A study of the effect of local scour on the flow field near the spur dike

•Investigated flow field evolution with deforming local scour hole to analyze scouring capacity of accelerated flow.•Early-stage presence of scour hole enhances accelerating effect of spur dike on deflected flow, indicating positive feedback mechanism.•Local sand transport increases as scour intensifies due to positive feedback between scour capacity and topographic changes.•Subsequent topographic changes weaken sand transport capacity, leading to eventual attainment of scour equilibrium state. The flow field near a spur dike such as down flow and horseshoe vortex system (HVS) are susceptible to the topographic changes in the local scouring process, resulting in variation of the sediment transport with time. In this study, large eddy simulations with fixed-bed at different scouring stages were conducted to investigate the changes in flow field. The results imply that the bed deformation leads to an increase in flow rate per unit area, which represent the capability of sediment transportation by water, in the scour hole. Moreover, the intensity of turbulent kinetic energy and bimodal motion near the sand bed induced by the HVS were also varied. However, the peak moments between the two sediment transport mechanisms were different. Hence, understanding the complex feedback mechanism between topography and flow field is essential for the local scour problem. [Display omitted]