Sediment transport and accretion and the hydrologic environment of Grove Creek near Kenansville, North Carolina

Water-Resources Investigations Report 89-4086




The Grove Creek basin includes an area of about 42 square miles in Duplin County, southeastern North Carolina. This report evaluates sediment transport and sediment-accretion rates in the lowermost 9-mile reach of Grove Creek by using hydrologic, dendrologic, and radioisotopic data collected at seven sites along the study reach. Hydrologic data indicate two discharge frequencies. In the swampiest reaches downstream of site 5, inundation occurs 35 percent of the time; above this site, inundation occurs about 15 percent of the time. For the period from October 1982 through September 1987, overbank flows at site 4 occurred 82 times and lasted a total of 632 days with a maximum duration of 3 months. Distribution of tree species indicates that water-tolerant bald cypress have developed along the lowermost 7 miles of Grove Creek where the flood plain is inundated 35 percent of the time. These swampy conditions have been in existence across limited parts of the flood plain for the last 80 to 150 years. In contrast, the upstream sites have been comparatively dry for the same period. The sediment that is transported in Grove Creek is predominately silt and clay. Measured suspended-sediment concentrations at discharges less than 100 cubic foot per second are less than 15 milligrams per liter; concentrations at higher discharges did not exceed 67 milligrams per liter. Calculated suspended-sediment loads ranged from 75 to 444 tons per year at the various data-collection sites on Grove Creek. Sediment-accretion rates estimated from dendrologic data ranged from 0.03 foot per year to 0.06 foot per year. The highest accretion rates occur in the downstream swampy reaches and are due to channel braiding, low channel gradients and flow velocities, and high frequency and duration percentages of overbank flow, which result in the deposition of clay and silt over wide areas of the flood plain. Sediment-accretion rates along Grove Creek were also estimated by radioisotope methods. Sediment cores from the flood plain showed detectable levels of cesium-137, lead-210, and radium-226. Cesium-137 was not present in the sediment cores below a depth of 10 inches; this indicates a maximum accretion rate of about 0.024 foot per year for the period 1952-87. Lead-210 and radium-226 data from these same sediment cores indicate an average accretion rate of 0.026 foot per year to a depth of about 2 feet. The maximum age of the flood-plain sediment at the 2-foot level is about 80 years. The atmosphere was confirmed as the source of excess lead-210 in flood-plain sediments by nearly matching calculated values of the lead-210 flux at each site with the measured value for atmospheric deposition.

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Sediment transport and accretion and the hydrologic environment of Grove Creek near Kenansville, North Carolina
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Water-Resources Investigations Report
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Dept. of the Interior, U.S. Geological Survey ; Books and Open-File Reports [distributor],
iv, 30 p. :ill. ;28 cm.