GEOLOGIC AND HYDROLOGIC EVALUATION OF A PROPOSED RESERVOIR IN SMITH COUNTY MISSISSIPPI FOR KARST

The United States Forest Service supported the study of a potential surface water reservoir impounding water from Oakohay Creek in the Bienville National Forest, Smith County, Mississippi. A previous study deemed the area suitability to be questionable due to certain geologic and hydrologic features at a proposed reservoir site, particularly a limestone unit that showed evidence of possible karst in the footprint area of the proposed reservoir. This reinvestigation focused on hydrology and geology to address those concerns. Modeling the proposed reservoirs daily water storage and evaluating the limestone unit were the two primary objectives of the study. Modeling the proposed reservoirs daily water storage was completed by installing a dedicated monitoring station and analyzing stream water quantity and quality data. The evaluation of the limestone unit was accomplished through field mapping, ground penetrating radar, sonic drill continuous coring, water quantity and quality measurements and analyses performed in the field and at a laboratory, and a dye trace study. Initial investigations with ground penetrating radar indicated the potential of significant karst in the footprint of the potential reservoir. However, subsequent sonic drill coring, and water quantity and quality analysis did not show evidence of karst. The final part of the investigation was a dye trace study which did suggest the potential for groundwater movement out of the proposed reservoir footprint‘s basin into a nearby basin. This study concludes that the location of the original reservoir footprint on the Oakohay Creek is questionable for the construction of the reservoir with the original proposed footprint. However, a different larger footprint impounding the nearby stream where the basin transfer of water might occur could be suitable. That stream connects with the Oakohay Creek less than two miles downstream from the originally proposed dam location.