Springshed Delineation in a Karst Aquifer in Hays County, Central Texas

Topic: Groundwater Tracing and Groundwater Flow Studies
Source: Sinkhole Conference
Format: Paper
Year: 2020

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 identify the geographic area where strategies to protect flow at Jacob’s Well from excessive pumping would be most effective. Many methods have been derived to set protection areas for water-supply wells, springs, and aquifers in karst settings. 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 conduit, fracture, and diffuse flow components. In this study we relied upon geologic structure maps, potentiometric maps, hydrographs, 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, generally upgradient of the spring. This information was used to delineate a groundwater management zone, which was then recommended to the local groundwater conservation district and a local stakeholder group. Using the springshed delineation, rules have been drafted by the groundwater conservation district to limit increases in permitted pumping, to further restrict the amount of groundwater pumped during drought, and to protect springflow. This springshed delineation could also be used to develop rules or actions to protect the aquifer and Jacob’s Well from sources of contamination.