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.

中文翻译：

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多年时间尺度河中坝曲流河段高分辨率水沙地貌动力模拟——以长江中游沙市河段为例

具有河道中部坝的蜿蜒河段被认为是世界上最大河流最普遍的平面配置之一，其中频繁出现的主要支流转移对航行造成了巨大障碍。以前的数值研究主要集中在短期再现或主导通道转换的单个事件上。这里，计算高效的二维水文沉积物地貌动力学模型成功应用于研究长江中游沙市河段典型曲流河段的主导河道移动的频繁事件。特别关注人为影响的杆通道相互作用如何影响优势分支的移动。结果表明，该模型在深度平均速度、悬浮泥沙浓度、年侵蚀率、坝体形态和引水比等关键水文沉积物形态因素方面表现良好。这些导致了6年间优势枝多次转移（从南到北到南）的连续数值再现。然后证明了主导支流移动同时受到河坝动力学和边界条件的影响，这可以通过水力半径和泥沙供应量的乘积来反映。此外，通过与未实施整治工程影响的数值比较表明，桑巴坦河道中部坝防护工程对维持河段稳定性的作用更为显着。最后，表明太平口河道中部坝（TPKMB）和SBTMB具有不同的演化特征，前者呈现平行分支模式，后者呈现蜿蜒分支模式，这在未来的航道中应予以考虑管理计划。