447 Physical Geography, 2006, 27, 5, pp. 447-463. Copyright © 2006 by V. H. Winston & Son, Inc. All rights reserved. DRAINAGE DITCHES AS SEDIMENT SINKS ON THE COASTAL PLAIN OF NORTH CAROLINA Scott A. Lecce and Paul A. Gares Department of Geography East Carolina University Greenville, North Carolina 27858 Patrick P. Pease Department of Geography University of Northern Iowa Cedar Falls, Iowa 50614 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.] INTRODUCTION Quantifying the components of sediment budgets provides a useful framework for understanding the effects of human disturbance in fluvial systems and formulat- ing watershed management strategies. Although it is widely recognized that human impacts on natural vegetation cover have produced large increases in historical rates of erosion (e.g., Knox, 1977), much remains to be learned about the transport, storage, and redistribution of the eroded soil (Phillips et al., 1993). Many studies have documented that only a small proportion of the sediment flux from upland source areas is transported to the outlets of larger basins (>100–200 km 2 ) where sediment delivery ratios are typically less than 10% (e.g., Trimble, 1977; Meade, 1982; Walling, 1983; Phillips, 1991, 1995). This implies extensive colluvial and alluvial storage within watersheds. The spatial and temporal complexity of this stor- age makes it difficult to quantify (e.g., Phillips, 1986, 1991; Walling et al., 2002), which has led many investigators to compute storage terms in sediment budgets as residuals (Kondolf and Matthews, 1991).