Springshed delineation in a karst aquifer in Hays County, Central Texas

Hays County is experiencing some of the highest growth rates in the country, and groundwater is the primary option for water in the county. One spring in the study area, Jacob’s Well, experiences periodic cessation of flow due to a combination of drought and pumping from nearby water supply wells. Jacob’s Well is important for ecological and water resources of the region. A springshed delineation study was conducted at the request of the local groundwater conservation district to protect flow at Jacob’s Well from excessive pumping. Much of the flow to Jacob’s Well emanates from a large phreatic cave passage with over a mile of surveyed passages in the Cow Creek Limestone of the Middle Trinity Aquifer. The aquifer has varying degrees of karst development with both conduit, fracture, and diffuse flow components. Many methods have been derived to set protection areas for water-supply wells, springs, and aquifers in karst settings. In this study we relied upon geologic structure maps, potentiometric maps, hydrographs, aquifer tests, dye traces, and a variety of water-balance analyses. Ultimately, the data indicated that the Jacob’s Well springshed boundaries were best explained by the watershed boundaries for Cypress Creek, upgradient of the spring. This information was used to delineate a groundwater management zone recommended to the local groundwater conservation district and a local stakeholder group. The next step is to develop groundwater management rules and other strategies for the protection of springflow. This springshed delineation could also be used to protect the aquifer and Jacob’s Well from sources of contamination