2013 Northwest Hydro Operators Forum

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Risk-Informed Decision Making – FERC Perspective

David Lord, P.E., D2SI Dam Safety Risk David Lord, P.E., D2SI Dam Safety Risk team – Portland, Orteam – Portland, Or

Natural Hazards: Seismicity Events

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What is Risk-Informed Decision What is Risk-Informed Decision Making (RIDM)Making (RIDM)

Decision-making, which has as an Decision-making, which has as an inputinput the the results of a risk assessment. results of a risk assessment.

Risk information will play a Risk information will play a key rolekey role in decisions in decisions related to dam safety but will not be the only related to dam safety but will not be the only information to influence the final decisions.information to influence the final decisions.

RIDM involves a RIDM involves a balancingbalancing of benefits and risks of benefits and risks while reducing risks as much as is practicablewhile reducing risks as much as is practicable..

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RiskRisk

RiskRisk = Probability of = Probability of FailureFailure x x ConsequencesConsequences

Probability of Probability of FailureFailure = Probability of = Probability of LoadLoad x x AdverseAdverse Structural Structural ResponseResponse Given Load (PF = PL x PAd )Given Load (PF = PL x PAd )

Adverse Response includes Adverse Response includes all stepsall steps of event tree leading to failure.of event tree leading to failure.

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From Deterministic to ProbabilisticFrom Deterministic to Probabilistic

Current standards-based program relied on Current standards-based program relied on conservative conservative deterministicdeterministic analyses. analyses.

Probable Maximum Flood (PMF) and Probable Maximum Flood (PMF) and Maximum Maximum Credible Earthquake (MCE)Credible Earthquake (MCE) estimates estimates

Structural analyses relied on these Structural analyses relied on these pointpoint estimatesestimates

Probabilistic Analyses give a Probabilistic Analyses give a curvecurve of frequency of frequency estimates for the loading, not one particular estimates for the loading, not one particular point.point.

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Probabilistic LoadingsProbabilistic Loadings Probabilistic loading has the Probabilistic loading has the benefitbenefit that that

different issues can be considered different issues can be considered including:including:

• Probable Probable level of reservoirlevel of reservoir during during earthquakeearthquake

• Range of inputsRange of inputs from far distance Cascadia from far distance Cascadia Subduction Zone source to nearby infrequent Subduction Zone source to nearby infrequent local sourceslocal sources

Current standards-based current Current standards-based current regulatory framework does not address regulatory framework does not address how to usehow to use this information for decision this information for decision making.making.

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Evaluating Frequency Loading Evaluating Frequency Loading EstimatesEstimates

Some form of Some form of fragilityfragility analyses are analyses are needed to evaluate how the dam performs needed to evaluate how the dam performs during a range of frequencies.during a range of frequencies.

If structure If structure okok for a 1/5000 annual for a 1/5000 annual exceedance probability (AEP) event, but exceedance probability (AEP) event, but not oknot ok for 1/10000 AEP, for 1/10000 AEP, is this is this acceptableacceptable??

Reclamation and US Corps of Engineers Reclamation and US Corps of Engineers have developed have developed techniquestechniques for for determining acceptability determining acceptability

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Consequence RiskConsequence Risk (Potential Life Loss) (Potential Life Loss)

The current hazard classification The current hazard classification system does system does not distinguishnot distinguish between one only potential life loss between one only potential life loss (PLL) and 10000.(PLL) and 10000.

Risk consequences Risk consequences evaluate a evaluate a rangerange of PLL from 0, to 1, to many of PLL from 0, to 1, to many thousand.thousand.

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Risk-Informed Decision Making Risk-Informed Decision Making (RIDM)(RIDM)

Decisions are made by using a Decisions are made by using a chartchart that compares F (the likelihood of that compares F (the likelihood of failure) to N (the PLL) failure) to N (the PLL)

The fN (or FN) charts have a The fN (or FN) charts have a one to one to oneone relationship between frequency relationship between frequency and PLL for societal risk and PLL for societal risk

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USACE Societal Tolerable Risk USACE Societal Tolerable Risk ChartChart

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Why Risk at the FERC?Why Risk at the FERC?

