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Roof Drain Modeling in StormCAD

I am analyzing a storm water problem for a civil engineering, senior capstone project. Our storm water problem occurs in a very urban environment. With this said, much of the runoff that the storm water pipes collect comes from roof drains. These are 6” PVC connected directly to the storm water system. The question I have is, how does one model a roof drain in StormCAD? Should it be modeled as a catch basin at ground elevation? Or is there a way to model it at the roof elevation and then model the 6” PVC connection?

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  • Hello Aaron,

    There are a few options you can work on to model roof top runoff in StormCAD.

    1. If your storm-water network is extensive, you can directly input the calculated runoff in a catch basin at ground elevation.

    2. However, if you want to model the collection drains surrounding your roof top area (which ultimately are connected to the storm-water network), you can create something like this.

    In the above image there is a rooftop area modeled as catchment (CM-1). The runoff from this catchment is collected by catch basin (CB-1). From CB-1 the runoff flows through a conduit (CO-1) which delivers the flow to a manhole (MH-1) at ground level. From here flow is going to the outfall (O-1). In this scenario, I have created a case of rooftop drainage system with CO-1 as 6" PVC circular PVC pipe and even the catch basin and manholes are having diameters of 6" to simulate vertical pipes. You can replace the conduit CO-1 with a open gutter if required. You can define additional parameters such as cross-slope, longitudinal-slope etc. for more accuracy.

    From the above profile you can see that the conduit CO-1 is placed at the roof level of your building and is carried to a manhole at ground level.

    Hope this helps.

    Regards,

    Yashodhan Joshi

    Bentley Technical Support.


    Regards,

    Yashodhan Joshi

    Answer Verified By: Sushma Choure 

  • This is fantastic. Thank you for the quick response!

  • I believe it would be typical to represent a roof drain system as a catchment (Yashodhan's option #1). If you can assume that the 6" pipe has sufficient capacity, then you would configure the catchment properties to represent the roof and the drain together. Meaning, the runoff from the catchment would be the runoff that leaves the end of the 6" pipe, into the storm drain system.

    If it ties into the vault of a catchbasin or manhole structure, you can set the catchment's "outflow node" to the node. For a catchbasin, if it connects sub-surface, set the catchbasin's inlet type to "full capture" (otherwise the runoff will approach the catchbasin's above-surface inlet).


    Regards,

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

    Answer Verified By: Sushma Choure 

Reply
  • I believe it would be typical to represent a roof drain system as a catchment (Yashodhan's option #1). If you can assume that the 6" pipe has sufficient capacity, then you would configure the catchment properties to represent the roof and the drain together. Meaning, the runoff from the catchment would be the runoff that leaves the end of the 6" pipe, into the storm drain system.

    If it ties into the vault of a catchbasin or manhole structure, you can set the catchment's "outflow node" to the node. For a catchbasin, if it connects sub-surface, set the catchbasin's inlet type to "full capture" (otherwise the runoff will approach the catchbasin's above-surface inlet).


    Regards,

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

    Answer Verified By: Sushma Choure 

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