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The increasing focus on dam safety is a problem of major concern to technicians and entities responsible for designing, licensing, constructing and managing such structures. In spite of the growing experience in designing and building dams, as well as in using more appropriate materials, dam safety is increasingly an issue of debate among the international community. Dam owners, engineers and regulators who are responsible for the safety of groups of dams need to prioritize dam safety evaluations or funding for structural and non-structural risk reduction measures. Traditionally "downstream hazard" assessment, weighting schemes, and judgment have been used for this purpose. However, these have significant weaknesses and cannot be relied on to provide the basis for an effective and efficient program for managing and reducing dam safety risks. Structural risk reduction measures are developed and costed for each dam safety issue which does not satisfy either the engineering standards or the risk-based criteria. Structural measures should be developed to a reconnaissance level as logically separable construction packages. A single measure is usually developed rather than evaluating alternatives measures during the PRA since the resolution of the evaluation may not be sufficient for a meanngful comparison. For similar reasons, only complete fixes (i.e. to bring a dam to an engineering standards level) rather than partial fixes are typically evaluated in the PRA. The benefits of early warning systems (EWSs) can be evaluated in an indicative manner based on reductions in estimated life loss due to dam failure, as the result of assumed increases in warning time. In contrast, structural measures usually achieve life loss risk reductions by lowering the probability of dam failure. Event tree risk models should be adapted to represent each risk reduction measure. Results for each risk reduction measure can be presented in the same way as for existing dams and in other ways to convey information about the estimated amount of risk reduction. Examples of risk reduction information include the following:
A useful initial basis for prioritizing risk reduction measures is maximizing the rate of risk reduction. Such a criterion can be applied to the life safety, economic/financial or probability aspects of dam safety risk. The resulting prioritization can be used as the basis for development of a Dam Safety Improvement Program (DSIP). The rate of risk reduction can be maximized by ranking measures in ascending order of cost effectiveness. An example of a measure of cost effectiveness for life safety risk reduction is cost per (statistical) life saved. |
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