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SewerGEMS+ Extreme load factor+DIversion

Hi

I am analyzing an existing complex sanitary system which has a diversion on the system and Harmon factor to be applied to it and surcharge to be check for the wet weather.

I prefer to go with the implicit option to calculate the diversion automatically (instead of rating curve table), but the issue is the implicit don't apply the extreme factor.

Actually there are lots of diversion structures in the system and I don't want to go with  rating curve table and steady state.

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  • Hamid,

    Extreme flow factors / peaking factors are a steady state concept, typically used for pipe sizing in sewers. The implicit solver solver provides you with an unsteady simulation.

    You could consider using the Implicit solver to construct the diversion rating table to use with the Convex solver, so you could then use it with the Extreme flow methods in steady state. You can read about how to do that in this article:

    Modeling a flow split (diversion) with the SewerCAD or StormCAD numerical solver

    Another option would be to consider using the Implicit solver with a multiplier applied to sanitary loads. You could use a new sanitary loading alternative with the scenario in question and global edit the loading information in the sanitary load control center.


    Regards,

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

  • Jesse,

    I just used implicit to get the rating curve table and set the calculation time to 1min.

    So, just select both four pipes in Mh-13, right click and went to Graph and chose Flow (first option) but seems that the incoming flow from time 0 to 0.4 hours is more!

    I will appreciate you if you could help me to develop the table.

    Best Regards,

    Hamid

  • Hamid,

    The results look correct to me, using the model you just sent, in the latest version of SewerGEMS (10.00.00.40). For simplicity I removed the small inflows on MH-13, MH-15 and MH-16. The key is to look at the next-downstream pipes; Pipe - (21) & Pipe - (23). The results in the pipes immediately downstream of MH-13 have some intermediate results. Because of the way that extreme flow factors need to be recomputed and that both sanitary and wet weather flow is split, it gets tricky. The total flow in and total flow out won't necessarily match, because the extreme flow factors will be readjusted as the flow combines and then splits. Here are my hand calcs, which match the results in the model:

    All loads use unit load "Unit Sanitary (Dry Weather) Load - 1" which uses the Harmon equation for extreme flow factor calculation.

    EFF = 1+(14/(4+((P/1000)^0.5)))

    Two upstream pipes:

    Pipe - (19)
    Population: 5309.5
    EFF (Harmon equation) = 3.221
    Upstream loading unit count: 5309.5 / 3.5 = 1517
    Sanitary flow: (0.009722222 (unit load) * 1517) * 3.221 = 47.5
    Wet weather flow: 0
    Total flow: 47.5

    Pipe - (14)
    Population: 752.5
    EFF (Harmon equation) = 3.876
    Upstream loading unit count: 752.5 / 3.5 = 215
    Sanitary flow: (0.009722222 (unit load) * 215) * 3.876 = 8.1
    Wet weather flow: 3.64
    Total flow: 11.74

    Sum of upstream flow:

    Population: 5309.5 + 752.5 = 6062
    EFF (Harmon equation) = 3.166
    Upstream loading unit count: 6062 / 3.5 = 1732
    Sanitary flow: (0.009722222 (unit load) * 1732) * 3.166 = 53.312
    Wet weather flow: 3.64
    Total flow: 56.952

    ------------

    From the diversion rating curve, for a total upstream flow of 56.952 the diverted flow is 26.26 (46.11%)

    Pipe downstream of diversion - Pipe - (21)

    Diverted flow per rating curve: 26.26
    portion from wet weather flow: 3.64 * 0.4611 (46.11%) = 1.678
    portion of population: 6062 * 0.4611 = 2795
    New EFF for split population: 3.468
    New Unit load count: 2795 / 3.5 = 798.571
    New total sanitary flow: (0.009722222 (unit load) * 798.571) * 3.468 = 26.925
    Total flow in diversion pipe: 26.925 + 1.678 = 28.6

    Pipe on other side of diversion - Pipe - (20)

    Remainder of flow per rating curve (not diverted): 56.95 - 26.26 = 30.69
    portion from wet weather flow: 3.64 * 0.5389 (53.89%) = 1.962
    portion of population: 6062 * 0.5389 = 3267
    New EFF for split population: 3.4107
    New Unit load count: 3267 / 3.5 = 933.4286
    New total sanitary flow: (0.009722222 (unit load) * 933.4286) * 3.4107 = 30.952
    Total flow in diversion pipe: 30.95 + 1.96 = 32.9

    The populations in the two downstream pipes add up to the total upstream population, and the highlighted total flows above match the total flow in the model pipes.

    In short, the diverted flow gets recalculated in the next downstream pipe, because the extreme flow factor changes since the population is less (due to the split). So, a lower EFF is calculated when the two upstream pipes combine, but then a higher EFF is calculated in each of the downstream pipes after the population splits.


    Regards,

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

    Answer Verified By: Hamid Akbari 

  • Hi Jesse,
    You got it.
    I really appreciate you for your kindly support.

    Regards,

    Hamid
  • You're welcome. Here's a new wiki article:

    Handling of Extreme flow factors with diversions


    Regards,

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

  • Hi Jesse,

    I finished the dry weather analysis by applying the peak factor and steady state.

    Our client asked us to do the following:

    For Post development diurnal patterns for new development sites should be created applying the Harmon Peaking Factor as the constant multiplier throughout the day and assigned to the sub-catchment(s) representing the development itself.

    I think It means I have to analysis the post development by EPS mode to find the surcharge level, please confirm.

    So, if I leave steady state all the peak factors will be ignored, how I analysis it by getting the "total peak flow of the steady state"

    Regards,

    Hamid

  • Hello Hamid,

    If you run the model in EPS, the peaking factors will not apply. You would need to model this as a sanitary load. It is possible to set up a pattern load (which is mentioned by the client) for this purpose. This is not the same thing as peaking factors though.

    Basically, if you run in EPS, there is no peaking factors or extreme flow setup involved. This is only applicable for steady state runs.

    Regards,
    Scott
Reply
  • Hello Hamid,

    If you run the model in EPS, the peaking factors will not apply. You would need to model this as a sanitary load. It is possible to set up a pattern load (which is mentioned by the client) for this purpose. This is not the same thing as peaking factors though.

    Basically, if you run in EPS, there is no peaking factors or extreme flow setup involved. This is only applicable for steady state runs.

    Regards,
    Scott
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