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PondPack outlet structure modeling

Hello Jesse, what's the best way to draw this in pondpack V8i...BEST WAY TO MODEL IT.

  • Hello Scott, how can i size the outlet pipes connecting the basin and control structure and the pipe connecting control structure and existing structure?  is it possible to model it as just channel?

  • Hi Simon,

    Thanks for providing the sketch. I recommend taking a look at the learning resources in the below Wiki article such as the sample files, lessons and training course, as they explain how to lay out and connect model elements.

    Learning resource guide for new users of Bentley PondPack

    Some things are still not quite clear to me from the sketch you provided:

    1. For the "basin" on the left side, you noted "13 barrels" and "with 60" pipes" - does that mean that this represents storage resulting from pipes, such as an underground storage chamber system? In my screenshot this is what I assumed, and it would be modeled as a single pond.
    2. For the "weir 1" and "weir 2" in the middle structure, are these leaving this structure and going somewhere else (this is what I assumed in my screenshot), or does the flow go over/through them in order to pass through the structure in the middle?
    3. What happens downstream of the "existing MH"? Is there a pipe that leaves, or would this point represent the final discharge point of the network? In my screenshot below I assumed that the storage effects of the manhole need to be accounted for so it is modeled as a pond, but if you have a pipe leaving the manhole, that would need to be an additional culvert pond outlet structure connected to the next-downstream structure, or a final outfall. If the manhole represents the end of the system, it would be modeled with the outfall element instead.

    Generally speaking if the capacity of the system downstream of the first "basin" pond is much greater than the flow that will be leaving the "basin", you could consider omitting it from the model and simply ending at a free outfall downstream of the "basin" pond's culvert outlet structure, or set the tailwater of the culvert outlet structure to "downstream channel" and select a conduit representative of the first 36" pipe, in order to get appropriate tailwater based on the depth of flow in the pipe.

    If you believe that the tailwater and potential storage and attenuation effects from the downstream system need to be modeled, see my screenshot below. Any structure between flow control devices would be modeled as a pond, with volume type set to either "no volume" if the volume is negligible, or elevation-area/elevation-volume with the appropriate small volume modeled in the elevation-area or elevation-volume table (note that a small calculation timestep would likely be needed in that case to achieve stable results). You would use "interconnected ponds" (ICPM) as the tailwater type for both of the pond outlet structure. See the training resources and sample files for more information on ICPM.

    The following articles also provide guidance on laying out and connecting elements:

    How do you attach a pond outlet to an outfall in PondPack?

    How do you direct flow from a channel or pipe into a pond?


    Regards,

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

  • Thank you Jesse for your reply, However, let me explain in detail what is going on so you will have a better understanding what i want to model.

    Firstly, I am using a pipe system(will serve as the Pond area; 60'' PIPES 13NUMBER OF THEM ) like this one in the screenshot.

    Secondly, from the pond, it will have a 36'' pipe that will connect it from the pond to a manhole(which is my control structure having a 2year flow(weir1) and 100yr flow(weir2), and they will flow out through a 36'' pipe connected to my manhole(control structure) to existing manhole(this is not to be considered because the capacity is high, will just be an outfall)

  • Clarifying your questions above.

    1. Yes it is storage resulting from pipes as show below from pondpack

    2. as below,  For the "weir 1" and "weir 2" in the middle structure, the flow go over/through them in order to pass through the structure in the middle

     

    3. What happens downstream of the "existing MH"? answer--- It would represent the final discharge point of the network

  • Thanks, Simon. Based on your clarification, here is my new feedback:

    • The pipe system would be modeled as a single pond, with the volume type set to storage chamber system. You can read more about storage chamber ponds in the article from my previous reply.
    • Given your description of your manhole outlet structure (with the weirs), I see a couple of possible approaches you could take:

    1) Model it with a single pond outlet structure between the storage chamber pond and the "existing manhole" (outfall), with the weirs controlling the outflow. Since the weirs are in parallel (from what I understand), you can't model the culvert (pipe between the pond and weirs) with this approach. You had included a screenshot showing a single outlet structure with what appears to be both the upstream pipe and the two weirs - if those weirs are in parallel, this is not possible because there can only be one single "downstream ID" for a given outlet element. In other words, you cannot tell the outflow pipe culvert component that both of the weirs are downstream of it (that the water first goes through the culvert and then approaches both weirs). If you set the "downstream ID" to "tailwater" for everything, then this means that everything is in parallel (which is not the case from my understanding). So, with this approach, you would be neglecting for any resistance caused by the first, upstream pipe, and would model the pond outlet structure as two weirs with downstream ID set to a culvert (representing the pipe between the weir manhole structure and the "existing manhole". If the first, upstream pipe has more capacity than the weirs, then this approach may be acceptable. Some adjustment may be necessary to achieve a stable EQTW table when modeling culverts in series with other outlet, as mentioned in the below article. So, you might also consider removing the culvert component to neglect resistance from the final 36" pipe.

    Convergence problems, very slow calculations or "out of range" message when using culvert in series with another outlet component


    2) Model the manhole as a no-volume pond element. This enables you to have the water go through the culvert first (culvert component in the first outlet link), and then approach both weirs. See my previous post for more on this. The second outlet link would have two weirs and one culvert, with the "downstream ID" of both weirs set to the culvert. As mentioned above, you could also consider omitting the second culvert if it does not have a notable hydraulic impact, as you may otherwise have difficulty achieving a stable EQTW curve when the culvert is in series with other components.


    Regards,

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