MID -DEPTH V AT STATION 5 



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p ... 



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MID- DEPTH V AT STATION 6 



■ Wind a Tide 



• — Tide Only 



Figure 8. Mid-Depth Along-Shore Velocity at Stations 5 and 6 

 20 Sept. to 23 Sept., 1980. Tide and Wind Forcings. 



from 



with the pressure gradient caused by the wind set-up, which is on the 

 order of 20 cm across the Mississippi Sound. According to a laboratory 

 flume study on the erodibility of the Mississippi Sound sediments 

 (Sheng, 1981), it is expected that the bottom shear stress generated by 

 the strong Westerly wind in winter may cause significant resuspension 

 of sediments. 



TRANSPORT, RESUSPENSION, AND DEPOSITION OF COHESIVE SEDIMENTS 



Transport Modes 



The transport of cohesive sediment in the water column can be 

 described by a conservation equation, similar to the heat or salinity 

 equation, for the suspended sediment concentration. An equation 

 similar to Eq. (5) can be written for the sediment concentration C. 

 However, the vertical velocity in the sediment concentration equation 

 should be composed of the sum of the fluid velocity (w) and a settling 

 speed of the particles ( Wg)_. _j:_rL_fresti.>water^ - the^settVi ng- speed—of— 

 cohesive sediment from a coastal environment shows a relatively flat 

 spectral distribution. As the salinity increases, the sediment 

 particles form aggregates and the spectral distribution becomes much 

 sharper (Fig. 10). In this study, for simplicity, we assume the 

 cohesive sediment in the Mississippi Sound can be described by one 

 single settling speed. The settling speed of bottom sediment samples 

 from the Sound was measured in laboratory, without adding dispersant to 

 the samples, and a median settling speed determined. 



The behavior of sediment In the water column depends on the 



280 



Sheng 



