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Safety of Existing flanks Evaluation anct 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

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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 Na- tional Academy of Sciences, the National Academy of Engineering, and the Institute of Medi- cine. 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 accor- dance with general policies determined by the Academy under the authority of its congres- sional charter of 1863, which establishes the Academy as a private, nonprofit, self-governing 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 EMW-C-0756, 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 safetyUnited States. I. Title. TC556.N37 1983 627'.8 83-12094 ISBN 0-309-03387-X Copyright (D 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

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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. CORT~GHT, Consulting Civil Engineer, Sacramento, California JAMES I. 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. ~DO, Purdue University, West Lafayette, Indiana DAN R. LAWRENCE, Department of Water Resources, Phoenix, Arizona ROBERT J. LEV=T, 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 ~e

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WORKSHOP PARTICIPANTS GEORGE L. BUCHANAN, Tennessee Valley Authority, Knoxville CATALINO B. CECILlO, 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. FOWL=, 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 LOUlE, 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. I, LAWRENCE J. VON THUN, U.S. Bureau of Reclamation, Denver, Colorado JACK G. WULFF, W. A. Wahier & Associates, Palo Alto, Calfifornia FEMA Representative WILLIAM BIVINS, Project Officer, Federal Emergency Management Agency, Washington, D.C. 1V

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COMMITTEE PANELS Panel on Risk Assessment Erik Vanmarcke, Chairman James J. Doody Joseph J. Eliam Haresh Shah Panel on Hydraulic/Hydrologic Considerations Homer B. Willis, Chairman Robert J. Levett Jacob H. Douma Bruce A. Tschantz Panel on Concrete and Masonry Dams Arthur G. Strassburger, Chairman William R. Judd Robert A. Burks Panel on Embankment Dams Hart P. Aldrich, Chairman Charles H. Gardner Clifford ]. Cortright James M. Duncan Panel on Instrumentation Dan R. Lawrence, Chairman Robert A. Burks Lloyd E. Fowler Vernon K. Hagen Lawrence I. VonThun Joseph S. Haugh Martin W. McCann, Jr. Catalino B. Cecilio Llewellyn L. Cross David Louie Jerome Raphael George L. Buchanan Thomas V. Swafford Jack G. Wulff Ray F. DeBruhl J. David Lytle Harry E. Thomas Panel on Geological/Seismological Consideration William R. Judd, Chairman Harry E. Thomas Charles H. Gardner v Jerome Raphael James M. Duncan

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! WATER SCIENCE AND TECHNOLOGY BOARD WALTER R. LYNN, Cornell University, Ithaca, New York, Chairman LEO R. BEARD, Espey, Huston & Associates, Inc., Austin, Texas JOHN I. BOLAND, Johns Hopkins University, Baltimore, Maryland JOHN CAIRNS, Virginia Polytechnic Institute and State University, Blacksburg PETER S. EAGLESON, Massachusetts Institute of Technology RICHA~ S. ENGELBRECHT, University of Illinois at Urbana-Champaign 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. MILEIMAN, 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 SHElEA D. DAVID, Staff Officer THEODORE M. SCHAD, Staff Officer JEANNE AQUILINO, Administrative and Project Secretary CAROLE B. CARSTATER, Administrative Secretary vi

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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 thou- sands 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 Exist- ing 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 exper- tise in the engineering of dams and in the related professional disciplines. To qualify, they had to be outstanding in their fields and willing to contrib- ute their knowledge and their ideas to the common purpose. The commit- tee was organized to include civil engineers, representatives of state agen- cies 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- vii

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viii Preface 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 au- thors contributed individually, while the work group chairmen, the con- sultant, 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 devel- opment 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 re- sponsible dam owner or to an engineer and to suggest practical ways to approach the analysis and remedy of a suspected or actual deficiency. Des- ignated tasks were designed to cover the gamut of problems, while avoid- ing 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 ap- proach 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 crite- ria. 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 ac- knowledged. 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

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Preface to inexpensive solution, but the committee believes that an inadequate dam should be examined without rigid adherence to convention, always search- ing 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 lim- ited. 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 cases be achieved only in this way setting sensible priorities and recognizing that some remedies may have to await later action. Those re- sponsible 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 re- straints. 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 expen- sive. In some cases such actions might cost more than correcting the inade- quacies. The emphasis of this report is on keeping a dam in service by using preventive and remedial engineering techniques, which the committee re- gards 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 accom- plished 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 structures3. 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 ade- quate precedent for resolving such governmental dilemmas. For example? 1X

