Before and afer construction of the

Before and afer construction of the TGR, the adjustment trends of the low-fow water level and food level of the river channel were diferent, suggesting that the infuentian factors driving the variation of these water levels were also diferent. Afer the impoundment was completed, scouring in reaches below the dam mainly occurred as a result of the basic fow channel, and the expansion of the water area below the low-fow water level was the main factor driving the water-level decline10. In addition to exceptional reasons, such as elevation of the erosion datum by sedimentation and fooding at the confuence with tributaries, the increase in river channel resistance due to the coarsening of the bed and increased growth of vegetation in the river channel are the major factors leading to higher food levels at the same discharge20,21. Due to the combined efect of natural and human factors, the decrease in the water level corresponding to the same fow was greater than the increase in water level. Te water level with the same fow exhibited a decreasing trend, which should otherwise have increased. Based on this concept, we analysed the efects of changes in any of the infuential factors on the drought and food water-levels under the same fow-rate conditions in the lower reaches of the Tree Gorges Dam.Efect of river channel geometry adjustment. According to the statistics of the Bureau of Hydrology, Changjiang Water Resources Commission, from 1981 to 2002, the volume of erosion of the Yichang to Hukou reach from the basic fow channel was 4.91×108 m3, the sediment volume of the basic fow channel-bankfull channel was 5.05×108 m3, such that the sediment volume of the bankfull channel was 0.14×108 m3, and the average annual sediment volume was 67.23×104m3(Fig. 6).