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

Parents
  • Paola,

    In general you will want to model the system as close as possible to the real system. What in the real system limits the outflow based on volume? (how is that accomplished?) 

    You can indeed model multiple outlets leaving the same pond. See the "Pond" section of this article: Modeling a flow split (diversion) in SewerGEMS or CivilStorm

    With the pond outlet structure component in SewerGEMS, you can control outflow based on the available outlet types: orifice, weir, riser, vortex valve, user defined rating table. If you want to assume a specific, constant outflow that yields a certain volume, you could use the user defined rating table pond outlet type, assign it to a second pond outlet node attached to the pond, then connect that to a free outfall via a conduit.

    Or, if this specific volume you're looking to "discard" is actually infiltration (water soaking into the ground around the pond), you can use one of the available seepage methods.


    Regards,

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

  • Jesse, would probably looking through the question and answer that I found on this thread (in bold below) help me walk through how I take into account the seepage infiltration for that pond?

    Sewergems | Seepage | Pond Flow Loss

    Thanks

  • Nevermind i see that I answered my own question regarding if they are soil properties. I did not see that it explains what the parameters are underneath when you click on it. 

    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?

    Thanks for helping!

  • Yes the Green-Ampt is the standard methodology which calculates the infiltration rate based on the Suction Head, Conductivity and Initial Deficit of the soil. If you click the name of the field you can see a description at the bottom of the Property Grid (plus they are documented in the Help). See: Where can I find the definition of a property?

    I have added a few more details about these parameters to the new article, based on the EPA-SWMM manual.

    Yes, if you graph the seepage result field, that will be the infiltration based on the parameters you set (flow lost to the system through soaking into the ground in the pond) 


    Regards,

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

  • 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.

Reply
  • 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.

Children
  • 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.

  • Jesse thanks!

    So i was just told that it seems we want to just infiltrate/discard the water quality storm event so it would be the same volume for all my 2 yr, 10 yr, 100 yr storm events I am running. I see that with the pond outlet method my cfs and volumes discarded have drastic differences between them even when using the same parameters for the outfall for the second pond outfall. 

    But then like I stated before the green ampt method practically the same between all three storm events so should I use the green ampt method if i do want to see same discard of volume/flow throughout all my three storm 2 yr, 10 yr and 100 yr?

    Thanks

  • You may need to use different Green-Ampt parameters between the different scenarios (different storm events) to achieve exactly the same seepage rate (while the elevation changes due to the different storms). With the pond outlet approach, you could force the same constant seepage rate regardless of the pond water surface elevation, by having a constant flow value for the full range of headwater. Example below.

    How will the real built system achieve this? (same infiltration regardless of storm/water surface)


    Regards,

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