In many urban drainage situations open channel floodways incorporate a low floe pipe beneath the invert of the channel section.

Where this is the case XPRafts allows for the separation of the pipe flow component from the total inflow hydrograph.

Lagging of the pipe flow is carried out separately to the Muskingum-Cunge Channel Routing Model of the surface flow.

At the bottom of the channel reach the two flow components are superimposed to form the total outflow hydrograph. The separation of pipe and overland flow hydraulic components allows effective simulation of complex urban piped drainage networks.

Additionally if a pipe slope only is input without a pipe diameter the Muskingum-Cunge Channel Routing computes a pipe diameter to contain the total inflow hydrograph using Manning’s equation.