WMS:Kerby Tc Equation: Difference between revisions
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where: | where: | ||
< | ''t<sub>c</sub>'' = time of concentration in minutes. | ||
''S'' = overland slope in ft/ft. | |||
''n'' = roughness coefficient. | |||
< | ''L<sub>o</sub>'' = length of overland flow in feet. | ||
A table of recommended values for | A table of recommended values for ''n'' is given below: | ||
| Line 19: | Line 19: | ||
|+Recommended surface roughness values | |+Recommended surface roughness values | ||
!width="250"|Surface Description | !width="250"|Surface Description | ||
!width="150"| | !width="150"|''n'' | ||
|- | |- | ||
|Smooth, impervious surface||align="center"|0.02 | |Smooth, impervious surface||align="center"|0.02 | ||
Revision as of 15:47, 7 December 2016
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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