Modeling orifice in horizontal plane in hydrocad 1

[PatrickK]

I am modeling a roof drain in HydroCAD and want to know how to model this as an orifice in a horizontal plane(Pipe draining vertically). How do I model this if I know the discharge rate coming from the roof and the size of the gutter is predetermined?
I have used the rational method to model the runoff rate for the roof.

 

[psmart]

I assume you are using a subcatchment to model the runoff from the roof. (You should do this in HydroCAD, rather than trying to enter the runoff directly.)

If the roof is flat and might detain water, then you should model it as a pond, using a horizontal orifice as the outlet. The routing results will tell you how much water is detained on the roof, and give you a discharge hydropgraph for the downspout.

For details please see

http://www.hydrocad.net/roof.htm