High-resolution hydro-sediment-morphodynamic modelling of a meandering river reach with mid-channel bars on multiyear timescales: A case study of Shashi Reach in Middle Yangtze River

Meandering river reach with mid-channel bars is identified as one of the most prevailing planform configurations of the world’s largest rivers, in which the occurrence of frequently dominant branch shift poses huge obstacles to navigation. Previous numerical studies have mostly focused on either short-period reproduction or a single event of dominant channel transitions. Here a computationally efficient two-dimensional hydro-sediment-morphodynamic model is successfully applied to investigate frequent events of dominant channel shift in a typical meandering river reach in Shashi Reach of the Middle Yangtze River (MYR). Particular attention is paid to how the anthropogenic-influenced bar-channel interaction affects the shift of the dominant branch. The results reveal that the model performs well in reproducing key hydro-sediment-morphology factors, in terms of depth-averaged velocity, suspended sediment concentration, annual erosion rate, bar morphology, and water diversion ratios. These have led to the successive numerical reproduction of multi-time shifts of the dominant branch (south-to-north-to-south) within a 6-year period. Then it is demonstrated that the dominant branch shift is affected by both channel-bar dynamics and boundary conditions, which can be reflected by the product of the hydraulic radius and sediment supply. Moreover, numerical comparisons with and without the effects of regulation projects indicate that the protection project of Sanbatan mid-channel bar (SBTMB) plays a more significant role in maintaining the stability of the reach. Finally, it is shown that the Taipingkou mid-channel bar (TPKMB) and the SBTMB have different evolutional features, with the former exhibiting a parallel-branch pattern and the latter featuring a meandering-branch pattern, which should be accounted for in future waterway management plans.