D-R-A-F-T
Capabilities Of SED2D
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
Limitations Of SED2D
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the user is no longer valid, then the SED2D WES run should be stopped, a new flow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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