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x i: Preface n some European countries the laws provide for periodic evaluations by consulting engineers retained by the owners. In the United States this has a successful parallel in the independent inspection programs required at wa- ter power projects licensed by the Federal Energy Regulatory Commission. These precedents suggest that the legislative barriers are not insurmounta- ble. Of course, a prerequisite is that the governing bodies be concerned enough about public safety that they will take the necessary initiative. Current dam safety standards have been developed on sound bases. The committee does not advocate their revision solely because of financial pres- sures; however, they must be justified by the benefits. In many jurisdic- tions standards are adjusted to suit individual conditions. For instance, a small dam in an unpopulated area would be required to withstand less se- vere tests than the probable maximum flood or the maximum credible earthquake. Most state safety programs make allowances for the wide ranges of dam characteristics, locations, and consequences of failure. They recognize the need for stricter rules in metropolitan areas than in isolated rural environments, including requirements for closer surveillance. Engineers experienced in the field of dam safety may question the em- phasis that this report gives to risk-based decision analysis. They know that the relative degree of risk at a dam is difficult and often impossible to quan- tify. Necessary approximations rely heavily on judgment, which comes from working with many kinds of dams and a myriad of conditions. In the evaluation of existing dams, numerical methods sometimes are less useful than empirical approaches. This report therefore may appear to give un- due prominence to sophisticated decision analyses based on assessments of probabilities. Since such analyses have been used successfully in only a few dam safety reviews, they could have been relegated to secondary status. Despite their lack of acceptance by practicing engineers, however, the committee believes that they hold promise and that they should be more fully explored by the profession. Such methods have generally been judged as being too theoretical, lacking input from practical experience, and pro- ducing after much study results that seem to be intuitively apparent to ex- perienced engineers. Furthermore, it has been argued that, although the calculations may tend to be complex, the concepts on which they are based are overly simplistic, evidencing minimal recognition of the uncertainties intrinsic in the study of existing dams. Despite these criticisms, which are shared to some extent by some of the contributors to this report, it was con- cluded that the underlying principles need to be expanded and developed with participation by those actually responsible for dams and that there is a need for merging apparently academic concepts with those of engineers who have firsthand knowledge of dams and their problems. It is hoped that the case histories presented in this report may serve to demonstrate the po-

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Preface X1 tential of such cooperative effort. In this difficult field the search for new methods to keep dams safe must be continuous. The members of the committee, the workshop participants, and the committee's technical consultant devoted much time and enthusiasm to their tasks. Their reward will be measured by acceptance and use of this report to ensure better dams. We owe much to the strong support provided by the National Research Council and the Federal Emergency Manage- ment Agency. The staffs of these institutions facilitated all aspects of the work program, including the very important phase of review and publica- tion of the report. Our hope is that we have made a useful contribution to public safety. Robert B. Jansen, Chairman Committee on the Safety of Existing Dams

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Contents INTRODUCTION Purpose, 1 Scope, 1 Background, 2 References, 3 2 THE SAFETY OF DAMS Causes of Dam Failures, 5 Field Inspections, 20 Maintenance, 24 Records, 25 Evaluation of Safety, 26 Emergency Action Planning, 31 References, 39 3 RISK-BASED DECISION ANALYSIS Summary, 41 Introduction, 43 Risk Assessment: Alternative Methods, 45 Method of Risk Assessment for Specific Conditions, 50 Consideration of Remedial Actions, 55 Examples of Risk Assessment and Decision Analysis, 60 . ague ........ 41

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XIV Contents References, 69 Recommended Reading, 70 4 HYDROLOGIC AND HYDRAULIC CONSIDERATIONS General Approach, 71 Bases for Assessing Spillway Capacities, 77 Spillway Capacity Criteria, 81 Design Floods, 83 Analysis Techniques, 89 Dam Break Analyses, 100 Mitigating Inadequate Hydraulic Capacities, 106 References, 111 Appendix 4A Generalized Estimates of Probable Maximum Flood Peaks, 114 Appendix 4B Storms Exceeding 50 % of Estimated Probable Maximum Precipitation, 122 Appendix 4C Guidelines for Breach Assumption, 129 5 GEOLOGIC AND SEISMOLOGICAL CONSIDERATIONS............. General Geologic Considerations, 132 Rock Types, 136 Geologic Structure, 141 Soils, 150 Earthquake Considerations, 169 References, 181 Recommended Reading, 182 6 CONCRETE AND MASONRY DAMS Gravity Dams, 183 Common Defects and Remedies, 188 Stability Analyses, 204 Improving Stability, 207 References, 211 Recommendecl Reading, 211 7 EMBANKMENT DAMS.... Types of Dams and Foundations, 213 Defects and Remedies, 218 ........ 71 . . .132 .183 ........... 213

