Contemporary fluvial geomorphology and suspended sediment budget of the partly confined, mixed bedrock-alluvial South River, Virginia, USA

GSA Bulletin
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Abstract

We developed a conceptual model and suspended sediment budget for a 38 km reach of the fifth-order South River, Virginia, for the past 75 yr. Bedrock, terraces, and alluvial fans confine 64% of the channel’s lateral boundaries, while bedrock exposures impose vertical confinement along 37% of the channel. Bedrock exposures in the bed separate pools and riffles developed in gravelly bed material, create unusual kilometer-long pools, and divide the study area into a gently sloping upstream reach and a steeply sloping downstream reach. Bedrock exposures upstream and downstream of an alluvial monitoring site limit changes in bed elevation (documented by scour chains and repeat surveys) by flows with up to 10 yr return periods. Fifty-seven islands (features rarely mentioned in previous studies), mostly created by avulsive floodplain incision, occur in the study reach. Rates of bank retreat, likely moderated by bedrock exposures, have modal values of only a few centimeters per year, while floodplain growth by lateral accretion is negligible. Overbank deposition dominates the sediment budget, but the areal of the extent of the floodplain is currently being reduced by bank erosion and channel widening. The South River stores 2.5% of its annual suspended sediment load per kilometer of downstream transport, demonstrating that suspended sediment storage along partly confined, mixed bedrock-alluvial rivers can be equivalent to storage along fully alluvial rivers. The future evolution of the South River will likely be controlled by bank stabilization designed to control mercury loading into the channel from erosion of contaminated floodplain sediments.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Contemporary fluvial geomorphology and suspended sediment budget of the partly confined, mixed bedrock-alluvial South River, Virginia, USA
Series title GSA Bulletin
DOI 10.1130/B31759.1
Volume 130
Issue 11-12
Year Published 2018
Language English
Publisher Geological Society of America
Contributing office(s) National Research Program - Eastern Branch
Description 16 p.
First page 1859
Last page 1874
Country United States
State Virginia
Other Geospatial South River