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Dam SafetyDam SafetyPortfolio Risk AssessmentPortfolio Risk Assessment

Jeff SchaeferJeff SchaeferGeotechnical Regional Technical Specialist Geotechnical Regional Technical Specialist

U.S. Army Corps of EngineersU.S. Army Corps of EngineersLouisville DistrictLouisville District

August 3, 2006August 3, 2006

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Stewardship ofStewardship ofNational Infrastructure National Infrastructure

Risk Assessment provides a defensible framework to Risk Assessment provides a defensible framework to support Performance Based Budgeting.support Performance Based Budgeting.

Understanding degradation of system performance.Understanding degradation of system performance.

Prioritization of Investments. Prioritization of Investments.

Allows for allocation of limited funds for projects where Allows for allocation of limited funds for projects where potential for overall risk reduction is greatest potential for overall risk reduction is greatest

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Levels of Risk AnalysisLevels of Risk AnalysisRisk analysis for dam safety is performed at Risk analysis for dam safety is performed at

three levels:three levels:ScreeningScreening portfolio risk analysis (SPRA)portfolio risk analysis (SPRA)PortfolioPortfolio risk analysis (PRA) for safety risk analysis (PRA) for safety improvementimprovementProject or site specificProject or site specific risk analysis for risk risk analysis for risk management actions or project management actions or project improvements improvements

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Probabilistic, RiskProbabilistic, Risk--Based Method of Based Method of Determining Relative RiskDetermining Relative RiskImplemented Via 3 Multidiscipline Implemented Via 3 Multidiscipline National Technical CadresNational Technical Cadres20% of Corps Dams Screened to Date.20% of Corps Dams Screened to Date.

SPRASPRA

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SPRASPRA

Results used to shape the Budget Results used to shape the Budget Specific products delivered include:Specific products delivered include:

Annualized Life RiskAnnualized Life RiskAnnualized Economic RiskAnnualized Economic RiskIndex of ConditionIndex of ConditionAnticipated five year funding needs for each projectAnticipated five year funding needs for each projectSorting of risks by project feature (seepage and Sorting of risks by project feature (seepage and piping, stability, erodibility) and loading condition piping, stability, erodibility) and loading condition (hydrologic and seismic events). (hydrologic and seismic events).

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SPRA MethodologySPRA Methodology

Initiating event frequencyInitiating event frequencyFailure mode performanceFailure mode performanceBreaching severityBreaching severityConsequence multipliersConsequence multipliersFatality and loss ratesFatality and loss rates

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SPRA MethodologySPRA Methodology

Risk =Risk = (Hazard rate, H) (Conditional failure probability, Pf) (Hazard rate, H) (Conditional failure probability, Pf) (Conditional breach probability, Pb) (Exposure, X) (Loss rate, L(Conditional breach probability, Pb) (Exposure, X) (Loss rate, L) )

1.1. R R -- Annual riskAnnual risk2.2. H H -- Hazard rate is the initiating event rateHazard rate is the initiating event rate3.3. Pf Pf -- Conditional failure probability of a feature given the initiatiConditional failure probability of a feature given the initiating eventng event4.4. Pb Pb -- Conditional dam breach probability (conditional breach probabilConditional dam breach probability (conditional breach probability per ity per

feature failure)feature failure)5.5. X X -- Exposure of developments due to breaching of the dam and uncontExposure of developments due to breaching of the dam and uncontrolled rolled

flooding (population or property at risk per breach)flooding (population or property at risk per breach)6.6. L is the loss rate of the uncontrolled flooding (lives or dollarL is the loss rate of the uncontrolled flooding (lives or dollars lost per s lost per

population, property at risk, economic loss of navigation). population, property at risk, economic loss of navigation). 7.7. The product of X L is called the consequences due to breaching oThe product of X L is called the consequences due to breaching of the dam f the dam

and uncontrolled flooding (lives or dollars lost per breach).and uncontrolled flooding (lives or dollars lost per breach).

