WMS:Ramser Tc Equation

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.

${\displaystyle t_{c}=0.008L_{c}^{0.77}S_{c}^{-0.385}}$

where:

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.