Roughness Values-Mannings Equation
Commonly used roughness values for different materials are:
Manning’s Coefficients n for Closed-Metal Conduits Flowing Partly Full
Channel Type and Description | Min. | Normal | Max. |
---|---|---|---|
a. Brass, smooth | 0.009 | 0.010 | 0.013 |
b. Steel | |||
1. Lockbar and welded | 0.010 | 0.012 | 0.014 |
2. Riveted and spiral | 0.013 | 0.016 | 0.017 |
c. Cast iron | |||
1. Coated | 0.010 | 0.013 | 0.014 |
2. Uncoated | 0.011 | 0.014 | 0.016 |
d. Wrought iron | |||
1. Black | 0.012 | 0.014 | 0.015 |
2. Galvanized | 0.013 | 0.016 | 0.017 |
e. Corrugated metal | |||
1. Subdrain | 0.017 | 0.019 | 0.021 |
2. Storm drain | 0.021 | 0.024 | 0.030 |