Safety of existing dams : evaluation and improvement PDF
Preview Safety of existing dams : evaluation and improvement
Page i Safety of Existing Dams Evaluation and Improvement Committee on the Safety of Existing Dams Water Science and Technology Board Commission on Engineering and Technical Systems National Research Council NATIONAL ACADEMY PRESS Washington, D.C. 1983 Page ii National Academy Press, 2101 Constitution Avenue, NW, Washington, DC 20418 <><><><><><><><><><><><> 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 competences and with regard for appropriate balance. This report has been reviewed by a group other than the authors, according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The National Research Council was established 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 of advising the federal government. The Council operates in accordance with general policies determined by the Academy under the authority of its congressional charter of 1863, which establishes the Academy as a private, nonprofit, selfgoverning membership corporation. The Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in the conduct of their services to the government, the public, and the scientific and engineering communities. It is administered jointly by both Academies and the Institute of Medicine. The National Academy of Engineering and the Institute of Medicine were established in 1964 and 1970, respectively, under the charter of the National Academy of Sciences. This report represents work supported by contract number EMWC0756, work unit number 6311F, between the Federal Emergency Management Agency and the National Research Council. Library of Congress Cataloging in Publication Data National Research Council (U.S.). Committee on the Safety of Existing Dams. Safety of existing dams. Includes index. 1. Dam safety—United States. I. Title. TC556.N37 1983 627'.8 8312094 ISBN 030903387X Copyright © 1983 by the National Academy of Sciences No part of this book may be reproduced by any mechanical, photographic, or electronic proc ess, or in the form of a phonographic recording, nor may it be stored in a retrieval system, transmitted, or otherwise copied for public or private use, without written permission from the publisher, except for the purposes of official use by the United States Government. Printed in the United States of America Page iii COMMITTEE ON SAFETY OF EXISTING DAMS ROBERT B. JANSEN, Consulting Civil Engineer, Spokane, Washington, Chairman HARL P. ALDRICH, Haley and Aldrich, Inc., Cambridge, Massachusetts ROBERT A. BURKS, Southern California Edison Company, Rosemead, California CLIFFORD J. CORTRIGHT, Consulting Civil Engineer, Sacramento, California JAMES J. DOODY, Department of Water Resources, Sacramento, California JACOB H. DOUMA, Consulting Civil Engineer, Great Falls, Virginia JOSEPH J. ELLAM, Pennsylvania Department of Environmental Resources, Harrisburg CHARLES H. GARDNER, North Carolina Department of Natural Resources, Raleigh WILLIAM R. JUDD, Purdue University, West Lafayette, Indiana DAN R. LAWRENCE, Department of Water Resources, Phoenix, Arizona ROBERT J. LEVETT, Niagara Mohawk Power Corporation, Syracuse, New York ARTHUR G. STRASSBURGER, Pacific Gas and Electric Company, San Francisco, California BRUCE A. TSCHANTZ, University of Tennessee, Knoxville ERIK H. VANMARCKE, Massachusetts Institute of Technology HOMER B. WILLIS, Consulting Civil Engineer, Bethesda, Maryland Technical Consultant CHARLES F. CORNS, Consulting Engineer, Springfield, Virginia NRC Project Manager SHEILA D. DAVID, Staff Officer Page iv WORKSHOP PARTICIPANTS GEORGE L. BUCHANAN, Tennessee Valley Authority, Knoxville CATALINO B. CECILIO, Pacific Gas and Electric Company, San Francisco, California LLEWELLYN L. CROSS, Chas. T. Main, Inc., Boston, Massachusetts RAY F. DEBRUHL, North Carolina Department of Administration, Raleigh JAMES M. DUNCAN, University of California, Berkeley LLOYD E. FOWLER, Goleta Water District, California VERNON K. HAGEN, U.S. Army Corps of Engineers, Washington, D.C. JOSEPH S. HAUGH, USDA Soil Conservation Service, Washington, D.C. DAVID LOUIE, Harza Engineering Company, Chicago, Illinois J. DAVID LYTLE, U.S. Army Corps of Engineers, St. Louis, Missouri MARTIN W. MCCANN, Stanford University, California JEROME RAPHAEL, University of California, Berkeley HARESH SHAH, Stanford University, California THOMAS V. SWAFFORD, Fairfield Glade Resort Developers, Crossville, Tennessee HARRY E. THOMAS, Federal Energy Regulatory Commission, Washington, D.C. LAWRENCE J. VON THUN, U.S. Bureau of Reclamation, Denver, Colorado JACK G. WULFF, W. A. Wahler & Associates, Palo Alto, Calfifornia FEMA Representative WILLIAM BIVINS, Project Officer, Federal Emergency Management Agency, Washington, D.C. Page v COMMITTEE PANELS Panel on Risk Assessment Erik Vanmarcke, Chairman James J. Doody Joseph J. Ellam Haresh Shah Vernon K. Hagen Lawrence J. VonThun Joseph S. Haugh Martin W. McCann, Jr. Panel on