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<br />Technical ~eport Documentation Page <br /> <br />1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. <br />FHWA-TS-84-204 <br />4. Title <:md Subtitle 5. Report Date <br />GUIDE FOR SELECTING MANNING'S ROUGHNESS COEFFICIENTS Anril 1984 <br />FOR NATURAL CHANNELS AND FLOOD PLAINS 6. Performing Organi:ilotion Code <br /> 8. Performing Organi:tatian Report No. <br />7. Author/s1 <br />G. J. Arcement, Jr. , and V. R. Schneider <br />9. Performing Organization Name and Address 10. Work Unit No. (TRAJS) <br />U. S. Geological Survey <br />Water Resources Division 1l. Contract or Gront No. <br />P.O. Box 66492 <br />RO>M TA 7n8Q6 13. Type of Report ond Period Covered <br />12. Sponsoring Agency Name ond Address <br />Office of Implementation Final Report <br />Federal Highway Administration <br />6300 Georgetown Pike 14. Sponsoring Agency Code <br />McLean Viro-inia 22101 <br />15. Supple-mentory Notes <br />Co-COTR: John M. Kurdziel <br /> Roy Trent <br /> Abstract - <br />16. <br />Al though much research has been done on Manning's roughness coefficients for stream <br />channels, very 1 i tt le has been done on the selection of roughnes s values for densely <br />vegetated flood plains, A procedure for the determination of Manning's roughness <br />coefficient (n) for channels and flood plains analyzes the different roughness <br />factors that a f fe c t the roughness coefficients for channe Is and flood plains. By <br />determining the value of each factor and combining thos e values, the n value can be <br />determined. Another procedure deals with densely vegetated flood plains where the <br />major roughness lS caused by trees, vines, and brush. The n value for this type <br />of flood plain can be determined by measuring the "vegetation densityll of the <br />flood plain. <br />Photographs of flood plain segments where n values have been verified are presented <br />as a comparison standard to aid in assigning n values to similar flood plains. <br />17. Ke~ Words Coefficient, Manning Equation, 18. Distribution Statement <br />Roughness No restrictions. This document lS <br />Channels, Stable, Uns tab le, Ch anne 1 Flow, avai lab le to the pub lic th rough the <br />Flood Plains, Flow Resistance, Hydraulic National Technical Information Service, <br />Roughness, Hydraulic Friction, Overl and Springfield, Virginia 22161, <br />Flow, Vegetation Effects <br />19. Security Classif. (of this report) 20, Security Clossi f. (of thi s page) 21. No. of Pages 22. Price <br />Unclassified Unclassified 68 <br /> <br />Form DOT F 1700.7 (8_72) <br /> <br />Reproduction of completed poge authorized <br />