Sediment Dynamics and Channel Adjustments Following Torrential Floods in an Upper Alpine Valley (Guil River, Southern French Alps)

International audienceIn the upper reaches of Alpine valleys, the shaping of active channels appears mostlydependent 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 thevulnerability of human installations to damage. In the frame of the implementation of a RiverScheme and a Flood Prevention Action Program, we try to improve our knowledge ofsediment transfers at the origin of disasters. Our analysis was carried after two high magnitudelow frequency hydroclimatic events (1957, 2000). It is based on desk and field data, accountfor active-channel width and area, sinuosity and braiding indexes, engineering structures andtheir variation in space and time. We show the major role played by the Guil tributaries insupplying debris to zones with important assets. Finally, we discuss about the difficulty toimplement efficient management tools at a local scale