Abstract: To investigate the impact of spur dike groups on water flow characteristics and local scour in the lower reach of the Luanhe River, a three-dimensional water and sediment model is constructed by using Flow 3D software. The model’s accuracy is validated using measured data in 2015. Simulations are conducted under both constant and unsteady flow conditions, considering 5-year and 10-year return periods, to analyze flow velocity distribution and local scour at groin head. Findings demonstrate that the spur dike group effectively reduces flow velocity, enhances river bank resistance to water erosion, and protects the river banks of Yaozhuang segment in the lower reaches of the Luanhe River. Under constant flow, the maximum velocity zone of the main stream gradually shifts towards the right bank during the 10-year return period, compared to the 5-year return period. Moreover, the velocity at groins impacted by the mainstream increases by approximately 1.7 m/s, while the flow velocity at the head of other groins rises by around 0.9 m/s. During flood discharge, typical groin head subjected to the mainstream experiences noticeable scour pits assuming a long and narrow strip shape aligned with the water flow direction. Additionally, with longer return periods, the depth of the scour pit at the head of a typical spur dike increases by about 1 m, and meanwhile the scour zone at groin head starts to propagate upstream.

Key words: spur dike group, water and sediment model, local scour, hydraulic characteristic