Lakes Marion and Moultrie are two large, interconnected reservoirs in the Coastal Plain of South Carolina. Bathymetric surveys during 1984-85 determined that, for the full-pool water surface elevation of 76.8 ft, the volume of Lake Marion is 1,425 ,000 acre-ft, and for the full-pool water surface elevation of 75.0 ft, the volume of Lake Moultrie is 1,060,000 acre-ft. These volumes are considered accurate to within 5%. Comparison with volumes determined in 1941, when the reservoirs were filled, shows decreased in volume of 73,000 acre-ft in Lake Marion and 30,000 acre-ft in Lake Moultrie. These changes in volume, however, are subject to relatively large possible error because they represent relatively small differences between relatively large volumes, and because the accuracy of the 1941 volumes is not known. Measurements of sediment inflow and outflow and of deposition rate suggest the volume losses were more likely about 29,000 acre-ft in Lake Marion and about 1,600 acre-ft in Lake Moultrie. The discrepancy in the estimate of volume changes does not affect the accuracy of the volume computation or the maps. (USGS)
