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How to model catch basin that acts as both a curb inlet and an area inlet on the back side

I am working on the design of a storm sewer system that will utilize a unique inlet. The inlet will function as a curb inlet on the road side and an area inlet on the back side. A depiction of the scenario is shown above. Two drainage areas drain to catch basin AA7 shown. The first drainage area is from a road that runs through the site. The second drainage area is a grassed area behind the inlet. The site will be graded such that the road is crowned and one lane will drain to the catch basin (AA7) and the grassed area is graded to drain to the back side of catch basin AA7. The road side of catch basin AA7 will be a curb inlet, and the back side of inlet AA7 will function as an area inlet.

I am looking for the best way to split the flow from these two areas up. The runoff from the road area needs to be applied to the catch basin in an "on grade" setting such that inlet capture, bypass, and spread are checked. The runoff from the grassed area needs to be applied to the inlet in an "on sump" setting such that it is all captured by the inlet and sent to the system (as the back side of this catch basin will not overflow and go into the roadside gutter. I am not sure how to apply a catchment to this inlet so that all the flow goes into the system and is not treated like a curb and gutter section.

  • Joshua, 

    It sounds like you need to separate out the elements. One catch basin set to on grade and the other to in sag with separate catchments attached if needed. 

    Mark

  • If I do separate things out into two separate catch basins, I'm not sure I will be able to send both catch basins to the same storm water conduit. Both catch basins need to drain to the same conduit if that makes sense. What is actually going to be built on this site will be a stormwater inlet where the side facing the road contains a curb inlet and the back side of that same inlet functions as an area inlet. Both sides of the same inlet will drain down to the same storm sewer system pipe.

  • It can be done. Here's how:

    Make CO-2 and CO-4 conduits with a large diameter like 99 in. with a user defined length that is short, such as 1 ft or 2 ft. You might also try setting both of these conduits to a section type of virtual, but you may run into issues depending on the solver the model is using. The former way is a virtual conduit workaround. T-1 is a transition element that will route the flow from both conduits into CO-3, which is the single conduit downstream of the real world catch basin. T-1 should have a shorter transition length, but honestly if something a little longer makes the more more stable use that. 

    Mark

    Answer Verified By: Joshua Hesting 

  • Here is an article from our Wiki related to Mark's answer: Modeling one structure with two inlets (grates)


    Regards,

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