Retour d'expérience sur les crues des 6 et 7 octobre 2014 à Montpellier-Grabels (Hérault, France) : caractéristiques hydro-météorologiques et contexte historique de l'épisode

Abstract

In the night of 6-7th October 2014, static storm cells stood over the North of Montpellier, and poured up to 260 mm of rain in 4 hours. Due to previous saturation of the soils, this rain caused major floods on the Mosson and Lez watersheds. The biggest damages occurred in Grabels where a part of the city was submerged by the Rieu Massel (a Mosson river tributary). The water level reached up to 1.5 m in some houses despite a flood retention dam upstream. In this paper we present the results of the post flood survey of this event, dealing with 15 peak discharge estimations on ungauged streams. Then we compare these peak discharge to those obtained from other recent post-flood surveys in South of France for the one hand, to those derived from regional formulas on the other hand. The relative frequency of such events during the period 1970-2014 suggests that the estimations of intense rainfalls and critical peak flows are underestimated in Montpellier area, and should be updated.

Keywords

• return period
• Mediterranean flood
• extreme event
• regional estimation