KARST OF DELAWARE COUNTY AND CLARK COUNTY, OHIO

Karst terrain forms by dissolution of carbonate rocks (limestone or dolomite) or evaporites (gypsum or salt) and is distinguished by features such as sinkholes, disappearing streams, caves, and springs. The enlarged fractures formed in karst terrain allow for high connectivity between the land surface and the water table and can bypass soil and rock layers that filter out contaminants. When materials such as fertilizer, pesticide, and waste enter sinkholes, they are rapidly transported to the water table and can quickly pollute water wells, streams, and rivers. Karst terrain also poses a risk of subsidence or collapse to roads, utilities, houses, and other facilities.

In order to test a process for determining areas at risk from karst in Ohio, an area encompassing Western Delaware and bordering counties was selected. Rapidly developing and known to contain karst, Delaware County is close to the Ohio Geological Survey’s main office, so field verification was easily accomplished while sink-locating methods were refined. Upon completion of the Delaware County area, the process is being continued in a portion of Clark County also known to have karst features. To locate sinks, LiDAR was used to create an ArcGIS layer of low, enclosed areas. These low spots were cross referenced with known karst points, bedrock geology, aerial photography (multiple sources/ages), soil maps, drift thickness, and water well logs to locate potential sinks. Suspect locations then were visited in the field, evaluated, and photographed. Through this process we quickly learned that many of the LiDAR returns were not sinks; features such as building foundations, broken field tile, steep-walled streams, and road culverts often produce enclosed areas similar in shape to sinkholes. Many of these features in Clark County were eliminated using aerial photography and experience from field verification in Delaware County. The resulting map of sinkholes and collection of photographs can be used to monitor the development of new karst features and growth of preexisting sinkholes. Furthermore, areas of land development should be carefully planned in regions of dense karst since they are highly susceptible to pollution and may subside.