THE INTERACTIONS OF STILLHOUSE HOLLOW RESERVOIR AND BELTON LAKE WITH THE TRINITY AND EDWARDS AQUIFERS OF CENTRAL TEXAS

Stillhouse Hollow Reservoir and Belton Lake are two systems built by the US Army Corps of Engineers approximately 50 years ago. They were constructed to ensure a reliable source of water for the cities in Bell County, notably Fort Cavasos, Belton, Temple, and Kileen, and to mitigate flooding of the Leon and Lampasas Rivers in Central, TX. Although these two reservoirs have sustained the current generation, an ongoing growth surge along the I-35 highway corridor continues to strain water resources and called attention to possible interactions between reservoirs and groundwater systems. These two reservoirs overlay the Trinity aquifer and their dams are adjacent to the Edwards Balcones Fault Zone aquifer. This study investigated the impacts on the underlying Trinity aquifer from increased head due to the interactions with the Edwards aquifer during flood pool levels. The interfaces between the Stillhouse Hollow Reservoir and the shallow unconfined Edwards aquifer during flood pool levels were confirmed but need more quantification regarding the magnitude of the impacts. Changes in ionic and isotopic chemistry as well as eDNA evidence from lake organisms were detected in the Edwards aquifer. Additionally, the reservoirs were studied to determine their impact on sustaining water levels in times of drought and the water quality in periods of high recharge. Head changes and water chemistry may have occurred in the Trinity aquifer, but the relationships are not yet understood. This study strives to further delineate the reservoirs’ impact on the water quality of the Trinity aquifer amidst increasing demands for water.