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Multiple Pond Model with Reverse Overflow

I've never had to do multiple pond modeling. So this is a first for me. I actually have a couple questions. 

1. How do you connect a pond outlet  to an Inlet (All of these will be risers)? (Pond 5 needs to overflow into the system using DA-3) .  (Pond 6 should  flow into DA-24.)

2. Why does the model keep crashing when I try to validate it and see the errors? ( I attached the model through the secure link.)

3. The Culverts connecting the two ponds work both forward and backward?  (Pond 2 acts as an overflow for Pond 1 but Pond 2 collects from a water park constantly so there is a chance that pond 2 may need to flow into Pond 1 as some time.)

4. The image attached.  This section has a primary function of collecting water from the gutter and it going to the pond. The secondary is to act as an overflow measure. Once the Pond hits a certain level they are hoping that the pressure from the pond will make the system work in reverse.  The slope of the gutter will lead to a different system if the water pushes in the opposite way. 

I attached the model through the secure link. 

Parents
  • Hello Mark,

    1. You can connect a pond outlet structure to an include with a conduit, similar to the screenshot you are using.

    2. This may be related the composite outlet structures in the model. If you go Components > Stormwater Controls > Composite Outlet Structures. You can compute the composite outlet structures here to view the rating table. However, three of the four composite outlet structures have an error based on the input when you compute these. Computing the model does not see the same issue, but resolving the issues with the composite outlet structures may help with the error.

    3-4. This may depend on the hydraulic grade in the elements. If the hydraulic grade in the downstream node is higher than the hydraulic grade in the pond, you may see reverse flow.

    One item of note here is that you are using the StormCAD, or at least the GVF-Rational solver, in this model. This solver does not model storage and the flow from ponds will simply be based on the initial pond elevation. If you need to see how the flow changes with time, the Implicit or Explicit solver. This link has detains on this. 

  • Thank you. 

    In what window do I go to connect the pond outlet structure to the conduit?  There isn't an option in inside the primary window. 

    Side question how easy is it to import a StormCAD model into Civil Storm? 

    Thanks, again.

  • Hello Mark,

    The pond outlet element is the end node for the conduit, similar to how you would connect conduit to other elements. You should be able to go to the Layout tab, select the conduit element, and click on the pond outlet element. The conduit will then use the pond outlet as the start node for the conduit.

    StormCAD and CivilStorm use the same file types. As long as you have a compatible version, you would simply need to open CivilStorm and go to File > Open to open the file. When you do this, the GVF-Rational solver will be the solver used, since that it what it is set to. However, you can open the Calculation Options in the properties and change the solver to the Implicit or Explicit solver.

    Regards,

    Scott

  • Thanks. 

    I have it all working now in stomCAD. 

    So I am importing my system into CivilStorm so we can model the ponding. How do I find the Peak flow time in Storm CAD so I can set my model in Civilstorm to that? Thanks

  • Hi Mark,

    Here is an article about opening your StormCAD model in CivilStorm: How can I open a StormCAD model in CivilStorm?

    Results in StormCAD are not comparable to CivilStorm - it is an apples to oranges comparison. StormCAD uses the Rational method which is a peak flow (the flow result you see in StormCAD is the peak flow). It would not make sense to use the same peak flow in CivilStorm and assume it lasts for the entire simulation, once the element of time is introduced. In a real storm, the peak would only occur for a short period of time. You can read more about this here: 

    Differences between solvers: GVF-Convex vs. GVF-Rational vs. Implicit vs. Explicit (SWMM)

    Why don't CivilStorm results for peak flow closely match StormCAD results for peak flow?

    The most "compatible" option in CivilStorm might be to use the Modified Rational Method for your catchments. This uses Rational Method principles (uses the IDF curve and Q=CIA) but constructs an approximate hydrograph based on a selected "Critical" storm duration. You can read more about how this works here: Understanding the Modified Rational Method

    Another option would be to change your catchments to use a different method like the Unit Hydrograph. If in doubt, you may need to check with your local reviewer or governing agency.

    If you really need to have the CivilStorm model use the same peak flow, to simulate a steady state simulation like StormCAD, you would need to look at the calculated "Flow" result for your catchments, use that as a constant hydrograph in the catchment or a constant inflow on the receiving catchbasin (and remove the catchments) and set the simulation duration to something short. However, you would not be able to properly account for time-variant aspects like change in pond level, since as mentioned above the peak flow would only occur for a short period of time in a real storm, with a rising and trailing hydrograph limb before and after it.


    Regards,

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

Reply
  • Hi Mark,

    Here is an article about opening your StormCAD model in CivilStorm: How can I open a StormCAD model in CivilStorm?

    Results in StormCAD are not comparable to CivilStorm - it is an apples to oranges comparison. StormCAD uses the Rational method which is a peak flow (the flow result you see in StormCAD is the peak flow). It would not make sense to use the same peak flow in CivilStorm and assume it lasts for the entire simulation, once the element of time is introduced. In a real storm, the peak would only occur for a short period of time. You can read more about this here: 

    Differences between solvers: GVF-Convex vs. GVF-Rational vs. Implicit vs. Explicit (SWMM)

    Why don't CivilStorm results for peak flow closely match StormCAD results for peak flow?

    The most "compatible" option in CivilStorm might be to use the Modified Rational Method for your catchments. This uses Rational Method principles (uses the IDF curve and Q=CIA) but constructs an approximate hydrograph based on a selected "Critical" storm duration. You can read more about how this works here: Understanding the Modified Rational Method

    Another option would be to change your catchments to use a different method like the Unit Hydrograph. If in doubt, you may need to check with your local reviewer or governing agency.

    If you really need to have the CivilStorm model use the same peak flow, to simulate a steady state simulation like StormCAD, you would need to look at the calculated "Flow" result for your catchments, use that as a constant hydrograph in the catchment or a constant inflow on the receiving catchbasin (and remove the catchments) and set the simulation duration to something short. However, you would not be able to properly account for time-variant aspects like change in pond level, since as mentioned above the peak flow would only occur for a short period of time in a real storm, with a rising and trailing hydrograph limb before and after it.


    Regards,

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

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