A numerical model based on the 3D shallow water equations is set up for a 90° angle open channel confluence. The model is first calibrated and validated using experimental data by (Shumate, 1998). Then a series of numerical simulations is carried out, systematically increasing the friction coefficient, in order to investigate the impact of hydraulic resistance on the flow features in an open channel confluence. The properties of the separation zone (width and length) are found to be substantially altered by the hydraulic resistance. The hydrodynamic processes are analysed zooming in onto lateral momentum fluxes
