Generally, this method applies for lengths less than about 1200 ft.
Where:
-
L=Length of flow path (ft)
-
S=Surface slope (ft/ft)
-
n=Coefficient (see accompanying table)
-
tc=in minutes.
|
Typical values of n: |
|
Smooth impervious surface |
0.02 |
|
Smooth bare packed soil |
0.10 |
|
Poor grass, cultivated row crops |
0.20 |
|
Moderately rough bare ground |
0.20 |
|
Pasture or average grass |
0.40 |
|
Deciduous timberland |
0.60 |
|
Conifer timberland or dense grass |
0.80 |