How to discard water quality volume to an arbitrary outfall?

Hi, 

I have a model in which a pond goes to an outlet structure to go directly to our storm system. However, we want to discard the water quality volume from that same pond to go to arbitrary outfall so it does not affect downstream of our system. I know what the volume that I need to discard is. 

Therefore, I was wondering if it would be as simple as having two outlet structures with pipe attached to each of them, one for the water quality volume and one for the rest of the flow? For the water quality volume the pipe after the outlet structure would end in an outfall. 

How would I make sure that only the amount of XXX of volume  is taken to that pipe? 

Thanks

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  • However, to get the desired infiltration rate. Is that something that I would see if I got the desired infiltration rate after I run the model or is that somewhere I can look someplace else before running it?

    You would need to compute the model first and graph the pond seepage result field.


    Regards,

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

  • Jesse, after I have run the model that I did with the seepage method approach would I be graphing the flow(seepage loss)? Would that tell me how much flow was lost due to infiltration? 

    I looked at it and supposedly we are trying to get 3.5 cfs discarded and my model resulted in higest result of 1.3 cfs for the flow(seepage loss). Therefore, would it be best to mess with the soil information until I get my desired cfs or try the approach of discarding flow with another outlet from the pond with a rating table.

    Should I also be looking at the seepage rate results? I looked at that and was getting 0 in/hr which does not seem right. 

    Thanks,

  • Jesse, after I have run the model that I did with the seepage method approach would I be graphing the flow(seepage loss)? Would that tell me how much flow was lost due to infiltration? 

    Yes, the "Flow (Seepage loss)" would show you the seepage flow rate over time. For the total volume, see the Hydraulic Reviewer. This is mentioned in the section "Reporting flow or volume loss from seepage" of the seepage article provided earlier.

    I looked at it and supposedly we are trying to get 3.5 cfs discarded and my model resulted in higest result of 1.3 cfs for the flow(seepage loss). Therefore, would it be best to mess with the soil information until I get my desired cfs or try the approach of discarding flow with another outlet from the pond with a rating table.

    Either approach could be considered. There are pros and cons to both. With the pond outlet structure approach you have more control over it, but you'd see some extra elements that aren't really in the real system (pond outlet node, pipe and outfall).

    Should I also be looking at the seepage rate results? I looked at that and was getting 0 in/hr which does not seem right. 

    Can you clarify a bit more? Are you referring to the "Flow (Seepage loss)" field in the pond properties. It may show zero in the first timestep - make sure you graph this result to see how it varies with the pond water surface elevation.


    Regards,

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

  • Hi, I am getting two different results when doing the seepage method vs. the pond outlet structure approach. Is that common? 

    Also for the seepage method i am geting practically same "Flow(seepage loss)" numbers for all my three storm event i am evaluating, 2 yr, 10 yr, and 100 yr. Is that common too? I would think they would be drastically more different. 

  • I am getting two different results when doing the seepage method vs. the pond outlet structure approach. Is that common? 

    Different results are to be expected (as these are two different methods) unless you were to configure the user defined pond outlet to exactly match the configuration of the Green-Ampt method, using trial-and-error.

    Also for the seepage method i am geting practically same "Flow(seepage loss)" numbers for all my three storm event i am evaluating, 2 yr, 10 yr, and 100 yr. Is that common too? I would think they would be drastically more different. 

    The degree to which the seepage results change depends on the difference in pond water surface/wetted area and the Green-Ampt parameters.

    I did a quick test in a sample file in the latest version (10.04.00.158) and in a scenario where the pond water surface elevation is higher, I see a high seepage flow. I used the SWMM solver with made-up numbers for the Green-Ampt parameters. If you are not seeing a larger difference, check the pond elevation results and Green-Ampt parameters. For example I see a much higher seepage as I increase the conductivity or initial deficit fields.


    Regards,

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