Manning’s n-values

Material	Manning's n
PIPES
Reinforced concrete	0.013
Vitrified clay pipe	0.013
Corrugated metal pipe	0.023
Polyvinyl chloride (PVC)	0.010
Smooth welded pipe	0.011

NATURAL CHANNELS
Gravel beds, Straight	0.025
Gravel beds, large boulders	0.040
Earth, straight, some grass	0.026
Earth, winding, no vegetation	0.030
Earth, winding	0.050

EXCAVATED CHANNELS
Clean, recently completed	0.018
With short grass and weeds	0.027
Earth bottom, rubble banks	0.030
Stony bottom, weedy banks	0.035
Not maintained, weeds high as flow depth	0.080

LINED, CONSTRUCTED CHANNELS
Concrete, trowel finish	0.013
Concrete, unfinished	0.017
Gravel bottom, riprap banks	0.033

OVERLAND "SHEET" FLOW
Smooth surfaces, Concrete, asphalt, bare Soil	0.011

Short grass	0.15
Dense grass	0.24
Bermuda grass	0.41

Light underbrush woods	0.40
Dense underbrush woods	0.80