USING LIDAR DATA TO CONDUCT KARST MAPPING IN SOUTH-CENTRAL OHIO

As part of the Great Lakes Geologic Mapping Coalition, the Ohio Geological Survey has been field mapping major karst regions of Ohio since 2009. Completed projects include twelve 1:24,000 quadrangles near the cities of Delaware and Springfield (central Ohio) and Bellevue (northern Ohio). With completion of the majority of central and northern karst areas, the Survey has shifted focus to southern Ohio, beginning with the four 1:24,000 quads encompassing Hillsboro that delimit the northwestern edge of the features in southern Ohio. These features were initially identified remotely using historic data sets (soil surveys and previous mapping projects), aerial photography, and a digital elevation map produced using LiDAR data. LiDAR data was processed to extract enclosed depressions (sinks) and to remove noise. Potential points were then field verified to identify LiDAR depressions that are not karst related (false positives), including old house foundations, broken field tiles, uprooted trees, steep-sided stream banks, and breached ponds. Field checking also located karst features, such as springs, caves, small depressions, and recently formed features, which don’t appear on LiDAR. The number of karst features (including verified, suspect, and unverified) currently mapped in Ohio is about 5,500. Of those, 800 are in central Ohio, and 2,200 are in northern Ohio. Southern Ohio contains at least 2,500 karst features with 723 in the current Hillsboro mapping area. Both of these numbers will change as false positives are identified and removed and unknown sinkholes are located. Furthermore, an old point classification, ‘multiple features,’ is being replaced by discrete points for each feature. To date, 206 points have been field verified in Hillsboro, along with 10 springs, 31 suspect points that were visited, and 476 points yet to be field checked. Four hundred and eighty six other points were identified either in the field or remotely as not karst and were eliminated.