Date Awarded

1996

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Virginia Institute of Marine Science

Advisor

L. D. Wright

Abstract

Sediment transport during a storm event on the inner continental shelf was detailed through the development of models based on field experiments conducted at Duck, North Carolina in October 1994. A vertical one-dimensional model (1DV model) was developed by coupling the Grant and Madsen (1986) model with bed stratigraphy to consider real seabeds. Sediment was divided into seven size classes and fractional transport was estimated. Mixing depth and total depth from a simplified sediment conservation equation provided the basis for changing bottom sediment, sediment availability for transport, and armoring processes. These processes involve a feedback between hydrodynamics and bed stratigraphy. A horizontal one-dimensional, depth-resolved model (1DH model) was developed to predict inner-shelf morphological changes. Flow and shear stress fields were calculated using a simple wave transformation model combined with the Jenter and Madsen (1989) model. Sediment flux was computed in relation to fractional transport and armoring processes. The sediment conservation equation was numerically solved to yield bed elevation changes associated with individual size classes. Predictions of suspended sediment concentrations from both models were adjusted by the resuspension coefficient &\gamma\sb0&, resulting in &\gamma\sb0& = 0.001 for the 1DV model and &\gamma\sb0& = 0.002 for the IDH model, respectively. The coupling in the 1DV model was critical to predicting suspended sediment concentrations. Hydrodynamic variables, however, were not significantly affected by changing bottom sediment. Predicted suspended sediment concentrations were higher during the waning phase of the storm than during the erosional phase. Modeled bed stratigraphy showed fining upward sequences. Wind-driven processes on the inner shelf were interpreted using the 1DH model. The magnitude and the direction of horizontal sediment flux were explained in terms of wind-driven currents. Waves produced a sigmoidal-shaped vertical concentration distribution, explaining horizontal gradients of suspended sediment concentrations. The steepness of the sediment flux gradient due to the waves was correlated with wave height. Synchronization of currents and waves was necessary for large flux divergence and morphological changes. During downwelling currents, deposition occurred on the shoreface whereas upwelling currents were accompanied by shoreface/inner shelf erosion. The inner shelf thus responded as either the sink of sediment or the source of sediment.

DOI

https://dx.doi.org/doi:10.25773/v5-gzcd-n430

Rights

© The Author

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