Landslide Risk Analysis & Assessment

Transcription

1 Landslide Risk Analysis & Assessment Eric LEROI PAU / ROQUEVAIRE France +33 (0) e.leroi@wanadoo.fr Mountain Risks Research And Training Network & FORM-OSE Post-Graduate Training School Intensive Course - Barcelona 1 st 4 th September 2008

2 Fairly good knowledge of phenomenon and their mecanisms High capability of calculation and modelling

3 What are you going to do with all this science?! saving the world?! not sure!

4 THE PARADOXE OF THE RISK The more we know The more efficient the technics is the higher the risk seems to be! Who / what is responsible for this situation? Science - Climate change Risk Management God?

5 R 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 T Political Aspirations Budget Other constraints Social demands Regulation Risk acceptance criteria DANGER CHARACTERISATION HAZARD ANALYSIS RISK ANALYSIS RISK EVALUATION Values Judgement RISK MITIGATION CONTROL OPTIONS & CONTROL PLAN Monitor and Review With landslide risk assessment and management, you enter a new world you meet the Human Being! and even before within risk analysis.

6 Landslide Risk Analysis & Assessment Single given landslide for protection or evacuation Ranking areas prone to landslides for risk mapping Tools, financial ressources, available time are different

7 Landslide Risk Analysis & Assessment Ranking areas vs risk level Assessing risk re acceptance criteria

8 Landslide Risk Analysis & Assessment Ranking areas vs risk level Assessing risk re acceptance criteria

9 Landslide Risk Analysis What? Slope Lithology Volume Water Triggers Vulnerability probability When? To Where? From Where? What? Classical approach from Earth sciences and modelling

10 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

11 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.

12 INTERDEPENDENCE OF ENVIRONMENTS CONSTRUCTED ENVIRONMENT NATURAL ENVIRONMENT HUMAN ENVIRONMENT

13 Natural environment Reaction Action Interactions Reaction Constructed environment Human environment Reaction

14 What is the principle of action / reaction?

15 ACTION

16 REACTION?!

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24 20 30 years later Landslides!

25 YESTERDAY Agriculture control of water.

26 Today excessive earth works Slopes are urbanized Natural drains blocked water no more managed.

27 MENTON Winter landslides 10 M of remedial works

28 History of the land use and land occupancy as well as the territory 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 Risk maps Which scale?

29 1/ / / /1.000? Which scale? Which level? Which mapping? Preliminary Advanced Detailed Phenomenon Susceptibility Hazard Risk

30 INFORMATION 1/ Basic 1/1 High Sophisticated LAND PLANNING Over estimation : socio-economical consequences Under estimation : responsibility

31 Results Methods available /required Data available /required Type of phenomenon Surface to be covered Budget available /required? Scale Level Mapping Choice Objectives Information Land-planning Protection Constraints Consequences None Recommandations Statutory obligations Expected victims None 1 victim >100 victims

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

33 Surface to be covered Budget available Information Land-planning / Future Protection / Existing EAR - population - dwellings -life-lines - Environment Methods available Data available Type of phenomenon? Objectives Constraints Consequences Scale Level Mapping

34 1/ / / /1.000 Methods available Data Preliminary available Type Advanced of phenomenon Detailed Phenomenon Susceptibility Hazard Risk Surface to be covered Budget available Scale Level Mapping Information Land-planning / Future Protection / Existing EAR - population - dwellings -life-lines - Environment Objectives Constraints Consequences

35 1/ / / /1.000 Surface to be covered Budget available Information Land-planning / Future Protection / Existing EAR - population - dwellings -life-lines - Environment Methods available Data Preliminary available Type Advanced of phenomenon Detailed Phenomenon Susceptibility Hazard Risk Scale Level Mapping Objectives Constraints Consequences None Recommandations Statutory obligations -Negligible ( ) -<10% ( ) -1 owner ( ) -Group of owners ( ) -

36 1/ / / /1.000 Methods available Data Preliminary available Type Advance of phenomenon Detailed Surface to be covered Budget available Information Land-planning / Future Protection / Existing EAR - population - dwellings -life-lines - Environment Objectives Constraints Consequences Phenomenon Susceptibility Hazard Risk Scale Level Mapping 1 victim 2-5 victims 5-10 victims victims >100 victims

