Extreme floods in the Roya valley (Alpes Maritimes): return times of the order of half a millennium. A challenge for societies.
Eric FOUACHE, UFR de Géographie et d'aménagement Sorbonne Université, UR Médiations, France
Stéphane DESRUELLES, UFR de Géographie et d'aménagement Sorbonne Université, UR Médiations, France
Christian GORINI, Sorbonne Université ISTEP UMR 7193, France
Nicoletta BIANCHI, Istituto Italiano di Archeologia Sperimentale (IIAS), Italy
Adrien MARCHIEL, Institut Polytechnique UniLaSalle., France
On October 2, 2020, the passage of storm Alex triggered very intense rainfall in the coastal valleys of the Alpes-Maritimes, particularly the Roya, which caused numerous devastating hydro-geomorphological processes, mainly floods and landslides. The destruction, which affected modern and old infrastructures, was considerable, with dramatic social and economic consequences. The processes have also unearthed archaeological remains dating from the Bronze Age to the modern era. Several months later many villages remain isolated. Meteorological analyses confirm the exceptional character of this Mediterranean episode, while marine sedimentary records made in the deltas of the Var and Roya rivers crossed with C14 dating of ancient torrential deposits indicate a return time of about half a millennium. In order to study this event, we have launched an interdisciplinary program entitled STORY: "Risks and societies in the Roya basin: multidisciplinary and multi-temporal analysis, from the slopes to the sea", aiming (i) to accomplish a transdisciplinary analysis of the October 2020 disaster, (ii) to reconstruct the history of risks, their management and their perception and (iii) to elaborate, with the local actors, recommendations for the reconstruction of their territory. The major difficulty in the case of the Roya is that the reactivation of the entire post-glacial active band has upset the geometry of the river's major bed compared to what it was before Storm Alex.This major modification implies that before defining the new risk zones and deciding on the reconstruction of the infrastructures, the impact of the floods recorded in the past should be modeled according to this new geometry of the bed. Moreover, in the context of global warming, it is not excluded that we observe a higher recurrence of events such as storm Alex. We present the preliminary results of our program and discuss the difficulties in reconciling the perceptions of the various actors,
Keywords: Holocene|extreme flooding|global change|geoarchaeology
A103616EF