Sediment transfers from settled rivers to margins

The occurrence of flash floods and dam failures in settled rivers promotes the intense erosion of the bed load and river banks which can lead to the formation of highly concentrated flows, such as hyperpycnal currents or mud flows. Such hazardous phenomena can have dramatic environmental and economical impacts, such as : overflows, the disappearance of fish spawning sites and the destruction of facilities on both onshore and offshore environments. They represent hence an important issue for the scientific community, especially at the Earth-Sea transition where significant transfers of sediments can control both the valley morphology and the margins stability with implications for the coastal line evolution. The description of such complex processes still lack of predictive models, gained from small-scaled experiments and numerical simulations, which represent an essential step for both land-use-planning and risk mitigation. This study deals with the modeling of highly-concentrated dam-break flows that travel along a horizontal transparent flume. Experiments are recorded with high speed video cameras, then analyzed using a software based on particle tracking velocimetry. After release, the front made of a particulate suspension of solid volume fraction closed to the packing state, travels at a quasi-constant speed whilst the rear sediment progressively from the base until the motion ceases. We present here a physical description which highlight the key parameters that control the flow dynamics as well as the deposit geometry.