Marsh Porosity parameters are transferred to the SED2D model by way of the

GFGEN geometry and RMA2 hydrodynamic input files.

deposition and erosion of both sands and clays. Methods of computing the alpha

coefficients depend on the sediment type and whether erosion or deposition is

occurring.

For sand transport, the supply of sediment from the bed (i.e., the sediment reservoir)

is controlled by the transport potential of the flow and availability of material in the

bed. The bed source term is

-*C*

where

S

=

source term

Ceq

=

equilibrium concentration (transport potential)

C

=

sediment concentration in the water column

=

characteristic time for effecting the transition

tc

There are many transport relations for calculating Ceq for sand size material. The

Ackers-White (1973) formula was adopted for this model because it performed

satisfactorily in tests by WES and others (White, Milli, and Crabbe 1975; Swart

1976), because it seems to be complete, and because it is reasonably simple. The

transport potential is related to sediment and flow parameters by the expressions in

the following paragraphs. The Ackers-White formula computes the total load,

including suspended load and bed load, and was developed originally for fine sand.

The formulation was later updated to include coarser sands and these revised

coefficients are included in the current model formulation. However, the

appropriateness of the use of SED-2D with the Ackers-White formula diminishes

with coarsening of the sediment.

The characteristic time, tc, is somewhat subjective. It should be the amount of time

required for the concentration in the flow field to change from C to Ceq. In the case

Integrated Publishing, Inc. |