A probability-based methodology to evaluate quantitatively and systematically the overtopping risk of dams is formulated. This study considers mainly the overtopping induced by occurrences of flood and wind. Risk models for overtopping consist of fault tree analysis and random process modelling of the flood, wind, and other geophysical forces. A load combination model is established to account for the combined effects resulting from concurrence of flood and wind. A complete procedure for evaluating the risk of overtopping induced by flood and wind including a detailed uncertainty analysis of relevant parameters is presented. The methodology can be generalized to consider other conditions affecting dam safety.;A medium sized earth dam located in northern Illinois is used as an example to demonstrate how to evaluate the risk of overtopping over a given period of time interval using the proposed risk model and procedure. Overtopping risk evaluated using the normal pool level of the reservoir together with an inflow flood generated by a 24-hour rainfall, which is the current practice of the U.S. dam safety inspection program, is found to be conservative.;Four risk computation techniques are studied and compared; namely, direct integration method, Monte Carlo simulation method, mean-value first-order second-moment method, and advanced first-order second-moment method. The advanced first-order second-moment method, which linearizes the Taylor series expansion of the performance function at the failure point, and utilizes the first and second moments of the component variables, is shown to be the preferred one at present for risk evaluation of dams.
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