routes. Upper Barton Springs is relatively low in chloride and sulfate, which increase along a different slope than in the other three Barton Springs. Main, Eliza, and particularly Old Mill Springs receive chloride and sulfate-enriched waters from the Saline-Line flow route. The 1 contribution of the Saline-Line flow route to Barton Springs is about 10 to 20% of the USGS-reported Barton Spring