Scour at Contracted Bridges (2006)

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i TABLE OF CONTENTS LIST OF FIGURES…..............................................................................……….........…ii LIST OF TABLES..…….................................................................................………......v ACKNOWLEDGMENTS...……..................................................................……....…..vii ABSTRACT..............................................................................….....……….........…....viii CHAPTER 1 Introduction and Research Approach.. .................................……......…1 Purpose and Objectives Scope and Approach of Research CHAPTER 2 Findings..........................................................................……..…........….. 7 Executive Summary of Literature Review and Field Data Scour at Bridge Contractions Contraction Scour Abutment Scour Scour with Debris Applying Numerical Models for Scour Analysis Erodibility and Geotechnical Properties of Materials CHAPTER 3 Interpretation, Appraisal, and Applications......…....…...................... 92 Recommended Modifications to Scour Prediction Methodology Guidelines for Numerical Modeling Erodibility and Geotechnical Properties of Materials CHAPTER 4 Conclusions and Suggested Research......….............….....…...........…101 Conclusions Recommendations Modification to Strategic Research Plan REFERENCES...............................................................................….......................….113 APPENDIX A: Case Study Reports...........................…..................................………A-1

ii LIST OF FIGURES 1. Example of single scour hole at shorter bridges, as shown at U.S. Route 301, crossing Douglas Swamp in Florence County, South Carolina, July 31, 1996.……..………………………………………... 15 2. Example of separate left and right abutment-scour holes at longer bridges, as shown at Road S-87 bridge, crossing the Coosawhatchie River in Jasper County, South Carolina, November 12, 1997.……….. 16 3. Plot of abutment scour measurements at the C.R. 22 bridge over the Pomme De Terre River near Fairfield, Minnesota in April 1997...…… 18 4. Plot of contraction scour measurements at (A) Conehoma Creek at State Highway 35, near Kosciusko, Mississippi, April 1979 and (B) Beaver Creek Overflow at US 2, 7 miles West of Saco, Montana... 19 5. Relation of observed and theoretical clear-water contraction-scour depth for the 100-year flow, in the Piedmont of South Carolina. (Theoretical contraction scour calculated with the Laursen (1963) equation.)……… 29 6. Example of scour-hole low point located upstream of S.R. 218 over the Cedar River near Janesville, Iowa……………………………………… 32 7. Example of scour-hole low point located downstream of S.R. 25 over the Minnesota River near Belle Plaine, Minnesota………………….….. 33 8. Site configuration, flow patterns and approach section location for S.R. 37 over the James River near Mitchell, South Dakota..…………… 34 9. Relation of longitudinal location for the low point of the abutment-scour hole and the 100-year-flow top width at the bridge for (A) shallow and deep scour holes in the Piedmont of South Carolina, and (B) sites in the Coastal Plain of South Carolina.………………………..……………… 36 10. Example of scour-hole low point located upstream of Road S-299, crossing Cannons Creek in Newberry County, South Carolina, November 24, 1997.…………………………………………………….. 37 11. Example of scour-hole low point located downstream of S.C. Route 41, crossing Maiden Down Swamp in Marion County, South Carolina, December 3, 1996...…………………..………………………………… 37 12. Illustration of flow contracted by an embankment constructed in a floodplain.…………………………………………………………….… 43

iii 13. Relation of observed clear-water abutment-scour depth and the 100-year-flow embankment length, normalized by the 100-year-flow depth near the abutment toe, for the Piedmont and Coastal Plain of South Carolina with (A) a complete horizontal axis, and (B) a truncated horizontal axis.………………………………………………….……… 46 14. Comparison of the embankment-length envelope for field observations of abutment-scour depth in South Carolina with the observed abutment- scour for selected sites from the National Bridge Scour Database (BSDMS)…………………………………………..…………………… 49 15. Comparison of field observations of abutment-scour depth with the theoretical abutment-scour depth computed with the original Froehlich (1989) and modified Froehlich (2001) equations for selected sites from the National Bridge Scour Database (BSDMS).……………………….. 51 16. Comparison of field observations of abutment-scour depth with theoretical abutment-scour depth computed with the HEC-18 (2001) Sturm equation (with and without the safety factor) for selected sites from the National Bridge Scour Database (BSDMS).……………….… 52 17. Aerial photograph of State Route 25 over the Minnesota River near Belle Plaine, Minnesota……………………..…………………………. 60 18. Comparison of observed and model-velocity distributions at U.S. Route 12 over the Pomme de Terre River, Minnesota for (A) April 5, 1997 and (B) April 9, 1997………………………………. 71 19. Comparison of observed and model velocity distributions at County Route 22 over the Pomme de Terre River, Minnesota for (A) April 5, 1997 and (B) April 9, 1997.………………………………. 72 20. Plan view of topography and channel alignment for County Route 22 over the Pomme De Terre River near Fairfield, Minnesota……………. 74 21. Sketch of the hydrodynamics observed during bridge scour measurements at County Route 22 over the Pomme de Terre River on April 5, 1997.………………………..…………………………………. 76 22. Modeled flow field for County Route 22 over the Pomme de Terre River for conditions on April 5, 1997 …………………………………………. 77 23. Computational mesh for the two-dimensional model of County Route 22 over the Pomme de Terre River.…………………………………………. 78

