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Earthfill dams, and even all dams, are designed to withstand different factors (meteorological, seismic, and human), which might be responsible for their failure. Yet there is no such thing as zero risk, and the possibilities of failure exist. With a view to optimize the safety of downstream areas, dam failures by overtopping can be studied from a probabilistic point of view, in order to go further than a simple failure - non failure evaluation. Probability calculation of the failure, mainly with flood studies, is the first step. Then, in order to improve the prediction of the failure, the failure hydrograph is probabilized by its maximum discharge and the time this discharge needs to be reached. [ABSTRACT FROM AUTHOR]

There is a direct connection between the breach developed within a dam subjected to an overflow and the resulting flood. A normative model based on statistical studies has been developed in the province of Quebec to initialize the process of the flood: it predicts a breach width four times as long as the breach height and a maximal breach discharge that occurs in 30 min. This norm is applied for all the earth and rockfill dams without any consideration of their own particular characteristics. However, the prediction of the breach's characteristics is still uncertain, which explains that this norm is not over yet and is still the most reliable and secure process to use. A theoretical model is presented in this dissertation predicting the dam failure of the first earth and rockfill dam in Quebec using a bituminous core: Nemiscau-1 dam. Three potential damages have been analysed: potential planes of failure; fracturing of the bituminous core; surface erosion. The results are encouraging: the resulting hydrograph seems to predict the degradation of the dam more precisely and more faithfully than the normative model. The proposed model is more suited for hybrid dams than the safety standards of Hydro-Québec. [ABSTRACT FROM AUTHOR]