A dataset on physico-chemical hyporheic variables in the Selune River: Towards understanding the impact of dam removal on riverbed clogging processes

This article presents field measurements that document the physical and chemical response of riverbeds to critical hydrological and sedimentary forcing in the Selune River (France). The river flows into the bay of Mont Saint-Michel and thus impacts numerous economic activities and the spawning of several key species such as Atlantic salmon and lamprey. To restore the hydro-sedimentary continuity of the river, two dams are currently being removed. Significant changes in the stream flow regime, stream-aquifer exchanges and sediment transport are expected, hence the monitoring campaign. A network autonomous sensor (water level, temperature, conductivity, oxygen and pressure differential) was installed on 18 October 2021 at various depths in the riverbed and the river for a one-year period. This was to continuously record variations in the main physico-chemical variables and relate them to surface processes. To assess the impact of dam removal on these variables, two measurement sites were chosen: one upstream of the dams where flow conditions remained stable, and another downstream of the dams where a large amount of fine sediment has been released. This original data can be used to determine the biogeochemical functioning of the hyporheic zone and its coupling with dynamical flow and sedimentary processes.