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Total System Outflow Volume Question

How does SewerGEMS calculate total system outflow (Implicit solver)? The calculation summary reported 975,000 gallons.

Have a system with 2 active outfalls. Ran a scenario with calculation time step = reporting time step in order to make sure I got all the flows that the application used to calculate the volume.

I pulled the flow data at the outfalls and calculated the total outflow volume to be 2.5 MG, which was very close to the total system inflow.

This would have produced a much better continuity error than what was reported in the calculation summary.

  • Hello Rick,

    The total system outflow volume should be the total volume that leaves the system, mots of which would typically be from outfalls set to free outfall. To look at specifics of mass balance (volume in/out/overflow/change) on a per-element basis, you can use the Hydraulic Reviewer

    In order to troubleshoot this issue, I have a few questions for you:

    1) What version of SewerGEMS are you using? You can check either under File > Help > About, or Help > About for older versions. The latest is 10.02.01.04.

    2) For the outfalls that you added up, are all of them set to "free outfall"? If some were set to "boundary element", then the flow out of the outfall will be directed to the selected element instead of leaving the system.

    3) Can you provide a copy of the model along with steps to reproduce? Sharing Hydraulic Model Files on the OpenFlows Forum


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.