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Open-File Report 2009–1260

Prepared in cooperation with the
U.S. Fish and Wildlife Service and the
U.S. Army Corps of Engineers

Bank Erosion, Mass Wasting, Water Clarity, Bathymetry and a Sediment Budget Along the Dam-Regulated Lower Roanoke River, North Carolina

By Edward R. Schenk,1 Cliff R. Hupp,1 Jean M. Richter,2 and Daniel E. Kroes3


1U.S. Geological Survey, National Research Program, Reston, Va.
2U.S. Fish and Wildlife Service, Roanoke River National Wildlife Refuge, Windsor, N.C.
3U.S. Geological Survey, Louisiana Water Science Center, Baton Rouge, La.
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Abstract

Dam construction and its impact on downstream fluvial processes may substantially alter ambient bank stability, floodplain inundation patterns, and channel morphology. Most of the world’s largest rivers have been dammed, which has prompted management efforts to mitigate dam effects. Three high dams (completed between 1953 and 1963) occur along the Piedmont portion of the Roanoke River, North Carolina; just downstream, the lower part of the river flows across largely unconsolidated Coastal Plain deposits. To document bank erosion rates along the lower Roanoke River, more than 700 bank erosion pins were installed along 124 bank transects. Additionally, discrete measurements of channel bathymetry, water clarity, and presence or absence of mass wasting were documented along the entire 153-kilometer-long study reach. Amounts of bank erosion in combination with prior estimates of floodplain deposition were used to develop a bank erosion and floodplain deposition sediment budget for the lower river. Present bank erosion rates are relatively high [mean 42 milimeters per year (mm/yr)] and are greatest along the middle reaches (mean 60 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 migrated downstream. Mass wasting and water clarity also peak along the middle reaches.

First posted January 2010

For additional information contact:

Edward Schenk
eschenk@usgs.gov
U.S. Geological Survey
12201 Sunrise Valley Drive
Reston, VA 20192

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Suggested citation:

Schenk, E.R., Hupp, C.R., Richter, J.M., and Kroes, D.E. 2010, Bank erosion, mass wasting, water clarity, bathymetry, and a sediment budget along the dam-regulated lower Roanoke River, North Carolina: U.S. Geological Survey Open-File Report 2009–1260, 112 p., available only at http://pubs.usgs.gov/of/2009/1260/.



Contents

Abstract

Introduction

Study Area

Methods

Bank Erosion

Channel Bathymetry, Water Clarity, and Mass Wasting

Bank- and Floodplain-Based Sediment Budget

Results

Bank Erosion

Mass Wasting and Water Clarity

Bathymetry

Bank- and Floodplain-Based Sediment Budget

Summary

References Cited

Appendix 1:
Summary of Bank Transect Locations, Number of Erosion Pins per Transect, Bank Erosion Index Values, Mean Bank Height, and Erosion Rates.
Appendix 2:
Erosion Pin Measurements for Each of the 701 Bank Erosion Pins.
Appendix 3:
Cross-Sectional Survey Data by Transect, Including Bathymetry.
Appendix 4:
Bathymetric, Water Clarity, and Mass Wasting Data Collected on an Approximately 200-Kilometer River Survey from Near Halifax, N.C., to the Alblemarle Sound.
Appendix 5:
Mean Floodplain Sedimentation from 2002 to 2005 Measured Using Feldspar Clay Pads on Transects Perpendicular to Channel.
Appendix 6:
Stage-Discharge Relationships at Selected USGS Streamgages, River Stage Information Between Pin Measurement Dates, and Pin Bank Erosion Rates Related to River Stage and Date.


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