Flood scouring and groundwater supply in rehabilitated side-channels of the Rhone River, France: sedimentation and aquatic vegetation responses.

Abstract

The Rhone River was impacted by the construction of submersible embankments to improve navigation at the end of the 19 th century, and by the completion of hydroelectric schemes during the 20 th century. These impacts in combination with side-channel terrestrialization have led to the disappearance of the water bodies. Returning the ecosystems back to their pristine conditions is no longer feasible. The presented rehabilitation experiments aimed to regress the ecological succession and to increase biodiversity within and between 3 side-channels that were terrestrialized. Two were designed to be flood scoured, one having an additional supply of groundwater, the other being connected to the river at both ends by embankment opening. The third cannot be scoured by floods because of upstream constructions, and has river backflow through a downstream connection. The 5 years monitoring of water physico-chemistry, sediment regime and aquatic vegetation demonstrates the expected differences between the 3 rehabilitated side-channels. However, the expected sustainability resulting from flood scouring needs to be assessed through a longer term study.