Saturday, January 1, 2011

What are Hours Above Full Normal Flow in SWMM 5?


Subject:  What is Hours Above Full Normal Flow in SWMM 5?

The Conduit Surcharge Summary Table in the Report text file or Status Report lists a column of results called “Hours above Full Normal Flow”.  This is the number of hours the flow in the link was above the REFERENCE full flow as calculated by Manning’s equation.  The flow in the link can be above full flow even if the link is not a full depth if the head difference across the link is high enough.  The head difference is the water surface elevation at the upstream end of the link minus the water surface elevation at the downstream end of the link.  The capacity or d/D of the link varies from 0 to 1 with 1 being a full pipe or link.
Figure 1.  Hours above Normal Flow in SWMM 5 Links

Figure 2. Flow versus Full Flow in SWMM 5

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