Abstract:
Sediment discharge in the Jingjiang reach has sharply reduced since the Three Gorges Project operation, and the channel has been scoured by the clear water in order to recover the sediment transport capacity. However, the recovery rate of nonuniform suspended sediment was different with the different bed material compositions along the Middle Yangtze River. Therefore, the equation of settling distance of nonuniform sediment is derived, based on the theories of Markov stochastic process and sediment motion. Then, according to the definition of saturation recovery coefficient (
α) based on the diffusion theory of suspended sediment, the formula of grouped saturation recovery coefficient (
αi) is modified using the equation of settling distance; However, it ignores the effect of bed material composition (BMC) on suspended sediment recovery. For the actual process of sediment transport in the Jingjiang reach, a formula of
αi is then proposed with the effect of the BMC being considered. These results show that: ① The value range of
αi in this study was 0.12—0.27 at Shashi and Jianli when the influence of the BMC was not taken into account, but it became to the range of 0.000 3—0.171 8 and 0.003 5—0.157 9 respectively when considering the BMC effect; ② Among
αi of different sediment groups, the relationship of
αif for fine sediment >
αim for medium sediment >
αic for coarse sediment existed when the BMC effect was not considered, but the relationship of
αif <
αim <
αic existed when considering the influence of BMC; and the recovery rate of suspended sediment at Shashi was higher than that at Jianli except for the recession period; ③ The variations of
αi at Shashi and Jianli were sensitive to different groups during different periods, in which
αi during the flood period was higher than the value during other periods. Through comparation and analysis, the proposed formula in this study can predict the value of
αi for the Middle Yangtze River well, and it also providing a basis for further research on the recovery mechanism of suspended sediment in the reach downstream of the Three Gorges Dam.