Restoring the lateral connectivity of rivers by dismantling old protective structures: first results of a multi-year study on the Rhône

Abstract

On the Rhone, engineering work has been carried out to dismantle the old riverbank protection structures. Sharing hydraulic and ecological objectives, these restoration actions aim to promote the development of riparian communities closely related to the river. To assess the effects of these works on the vegetation of the alluvial margins, a monitoring program of the restored sites was initiated in 2017. By studying temporal variations in several environmental parameters (topographic and pedological) and numerous plant species sampled in quadrats, the structure and dynamics of riparian communities were characterized. The results show a progressive and coherent structuring of plant communities along the recreated topographic profiles. While the ecological gains of this restoration action appear undeniable in the short term, the unfolding of the ecological succession should quickly lead to the development of competitive species with high cover and exotics that could induce a certain homogenization of the communities. This case study illustrates the complexity of the restoration of highly anthropized hydrosystems and invites the deployment of more functional restoration actions, including the reactivation of the river's erosive capacities, associated with the solid transport of the coarse load and the mobility of the riverbed.