In the following, a three-dimensional hydrodynamic model will be 

 presented first, followed by a realistic simulation of tide- and 

 wind-driven currents in the Mississippi Sound and adjacent shelf 

 waters. Transport, resuspension, and deposition of cohesive sediments 

 are then discussed, followed by a discussion on the bottom boundary 

 layer and wave effect. 



WIND 



RIVER LOADING 



WIND WAVES (T ~ 2 to 10 sec) 



Figure 1. Schematics of Dominant Mechanisms Affecting Sediment 

 Distribution in Shallow Coastal Waters. 



A THREE-DIMENSIONAL NUMERICAL MODEL OF COASTAL CURRENTS 



In order to study the dynamic response of coastal waters to tides, 

 winds, and meteorological forcing, a three-dimensional, free-surface, 

 time-dependent model is often desired. In addition, stratification and 

 complex topography have to be properly resolved. For relatively 

 long-term application, computational efficiency of the model is 

 extremely important. Traditional three-dimensional, free-surface 

 models (e.g., Leendertse and Liu, 1975) require an exceedingly small 

 time step (associated with the propagation of gravity wave over the 

 distance of a horizontal grid spacing), and hence require extraneous 

 computational costs. 



Special features of the present model include (1) a 

 "mode-splitting" procedure which allows efficient computation of the 

 vertical flow structures (internal mode), (2) an efficient ADI scheme 

 for the computation of the vertically-integrated variables (external 

 mode) (3) an implicit scheme for the vertical diffusion terms, (4) a 

 vertically and horizontally stretched coordinate system, and (5) a 

 turbulence parameterization which requires relatively little tuning. 



Governing Equations and Boundary Conditions 



The basic equations describing the large-scale motion in a large 

 body of water consist of a continuity equation, momentum equations, 

 conservation equations of heat and salinity, and an equation of state. 

 For simplicity here, the last three equations have been combined into 

 an equation for the density. Inherent assumptions are: (1) pressure 



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