Friday, March 27, 2009

Q full vs Q dynamic vs Q normal in SWMM5

Introduction – the reason for these series of blogs are as an expanded view of the input, engine and output of #SWMM5 It is a companion to the EPA Documentation which I describe here:

I have noticed based on email questions and postings to the SWMM List Sever (a great resource hosted by CHI, Inc.) that many SWMM 5 users do not know about the really outstanding documentation on SWMM 5 posted on the EPA Website It consists of two now and in the near future three volumes on Hydrology, Water Quality, LID’s and SuDS and Hydraulics. The documentation is fantastically complete with detailed background on the theory, process parameters and completely worked out examples for all of the processes in SWMM5. It is truly an outstanding aid to modelers and modellers worldwide. It would benefit you to read them (if you have not already downloaded the PDF files)
1. It gets more flow than qFull because the water in the pipe has more than just the bed slope to push it - it also has the water surface slope.
There is about a 5 meter head pushing the water out if you the bed slope to the water surface slope - see the HGL Plot.

2. The Q dynamic or St. Venant flow uses ALL of the information you have about the condition in the link (see the next image) so the flow is greater than Qfull and Q normal flow. The information includes the hydraulic radius and cross sectional areas for upstream, midpoint and the downstream ends of the links.

Normal Flow, Q and St Venant Flow.   Fraction Normal Flow Limited is the fraction of time SWMM5 uses Normal Flow for the Conduit.

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 🌟 SWMM5 (Storm Water Management Model 5) is a widely used urban hydrology and hydraulic modeling software developed by the United States E...