Transcript Slide 1

Watershed Modeling using
HEC-HMS and EPA-SWMM
©T. G. Cleveland, Ph.D., P.E.
25 July 2012
Lesson 14
Routing in SWMM
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Hydraulic routing by
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Normal Flow
Kinematic Wave
Dynamic Routing
Routing occurs in conduits
Conduits
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Open conduits
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Normal and Kinematic, Manning’s only.
Dynamic, Unsteady GVF Equations (St.
Venant)
Closed conduits
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Preissman slots except:
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Identified culverts (new feature, am not
familiar)
Identified force mains (after a pump)
Conduits
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Data
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Length
Geometric shape
Resistance and added head losses
Inlet and outlet offsets
Maximum depth
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For closed geometry, sets fill depth
For open geometry sets how deep water
gets before program “wastes” water for
numerical stability.
Conduits
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Data
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Slope is NOT supplied, it is computed
from node invert elevations.
Special Element Routing
• Level pool routing in storage elements.
• Diversions and weirs are “special”
conduits.
– Flow over weirs is by weir equations and
coefficients
– Diversions is usually a fraction flow is
diverted above some minimum value
• Pumps are “special” conduits.
– Flow by pump curves
Guidelines
• In SWMM most useful routing is using the
Full Dynamic method.
– Normal flow does not handle backwater well.
– Kinematic wave does not capture backwater
well.
• Approximate “steady” conditions using long
simulation times (and constant forcing
functions), ignore early time.
Uses
• HMS routes, why bother?
– HMS is not best tool when you have to
estimate water surface elevations as part of
the analysis.
– SWMM can handle the water surface
computations in a straightforward manner.
• HMS routes upstream to downstream;
there is NO feedback – usually fine, except
in low-relief regions where backwater (or
reverse flows) matter.