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Contents Stability Analyses, 251 References, 257 Recommended Reading, 258 APPURTENANT STRUCTURES Introduction, 259 Defective Spillways, 259 Obstructions in Spillways and Outlets, 265 Defective Conduits, 266 Defective Gates and Hoists, 268 Defective Drainage Systems, 269 Erosion, 269 Earthquakes, 270 References, 271 Recommended Reading, 271 9 RESERVOIR PROBLEMS. Introduction, 272 Slope Instability, 272 Induces] Earthquakes, 274 Excessive Seepage, 274 Backwater Flooding, 275 Ice, 275 References, 277 Recommended Reading, 277 i0 INSTRUMENTATION Introduction, 278 Monitoring of Concrete and Masonry Dams, 279 Monitoring of Embankment Dams, 284 Reservoir Rim, 287 Induced Seismicity, 289 Types of Instruments, 294 Methods of Installation, 295 Data Collection and Analysis, 302 References, 307 Recommended Reading, 307 xv ......... 259 ......... 272 ...... 278

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xvi it RECOMMENDED GLOSSARY .. APPENDIXES Contents .309 A BIOGRAPHICAL SKETCHES OE COMMITTEE MEMBERS, 329 B BIOGRAPHICAL SKETCHES OF WORKSHOP PARTICIPANTS, 334 INDEX .............. 339

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List of Figures and Tables FIGURES 2-1 Cause of failure, 6 2-2 Age at failure, 7 2-3 Height of dams, 8 2-4 Dam types (Western Europe and USA, 1900-1969), 9 2-5 Probability of failure (Western Europe and USA), 10 2-6 3-1 3-2 Sample inundation mapping, 34 Risk of overtopping versus reservoir elevation of Jackson Lake, 62 Jackson Lake flood and flood effects versus reservoir restriction level, 63 3-3 Costs for each alternative, 66 4-1 Comparison of regional flood peaks, 74 4-2 Estimated flood peaks from dam failures, 76 4-3 Peak discharge from significant dam failures, 78 4-4 Probable maximum precipitation study regions, 88 4-5 Sample probable maximum precipitation time sequences, 92 4-6 Harza Engineering Co. scheme for constructing fuse plug spillways, 108 4A-1 Probable maximum flood (enveloping PMF isolines) for 100 square miles, 115 4A-2 Probable maximum flood (enveloping PMF isolines) for 500 square miles, 116 4A-3 Probable maximum flood (enveloping PMF isolines) for 1,000 square miles, 117 . XV11

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xviii List of Figures and Tubas 4A-4 Probable maximum flood (enveloping PMF isolines) for 5,000 square miles, 118 4A-5 Probable maximum flood (enveloping PMF isolines) for 10,000 square miles, 119 4A-6 Probable maximum flood (enveloping PMF isolines) for 20,000 square miles, 120 4A-7 Example of use of enveloping isolines, 121 4B-1 Observed point rainfalls exceeding 50 % of all-season PMP, United States east of 105th meridian for 10 square miles, 6 hours, 122 4B-2 Observed point rainfalls exceeding S0 % of all-season PMP, east of 105th meridian for 200 square miles, 24 hours, 123 4B-3 Observed point rainfalls exceeding So % of all-season PMP, east of 105th meridian for 1,000 square miles, 48 hours, 123 4B-4 Observed point rainfalls exceeding 50 % of all-season PMP, west of continental divide for 10 square miles, 6 hours, 124 5-1 5-2 5-3 5-4 5-5 5-6 5-7 5-8 4B-5 Observed point rainfalls exceeding 50 No of all-season PMP, west of continental divide for 1,000 square miles and duration between 6 and 72 hours, 124 Caverns in (lolomite foundation of a gravity concrete dam, 135 Embankment sections of Waco Dam, 146 Pore pressure contours at mid-pepper after slide, 147 Baldwin Hills Reservoir after failure, 148 Malpasset Dam, 149 Grain size chart and ASTM-ASCE grain size scale, 152 Soil triangle of the basic soil textural classes, 153 Unified soil classification, including identification and description, 154 5-9 Soil performance in or under dams, 156 5-10 Surface deposits in the United States, except Alaska and Hawaii, 160 5-18 5-19 6-1 5-11 Erosion caused by seepage through floor of Helena Valley Reservoir, 164 5-12 Seismic zone map of the Uniter] States, 168 5-13 Seismic zones for Alaska and Hawaii, 170 5-14 Procedure to determine ground motion at a site, 172 5-15 Average values of maximum accelerations in rock, 175 5-16 Linear plot of response spectra, 177 5-17 Relationship of earthquake magnitude to length of surface rupture along the main fault zone, 178 Duration of strong shaking, 179 Attenuation factor versus distance, 180 Gravity dam, 184

