Surface Cover
|
Manning's "n" Value
|
Permissible Velocity
(fps)
| |
---|---|---|---|
Concrete
|
0.014
|
12
| |
Asphalt
|
0.016
|
8
| |
Riprap, 3-inch
|
0.025
|
6
| |
Riprap, 6-inch
|
0.025
|
9
| |
Riprap, 9-inch
|
0.030
|
11
| |
Riprap 12-inch
|
0.030
|
13
| |
Riprap 15-inch
|
0.035
|
14
| |
Seeded grass swales
|
0.030
|
4
| |
Sod grass swales
|
0.040
|
5
| |
Existing grass swales
|
0.050
|
6
|
Pipe Type
|
Manning's "n" Value
| |
---|---|---|
Smooth lined polyethylene
|
0.012
| |
Corrugated polyethylene
|
0.021
| |
Reinforced concrete
|
0.013
| |
Helical galvanized corrugated metal, 15 to 18
inches
|
0.016
| |
Helical galvanized corrugated metal, 21 to 30
inches
|
0.019
| |
Helical galvanized corrugated metal, greater
than 30 inches
|
0.023
| |
Annular galvanized corrugated metal
|
0.025
|