Benoît Carlier

In the upper reaches of Alpine valleys, the shaping of active channels appears mostly dependent upon hydroclimatic variability, as illustrated by the upper Guil River. In this valley, recent land-use changes have reduced the channel capacity of the Guil River, and increased the vulnerability of human installations to damage. In the frame of the implementation of a River Scheme and a Flood Prevention Action Program, we try to improve our knowledge of sediment transfers at the origin of disasters. Our analysis was carried after two high magnitude low frequency hydroclimatic events (1957, 2000). It is based on desk and field data, account for active-channel width and area, sinuosity and braiding indexes, engineering structures and their variation in space and time. We show the major role played by the Guil tributaries in supplying debris to zones with important assets. Finally, we discuss about the difficulty to implement efficient management tools at a local scale.

In the frame of SAMCO (ANR 12 SENV-0004) project designed for mountain hazard mitigation in a context of Climate Change, one of our purposes is to understand the hydro-geomorphological specificities of French Alpine catchments. Part of our study deals with a better assessment of the sediment transfers, and adjacent sediment supply (i.e. from hillslope to channel, and from tributaries to the trunk river) during seasonal meteorological events, and major event inducing floods and/or avalanches. Our research focuses on the Guil River catchment (Queyras, Southern French Alps), prone to catastrophic floods (June 1957 (> R.I. 100 yr), June 2000 (R.I. 30 yr)...) with serious damages to infrastructure and buildings located in the valley bottoms. Such floods are characterized by considerable sediment transport from debris flow prone tributaries to downvalley, together with strong hillslope-channel connectivity. The " schistes lustrés " bedrock is an aggravating factor that explai...

In mountainous areas, especially in large river catchments with torrential tributaries, the production and sediment transport significantly increase flood impacts in the valley bottoms. For a better understanding of Alpine river catchments considered as complex systems, we focused our research on the Guil River catchment (Queyras, Southern French Alps-317km 2). This catchment is prone to catastrophic summer floods (June 1957 (> R.I. 100 yr), June 2000 (R.I. 30 yr)...) characterized by considerable sediment transport from tributaries to downvalley, very much facilitated by strong hillslope-channel connectivity (≈12,000 m3 volume of sediment aggraded during the June 2000 flood event). During the last flood events, several infrastructures and buildings were seriously damaged. Most of them were located at confluences and, at specific reaches such as canyon reaches constrained by infrastructures. For risk mitigation some protection equipments were built after the 1957 event, but most ...

The Guil River catchment (Queyras, Southern French Alps) is prone to hydro-geomorphic hazards related to catastrophic floods, with an amplification of their impacts due to strong hillslope-channel connectivity such as in 1957 (> R.I. 100 yr), and more recently in 2000 (R.I. 30 yr). In both cases, the rainfall intensity, aggravated by pre-existing saturated soils, explained the immediate response of the fluvial system and the subsequent destabilisation of slopes. This resulted in serious damages to infrastructure and buildings in the valley bottom, mostly along some specific reaches and confluences with debris flow prone tributaries. After each event, new protective structures are built. One of the purposes of this study, undertaken in the frame of the SAMCO (ANR) project, was to understand the hydro-geomorphological functioning of this upper Alpine catchment in a context of hazards mitigation and sustainable management of sediment yield, transfer and deposition. To determine the ...