Application de la méthode du gradex à des grands bassins versants cas de la Loire au Bec d'Allier (32 000 km²)

Gradex method application to large watersheds: the case of the Loire river at Bec d'Allier (32,000 km²)

¹ Stagiaires de l'Ecole Nationale Supérieure d'Hydraulique et de Mécanique de Grenoble
² Ecole Nationale Supérieure d'Hydraulique et de Mécanique de Grenoble
³ Equipe Pluridisciplinaire Plan Loire Grandeur Nature, Orléans

Abstract

The probabilistic Gradex method was applied to both watersheds of the Loire River at Nevers and the Allier River at Veurdre, and then to the confluence of these rivers at Givry, in order to define a strategy for reducing inundation risks due to more-than-50-year floods on the medium Loire, which is a priority of the Plan Loire Grandeur Nature.

The present study is mostly based on daily precipitation values measured by a 108 pluviometer net from 1949 to 1996, as well as discharge chronicles. It also benefits from precious historical data of precipitation events, and particularly of the discharge data of floods that have been observed and reconstituted since 1856, especially the major ones in the end of the 19th and the beginning of the 20th centuries.

This study, beyond the usual Gradex method application field, gave results in coherence with other approaches.

A few application examples to big sized watersheds show the interest of studying the spatial rain distribution and of detecting the occurrence of intense and generalized rainfalls, towards the calculation feasibility.