SUBSTRUCTURE GROUNDWATER FLOODING POTENTIAL OF THE GREAT MIAMI RIVER AQUIFER IN DAYTON, OHIO

Since the 1970s, groundwater within the Great Miami River aquifer in Dayton, Ohio has been rising, primarily due to declines in groundwater pumpage associated with industry. The incidents of basement flooding has increased in areas along the Great Miami River, causing building owners and managers to seek methods to prevent future flooding damage. The Miami Conservancy District (MCD) commissioned a study to define substructure flooding potential and to aid in managing groundwater and property damage in the Dayton area.

The U.S. Geological Survey finite-difference computer model MODFLOW was used to construct a groundwater flow model to identify areas prone to flooding based on stream recurrence intervals for the Great Miami River in the City of Dayton. A fixed elevation grid method using a 30-layer vertical construct was used to simulate the complex buried valley aquifer system. Surface water simulations with recurrence intervals of 10-years, 50-years and 100-years were used to model the streams and rivers during flood stages.

To identify areas with potential for substructure and basement flooding, a depth of 10 feet below ground surface was used to define the minimum depth for groundwater seepage into a substructure or basement. Areas with a difference of 10 feet or less between the ground surface elevation and the simulated water table elevation were then identified as zones with potential for substructure flooding. Results were then geographically developed to define areas in Dayton that have potential for groundwater flooding as a result of the three flood recurrence intervals. Study results with potential for substructure flooding are found most commonly along the outwash aquifer of the Great Miami River and its tributaries where land surface elevations range from 720 to 750 feet mean sea level. Structures that occur on the kames and ground moraines at an elevation of 750 feet mean sea level or higher in the downtown Dayton area appear to have some measure of natural protection against substructure flooding.