Evaluation of two existing flood management structures in U.S. Army Garrison Fort Gordon, Georgia, 2020

Two existing flood management structures in U.S. Army Garrison Fort Gordon, Georgia, were evaluated for potential retrofitting to address water-quality impacts, pursuant of U.S. Army Garrison Fort Gordon’s storm water management program. Stormwater calculations were computed according to the Georgia Stormwater Management Manual, including drainage area delineations, design-storm runoff volumes and peak discharges, stage-storage and stage-discharge curves, and outflow calculations. The results of these analyses were compared to Georgia’s regulatory requirements for dry detention basins. The two existing flood management structures did not meet the requirements for a dry detention basin. Planning-level analyses for these basins indicate that the existing structures do not have adequate storage capacity for the overbank flood design-storm runoff volume (25-year, 24-hour storm) or the extreme flood design-storm runoff volume (100-year, 24-hour storm) and neither storm water structural control 2 nor storm water structural control 3 has the emergency spillway needed to safely convey overflows. Furthermore, land use changes (forest removal) and the risk for additional sediment loads to these structures may reduce available storage volume, increasing the risk for design failure. Three potential retrofit alternatives were provided for planning purposes only, with a brief discussion of advantages and disadvantages of each alternative retrofit strategy.