DELINEATING KARST HYDROLOGIC PATHWAYS IN THE HANGING ROCK VALLEY, VIRGINIA

Karst hydrologic pathways are difficult to predict because they commonly follow irregular, non-linear routes beneath surface topographic divides through conduits, fractures, and voids. Three closely spaced karst springs at the southwest end of Hanging Rock Valley supply water to the Paint Bank (VA) Fish Hatchery. The recharge areas for these springs are not delineated, rendering decision-making for land managers regarding water resource protection difficult. Bedrock units in the study area consist of valley-forming Ordovician limestones and dolostones overlain by shales exposed along slopes capped by ridge-forming Silurian sandstones. Streams and springs along the mostly siliciclastic slopes sink at or near the carbonate contact. We hypothesized that these allogenic waters flow along discrete pathways to one or more of the hatchery springs. To test this hypothesis, dye injections were performed in October 2024 at two sinking streams on the southeastern side of Hanging Rock Valley along the northwestern slope of Potts Mountain. Rhodamine WT injected in a sinking stream ~2km northeast of the spring complex was recovered only in the northeastern most spring. Fluorescein injected into a sinking stream ~1km southwest of the spring complex was recovered only in the southwestern most spring. No dye was recovered in the central spring. In addition, measurements of specific conductance and temperature revealed differences between springs. In October 2024, the northeastern most spring had an average temperature of 11.26 C and an average specific conductivity of 225 µS/cm, the central spring had an average temperature of 11.45 C and an average specific conductivity of 176 µS/cm, and the southwestern most spring had an average temperature of 11.55 C with an average specific conductivity of 288 µS/cm. The dye traces and specific conductivity and temperature data all point to discrete flow paths despite the springs’ close geographic proximity. Dye tracing data confirmed flow from two stream sinks to the springs. Further dye injections are needed to fully delineate the springs’ recharge areas, including the third, central spring. Continued monitoring of specific conductivity and temperature can help us understand how the system reacts to precipitation which can inform our understanding of how water moves through the system.