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Why Risk at the FERC?Why Risk at the FERC?

Enables a better Enables a better informedinformed decision. decision.

Enables a better Enables a better understandingunderstanding of of the damthe dam

Provides a better Provides a better justificationjustification for for decision-makingdecision-making

Makes dams Makes dams safersafer..

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Mid-Columbia Prototype Risk Mid-Columbia Prototype Risk AnalysesAnalyses

SixSix prototype sections prototype sections

Workshop No. 1Workshop No. 1 held on May 22 and 23, held on May 22 and 23, 20122012

• Grant Co PUD: Grant Co PUD: Wanapum Gate SystemWanapum Gate System

• Developed a Developed a system modelsystem model of gate system of gate system under seismic loadingunder seismic loading

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Prototype Risk AnalysesPrototype Risk Analyses

Workshop No. 2Workshop No. 2 held on November held on November 6 through 9, 20126 through 9, 2012

• Chelan Co PUD: Chelan Co PUD: Chelan Surge TankChelan Surge Tank

• Chelan: Chelan: Rocky Reach Spillway Gate Rocky Reach Spillway Gate SystemSystem

• Grant: Grant: Priest EmbankmentPriest Embankment (Liquefaction)(Liquefaction)

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Prototype Risk AnalysesPrototype Risk Analyses

Workshop No. 3Workshop No. 3 to be held in June to be held in June 20132013

• Chelan: Chelan: Rock Island North Abutment Rock Island North Abutment WallWall

• Grant: Grant: Wanapum Future Unit System Wanapum Future Unit System - Anchors- Anchors

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Mid-Columbia Risk AnalysesMid-Columbia Risk Analyses

The FERC The FERC likeslikes the prototype studies for many the prototype studies for many reasonsreasons

RIDM can provide RIDM can provide more understandingmore understanding of of particular issues as follows:particular issues as follows:

• Combining the frequency of loading with consequences Combining the frequency of loading with consequences

can provide a can provide a better perspectivebetter perspective on the risk of a on the risk of a particular loadingparticular loading

• Frequency aspects of loading event can be evaluated Frequency aspects of loading event can be evaluated using risk, e.g., using risk, e.g., more likely loading versus more more likely loading versus more unlikely.unlikely.

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Mid-Columbia Risk AnalysesMid-Columbia Risk Analyses

RIDM provides RIDM provides moremore understanding (cont.) understanding (cont.)

• Many MCE values are Many MCE values are typically comparabletypically comparable to 2% in 50 year ground motions, an to 2% in 50 year ground motions, an approximately 1/2500 AEP loading. (Note that approximately 1/2500 AEP loading. (Note that not all MCEs are comparable to a 2% in 50 year not all MCEs are comparable to a 2% in 50 year ground motion.)ground motion.)

• This calls into This calls into questionquestion whether an MCE is whether an MCE is actually the maximum load that needs to be actually the maximum load that needs to be considered for dam evaluation. considered for dam evaluation.

• Note that Wanapum Dam deterministic loading Note that Wanapum Dam deterministic loading are well above the are well above the 1/100001/10000 AEP loading. AEP loading.

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Wanapum Deterministic vs Wanapum Deterministic vs Probabilistic LoadingProbabilistic Loading

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Wanapum Seismic LoadingWanapum Seismic Loading

Wanapum probabilistic results Wanapum probabilistic results may may be adequately conservativebe adequately conservative at a at a higher frequency earthquake, e.g., higher frequency earthquake, e.g., 1/5000 AEP, than the equivalent 1/5000 AEP, than the equivalent deterministic result. deterministic result.

Using the probabilistic loading would Using the probabilistic loading would then result in then result in less potentialless potential for for remedial work.remedial work.

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Risk ScalabilityRisk Scalability

The prototype risk analysis technique is The prototype risk analysis technique is simplified and scalablesimplified and scalable. .

Simplifying assumptions are made to determine Simplifying assumptions are made to determine if the dam system if the dam system meetsmeets the selected tolerable the selected tolerable risk guidance. risk guidance.

Process ends at any of four steps after Process ends at any of four steps after

acceptable performanceacceptable performance at the lower step at the lower step based on PLL.based on PLL.

