Roughness Values-Kutters Equation

Roughness Values--Kutter’s Equation

Channel Type and Description	Minimum	Normal	Maximum
Brass, smooth	0.009	0.010	0.013
Steel; Lockbar and welded	0.010	0.012	0.014
Steel; Riveted and spiral	0.013	0.016	0.017
Cast iron; Coated	0.010	0.013	0.014
Cast iron; Uncoated	0.011	0.014	0.016
Wrought iron; Black	0.012	0.014	0.015
Wrought iron; Galvanized	0.013	0.016	0.017
Corrugated metal; Subdrain	0.017	0.019	0.021
Corrugated metal; Storm Drain	0.021	0.024	0.030

Kutter’s Coefficients n for Closed Non-Metal Conduits

Channel Type and Description	Minimum	Normal	Maximum
Lucite	0.008	0.009	0.010
Glass	0.009	0.010	0.013
Cement; Neat, surface	0.010	0.011	0.013
Cement; Mortar	0.011	0.013	0.015
Concrete; Culvert, straight and free of debris	0.010	0.011	0.013
Concrete; Culvert with bends, connections, and some debris	0.011	0.013	0.014
Concrete; Finished	0.011	0.012	0.014
Concrete; Sewer with manholes, inlet, etc., straight	0.013	0.015	0.017
Concrete; Unfinished, steel form	0.012	0.013	0.014
Concrete; Unfinished, smooth wood form	0.012	0.014	0.016
Concrete; Unfinished, rough wood form	0.015	0.017	0.020
Wood; Stave	0.010	0.012	0.014
Wood; Laminated, treated	0.015	0.017	0.020
Clay; Common drainage tile	0.011	0.013	0.017
Clay; Vitrified sewer	0.011	0.014	0.017
Clay; Vitrified sewer with manholes, inlet, etc.	0.013	0.015	0.017
Clay; Vitrified subdrain with open joint	0.014	0.016	0.018
Brickwork; Glazed	0.011	0.013	0.015
Brickwork; Lined with cement mortar	0.011	0.013	0.015
Sanitary sewers coated with sewage slimes, with bends and connections	0.012	0.013	0.016
Paved invert, sewer, smooth bottom	0.016	0.019	0.020
Rubble masonry, cemented	0.018	0.025	0.030