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--> Improving American River Flood Frequency Analyses Committee on American River Flood Frequencies Water Science and Technology Board Commission on Geosciences, Environment, and Resources National Research Council NATIONAL ACADEMY PRESS Washington, D.C. 1999
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--> NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competencies and with regard for appropriate balance. Support for this project was provided by U.S. Army Corps of Engineers under DACW05-98-C-0031. International Standard Book Number 0-309-06433-3 Copies available from National Academy Press 2101 Constitution Avenue, N.W. Washington, D.C. 20418 800-624-6242 202-334-3313 (in the Washington metropolitan area) http://www.nap.edu Cover by Van Nguyen, National Academy Press, using photos from the U.S. Army Corps of Engineers Sacramento District. Copyright 1999 by the National Academy of Sciences. All rights reserved. Printed in the United States of America.
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--> COMMITTEE ON AMERICAN RIVER FLOOD FREQUENCIES KENNETH W. POTTER, Chair, University of Wisconsin, Madison SANDRA O. ARCHIBALD, University of Minnesota, Minneapolis DUANE C. BOES, Colorado State University, Fort Collins TIMOTHY A. COHN, U.S. Geological Survey, Reston, Virginia S. ROCKY DURRANS, University of Alabama, Tuscaloosa C. THOMAS HAAN, Oklahoma State University, Stillwater ROBERT D. JARRETT, U.S. Geological Survey, Lakewood, Colorado UPMANU LALL, Utah State University, Logan KELLY T. REDMOND, Desert Research Institute, Reno, Nevada JERY R. STEDINGER, Cornell University, Ithaca, New York Consultant CHARLES A. RODGERS, University of Wisconsin, Madison Staff STEPHEN D. PARKER, Study Director MARK GIBSON, Research Associate ELLEN A. DE GUZMAN, Senior Project Assistant
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--> WATER SCIENCE AND TECHNOLOGY BOARD HENRY J. VAUX, Jr., Chair, University of California, Oakland CAROL A. JOHNSTON, Vice Chair, University of Minnesota, Duluth RICHELLE ALLEN-KING, Washington State University, Pullman JOHN S. BOYER, University of Delaware, Lewes JOHN BRISCOE, The World Bank, Washington, D.C. DENISE FORT, University of New Mexico, Albuquerque EVILLE GORHAM, University of Minnesota, St. Paul CHARLES D. D. HOWARD, Charles Howard and Associates, Ltd., Victoria, British Columbia WILLIAM A. JURY, University of California, Riverside WILLIAM M. LEWIS, Jr., University of Colorado, Boulder GARY S. LOGSDON, Black & Veatch, Cincinnati, Ohio RICHARD LUTHY, Carnegie Mellon University, Pittsburgh, Pennsylvania JOHN W. MORRIS, J.W. Morris, Ltd., Arlington, Virginia CHARLES R. O'MELIA, The Johns Hopkins University, Baltimore, Maryland PHILIP A. PALMER, E.I. du Pont de Nemours & Co., Wilmington, Delaware REBECCA T. PARKIN, The George Washington University, Washington, D.C. JOAN B. ROSE, University of South Florida, St. Petersburg ERIC F. WOOD, Princeton University, Princeton, New Jersey Staff STEPHEN D. PARKER, Director JACQUELINE A. MACDONALD, Associate Director CHRIS ELFRING, Senior Staff Officer LAURA J. EHLERS, Staff Officer JEFFREY W. JACOBS, Staff Officer MARK GIBSON, Research Associate JEANNE AQUILINO, Administrative Associate ANITA A. HALL, Administrative Assistant ELLEN A. DE GUZMAN, Senior Project Assistant KIMBERLY SWARTZ, Project Assistant
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--> COMMISSION ON GEOSCIENCES, ENVIRONMENT, AND RESOURCES GEORGE M. HORNBERGER, Chair, University of Virginia, Charlottesville PATRICK R. ATKINS, Aluminum Company of America, Pittsburgh, Pennsylvania JERRY F. FRANKLIN, University of Washington, Seattle B. JOHN GARRICK, PLG, Inc., Newport Beach, California THOMAS E. GRAEDEL, Yale University, New Haven, Connecticut DEBRA KNOPMAN, Progressive Policy Institute, Washington, D.C. KAI N. LEE, Williams College, Williamstown, Massachusetts JUDITH E. McDOWELL, Woods Hole Oceanographic Institution, Massachusetts RICHARD A. MESERVE, Covington & Burling, Washington, D.C. HUGH C. MORRIS, Canadian Global Change Program, Delta, British Columbia RAYMOND A. PRICE, Queen's University at Kingston, Ontario H. RONALD PULLIAM, University of Georgia, Athens, Georgia THOMAS C. SCHELLING, University of Maryland, College Park VICTORIA J. TSCHINKEL, Landers and Parsons, Tallahassee, Florida E-AN ZEN, University of Maryland, College Park MARY LOU ZOBACK, U.S. Geological Survey, Menlo Park, California Staff ROBERT M. HAMILTON, Executive Director GREGORY H. SYMMES, Associate Executive Director JEANETTE SPOON, Administrative & Financial Officer SANDI FITZPATRICK, Administrative Associate MARQUITA SMITH, Administrative Assistant/Technology Analyst
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--> The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. William A. Wulf is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. William A. Wulf are chairman and vice chairman, respectively, of the National Research Council.
