I am trying to model a municipal SW system which has several outlets/headwalls in which the storm sewer empties into an open field. During small rain events, the water would infiltrate but during larger events it will flow overland to a stream channel some distance away. I would like to be able to connect the outlet/headwall to a subcatchment in order to capture the infiltration and overland flow. Is there a way to do this in SWMM?
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Replies
I would think that if the flows into the field were significant during your design storm, they would form or follow a natural channel so I would model that natural channel (wide, low sideslopes, large mannings) as a link into your downstream channel in which your second subcatchment also is connected.
Another option would be to add the flows from the upstream system as baseline or RDII flow in the node that your second subcatchment is connected.
It might be possible to use the LID feature so that the runoff from the subcatchment infiltrates for low runoff and flows to your stream for larger runoff rates.
Bob
Thanks for the reply. However, the problem I am having is that SWMM does not recognize that the subcatchment is receiving flow from the outlet/headwall (in addition to direct precip). SWMM will allow me to direct runoff from a subcatchment to another subcatchment, but I can't seem to find a way to direct runoff from a subcatchment, into a storm sewer system and then to another subcatchment.