Transcript Risk Informed Decision Support The Emergence of Risk Tolerance Guidelines and Seepage Failure Modes of Dams and Levees Keith A.

Risk Informed Decision Support
The Emergence of Risk Tolerance Guidelines
and
Seepage Failure Modes of Dams and Levees
Keith A. Ferguson, P.E.
National Water Resources Program Director
Kleinfelder, Inc.
Presentation to the 3rd NACGEA Geotechnical Workshop
October 2, 2009
Irvine, California
The Mandate
Source:
Adoption of Risk Methodologies
ANCOLD, BC Hydro
USBR – early 1990’s (dams)
FERC – early 2000’s (dams)
USACE - mid 2000’s (dams, levees, locks)
Adoption of Risk Methodologies
Why?
Prioritize decisions and funding (get largest
benefit per $)
Public communication
Understand cumulative (portfolio) risks
Improved dam and levee safety
Training and knowledge transfer
ANCOLD
USBR
FERC
USACE
CORPS OF ENGINEERS DAM SAFETY PORTFOLIO RISK MANAGEMENT PROCESS
Hurricane Katrina
Figure 3.1
Screening for Portfolio Risk Analysis (SPRA) (One time only)
28 Aug 2008
Dam Safety Action Classification (DSAC) (D 1a)
No
DSAC I
DSAC III
DSAC II
DSAC IV
All Dams
Develop and
Implement
IRRM Plan for
DSAC I.
Validation by
External Peer
Review (D 2a)
Develop and Implement
IRRM Plan for DSAC II (D 2a)
Heightened
Monitoring for
DSAC IV (D 2b)
Develop and Implement
IRRM Plan DSAC III (D 2a)
Yes
Prioritize and Schedule Issue Evaluation
Studies (P 1)
Resource Queue
DSAC I
Corps Accepts
As DSAC I? (D 1b)
No.
(More studies
and
investigations
required.
Modify study plan)
Study Plan
Issue Evaluation Studies
Routine dam
safety activities,
normal O&M
Yes
New Regulation
ER 1110-2-1156
Review DSAC and modify as appropriate.
Review and modify IRRM Plan. (D 1c)
Prepare Project
Management Plan
Dam Safety Modification
Studies
Decision document*
Incident triggers
DSAC Review?
(D 1d)
DSAC II, III, or IV
Resource
Queue
Prioritize and
Schedule
Modification
Studies (P 2)
No
Yes
For DSAC II, III, or IV
dams are Modification
Studies Justified?
(D 3)
No. (More studies
and investigations
required.)
Report
Approved?
(D 4)
Resource
Queue
Yes
Implement Decision
Review DSAC and modify
as appropriate. Review and
modify IRRM Plan. (D 1c)
Prioritize Projects
for funding (P 3)
Decision Point (D 1a) Prioritization Point (P 1) – Details for each point explained in Chapter 2
* Independent External Peer Review requirements are to be addressed per guidance in the Dam Safety
Modification chapter.
Periodic
Assessment
and
Implement
Lessons
Learned
Risk Tolerance
Generalized and Project Specific Tolerability of Risk Framework
General Framework
Increasing individual risks and societal concerns.
Unacceptable Region
Project-Specific
Framework
Risk cannot be justified
except in extraordinary
circumstances.
Range of Tolerability
People and society
are prepared to accept
risk in order to secure
benefits.
Intolerable
Residual
Risk
Tolerable
Residual
Risk
Lower risk to a
tolerable level by
meeting projectspecific ALARP
requirements.
Broadly Acceptable Region
Risk regarded as negligible with
no effort to review, control, or
reduce the risk.
Source: Draft ER 1110-02-1156 (August 2008)
Risk Tolerance Guidelines
Bureau of Reclamation f-N chart for Displaying Probability
of Failure, Life Loss, and Risk Estimates - Portrayal of Risk
1.E-01
Annual Failure Probability, f
1.E-02
Justification to take action to
reduce risk
1.E-03
Justification to take expedited
action to reduce risk
1.E-04
1.E-05
Source:
Diminishing justification to take
action to reduce risk
ER 1110-2-1156
USACE, 2008
1.E-06
1.E-07
1.E-08
0
1
10
100
Loss of Life, N
1,000
10,000
100,000
March 2003
Risk Characterization – Common
Elements
Comprehensive Data
Review and
Characterization
Potential Failure Modes
Assessment (PFMA)
Detailed PFM
Descriptions
Event Trees
Subjective Probability and
Expert Elicitation
Reliability and
Probabilistic Analysis
Risk Assessment Levels
SPRA (Screening for Portfolio Risk
Assessment – qualitative)
Issue Evaluation Study (IES - Comparable
to the USBR Comprehensive Facility
Review - quantitative)
Detailed Risk Assessment – highly
quantitative)
Portfolio Screening
DSAC I
DSAC I
DSAC II
Isabella Dam
Martis Creek Dam
Wolfcreek Dam
Center Hill Dam
Herbert Hoover Dike
Clearwater Dam
Howard Hansen Dam
Zoar Levee
Hidden Dam
Success Dam
Keystone Dam
Canton Dam
Lewisville Dam
Patoka Dam
Risk Quantification – Seepage
Failure Modes
Decomposition/De-aggregation
Physical systems characteristics
Embankment
Embankment/Foundation Contact
Foundation
Failure Mode Development Process
De-aggregation by Physical
System Characteristics
River
1
Levee
Pervious Sands and Gravels
Failure Mode
2
Levee on Pervious Foundation
River
Levee
1
Confining Silt/Clay Layer
Pervious Sands and Gravels
Levee on Pervious Foundation
With Confining Layer
3
1
Embankment Seepage
And Piping/Erosion
2
Foundation Seepage
And Piping/Erosion
3
Foundation Seepage
And Piping/Backward
Erosion Under
Confining Layer
IES/Detailed Risk Analysis
Stages of Failure Mode
Development
Loading occurs
Initiation
Continuation
Progression
Breach formation
Initiation
Picture of Sand Boil
Continuation
Backward erosion and slope
raveling due to seepage
through levee
Continuation of piping
concludes with break
through to water source
Progression
Opening expands due
to large flows
Collapse of overlying
foundation and
embankment soils
occurs
Localized slope
raveling and instability
Breach Formation
1. Collapse allows overtopping
to begin breach formation
2.
Breach reaches full
Height of levee
3.
Breach widens with
continued flows
Example IES Risk Estimation
Example IES Risk Estimation
P-5,6,7
CD-106
Step 1 - Detailed Review of Data and
Characterization
Step 2 – Load Partitioning and Decomposition of Failure Mode for Risk Estimation
Step 3 – Risk Quantification
Example IES Risk Estimation
Step 4 – Evaluation of Risk Rating
and Risk Informed Decision
Making
Risk Toolbox
28 Initiation Mechanisms (IM’s)
Summary
Risk Informed Decision Making is the
future of dam and levee safety
New risk tolerance guidelines will be
central
New skill set required
Many benefits
Prioritization to achieve biggest benefit per $
Communication
Knowledge transfer