Influence of tributary widening on morphology and hydraulic variability in confluence zones

In the aim of assessing the potential of tributary widening with respect to river rehabilitation in fluvial systems, attention is focused on the effects of tributary widening on the morphodynamic processes of confluence zones. Systematic tests were performed in a confluence flume where the confluent channels are connected with an angle of 90° and the main channel is 0.50 m wide. Three different widening of the tributary are compared to a reference configuration with a constant tributary width of 0.15 m for different discharge scenarios. All experiments were performed with mobile bed conditions and poorly sorted sediments supplied in the tributary channel and run until equilibrium conditions. Water levels, morphology and sediment size distribution were measured. Local widening of the tributary is shown to increase the variability of flow depth, flow velocity and particle size distribution, which enhances the ecological value of confluence zones without reducing the conveyance capacity of a given network.