I am builidng a pluvial model of an urban area in ICM with a 2D zone used for the overland flow and a 1D network to represent the sub-surface drainage network. There is a foul and surface water component to the drainage system. The flow both into and out of the surface water syetem is via manholes using the flood type "2D", thus allowing the representation of collection of overland flow by the system but also allowing surcharging flows to enter the 2D domain.

The problem I am having is with the foul system. Inflow to the system is via subcatchments connected to manholes. The subcatchments include impermeable areas and thus have a rainfall response. I would like flow to exit the system and flow onto the 2D domain when the system surcharges but if I use the "2D" flood type I also get inflow into the system via these manholes from the 2D zone when the system is not surcharged. I therefore am wondering if there is a way of limiting flow via manholes to one direction?

The way I thought this could would be to use the user defined head-discharge (H-Q) option for flood type and limit the flow entering the manholes to zero. The problem I can see is that even if I use the Standard Weir Equations as the flood type "2D" would to define my H-Q curve, when the manhole is drowned by flow on the 2D surface there would be no way of switching the equation to used the drowned orifice equation. I would also need to create a number of H-Q curves to apply to the various sizes of manhole across the network.

If anybody has any suggestions it would be greatly appreacited.