7. SIMULATION OF SEDIMENT DISPERSION WITHIN THE MISSISSIPPI SOUND 



7.1 Mathematical Model 



Equations and Boundary Conditions 



The transport of sediments within the water column is described by the 

 conservation equation for the suspended sediment concentration written in 

 dimensional form as: 



iC ^ iiCui ^ llCvl ^ ^'^^(^"^^J , ± L 9_c\ ^ _3_ / 9C\ 

 3t ax 8y 82 3x \^^ 8xy 3y \ ^ 3y/ 



(<) 



+ ^lDv^|+S (7.1) 



where C is the suspended sediment concentration, (u,v,w) are the 

 three-dimensional fluid velocities in (x,y,z) directions computed from the 

 hydrodynamic model, w^ is the vertical settling velocity of the sediments 

 relative to the fluid, D^ and Dy are the turbulent eddy di ffusivities in the 

 horizontal and vertical directions, and S is a source term. The net vertical 

 flux of sediments is specified at both the surface and the bottom: 



W3C + Dy 1^ = @ z = (7.2) 



- W3C + Dy -^ = v^C - E 



= ^d (C - Cgq) (3 z = -h(x,y) (7.3) 



where h(x,y) is the water depth, v^ is the deposition velocity, E is the rate 



of entrainment, and Cg„ is defined as E/v^. v^ and E are generally functions 



of many parameters, as described in the previous section. 



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