Conséquences d'une chasse de barrage sur la concentration et les flux de sédiments en suspension et de contaminants associés dans le Rhône

Abstract

International audienceThe increasing need for energy and fluvial transport due to industrialization during the last century resulted in the construction of infrastructures along rivers, as dams or sluices. Thus, nineteen hydroelectrical dams have been built along the Rhône River since 1950. To improve the production of electricity and avoid problems due to sediment storage within these infrastructures, dam flushing operations are organized periodically. Investigations were conducted in the upper Rhône River to evaluate the impacts of dam flushing operations on suspended sediment and associated contaminants (metals, organic contaminants and radionuclides) concentrations and fluxes. Results demonstrated that suspended sediment fluxes were very high in the vicinity of the dam, but similar to fluxes registered during flood events at other stations (approx. 100km downstream). For several contaminants (Cu, Hg, PCB101...), concentrations were lower during dam flushing periods than during flood events or normal flow condition. This difference could be explained by particulate organic carbon concentrations that were also lower and the variation of particle size. Concentration of these elements tends to increase with distance from upstream dams. Finally, dam flushing fluxes of contaminants were similar to flood-related fluxes and represent a non-negligible part of the annual fluxes