Impacts of Muddy Bed Aggregates on Sediment Transport and Management in the Tidal James River, VA

Aggregation state significantly influences the size, density, and transport characteristics of fine sediment. Understanding sediment transport and deposition processes in the nation's navigable waterways is a primary mission for the US Army Corps of Engineers (USACE), particularly when it comes to infilling of navigation channels. In this study, a newly developed camera system was used to evaluate the aggregation state of eroded sediment from cores collected in the tidal James River, VA. Results showed that bed sediments were composed mostly of mud, but that erosion predominately occurred in the form of aggregates with median sizes 50-270 times larger than the disaggregated sediment. Aggregate size weakly correlated to shear stress at levels <2 Pa, as well as sand content and bed density. A numerical simulation demonstrated that mud aggregates were predicted to transport in incipient suspension or bedload, while disaggregated fines were predominately maintained in full suspension. This difference in transport mode has significant implication for channel infilling and sediment transport within the system. This work is made available under the terms of the Creative Commons Attribution 4.0 International license, http://creativecommons.org/licenses/by/4.0/.