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List of Figures and Tables 6-2 Simple buttress dam, 185 6-3 Plan, profile, and section of a symmetrical arch dam, 186 6-4 Concrete arch dam under construction; shows keys between blocks, 187 6-5 Double-wall buttress multiple-arch type, 188 6-6 Relation of geologic structure to arch thrust, 196 6-7 Favorable topography for arch dams (A and B); unfavorable topography-unshaded parts of arrows indicate part of thrust that is daylighting (C and D), 198 6-8 Expected loads on a concrete dam, 205 7-1 Geotextiles (filter fabric) used to encapsulate sand and gravel filter in repair of dam for cooling water reservoir in Indiantown, Florida, 240 9-1 Vaiont reservoir slide (aerial view), 273 9-2 Ice pressure versus ice thickness, 276 10-1 Typical observation well installations, 289 10-2 Water-leve} measurements by (A) steel tape, (B) air-line probe, (C) electric probe, (D) sonic sounder, (E) pressure transducer, and (F) float, 290 10-3 Typical 90 V-notch weir, 292 10-4 Typical parshall flume, 293 10-5 Point Loma landslide, California, 293 10-6 Piezometer heads and contours in embankment at end of construction, Table Rock Dam, 299 10-7 Piezometric heads and contours in the foundation, Waco Dam, 300 10-8 Displacements and settlements of central points at crest, 303 10-9 Horizontal (river direction) displacements versus pool levels, Monument 10, 305 TABLES 2-1 Causes of Dam Incidents, 11 2-2 Causes of Concrete Dam Incidents, 12 2-3 Earth Dam Failures, 14 3-1 Hazard Rating Criteria in Hagen's Procedure, 51 3-2 Cost Analysis of Design Alternatives, 69 4-1 4-2 4-3 Dam Size Classification, 82 Hazard Potential Classification, 83 Hydrologic Evaluation Guidelines: Recommended Spillway Design Floods, 84 4-4 Summary of Seven Selected Dam Break Model Capabilities, 104 X1X

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xx List of Figures and Tables 4B-1 Identification of Storms Exceeding 50 % PMP, East of 105th Meridian, 125 4B-2 Storms with Rainfall Exceeding 50 % of PMP, West of Continental Divide, 128 5-1 Strengths of Rocks, 140 5-2 Major Cause of Defect, 142 5-3 5-4 Surface Defects, 143 Approximate Relationships: Earthquake Intensity, Acceleration, and Magnitude, 174 5-5 Earthquake Acceleration, 176 6-1 Evaluation Matrix of Masonry Dams, 190 7-1 Evaluation Matrix of Embankment Dams, 220 7-2 Loading Conditions, Required Factors of Safety, and Shear Strength for Evaluations for Embankment Dams, 254 Evaluation Matrix of Appurtenant Structures, 260 Causes of Deficient Behavior, Means of Detection, 280 8-1 10-1 10-2 Inventory of Geotechnical Instruments, 295 10-3 Names and Addresses of Manufacturers and North American Suppliers, 296 10-4 Frequency of Readings for Earth Dam Instrumentation, 304 10-5 Frequency of Readings for Concrete Dam Instrumentation, 306

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- - - \ / ~- :} ) - - - Safety of << Existing Dams Evaluation and Improvement \\

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