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Failure Mode ProbabilityFailure Mode Probability

Evaluation of Major Components and SystemsEvaluation of Major Components and SystemsComparisons made to a new structureComparisons made to a new structureBaseline failure probabilities:Baseline failure probabilities:

Feature performance MultipliersFeature performance MultipliersBreaching severityBreaching severity

Design and construction USACE criteria and Design and construction USACE criteria and standardsstandards

Baseline ProbabilitiesBaseline Probabilities

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Feature Failure Mode PerformanceFeature Failure Mode Performance

All features rated against a baselineAll features rated against a baselineExisting DataExisting DataNumerical multipliers applied to baseline failure Numerical multipliers applied to baseline failure probabilitiesprobabilities to model site conditionsto model site conditions

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Feature Failure Mode PerformanceFeature Failure Mode Performance

Breach Severity FactorsBreach Severity FactorsLevel of breaching resulting from feature failure Level of breaching resulting from feature failure mode performance.mode performance.Adjusted to reflect linked failure modes and site Adjusted to reflect linked failure modes and site specific conditions.specific conditions.

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ConsequencesConsequences

Project and event specificProject and event specificLoss of Life (LOL)/eventLoss of Life (LOL)/event

Population At Risk (PAR) within inundation zonePopulation At Risk (PAR) within inundation zoneFatality rate within PARFatality rate within PAR

Economic damage/eventEconomic damage/eventProperty damage within inundation zoneProperty damage within inundation zoneLoss of NavigationLoss of NavigationLoss of lifelinesLoss of lifelines

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Districts give a presentation based on information request sent out by Headquarters

Districts give a presentation based on Districts give a presentation based on information request sent out by information request sent out by HeadquartersHeadquarters

ProcessProcess

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Cadre then interviews (interrogates) District personnel to extract more information

Cadre then interviews (interrogates) Cadre then interviews (interrogates) District personnel to extract more District personnel to extract more informationinformation

ProcessProcess

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Review all relevant documents•Pi’s

•Foundation reports

•As-built drawings

•Construction photos

•Water control manuals

•Special studies

Economist works with District to develop consequences

Review all relevant documents•Pi’s

•Foundation reports

•As-built drawings

•Construction photos

•Water control manuals

•Special studies

Economist works with District to develop consequences

ProcessProcess

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Cadre members then individually rate each feature. Cadre members then individually Cadre members then individually rate each feature. rate each feature.

ProcessProcess

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•Team then agrees on final ratings for each feature and any adjustments to release severity weighting.

•Loading info and ratings are then entered in spreadsheet.

••Team then agrees on final ratings Team then agrees on final ratings for each feature and any for each feature and any adjustments to release severity adjustments to release severity weighting.weighting.

••Loading info and ratings are then Loading info and ratings are then entered in spreadsheet. entered in spreadsheet.

ProcessProcess

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Consequences are then input and the spreadsheet is completed.Consequences are then input and Consequences are then input and the spreadsheet is completed.the spreadsheet is completed.

ProcessProcess

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Cadre will then prepare A report that documents: •General description of the project

•All PI and I ratings

•Release severity adjustments

•Basis for PAR and LOL estimates

•Basis for economic damages

•5 year funding need.

Cadre will then prepare A report Cadre will then prepare A report that documents: that documents: ••General description of the projectGeneral description of the project

••All PI and I ratingsAll PI and I ratings

••Release severity adjustmentsRelease severity adjustments

••Basis for PAR and LOL estimatesBasis for PAR and LOL estimates

••Basis for economic damagesBasis for economic damages

••5 year funding need.5 year funding need.

