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. FHWA-NHI-05-114 HEC 15

2. Government Accession No. 3. Recipient's Catalog No.

4. Title and Subtitle Design of Roadside Channels with Flexible Linings Hydraulic Engineering Circular Number 15, Third Edition

5. Report Date September 2005

6. Performing Organization Code

7. Author(s) Roger T. Kilgore and George K. Cotton

8. Performing Organization Report No.

9. Performing Organization Name and Address Kilgore Consulting and Management2963 Ash Street Denver, CO 80207

10. Work Unit No. (TRAIS)

11. Contract or Grant No. DTFH61-02-D-63009/T-63044

12. Sponsoring Agency Name and Address Federal Highway Administration National Highway Institute Office of Bridge Technology4600 North Fairfax Drive 400 Seventh Street Suite 800 Room 3202 Arlington, Virginia 22203 Washington D.C. 20590

13. Type of Report and Period Covered Final Report (3rd Edition) April 2004 August 2005

14. Sponsoring Agency Code

15. Supplementary Notes Project Manager: Dan Ghere FHWA Resource CenterTechnical 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 channel lining, channel stabilization, tractive force,resistance, permissible shear stress, vegetation,riprap, manufactured linings, RECP, gabions

18. Distribution Statement This document is available to the public from theNational Technical Information Service, Springfield, Virginia, 22151

19. Security Classif. (of this report) Unclassified

20. Security Classif. (of this page) Unclassified

21. No. of Pages 153

22. Price

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.

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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.........................................................