Risk assessment required in the framework of new french regulation on dams. Methodology developped by INERIS

Abstract : The new French dam safety regulation classifies each dam in four classes depending on its height and the volume of water it stores. The first two classes require each owner to establish a safety report for an authority review. A main objective of this report is to demonstrate that all hazardous scenarios have been taken into account by the dam owner in assessing the risk level and also that sufficient safety measures have been specified to reach a global risk as low as reasonably possible. First, considering all existing data and characteristics of the dam, the owner has to carry out a risk analysis to identify all failure modes that may occur on dam structure and hydraulic equipment. Every potential accident is then characterised in terms of severity of consequences and annual occurrence probability. The severity level is assessed quantitatively or qualitatively, using a combination of maps representing the effects of the flood waves and the Population At Risks. The probability is assessed using a semi-quantitative method analyzing all scenarios and safety measures involved in prevention and protection: the bow-tie approach. This cross analysis implements an iterative approach to highlight complementary measures and recommendations and therefore enhance global safety level.