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OCR for page R1
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
OCR for page R2
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 safety—United 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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