National Centre for Risk Analysis and Options Appraisal

Risk Assessment, RASP and Risk Assessment, RASP and IMPACTIMPACT

Ian Meadowcroft

National Centre for Risk Analysis and Options Appraisal

Meanings of RiskMeanings of Risk

• Combination of likelihood and consequences of specified outcome

• Likelihood - usually annual probability

• Outcomes include flooding, damage (properties / infrastructure), effects on people, environmental harm

• Individual and aggregate risk

• Concepts / definitions / tools reviewed in SR587

National Centre for Risk Analysis and Options Appraisal

Conceptual Model: Source - Conceptual Model: Source - Pathway - ReceptorPathway - Receptor

RECEPTORS: people, property,warning effectivenessSOURCE - High river,

Tide, Waves

PATHWAY: Defenceoperations, flooding

National Centre for Risk Analysis and Options Appraisal

National Centre for Risk Analysis and Options Appraisal

Risk-based decision-makingRisk-based decision-making

• New defences

• Maintaining and operating defence systems

• Flood warning

• Restricting development in flood and erosion prone areas

• Strategic planning, policy analysis

National Centre for Risk Analysis and Options Appraisal

National Centre for Risk Analysis and Options Appraisal

Risk-based decisions.....Risk-based decisions.....• What is the national / regional risk?

• What is the appropriate level of spending to reduce risk?

• Which reach / defence poses the greatest risk?

• Where are the maintenance priorities?

• What impact might climate change have?

• What combination of risk management most effective?

• What is the ‘residual risk’, how will it change?

National Centre for Risk Analysis and Options Appraisal

RASP - Risk Assessment for RASP - Risk Assessment for Strategic PlanningStrategic PlanningRASP methodology will deliver:

• Failure probabilities for individual defences

• Failure probabilities for the defence “system”

• Total flood risk for identified community (impact zone)

• An indication of the risk associated with each defence (using information on failure probability and consequences - economic or social)

National Centre for Risk Analysis and Options Appraisal

Indicative Floodplain

National Centre for Risk Analysis and Options Appraisal

Urban area

Agricultural land

National Centre for Risk Analysis and Options Appraisal

0

0.1

0.2

0.3

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1

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

P(B¦OT, CG=1)

P(B¦OT, CG=2)

P(B¦OT, CG=3)

P(B¦OT, CG=4)

P(B¦OT, CG=5)

Estimate the probability of overtopping and breaching for each defence section

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Condition Good

Condition PoorProbability ofBreach

National Centre for Risk Analysis and Options Appraisal

Risk: Annual Average Damage in each land use zone

National Centre for Risk Analysis and Options Appraisal

Approach to Risk AssessmentApproach to Risk Assessment

Ian Meadowcroftian.meadowcroft@environment-agency.gov.uk