Whilst talking about direct rainfall modelling using rainfall directly onto the 2D mesh in a training course, the discussion went to what approaches people take to avoid double-counting of rainfall? Within ICM there are a number of options. Most models have existing subcatchments which have a 1D representation of rainfall runoff, is the general approach when applying direct rainfall to delete these subcatchments (or remove the stormwater component?) or use the 'Outside Subcatchments' option in the 2D zone? If so what about the foul component, are these added to the model?

Also how do people represent buildings? Voids, Roughness Zones or porous polygons? If porous polygons are used, is direct rainfall applied to these or is the 'No Rainfall' option used? If the 'No Rainfall' option is used, or the buildings are represented as voids, is the rainfall that falls on the roofs of buildings represented in other seperate subcatchments represented the building footprints?

It seems, talking to people and looking at models that there is no common approach, would this be a fair assumption? ICM has a number of tools and a number of options to what approach can be taken, I was just wondering whether some are favoured over others?