Deposition and erosion of fines sediments in alpine rivers – DEAR

During the DEAR project, processes associated with fine sediments will be investigated through the combination of laboratory experiments (HHLab, INRAE Lyon and EDF Chatou), field measurements (Arc-Isère and Galabre river systems), and numerical modelling (1D and 2D) and at three complementary spatial and temporal scales: from (i) local (~meters) and instantaneous (~seconds) scale, (ii) reach scale (~kilometers) on event scale periods (~days to months), to (iii) river scale (~100km) on long-term periods (decades).

Two papers ont the fine sediment flux analyse following the Arc River dam flushing and on the impact of bed surface on bedload transport are published. Two papers on the deposit dynamics using image analyse are in preparation.

Thanks to the collaboration between the two French public research centres (INRAE, IGE) and the private company EDF involved in the river management of the Arc-Isère river system, a methodological guide will include recommendations on river management to limit sediment deposits on gravel bars and reduce flood risk. This guide will be designed for operational users and control authorities.

Perret, E., Berni, C., & Camenen, B.(2020) How does the bed surface impact low-magnitude bedload transport over gravel-bed rivers? Earth Surface Processes & Landform, 45(5):1181-1197. doi: 10.1002/esp.4792
Antoine, G., Camenen, B., Jodeau, M., Némery, J. & Esteves M. (2020). Downstream erosion and deposition dynamics of fine suspended sediments due to dam flushing. J. Hydrology. doi: 10.1016/j.jhydrol.2020.124763

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).