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Potential Drift Accumulation at Bridges

LIST OF FIGURES

Figure 1. Map showing States with potential-scour study data used in this study

Figure 2. Generalized map of drift sites reported by States in response to request

Figure 3. Generalized map of drift field-study sites

Figure 4. Generalized map of drift sites in the United States from publications and written and oral communications

Figure 5. Sample State drift-accumulation report form

Figure 6. Vertical cross sections of assumed maximum drift accumulations on single piers

Figure 7. Fallen tree with asymmetric root mass and slightly curved trunk

Figure 8. Bank erosion along outside of curve

Figure 9. Logs floating along the center of the Harpeth River at Wray Bridge, Williamson County, Tennessee

Figure 10. Generalized plan view of the path of floating drift in a meandering river

Figure 11. Patterns of secondary flow in straight and curving channels

Figure 12. Narrow channel bridged by fallen trees

Figure 13. Trash rack and accumulated drift in Georges Creek near New Columbia, Illinois.

Figure 14. Nearly complete channel blockage of the Harpeth River at Interstate 40, Davidson County, Tennessee

Figure 15. Large log supporting a single-pier drift accumulation

Figure 16. Drift accumulation at the upstream end of an island

Figure 17. Raft of floating drift at the FM 2004 bridge over the Brazos River near Lake Jackson, Texas

Figure 18. Width of inferred single-pier drift accumulations at scour-potential sites in Indiana

Figure 19. Width of inferred single-pier drift accumulations at scour-potential sites in Tennessee

Figure 20. Logs lodged from pier to pier and from pier to bank

Figure 21. Definition sketch of the effective width of horizontal gaps

Figure 22. Effective width of drift-blocked spans outside the Pacific Northwest

Figure 23. Blockage of a 27-meter span over the White River at Paragon, Indiana, by drift accumulation and island formation, September 25, 1992

Figure 24. Design log length and upstream channel width for the eastern United States and the Olympic Peninsula

Figure 25. Widest observed single-pier accumulation, in the Queets River, Washington, at Clearwater River Road

Figure 26. Downstream side of a pile cluster with accumulated drift

Figure 27. Drift under the upstream side of a bridge deck

Figure 28. Flow chart for evaluating potential for drift delivery

Figure 29. Location categories relative to local drift delivery

Figure 30. Flow chart for determining location category

Figure 31. Flow chart for determining potential for accumulation across a span or vertical gap

Figure 32. Flow chart for determining potential for drift accumulation on a single pier


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