ProcessProcess

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When all projects at a location are complete the cadre will present a debriefing covering:•Cadre members

•Purpose of SPRA

•Summary of the ratings for each project

•Relative ranking for each districts projects

•Address the Districts questions and concerns

When all projects at a location are When all projects at a location are complete the cadre will present a complete the cadre will present a debriefing covering:debriefing covering:••Cadre membersCadre members

••Purpose of SPRAPurpose of SPRA

••Summary of the ratings for each projectSummary of the ratings for each project

••Relative ranking for each districts projectsRelative ranking for each districts projects

••Address the Districts questions and concernsAddress the Districts questions and concerns

ProcessProcess

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Feature Flood Control Dam

Normal Water Level

50% Exceedence Duration Normal Water Level with

OBE

50% Exceedence Duration Normal Water Level with

MDE

Unusual (300yr) Extreme - (PMF)

Concrete Gravity SectionExternal Stability NA NA NA NA NAInternal Stability NA NA NA NA NAFoundation Stability NA NA NA NA NAFoundation - Seepage & Piping NA NA NA NA NA…………………...Void ………………………………… NA NA NA NA NAAbutment Foundation Stability (Dam Structure) NA NA NA NA NA

Spillway and/or Stilling Basin SystemStructural Stability A A PA A PAStructural Capacity A A A A PAWalls - Overtopping A A A A IGates - Structural, Electrical and Mechanical NA NA NA NA NAGate Piers - Structural Capacity NA NA NA NA NAErodibility A A A PI PI…………………...Void ………………………………… NA NA NA NA NASill A A A PA PA

Outlet Works and ConduitsEmbankment Piping at Conduit PA A A PA PAGates - Structural, Electrical and Mechanical A A A A IIntake Tower Stability A PA PI A AIntake/Tunnel/Conduit Structural Failure A PA PI A ATunnel/Conduit Joint Failure PI A A PI PI

EmbankmentEmbankment Seepage & Piping PA A A PI PIErosion: Toe, Surface & Crest A A A A IAbutments Seepage & Piping A A A PA PAAbutments Stability and/or Liquefaction A PA PA A AFoundation Seepage & Piping PI A A I IEmbankment Stability and/or Liquefaction A PI I A AFoundation Stability and/or Liquefaction A PI I A A

Reservoir RimStability - Landslide A A PA A ALoss of Storage Capacity - Silt A A A A AErosion A A A A AMines A A A A A

Other FeaturesFeature 1 NA NA NA NA NAFeature 2 NA NA NA NA NAFeature 3 NA NA NA NA NAFeature 4 NA NA NA NA NA

Engineering Rating Summary

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General CommentsGeneral Comments

Several projects found to be on the Several projects found to be on the continuum of failurecontinuum of failure

Projects screened in 06 were mixed with 05 Projects screened in 06 were mixed with 05 projects (i.e. we did not get top 10% in 05).projects (i.e. we did not get top 10% in 05).Independent screening has identified Independent screening has identified significant safety issues significant safety issues

Time

Failu

re

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Basis of RankingBasis of Ranking

Flood Damage Reduction ProjectsFlood Damage Reduction ProjectsAnnualized Life RiskAnnualized Life RiskRelative Condition Ratio (Life Risk/Baseline Relative Condition Ratio (Life Risk/Baseline Life Risk)Life Risk)

Navigation ProjectsNavigation ProjectsAnnualized Economic RiskAnnualized Economic RiskRatio (Economic Risk/Baseline Economic Ratio (Economic Risk/Baseline Economic Risk)Risk)

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Priority CategoriesPriority Categories

Active Failure Continuum (progressive Active Failure Continuum (progressive deterioration)deterioration)Significantly InadequateSignificantly InadequateImportant Dam Safety DeficienciesImportant Dam Safety DeficienciesAll OthersAll Others

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05 and 06 Results05 and 06 ResultsUSACE DAM SAFETY PROGRAM - SPRA RESULTS

(FY05 and FY06)

Increasing Life Risk

Incr

easi

ng P

roba

bilit

y of

Uns

atis

fato

ry P

erfo

rman

ce

Progressive DeteriorationSignificantly InadequateImportant Dam Safety DefecienciesAll Others

Priority Projects for Risk Reduction Investments(Investigations, Studies, Reports, P&S, etc)

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Review of DeficienciesReview of Deficiencies

Due To Ageing And The State Of The Art At Due To Ageing And The State Of The Art At The Time Of Design And Construction The Time Of Design And Construction Significant Dam Safety DeficienciesSignificant Dam Safety Deficiencies Exist At Exist At Many USACE Dams.Many USACE Dams.

