DETERMINING FLUVIAL SEDIMENT CONTRIBUTION TO THE SOUTH ATLANTIC BIGHT AND ASSESSING ANTHROPOGENIC IMPACT ON DELIVERY: A MODELING APPROACH

Temporal variation of suspended sediment load contribution from five major watersheds along a portion of the southeastern Atlantic coast of the United States was considered over two periods of Anthropocene time. The headwaters of the Cape Fear, Pee Dee, Santee, Savannah, and Altamaha rivers originate in the Piedmont region, an area that supplies one of the highest sediment yields on the Atlantic coast. All five of these rivers drain into the southeastern Atlantic Ocean and continually modify the landscape along the highly populated southeastern Atlantic coast. An increase in coastal erosion along much the South Atlantic Bight has been an obvious trend over recent decades making the practice of beach nourishment a necessity. A controlling factor that commonly attributes to beach erosion is a reduction in suspended sediment from upland rivers. The presence of hundreds of large and small reservoirs and dams on these alluvial rivers is a strong indicator that reservoir retention has affected sediment loads since their construction in the mid-20th century, altering the coastal zones as well as the upland areas. An analysis of current total suspended sediment contribution to the South Atlantic Bight was carried out through application of a climate-driven hydrological transport numerical model, HydroTrend. A modeling approach was employed due to the fact that the rivers in question have no record of, or very limited records of, suspended sediment load or bedload estimates derived from instrumentation or observation at their respective river mouths. Additionally, a detailed analysis was performed in order to simulate sediment loads prior to major dam construction. Comparative evaluation of these two studies provided a quantitative estimate of fluvial sediment flux over Anthropocene time, how recently-constructed reservoirs affect sediment loads, and how the coastline has been impacted.