RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES

Committee on Risk-Based Analysis for Flood Damage Reduction

Water Science and Technology Board

Commission on Geosciences, Environment, and Resources

National Research Council

NATIONAL ACADEMY PRESS
Washington, D.C.



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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES Committee on Risk-Based Analysis for Flood Damage Reduction Water Science and Technology Board Commission on Geosciences, Environment, and Resources National Research Council NATIONAL ACADEMY PRESS Washington, D.C.

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES 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 the U.S. Army Corps of Engineers under DACW72-98-C-0003. International Standard Book Number 0-309-07136-4 Library of Congress Catalog Card Number 00-108527 Risk Analysis and Uncertainty in Flood Damage Reduction Studies is available from the National Academy Press , 2101 Constitution Avenue, N.W., Washington, D.C. 20418; (800) 624-6242 or (202) 334-3313 (in the Washington metropolitan area); Internet <http://www.nap.edu>. Sketch on the book cover is courtesy of the California State Library. It is a contemporary sketch of the city of Sacramento during the high water of the winter of 1849-1850. Copyright 2000 by the National Academy of Sciences. All rights reserved. Printed in the United States of America.

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES THE NATIONAL ACADEMIES Advisors to the Nation on Science, Engineering, and Medicine National Academy of Sciences National Academy of Engineering Institute of Medicine National Research Council 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 achievement 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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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES COMMITTEE ON RISK-BASED ANALYSES FOR FLOOD DAMAGE REDUCTION GREGORY B. BAECHER, Chair, University of Maryland, College Park EFI FOUFOULA-GEORGIOU, University of Minnesota, Minneapolis RALPH L. KEENEY, University of Southern California, Los Angeles LESTER B. LAVE, Carnegie Mellon University, Pittsburgh, Pennsylvania HARRY F. LINS, U.S. Geological Survey, Reston, Virginia DANIEL P. LOUCKS, Cornell University, Ithaca, New York DAVID R. MAIDMENT, University of Texas, Austin MARTIN W. MCCANN, Jack R. Benjamin and Associates, Inc., Menlo Park, California JERY R. STEDINGER, Cornell University, Ithaca, New York BEN CHIE YEN, University of Illinois, Urbana-Champaign National Research Council Staff JEFFREY W. JACOBS, Study Director ELLEN A. DE GUZMAN, Senior Project Assistant

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES WATER SCIENCE AND TECHNOLOGY BOARD HENRY J. VAUX, Jr., Chair, Division of Agriculture and Natural Resources, University of California, Oakland RICHARD G. LUTHY, Vice-Chair, Stanford University, Stanford, California RICHELLE M. ALLEN-KING, Washington State University, Pullman GREGORY B. BAECHER, University of Maryland, College Park JOHN BRISCOE, The World Bank, Washington, D.C. EFI FOUFOULA-GEORGIOU, University of Minnesota, Minneapolis STEVEN P. GLOSS, University of Wyoming, Laramie WILLIAM A. JURY, University of California, Riverside GARY S. LOGSDON, Black & Veatch, Cincinnati, Ohio DIANE M. MCKNIGHT, University of Colorado, Boulder JOHN W. MORRIS, J.W. Morris Ltd., Arlington, Virginia PHILIP A. PALMER, (Retired) E.I. du Pont de Nemours & Co., Wilmington, Delaware REBECCA T. PARKIN, The George Washington University, Washington, D.C. RUTHERFORD H. PLATT, University Massachusetts, Amherst JOAN B. ROSE, University of South Florida, St. Petersburg JERALD L. SCHNOOR, University of Iowa, Iowa City R. RHODES TRUSSELL, Montgomery Watson, Pasadena, California Staff STEPHEN D. PARKER, Director LAURA J. EHLERS, Senior Staff Officer CHRIS ELFRING, Senior Staff Officer JEFFREY W. JACOBS, Senior Staff Officer MARK C. GIBSON, Staff Officer WILLIAM S. LOGAN, Staff Officer M. JEANNE AQUILINO, Administrative Associate PATRICIA A. JONES, Study/Research Associate ANITA A. HALL, Administrative Assistant ELLEN A. DE GUZMAN, Senior Project Assistant ANIKE L. JOHNSON, Project Assistant

