2013 NWHA CONFERENCE
FERC’S RISK-INFORMED
DECISION MAKING
From PFMA to Risk
Assessment
Doug Johnson – Regional Engineer - Portland
834 High Hazard Potential
234 Significant Hazard Potential
In the Beginning… for FERC
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Risk Assessments begin with a
Potential Failure Mode Analysis (PFMA)
The FERC first began using risk in a
dam safety context in 2003 when it
documented the PFMA process into its
dam safety guidelines (Chapter 14).
PFMA
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A PFMA is an exercise to
• identify all potential failure modes under static
loading, normal operating water level, flood,
and earthquake conditions including all
external loading conditions for water retaining
structure
• assess those potential failure modes of enough
significance to warrant continued awareness
and attention to visual observation, monitoring
and remediation as appropriate.
PFMA (cont.)
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PFMs are developed by the core team
Likely and unlikely factors affecting
the chances of occurrence are
documented.
PFMs are categorized by level of
seriousness.
PFMA Progress
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Since the program was initiated all
high hazard potential dams have
been analyzed.
Significant and Low hazard potential
dams are still in progress.
What is Risk-Informed Decision
Making (RIDM)
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Decision-making, which has as an input the
results of a risk assessment.
Risk information will play a key role in decisions
related to dam safety but will not be the only
information to influence the final decisions.
RIDM involves a balancing of social and other
benefits and the residual risks.
Extension of PFMA process
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PFMAs detail how a dam might fail
PFMAs do not directly consider the
scope of potential consequences
PFMAs do not estimate the likelihood
of an adverse event
RIDM will consider these items
Why Risk?
Tolerable Risk
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Risk society is willing to live with in order
to secure certain benefits,
Risk society does not regard as negligible
or something it might ignore,
Risk that society is confident that are
being properly managed by the owner,
and
Risk the owner keeps under review and
reduces still further as practicable.
Joint Federal Risk Group
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Includes Reclamation, Army Corps,
TVA, FEMA
A common federal approach to Risk
Standards for risk reduction:
Governance vs. Tolerance
RIDM Engineering Guidelines
1. Concrete Dams
2. Embankment Dams
3. Internal Erosion and Piping
4. Spillway Gates and Outlet Works
5. Operational Issues, SCADA
6. Hydrologic Hazard Analysis
7. Probable Seismic Hazard Analysis
8. Consequences
9. Risk Analysis
10.Risk Assessment
Benefits to Owners and FERC
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Provides a process to better understand
and quantify potential failure modes;
Identifies previously unidentified failure
modes with high risk, in particular, nontraditional failure modes;
Builds on the work completed in PFMAs
Provides a means to compare the safety of
different dams using a common basis risk;
Benefits to Owners and FERC
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Improves understanding of the uncertainty
and variability in traditional analyses;
Provides a way to understand the risk
associated with a single dam or an entire
inventory of dams;
Allows evaluation of risk reduction
alternatives and effectively reduces the risk
regulated dams pose to the public in
quantifiable and defensible terms;
Focuses resources on those structures that
pose the greatest risk. (FERC Strategic
Plan)
Final Thoughts
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FERC RIDM program will proceed in
parallel with deterministic methods
for the near future.
Phased approach to implementation.
Dams requiring full quantitative risk
will be few.
In longer run, PFMA process may be
expanded to include Qualitative Risk
Assessment