Forcemain Flow modeling

[CSohm]

I'm using the dynamic wave modeling for our wastewater system, being sure to put the surcharge depth of all the FM nodes quite high.

I noticed that the flow through various links changes wildly from link to link. For instance, the modeled flow in one link on, say, day 6 would hold quite steady around 600 gpm or so, but the next link down the line would have a flow that looks more like a seismograph than steady flow, and the next one would go just as negative as positive. Can anyone explain why the modeled flow through a force main is not more uniform from link to link?

[Robert Dickinson]

Hello CSohm,
We can answer this better if you send us the model to support@innovyze.com but from you description I would suggest using a smaller time step, use HW losses for your force mains, increase the number of iterations and lower the tolerance. You have reverse flow, you can add a flap gate to the force main. The pump curve works better if there are two or more points - see the 2nd image in this post.
Regards,
Robert Dickinson
Innovyze Inc.
2014-12-04_2229.jpg

444.jpg

[CSohm]

I had Hazen-Williams already set, and had flap gates on all my FMs coming out of the LSs. All I did was change the iterations from 4 to 8 and lower the tolerance from 0.005 to 0.001. That seemed to do the trick! Thanks for your help.

[Robert Dickinson]

Robert E Dickinson ‏@RDickinson Nov 26Tampa, FL
Five ways to make a HGL or Hydraulic Grade Line Graph in InfoSWMM from Innovyze




Options for showing a depth in an InfoSWMM HGL plot can be either in/mm or feet/meters by using User Defined Units





The above inages show a few more ways to look at the HGL around a pump in InfoSWMM

[Stewart Sargent NZ]

Hello CSohm,
I often see similar seismographs.
Roberts suggestions are the best course of action I have found. Somethimes however all that can be achieved is to reduce the effect somewhat -- especially for seismographs along gravity pipes. In the end, plain basic engineering has to be used to interpret the results from Summary info (tables, graphs, HGLS maxs etc) and for hydraulic behavour at specific places. Often the peak values are false-alarms rather than real-world performance. Forensic work and examination of lots of different HGLS and graphs often enables one to elliminate these false alarms. But it takes time before one gains Professional Confidence in ones Conclusions. All.. just traps to keep us on our toes.... as they say "Modelling can be a powerful way of making big mistakes (in conclusions) in a very fast way" <grin>.
Having said all that ... infoSWMM is a great tool -- and the best I have used for such work ... and we are very fortunate to have Roberts expertise.