Problem

Can SewerGEMS, CivilStorm or StormCAD use the Weighted Q method to calculated catchment runoff, where flow from each land type is calculated separately and then added together? 

Solution

Currently SewerGEMS, CivilStorm and StormCAD can use a Composite runoff coefficient (such as composite CN/Area) or the "Subarea" feature, in which an overall weighted runoff coefficient (such as the overall SCS CN) is calculated and the catchment runoff is then calculated as a whole. This is different from the "weighted q" method.

The Weighted Q method will be considered for a future version via Enhancement # 538362.

In the meantime, the solution you can use is to model each land type as a separate catchment area, with its "Outflow Element" set to a single common discharge point (the same that you would have chosen for the single catchment). This will also enable you to align your model more closely to the real system (by drawing the catchment polygons for each type of land). 

See Also

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