landslide risk analysis & assessment - unicaen · landslide risk analysis & assessment eric...

Landslide Risk Analysis& Assessment

Eric LEROI

PAU / ROQUEVAIREFrance

+33 (0)6 81 95 88 [email protected]

Mountain Risks Research And Training Network& FORM-OSE Post-Graduate Training School

Intensive Course - Barcelona1st –4th September 2008

Fairly good knowledge of phenomenon and their mecanismsHigh capability of calculation and modelling

What are you going to do with all thisscience ?!…

… saving the world ?! …

… not sure !

The more we know …The more efficient the technics is …

… the higher the risk seems to be !

THE PARADOXE OF THE RISK

Who / what is responsible for this situation ?

Science - Climate change – Risk Management … God ?

Political Aspirations

Budget

Other constraints

Social demands

Regulation

Risk acceptance

criteria

ValuesJudgement

R I S K M A N A G E M E N TR I S K M A N A G E M E N T

R I S K A S S E S S M E N TR I S K A S S E S S M E N T

RISK ANALYSIS

Monitor and Review

RISKEVALUATION

RISK MITIGATIONCONTROL OPTIONS & CONTROL PLAN

HAZARD ANALYSIS

DANGERCHARACTERISATION

With landslide risk assessment and management, you enter a new world … you meet the Human Being ! … and even before withinrisk analysis.

Landslide Risk Analysis & Assessment

Single given landslidefor protection or

evacuation

Ranking areas prone to landslides for risk mapping

Tools, financial ressources, available time are different


Ranking areas vs risk level

Assessing risk re acceptance criteria

Landslide Risk Analysis

What ?

FromWhere ?

To Where ?

What ?

When ?SlopeLithologyVolumeWaterTriggersVulnerability…probability

Classical approach fromEarth sciences and modelling

Landslide Risk Analysis

Hazard assessment mainly relies on empirical / statistical approaches using :

- Long-time series- principle of causality« the past is the key of the future »- Modelling

Is principle of causality still valid, where human impact is high ?

The past is no longer the key of the future …at least, used in a classic way.

The series are not stable !Because the boundaries conditions have changed and still continue to change … because of human activities and interactions.

INTERDEPENDENCE OF ENVIRONMENTS

NATURALENVIRONMENT

CONSTRUCTEDENVIRONMENT

HUMANENVIRONMENT

Naturalenvironment

Constructedenvironment

Humanenvironment

Interactions

Action

Reaction

Reaction

Reaction

What is theprinciple of

action / reaction ?

ACTION

?!

REACTION

20 – 30 years later …

…Landslides !

YESTERDAYAgriculture …

…control of water.

Today … excessive earth works …

… water no more managed.Slopes are urbanized …Natural drains blocked

MENTONWinter 2000

4000 landslides

10 M€of remedial works

History of the land use and land occupancy as well as theterritory itself have to be better understood

-As stakes for risk analysis-As triggers for hazard analysis-As a system that changes the boundary conditions

-Need for systemic analysis of the territory

Which scale ?

Risk maps

Which scale ?

Which level ?

1/1.000.0001/50.0001/25.0001.10.0001/1.000

PreliminaryAdvancedDetailed

Which mapping ?

PhenomenonSusceptibilityHazardRisk

?

1/1High Sophisticated

INFORMATION

LAND PLANNING

Over estimation : socio-economical consequencesUnder estimation : responsibility

1/100.000Basic

ObjectivesMethods availableData available

ScaleLevel

Mapping

Budget available

ConstraintsConsequences

?/required/required

/requiredSurface to be covered

Type of phenomenon

Results

Choice

InformationLand-planningProtection

NoneRecommandationsStatutory obligations

Expected victimsNone1 victim…>100 victims

Mapping choice (scale, level,type) : A choice on how far we can make mistakes thatare supposed to be accepted by population, basedon the objectives and consequences of the maps

ObjectivesMethods availableData availableType of phenomenon

ScaleLevel

Mapping

Surface to be coveredBudget available


InformationLand-planning / FutureProtection / Existing EAR

- population- dwellings- life-lines- Environment

?


ScaleLevel

Mapping





1/1.000.0001/50.0001/25.0001.10.0001/1.000




ScaleLevel

Mapping





1/1.000.0001/50.0001/25.0001.10.0001/1.000


NoneRecommandationsStatutory obligations-Negligible (€)-<10% (€)-1 owner (€)-Group of owners (€)-…



ScaleLevel

Mapping





1/1.000.0001/50.0001/25.0001.10.0001/1.000

PreliminaryAdvanceDetailed


1 victim2-5 victims5-10 victims10-100 victims>100 victims

MAPPING

Uncertainty / Principle of precautionQuestion of uncertainty : a scientific problem

For decision-maker, no uncertainty: decision and action

For the judge, no uncertainty: responsibility and decision

Uncertainty is transformedin principle of precaution

Being over-conservative is not acceptable for the society

Mapping choice (scale, level,type) : A choice on how far you canmake mistakes that are supposed to be accepted by population, based on theobjectives and consequencesof the maps


Ranking areas vs risk level

Assessing risk re acceptance criteria

Landslide Risk Assessment

Defines the way you use your risk map :

-prohibiting construction-Protecting stakes

Existingbuildings

New dwellings

Which solution for existing buildings?

