Scouring and silting law of the Lower Yellow River and water and sediment regulation indicators after the regulation of Xiaolangdi Reservoir

In order to scientifically guide the practice of water and sediment regulation of the Yellow River, an optimization was necessary for water and sediment regulation indicators according to the law of scouring and silting in the Lower Yellow River after water and sediment regulation of the Xiaolangdi Reservoir. For this purpose, 121 water and sediment processes at different sediment concentrations measured in the Lower Yellow River from 2011 to 2022 were selected to analyze the water and sediment characteristics, and the relationship between the efficiency of scouring and silting and the water and sediment conditions. On this basis, water and sediment regulation indicators were proposed to ensure generally no siltation in the Lower Yellow River and no reduction of the discharge capacity of main channel. The results showed that: ① The Xiaolangdi Reservoir has a polarized regulation effect on the water and sediment process in the Lower Yellow River, that is, the sediment in the high sediment concentration flow (average sediment concentration S_av>10 kg/m³) accounts for 94% in the whole year, and the water in the clear water flow (S_av < 1 kg/m³) accounts for 85% in the whole year. ② The silting efficiency of high sediment concentration flow has a positive linear correlation relationship with the average sediment concentration. ③ The scouring efficiency of clear water flow has a positive logarithmic correlation relationship with the average discharge. ④ For high sediment concentration flow, in a high flow year, the water volume regulated is 8 billion m³, the average discharge is 2 000—4 600 m³/s and the average sediment concentration is 50 kg/m³; in a normal flow year, the water volume regulated is 1 billion m³, the average discharge is 2 000—4 600 m³/s and the average sediment concentration is 150 kg/m³; and in a low flow year, no sediment is discharged from the reservoir. For clear water flow, it is necessary to avoid water flow process with an average discharge of 800—1 800 m³/s.