Inlet capacity creates a second node internally to XPSWMM. Currently, the rating curve methods for it are calculated based on node depth, rather than head differential, which doesn’t work right with 2D if the storm sewer HGL is above the gutter.

I really like how inlet capacity doesn’t require adding an extra node. I would like to suggest it be expanded as follows:

1) Simply add a head differential rating curve.

2) Add a structure-based option for inlets,

For a structure-based inlet, it could essentially be a multi-link. I would like to have a global database of standard inlet types that describe the geometry and choose which one to apply, set the inlet invert/grate elevation, and have XPSWMM handle splitting the node to create the link.

This is mostly good for sag inlets. For on-grade inlets and 2-D, I haven’t tested, but the “rated by approach flow” seems promising. I suggest to have a 1D/2D interface where XPSWMM calculates the total flow across the line, then uses that flow and the gutter geometry to calculate the depth and inlet capture. That would, of course need to have a submergence reduction, where high head in the storm sewer would reduce the capture or cause reverse flow.