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]:ntroduct:ion
PURPOSE
The goal of this report is the enhancement of dam safety. It was prepared
by the Committee on the Safety of Existing Dams, National Research
Council (NRC), to present in a single volume all essential aspects of dam
safety. A major objective of the report is to provide guidance for achieving
improvements in the safety of existing dams within financial restraints.
Many dam owners are faced with problems of such a nature and extent that
they are unable to finance remedial measures. In May 1982 the U.S. Army
Corps of Engineers reported that no remedial measures had been instituted
at 64% of the unsafe dams found during its 4-year inspection program,
principally because of the owners' lack of resources. To these owners, as
well as to regulatory agencies and others concerned with the engineering
and surveillance of dams, the committee presents its suggestions and guid-
ance for assessing and improving the safety of existing dams. The contents
of this report are intended to be informational and not to advocate rigid
criteria or standards. In no instance does the committee intend to recom-
mend the lowering of existing dam safety standards.
SCOPE
The scope of the committee's study and the conclusions of this report con-
cern technical issues pertinent to dam safety. The study includes examina-
tions of risk assessment techniques; engineering methodologies for stability
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SAFETY OF EXISTING DAMS
and hydrologic evaluations; and methods and devices to identify, reduce,
and/or eliminate deficiencies in existing dams. Included are case histories
demonstrating economical solutions to specific problems and also possible
nonstructural approaches.
The Committee on the Safety of Existing Dams, operating under a June
1983 completion deadline, arranged a relatively brief but intensive study of
its assigned task. It conducted a 2-day meeting in Washington, D.C., on
June 2-3, 1982, to initiate the effort; a meeting of the panel chairmen in
Spokane, Washington, on August 10, 1982, to plan a workshop; and a 3-
day workshop meeting in Denver, Colorado, on October 5-7, 1982. A com-
mittee meeting was also held on March 7 and 8, 1983, to complete the draft
of the report.
Participants in the workshop included committee members, members of
NRC staff, and other experts with a broad range of experience in dam engi-
neering and dam safety. Task assignments for the workshop were divided
among five working groups: (1) Risk Assessment, (2) Stability of Embank-
ment Dams and Their Foundations, (3) Stability of Masonry Dams and
Their Foundations, (4) Hydraulic/Hydrologic Considerations, and (5) In-
strumentation. Advance assignments were made to individual participants
for specific contributions to the workshop to ensure complete coverage of
all issues. During the workshop a separate task group was designated to
address the general subjects of geology and seismology.
The participants discussed the various technical aspects of enhancing
dam safety with a view to reaching a consensus on desirable approaches
whenever possible. From these presentations and discussions, the commit-
tee reached the conclusions presented in this report.
BACKGROUND
This study by the Committee on the Safety of Existing Dams is the second
phase of a comprehensive study concerning policy and technical issues re-
lated to the safety of dams. In October 1981 the Federal Emergency Man-
agement Agency (FEMA3 asked the NRC to undertake such a study. For
the first phase, FEMA asked the NRC to identify impediments to state-run
programs for dam safety, to suggest federal actions to remove or mitigate
those impediments, and to define how the U.S. government could help
make nonfederal dams safer. In response, the NRC created the Committee
on Safety of Nonfederal Dams to review and discuss the issues involved.
The efforts of that committee were completed in February 1982 and re-
ported in the 1982 publication entitled Safety of Nonfederal Dams, A Re-
view of the Federal Role.
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Introduction
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Unlike the first phase, the second phase concerns the technical consider-
ations relating to dam safety and is applicable to all existing dams, federal
as well as nonfederal. The NRC created a new Committee on the Safety of
Existing Dams in May 1982 to examine the technical issues of dam safety
and to develop guidance on how to achieve improvements in the safety of
dams, with due recognition of financial constraints. The committee's task
as defined by FEMA was as follows:
· To inventory and assess risk techniques and formulate guidelines on
their use to rectify problems faced by dam owners and states with limited
financial resources.
· To review and evaluate methods and devices that can be applied,
along with risk assessments, to identify, reduce, and/or eliminate deficien-
cies in existing dams (includes development of a glossary of terms; evalua-
tion of hydrologies and stability parameters; and formulation of guidance
for mitigation of such problems as overtopping, weak foundations, piping,
and seismicity).
· To examine methodologies for assessing the potential impact of ad-
verse conditions (e.g., maximum credible earthquake, probable maximum
flood) on existing dams and potential modifications in order to set limits of
acceptable damage to a dam. The methodologies must support the assump-
tion of nonfailure of the structure. Additionally, the methodologies are not
to be applied to major structures where failure is catastrophic. Guidance
here is intended to be offered on how to achieve improvements in the safety
of existing dams within financial constraints.
REFERENCES
National Research Council, Committee on Safety of Nonfederal Dams (1982) Safety of Nonfe-
deral Dams—A Review of the Federal Role, National Academy Press, Washington, D.C.
U.S. Army Corps of Engineers (1982) National Program for Inspection of Nonfederal Dams—
Final Report to Congress.
Representative terms from entire chapter:
dam safety
