Richard Styles PhD Thesis - May, 1998

A Continental Shelf Bottom Boundary Layer Model: Development, Calibration and Applications to Sediment Transport in the Middle Atlantic Bight

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Abstract

A continental shelf bottom boundary layer model is presented for use over a noncohesive movable sediment bed. Model features include a continuous eddy viscosity, a correction for suspended sediment-induced stratification and improved bottom roughness and referece concentration models. Predicted concentration and current profiles are sensitive to changes in selected internal model parameters and grain size.
High-resolution current and concentration profile data collected simultaneously over a 6-week summer deployment in 1995 off the southern coast of New Jersey are used to calibrated sensitive model coefficients and to determine the accuracy of the model at predicting the shear velocity and hydrodynamic roughness. Calibration of the internal parameters a, which regulates the cutoff point of the eddy viscosity near the bed, and y, which regulates the vertical decay of the suspended sediment concentration, are shown to be consistent with past estimates obtained in the field. Estimates of ripple height, n, and ripple length, h, are also shown to give good agreement with available field data. Bottom roughness is shown to be a function of not only ripple height, but also of the angle between the wave and combined wave and current shear stress components.
Nearly two-years of current and wave data collected on the inner shelf offshore of New Jersey are used to run the model to investigate long-term sediment transport. Model results indicate that all transport events are related to waves and that the seasonal distribution includes a number of summer storms that are comparable in sediment transport potential to other systems in the spring and fall. Modes of longshore transport follow established patterns for a wide, gently sloping continental shelf with the transport directed primarily alongshore. Cross-shore patterns exhibit an onshore bias which may be caused by multi-scale topographic features that may introduce 3-dimensional flow effects.