Approches probabilistes de la prédétermination des crues de la normale à l'extrême

Probabilistic approaches of flood predetermination

Enshmg, Lthe, Inpg, Cnrs

Abstract

Since it is not possible to determine in a reasonable manner the value of the peak flood of a river, only a probabilistic approach may provide satisfactory results. Such an approach only has a meaning in a decision-making framework to design for example hydraulic facilities. Hence, to talk about a flood with a 1000 year return period does not mean that one makes the hypothesis that the hydrological conditions remain stable in the 1000 years to come, but it is the flood that has a probability of one in thousand of occuring in a given year.

These probabistic methods are based on historical flood data for the oldest, and on floods and precipitations for the more recent. The associated problems of risk and sampling are presented by means of examples. The GRADEX method allows to evaluate, under certain hypotheses, the floods with long return periods and the AGREGEE method relates that method to floods with shorter return periods.