WMS:Kerby Tc Equation: Difference between revisions
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where: | where: | ||
t<sub>c</sub> | t<sub>c</sub> = time of concentration in minutes. | ||
S | S = overland slope in ft/ft. | ||
n | n = roughness coefficient. | ||
L<sub>o</sub> | 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.
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:
| 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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