Mouvements de masse et torrentialité : cas du Tuébi et de la haute-Tinée, Alpes-Maritimes (France)/Mass movements and torrential activity: two typical examples in the French Maritime Alps: Tuébi and Upper Tinée valleys

摘要

Abstract The extreme manifestations of torrential activity sometimes observed along some reaches of mountain rivers are commonly due to sediment inputs by feeder torrents but even more by inputs from hillslope mass movements. This relationship is illustrated by two typical examples of torrents on the steep, high-relief setting of the Alpes-Maritimes in southeastern France. The Tuébi has been characterized, in historic times, by a considerable increase in its bedload and by morphodynamic activation of its channel as a result of the progressive gully erosion of a major ancient feeder landslide located a few kilometers upstream. The Upper Tinée exhibits a channel overfilled by alluvium derived from the erosion of the rockslide of the Pra. Torrential reworking of the stream bed fill undermines the efficiency of a sediment dam and an underground tunnel constructed so as to minimize the flood hazards liable to be caused by another mass movement, the megalandslide of La Clapière situated downstream and capable of blocking the valley. A few recent floods have clearly highlighted the inadequacy of the sediment dam, incapable of stopping boulders that are liable to damage houses and infrastuctures.