Assessment of risk mitigation measures effectiveness: application to natural risks in mountains

International audienceMitigation actions against natural risks in mountains are basedboth on non-structural measures such as land-use control andon structural measures such as civil engineering protectionworks. To prevent or, at least, limit risks, protection works playan essential part in reducing both the causes and effects ofphenomena. The analysis of their effectiveness is an essentialstage of the risk management process. Decision support toolsare needed to take into account their structural state andfunctional effects on phenomena (stopping, braking, guiding,diverting etc.) but also their economic efficiency, comparingtheir construction and maintenance costs to direct and indirecteconomic losses reduction. The concepts of dependabilityanalysis, functional analysis and failure modes and effectsanalysis (FMEA), already used in civil engineering especially forhydraulic dams, are extended to assess and evaluate thestructural and functional effectiveness of protection works. Themethodology elicits the expert reasoning process and evaluatesthe danger level of the protection works. It uses of bothdependability analysis, an emerging technique for naturalhazards domain and uncertainty theories such as fuzzy logics,possibility theory to take into account the imperfection ofinformation. Fuzzy intervals and possibility distributions areused to assess the indicators that describe the possible failuresand the performance level of disposals. Indicators are definedas information formalised so as to make its use repeatable andreproducible. They provide indications on a functionperformance. Their implementation is based first on a systemdescription and on the proposal of indicators related tostructural and functional failure modes. The concept of risk, theconditions and limits of cost-benefit analysis are discussed withregard to imperfect of knowledge about frequency, physicaleffects on phenomena, vulnerability curves and economicvaluations of losses