Engineered alpine rivers are often characterised by alternated bar systems and substantial sediment transport, particularly of fine sediments (clay, silts and sands). A current problem is the gravel bar aggradation due to successive deposits of fine materials and the growth of riparian vegetation. Such evolution can increase the flood risk in mid and long-term. Many restoration projects were recently financed but they are often limited to mechanical operations and reprofiling of gravel bars. Such projects are very expensive and their sustainability is not guaranteed. The purpose of this project is to study the fine sediment dynamics (erosion and deposition) for typical hydrological events. In particular, we will try to quantify which part of the stocks in the riverbed or in the watershed contributes predominantly on the fluxes measured downstream. Specifically on the river stocks, we will differentiate surface deposits that can be directly resuspended by the flow from stocks infiltrated in the bed matrix that can be resuspended thanks to bank erosion or mobilisation of the armoured layer. The impact of hydrology will be studied by differentiating dam flushing event, natural floods, and the snow-melt period. A major effort will be made on the effects of gravel bar geometry and their different features on the fine sediment dynamics. The study will be carried out at different temporal and spatial scales, from local (instantaneous processes), to a few kilometer reach (processes on the event scale) to the whole river system (long-term processes, i.e. decades), coupling field and laboratory experiments with the use of 1D and 2D numerical modelling. The final objective is to be able to reproduce and predict in mid and long terms the fine sediments dynamics including effects of vegetation, unsteady flow (bar covering and uncovering). Thanks to this project, tools and recommendations will be suggested for a better management of alpine rivers and to limit the fine sediment deposits on gravel bars. This project will be carried out with the help of two academic partners (Irstea and IGE) and an industrial partner (EDF) with the support of local river managers (SPM, SISARC, SIMBHI).
All the information about this project is available on the following website:
