HEC-22 Open Channel and Pipe Flow

This equation is declared in Hydraulic Engineering Circular No. 22 (HEC-22) Urban Drainage Design Manual for computing the travel time watershed runoff that is conveyed in a channel.

T_c	Time of concentration (min)
V	Velocity of Channel Flow (ft/s)
L	Flow length (ft)
i	Rainfall intensity (in/hr)
S	Slope (ft/ft)
n	Manning's Roughness
R	Hydraulic Radius (ft)