Publication No. FHWA-NHI-05-114 September 2005 U.S. Department of Transportation Federal Highway Administration Hydraulic Engineering Circular No. 15, Third Edition Design of Roadside Channels with Flexible Linings National Highway Institute Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. FHWA-NHI-05-114 HEC 15 4. Title and Subtitle 5. Report Date Design of Roadside Channels with Flexible Linings September 2005 Hydraulic Engineering Circular Number 15, Third Edition 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Roger T. Kilgore and George K. Cotton 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Kilgore Consulting and Management 2963 Ash Street 11. Contract or Grant No. Denver, CO 80207 DTFH61-02-D-63009/T-63044 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Federal Highway Administration Final Report (3rd Edition) National Highway Institute Office of Bridge Technology April 2004 – August 2005 4600 North Fairfax Drive 400 Seventh Street Suite 800 Room 3202 14. Sponsoring Agency Code Arlington, Virginia 22203 Washington D.C. 20590 15. Supplementary Notes Project Manager: Dan Ghere – FHWA Resource Center Technical Assistance: Jorge Pagan, Joe Krolak, Brian Beucler, Sterling Jones, Philip L. Thompson (consultant) 16. Abstract Flexible linings provide a means of stabilizing roadside channels. Flexible linings are able to conform to changes in channel shape while maintaining overall lining integrity. Long-term flexible linings such as riprap, gravel, or vegetation (reinforced with synthetic mats or unreinforced) are suitable for a range of hydraulic conditions. Unreinforced vegetation and many transitional and temporary linings are suited to hydraulic conditions with moderate shear stresses. Design procedures are given for four major categories of flexible lining: vegetative linings; manufactured linings (RECPs); riprap, cobble, gravel linings; and gabion mattress linings. Design procedures for composite linings, bends, and steep slopes are also provided. The design procedures are based on the concept of maximum permissible tractive force. Methods for determination of hydraulic resistance applied shear stress as well as permissible shear stress for individual linings and lining types are presented. This edition includes updated methodologies for vegetated and manufactured lining design that addresses the wide range of commercial products now on the market. This edition also includes a unified design approach for riprap integrating alternative methods for estimating hydraulic resistance and the steep slope procedures. Other minor updates and corrections have been made. This edition has been prepared using dual units. 17. Key Word 18. Distribution Statement channel lining, channel stabilization, tractive force, This document is available to the public from the resistance, permissible shear stress, vegetation, National Technical Information Service, riprap, manufactured linings, RECP, gabions Springfield, Virginia, 22151 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 153 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized ACKNOWLEDGMENTS First Edition Mr. Jerome M. Normann of Federal Highway Administration wrote the first edition of this Hydraulic Engineering Circular. FHWA reviewers included Frank Johnson, Dennis Richards and Albert Lowe of the Hydraulics Branch. The manual was dated October 1975. Second Edition Dr. Y. H. Chen and Mr. G. K. Cotton of Simons, Li & Associates wrote the second edition of this Hydraulic Engineering Circular. It was published as report number FHWA-IP-87-7 dated April 1988 under contract number DTFH61-84-C-00055. The FHWA project managers were John M. Kurdziel and Thomas Krylowski. Philip L. Thompson, Dennis L. Richards, and J. Sterling Jones were FHWA technical assistants Third Edition Mr. Roger T. Kilgore and Mr. George K. Cotton wrote this third edition of this Hydraulic Engineering Circular. The authors appreciate guidance of FHWA technical project manager, Mr. Dan Ghere and the technical review comments of Jorge Pagan, Joe Krolak, Brian Beucler, Sterling Jones, and Philip Thompson. i TABLE OF CONTENTS Page ACKNOWLEDGMENTS ................................................................................................................i TABLE OF CONTENTS ................................................................................................................ ii LIST OF TABLES......................................................................................................................... iv LIST OF FIGURES ....................................................................................................................... v LIST OF SYMBOLS ..................................................................................................................... vi GLOSSARY ................................................................................................................................viii CHAPTER 1: INTRODUCTION .................................................................................................1-1 1.1 SCOPE AND APPLICABILITY .........................................................................................1-1 1.2 BACKGROUND................................................................................................................1-2 1.3 RIGID LININGS ................................................................................................................1-4 1.4 FLEXIBLE LININGS .........................................................................................................1-5 1.4.1 Long-term Flexible Linings .................................................................................1-5 1.4.1.1 Vegetation..........................................................................................1-5 1.4.1.2 Cobble Lining .....................................................................................1-6 1.4.1.3 Rock Riprap .......................................................................................1-7 1.4.1.4 Wire-Enclosed Riprap ........................................................................1-8 1.4.1.5 Turf Reinforcement ............................................................................1-9 1.4.2 Transitional and Temporary Flexible Linings....................................................1-10 1.4.2.1 Bare Soil ..........................................................................................1-11 1.4.2.2 Gravel Mulch....................................................................................1-11 1.4.2.3 Vegetation (Annual Grass)...............................................................1-11 1.4.2.4 Open-weave Textile (OWT) .............................................................1-11 1.4.2.5 Erosion control blanket (ECB)..........................................................1-12 CHAPTER 2: DESIGN CONCEPTS ..........................................................................................2-1 2.1 OPEN CHANNEL FLOW..................................................................................................2-1 2.1.1 Type of Flow.......................................................................................................2-1 2.1.2 Normal Flow Depth.............................................................................................2-1 2.1.3 Resistance to Flow .............................................................................................2-2 2.2 SHEAR STRESS ..............................................................................................................2-3 2.2.1 Equilibrium Concepts .........................................................................................2-3 2.2.2 Applied Shear Stress..........................................................................................2-4 2.2.3 Permissible Shear Stress ...................................................................................2-6 2.3 DESIGN PARAMETERS ..................................................................................................2-7 2.3.1 Design Discharge Frequency .............................................................................2-7 2.3.2 Channel Cross Section Geometry ......................................................................2-8 2.3.3 Channel Slope....................................................................................................2-8 2.3.4 Freeboard...........................................................................................................2-8 CHAPTER 3: GENERAL DESIGN PROCEDURE .....................................................................3-1 3.1 STRAIGHT CHANNELS...................................................................................................3-1 3.2 SIDE SLOPE STABILITY .................................................................................................3-6 3.3 COMPOSITE LINING DESIGN ........................................................................................3-7 3.4 STABILITY IN BENDS....................................................................................................3-12 3.5 STEEP SLOPE DESIGN ................................................................................................3-16 3.6 MAXIMUM DISCHARGE APPROACH...........................................................................3-17