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--> Preface This report is the result of an intensive eight-month study effort by the Committee on American River Flood Frequencies, a group of experts organized to assist the U.S. Army Corps of Engineers (USACE) by providing an independent scientific assessment of flood frequency relationships for the American River at Sacramento, California. The study was designed and the committee formed under the auspices of the Water Science and Technology Board (WSTB) of the National Research Council (NRC). It extends the work of the former WSTB Committee on Flood Control Alternatives in the American River Basin (whose findings were published in 1995) and aims to achieve better estimation of flood frequency relationships for the American River in light of a major flood in January 1997 and other technical considerations. In its review, the committee considered issues such as the following that were specified by the USACE as technically controversial in the agreement enabling support for the study: applicability of (the federally-prescribed) Bulletin 17-B based statistical approach; appropriateness of skew factor development; potential censoring of water year 1977 data, considering validity of Bulletin 17-B criteria; updated river basin probable maximum flood, and its supportive relationship to the selected flow frequency curve; methodologies to 'bend over' the less frequent portion of the flow frequency curve to reflect the American River basin's realistic maximum flow productivity; applicability of paleoflood methodologies to this flow frequency analysis; and climatologic/meteorologic/hydrologic trends and American River basin parameters that may influence the American River flow frequency curve. This report's findings are based on a review of relevant technical literature, extensive flood frequency analyses by the committee, and deliberations among committee members. The committee consisted of 10 volunteer experts in hydrologic and geophysical statistics, hydrologic engineering, geomorphology, hydroclimatology, climatology, and economics (see Appendix A). The committee incorporated input,
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--> when appropriate, from a wide range of stakeholders and USACE personnel concerned about flood risk management for Sacramento and environmental quality of the American River and its tributaries. Much of this interaction with interested parties occurred at a committee-hosted workshop and meeting in Sacramento on July 12-15, 1998. At that workshop, the committee gathered input, deliberated on the issues, outlined this report, and took on work assignments. Following the meeting, the committee members made calculations and drafted and refined this report, which represents a consensus of our multidisciplinary committee. The first chapter of this report provides a brief overview of the historical and ongoing development of flood control measures on the American River, associated technical issues, and policy implications. Chapter 2 provides a description of the data types that can be used in estimating flood exceedance probabilities for the American River. Chapter 3 presents and discusses the committee's flood frequency estimates for the American River. Chapter 4 reviews the meteorology of floods associated with the hydrologic cycle of the American River. Lastly, Chapter 5 provides a summary of the committee's findings and recommendations for the improvement of flood frequency analyses for the American River. The committee expects that its report will be helpful in planning for flood risk reduction in Sacramento, but so many general technical and policy issues presented themselves in Sacramento that, as the study progressed, we began to see our analyses as a case study with broader implications. We hope those with interests outside Sacramento will find our report useful. Leading this project was a special pleasure. It is not often that one has the opportunity to address a problem as technically challenging and politically charged as the one assigned to our committee. To lead a group as experienced and intellectually powerful as ours was both an honor and a challenge. I am grateful for the opportunity to have led the members of this group, and I thank them for their many contributions. Our work was supported by three WSTB staff members, Ellen de Guzman, Mark Gibson, and Stephen Parker, and a consultant, Charles Rodgers of the University of Wisconsin, who were of great assistance in facilitating our work. On behalf of the committee and the Water Science and Technology Board, I also would like to express our appreciation to the fine staff of the U.S. Army Corps of Engineers with whom we interacted during this study. Our principal liaisons were Robert Childs and John Mack of the Sacramento District. Interaction with them and their colleagues at the district and at the Corps Hydrologic Engineering Center in Davis, California was critical to the success of this study. Additionally, the committee was briefed, informed, and assisted—principally at its July 1998 workshop—by numerous other individuals from other agencies and organizations familiar with the issues at hand. They are too numerous to list (more than 30) but we are indebted for the information and perspectives they provided. The report has been reviewed by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the NRC's Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the authors and the NRC in making the published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The content of the review comments and draft manuscripts remain confi-
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--> dential to protect the integrity of the deliberative process. We wish to thank the following individuals for their participation in the review of this report: Joseph D. Countryman, consulting engineer, Sacramento, California; Katherine K. Hirschboeck, University of Arizona; George M. Hornberger, University of Virginia; Charles D. D. Howard, Charles Howard and Associates, Victoria, British Columbia; L. Allan James, University of South Carolina; William H. Kirby, U.S. Geological Survey, Reston, Virginia; and Rutherford H. Platt, University of Massachusetts. While these individuals provided many constructive comments and suggestions, responsibility for the final content of this report rests solely with the authoring committee and the NRC. KENNETH W. POTTER, CHAIR COMMITTEE ON AMERICAN RIVER FLOOD FREQUENCIES
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--> Contents Executive Summary 1 1 Sacramento And The Struggle To Manage Flood Risk 9 Settling in the Floodplain, 9 Risk Reduction Efforts, 9 Current Planning Efforts and Controversies, 11 Technical Issues and Policy Implications, 13 2 Data Sources 16 General Description of Flood Frequency Data, 16 American River Data, 24 Summary, 37 3 Flood Frequency Estimates For The American River 39 Introduction, 39 Bulletin 17-B 40 Expected Probability, 44 Summary of Committee Approach, 44 Analysis of American River Data, 45 Summary, 64 4 Climate And Floods: Role Of Non-Stationarity. 67 General Meteorological Features of Major Floods, 68 Observed Climate and Streamflow Variability, 73 Sources of Sierra Nevada Climate Variability, 86 Global Changes Issues, 94 Summary, 97 5 Summary And Recommendations 101 Recommended Flood Frequency Distribution, 101 Beyond Bulletin 17-B 102
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--> Post-1950 Increase in Frequency of Large Floods, 103 Implications for Floodplain Certification, 103 Research Needs, 104 References 107 Appendix Biographical Sketches Of Committee Members 119