Sediment characteristics of streams in the eastern Piedmont and western Coastal Plain regions of North Carolina

Abstract

The sediment-transport characteristics of streams were determined in a 15,500-square-kilometre (6,000-square-mile) area of the Coastal Plain and Piedmont regions of eastern North Carolina during 1969-73. The study covered all or parts of 21 counties and included data for 28 sediment-sampling stations in parts of 4 major river basins?the Roanoke, Pamlico, Neuse, and Cape Fear. Annual suspended-sediment yields ranged from 117 to 4.2 tonnes per square kilometre (333 to 12 tons per square mile). Streams in the Piedmont region have the highest yields. Suspended-sediment yield decreases in an eastward direction from the Piedmont to the Coastal Plain region. Sediment characteristics are directly affected by topography, storm runoff, geology, land use, and man-made detention structures. At one sampling station in the 1973 water year 44 percent of the suspended sediment tonnage was transported during 34 days of high flow. In the Piedmont region, sediment yields vary indirectly with the percentage of forest cover in the basin, but there appears to be no definite relationship between forest cover and sediment yield in the Coastal Plain region. Large lakes act as sediment-detention reservoirs. Average annual sediment yields ranged from 34 to 117 tonnes per square kilometre (98 to 333 tons per square mile) for 3 headwater streams which flow into Hyco Lake in Person County; however, the yield for the station less than 3.2 kilometres (2 miles) downstream from Hyco Dam was about 4.2 tonnes per square kilometre (12 tons per square mile). Most suspended sediment during floods in Piedmont streams ranges in size from sand to silt, whereas the suspended material in flooding streams in the Coastal Plain is generally clay size.