Drainage Ditches as Sediment Sinks on the Coastal Plain of North Carolina

Abstract

This paper examines the role that slope-channel linkages and seasonal vari- ations in vegetation play in explaining spatial and temporal variations in sediment flux through agricultural drainage ditches in eastern North Carolina. We used biannual cross- sectional surveys of drainage ditches to assess erosion/deposition during a five-year period in the headwaters of a small agricultural watershed. Although net accumulations of sedi- ment were observed in three-fourths of the cross sections surveyed, the rate of sedimenta- tion varied considerably from ditch to ditch and cross section to cross section. The ditches were sediment sinks during the growing season in summer and autumn when they became choked with dense vegetation growth, and more hydraulically efficient after removal of vegetation in December during annual maintenance operations. The ditches experienced erosion or modest deposition while the vegetation was dormant during the late winter/ early spring. Sediment was delivered to the ditches from isolated gullies that linked the primary source of sediment, soil eroded on agricultural fields, to the channels. Except for these isolated linkages, ditches and fields are largely decoupled. (Key words: drainage ditches, sedimentation, Coastal Plain, North Carolina.)