2001 Lake Mead Sedimentation Survey U.S. Department of the Interior Bureau of Reclamation Technical Service Center Denver, Colorado February 2008 2001 Lake Mead Sedimentation Survey prepared by Ronald L. Ferrari U.S. Department of the Interior Bureau of Reclamation Technical Service Center Water Resources Services Division Sedimentation and River Hydraulics Group Denver, Colorado February 2008 ACKNOWLEDGMENTS Bureau of Reclamation’s (Reclamation) Sedimentation and River Hydraulics (Sedimentation) Group of the Technical Service Center (TSC) was the technical field lead and conducted the analysis for this report. Kevin Fagot, Lower Colorado Region (LCR), coordinated the funding for collection and initial analysis of the extensive data sets. Ronald Ferrari and Kent Collins, Sedimentation Group, and Steve Belew, LCR, conducted the underwater data collection. Ron Ferrari processed the bathymetric survey information into x,y,z data sets. Steve Belew completed the extensive topographic mapping from these data sets. Ron Simms, LCR, coordinated several study meetings and the 2001 aerial collection for a portion of the upper reservoir area. Ron Ferrari completed the data processing to generate the area-capacity and sedimentation computations presented in this report. Kent Collins of the Sedimentation Group performed the technical and editorial peer review of this documentation. 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. Reclamation Report This report was produced by the Bureau of Reclamation’s Sedimentation and River Hydraulics Group (Mail Code 86-68540), PO Box 25007, Denver, Colorado 80225-0007. http://www.usbr.gov/pmts/sediment/ 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. Cover – Multibeam data topographic image looking downstream towards Hoover Dam (developed by Steve Belew, LCR). 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) February 2008 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER 2001 Lake Mead 5b. GRANT NUMBER Sedimentation Survey 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER Ronald L. Ferrari 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT Bureau of Reclamation, Technical Service Center, Denver, CO 80225 NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S) Bureau of Reclamation, Denver Federal Center, PO Box 25007 Denver, CO 80225-0007 11. SPONSOR/MONITOR'S REPORT NUMBER(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT 13. SUPPLEMENTARY NOTES 14. ABSTRACT The 2001 Lake Mead survey measured an increase in reservoir capacity of 219,150 acre-feet since the 1963-64 (1963) reservoir survey. The increased capacity was attributed to a significant decrease of sediment inflow due to the March 1963 closure of Glen Canyon Dam, located upstream of Lake Mead, and compaction of the previous sediment deposition. Since Hoover Dam closure in 1935, the 2001 study measured 2,402,770 acre-feet of sediment deposition compared to the 1963 survey result of 2,621,920 acre-feet. As of September 2001, at water surface elevation 1,229.0, the surface area was 162,548 acres with a total capacity of 29,979,010 acre-feet. The 2001 study measured an average annual rate of sediment accumulation, since dam closure, of 36,024 acre-feet compared to the 1963 average annual rate of 88,028 acre-feet. Since the 1963 closure of Glen Canyon Dam and the significant trapping of the Colorado River sediments within Lake Powell, the Lake Mead average sediment inflow rate has significantly decreased to an estimated rate of less than 10,000 acre-feet per year. Reclamation’s Sedimentation Group surveyed Lake Mead in 2001 to develop a storage-elevation relationship. The underwater survey, conducted over 22 days between April 5 and May 16, used a multibeam depth sounder interfaced with a global positioning system (GPS) that gave continuous sounding positions throughout the reservoir covered by the survey vessel. Updated topography of Lake Mead was developed by combining the 2001 survey data and original digital data from the U.S. Geological Survey quadrangle (USGS quad). A complete hydrographic survey, above and below water, would provide the most accurate reservoir topography. However, cost prohibits or delays such data collections. Over the years limited budgets have affected survey frequencies resulting in limited knowledge of our nation’s reservoirs. Reconnaissance techniques combine streamlined collection and analysis procedures with modern instrumentation to produce quality results in a timely and effective manner by surveying only where the majority of the sediment accumulates. The technique requires original digital reservoir topography to guide the survey vessel along the sediment deposit areas and for computing the updated reservoir information. Reconnaissance techniques for the 2001 survey of Lake Mead greatly reduced collection and analysis costs, but still produced quality results. The reconnaissance techniques presented in this report illustrate how to update the area and capacity on reservoirs like Lake Mead more frequently, but at a much lower cost than a complete hydrographic survey. 15. SUBJECT TERMS reservoir area and capacity/ sedimentation/ surveys/ GPS/ multibeam sounders/ reconnaissance techniques/ contour area/ Hoover Dam, Lake Mead 16. SECURITY CLASSIFICATION OF: 17. LIMITATION 18. NUMBER 19a. NAME OF RESPONSIBLE PERSON OF ABSTRACT OF PAGES a. REPORT b. ABSTRACT a. THIS PAGE 19b. TELEPHONE NUMBER (Include area code) Standard Form 298 (Rev. 8/98) Prescribed by ANSI Std. Z39.18 iii iv Table of Contents Page 2001 Lake Mead............................................................................................................................... 1 Abstract ............................................................................................................................................ 1 Dam and Reservoir........................................................................................................................... 1 Cofferdams................................................................................................................................ 5 Drainage Area ........................................................................................................................... 6 Summary and Conclusions............................................................................................................... 7 Reservoir Operations...................................................................................................................... 11 Purpose of Reservoir Surveys ........................................................................................................ 12 Hydrographic Survey Equipment and Method............................................................................... 18 Methodology ........................................................................................................................... 22 GPS Technology ..................................................................................................................... 23 Depth Measurements............................................................................................................... 25 Additional Studies and Information ............................................................................................... 26 Original Topography of Lake Mead........................................................................................ 26 1948-49 Lake Mead Sedimentation Survey ............................................................................ 33 1963-64 (1963) Lake Mead Sedimentation Survey................................................................. 34 1998 Sediment Sampling ........................................................................................................ 35 Biological Monitoring Cross Sections ...................................................................................