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES COMMISSION ON GEOSCIENCES, ENVIRONMENT, AND RESOURCES GEORGE M. HORNBERGER, Chair, University of Virginia, Charlottesville RICHARD A. CONWAY, Union Carbide Corporation (Retired), S. Charleston, West Virginia LYNN GOLDMAN, Johns Hopkins School of Hygiene and Public Health, Baltimore, Maryland THOMAS E. GRAEDEL, Yale University, New Haven, Connecticut THOMAS J. GRAFF, Environmental Defense, Oakland, California EUGENIA KALNAY, University of Maryland, College Park DEBRA KNOPMAN, Progressive Policy Institute, Washington, D.C. BRAD MOONEY, J. Brad Mooney Associates, Ltd., Arlington, Virginia HUGH C. MORRIS, El Dorado Gold Corporation, Vancouver, British Columbia H. RONALD PULLIAM, University of Georgia, Athens MILTON RUSSELL, Joint Institute for Energy and Environment and University of Tennessee (Emeritus), Knoxville ROBERT J. SERAFIN, National Center for Atmospheric Research, Boulder, Colorado ANDREW R. SOLOW, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 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 and Financial Officer SANDI FITZPATRICK, Administrative Associate

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES Preface Any review of the U.S. Army Corps of Engineers's approach to technical issues and their applications tends to be complicated because of the Corps's size, its lengthy and rich history, its relations with other federal agencies, and controversies that have followed the Corps for decades. This review and study were no different. Our study committee was challenged to analyze the Corps 's risk analysis techniques in its flood damage reduction studies, a challenge that was magnified by the need to understand several related issues. Our committee experts in hydrology, engineering, and statistics found themselves analyzing not only risk analysis applications, but also considering levee certification policy and history, federal flood insurance programs, and U.S. floodplain management strategies. The committee undertook these peripheral investigations partly because of the need to adequately address its statement of task and partly out of intellectual curiosity. In any event, one implicit conclusion of our study is that an appreciation of the Corps 's historical roles in addressing the nation's flood problems is necessary to understand the current issues the Corps faces in engineering and hydrologic applications. The Corps's relatively new applications of risk analysis represent a significant departure from long-held, traditional approaches to addressing hydrologic, hydraulic, and geotechnical uncertainties. The former approach of adding freeboard to its levees was for several decades a sound strategy for coping with unquantifiable uncertainties. Because of historical momentum, this former approach has left a legacy that is not easily jettisoned. Several Corps of Engineers techniques and policies

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES were based upon the concept of freeboard, and it will take some time for the agency to fully adjust to the new techniques. In watching these changes within the agency, our committee gained an appreciation for the dedication of several Corps of Engineers staff members who assisted with this study. Much of the development of the risk analysis techniques has taken place at the Corps's Hydrologic Engineering Center in Davis, California. The committee expresses its gratitude and appreciation to Darryl Davis, the Center's director. Darryl has been a leader in promoting risk analysis applications within the Corps. The committee appreciates Darryl's frankness and cooperation during this study. David Goldman, also of the Hydrologic Engineering Center, has been central to tailoring the risk analysis techniques to Corps applications and deserves major credit for advancing risk analysis within the Corps. Several other Corps of Engineers staff members shared their knowledge and views with the committee. Earl Eiker and Harry Kitch at Corps Headquarters in Washington, D.C., and David Moser of the Corps's Institute for Water Resources, spoke with the committee at its first meeting in Washington in December 1998. Staff from the Corps's Louisville district office hosted a visit by a committee member in the summer of 1999 and provided information for the committee's Beargrass Creek case study. The committee thanks Neil O'Leary, Richard Pruitt, and Matt Scheuler in the Louisville district office for their assistance. The committee thanks Joe Countryman of MBK Consultants (Sacramento), Michael Grimm of the Federal Emergency Management Agency (Washington, D.C.), and Doug Plascencia of Kimley-Horn (Phoenix) and member of the Association of State Floodplain Managers—all of whom spoke with the committee at its second meeting in Davis in February 1999. Joe, Mike, and Doug provided compelling remarks that helped the committee consider wider implications of the Corps's use of risk analysis. Peter Andrysiak, U.S. Army, and Mitchell Laird of the Louisville district also provided significant assistance in acquiring project documents and data. The committee also thanks Stephen Parker, director of the Water Science and Technology Board (WSTB). Steve followed the progress of this committee closely, and the committee frequently drew upon his knowledge of risk analysis and the Corps of Engineers planning procedures. His experience in managing numerous WSTB reports was useful in helping the committee reach agreement on some key technical issues.

