Documentation of a recharge-discharge water budget and main-streambed recharge volumes, and fundamental evaluation of groundwater tracer studies for the Barton Springs segment of the Edwards Aquifer

Raymond Maurice Slade Jr.

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Data and information reveal that the Edwards Aquifer between Lady Bird Lake (the Colorado River) in Austin, Texas and the "groundwater divide" near Kyle, Texas discharges to 2 major springs: Barton Springs and Cold and Deep Eddy Springs. The long-term mean discharges for the springs are 51 cubic feet per second and 5.5 cubic feet per second, respectively. The source for Cold and Deep Eddy Springs probably represents Dry Creek in the Rollingwood, Texas area and a small amount of recharge water from Barton Creek. Additional springflow, which periodically discharges from the lower reach of Barton Creek immediately upstream from Barton Springs, varies from zero when Barton Springs is flowing about 50 cubic feet per second to about 5 cubic feet per second during extreme high-flow conditions at Barton Springs. Two streamflow gain-loss studies on the Colorado River document any other discharges from the Edwards Aquifer to the Colorado River to be nonexistent or minor. A recharge-discharge water budget for a 32-month period reveals that the total discharge from Barton Springs, Cold and Deep Eddy Springs, the lower reach of Barton Creek, and groundwater pumpage is about 3% less than the surface recharge—a value within the potential error of the measurements. Additionally, for the budget period, recharge within the main channels of the 6 major streams crossing the recharge area account for a minimum of 75% of total recharge. Therefore, long-term recharge within the recharge area from overland flow or tributaries to the main channels represents a maximum of 25% of total recharge, a value equivalent to a mean depth of 2.1 inches per year over the 90-square-mile recharge area, or no more than 6.6% of the long-term mean precipitation of 32 inches per year over the recharge area.