009468-Guide for Selecting Manning's Roughess Coefficients for Natural Channels and Flood Plains

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GUIDE FOR SELECTING MANNING’S ROUGHNESS COEFFICIENTS FOR NATURAL CHANNELS AND FLOOD PLAINS 3 Turner-Fairbank Research Center 6300 Georgetown McLean, Virginia Highway Pike 22101 Report No. t u FHWA-TS-84-204 Final April Report 1984 U.S. Department of Transportation -1 AdministrWon HishrwaV ‘This document is available to the U.S. public through the National Technical Information Service, Springfield, Virginia 2216 FOREWORD This Technology Sharing Report provides procedures for d
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  GUIDE FOR SELECTING MANNING’S ROUGHNESS COEFFICIENTS FOR NATURAL CHANNELS AND FLOOD PLAINS Turner-Fairbank Highway Research Center 6300 Georgetown Pike McLean, Virginia 22101 t 3 u U.S. Department of Transportation -1 HishrwaV AdministrWon Report No. FHWA-TS-84-204 Final Report April 1984 ‘This document is available to the U.S. public through the National Technical Information Service, Springfield, Virginia 2216  FOREWORD This Technology Sharing Report provides procedures for determining Manning's roughness coefficient for densely vegetated flood plains. The guidelines should be of interest to hydraulic and bridge engineers. Environmental specialists concerned with flood plains and wetlands may also find this report useful. The report was prepared by the United States Geological Survey, Water Resources Division, with technical guidance from the FHWA Office of Engineering and Highway Operations Research and Development. Sufficient copies of the publication are being distributed to provide a minimum of one copy to each FHWA region office, division office, and to each State highway agency. Additional copies of the report can be obtained from the National Technical Information Service, Springfield, Virginia 22161. DirectdrJ Office of / Engineering and Highway Operations R&D Director, Office of Implementation NOTICE This document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange. The United States Government assumes no liability for its contents or use thereof. The contents of this report reflect the views of the contractor, who is responsible for the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policy of the Department of Transportation. This report does not constitute a standard, specification or regulation. The United States Government does not endorse products or manufacturers. Trade or manufacturer's names appear herein only because they are considered essential to the object of this document.  1. Report No. 'FHWA-TS-84-204 Technical Report Documentation Page 2. G overnment Accession No. 3. Recipient’s Catalog No. 4. Title and Subtitle I I 5. Report Dote GUIDE FOR SELECTING MANNING'S ROUGHNESS COEFFICIENTS . April 1984 FOR NATURAL CHANNELS AND FLOOD PLAINS 6. Performing Organization Code 7. Author’s) 8. Performing Organization Report No. G. J. Arcement, Jr., and V. R. Schneider 9. Performing Organization Name and Address U. S. Geological Survey Water Resources Division P.O. Box 66492 Baton Rouge, LA 70896 10. Work Unit NO. (TRAIS) 11. Contract or Grant No. 13. TYPO of Report and Period Covered 9 12. Sponsoring Agency Name and Address Office of Implementation Federal Highway Administration 6300 Georgetown Pike McLean, Virginia 22101 15. s upplementory Notes Co-COTR: John M. Kurdziel Roy Trent Final Report 14. Sponsoring Agency Code 16. Abstract Although much research has been done on Manning's roughness coefficients for stream channels, very little has been done on the selection of roughness values for densely vegetated flood plains. A procedure for the determination of Manning's roughness coefficient (n) for channels and flood plains analyzes the different roughness factors that affect the roughness coefficients for channels and flood plains. By determining the value of each factor and combining those values, the n value can be determined. Another procedure deals with densely vegetated flood plains where the major roughness is caused by trees, vines, and brush. The n value for this type of flood plain can be determined by measuring the vegetation density of the flood plain. Photographs of flood plain segments where n values have been verified are presented as a comparison standard to aid in assigning n values to similar flood plains. 17. Key Words Roughness Coefficient, Manning Equation, 18. Distributiov Statement No restrictions. This document is Channels, Stable, Unstable, Channel Flow, available to the public through the Flood Plains, Flow Resistance, Hydraulic National Technical Information Service, Roughness, Hydraulic Friction, Overland Springfield, Virginia 22161. Flow, Vegetation Effects 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Prtce Unclassified Unclassified 68 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized  Page 1 2 3 4 8 8 8 12 12 13 13 13 16 16 16 16 17 17 18 18 23 39 39 39 50 51 60 61 Introduction------------------------------------------------------- Approach--- ------- _________________-------------------------------- Method for assigning n values for channels------------------------- Selection of base n values (nb)------------------------------- Adjustment factors for channels- ----------------------~~~~~~~- Irregularity (nl)---------------------------------------- Variation in channel cross section (n2)------------------ (&stru&ions (n3)---------------------------------------- Vegetation (n4) ____-------------------------------------- Meandering (m) --------------------~~~~~~~-~~~-----~---~~ Methods for assigning n values for flood plains-------------------- Modified channel method--------------------------------------- Adjustment factors for flood plains---------------------- Surface irregularities (nl)------------------------- &structions (n3)----------------------------------- Vegetation (n4)---------------------------------------- Vegetation density methods------------------------------------ Techniques for determining vegetation density------------ Indirect technique---------------------------------- Direct technique------------------------------------ Pho+-ogra@s of flood plains---------------------------------------- procedures for assigning n values---------------------------------- Description of steps for assigning n values------------------- Channel roughness (steps 3-13)--------------------------- Flood-plain roughness (steps 14-23)---------------------- Examples of procedures for determining n values---------- lw+- references------------------------------------------------ ii
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