DELINEATING THE SPRINGSHED OF CAVE WITHOUT A NAME: DYE TRACING IN THE LOWER GLEN ROSE LIMESTONE

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 large Trinity Aquifer System. The primarily rural Kendall County lies just northwest of San Antonio in the Texas Hill Country and has the third highest population growth rate by percent increase of all Texas counties. The Trinity Aquifer is the primary source of freshwater for this and many other Hill Country counties, although its yields are relatively low and groundwater generally has higher TDS compared to the adjacent Edwards Aquifer.

CWAN is a dendritic network of gravity drained vadose passages with hydraulic gradient dominating passage development. Some passages show evidence of an earlier phase of phreatic development prior to the incision of nearby Spring Branch, though currently active conduits appear to have formed at the watertable. Geologically, the cave has formed in a calcarenite member above a dolomitic member.

A springshed is the area of land that contributes water via recharge features to a spring and is similar to a watershed. To delineate a contributing zone for Cave Without a Name, dye tracing will be performed after conducting a thorough spring and karst-feature inventory in the surrounding area. Dye tracing utilizes conservative tracers (dyes) to trace recharging waters from either diffuse or direct recharge sites to a point of discharge (e.g., springs). For this project, multiple traces will be performed from direct recharge sites (sinkholes and/or caves) in an attempt to perform relatively rapid traces via active conduits. Regional flow near CWAN is to the Southeast while local flow is towards springs and river, and both the Guadalupe River and Spring Creek are assumed to act as local discharge boundaries, where a number of known springs occur. Prior work by Veni (1994) and preliminary field work suggests that there may be several adjacent springsheds that have formed in the area, which is near a large oxbow in the Guadalupe River, just upstream from the confluence with Spring Creek.