Date Awarded

2008

Document Type

Thesis

Degree Name

Master of Science (M.Sc.)

Department

Virginia Institute of Marine Science

Abstract

A cohesive sediment bed model was implemented in the Community Sediment Transport Modeling System (CSTMS) to examine processes influencing sediment erodibility and suspended sediment concentrations. 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. A constant erosion rate parameter combined with depth-varying critical shear stress was sufficient to model erosion observations of depth-limited sediment cores. 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. Di fferences 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.

The cohesive sediment bed model was then implemented within a numerical model of the York River Estuary to examine feedbacks between sediment ux convergence and erodibility. Model results show the development of a highly erodible pool of sediment near the ETM location. Even when sediment convergence processes were diminished, suspended sediment concentrations remain high due to high sediment erodibility. Sediment concentrations and erodibility exhibited high spatial variability in both the along and across channel directions. As opposed to the results of the one-dimensional model, sediment concentrations and erodibility estimates were less sensitive to variations in the consolidation rate than to the initial bed conditions. Model calculations of sediment concentrations and erodibility showed similar patterns to observational data.

DOI

https://dx.doi.org/doi:10.25773/v5-n5nc-2296

Rights

© The Author

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