The flow dynamics at river confluences exhibit complex three-dimensional characteristics,which are further influenced by the daily flow regulation of upstream hydropower stations.These factors result in flow conditions at confluences that are more intricate than those in typical river reaches,with notable impacts on navigation at river mouths.This study addresses navigation flow conditions at river confluences affected by daily hydropower regulation,utilizing numerical simulations to systematically analyze the hydrodynamic variations at open-channel confluences under unsteady flow conditions.Using navigation-related hydraulic indices,the study examines the effects of unsteady flow periods,flow fluctuation amplitudes,confluence angles between main and tributary streams,and tributary discharge on key hydrodynamic parameters,including longitudinal water surface profiles,water level fluctuations,water surface gradients,flow velocities,and flow field distributions at the confluence.Findings indicate that the water level difference between upstream and downstream decreases as unsteady flow periods increase but rises with higher tributary discharge.Water level fluctuations decrease with increasing confluence angles and increase with larger flow fluctuation amplitudes,while the water surface gradient at the confluence increases with greater flow fluctuation amplitudes,larger confluence angles,and higher tributary discharge.Furthermore,the area of crescent-shaped high-velocity flow zones responds differently to various influencing factors during rising and falling water stages.This study clarifies the hydrodynamic processes at river confluences affected by unsteady flow conditions and daily hydropower regulation,providing a scientific foundation for understanding unsteady flow propagation in confluence zones and its implications for navigation.