Coupled effects of riverbed topography and entrainment probability on bedload transport in the Middle Yangtze River

The operation of the Three Gorges Dam (TGD) has induced a 60 ~ 90% reduction in suspended sediment concentrations in the Middle Yangtze River (MYR), which led to significant channel degradation and riverbed coarsening, and further affects the flood control and riverbank protection in the Middle Yangtze River. However, the influence of the riverbed adjustment on the bedload transport process in the near-dam reaches remains unclear. Based on the measured data in the MYR, a bedload transport formula was proposed that considered the coupled effects of riverbed topography and entrainment probability. The results showed that: (i) the proposed formula in this study can reasonably reflect the impact of cross-sectional morphology and bedload transport on the riverbed erosion and deposition process, and it consistent well with the observations; (ii) after the TGD operation, the bedload transport rate in the Jingjiang Reach significantly decreased, accompanied by a reduction in sediment entrainment probability; the transport rate at Zhicheng station decreased from 163.66 kg/s to 2.55 kg/s, and the entrainment probability decreased from 0.994 to 0.001, but the transport rate and entrainment probability remained relatively stable at Shashi and Jianli stations; (iii) riverbed scouring in the Jingjiang Reach intensified, with reduced bank slope angles leading to weakened bedload transport intensity; and the transport rate revealed a negative correlation with riverbed coarsening and longitudinal riverbed stability. The results of this research are an enrichment to the sediment movement theory and can be used in the prediction of riverbed evolution in the alluvial rivers.