In this simulation, a relatively large time step of 12 minutes was used 

 for both the external and the internal modes. Seven grid points were used in 

 the vertical direction. A relatively smooth bottom with a roughness length, 

 Zq, of 0.1 cm was assumed. A parabolic length scale. A, no more than 25% of 

 the local depth, was assumed in the vertical direction. River inflows from 

 six rivers were considered: Pearl, Jourdon Wolf, Biloxi, W. Pascagoula, 

 Pascagoula, and Mobile. 



Currents during the 5-day Simulation (9/20/80 to 9/25/80) 



The tide-driven horizontal currents at mid-depth are shown in Figure 5.6 

 for two stations in the Mississippi Sound. Currents on the order of 1 ft/sec 

 (30 cm/sec) exist at both stations. Again, reasonable agreement is found 

 between data and model results. 



The horizontal velocity field at 1 m depth, after 3 days of simulation, 



is shown in Figure 5.7(a). Relatively large currents exist at the various 



tidal inlets and in the area between the Ship Island and the 



Chandeleur Island. Except in these areas, at this instant of time, bottom 



shear stress generated by the tidal currents are generally less than 



2 

 0.8 dyne/cm . Hence, little sediment resuspension is expected. The 



horizontal currents at a constant depth of 10 m are shown in Figure 5.7(b). 



Within the Mississippi Sound and the Chandeleur Sound, the depths are 



shallower than 10 m and hence no currents are shown. 



The velocity field across a transect along the x-z plane, which crosses 

 into the Mobile Bay, is shown in Figure 5.8. Large currents over the left 

 portion of the domain represent flow through the narrow entrance into the 

 Mobile Bay. Once through the entrance, the flow gradually decreases towards 

 the head of the Mobile Bay. The distribution of eddy viscosity within a 

 transect across the Horn Island Pass is shown in Figure 5.9. The values of 



2 



eddy viscosity at this instant of time are generally less than 20 cm /sec. Of 

 course, these values are functions of time. 



79 