Hydraulic/Hydrologic Considerations Homer B. Willis, Chairman Robert J. Levett Jacob H. Douma Bruce A. Tschantz Catalino B. Cecilio Llewellyn L. Cross David Louie Panel on Concrete and Masonry Dams Arthur G. Strassburger, Chairman William R. Judd Robert A. Burks Jerome Raphael George L. Buchanan Panel on Embankment Dams Harl P. Aldrich, Chairman Charles H. Gardner Clifford J. Cortright James M. Duncan Thomas V. Swafford Jack G. Wulff Ray F. DeBruhl Panel on Instrumentation Dan R. Lawrence, Chairman Robert A. Burks Lloyd E. Fowler J. David Lytle Harry E. Thomas Panel on Geological/Seismological Consideration William R. Judd, Chairman Harry E. Thomas Charles H. Gardner Jerome Raphael James M. Duncan Page vi WATER SCIENCE AND TECHNOLOGY BOARD WALTER R. LYNN, Cornell University, Ithaca, New York, Chairman LEO R. BEARD, Espey, Huston & Associates, Inc., Austin, Texas JOHN J. BOLAND, Johns Hopkins University, Baltimore, Maryland JOHN CAIRNS, Virginia Polytechnic Institute and State University, Blacksburg PETER S. EAGLESON, Massachusetts Institute of Technology RICHARD S. ENGELBRECHT, University of Illinois at UrbanaChampaign JEROME. B. GILBERT, East Bay Municipal Utility District, Oakland, California YACOV Y. HAIMES, Case Western Reserve University, Cleveland, Ohio HELEN INGRAM, University of Arizona, Tucson L. DOUGLAS JAMES, Utah State University, Logan ROBERT B. JANSEN, Consulting Civil Engineer, Spokane, Washington JOHN F. KENNEDY, University of Iowa, Iowa City ORIE LOUCKS, Butler University, Indianapolis, Indiana DAVID W. MILLER, Geraghty & Miller, Inc., Syosset, New York JEROME W. MILLIMAN, University of Florida, Gainesville STEPHEN E. REYNOLDS, State Engineer, Santa Fe, New Mexico DANIEL SHEER, Interstate Commission on the Potomac River Basin, Rockville, Maryland ROBERT L. SMITH, University of Kansas, Lawrence GARY WEATHERFORD, Center for Natural Resources Studies, Berkeley, California Staff STEPHEN D. PARKER, Executive Director SHEILA D. DAVID, Staff Officer THEODORE M. SCHAD, Staff Officer JEANNE AQUILINO, Administrative and Project Secretary CAROLE B. CARSTATER, Administrative Secretary Page vii Preface Because of several disasters in recent years, the safety of dams has received increasing attention throughout the world. Governments at all levels have come to recognize and, in many cases, to accept their responsibilities in this area. In the United States, federal and state agencies have been active in inventorying and inspecting dams in the interest of improved safeguards. The results point to deficiencies that are widespread and to a problem of national importance. From the disasters and from the evaluations of thousands of dams, the message is clear that the threat to public safety is large and must be reduced. Although the danger is evident, its elimination will be difficult for at least two principal reasons: those responsible must be ready to take action and the funds for remedial programs must be found. In recognition of the need for a nationwide initiative that would foster a cooperative approach to dam safety, the Committee on the Safety of Existing Dams was created under the auspices of the National Research Council at the request of the Federal Emergency Management Agency. Members of the committee and its work groups were enlisted on the basis of their expertise in the engineering of dams and in the related professional disciplines. To qualify, they had to be outstanding in their fields and willing to contribute their knowledge and their ideas to the common purpose. The committee was organized to include civil engineers, representatives of state agencies responsible for dam safety, private corporate dam owners, geologists, hydraulic engineers, risk analysts, and others knowledgeable about federal and state dam safety programs. The charge that was laid out for each of them was demanding, and they responded commendably without excep Page viii tion. In composing the work groups, care was taken to ensure a range of experience and viewpoint so that the product would be balanced. Rather than a committee and work groups in the usual sense, an assembly of authors contributed individually, while the work group chairmen, the consultant, and the committee chairman served as planners, coordinators, and editors providing their own technical input. In structuring the effort we were guided by the belief that a collection of individual works, properly integrated, would be worth more than a blended group offering, the development of which might be burdened by excessive oral exchange. With such an array of special and dedicated talent, the opportunity for accomplishment was large. To maximize this potential, work assignments were made in advance, and the contributors were encouraged to volunteer freely from their experience. The challenge was unanimously accepted. Each member was asked to consider himself in the role of adviser to a responsible dam owner or to an engineer and to suggest practical ways to