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<br /> Table 4 - Manning's n Values for Culverts* , <br /> J <br /> Roughness or <br />Tvoe of Culvert Corrueation Mannine's n Reference <br />Concrete Pipe Smooth 0,010-0.011 (64, 66, 67, 70) <br />Concrete Box Smooth 0,012-0,015 (23) <br />Spiral Rib Metal Pipe Smooth 0.012-0.013 (65, 69) <br />Corrugated Metal Pipe, 68 by 13 nun 0,022-0,027 (25) , <br />Pipe-Arch and Box 2-2/3 by 1/2 in <br />(Annular and Helical Annular <br />Corrugations -- See <br />Figure B-3, Manning's 68 by 13 nun O,Oll-O,023 (25, 68) <br />n varies with barrel size) 2-2/3 by 1/2 in <br /> Helical <br /> 150 by 2S nun 0,022-0.025 (25) <br /> 6bylin <br /> Helical <br /> 125 by 25 nun 0,025-0.026 (25) <br /> 5bylin <br /> 75 by 25 nun 0.027-0.028 (25) <br /> 3bylin <br /> ISO by 50 nun 0.033-0.035 (25) <br /> 6 by 2 in <br /> Structural Plate <br /> 230 by 64 nun 0.033-0,037 (25) <br /> 9 by 2-1/2 in <br /> Structural Plate <br />Corrugated Polyethylene Smooth 0.009-0.015 (71, 72) <br />Corrugated Polyethylene Corrugated 0.018-0,025 (73, 74) <br />Polyvinyl chloride (PVC) Smooth 0.009-0,011 (75, 76) <br />'NOTE: The Manning's n values indicated in this table were obtained in the laboratory and are supported <br /> by the provided reference, Actual field values for culverts may vary depending on the effect of <br /> abrasion, corrosion, deflection and joint conditions, <br /> <br />34 <br />