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Manning's Roughness Coefficients

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The Manning's roughness coefficient is used in the Manning's equation to calculate flow in open channels.

Coefficients for some commonly used surface materials:

Manning's Roughness Coefficients vs. Channel Type
Surface MaterialManning's Roughness
- n -
Asbestos cement 0.011
Asphalt 0.016
Brass 0.011
Brick and cement mortar sewers 0.015
Canvas 0.012
Cast or Ductile iron, new 0.012
Clay tile 0.014
Concrete - steel forms 0.011
Concrete (Cement) - finished 0.012
Concrete - wooden forms 0.015
Concrete - centrifugally spun 0.013
Copper 0.011
Corrugated metal 0.022
Earth, smooth 0.018
Earth channel - clean 0.022
Earth channel - gravelly 0.025
Earth channel - weedy 0.030
Earth channel - stony, cobbles 0.035
Floodplains - pasture, farmland 0.035
Floodplains - light brush 0.050
Floodplains - heavy brush 0.075
Floodplains - trees 0.15
Galvanized iron 0.016
Glass 0.010
Gravel, firm 0.023
Lead 0.011
Masonry 0.025
Metal - corrugated 0.022
Natural streams - clean and straight 0.030
Natural streams - major rivers 0.035
Natural streams - sluggish with deep pools 0.040
Natural channels, very poor condition 0.060
Plastic 0.009
Polyethylene PE - Corrugated with smooth inner walls 0.009 - 0.015
Polyethylene PE - Corrugated with corrugated inner walls 0.018 - 0.025
Polyvinyl Chloride PVC - with smooth inner walls 0.009 - 0.011
Rubble Masonry 0.017 - 0.022
Steel - Coal-tar enamel 0.010
Steel - smooth 0.012
Steel - New unlined 0.011
Steel - Riveted 0.019
Vitrified clay sewer pipe 0.013 - 0.015
Wood - planed 0.012
Wood - unplaned 0.013
Wood stave pipe, small diameter 0.011 - 0.012
Wood stave pipe, large diameter 0.012 - 0.013
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