Debris-flows mobilize high sediment loads and are often responsible for most of the sediment yield from upland headwaters and may endanger the safety of life and infrastructure in the vicinity of torrent channels. Two very active debris-flow torrents with different physiographic settings have been equipped in the French Alps, the Manival Torrent (3.6 km²) and the Réal Torrent (2.3 km²). At these two sites, debris-flow monitoring systems are based on a combination of different techniques involving rain gauges, soil vibrations and flow elevation measurements and high-resolution/frequency imagery acquisition. Only flash floods with bed load transport have been observed on the Manival Torrent. Conversely, in spring/summer 2011 four meteorological events triggered debris flows on the Réal Torrent. Most of the debris fronts deposited immediately in the upstream part of the channel. Only one debris-flow propagated from the sediment source area to the basin’s outlet. A 1.8 m high debris front propagated with a mean velocity of about 3 m s-1. Its volume was 4,400 m3 upstream and it increased because of bed erosion. The debris flow reached 6,100 m3 in the middle part of the basin and then decreased slightly further downstream (8,600 m3). These measurements highlight the interaction between the debris flow and the torrent channel in the first part of the basin. These results are in accordance with previous sediment budgets estimated for the debris flows which occurred in 2009 and 2010.