Surface-water Reservoir Effects In A Shallow Karst Aquifer: Quantity, Quality Or Both

The Anthropocene has resulted in numerous modifications to surface water/groundwater interactions. Understanding these changes is critical to effective and efficient water management. Surface-water reservoir construction in carbonate terrain may affect adjacent shallow karst groundwater systems by elevating local water levels and the resulting increased flow may cause safety concerns if dissolution accelerates. Causes for changes in the adjacent heterogeneous karst groundwater system are challenging to determine, and solutions to the associated problems lend themselves to local flow-system approaches rather than aquifer concepts. Stillhouse Hollow Reservoir in Central Texas is exemplary of many reservoirs designed for both water supply and flood control which results in large water level fluctuations. Increased spring flow in the nearby Edwards aquifer has been hypothesized as the response to reservoir water levels but this connection remains unconfirmed. Deployment of dataloggers and routine measurements of spring flow compared to reservoir levels and precipitation events have proved challenging and helpful, but not conclusive. Analyses of temperature, specific conductance, ionic chemistry, and stable isotopes in both the springs and the reservoir added information critical to understanding the karst heterogeneity and hydraulic connections.

The results indicate hydraulic connections are related to the karst heterogeneity in response to reservoir management and vary in location and magnitude. The conclusion is that there is a need for creative investigative approaches combined with a variety of analytical methods to understand hydrogeologic changes in the Anthropocene such as those observed in this portion of the Edwards aquifer affected by Stillhouse Hollow Reservoir.