Abstract: Sediment carrying capacity (SCC) is a crucial factor in the study of suspended sediment transport and channel evolution in the downstream of reservoirs. This study focuses on the river reach from Shashi to Hankou in the midstream of Yangtze River. By introducing two concepts in the non-equilibrium suspended sediment transport theory proposed by Han Qiwei, namely, the percentage of flow discharge which changes bed load into suspended load, and the particle gradations of sediments carried in flows, we examined the changes, and factors affecting the changes in the non-uniform suspended sediment carrying capacity after the construction of the Three Gorges Dam (TGD). Following the completion of TGD, Shashi and Jianli stations witnessed a significant increase in the percentage of flow discharge under various discharge levels. Specifically, when the discharge exceeded 30 000 m³/s at Luoshan station and 35 000 m³/s at Hankou station, the percentage of flow discharge increased. Shashi-Chenglingji reach experienced a more pronounced decrease in sediment carrying capacity than Chenglingji-Hankou reach. Moreover, the carrying capacity for sediment particles smaller than 0.125 mm declined significantly in Shashi-Chenglingji reach, while particles smaller than 0.25 mm reduced in Chenglingji-Hankou reach. The reduction of sediment carrying capacity in Shashi-Chenglingji reach is primarily attributed to the influence of ω^* (which is the average settling velocity of sediments), while in Chenglingji-Hankou reach, it is jointly affected by U³/h (a factor of SCC) and ω^*. Notably, U³/h plays a more prominent role when the critical discharge at Luoshan and Hankou does not exceed 30 000 m³/s and 35 000 m³/s, respectively.

Key words: sediment carrying capacity, non-equilibrium sediment transport, non-uniform suspended load, Three Gorges reservoir, midstream of Yangtze River