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:
|
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 |
Related Topics:
Computing Lag Time or Time of Concentration from Basin Data