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES Finally, the entire committee expresses its gratitude to project assistant Ellen de Guzman. Ellen demonstrated superb organizational skills, reviewed and organized several drafts of the committee's report, and also showed a great deal of patience and aplomb in dealing with too many last-minute requests from the chair and study director. This report has been reviewed by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the Report Review Committee of the National Research Council (NRC). 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 contents of the review and draft manuscripts remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their participation in the review of this report: Paul Barton, U.S. Geological Survey Leo Beard, Professor Emeritus, University of Texas Stephen Burgess, University of Washington John Cassidy, consultant, Concord, California Susan Cutter, University of South Carolina Des Hartford, British Columbia Hydro Debra Knopman, Progressive Policy Institute Eric Wood, Princeton University Although the individuals listed above provided many constructive comments and suggestions, responsibility for the final content of this report rests solely with the authoring committee and the NRC. GREGORY B. BAECHER Chair JEFFREY W. JACOBS Study Director

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES Contents     EXECUTIVE SUMMARY,   1  1   THE CORPS AND U.S. FLOOD DAMAGE REDUCTION PLANNING, POLICIES, AND PROGRAMS,   12      Risk Analysis Approach,   14      The Corps's Water Resource Project Planning Procedures,   15      U.S. Federal Flood Preparedness, Mitigation, and Response Activities,   24  2   DECISION MAKING AND COMMUNICATION ISSUES,   29      The Goal of Floodplain Management,   30      Multiple Objectives,   31      Comparing Project Alternatives,   33      Floodplain Management Alternatives,   36      Risk Communication,   37  3   RISK ANALYSIS CONCEPTS AND TERMS,   40      Uncertainty,   40      Consistency Across Program Areas,   45      Risk Analysis and Decision Making,   47  4   RISK ANALYSIS TECHNIQUES,   51      Corps Framework,   53      Natural Variability and Imperfect Knowledge,   54      Risk Analysis,   59      Monte Carlo Simulation,   62      Assessment of Engineering Performance,   64

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES      Geotechnical Reliability,   67  5   CASE STUDIES,   71      Beargrass Creek,   72      Red River of the North at East Grand Forks, Minnesota, and Grand Forks, North Dakota,   98  6   EVALUATION AND PROPOSED IMPROVEMENTS,   114      Concerns with the Risk Analysis Methods,   114      Engineering Performance,   115      Hydrologic Analysis,   119      Geotechnical Reliability,   122      Economic Performance,   123      Interdependence in Risk Analysis for Flood Damage Assessment,   127      Correlation Length,   128      Spatial Aggregation,   129      Computational Alternatives to Minimize Correlation Effects,   133  7   LEVEE CERTIFICATION,   139      History of Levee Certification,   139      Current Certification Criterion,   147      Analysis of Levee Sizing Criteria,   149      Technical Corrections to the Current Certification Procedure,   155      An Alternative Criterion: A Longer-Term Change,   156  8   CONCLUSIONS AND RECOMMENDATIONS,   159      Risk Analysis Techniques,   161      Consistent Terminology,   164      Levee Certification,   165      Floodplain Management,   166     REFERENCES,   168     APPENDIXES    A   Glossary,   175  B   Corps–FEMA Levee Certification Documentation,   181  C   Economic and Environmental Principles for Water Related Land Resources Implementation Studies,   193  D   Functions of Random Variables,   196  E   Biographical Information,   199