Qualitative Evaluation of Rock Weir Field Performance and Failure Mechanisms U.S. Department of the Interior Bureau of Reclamation Technical Service Center Denver, Colorado September 2007 U.S. Department of the Interior Mission Statement The mission of the Department of the Interior is to protect and provide access to our Nation’s natural and cultural heritage and honor our trust responsibilities to Indian tribes and our commitments to island communities. Mission of the Bureau of Reclamation The mission of the Bureau of Reclamation is to manage, develop, and protect water and related resources in an environmentally and economically sound manner in the interest of the American public. Qualitative Evaluation of Rock Weir Field Performance and Failure Mechanisms Authored by David M. Mooney, PhD, PE Hydraulic Engineer Division of Planning, MP-700 Mid Pacific Regional Office Sacramento, CA Christopher L. Holmquist-Johnson, MS, PE Hydraulic Engineer Sedimentation and River Hydraulics Group, 86-68240 Technical Service Center Denver, CO Elaina Holburn, MS, PE Hydraulic Engineer Sedimentation and River Hydraulics Group, 86-68240 Technical Service Center Denver, CO Reviewed by Blair P. Greiman, PhD, PE Hydraulic Engineer Sedimentation and River Hydraulics Group, 86-68240 Technical Service Center Denver, CO i Acknowledgements The following persons and/or entities contributed to this report: • Reclamation Funding: o Albuquerque Area Office o Pacific Northwest Regional Office o Science and Technology Office o Snake River Area Office • Technical Consultation: o Chester Watson, PhD, PE, Colorado State University o Christopher Thornton, PhD, PE, Colorado State University o Paula Makar, PE Bureau of Reclamation o Timothy Randle, MS, PE, Bureau of Reclamation • Field Data Collection: o Canyon R.E.O Rafting o Colorado State University o Pagosa Springs o 3-Forks Ranch o Snake River Area Office o Salmon Field Office ii Table of Contents 1 INTRODUCTION............................................................................................................................... 1 2 METHODS.......................................................................................................................................... 5 3 RESULTS .......................................................................................................................................... 13 3.1 STRUCTURE PERFORMANCE ....................................................................................................... 14 3.2 FLOW PATTERNS ........................................................................................................................ 17 3.3 SEDIMENT DEPOSITION AND EROSION PATTERNS ...................................................................... 20 3.4 SCOUR POOL LOCATION AND DIMENSION.................................................................................. 20 3.5 STRUCTURE MATERIALS AND CONSTRUCTION........................................................................... 21 4 DISCUSSION.................................................................................................................................... 23 4.1 STRUCTURES INFLUENCE ON FLOW AND SEDIMENT PATTERNS................................................... 23 4.2 FAILURE MECHANISMS .............................................................................................................. 24 4.2.1 Growth of the Scour Pool ..................................................................................................... 24 4.2.2 Filling and Burying .............................................................................................................. 26 4.2.3 Sliding or Rolling.................................................................................................................. 27 4.2.4 General Bank Migration/Flanking ....................................................................................... 28 4.2.5 Piping Underneath the Header Rocks .................................................................................. 29 4.2.6 Piping through the Arm Resulting in Flanking..................................................................... 29 4.3 SUCCESSFUL TECHNIQUES ......................................................................................................... 30 4.3.1 Foundations.......................................................................................................................... 30 4.3.2 Grout..................................................................................................................................... 30 4.3.3 Series not Singles.................................................................................................................. 30 4.3.4 Interlocking and Rock Shape................................................................................................ 31 5 CONCLUSIONS ............................................................................................................................... 33 6 REFERENCES.................................................................................................................................. 35 7 LIST OF APPENDIXES .................................................................................................................. 37 iii List of Figures Figure 1. Example Component Diagram using an A-Weir Structure................................. 6 Figure 2. Depiction of Weir Structure Types. Arrows indicate direction of flow. ............. 6 Figure 3. Examples of submergence conditions at high flow. Little Snake River, CO...... 7 Figure 4. Example of Bank Disturbance. Little Snake River, CO...................................... 8 Figure 5. Rocks Out of Alignment Example Photo Documentation. Rio Blanco, CO....... 9 Figure 6. Tilted/Rotated Rocks Example Photo Documentation, San Juan River, CO...... 9 Figure 7. Structure without a tie-in showing flanking around the right arm. Little Snake River, CO. ................................................................................................................. 10 Figure 8. Rock Shape a) Blocky versus b) Angular......................................................... 10 Figure 9. Rock Spacing a) Interlocking versus b) Small gaps versus c) Spaced apart..... 11 Figure 10. Staggering of header and footer rocks. Beaver Creek, WA. ........................... 11 Figure 11. Header-Footer configuration with exposed bedrock in scour pool. Little Snake River, CO. ................................................................................................................. 12 Figure 12. Evaluated Structure and the Breakdown by Type. ......................................... 13 Figure 13. Percentage of failures of all structures evaluated as part of this study........... 15 Figure 14. Number and Percentage of partial and full failures for each type of structure.15 Figure 15. Backwater Effects of (a) Submerged, (b) transitional, and (c) Free-Flow Conditions. Rio Blanco, CO. .................................................................................... 18 Figure 16. Lemhi River, ID a) before failure versus b) after right arm failure................. 19 Figure 17. Longitudinal Profile of Sediment Deposition and Pool Patterns..................... 20 Figure 18. Failure of structures with large voids between header rocks. Grande Ronde River, OR. ................................................................................................................. 21 Figure 19. Steep sloped ramps frequently used in PN Regional Designs. Lemhi River, ID ................................................................................................................................... 22 Figure 20. Typical Rosgen design with a single rock width of rocks defining structure. Little Snake River, CO.............................................................................................. 22 Figure 21. Pre- and Post- construction photos on the East Salmon River. Note changes in velocities and water surface profiles. East Fork Salmon River, ID.......................... 23 Figure 22. Footer pushed out, header tilted upstream. Little Snake River, CO................ 25 Figure 23. Footer shifted, header tilted downstream. Bear Creek, OR............................. 25 Figure 24. Header/footer pulled away from bank. Little Snake River, CO...................... 26 Figure 25. Structure has completely filled in with sediment. Grande Ronde River, OR.. 27 Figure 26. Structure tie-in and flanking. Little Snake River, CO..................................... 28 Figure 27. Piping through the Arm Resulting in Flanking. Little Snake River, CO. ....... 29 Figure 28. Interlocking of rocks providing additional structure support.......................... 31 v List of Tables Table 1. Descriptions of each hypothesized failure mechanism....................................... 16 Table 2. Primary failure mechanisms hypothesized for partial and full failures.............. 16 Table 3. Secondary failure mechanisms hypothesized for partial and full failures.......... 17 vii 1 Introduction River spanning loose-rock structures provide sufficient head for irrigation diversion, permit fish passage over barriers, protect banks, stabilize degrading channels, activate side channels, reconnect floodplains, and create in-channel habitat. These structures are called by a variety of names including rock weirs, alphabet (U-, A-, V-, W-) weirs, J- hooks, and rock ramps. These structures share the common characteristics