Monitoring debris flow propagation in steep erodible channels

Abstract

Debris flows mobilize high sediment loads especially during intense rainfall events. The volume of these surges is known to dramatically grow during propagation by scouring of the unconsolidated sediment stored in the channel before the event. The current prediction tools used by engineers to manage debris flow hazards are mostly based on empirical relationships with a high level of uncertainty. This situation arises in particular because of our insufficient understanding of interactions between the flow and the erodible bed of the torrent. In order to address this issue, field monitoring stations were deployed in 2010 in the Manival and the Real Torrents, two very active sites in the French Alps. Several stations were installed in different locations along the same torrent to investigate the spatial variability of the measured parameters. Each station was equipped with rain gauges, flow stage sensors, set of geophones and camera. The collected information allows developing a data base including the rainfall duration-intensity-volume, the flow depth, the front velocity and the surge volume. The objective is to characterize the changing nature of the debris-flow properties along the torrents and then to analyse the effect of channel conditions on debris-flow scouring.