Springshed Delineation at Cave Without a Name, TX: Dye Tracing in the Lower Glen Rose Limestone
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Cave Without a Name (CWAN) in Kendall County, TX contains ~5.5 km of active stream conduits formed in the karstic Lower Glen Rose Limestone which forms part of the Trinity Aquifer System. The primarily rural Kendall County lies just northwest of San Antonio in the Texas Hill Country. The Trinity Aquifer is the primary source of freshwater for this and many other Hill Country counties, although its yields are relatively low compared to the adjacent Edwards Aquifer. Springsheds contribute water via recharge features to a spring and are similar to watersheds, except that their boundaries are not constrained by topography. To delineate a springshed for Cave Without a Name, dye tracing was performed by injecting dyes into recharge features in the land surface. Dye tracing utilizes conservative tracers (dyes) to trace recharging waters from direct recharge sites to a point of discharge (e.g., springs). For this project, multiple traces were performed from direct recharge sites (sinkholes and/or caves). Regional flow near CWAN is to the Southeast while local flow is towards springs and streams. The Guadalupe River, Spring Creek, and Sabinas Creek are assumed to act as local discharge boundaries, along which a number of known springs occur. This work supports prior work by Veni (1994 that suggested there may be several adjacent springsheds in the area, which is near a large oxbow in the Guadalupe River, just upstream from the confluence with Spring Creek. Results showed groundwater flow velocities in the area ranging from ~0.36 km/day through preferential flowpaths to diffuse flow through the epikarst of ~0.02 km/day. Type of recharge feature, injection method, and hydrologic conditions were found to play significant roles in the behavior of each dye trace. Results may help with future efforts to manage water quality in the area.