Analyzing the Effects of the Saluda Dam on the Surface-Water Hydrology of the Congaree National Park Floodplain, South Carolina

The Congaree National Park includes extensive swamps of old growth bottomland hardwood forest. Since 1930, the Congaree River (created by the confluence of the Saluda and Broad Rivers) has been influenced by regulation of the Saluda Dam on the Saluda River. Many ecologists and water-resource managers have hypothesized that the regulated flows on the Saluda River have substantially decreased the magnitude and frequency of flooding of the riparian wetlands in the Park. To evaluate the effect of the dam on the flow and water levels of the Congaree River, the U.S. Geological Survey, in cooperation with the National Park Service, analyzed the historical data of the Saluda, Broad, and Congaree Basins. Results from the study show that the Saluda Dam had much more of an effect on low and medium water levels than high water levels. The dam increased monthly minimum river stages by up to 23.1 percent and decreased monthly maximum river stage by up to 7.9 percent. Analyses of annual peak flows indicated that changes in the magnitude and frequency of floods on the Congaree River for pre- and post-regulation periods may be more related to climatic variations rather than changes in regulation of the Saluda River basin.