Flow partition ratios of branching channels are easily altered by sand mining activities in bifurcating reaches,which affects flow conditions of shipping channels and may threaten navigation safeties.To investigate the impact of sand mining in Jinshi and Taihu embankments at the lowest reach of Yuanjiang River on hydrodynamics of nearby shipping channel,we use data of riverbed terrain and hydrology in 2016 and 2022 to establish numerical model of planar 2D flow motion,from which hydrodynamic changes are calculated for different terrain and hydrology combinations before and after sand mining.The results show that beach-channel regime is stable in the study reach,and no obvious change of the navigation-channel dimension and sediment deposition is triggered by sand mining.The flow partition ratio of the middle branch will be enhanced by larger than 7.12% if blocking dams within this branch are destroyed by rush of water after sand mining.The minimum water depth in the navigation channel is still larger than 3 m after sand mining,which meets the navigation requirement.The blocking dams reduce the water surface slope by 4‰ between the entrances of the study reach and the bifurcating area.If blocking dams are destroyed after sand mining,water level along the main shipping channel will drop by 0.10 m in dry season.The whole flow field changes little before and after sand mining.Flow velocities around the two embankments decrease and the maximum deflection angle is smaller than 23°,which do not hamper sand dredger access.Blocking dams reduce flow velocity in the middle branch by 0.52 m/s in wet season.Blocking dams control the overall stability of river regime and prevent the middle branch from erosion and development which might lead to steep water-level drop,dimension shrinkage and even rerouting in the shipping channel.Meanwhile,high flow velocities occur around mining area boundaries and scour beaches,so it is recommended to protect the blocking dams and beaches.