approach the analysis and remedy of a suspected or actual deficiency. Designated tasks were designed to cover the gamut of problems, while avoiding inefficient duplication of effort. This report thus presents the advice of experts on how to solve the puzzle of an inadequate structure and how to apply economical and professionally acceptable remedies. We have been guided by the need to optimize benefits from a given level of expenditure. The basic premise is that improvement of deficient dams must begin without delay, even though initial funding may be insufficient for comprehensive solutions. In some cases this may entail a staged approach to corrective work, but this is regarded as better than no action. Some solutions based on the risk assessment methods discussed in this report may not fully comply with the highest current standards of some federal agencies. We emphasize that we do not advocate a lowering of such criteria. A high level of excellence must continue to be the ultimate goal of those who strive for improvement of dams. The limitations inherent in an evaluation of existing dams must be acknowledged. Although those unschooled in the intricacies might expect it to be an exact science, it is in fact full of uncertainty and dependent on judgment. The total range and character of risk may not be predictable, due in large part to the unknowns of a site and a structure. The goal of preventive and remedial engineering is to reduce uncertainties, recognizing that absolute safety may not be ensured in every case. Professionals experienced in the evaluation and improvement of dam safety know that their job is to lower risk to the minimum that is practically attainable. This requires incremental investment in removal of deficiencies in the order of the hazard that they present. No matter how much money is spent, some unknown risk may remain. Many problems are not amenable Page ix to inexpensive solution, but the committee believes that an inadequate dam should be examined without rigid adherence to convention, always searching for ways to lessen risk within the unavoidable limits that are present. The idealist may think that this report does not confront all the problems faced by those who are responsible for dams but whose resources are limited. Of course, the remedies may not be as complete as they would be with the availability of abundant funds. Some states and owners cannot afford the preventive and corrective work that common standards would dictate. A perfectionist might suggest that states and owners should save their money until the job can be done completely. The message of this report is that there are ways to remedy deficiencies progressively, attacking the most serious problems first and economizing where possible but not to the extent that applicable guidelines are disregarded. The experienced professional knows that through years of perseverance the reduction of risks can in many eases be achieved only in this way—setting sensible priorities and recognizing that some remedies may have to await later action. Those responsible for repairs sometimes adopt the contrary view, that the corrective effort would cost too much and must therefore be postponed indefinitely. Total elimination of risk may not be attainable because of financial restraints. The practical objective is to reduce risk to a more tolerable level. Even if this falls short of highest standards, it is certainly preferable to waiting for money that may never arrive. Inevitably, the question arises regarding the extent of deficiency that can be allowed while necessary funding is sought. If that limit is exceeded, an alternative that could be weighed would be to abandon the dam. However, the hazard might not be eliminated simply by abandonment. Breaching or removal of a dam also requires engineering, and such work can be expensive. In some cases such actions might cost more than correcting the inadequacies. The emphasis of this report is on keeping a dam in service by using preventive and remedial engineering techniques, which the committee regards as the most positive approach to dam safety. Several reasons can be cited for lack of compliance with standards. A shortage of financial resources is common. Sometimes a dam owner needs to be convinced that the deficiencies are intolerable. This is best accomplished by practicing engineers and state officials rather than by the courts, although the judicial process remains as a last recourse. In the United States each state must ensure that its dams are inspected and that their safety is evaluated (excluding federal structures). Some states do not provide enough money for this. Such problems are inseparable from the technical considerations that serve the primary purpose of this report. While their solution is largely beyond the scope of this report, there is adequate precedent for resolving such governmental dilemmas. For example,
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