WMS:Ramser Tc Equation

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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.

t_c = 0.008 L_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.


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