USACE Levee Safety Risk Analysis Process and Methodology Overview

US Army Corps of EngineersBUILDING STRONG®

USACE Levee Safety Risk AnalysisProcess and Methodology Overview

Jason Needham, P.E.Consequence Specialist

USACE Risk Management Center

09 December 2011

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Levees pose risk to people and property► Inherent risk associated with living near rivers and oceans► Degradation of existing structures► Changing construction techniques► Increase in population, climate change, etc

Increase in public awareness► Katrina and other recent events► Congress points to USACE

Large portfolio - limited funds► How do you decide what to fix first?

Problem

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Previous Situation

HQ

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Assess the integrity and viability of levees and recommend actions to assure they do not present unacceptable risks to the public, property, and the environment.

► Hold public safety paramount► Reduce economic damage► Maximize cost effectiveness► Develop reliable and accurate

information (decision driven)► Build and maintain public trust

USACE Levee Safety Program

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Levee Safety Portfolio Risk Management

Process

5

RoutineInspections

Incident or inspection

finding triggers LSAC

review?

NO

IRRM

Levee issue requires further

evaluation?

No

Implement Risk Management

Measures

Yes

Reassess Risk & Revise LSAC

YES

All Levees

PeriodicInspections

Classification(LSAC)Screening

No Routine O&M& Monitoring

Yes

Study Justified?

Base Condition Risk Assessment

LSAC Communicationand

Plan Non-routine ActivitiesLevee Safety Risk Management Study

(Major Rehab/Feasibility)

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Process

Routine Activities

6

RoutineInspections



review?

NO

IRRM


evaluation?

No


Measures

Yes


YES

All Levees

PeriodicInspections



Yes

Study Justified?





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Levee Safety Action Classification System

Transition from Routine to Non-routine Reflects urgency of action Depicts range of risk

►combination of • likelihood of inundation • consequences of inundation• with an emphasis on life-safety

Provides consistent and systematic guidelines for actions commensurate with the risk

7

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Levee Safety Action Classification

Class Urgency Characteristics Actions

I Urgent and Compelling(Unsafe)

Likelihood of inundation with

associated consequences

characterizing each class.

Actions recommended for each class and level of

urgency.

II Urgent(Unsafe or Potentially Unsafe)

III High Priority(Potentially Unsafe)

IV Priority(Marginally Safe)

V Normal(Adequately Safe)

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Process

Non-Routine Activities

9

RoutineInspections



review?

NO

IRRM


evaluation?

No


Measures

Yes


YES

All Levees

PeriodicInspections



Yes

Study Justified?





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RoutineInspections



review?

NO

IRRM


evaluation?

No


Measures

Yes


YES

All Levees

PeriodicInspections



Yes

Study Justified?





Levee Screening Tool► Developed to quickly assess

the condition and consequences of levees in the Corps of Engineers portfolio

► Combines information from:• National Levee Database;• Levee inspection process;• Limited Engineering

Assessment of project features.

► Relative Risk Index► Philosophy

• Data consistency• Conservative judgements

► Largo portfolio• Simplify!

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Plotting – Prior to Overtopping

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Initial Results – New Orleans

System levees designed to reduce flooding from Mississippi River and Lake Pontchartrain

FOR OFFICIAL USE ONLY

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Segment Screenings

Vicinity/Segment Map

Pontchartrain LD

East Jefferson LD Orleans LD

2

1

3

5

46

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Plotting – Overtopping

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Initial Results – New Orleans► Recommended LSAC Rating = LSAC 2► Combination of life, economic, or environmental consequences

with the probability of inundation due to overtopping with subsequent breach, is very high.

► Justification:• Performance concern: Breach during overtopping• Evidence:

Good performance expected for events up to 100% loading Incipient overtopping frequency estimated at 200-year return period Studies show breach likely for event at or about 200-500 yr event Breach during overtopping would significantly increase consequences Critical infrastructure includes numerous hospitals, oil & gas refineries, and

chemical industry facilities that could lead to major impacts well beyond the protected area

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RoutineInspections



review?

NO

IRRM


evaluation?

No


Measures

Yes


YES

All Levees

PeriodicInspections



Yes

Study Justified?






Process

16

When We Use Risk Analysis

Risk Analysis Approach is

Decision Driven

Relative

Absolute

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USBR Public Protection Guidelines

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

0.1 1 10 100 1000 10000

Average Incremental Life Loss Per Failure

Ave

rage

Ann

ual P

roba

bilit

y of

Fai

lure

USBR Justification to take expedited action to reduce risk

USBR Justification to take action to reduce risk

USBR Justification to take action to reduce probability of failure

USBR Diminishing justification to take action to reduce risk

ANCOLD Tolerable Risk Guidelines

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1 10 100 1000

Incremental Life Loss Due to Dam Failure (N)

Ann

ual P

roba

bilit

y of

Incr

emen

tal L

ife L

oss

>= N

ANCOLD Limit Of Tolerability For Existing Dams

ANCOLD Limit Of Tolerability For New Dams and Major Modifications

USACE Levee Safety Risk Analysis Process and Methodology Overview

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