Sources of Shoaling in Charleston Harbor Fourier Grain Shape Analysis

Abstract

ABSTRACT Shoaling in Charleston Harbor, South Carolina, is a severe economic problem requiring major expenditures for dredging as well as proposals for drastic modifications of the sediment carrying capacities of the rivers discharging into the harbor. Sediment accumulating in dredged channelways consist mostly of sand whereas silts and clays dominate the shallows. Although previous studies agree on the hydrodynamic responses to diversion of the Santee River's 15,000 cfs (425 m3 per sec) flow into Charleston Harbor, no concensus exists concerning the source of sediment accumulating in the dredged channels (i.e. whether or not the source of the shoaling material is from the Cooper River or the proximal continental shelf). The sources of sediment influx into Charleston Harbor and the relative contributions of each source have been determined using the Fourier Series grain shape analysis. Results of the shape analysis on the sand fraction indicate that the major cause of shoaling in the harbor channels is sand derived from a seaward source. Shape analysis of the silt fraction reveals that the silt accumulations are derived primarily from the Cooper River. These results indicate that the deepening of the harbor channels has played a major role in the shoaling of Charleston Harbor as well as the increased freshwater flow from the Santee River.