Table 2.1. Manning's Roughness Coefficients for Various Boundaries.
Manning's n
Rigid Boundary Channels
Very smooth concrete and planed timber
0.011
Smooth concrete
0.012
Ordinary concrete lining
0.013
Wood
0.014
Vitrified clay
0.015
Shot concrete, untrowelled, and earth channels in best condition
0.017
Straight unlined earth canals in good condition
0.020
Mountain streams with rocky beds
0.040 - 0.050
Minor Streams (top width at flood stage < 30 m (100 ft)
Streams on Plain
0.025-0.033
1.
Clean, straight, full stage, no rifts or deep pools
0.030-0.040
2.
Same as above, but more stones and weeds
0.033-0.045
3.
Clean, winding, some pools and shoals
0.035-0.050
4.
Same as above, but some weeds and stones
0.040-0.055
5.
Same as above, lower stages, more ineffective slopes and sections
0.045-0.060
6.
Same as 4, but more stones
0.050-0.080
7.
Sluggish reaches, weedy, deep pools
0.075-0.150
8.
Very weedy reaches, deep pools, or floodways with heavy stand of timber
and underbush
Mountain Streams, no vegetation in channel, banks usually steep, trees and
brush along banks submerged at high stages
0.030-0.050
1. Bottom: gravels, cobbles, and few boulders
0.040.0.070
2. Bottom: cobbles with large boulders
Floodplains
Pasture, No Brush
1. Short Grass
0.025-0.035
2. High Grass
0.030-0.050
Cultivated Areas
1. No Crop
0.020-0.040
2. Mature Row Crops
0.025-0.045
3. Mature Field Crops
0.030-0.050
2.22
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