Consequences of the extreme flood of October 2, 2020 in the Roya Valley (Alpes Maritimes) on transport, and communication networks: lessons for reconstruction

On October 2, 2020, the storm “Alex” has favored the triggering of very intense rainfall in the coastal valleys of the Alpes-Maritimes, including that of the Roya, which have caused many devastating hydro-geomorphological processes, as flash floods and landslides. The destruction, which affected modern and old infrastructures, was considerable, with dramatic social and economic consequences. All the bridges were destroyed between Tende and Breil-sur-Roya municipalities, while the railroad was cut in several places. Entire sections of roads were destroyed in the valley, as well as large portions of the electrical, water supply and fiber optic networks. The isolation of the villages lasted for several months, and the reconstruction is not complete.
Driven by researchers at Sorbonne University, a research group, entitled “Story: risk to society in the Roya basin: multi-temporal and transdisciplinary analysis, from the slopes to the sea”, was formed, with the objective of associating specialists in geosciences and humanities in order to (i) analyze the October 2020 disaster, (ii) reconstruct the history of risks, their management and their perception, and (iii) elaborate, together with local actors, recommendations for the reconstruction of their territory, with the objective of reducing the impacts of future extreme events.
This paper explains the preliminary results of our first field surveys and data analyses. The exceptional character of the flood is confirmed by the fact that all the bridges between Breil-sur-Roya and Tende were destroyed, which had never happened in the past. An aggravating factor was the construction in the 20th century of embankment roads in the riverbed. The railroad was more affected by rockfalls and landslides induced by the hydro-climatic episode.
The mapping of the destroyed sectors leads us to make recommendations that are sometimes in contradiction with the directives retained by the planning departments in their very rapid reconstruction of infrastructures. Finally, we discuss the difficulties in reconciling the perceptions of the different actors, the necessary time of research not always easy to articulate with the urgency of reconstruction and the vital need to open up sectors that otherwise risk being permanently abandoned by the populations.