Estimating Cohesive Sediment Erosion and Consolidation in a Muddy, Tidally-Dominated Environment: Model Behavior and Sensitivity

Erodibility of cohesive sediment varies with sediment depth and with erosional and depositional history. A cohesive sediment bed model was implemented in the Community Sediment Transport Modeling System (CSTMS) to examine processes influencing sediment erodibility and water column turbidity. Estimates of eroded mass from the sediment bed model were calibrated and verified with erosion chamber measurements from the York River, Virginia, a tidally-dominated environment. The model performs well when a constant erosion rate parameter is used and critical stress is varied with depth. Sensitivity of total eroded mass to seasonal variations in erodibility and changes in consolidation time scale was evaluated during spring-neap variations in bottom stresses. Differences were greatest during spring tide and varied by as much as a factor of 2.5. Consolidation created an asymmetry between the spring-to-neap and neap-to-spring transitions with more sediment being eroded during the decreasing phase of maximum tidal stress. Consolidation time scales controlled the magnitude of this asymmetry with larger asymmetries occurring when slower consolidation time scales were assumed. Eroded mass estimates were potentially as sensitive to uncertainties in the consolidation time scale as they were to observed seasonal variability in critical stress.