Benoit Carlier

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

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.