Ramser (1927) developed an equation for computing the time of concentration in well-defined channels. The equation is based on the length and slope of the channel.
tc - time of concentration in minutes.
Lc - length of channel reach in feet.
Sc - average channel slope in ft/ft.
For flow in concrete channels, tc should be multiplied by 0.2.
Computing Lag Time or Time of Concentration from Basin Data