Sediment transport during a flushing flow in the lower Ebro River

This study describes the sediment transport which occurred during the double peak flushing flow of November 2003 in the gravel-bedded lower Ebro River (northeast Spain). The experimental release was designed and undertaken to control the excess of aquatic vegetation in the river channel downstream from dams. Macrophytes cause problems to several water users, especially to the hydroelectric and the nuclear power plants located in the vicinity of the river. Observations show a distinct pattern of sediment transport between the two flood peaks owing to the particular channel conditions (i.e. exhaustion of fine sediment and removal of the surface layer). Gravel was mobilized during the flood. However, since bed load rates were low and the flood duration was short, no incision was caused in the river bed. In spite of that, large quantities of macrophytes were removed. The combination of hydraulic and sedimentary parameters during the designed flood maximized the ecological and management benefits of the experimental release without significant adverse geomorphological impacts on the river channel.