This scaling technique means that This scaling technique means that only only necessary detailed analysesnecessary detailed analyses are completed, are completed, and unnecessary steps are not completed.and unnecessary steps are not completed.

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CompletenessCompleteness

Simplifying assumptions reduce the cost Simplifying assumptions reduce the cost withoutwithout sacrificing completeness. sacrificing completeness.

• A full risk quantitative risk analysis (QRA) of spillway A full risk quantitative risk analysis (QRA) of spillway gate systems can be quite gate systems can be quite costlycostly. .

• The prototype captures the The prototype captures the full system modelfull system model without analyzing every detail reducing the cost.without analyzing every detail reducing the cost.

• IfIf it is clear that the dam’s fragility is it is clear that the dam’s fragility is acceptable acceptable under the loading used, no further work is needed.under the loading used, no further work is needed.

• A full QRA could be A full QRA could be completedcompleted if needed. if needed.

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Systems ModelSystems Model

Analysis of selected dam sections as Analysis of selected dam sections as systemssystems rather than just individual components.rather than just individual components.

• The full The full system modelsystem model is described is described

• The models develop for the Wanapum and Rocky The models develop for the Wanapum and Rocky Reach gate systems revealed Reach gate systems revealed very usefulvery useful information information about the various aspects of the spillway gate systemabout the various aspects of the spillway gate system

• This information allows the dam owner to This information allows the dam owner to fix issuesfix issues that had not been previously appreciated. that had not been previously appreciated.

• For example, For example, anchorageanchorage of backup power systems of backup power systems and safety of and safety of dam operatorsdam operators and their continued and their continued ability to operate the spillway gates.ability to operate the spillway gates.

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Usefulness of New Risk Analysis Usefulness of New Risk Analysis ToolTool

Tool is a Tool is a useful useful way to develop a result way to develop a result during the FERC’s integration of risk into during the FERC’s integration of risk into its dam safety program. its dam safety program.

Any necessary modifications to the tool Any necessary modifications to the tool can be made at a can be made at a laterlater date building date building upon the previous effort.upon the previous effort.

Refining the tool is part of the Refining the tool is part of the on-goingon-going work of the prototype development.work of the prototype development.

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Potential IssuesPotential Issues

Tool assumes seismic hazard uses Tool assumes seismic hazard uses halfhalf the risk space.the risk space.

Future work includes the need to Future work includes the need to understand where the risk is in relation understand where the risk is in relation to the to the tolerable risktolerable risk guideline including guideline including analyzing all of the PFMs.analyzing all of the PFMs.

We recognized that the FERC does not We recognized that the FERC does not

currently have a tolerable risk guideline currently have a tolerable risk guideline which which may varymay vary from current guidance. from current guidance.

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Tolerable RiskTolerable Risk

Risks are tolerable if they are Risks are tolerable if they are adequately managed and driven adequately managed and driven “as low as reasonably practicable” “as low as reasonably practicable” ((ALARPALARP). ).

An ALARP evaluation will be needed An ALARP evaluation will be needed in the in the futurefuture to fully establish to fully establish tolerability. tolerability.

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ConclusionsConclusions

Prototype Risk Tool is a potentially Prototype Risk Tool is a potentially useful useful tooltool

Risk-informed decision-making can provide Risk-informed decision-making can provide more understandingmore understanding of dam safety of dam safety issues because it includes likelihood of issues because it includes likelihood of failure and consequence.failure and consequence.

Prototype Risk Tool is Prototype Risk Tool is simplified and simplified and scalable.scalable.

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ConclusionsConclusions

Reasonably Reasonably complete complete analysis of analysis of complete dam systems can be done at complete dam systems can be done at relatively low cost.relatively low cost.

Developing a Developing a system modelsystem model is a very is a very productive effort in understanding risks.productive effort in understanding risks.

This technique is a This technique is a usefuluseful tool. tool.

Any potential changes and needed Any potential changes and needed modificationsmodifications can be made at a later can be made at a later date.date.

2013 Northwest Hydro Operators Forum

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QUESTIONS?QUESTIONS?