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EPD-RIV1 USER’S GUIDE: DRAFT 4/10/02
abrupt changes in cross-sectional area, roughness, lengths, etc. may
cause stability problems in both the hydrodynamic and quality model.
Factors affecting the computational grid. A number of factors must be
evaluated and weighed against each other when setting up the
computational grid. These include:
Boundary Conditions: The computational grid must be set
up so that the upstream boundary conditions, for both the
hydrodynamic (e.g. flows) and water quality model (e.g.
constituent inflow concentrations), are known and well
characterized. A common practice is to locate a boundary
where flow or water quality data are available, such as at USGS
gaging stations. It is also often best to locate model boundaries
at some point of control. A "control" is a location where there is
physical dependence between water surface elevation and
discharge, which may be a structure, constriction, or change in
bottom elevation. U.S. Geological Survey gage stations, for
example, are normally established at control points in a river.
Likewise, the downstream boundary must either be well
characterized or sufficiently below the area of interest so that
errors in its specification do not affect predictions in the area of
interest. Care needs to be exercised in establishing model
boundaries at areas which are not controls since unless flow is
uniform the discharge is not a function of elevation alone
(Henderson 1966).
Location of Control Structures: If there are control
structures within the system, such as dams with a controlled
release, then the grid must be broken into two or more
branches. Boundary conditions (such as a release) can only be
specified for a branch.
Tributary Impacts:
In many cases the impacts of
tributaries on the main river or stream can be described rather
than predicted. That is the user specifies the flows and
constituent concentrations for the tributary (e.g. in the lateral
inflow file read by EPD-RIV1). Alternatively, if the flows in the
main channel and tributary are linked in some way, or it is
necessary to predict (rather than describe) the flows and quality
of the tributary, then it may be necessary to include it in the
modeled grid as a separate branch.
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EPD-RIV1