Some Remarks on Practice of Flood Frequency and Risk Analysis by the Federal Energy Regulatory Commission

The Federal Energy Regulatory Commission, formerly the Federal Power Commission, has been in dam safety regulation since 1920. As of October 1, 1985, there were about 2,050 dams under our jurisdiction. Almost all of our spillway inflow design floods creep higher and higher with passing years. Mathematical probability methods provide no guidance to the shape and magnitude of the hydrographs of rare floods which would be substantially above the measured data. Risk analysis should include the probability of engineering, administrative, or other human error. Therefore, we require that the adequacy of both new and existing dams be evaluated by considering the hazard potential which would result from failure of the project works during flood flows. If structural failure would present a hazard to human life or cause significant property damage, the dam must withstand the loading or overtopping which may occur from a flood up to the probable maximum (risk analysis that involves loss of life is not permitted). We do in most cases, allow the dam owner to use risk analysis, if the failure will not cause loss of life or significant property damage.