Efficiency of suspended sediment recovery in the downstream reaches of the Three Gorges Reservoir

In the riverbed erosion process caused by unsaturated water and under the influence of multiple factors, the process of suspended sediment recovery along the downstream reach of a dam is quite complex. To comprehensively explore the mechanism of suspended sediment recovery, the suspended sediment saturation (SSS) and the saturation recovery efficiency coefficient (SREC) were selected as key parameters to describe the suspended sediment recovery degree and efficiency, respectively. Based on field-measured flow and sediment data for the Yichang—Datong reach, the variation tendency and influencing factors of the SREC were analyzed and described, and empirical equations to quantify the SREC were established. The results revealed that: ① In the downstream reaches of the TGR, the SREC shows no consistent variation trend over time, but generally decreased with increasing erosion distance. Among the whole reach, the degree of total suspended sediment recovery per unit river length in the Zhicheng—Shashi reach is the highest, whereas the lowest in the Luoshan—Hankou reach. The former is approximately 23 times more than the latter. ② The efficiency of suspended sediment recovery is affected by the inlet SSS, bed material supply intensity and flow discharge. The SREC decreased with increasing inlet SSS and increased with increasing bed material supply intensity. The SREC decreased with increasing flow discharge under a positive bed material supply intensity and increased with increasing flow discharge under a negative bed material supply intensity. ③ Based on the relationship between the SREC and the influencing factors, i.e., the inlet SSS, bed material supply intensity and flow discharge, the empirical models for calculating the suspended sediment concentrations in total and each size group were established at the reach outlet.