Modeling stratified wave and current bottom boundary layers on the continental shelf

The Glenn and Grant [1987] continental shelf bottom boundary layer model for the flow and suspended sediment concentration profiles in the constant stress layer above a noncohesive movable sediment bed has been updated. The Reynolds fluxes for sediment mass and fluid momentum are closed using a continuous, time-invariant linear eddy viscosity modified by a continuous stability parameter to represent the influence of suspended sediment-induced stratification throughout the constant stress region. Glenn and Grant [1987] use a less realistic discontinuous eddy viscosity and neglect the stratification correction in the wave boundary layer. For typical model parameters the two models produce currents above the wave boundary layer that are in better agreement than the suspended sediment concentrations. Within the wave boundary layer the differences are much greater for both the current and the sediment concentration. This leads to significant differences in the sediment transport throughout the constant stress layer. Sensitivities of the updated model were examined on the basis of observed wave and current data acquired during storms on the inner continental shelf. Comparisons between the stratified and neutral versions of the updated model indicate that the stratified version produces a total depth-integrated sediment transport that can be 2 orders of magnitude less than, and time-averaged shear velocities that can be nearly half of, that predicted by the neutral version. Sensitivities to grain size distributions indicate that even a small amount of finer sediment can stratify the storm-driven flows. Sensitivities to closure constants within the range of reported values also produce up to an order of magnitude variation in sediment transport, illustrating the need for dedicated field experiments to refine further estimates of these parameters.

[1]  Scott Glenn,et al.  A suspended sediment stratification correction for combined wave and current flows , 1987 .

[2]  L. Wright,et al.  Wind stress, bed roughness and sediment suspension on the inner shelf during an extreme storm event , 1993 .

[3]  Palitha Nalin. Wikramanayake,et al.  Simple Models for Turbulent Wave-Current Bottom Boundary Layer Flow , 1991 .

[4]  C. Villaret,et al.  Effects of stratification by suspended sediments on turbulent shear flows , 1991 .

[5]  S. Mclean.  On the calculation of suspended load for noncohesive sediments , 1992 .

[6]  R. Stull.  An Introduction to Boundary Layer Meteorology , 1988 .

[7]  D. Cacchione,et al.  Shear stress and bed roughness estimates for combined wave and current flows over a rippled bed , 1992 .

[8]  S. Glenn,et al.  A Coupled Hydrodynamic–Bottom Boundary Layer Model of Ekman Flow on Stratified Continental Shelves , 1994 .

[9]  P. Nielsen.  Coastal Bottom Boundary Layers and Sediment Transport , 1992 .

[10]  O. Madsen,et al.  Movable bed roughness in unsteady oscillatory flow , 1982 .

[11]  Palitha Nalin. Wikramanayake,et al.  Calculation of Suspended Sediment Transport by Combined Wave-Current Flows. , 1994 .

[12]  S. Glenn.  A continental shelf bottom boundary layer model : the effects of waves, currents, and a movable bed , 1983 .

[13]  Irene A. Stegun,et al.  Handbook of Mathematical Functions. , 1966 .

[14]  D. Cacchione,et al.  Estimates of the suspended sediment reference concentration (Ca) and resuspension coefficient (γ0) from near-bottom observations on the California shelf , 1989 .

[15]  T. Gross,et al.  Acoustic measurements of the spatial and temporal structure of the near-bottom boundary layer in the 1990-1991 STRESS experiment , 1997 .

[16]  J. Wieringa,et al.  A revaluation of the Kansas mast influence on measurements of stress and cup anemometer overspeeding , 1980 .

[17]  Ivar G. Jonsson,et al.  EXPERIMENTAL AND THEORETICAL INVESTIGATIONS IN AN OSCILLATORY TURBULENT BOUNDARY LAYER , 1976 .

[18]  C. Vincent,et al.  Field measurements of the suspended sand concentration profiles and fluxes and of the resuspension coefficient γ0 over a rippled bed , 1990 .

[19]  Palitha Nalin. Wikramanayake,et al.  Calculation of movable bed friction factors , 1994 .

[20]  A. R. Nowell,et al.  Flume evaluation of the relationship between suspended sediment concentration and excess boundary shear stress , 1988 .

[21]  D. Hanes,et al.  Comparison of field observations of the vertical distribution of suspended sand and its prediction by models , 1996 .

[22]  O. Madsen,et al.  Combined wave and current interaction with a rough bottom , 1979 .

[23]  C. Harris,et al.  Ripple geometry in wave‐dominated environments , 1994 .

[24]  James D. Irish,et al.  Geometry, migration, and evolution of wave orbital ripples at LEO-15 , 1999 .

[25]  U. Högström.  Non-dimensional wind and temperature profiles in the atmospheric surface layer: A re-evaluation , 1988 .

[26]  Patricia L. Wiberg.  A theoretical investigation of boundary layer flow and bottom shear stress for smooth, transitional, and rough flow under waves , 1995 .

[27]  J. Turner,et al.  Buoyancy Effects in Fluids , 1973 .

[28]  Patricia L. Wiberg,et al.  A comparison of field data and theoretical models for wave-current interactions at the bed on the continental shelf , 1983 .

[29]  E. F. Bradley,et al.  Flux-Profile Relationships in the Atmospheric Surface Layer , 1971 .

[30]  O. Madsen,et al.  The continental-shelf bottom boundary layer , 1986 .

[31]  Scott Glenn,et al.  A Coupled Hydrodynamic–Bottom Boundary Layer Model of Storm and Tidal Flow in the Middle Atlantic Bight of North America , 1995 .

[32]  L. D. Wright,et al.  Tests of bed roughness models using field data from the Middle Atlantic Bight , 1995 .