Revised Clear-Water and Live-Bed Contraction Scour Analysis (2021)

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2021 N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP RESEARCH REPORT 971 Revised Clear-Water and Live-Bed Contraction Scour Analysis P.F. Lagasse Ayres Associates Fort Collins, CO R. Ettema Colorado State University Fort Collins, CO W.M. DeRosset Ayres Associates Fort Collins, CO A. Nowroozpour Colorado State University Fort Collins, CO P.E. Clopper Ayres Associates Fort Collins, CO Subscriber Categories Design • Hydraulics and Hydrology • Bridges and Other Structures Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed, and implementable research is the most effective way to solve many problems facing state departments of transportation (DOTs) administrators and engineers. Often, highway problems are of local or regional interest and can best be studied by state DOTs individually or in cooperation with their state universities and others. However, the accelerating growth of highway transporta- tion results in increasingly complex problems of wide interest to high- way authorities. These problems are best studied through a coordinated program of cooperative research. Recognizing this need, the leadership of the American Association of State Highway and Transportation Officials (AASHTO) in 1962 ini- tiated an objective national highway research program using modern scientific techniques—the National Cooperative Highway Research Program (NCHRP). 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Published research reports of the NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM are available from Transportation Research Board Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet by going to https://www.mytrb.org/MyTRB/Store/default.aspx Printed in the United States of America NCHRP RESEARCH REPORT 971 Project 24-47 ISSN 2572-3766 (Print) ISSN 2572-3774 (Online) ISBN 978-0-309-67407-2 Library of Congress Control Number 2021940098 © 2021 National Academy of Sciences. All rights reserved. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. 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C O O P E R A T I V E R E S E A R C H P R O G R A M S AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 24-47 by Ayres Associates, Fort Collins, Colorado. Dr. P.F. Lagasse, Senior Water Resources Engineer, served as Principal Investi- gator. Dr. R. Ettema, Professor, Colorado State University (CSU), served as a Co-Principal Investigator. Mr. P.E. Clopper, formerly Director, Applied Technology, Ayres Associates, also served as a Co-Principal Investigator. All laboratory testing was performed at the CSU Engineering Research Center Hydraulics Labora- tory under the direction of Dr. Ettema at CSU. The assistance of the CSU Engineering Center Hydrau- lics Laboratory staff is gratefully acknowledged. In particular Mr. A. Nowroozpour (PhD candidate) and Mr. A. Fakhri (MS candidate) were responsible for conducting the laboratory experiments described in this report. At Ayres, Mr. Scott Zey was an important member of the project team. His significant contri- butions to the 1D, 2D, and 3D analyses and the production of the final report, including development of the case study, are gratefully acknowledged. CRP STAFF FOR NCHRP RESEARCH REPORT 971 Christopher J. Hedges, Director, Cooperative Research Programs Lori L. Sundstrom, Deputy Director, Cooperative Research Programs Camille Crichton-Sumners, Senior Program Officer Tyler Smith, Senior Program Assistant Eileen P. Delaney, Publications Senior Advisor Natalie Barnes, Director of Publications Kami Cabral, Editor NCHRP PROJECT 24-47 PANEL Field of Soils and Geology—Area of Foundations and Scour Wesley Peck, Tennessee Department of Transportation, Nashville, TN (Chair) Edward Paul Foltyn, Oregon Department of Transportation, Salem, OR Casey M. Kramer, Natural Waters, Olympia, WA Nick Wark, Vermont Agency of Transportation, Barre, VT Solomon T. Woldeamlak, Minnesota Department of Transportation, Oakdale, MN Xiong Bill Yu, Case Western Reserve University, Cleveland, OH Kornel D. Kerenyi, FHWA Liaison

