WMS:Kerby Tc Equation: Difference between revisions

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where:
where:


t<sub>c</sub> - time of concentration in minutes.
t<sub>c</sub> = time of concentration in minutes.


S - overland slope in ft/ft.
S = overland slope in ft/ft.


n - roughness coefficient.
n = roughness coefficient.


L<sub>o</sub> - length of overland flow in feet.
L<sub>o</sub> = length of overland flow in feet.


A table of recommended values for n is given below:
A table of recommended values for n is given below:

Revision as of 15:39, 27 February 2013

Kerby (1959) developed an equation for computing the time of concentration for overland flow distances of less than 500 feet and greater than 300 feet.

File:Image125.gif

where:

tc = time of concentration in minutes.

S = overland slope in ft/ft.

n = roughness coefficient.

Lo = length of overland flow in feet.

A table of recommended values for n is given below:


Recommended surface roughness values
Surface Description n
Smooth, impervious surface 0.02
Smooth, packed bare soil 0.1
Poor grass, cultivated row crops of moderately rough bare soil 0.2
Pasture or average grass 0.4
Deciduous timberland 0.6
Timberland with deep forest litter or dense grass 0.8


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