Manning's n Coefficients for Open Channel Flow

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Manning n values compiled from the references listed under Discussion and References as well as the references at the bottom of this page.  Manning n has no units.

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Material Manning n Material Manning n
Natural Streams Excavated Earth Channels
Clean and Straight 0.030 Clean 0.022
Major Rivers 0.035 Gravelly 0.025
Sluggish with Deep Pools 0.040 Weedy 0.030
    Stony, Cobbles 0.035
 
Metals Floodplains
Brass 0.011 Pasture, Farmland 0.035
Cast Iron 0.013 Light Brush 0.050
Smooth Steel 0.012 Heavy Brush 0.075
Corrugated Metal 0.022 Trees 0.15
 
Non-Metals
Glass 0.010 Finished Concrete 0.012
Clay Tile 0.014 Unfinished Concrete 0.014
Brickwork 0.015 Gravel 0.029
Asphalt 0.016 Earth 0.025
Masonry 0.025 Planed Wood 0.012
    Unplaned Wood 0.013
Corrugated Polyethylene (PE) with smooth inner walls a,b 0.009-0.015
Corrugated Polyethylene (PE) with corrugated inner walls c 0.018-0.025
Polyvinyl Chloride (PVC) with smooth inner walls d,e 0.009-0.011

 

References
Footnotes refer to Manning n table above.  All other Manning n values were obtained from the references listed in our Discussion and References page.

a Barfuss, Steven and J. Paul Tullis.  Friction factor test on high density polyethylene pipe.  Hydraulics Report No. 208.  Utah Water Research Laboratory, Utah State University.  Logan, Utah.  1988.

c Barfuss, Steven and J. Paul Tullis.  Friction factor test on high density polyethylene pipe.  Hydraulics Report No. 208.  Utah Water Research Laboratory, Utah State University.  Logan, Utah.  1994.

e Bishop, R.R. and R.W. Jeppson.  Hydraulic characteristics of PVC sewer pipe in sanitary sewers.  Utah State University.  Logan, Utah.  September 1975.

d Neale, L.C. and R.E. Price.  Flow characteristics of PVC sewer pipe.   Journal of the Sanitary Engineering Division, Div. Proc 90SA3, ASCE.  pp. 109-129.  1964.

b Tullis, J. Paul, R.K. Watkins, and S. L. Barfuss.  Innovative new drainage pipe.  Proceedings of the International Conference on Pipeline Design and Installation, ASCE.  March 25-27, 1990.

 

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