Predicting grain size patterns and the propensity to accumulate fine particle deposits of restored floodplain channels (Rhône River)

International audienceWe report here a successful predictive approach of the adjustment of hydromorphological conditions in the first decade following works in a set of restored floodplain channels. We demonstrate that both (i) grain size patterns and (ii) fine sediment accumulation rates can be predicted using simple hydrologic and/or hydraulic descriptors (e.g. upstream overflow frequency, shear stress, back-flowing capacity), which reflect the control exerted by the geometry of floodplain channels on their flooding regime. These important and original results suggest that it is possible to quantify how changes in the geometry of floodplain channels can modify the grain size patterns and the quantity of in-channel fine particle deposits. Such empirical statistical relationships can be used to guide future restoration actions in the Rhône and other similar hydrosystems. For example, they would be helpful for managers wanting to design floodplain channel types that are infrequent or missing at the floodplain scale in order to maintain a high level of beta-diversity. On this basis, we will discuss the floodplain channel restoration strategies, which have been implemented along the Rhône until now (restoration of forms and not of processes), as well as future restoration options already programmed, with a special focus to the processes affecting the long term persistence of floodplain channels as aquatic habitats