MAPPING KARST IN THE NORTH-CENTRAL OHIO REGION

Since 2009, the Ohio Geological Survey has undertaken reconnaissance mapping of karst areas in Ohio, beginning with the cities of Delaware and Springfield and their vicinities. Currently, karst is being mapped near the cities of Bellevue, Castalia, and Clyde in north-central Ohio—a densely karstic area featuring some of the largest sinkholes in the state. To locate these sinkholes, LiDAR (Light Detection and Ranging) data is used to generate a digital elevation model (DEM). This DEM pinpoints depressions that may have internal drainage. These depressions are cross referenced with known karst locations, bedrock geology, aerial photography, soil maps, drift thickness maps, and water well logs. Many features were dismissed by using both aerial photography and knowledge gained from previous field verification of how LiDAR interacts with streams, culverts, and infrastructure as opposed to sinkholes. LiDAR lows and areas that could not be eliminated remotely are being visited in the field and documented.

In total there are 1,208 distinct locations under review for karst in this 428-km² area. To date, the Ohio Geological Survey has confirmed 52 sinkholes and 24 springs, and eliminated 142 suspect sites either remotely or in the field. In addition to the newly located features, 240 karst points that were field verified by previous workers will be rechecked against the LiDAR and in the field. The remaining suspect locations will be field checked to determine if they are karst or not. Also, records on size and depth of 218 features from a 1980 project are being compared to the LiDAR to see if change over time can be observed.

Karst regions are highly susceptible to pollution, and structures built near them may subside. Karst features in the Bellevue region have also served as conduits of groundwater discharge during periods of unusually high precipitation. This groundwater discharge has led to severe, localized flooding. The maps produced from this effort will allow areas of land development near karst features to be better planned and maintained.