Recent Evolution Characteristics and Hydrodynamic Response of Emeizhou Braided Channel in Anqing Section of Yangtze River

[Objective] The Emeizhou braided channel in the lower section of Anqing is situated in the lower reaches of the Yangtze River. Due to the significant variations in scouring and silting in the braided channel of the Anqing section, the variations in diversion ratio exhibit certain periodicity under the new water-sediment regime. This study aims to investigate the variations in the diversion ratio of the left branch and the stability of the main navigation channel conditions under the new water-sediment regime, as well as the potential impacts on water-related projects in the Mawo area of the left branch that may arise from near-bank siltation at the confluence of the braided channels in the near future. [Methods] By integrating a two-dimensional hydrodynamic model and utilizing the latest field observation data on water and sediment, this study tracked and analyzed the periodic evolution characteristics, influencing factors, and flow characteristics of this braided channel. Additionally, recommendations for the future management direction of the Anqing section were proposed. [Results] In recent decades, the thalweg swing amplitude in the Emeizhou braided channel was relatively small overall, and the river regime remained relatively stable, except for areas near the diversion point of Emeizhou, the head of the right branch, and certain localized river sections of the middle branch. After the impoundment of the Three Gorges Reservoir, the left branch of Emeizhou has experienced slight scouring, while the right branch was expected to maintain a shrinking trend for some time. Numerical simulation results of the flow characteristics of the braided channel showed that from 1998 to 2006, the middle branch developed rapidly, characterized by increased flow velocity and a shift of the main flow towards the Emeizhou on the right bank, while the flow velocities in the left and right branches decreased slightly. From 2006 to 2021, under the guidance and regulation of river (navigation) channel engineering, the diversion ratio of the Emeizhou braided channel remained basically stable, the development of the middle branch slowed down, and changes in flow velocity were mainly concentrated in the lower section of the middle branch. [Conclusion] We recommend to closely monitor the effectiveness of the existing river regulation projects in the Anqing section and to implement relevant measures when necessary.