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A
non-prismatic channel link is one that has different geometry and/or
hydraulic properties at the upstream and downstream ends of the
link. Many hydrodynamic models require an average
cross section and roughness characteristics for the entire length of a
link (e.g., EPA's SWMM). Although this approach simplifies the input data slightly, it
limits the modeler's ability to account for variations that could be
important if not critical such as contraction and expansion losses.
Non-prismatic
channel links are easily modeled in ICPR. Consider the example
depicted below with three nodes (A, B and C) and two channel links (A-B
and B-C). Not only does the geometry change as indicated by the
cross sections (X-A, X-B and X-C), but Manning's n also varies
significantly. ICPR includes several options for averaging friction
slopes between the two end of a channel link.
A
portion of the channel link data form is shown below. Notice that
there are data requirements for the upstream end of the link and for the
downstream end of the link. In this example, irregular cross
sections are used to describe the geometry and roughness characteristics
of the channel. The cross sections are loaded into tables and named,
and then referenced in the channel data form as shown below. For
link A-B, cross section X-A is specified at the upstream end of the link
and cross section X-B is specified at the downstream end. Note also that
there are contraction and expansion losses included in the computations.
The
channel data form for link B-C is shown below. Note that cross
section X-B is used at the upstream end of this channel link. It is
also used at the downstream end of channel link A-B. Cross sections
can be entered one time and then used many times. Basically, they
are considered templates by ICPR and are moved vertically into the
designated invert elevation.
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