Appendix B.5




SURFACE                                                                                                                                                 n


Uncoated cast-iron pipe


Coated cast-iron pipe


Commercial wrought-iron pipe, black


Commercial wrought-iron pipe, galvanized


Smooth brass and glass pipe


Smooth lockbar and welded “OD” pipe


Riveted and spiral steel pipe


Vitrified sewer pipe 0.013
Common clay drainage tile 0.012
Glazed brickwork 0.013
Brick in center mortar; brick sewers 0.015
Neat cement surfaces 0.011
Cement mortar surfaces 0.013
Concrete pipe 0.012
Concrete pipe 0.012
Wood stove pipe 0.011
Plank flumes: Planed 0.012
Plank flumes: Unplaned 0.013
Plank flumes: With battens 0.015
Concrete-lined channels 0.014
Cement-rubble surface  0.020
Dry-rubble surface 0.030
Dressed-ashlar surface 0.014
Semi-circular metal flumes, smooth 0.012
Semi-circular metal flumes, corrugated 0.025
Canals and ditches: Earth, straight and uniform 0.025
Canals and ditches: Rock cuts, smooth and uniform 0.033
Canals and ditches: Rock cuts, jagged and irregular 0.040
Canals and ditches: Winding sluggish canals 0.025
Canals and ditches: Dredged earth channels 0.0275
Canals and ditches: Canals with rough stony beds, weeds on earth banks 0.035
Canals and ditches: Earth bottom, rubble sides 0.030
Natural stream channels: (1) Clean, straight bank, full stage, no rifts or deep pools 0.029
Natural stream channels: (2) Same as (1), but some weeds and stones 0.035
Natural stream channels: (3) Winding, some pools and shoals, clean 0.039
Natural stream channels: (4) Same as (3), lower stages, more ineffective slope and sections  0.047
Natural stream channels: (5) Same as (3), some weeds and stones 0.042
Natural stream channels: (6) Same as (4), stony sections 0.052
Natural stream channels: (7) Sluggish river reaches, rather weedy\or with very deep pools 0.065
Natural stream channels: (8) Very weedy reaches 0.112

For additional “n” values, refer to Table