Hydraulic Design of Energy Dissipators for Culverts and ...

1 Department of Transportation Federal Highway Administration Publication No. FHWA-NHI-06-086 July 2006 Hydraulic Engineering Circular No. 14, Third Edition Hydraulic Design of Energy Dissipators for Culverts and Channels National Highway Institute 1. Report No. FHWA-NHI-06-086 HEC 14 2. Government Accession No. 3. Recipient's Catalog No. 4. Title and Subtitle Hydraulic Design of Energy Dissipators for Culverts and Channels Hydraulic Engineering Circular Number 14, Third Edition 5. Report Date July 2006 6. Performing Organization Code 7. Author(s) Philip L. Thompson and Roger T. Kilgore 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-63047 12. Sponsoring Agency Name and Address Federal Highway Administration National Highway Institute Office of Bridge Technology4600 North Fairfax Drive 400 Seventh Street, SW Suite 800 Room 3203 Arlington, Virginia 22203 Washington 20590 13.

2 Type of Report and Period Covered Final Report (3rd Edition) July 2004 July 2006 14. Sponsoring Agency Code 15. Supplementary Notes Project Manager: Cynthia Nurmi FHWA Resource CenterTechnical Assistance: Jorge Pagan, Bart Bergendahl, Sterling Jones (FHWA); Rollin Hotchkiss(consultant) 16. Abstract The purpose of this circular is to provide Design information for analyzing and mitigating Energy dissipation problems at culvert outlets and in open channels. The first three chapters provide general information on the overall Design process (Chapter 1), erosion hazards (Chapter 2), and culvert outlet velocity and velocity modification (Chapter 3). These provide a background and framework for anticipating dissipation problems. In addition to describing the overall Design process, Chapter 1 provides Design examples to compare selected Energy Dissipators . The next three chapters provide assessment tools for considering flow transitions (Chapter 4), scour (Chapter 5), and Hydraulic jumps (Chapter 6).

3 For situations where the tools in the first six chapters are insufficient to fully mitigate a dissipation problem, the remaining chapters address the Design of six types of constructed Energy Dissipators . Although any classification system for Dissipators is limited, this circular uses the following breakdown: internal (integrated) Dissipators (Chapter 7), stilling basins (Chapter 8), streambed level Dissipators (Chapter 9), riprap basins and aprons (Chapter 10), drop structures (Chapter 11), and stilling wells (Chapter 12). Much of the information presented has been taken from the literature and adapted, where necessary, to fit highway needs. Research results from the Turner Fairbank Highway Research Center and other facilities have also been incorporated. A survey of state practices and experience was also conducted to identify needs for this circular. 17. Key Word Energy dissipator, culvert , channel, erosion, outletvelocity, Hydraulic jump, internal dissipator, stillingbasin, impact basin, riprap basin, riprap apron, drop structure, stilling well 18.

4 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 287 22. Price Form DOT F (8-72) Reproduction of completed page authorized Technical Report Documentation Page Hydraulic Engineering Circular 14 Energy Dissipators Listing of Updates and Corrections (errata & corrigenda) DATE ACTION BY 13 Aug 2012 Page 4-2, first paragraph: text should have parentheses around the 3Fr quantity: .. if the tan is greater than 1/(3Fr), .. JSK 1 Oct 2012 Page 4-2 Figure Blaisdell s (1/3Fr) should be Blaisdell s (1/(3Fr)) CLN 13 Aug 2012 Page 4-4, Equation should be: = tan 1(1/(3Fr)) JSK 13 Aug 2012 Page 4-4, third paragraph: text should have parentheses around the 3Fr quantity.

5 Flaring the wingwall more than 1/(3Fr) (for example 45 ) .. JSK 13 Aug 2012 Page 4-5, Step 3: equation should depict: tan = 1/(3Fr) = 1/(3( )) = JSK 1 Oct 2012 Page 4-6, Alternative 2 .. tan = 1/3Fr should be tan = 1/(3Fr) CLN 13 Aug 2012 Page 4-7, Step 3: equation should depict: tan = 1/(3Fr) = 1/(3( )) = JSK 1 Oct 2012 Page 4-8, Alternative 2 .. tan = 1/3Fr should be tan = 1/(3Fr) CLN This list includes all known items as of Monday 1 October 2012 Notes: No update to the publication is planned at this time. FHWA does not have any printed copies of this document. NHI allows purchase of some FHWA documents. See the FHWA Hydraulics website to report any additional errata and corrigenda. ACKNOWLEDGMENTS First Edition The first edition of this Circular was prepared in 1975 as an integral part of Demonstration Project No. 31, " Hydraulic Design of Energy Dissipators for Culverts and Channels," sponsored by Region 15. Mr. Philip L.

6 Thompson of Region 15 and Mr. Murray L. Corry of the Hydraulics Branch wrote sections, coordinated, and edited the Circular. Dr. F. J. Watts of the University of Idaho (on a year assignment with Hydraulics Branch), Mr. Dennis L. Richards of the Hydraulics Branch, Mr. J. Sterling Jones of the Office of Research, and Mr. Joseph N. Bradley, Consultant to the Hydraulics Branch, contributed substantially by writing sections of the Circular. Mr. Frank L. Johnson, Chief, Hydraulics Branch, and Mr. Gene Fiala, Region 10 Hydraulics Engineer, supported the authors by reviewing and discussing the drafts of the Circular. Mr. John Morris, Region 4 Hydraulics Engineer, collected research results and assembled a preliminary manual that was used as an outline for the first draft. Mrs. Linda L. Gregory and Mrs. Silvia M. Rodriguez of the Region 15 Word Processing center and Mrs. Willy Rudolph of the Hydraulics Branch aided in manual preparation.

