PALEOKARST: AN OFTEN UNDER EVALUATED GEOHAZARD ASSOCIATED WITH SURFACE WATER RESERVOIRS ON THE CINCINNATI ARCH

The Cincinnati Arch is a structural bedrock feature that can only be seen on regional geologic maps and cross sections. This bedrock feature provides for the structural relief that brought several thick limestone units to the surface for exposure and weathering in the past. More recent glacial activity has covered much of the weathered bedrock surface. A significant amount of the buried limestone surface had karst or karstic features prior to the glacial advance. When karst features are buried, the new term is paleokarst.

Many existing reservoirs are located in areas where karst or karstic conditions are known to exist. Some are located in areas where karstic conditions may exist but have not yet been identified or found to be problematic to the dam and outlet works. In the past, karstic conditions in the bedrock were often under evaluated during design and construction. This is especially true when the karstic conditions have been altered and buried by glacial action, as is the case for much of the region associated with the northern portions Cincinnati Arch.

Three reservoirs in Indiana that have required significant remedial actions to deal with problematic flow associated with karstic conditions will be discussed. The problems and solutions for each case will be presented as an overview. Each reservoir is unique as are the problems associated with karstic flow. The remedial project conducted on Brush Creek Reservoir in Jennings County, SE Indiana, will be the focus of the presentation.

Presentation taken from the published article, ‘Dams on the Arch,' Journal of Dam Safety, Association of State Dam Safety Officials, Summer 2007.