I am trying to delineate drainage basins that contribute to an urban stormdrain network (hundreds of inlets collect the surface runoff, and convey it thru underground infrastructure). The ArcHydro / GeoHMS tools are great at delineating surface drainage networks, but I am at a loss for how best to proceed. I will try delineating basins without filling sinks (many of the stormdrain inlets are in local low points) and with the stream definition set quite small, then go thru visually combining sub-basins, but this will be more laborious than desired.
the only application I have seen similar to this, is the individual had to create "trenches" in the DEM so that water could "flow" from one side of the road to the other. It was for a thesis and looked pretty good but it required manual editing to connect one side of the road to the other.
The way I'm thinking about this, you can make two watershed layers: one over ground, one underground. The pour points over ground would be your drains. The pour points underground are up to you (sewer junctions or something). Then Extract Values to Points, to transfer underground watershed number to the drains. If the values are the same, then merge those corresponding over ground watersheds together.
edit: this assumes you have some sort of underground sewer data. Do you?
I just went through this process and didn't really find a great automated approach. Even the Hydro tools didn't seen to give me exactly what I needed. I ended up doing a combination of arc hydro and manual editing to delineate tributary area to each inlet. I essentially started at the larger watershed scale (huc 12) and then worked my way back from every outfall. 2nd Nature llc. outlines, nicely, a methodology for doing this. They have a tutorial on their site under MAP MS4 TO MEET PHASE II PERMIT REQUIREMENTS- http://www.2ndnaturellc.com/client-access/central-coast-stormwater-ms4-support/ .