7 The authors wish to express their gratitude to the many individuals and organizations whose research and designs are incorporated into this Circular. Second Edition Mr. Philip Thompson and Mr. Dennis Richards updated the first edition in 1983 so that HEC 14 could be reprinted and distributed as a part of Demonstration Project 73. The 1983 edition did not add any new Dissipators , but did correct all the identified errors in the first edition. A substantial revision for Chapter 5, Estimating Erosion at culvert Outlets, was accomplished using material that was published by Dr. Steven Abt, Dr. James Ruff, and Dr. A Shaikh in 1980. The second edition was prepared in customary units. Third Edition Mr. Philip Thompson and Mr. Roger Kilgore prepared this third edition of the Circular with the assistance of Dr. Rollin Hotchkiss. This edition retains all of the Dissipators featured in the second edition, except the Forest Service (metal), USBR Type II stilling basin, and the Manifold stilling basin.

8 The following Dissipators have been added: USBR Type IX baffled apron, riprap aprons, broken-back Culverts , outlet weir, and outlet drop followed by a weir. This edition is in both customary and System International (SI) units. A previous SI unit version of HEC 14 was published in 2000 as a part of the FHWA Hydraulics Library on CDROM, FHWA-IF-00-022. i TABLE OF CONTENTS Page ACKNOWLEDGMENTS ..i TABLE OF CONTENTS .. ii LIST OF v LIST OF FIGURES .. vii LIST OF SYMBOLS ..viii GLOSSARY .. x CHAPTER 1: Energy DISSIPATOR Design ..1-1 Energy DISSIPATOR Design Design EXAMPLES ..1-4 CHAPTER 2: EROSION HAZARDS ..2-1 EROSION HAZARDS AT culvert Channel Alignment and Approach Velocity ..2-1 Depressed Inlets ..2-1 Headwalls and Wingwalls ..2-2 Inlet and Barrel EROSION HAZARDS AT culvert Local Channel Standard culvert End Treatments ..2-3 CHAPTER 3: culvert OUTLET VELOCITY AND VELOCITY Culverts ON MILD Submerged Unsubmerged Outlets (Critical Depth) and Tailwater.

9 3-2 Unsubmerged Outlets (Brink Depth)..3-3 Culverts ON STEEP SLOPES ..3-7 Submerged Outlets (Full Flow) ..3-7 Unsubmerged Outlets (Normal Depth) ..3-7 Broken-back culvert ..3-10 CHAPTER 4: FLOW TRANSITIONS ..4-1 ABRUPT SUBCRITICAL FLOW TRANSITION ..4-8 SUPERCRITICAL FLOW CONTRACTION ..4-10 SUPERCRITICAL FLOW EXPANSION ..4-11 CHAPTER 5: ESTIMATING SCOUR AT culvert OUTLETS ..5-1 COHESIONLESS SOILS ..5-1 Scour Hole Geometry ..5-2 Time of Scour ..5-2 Headwalls ..5-2 Drop Design Procedure ..5-3 COHESIVE SOILS ..5-6 ii CHAPTER 6: Hydraulic JUMP ..6-1 TYPES OF Hydraulic JUMP ..6-1 Hydraulic JUMP IN HORIZONTAL CHANNELS ..6-3 Rectangular Channels ..6-4 Circular Channels ..6-8 Jump Hydraulic JUMP IN SLOPING CHAPTER 7: INTERNAL (INTEGRATED) Dissipators ..7-1 TUMBLING FLOW ..7-1 Tumbling Flow in Box Culverts /Chutes ..7-2 Tumbling Flow in Circular Culverts .

10 7-9 INCREASED RESISTANCE ..7-14 Increased Resistance in Circular Culverts ..7-16 Isolated-Roughness Flow ..7-17 Hyperturbulent Flow ..7-18 Regime Boundaries ..7-19 Increased Resistance in Box Culverts ..7-25 USBR TYPE IX BAFFLED APRON ..7-32 BROKEN-BACK Culverts /OUTLET Broken-back culvert Hydraulics ..7-37 Outlet Outlet Drop Followed by a CHAPTER 8: STILLING EXPANSION AND DEPRESSION FOR STILLING BASINS ..8-2 GENERAL Design PROCEDURE ..8-5 USBR TYPE III STILLING BASIN ..8-11 USBR TYPE IV STILLING SAF STILLING BASIN ..8-25 CHAPTER 9: STREAMBED LEVEL Dissipators ..9-1 CSU RIGID BOUNDARY BASIN ..9-1 CONTRA COSTA BASIN ..9-12 HOOK BASIN ..9-18 Hook Basin with Warped Wingwalls ..9-18 Hook Basin with Uniform Trapezoidal Channel ..9-26 USBR TYPE VI IMPACT BASIN ..9-35 CHAPTER 10: RIPRAP BASINS AND APRONS ..10-1 RIPRAP BASIN ..10-1 Design Development.