Karst of Western Delaware County, Ohio, Region

Abstract

Karst terrain forms by dissolution of carbonate rocks (limestone or dolomite) and occasionally evaporates (gypsum or salt) and is characterized by features such as sinkholes (or sinks), disappearing streams, caves, and springs. The many passageways 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 quickly pollute water wells, streams, and rivers. Karst also poses infrastructure complications: roads, utilities, houses, and other facilities built in karst areas are at risk of subsidence or collapse.

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 could be easily accomplished while sink-locating methods were refined. To locate sinks, LiDAR was used to create an ArcGIS layer that identified 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 produced enclosed areas similar in shape to sinkholes. Many of these features were eliminated using 6-inches-per pixel aerial photography and experience from field verification.

The resulting map of sinkholes and collection of photographs can be used to monitor the growth of preexisting sinkholes and the development of new karst features. Furthermore, areas of land development should be carefully planned in regions of dense karst since they are highly susceptible to pollution and may subside.