A lot of existing hydroelectric developments do not meet current spillway capacity design standards. Statistics compiled indicate this is one of the main causes of dam failure. It is not, however, necessary to continually increase discharge capacity to maintain an acceptable risk level at a given development. In hydroelectric systems with large reservoirs, the very design of the many structures controlling the reservoirs and the introduction of the concept of fuse-plug spillways offer attractive alternative solutions. The digital tools required for a real impact and risk analysis were developed. This paper describes their use in a preliminary study of the La Grande 3 reservoir in Quebec. Key words: dams, safety, failure flow.[Journal translation]