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Catchbasin Capturring Efficiency more than 100%

I am getting at few catchbasins the capturing efficiency is very high (more than 100%), I guess that due to the backflow at the gutter for the certain timestep, would you please assist in the followings;

1- is the backflow is the reason?

2-  Why SewerGEMS reporting more than 100%, the program should not exceed reporting 100% even there is backflow, the sewegems help says: "

100% capture means that the inlet capacity is larger than the actual local inflow so the model will attempt to put the entire local inflow into the manhole. If the manhole is flooded it there may be flow lost from the flooding although the inlet is still reporting 100% capture.

Moreover; the logic says the capturing efficiency should be (the amount of flow access the inlet/maximum inlet capacity), and accordingly at starting the simulation should be the efficiency =0 and by the time the efficiency should be increased to the peak then decreased to back to zero (this is only thought).

 3- According to above mentioned in the help, the program shows that at the beginning of the simulation the capturing efficiency is 100% and during the simulation, it does go less, but the model I have does not show efficiency back to 100% at the end of the simulation, the model shows that 77.6% as fixed to the end.

4- why the file in the model folder "Peak scenario-180min.stsw_1_123.txt" does not show the SI units in spite of the model having SI units?

Would you please check and elaborate on the above points (The model is uploaded and the screenshots as below)

Regards,

Mohamad Azzam

  • Hello Mohamad,

    In your model you are using the SWMM (BENTLEY 5.1.015) solver which does inlet calculations based on the HEC-22. This means the capture efficiency is first calculated and then the flow is captured based on it. However with the SWMM (EPA 5.1.015) solver the capture efficiency will always be 100% because EPA-SWMM does not account for capture efficiency calculations.

    There was a similar post you posted which I answered a while ago here: On Grade Inlet with SWMM

    Is this a similar query?


    Regards,

    Yashodhan Joshi

  • Thank you Yashodhan - the queries are not similar to the previous post. it is about the (Bentley SWMM Solver), the capture efficiency is higher 100%, the reason and the theory about that? also about the start and end value of the capture as shown in the graph? in addition to the txt file unit in the model folder. (refer to the listed query in this post).

    Regards,

    Mohamad Azzam

  • Mohamad, the issue appears to be related to the reverse flow occurring through gutter "GU-N-1026". It appears that SewerGEMS may only be "seeing" the forward flow from the catchment and the other gutter, so the extra reverse flow from the other gutter is causing it to go above 100%. We are investigating this further and will keep you updated.  


    Regards,

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

  • Mohamad,

    Just a quick update on the issue with capture efficiency above 100%. Our developers confirmed that the problem is indeed due to the reverse flow in gutter "GU-N-1026". We are looking into how this can be better handled, but it is a rare situation. For right now, we would suggest that you consider this as a sign that there may be other problems you may need to address (the reverse flow situation from the other gutter is likely not desirable).


    Regards,

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

  • Thank you Jesse for following this issue - please keep me posted and if you create a service patch ticket let us know?

    what about the other part of point NO.2 in the post; regarding the definition of capturing efficiency?

    Regards,

    Mohamad Azzam