For each case, solutions are numerous

NET

EARTH FENCE

EVACUATION

DO NOTHING

: Technical choice

PROTECTION

What about the safetybehing the wall ?

PROTECTION

PROTECTION

oversizing

ImpactCost

PROTECTION

Optimization

Résidual RiskP(t)

NEED FOR CRITERIA

The objectives of protection and development have to beclearly defined, both in term of:

-Acceptable and tolerable risk-Acceptable cost

Societal choice

Tolerable risk :• Risk that society can live with• Non-negligible risk• To be reduced further as possible.

Acceptable risk:• Risk which everyone affected is prepared to accept.• Action to further reduce such risk is usually not required

Risk Assessment criteriaTolerable risk / Acceptable risk

•Calculated risk is evaluated against acceptance criteria ; Theymay be related to:

• Loss of life• Financial value• Socio-environnemental value

(individual risk, societal risk, total risk…)(cost to save a life, cost-benefit ratio…)

( frequency of accidents…)

•Should involve owner / regulator / professionals / population…

•Iterative process with risk analysis because of uncertainty

Risk Assessment criteriaTolerable Risk : general principles (IUGS-1997)

• Incremental risk from hazard should be negligible•ALARP (As Low As Reasonably Practicable) principle is generalyused•If possibility of loss of life is high, probability of phenomenonshould be low•Higher risk than acceptable will be tolerated if control or reductionof risk is not possible•Higher risk is tolerated for existing slope than for planned projects

•Higher risk is tolerated for natural slope than for engineered slopes

•Monitored natural slopes are considered as for engineered slopes• Tolerable risk may vary from country to country

NEED FOR CRITERIA

It’s better to define the objectives of protection and development in a quantitative way, else:- Problem of design / studies- Problem of responsibility

The objectives of protection and development can be defined :In a qualitative way : red = no buildingIn a quantitative way : 10-4 is an acceptable risk

Risk Assessment criteriaSocietal Risk (SR): Principles

Untolerable

Tolerable

Acceptable

ALARP

110-8

10 100 10 0001 000

10-4

10-5

10-6

10-7

1 000 000100 000N

F

€?


Untolerable

Tolerable

Acceptable

ALARP

110-8

10 100 10 0001 000

10-4

10-5

10-6

10-7

1 000 000100 000N

F

€?

« Normal » life

Risk Assessment criteriaSocietal Risk (SR): Examples

Hong Kong Special Administrative Region Government

1

3

2

1

3

22

1

5000


Untolerable

Tolerable

Acceptable

ALARP

110-8

10 100 10 0001 000

10-4

10-5

10-6

10-7

1 000 000100 000N

F

€?

« Normal » life

10-5

10-9

10-2 10-4

10-610-3

10-710-3

10-1

10-510-710-5

10-9

10-2 10-4

10-610-3

10-710-3

10-1

10-510-7

Landslide Risk Assessment & Management are not only scientific problems nor technical ones.

+ Seismic risk

Un territoirecontraint

Environnemental Protections(Loi Littoral Law, ZNIEFF…)

PPR

Flooding

How to develop a territory with such level

of constraints

Costs

FreedomProtection

POPULATION WISHES

LANDSLIDE RISK MANAGEMENT AND MITIGATION

All the solutions have to be included in this global process

LAND-USE MANAGEMENT

SUSTAINABLE DEVELOPMENT

RISK RISK ASSESSMENT ASSESSMENT

&&MANAGEMENTMANAGEMENT

SOCIETALSOCIETALDEMANDSDEMANDS

POLITICALPOLITICALASPIRATIONSASPIRATIONS

REGULATIONSREGULATIONS

FINANCIALFINANCIALRESSOURCESRESSOURCES

RISKRISKANALYSISANALYSIS

OTHEROTHERCONSTRAINTSCONSTRAINTS

MITIGATION MEASURESMITIGATION MEASURESACTIONS ACTIONS –– REMEDIAL REMEDIAL

WORKSWORKS

ACCEPTABLE

SCIENTIFIC RESPONSIBILITY

Scientists vs decision-makers

Model - Past Model - futureUncertainty

LimitationsCommon languageImmediat answer

DecisionTime - Long term series

Scientific languageSuccess

Risk analysis - problems Risk management - solutions

fill the gap

feel the gap

CONCLUSIONS

-Do science you understand

-Go in the fiel / meet people they know-Help decision-makers they decide

Systemic / Intergrated based approach

You are the lonely ones who can fill the gap between the Nature and the Judge

therefore …

10-5

10-9

10-2 10-4

10-610-3

10-710-3

10-1

10-510-710-5

10-9

10-2 10-4

10-610-3

10-710-3

10-1

10-510-7

Do more science but speak less (or differently) about it

Fill the Gap !

You don’t only manage landslides !

You help people improving their life !

landslide risk analysis & assessment - unicaen · landslide risk analysis & assessment eric...

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