GEOPHYSICAL PROSPECTING FOR CONCEALED KARST NEAR BELLEVUE, OH

The Bellevue area, Ohio is characterized by sinkholes and dolines that allow surface water to rapidly drain into the carbonate aquifer. During episodes of excessive precipitation, part of the state Route 269 floods due to groundwater welling up. Ver Steeg and Yunck (1932) report water seeping in areas without visible sinkholes causing 3-4 foot high flood during the spring of 1930.

We are using gravity and electrical resistivity methods to investigate concealed karst and underground conduits north of Bellevue. We occupied closely spaced (20 and 50 m) gravity stations along three east-west profiles, two adjacent to a topographic depression we interpret as a sinkhole complex. At this stage there is only a marginal suggestion of gravity lows that might indicate subsurface voids. Four dipole-dipole resistivity profiles totaling 2 km show only one obvious void, adjacent to a sinkhole. However, most resistivity measurements were made during the drought of summer 2012, making the distinction between voids and carbonate bedrock difficult. Repeat measurements will be conducted when the groundwater rises. A rise in groundwater level will convert air-filled voids (high resistivity) to water-filled voids (low resistivity). Electrical resistivity was used to detect air and water filled cavities at Seneca Caverns to the south, confirming this methodology.

In January 2013, the static water level at USGS monitoring well at Bellevue rose 10 feet in response to 2 inches of precipitation. Stage level recorded at the Huron River east of the city shows a strong agreement with the static water level rise but dropped fast after the peak flow while the groundwater water level remained constant. The strong response of the groundwater to precipitation suggests that karstic porosity is quite low. Knowledge of the size and extent of the concealed karst will help in reducing impact of pollution on groundwater resources and delineating hazard prone areas.