Either steady-state or transient flow problems can be analyzed. The exchange of

material with the bed can be calculated or suppressed. Default values may be used

for many sediment characteristics or these values may be prescribed by input data.

Either the smooth wall velocity profile or the Manning's equation may be used to

calculate bed shear stress due to currents. Shear stresses for combined currents and

wind waves may be calculated

Both clay and sand may be analyzed, but the model considers a single, effective

grain size during each simulation. Therefore, a separate model run is required for

each effective grain size. Fall velocity must be prescribed along with the water

surface elevations, x-velocity, y-velocity, diffusion coefficients bed density, critical

shear stresses for erosion, erosion rate constants, and critical shear stress for

deposition.

The program does not compute water surface elevations or velocities; these data

must be provided from an external calculation of the flow field. For most problems,

a numerical model for hydrodynamic computations, RMA2-WES, is used to generate

the water surface elevations and velocities. An implicit assumption of the SED2D

WES model is that the changes in the bed elevation due to erosion and/or deposition

do not significantly affect the flow field. When the bed change calculated by the

model does become significant and the externally calculated flow field supplied by

the user is no longer valid, then the SED2D WES run should be stopped, a new flow

field calculation should be made using the new channel bathymetry generated by

SED2D WES, and the SED2D WES run should be restarted with the new flow field

as input.

In addition, the sediment transport model formulation assumes that the input

geometric mesh and the resulting hydrodynamic solution from RMA2 are of

adequate resolution, accuracy and quality to allow for an accurate and reasonable

solution to the governing sediment transport equation to be solved. This may not

always be true. In such a case, then the mathematical solution from SED2D or

STUDH will potentially have severe oscillations with negative concentrations. The

resolution of such "unstable" solutions cannot always be obtained within the

coefficient adjustments of the sediment model. It may be necessary to return to the

basic mesh resolution and obtain a better hydrodynamic solution.

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