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38 MAPPING

39 Question of uncertainty : a scientific problem For the judge, no uncertainty: responsibility and decision For decision-maker, no uncertainty : decision and action Uncertainty / Principle of precaution Mapping choice (scale, level,type) : A choice on how far you can make mistakes that are supposed to be accepted by population, based on the objectives and consequences of the maps Uncertainty is transformed in principle of precaution Being over-conservative is not acceptable for the society

40 Landslide Risk Analysis & Assessment Ranking areas vs risk level Assessing risk re acceptance criteria

41 Landslide Risk Assessment Defines the way you use your risk map : -prohibiting construction -Protecting stakes

42 Existing buildings New dwellings

43 Which solution for existing buildings?

44 For each case, solutions are numerous: Technical choice DO NOTHING NET EARTH FENCE EVACUATION

45 What about the safety behing the wall? PROTECTION

46 PROTECTION

47 PROTECTION oversizing Impact Cost

48 PROTECTION Optimization Résidual Risk P(t)

49 NEED FOR CRITERIA The objectives of protection and development have to be clearly defined, both in term of: -Acceptable and tolerable risk -Acceptable cost 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 Societal choice

50 Risk Assessment criteria Tolerable risk / Acceptable risk Calculated risk is evaluated against acceptance criteria ; They may be related to: Loss of life (individual risk, societal risk, total risk ) Financial value (cost to save a life, cost-benefit ratio ) Socio-environnemental value ( frequency of accidents ) Should involve owner / regulator / professionals / population Iterative process with risk analysis because of uncertainty

51 Risk Assessment criteria Tolerable Risk : general principles (IUGS-1997) Incremental risk from hazard should be negligible ALARP (As Low As Reasonably Practicable) principle is generaly used If possibility of loss of life is high, probability of phenomenon should be low Higher risk than acceptable will be tolerated if control or reduction of 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

52 NEED FOR CRITERIA The objectives of protection and development can be defined : In a qualitative way : red = no building In a quantitative way : 10-4 is an acceptable risk It s better to define the objectives of protection and development in a quantitative way, else: - Problem of design / studies - Problem of responsibility

53 Risk Assessment criteria Societal Risk (SR): Principles 10-4 F 10-5 Untolerable 10-6 Tolerable 10-7 Acceptable ALARP? N

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55 Risk Assessment criteria Societal Risk (SR): Principles 10-4 F «Normal» life 10-5 Untolerable 10-6 Tolerable 10-7 Acceptable ALARP? N

56 Risk Assessment criteria Societal Risk (SR): Examples Hong Kong Special Administrative Region Government

57 Risk Assessment criteria Societal Risk (SR): Principles 10-4 F «Normal»life 10-5 Untolerable Tolerable Acceptable ALARP ? N

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

59 Flooding Environnemental Protections (Loi Littoral Law, ZNIEFF ) PPR + Seismic risk How to develop a territory with such level of constraints Un territoire contraint

60 POPULATION WISHES Protection Freedom Costs

61 LANDSLIDE RISK MANAGEMENT AND MITIGATION LAND-USE MANAGEMENT SUSTAINABLE DEVELOPMENT All the solutions have to be included in this global process

62 RISK ANALYSIS OTHER CONSTRAINTS SOCIETAL DEMANDS REGULATIONS POLITICAL ASPIRATIONS RISK ASSESSMENT & MANAGEMENT FINANCIAL RESSOURCES MITIGATION MEASURES ACTIONS REMEDIAL WORKS ACCEPTABLE

63 SCIENTIFIC RESPONSIBILITY Scientists vs decision-makers feel the gap Model - Past Uncertainty Time - Long term series Scientific language Success Risk analysis - problems Model - future Decision Immediat answer Common language Limitations Risk management - solutions fill the gap

64 CONCLUSIONS -Do science -Go in the fiel / meet people -Help decision-makers you understand they know they decide Systemic / Intergrated based approach You are the lonely ones who can fill the gap between the Nature and the Judge therefore

65 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!