TABLE 4: TYPICAL VALUES OF MANNING’S n

Material	Manning’s n	Desirable Maximum Velocities
Closed conduits
Concrete	0.013	15 f.p.s.
Vitrified clay	0.013	15 f.p.s.
Brick	0.015	15 f.p.s.
Cast iron	0.013	15 f.p.s.
Circular corrugated metal pipe, annular corrugations, 2-2/3 x 1/2 inch
Unpaved	0.024	7 f.p.s.
25% paved	0.021	7 f.p.s.
50% paved	0.018	7 f.p.s.
100% paved	0.013	7 f.p.s.
Circular corrugated metal pipe, helical, 2-2/3 x 1/2 inch, unpaved corrugations
12 inch	0.011
18 inch	0.013
24 inch	0.015
36 inch	0.018
48 inch	0.020
60 inch or larger	0.021
Corrugated polyethylene smooth interior pipe	0.012	15 f.p.s.
Concrete culverts	0.013
Open channels
Concrete, trowel finish	0.013
Concrete, broom or float finish	0.015
Gunite	0.018
Riprap placed	0.030
Gabion	0.028
New earth (uniform, sodded, clay)	0.025
Existing earth (fairly uniform, with some weeds)	0.030
Dense growth of weeds	0.040
Dense weeds and brush	0.040
Swale with grass	0.035

 

(Ord. 1995-10 Tab. 3, passed 10-13-1995)