Manning's Roughness Coefficient

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

Coefficients (n) for some commonly used surface materials:

Asbestos cement 0.011

Asphal t0.016

Brass0.011

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