Material | Manning's "n" | Desirable Maximum Velocities |
Material | Manning's "n" | Desirable Maximum Velocities |
Closed Conduits | ||
Concrete | 0.013 | 15 feet per second |
HDPE | 0.011 | 15 feet per second |
PVC | 0.010 | 15 feet per second |
Vitrified Clay | 0.013 | 15 feet per second |
Brick | 0.015 | 15 feet per second |
Cast Iron | 0.013 | 15 feet per second |
Circular Corrugated Metal Pipe, Annular Corrugations, | ||
2
2/3
x ½ inch Unpaved | 0.024 | 7 feet per second |
25% Paved | 0.021 | 7 feet per second |
50% Paved | 0.018 | 7 feet per second |
100% Paved | 0.013 | 7 feet per second |
Circular Corrugated Metal Pipe, Helical, 2
2/3
x ½ inch, Unpaved Corrugations | ||
12" | 0.011 | |
15" | 0.012 | |
18" | 0.013 | |
24" | 0.015 | |
36" | 0.018 | |
48" | 0.020 | |
60" or larger | 0.021 | |
Open Channels | ||
Concrete, trowel finish | 0.013 | |
Concrete, broom or float finish | 0.015 | |
Gunite | 0.018 | |
Riprap, placed | 0.030 | |
Riprap, dumped | 0.035 | |
Gabion | 0.030 | |
Earth (uniform, short grass, few weeds) | 0.025 | (See Table 7) |
Existing earth (fairly uniform, with some weeds) | 0.030 | (See Table 7) |
Uniform channel, dense growth of weeds | 0.035 | (See Table 7) |
Channel not maintained, dense weeds and brush | 0.08 - 0.12 | (See Table 7) |
Swale with grass | 0.05 | (See Table 7) |
(1) "n" values from Federal Highway Administration, 197