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Troubleshooting Overflow in an Existing Municipal Sewer Network

I am trying to reduce the "overflow volume" in the model calculation summary. 

I have achieved this partially by -

- Adding overflow links (link to outfall structure with boundary condition set to discharge at next downstream node)

- Adding surface storage at local low points

- Adding additional (dummy) manholes at low points along the sewer line to account for local ponding

This seems to be working locally, but ends up pushing the flooding issues to subsequent upstream or downstream nodes.

I understand that this means the existing system is undersized, but I want to make sure that the model is not losing flow.

Any suggestions to address this issue?

Thanks.

Parents
  • I wanted to update that I am somewhat confused about adding "overflow" conduits (trap. channels).  Based on some results I was just looking over, it  looks like the overflow link is continuing to increase in flow, even though the manhole only is surcharging for a short amount of time (see two graphs below).

    Is this an error?  I am going to try removing the "overflow" conduit so that I am not losing flow.

    Thanks, Seth

Reply
  • I wanted to update that I am somewhat confused about adding "overflow" conduits (trap. channels).  Based on some results I was just looking over, it  looks like the overflow link is continuing to increase in flow, even though the manhole only is surcharging for a short amount of time (see two graphs below).

    Is this an error?  I am going to try removing the "overflow" conduit so that I am not losing flow.

    Thanks, Seth

Children
  • Update:

    Here is the result when I turned off the overflow.  It looks like the manhole HGL dropped almost 1.5 ft from the previous graph.  Am I missing something?  It seems odd that the HGL dropped despite removing the overflow conduit.  (Note that the manhole already discharges to two (non-overflow) conduits.

    Sorry for flooding the Bentley community with posts.  Thanks, Seth

  • Hello Seth,

    What program are you using? If you are using SewerGEMS or CivilStorm, it's possible that by making adjustments to the model that you improved the continuity error, which impacted the overflow volume. Information troubleshooting the continuity error can be found at the following link: communities.bentley.com/.../21403.troubleshooting-unstable-sewergems-and-civilstorm-results-using-the-implicit-solver.

    Otherwise, it would be good to have more information on the system. If needed, you can provide the model as well. There are two options for sharing your model on Communities, whichever you choose please be sure to zip your files first. The first option is to attach the zip file containing your model to your reply on the forum using the Advanced Reply Editor (you'll find the link below and to the right of the reply box). If your data is confidential please use the instructions in the link below to send it via Bentley Sharefile. Files uploaded to Sharefile can only be viewed by Bentley employees. Please be sure to reply on this thread with the name of the file after it has been uploaded.

    communities.bentley.com/.../7079.be-communities-secure-file-upload

    If you upload the files to the Sharefile site, make sure to post here so we know it's available.

    Regards,
    Scott
  • Graphs with overflow conduit in place: