Effects of tributary floodplain on obtuse-angle bifurcation hydrodynamics

Compound-channel tributary river bifurcations are a widespread occurrence across many watersheds. The complex hydrodynamics of these bifurcations are vital for the morphological evolution of the channel and fish migration.Alaboratory-scale study was conducted to investigate two distinct bifurcation scenarios: with and without a tributary floodplain. An analysis of experimental data on three-dimensional velocity and turbulence indicated the floodplain predominantly influenced the tributary’s hydrodynamics. Near the tributary entrance, as the floodplain mainly occupies the separation zone, it had little impact on the tributary primary velocity. However, the floodplain led to a more pronounced flow curvature and contracted the tributary near the bed. In turn, this amplified the secondary motion, enhancing the transport of higher-velocity flows to the floodplain’s corner. The upwelling from the intensified secondary motion penetrated the separation zone, thereby promoting mixing. Downstream, the tributary exhibited hydrodynamic characteristics typical of a compound channel, with transverse flow dominating mixing.