Analysis of the evolution trends and influential factors of bankfull discharge in the Lower Yellow River

After the Xiaolangdi Reservoir (XLDR) was put into operation, new water and sediment conditions have improved the silting condition of the Lower Yellow River (LYR), but against this background, the flow capacity of the LYR has become more complex. In this research, the measured water and sediment data of seven hydrological stations in the LYR from 1950 to 2020 were systematically collated. The evolution trend and development period of the bankfull discharge in this area were studied based on the wavelet analysis method, and the main factors influencing the evolution of the bankfull discharge were explored. The results indicate that the evolution process of bankfull discharge in the LYR has experienced two phases in the last 70 years. XLDR has been impounded since October 1999. Before XLDR operation, the bankfull discharge of the LYR has a main time scale of about 26 years. After XLDR operation began, it has a time scale of about 10 years. The bankfull discharge of the LYR shows two phases of evolution, and these phases are mainly influenced by the factors of water and sediment conditions. This research is needed for a deeper understanding of flow-bed and river discharge and sediment transport capacity under the water and sediment conditions in the LYR.