Manning's n values (roughness coefficients) were 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.
The Manning Equation using the Manning n value is semi-empirical and requires specific units for variables.
| 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 (roughness coefficients) 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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