Ponded Area for Modeling Storm Water With Catch Basin

When create a Storm Water model equipped with catch basins elements and gutters; do we apply "Ponded Area" to the catch basins? Is it usually for the Manholes only or it is recommended to do applying that to the Inlets as well, especially we are creating a model for the existing system which already under sized and facing a flooding issues.

If it is recommended to add "Ponded Area" to the inlets, what is technical reason in terms of modelling ? and need an advise how to define that with respect to the curb's height and the flood volume?

Regards,

Mohamad Azzam

  • Hello Mohamad,

    Surface storage, such as using Ponded Area, would apply in cases where the node (like a manhole or catch basin) will overtop and you want to account for that overlow volume to return to the subsurface network. If you have a catch basin overtop without surface storage, the volume will apply directly to the outfall at the end of the subnetwork. By using surface storage, the overflow volume will recede back into the node and out through the subsurface network. See this link for more information: Interpreting overflow results when using manhole or catchbasin Surface Storage.

    The following link has information on the workflow to model catch basin overflow into a gutter: Modeling catch basin overflow into gutter.

    Regards,

    Scott

  • To add to Scott's response - ponded area would make sense (and in some cases is required) for in-sag inlets since by definition they are at a low point which would experience ponding. In an "on grade" situation where the land/road is sloping away from the inlet rim, ponded area likely would not make sense since the water would flow away in an overflow situation (and you would want to include a downstream gutter to carry the overflow away).


    Regards,

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

  • Thank you Jesse & Scott

    In the model created; the all catchments are connected to the inlets only (no catchment connected to the manholes), just to clarify what I understood, the ponded area should applied to the manholes and in-sag inlets only since for the “on grade” is connected to gutter and in case bypass flow will be carried via the gutter, is the correct?

    If it is not recommended to apply ponded area to the “on grade” inlets; what will happen if the flow is big and the depth exceeds the curb height? I guess that flow will be lost from the system, isn’t it? What is recommended in such situation?

    lastly, any guide or advise how to assume the “ponded area”  and what is the impact in case the assumption is exaggerated, this is always creates debate in applying that factor to the model, so your suggestion is very valuable.

    Sincerely,

    Mohamad

  • the ponded area should applied to the manholes and in-sag inlets only since for the “on grade” is connected to gutter and in case bypass flow will be carried via the gutter, is the correct?

    Yes. Ponded area is used when there is a ponded area above the inlet where the water has the possibility of receding back into the inlet later on, as Scott explained.

    If it is not recommended to apply ponded area to the “on grade” inlets; what will happen if the flow is big and the depth exceeds the curb height? I guess that flow will be lost from the system, isn’t it? What is recommended in such situation?

    If the depth exceeds the curb, you likely need to make an adjustment to the system. Overflow (lost from the system) may still make sense in this case though - some water may bypass down the gutter in the road while some may spill over the curb and travel another direction (over land?).

    lastly, any guide or advise how to assume the “ponded area”  and what is the impact in case the assumption is exaggerated, this is always creates debate in applying that factor to the model, so your suggestion is very valuable.

    The ponded area is an approximation of the surface area that the water would occupy when ponding above the rim elevation. Every modeling situation will be different. A good fall-back to consider is to make a conservative assumption when in doubt. If you do not feel that you can estimate a constant surface area to represent the ponding above the inlet, consider using one of the other surface storage methods.

    Also consider waiting for our upcoming new version of SewerGEMS which will include built-in 2D modeling of overflow, where the "surface storage" is essentially more advanced and not only represents the specific contour of the area above the inlets/manholes, but you can observe where that overflow goes based on the terrain.


    Regards,

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

    Answer Verified By: Mohamad Azzam