Stream Recharge Water Balance for the Barton Springs Segment of the Edwards Aquifer

Nico M. Hauwert

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Channel water balance analysis based on streamflow loss coupled with traced groundwater basins allow refinement of upland autogenic recharge values comparable to those derived from more precise site‐scaled measurements. Based on total discharge and calculated flow loss in major stream channels, the channel contributions to recharge on the Barton Springs Segment of the Edwards (Balcones Fault Zone) Aquifer are: Onion Creek (32.6%), Barton Creek (less than 10.5%), Slaughter Creek (7.2%), Bear Creek (6.2%), Blanco River (6%), Little Bear Creek (3.4%), and Williamson Creek (1%). Major stream channels contributed from 56% to 67% of total groundwater recharge to the groundwater system, 17% of which was stream autogenic recharge, while upland autogenic recharge and other smaller sources contributed the remaining 33% to 44%. As a percent of precipitation over the Edwards Aquifer outcrop source area, autogenic recharge (upland and tributary recharge in the major stream channels) was 22% to 28%, compared with a recharge value of 28% of precipitation from climate tower water balances in Central Texas. Prior to delineation of groundwater basins using injected tracers, older channel water balance studies determined that upland autogenic recharge was only 15% of the total groundwater recharge (about 1% of precipitation). This study suggests that the channel water balance approach, based on gauged streamflow and spring discharge, is more accurate when one incorporates groundwater basins delineated by groundwater tracing, especially in karst aquifers. Refinement of an appropriate catchment area for the calculation of autogenic recharge also significantly affected the results of a precipitation water balance.