Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


L. Donelson Wright


An experiment conducted over the shoreface at Duck, North Carolina in 1985 embraced both fair-weather low energy and storm-related high energy conditions. to differentiate the diffusion and advection processes of suspended sediments under the high energy conditions from those under the low energy conditions, numerical modeling and the analysis of field data are exercised. A simple two-layer eddy viscosity wave-current combined boundary layer model is developed. The modeled characteristics of the boundary layer are incorporated with a diffusion equation to give suspended sediment concentration profiles. A velocity scale related to factors other than turbulent diffusion is formulated, representing the diffusion under varying energy conditions. With increasing bed friction, the vertical diffusion of sediment is reduced due to stratification, thus reducing velocity. From the measured suspended sediment concentration profiles, the resuspension coefficient, &\gamma&, shows a tendency to decrease with increased flow intensity, suggesting the role of the armoring effect. The coefficient, &\gamma&, varies between 0.0003 for high-energy conditions and 0.002 for low-energy conditions. The energetics approach to predicted sediment transport overestimates the role of wave transport for the low energy conditions. Cross-correlations between cross-shore velocity and sediment concentration show that the role of wave for the transport under low energy conditions is not substantial. The direction of transport under low energy conditions is governed by the mean current. Under high energy conditions, transport by waves is onshore but superseded by offshore transport by the mean current, resulting in net offshore transport. The energetics model based on the surfzone dynamics underestimates the transport rate by an order of magnitude compared to the depth integration of the average product of mean cross-shore velocity and mean concentration. This indicates that the calibration of the efficiency factors &\epsilon\sb{lcub}\rm s{rcub}& and &\epsilon\sb{lcub}\rm b{rcub}& in an energetics model is essential.



© The Author

Included in

Oceanography Commons