MODERN SEDIMENT ROUTING ALONG THE MID-ATLANTIC COAST: INSIGHTS FROM NORTHEASTERN NORTH CAROLINA

Rivers transport water, sediment, and other constituents from the continent to the ultimate depositional sink, the deep sea. But in route, materials can be stored in many areas for variable periods of time. Along the Atlantic Coast of the United States, rivers drain across an extensive coastal plain and are often characterized as low-gradient meandering systems that develop wide floodplains that are subjected to frequent and prolonged flooding. As a result, these rivers and their flooded valleys (i.e., their adjoining estuaries) are thought to trap much sediment, although damming upstream has certainly affected the sediment loading.

Using radionuclide measurements of Pb-210 and Cs-137, relatively high rates of floodplain sedimentation (mm/y) are documented along the Tar-Pamlico River. These data coupled with LiDAR-mapped floodplains are used to demonstrate that about 60% of the load entering from the piedmont is sequester before much marine influence. Despite this removal, radionuclide studies in the adjacent sounds indicate material continues to fill the extensive estuarine systems (i.e., the Albemarle and Pamlico sounds) at comparable rates. Detailed studies along the coast indicate that cannibalization of ancient floodplain and marine (e.g., marsh) deposits appear to be providing much of the material filling the estuarine basins. Although the storage ratio is likely well above 90% for the northeastern NC river systems, an unquantified portion appears to be escaping coastal containment and reaching the deep Atlantic Ocean.