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Review of DeficienciesReview of Deficiencies

The top 25 projects from the initial round The top 25 projects from the initial round SPRA FY05 were reviewed and examples of SPRA FY05 were reviewed and examples of deficiencies that were considered inadequate deficiencies that were considered inadequate are presented.are presented.

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Foundation SeepageFoundation Seepage

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Inadequate Seepage ControlInadequate Seepage Control

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High Toe PressuresHigh Toe Pressures

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Foundations Seepage and Piping (Karst)Foundations Seepage and Piping (Karst)

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Foundations Seepage and Piping (Karst)Foundations Seepage and Piping (Karst)

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Foundations Seepage and Piping (Karst)Foundations Seepage and Piping (Karst)

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Abutment Seepage (Karst)Abutment Seepage (Karst)

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Abutment SeepageAbutment Seepage

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Inadequate Abutment TreatmentInadequate Abutment Treatment

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Inadequate FilterInadequate Filter

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Inadequate FilterInadequate Filter

Rock Toe

Sinkhole

Earth Embankment

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Blanket Drain Short CircuitBlanket Drain Short Circuit

UPSTREAMDOWNSTREAM

IMPERVIOS FILL

ROCK TOE

EL. 471

SAND DRAINS BEDROCK

14

11

40’

20’

VERTICAL DRAIN

SAND DRAINS

BLANKET DRAIN

BLANKET DRAIN

ALLUVIAL SOIL

IMPERVIOS FILL

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PIPING INTO A CONDUITPIPING INTO A CONDUIT

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Slope StabilitySlope Stability

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Spillway ErosionSpillway Erosion

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Spillway ErosionSpillway Erosion

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Monolith Stability (PMF)Monolith Stability (PMF)

Inspection GalleryEl. 1375.0’

CurrentFoundationDrains

El. 1535.0’

Axis of Dam

137’

GroutCurtain

Groundline

El. 1410.0’

Top of Rock

Monolith12

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Seismic DeformationSeismic Deformation

455

475

495505515526533540547555

570

590

610

630

652662.5670680691.5

EL, Ft

DISTANCE FROM CENTER LINE F

-870 -800 -700 -600 -500 -400 -300 -200 -100 0 100 200 300 400 500

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Spillway StabilitySpillway Stability

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Foundation StabilityFoundation Stability

Open bedding planes; fault-damaged discontinuities

•Uplift Pressures

•Better Understanding of Rock Strengths

•Revised PMF’s

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Gate DeteriorationGate Deterioration

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A. Diaphragm: corrosion and holes developing in the steel.B. End panel: corrosion and loss of structural support.

Loss of StiffenerA B

Gate DeteriorationGate Deterioration

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A. Gate pickup assembly.B. Guide wheel truck assembly.C. Truck assembly removed for repair.D. Bolts, nuts, and rivets are beyond recognition.

A

C

D

A

B

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2005 SPRA TOTAL CONTRIBUTION TO 2005 SPRA TOTAL CONTRIBUTION TO RISKRISK

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%G

ates

Seep

age

Erod

ibili

ty

Stab

ility

Seis

mic

OB

E

Seis

mic

MDE

Deficiencies That Could Lead to Breach and Are Present in NormalLoad Conditions Generate the Highest Risk.

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WHATS NEXT?WHATS NEXT?

Continue SPRA For The Next 10% (SPRA Continue SPRA For The Next 10% (SPRA Team)Team)Develop A Rigorous PRA Tool (Methodology Develop A Rigorous PRA Tool (Methodology Team) Will Be Incorporated Into PI ProcessTeam) Will Be Incorporated Into PI ProcessOverhaul Dam Safety Program Based On Risk Overhaul Dam Safety Program Based On Risk (Policy Team) (Policy Team)