Bank erosion along the dam-regulated lower Roanoke River, North Carolina

Abstract

Dam construction and its impact on downstream fl uvial processes may substantially alter ambient bank stability and erosion. Three high dams (completed between 1953 and 1963) were built along the Piedmont portion of the Roanoke River, North Carolina; just downstream the lower part of the river fl ows across largely unconsolidated Coastal Plain deposits. To document bank erosion rates along the lower Roanoke River, >700 bank-erosion pins were installed along 66 bank transects. Additionally, discrete measurements of channel bathymetry, turbidity, and presence or absence of mass wasting were documented along the entire study reach (153 km). A bank-erosion– fl oodplain-deposition sediment budget was estimated for the lower river. Bank toe erosion related to consistently high low-fl ow stages may play a large role in increased midand upper-bank erosion. Present bank-erosion rates are relatively high and are greatest along the middle reaches (mean 63 mm/yr) and on lower parts of the bank on all reaches. Erosion rates were likely higher along upstream reaches than present erosion rates, such that erosion-rate maxima have since migrated downstream. Mass wasting and turbidity also peak along the middle reaches; fl oodplain sedimentation systematically increases downstream in the study reach. The lower Roanoke River is net depositional (on fl oodplain) with a surplus of ~2,800,000 m3/yr. Results suggest that unmeasured erosion, particularly mass wasting, may partly explain this surplus and should be part of sediment budgets downstream of dams. Hupp, C.R., Schenk, E.R., Richter, J.M., Peet, R.K., and Townsend, P.A., 2009, Bank erosion along the dam-regulated lower Roanoke River, North Carolina, in James, L.A., Rathburn, S.L., and Whittecar, G.R., eds., Management and Restoration of Fluvial Systems with Broad Historical Changes and Human Impacts: Geological Society of America Special Paper 451, p. 97–108, doi: 10.1130/2009.2451(06). For permission to copy, contact editing@geosociety.org. ©2009 The Geological Society of America. All rights reserved.