Effect of the Riverbed Deformation on Bed-Load Transport in the Middle Yangtze River

After the Three Gorges Dam operation in 2003,suspended sediment concentrations in the Middle Yangtze River decreased by 60%~90%,resulting in significant channel degradation and riverbed coarsening.These changes have impacted flood control and riverbank protection in the middle and lower reaches,yet the effect of riverbed adjustment on sediment transport processes near the dam remains unclear.Based on the hydrological,sediment,and topographic data from 2003 to 2019,this study developed a formula of bedload transport rate that accounts for riverbed deformation,and then analyzed its influencing mechanisms.The results indicate that:(1) an empirical relationship between bedload transport rate and incoming sediment coefficient was established for the Jingjiang Reach,with validation against measured data from 2003 to 2019.The proposed formula,which considers riverbed topography,showed lower error than methods ignoring morphological changes and better reflected the interaction between bedload transport and riverbed evolution;(2) after the reservoir operation,bedload transport rates in the Jingjiang Reach decreased markedly,accompanied by reduced sediment threshold probabilities.At Zhicheng station,the bedload transport rate decreased from 163.66kg/s to 2.55kg/s,and the threshold probability decreased from 0.994 to 0.001;(3) intensified riverbed scouring led to reduced bank slope angles,weakening bedload transport intensity;sediment transport rates correlated negatively with bed sediment coarsening and longitudinal riverbed stability.This study enriches sediment transport theory and supports analysis of riverbed evolution in the alluvial rivers.