iv 24. Comparison of the velocity distribution for the two-dimensional model and field measurements at the upstream bridge face of County Route 22 over the Pomme de Terre River on (A) April 5, 1997 and (B) April 9, 1997.……………………………………………………..…. 79 25. Difference in bed elevation (in meters) between two-dimensional sediment-transport model output and field data collected during flood conditions on the Pomme de Terre River at County Route 22, April 4-9, 1997.…………………………………………………………. 81 26. Comparison of the velocity distribution for the two-dimensional model, one-dimensional models and field measurements at the upstream bridge face of County Route 22 over the Pomme de Terre River on (A) April 5, 1997 and (B) April 9, 1997…………………………..….…. 82 27. Comparison of the original one-dimensional and two-dimensional model- approach section location with an approach section in a location more representative of the actual blocked and main channel hydraulics at County Route 22 over the Pomme de Terre River ……………………… 83 28. Looking upstream from the east-bound bridge deck of Highway 70 over Bear Creek near Lagrange, North Carolina during low-low.……………. 90

v LIST OF TABLES 1. Summary of live-bed contraction-scour equation exponents…………….. 22 2. Comparison of observed and theoretical contraction-scour depth (clear-water and live-bed) for bridge sites in the National Bridge Scour Database (BSDMS)………………………………………………………. 26 3. Comparison of observed abutment scour with scour calculated using the HEC-18 (2001) Froehlich and Sturm prediction equations using HEC-RAS modeled hydraulics for eight abutment scour sites in the National Bridge Scour Database (BSDMS).……………………………... 53 4. Comparison of observed abutment scour with scour calculated using the HEC-18 (2001) prediction equations using hydraulic parameters measured in the field for two sites in the National Bridge Scour Database (BSDMS).……………………………………………………………..….. 55 5. Comparison of measured and modeled abutment-tip velocities for use in the HIRE abutment scour prediction equation...…………..……………… 57 6. Comparison of observed abutment scour with scour calculated using the HEC-18 (2001) Froehlich and HIRE prediction equations using modeled and field hydraulics for two abutment scour sites in the National Bridge Scour Database (BSDMS). …………………………………………..…… 58 7. Comparison of observed abutment scour with scour calculated using the HEC-18 (2001) Sturm and Maryland prediction equations using modeled and field hydraulics for two abutment scour sites in the National Bridge Scour Database (BSDMS)……..…………………………………………. 59 8. Comparison of observed abutment scour with scour calculated using the HEC-18 (2001) Froehlich and HIRE prediction equations using flood and pre-flood geometry for four abutment scour sites in the National Bridge Scour Database (BSDMS)………………………………………………… 62 9. Comparison of observed abutment scour with scour calculated using the HEC-18 (2001) Sturm and Maryland prediction equations using flood and pre-flood geometry for four abutment scour sites in the National Bridge Scour Database (BSDMS)……………….………………………... 63 10. Comparison of Melville’s debris scour estimating procedure with HEC-18 procedures and observed debris scour at S.R. 129 over the Chariton River near Prairie Hill, Missouri……….………………………... 67

vi 11. Comparison of debris-width design-criteria relation (Diehl, 1997) and measured debris raft diameters for S.R. 129 over the Chariton River near Prairie Hill, Missouri…….…………………………………………… 68 12. Comparison of HEC-18 scour estimates (Froehlich, HIRE, and live-bed equations) from the one-dimensional and two-dimensional models (original and adjusted approach-section locations) relative to the sediment transport model results and observed scour at County Route 22 over the Pomme de Terre River on April 9, 1997…………………………. 84