The following values are recommended for channel and overland flow.
Refer also to Chow's recommendations.
The following Manning Coefficient values are appropriate for various channel conditions.
|
Category
|
Surface or Condition |
Value |
|
Rivers and Streams |
Earth, free from weed, with straight alignment, stones up to 75mm average size Earth, free from weed, with poor alignment, stones up to 75mm average size Earth, with weeds and poor alignment, stones up to 75mm average size Gravel, free from weed, with straight alignment, stones from 75mm to 150mm average size Gravel, free from weed, with poor alignment, stones from 75mm to 150mm average size Gravel with stones and boulders exceeding 150mm average size, mountain rivers |
0.020 - 0.025 0.030 - 0.050 0.050 - 0.150 0.030 - 0.040 0.040 - 0.080 0.040 - 0.070 |
|
Unlined Canals and Artificial Channels |
Earth, good alignment Earth, poor condition, stony bed Rock |
0.018 - 0.025 0.025 - 0.040 0.025 - 0.045 |
|
Lined Channels |
Concrete Hand placed pitching Dressed stone, jointed |
0.012 - 0.017 0.025 - 0.035 0.013 - 0.020 |
|
Pipes |
Cast iron Concrete Salt-glazed stoneware Clay drainage tile Riveted steel |
0.010 - 0.014 0.011 - 0.015 0.011 - 0.015 0.012 - 0.016 0.014 - 0.017 |
The following Manning Coefficient values are appropriate for various overland flow conditions.
|
Surface
|
n |
|
Smooth asphalt |
0.011 |
|
Smooth concrete |
0.012 |
|
Ordinary concrete lining |
0.013 |
|
Good wood |
0.014 |
|
Brick with cement mortar |
0.014 |
|
Vitrified clay |
0.015 |
|
Cast iron |
0.015 |
|
Corrugated metal pipes |
0.024 |
|
Cement rubble surface |
0.024 |
|
Fallow soils (no residue) |
0.05 |
|
Cultivated soils |
|
|
Residue cover < 20% |
0.06 |
|
Residue cover > 20% |
0.17 |
|
Range (natural) |
0.13 |
|
Grass |
|
|
Short, prairie |
0.15 |
|
Dense |
0.24 |
|
Bermuda grass |
0.41 |
|
Woods |
|
|
Light underbrush |
0.40 |
|
Dense underbrush |
0.80 |