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Deferent engine Results in SewerGEMS

I am getting big difference when I run the Storm Network model using Bentley EPA SWMM than the supplied EPA SWMM 5.0.12, it is the same model and the same parameter, I just switch between two engines; 

I got 8.17 m3/s at the outfall by using Bentley EPA SWMM, and I got 10.55 m3/s when I run the model with EPA SSWMM 5.0.12. That is a huge difference. the model shared for troubleshooting (Bentley EPA SWMM & EPA SWMM).

Why that difference? which one is more accurate and to be used? please justify both results.

Bentley EPA SWMM

EPA SWMM:

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Regards .... Mohamad Azzam

  

  • So, if a catchment is directed to a "node" in EPA-SWMM, all of the flow from the catchment enters the system. Meaning, 100% of the catchment flow is "captured"

    But when I run the model by using EPA SWMM, there are flow going to the gutter. Do you mean that flow is the excess gully capacity 100% goes to the next gully thru the gutter?

    And when I used the enhanced EPA the gully capacity percentage will be considered and that percentage will enter to the system and the rest will go to the next gully by gutter ?

    is that correct?

    Regards,

    Mohamad

  • But when I run the model by using EPA SWMM, there are flow going to the gutter. Do you mean that flow is the excess gully capacity 100% goes to the next gully thru the gutter?

    Almost all of your gutters have zero flow during the entire simulation, because when using the EPA version of the engine, catchbasin elements capture 100% of the connected surface flow (since as explained previously, EPA-SWMM itself does not have an inlet capture capability). 

    There are a few gutters that do have flow and these are because of catchbasin overflow. When a catchbasin floods and the hydraulic grade rises above the rim elevation, overflow passes into the downstream gutter if it exists. Below is one example. See more here: Modeling catch basin overflow into gutter

    And when I used the enhanced EPA the gully capacity percentage will be considered and that percentage will enter to the system and the rest will go to the next gully by gutter ?

    If you mean the "SWMM (BENTLEY 5.1.13)" option in the "Solver Compatibility" calculation option then yes - we have enhanced the SWMM solver to add the capability to calculate inlet capture whereby a percentage of the flow is captured (and enters the subsurface pipe system) and the rest bypasses the inlet and passes down the next gutter.


    Regards,

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

    Answer Verified By: Mohamad Azzam