Les impacts morphodynamiques sur un cours d'eau soumis à un aménagement hydroélectrique à dérivation : le Rhône en Chautagne (France) / Morphodynamic impacts on a river affected by a hydro-electric diversion scheme : the Rhône in the Chautagne region of France

摘要

Although forecast by the National Company of the Rhône, the floods of February 1990, caused by the overflowing of the 'old Rhône', produced unusual afects on the Chautagne marsh. An hypothesis was formulated that movements of the bed of the old Rhône were responsible for this condition. This led the Syndicate of Defense of Embankments and Borders of the Upper Rhône to request a morphodynamic study, which is presented here in condensed manner. The hydroelectric diversion scheme has little effect on the transit of flood flows in the old Rhône but has stopped the transit of bed load, which had been left strongly reduced by the works completed upriver prior to the 20th century. Analysis of available data shows evidence of a lowering of the longitudinal profile, rendered complex by the fact that the Rhone's course is influenced by a morphology of fluvial braiding moderately affected by old dykes. Sediment transport is initiated by a flow of approximately 400 m3/s and occurs on average only three days per year. The bed degradation extends itself progressively through space whenever the flood discharge occurs, but with a reduced recurrence interval. The analysis demonstrates that the movement of coarse material will continue into the future. In order to maintain the flooding of the marsh, the water line for minimum discharge and the level of the water table in the old Rhône, civil engineering work is recommended. Its purpose is to minimize the transport that affects the final supply of bedload and to ensure a sustainable development of the floodplain.