Hydraulic Laboratory Report HL-2006-02 Hydraulic Investigations of the Erosion Potential of Flows Overtopping Gibson Dam Sun River Project, Montana Great Plains Region 1. 2. U.S. Department of the Interior Bureau of Reclamation Technical Service Center Water Resources Research Laboratory Denver, Colorado April 2006 Form Approved REPORT DOCUMENTATION PAGE OMB No. 0704-0188 The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 1. REPORT DATE (DD-MM-YYYY) 2. REPORT TYPE 3. DATES COVERED (From - To) April 2006 Technical December-April 2006 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Hydraulic Investigations of the Erosion Potential of Flows Overtopping Gibson Dam 5b. GRANT NUMBER Sun River Project, Montana Great Plains Region 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER Kathleen H. Frizell 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT Bureau of Reclamation NUMBER Technical Service Center HL-2006-02 Water Resources Research Laboratory Denver, Colorado 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S) U.S. Department of the Interior Bureau of Reclamation PO Box 25007 11. SPONSOR/MONITOR'S REPORT Denver, CO 80225 NUMBER(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161 http://www.ntis.gov 13. SUPPLEMENTARY NOTES 14. ABSTRACT This report discusses the results of the hydraulic investigation of the potential overtopping of Gibson Dam. Overtopping protection has been constructed on both the right and left abutments at Gibson Dam since 1984. This report documents the hydraulic investigations that were completed to determine if the jet from the new 2005 Probable Maximum Flood would impact on the extent of the existing overtopping protection. The analysis techniques used to determine the overtopping jet characteristics and the results from the analysis are provided. The jet impacts beyond the protection on the right abutment between El. 4710 and 4650. The stream power density in the flow was also determined at various impact locations, both on and off the right abutment protection, to provide geotechnical engineers the information needed to determine if further protection is needed based upon the quality of the rock or the concrete repairs. 15. SUBJECT TERMS concrete dam overtopping, jet trajectory, hydraulic investigations, dam abutment protection, stream power, Gibson Dam, Sun River Project, Montana 16. SECURITY CLASSIFICATION OF: 17. LIMITATION 18. NUMBER 19a. NAME OF RESPONSIBLE PERSON OF ABSTRACT OF PAGES Clifford A. Pugh a. REPORT b. ABSTR ACT a. THIS PAGE 19b. TELEPHONE NUMBER (Include area code) UL UL UL 43 303-445-2151 SAR Standard Form 298 (Rev. 8/98) Prescribed by ANSI Std. Z39.18 Hydraulic Laboratory Report HL-2006-02 Hydraulic Investigations of the Erosion Potential of Flows Overtopping Gibson Dam Sun River project, ~ontana Great Plains Region prepared: Kathleen H. Frizell - ~~draulicEngineer, Water Resources Research Laboratory, D-8560 ~echnica@~~roval:Tony L. Wahl, P.E. Hydraulic Engineer, Water Resources Research Laboratory Group, D-8560 Peer ~evie\f;:FliffordA. pugh, P.E. 4 * Date Hydraulic Engineer, Water Resources Research Laboratory Group, D-8560 1 REVISIONS I Date Description .-5, B B P Y 3 U.S. Department of the Interior Bureau of Reclamation Technical Service Center Water Resources Research Laboratory Denver, Colorado April 2006 Gibson Dam Overtopping Investigations 4/12/2006 Mission Statements 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. ___________________________ 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. Acknowledgments This project was requested by John Steighner, Geotechnical Engineering Group 2, D- 8312, to assist with the Corrective Action Study for Gibson Dam. Elisabeth Cohen, Waterways and Concrete Dams Group, D-8130, provided invaluable reference material regarding analysis techniques. Rudy Campbell, Water Resources Research Laboratory, D-8560, provided assistance with the ACAD presentation of the results. Technical peer review was provided by Tony L. Wahl, Water Resources Research Laboratory, D-8560. Hydraulic Laboratory Reports The Hydraulic Laboratory Report series is produced by the Bureau of Reclamation’s Water Resources Research Laboratory (Mail Code D-8560), PO Box 25007, Denver, Colorado 80225-0007. At the time of publication, this report was also made available online at http://www.usbr.gov/pmts/hydraulics_lab/pubs/HL/HL-2006-02.pdf Disclaimer No warranty is expressed or implied regarding the usefulness or completeness of the information contained in this report. References to commercial products do not imply endorsement by the Bureau of Reclamation and may not be used for advertising or promotional purposes. i TABLE OF CONTENTS I. Executive Summary .................................................................................................. 1 II. Introduction ............................................................................................................... 3 A. Purpose.................................................................................................................... 3 B. Background............................................................................................................. 3 III. Site Geology.............................................................................................................. 5 IV. Site History................................................................................................................ 7 V. Hydrologic Issues.................................................................................................... 10 VI. Flood Routings ........................................................................................................ 10 VII. Freeboard .............................................................................................................. 13 VIII. Tailwater Information ........................................................................................... 14 IX. Hydraulic Loading................................................................................................... 15 A. Definitions............................................................................................................. 16 B. Trajectory Calculations......................................................................................... 18 1. Jet Spread in the Free Fall................................................................................. 22 2. Jet Break Up Length in Free Fall...................................................................... 24 a) Jet Trajectories for Various Overtopping Flows........................................... 25 C. Jet Plunge Pool Characteristics............................................................................. 28 D. Stream Power........................................................................................................ 32 X. Recommendations ................................................................................................... 35 XI. References ............................................................................................................... 35 Appendix A - Drawings Appendix B – Sensitivity of the jet trajectory to the “K” factor in the equation of motion FIGURES Figure 1. - Gibson Dam downstream right abutment before construction of the concrete cap............................................................................................................................... 6 Figure 2. - Gibson Dam downstream right abutment after installation of the concrete cap and rock bolts.............................................................................................................. 9 Figure 3. - Gibson Dam frequency flood routing results for the various storm events, initial reservoir elevations and spillway gate operations. ......................................... 13 Figure 4. - Result of a preliminary tailwater study for the toe of Gibson Dam under the PMF. The maximum tailwater occurs about 38 hours into the routing with an elevation of 4669.9 ft. ............................................................................................... 15 Figure 5. – Free jets (a) overtopping a dam, (b) issuing from an orifice through