NCHRP Research Report 971: Revised Clear-Water and Live-Bed Contraction Scour Analysis provides state transportation engineers and other practitioners with revised scour contrac- tion estimation equations for use on live-bed and clear-water channels with fine sand and introduces a new computational paradigm that results in less variability. Scour is the result of the erosive action of flowing water, entraining and removing boundary material from channel beds, banks, and around bridge foundations. This increase in sediment mobility compromises structural integrity. Contraction scour in sand-bed rivers is the result of the interaction of sediment particles with the oncoming flow that can generate complex turbulent structures in the flow. This complexity leads to only approximate esti- mates of the depth of contraction scour. Under NCHRP Project 24-47, “Revised Clear-Water and Live-Bed Contraction Scour Analysis,” Ayres Associates developed live-bed and clear-water contraction scour equations for risk-based bridge design. This study introduces the concept of calculating contraction scour at the “vena-contracta,” which is formed where the flow enters the contracted channel. Except for corner (abutment) scour at the contraction entrance, the scour depth in the vena- contracta region gives the deepest scour along a contracted channel. The Research Team developed a regression equation from data obtained from flume experiments to estimate a vena-contracta correction coefficient, Kv. Using modeling and laboratory tests from Colorado State University, this study re-examined the FHWA’s Hydraulic Engineering Circular No. 18 (HEC-18) equations used for the clear-water and live-bed conditions and the NCHRP Project 24-20, “Estimation of Bridge Scour Depths at Bridge Abutments,” scour equations used for estimating the contrac- tion scour component of abutment scour. Both contraction scour prediction methods were adjusted to include the vena-contracta coefficient. These revised equations are for use when estimating both live-bed and clear-water contraction scour in channels whose beds are formed of fine sand and have the width-to-depth ratio and entrance conditions comparable with those used for this study. For bridges that do not meet these criteria, the application of the existing best-practice modeling methods (see, for example, Robinson et al. 2019) and the NCHRP Project 24-20 contraction scour equations are recommended. Improved evaluation techniques and reliability considerations found in NCHRP Research Report 971 should be of direct use to those responsible for the evaluation and design of highway bridges in state transportation agencies. The accompanying Training Manual is available as NCHRP Web-Only Document 294: Revised Clear-Water and Live-Bed Contraction Scour Analysis Training Manual, and the PowerPoint presentation supporting the manual is avail- able on the TRB website (www.trb.org) by searching for “NCHRP Research Report 971”. F O R E W O R D By Camille Crichton-Sumners Staff Officer Transportation Research Board

S-1 Summary 1-1 Chapter 1 Introduction and Research Approach 1-1 1.1 Scope and Research Objectives 1-3 1.2 Research Approach 2-1 Chapter 2 Findings 2-1 2.1 Review of Current Practice 2-15 2.2 Evaluation of Existing Clear-Water and Live-Bed Contraction Scour Laboratory Data 2-22 2.3 Evaluation of Field Data on Clear-Water and Live-Bed Contraction Scour 3-1 Chapter 3 Laboratory Testing Setup and Test Plan 3-1 3.1 Overview 3-1 3.2 Test Setup 3-3 3.3 Data Measurements and Instrumentation 3-4 3.4 Laboratory Test Plan 3-7 3.5 1D Hydraulic Model Calibration Procedure 4-1 Chapter 4 Clear-Water Laboratory Testing Results 4-1 4.1 Severe Contraction Ratio 4-8 4.2 Moderate Contraction Ratio 4-15 4.3 Mild Contraction Ratio 5-1 Chapter 5 Live-Bed Laboratory Testing Results 5-1 5.1 Severe Contraction Ratio 5-1 5.2 Moderate Contraction Ratio 5-8 5.3 Mild Contraction Ratio 6-1 Chapter 6 Rigid-Bed Laboratory Testing Results 6-1 6.1 Overview 6-1 6.2 Rigid-Bed Testing at a Severe Contraction Ratio 7-1 Chapter 7 Computational Applications 7-1 7.1 Overview 7-2 7.2 Applications 7-4 7.3 Calibration to Clear-Water Contraction Scour Test CW_0.25-0.75 7-8 7.4 Calibration to Live-Bed Contraction Scour Test LB_0.50-2.0 7-11 7.5 Results 7-13 7.6 3D Flow Visualization C O N T E N T S

8-1 Chapter 8 Revised Contraction Scour Analysis: Appraisal, Results, and Applications 8-1 8.1 Overview 8-1 8.2 Appraisal of Results 8-13 8.3 Revised Contraction Scour Analysis 8-30 8.4 Application Example 8-36 8.5 Reliability of Contraction Scour Equations 8-42 8.6 Implementation of Research Results 8-45 8.7 Training Manual for Implementation of Research Results 9-1 Chapter 9 Observations, Conclusions, and Suggested Research 9-1 9.1 Observations 9-2 9.2 Conclusions 9-5 9.3 Suggestions for Further Research R-1 References A-1 Abbreviations and Acronyms Note: Photographs, figures, and tables in this report may have been converted from color to grayscale for printing. The electronic version of the report (posted on the web at www.trb.org) retains the color versions.