APPENDIX C-5: MANNING “n” VALUES

Manning “n” Values by Typical Reach Description
Reach Description	Manning “n”
Concrete pipe, culvert or channel	0.012
Corrugated metal pipe	0.012—0.027*
Natural stream, sluggish with deep pools and weeds	0.070
Natural stream or swale, very weedy or with timber under brush	0.100
Natural stream, clean, straight, no rifts or pools	0.030
Natural stream, winding, pools, shoals, stony with some weeds	0.050
Natural stream, clean, winding, some pools and shoals	0.040
*Depending upon type and diameter

Roughness Coefficients (Manning “n”) for Sheet Flow
Surface Description	Manning “n”1
Cultivated soils
Residue cover 20%	0.060
Residue cover > 20%	0.170
Fallow (no residue)	0.050
Grass
Bermuda grass	0.410
Dense grasses2	0.240
Short grass prairie	0.150
Range (natural)	0.1.10
Smooth surfaces (concrete, asphalt, gravel or bare soil)	0.011
Woods3
Dense underbrush	0.800
Light underbrush	0.400
1   The n values are a composite of information compiled by Engman (1986)
2    Includes species such as weeping lovegrass, blucgrass, buffalo grass, blue grama grass and native grass mixtures(Ord. 226-2007, passed 5-7-2007)
3   When selecting “n”, consider cover to a height of about 0.1 ft. this is the only part of the plant cover that will obstruct sheet flow