DETAILED KARST MAPPING OF HAMILTON COUNTY, OHIO

The Ohio Department of Natural Resources, Division of Geological Survey has continuously mapped karst features throughout the state since 2009. Hamilton County, in southwestern Ohio, was recently selected for karst mapping because of the growth of the greater Cincinnati area and to further understand this understudied karst region. The potential for karst features in this region depends on the lithology of bedrock and thickness of overlying glacial sediments. Historical karst data for the county came from theses, soil surveys, and various reports. Less than 100 karst features were documented in the study area prior to this project.

A Digital Elevation Model (DEM) was processed for enclosed depressions and subsequent features analyzed for likelihood of karst. A total of 1,849 potential karst features were preliminarily identified using the DEM, and 1,332 were field verified during the 2019–2020 and 2021–2022 field seasons. During fieldwork, sinkholes are often found to be as much as 3.4 m (11 ft) deeper than remotely sensed data suggests. Similarly, 30% of the mapped features were discovered in the field and were generally too small to be visible on the DEM. All features were developed in Ordovician bedrock: 62% in the Grant Lake Formation, 35% in the Miamitown-Fairview Formation, and 3% others. These formations average 50-90% shale, interbedded with limestone, which likely accounts for overall shallower depressions when compared to other karst areas in Ohio.

Distribution of the bedrock units and areas of thin glacial sediment would suggest sinkhole formation over a larger area of Hamilton County. However, the majority of sinkholes (61%) are concentrated or greenspaces that cover only 5% of the county. These data could be used to study the uneven distribution of these karst features and determine if they are perhaps a result of successful mitigation in developed areas or if areas of densely packed sinkholes were undesirable for building and were only suitable as minimally developed parks or natural areas. Understanding the history of city infrastructure and karst development could have important implications for emergency response planning with regards to geohazards.