Dam Failure Risk: Its Definition and Impact on Safety Assessment of Dam Structures

The dam structure is typical of facilities which are built to withstand unfavorable natural conditions. Of the 30 000 recorded dams worldwide, only a few are reported in any given year to fail. Structures must now meet design standards intended to make dams withstand extreme phenomena and disasters as damaging as maximum probable flood (MPF). New facilities are therefore safer. The existing facilities also have to conform to the new standards. Risk analysis is a new approach that has become more frequently used the last few years to assess the safety of dam facilities and to establish a priority classification which would make these facilities conform to the recently established standards. The failure of the dyke Cut-away in Saguenay (Canada), the study case referred to in this paper, shows the limits of conventional risk analysis methods. The latter would not clearly detect the dyke’s critical state; other methods of risk qualification are therefore proposed. These methods disclose supplementary aspects of the safety of the construction but they do not necessarily integrate hazards and consequences. The application of these methods to the identified objectives in our paper gives a synthesis of the risks posed by an unsafe construction. When viewed jointly, the methods and synthesis suggest the most effective ways to minimize those risks.