The characteristics of sediments in the middle and lower Yangtze River influenced by dam operation

Abstract

Since the Three Gorges Dam (TGD) was operated, the sediment characteristics in the downstream river have changed significantly. The characteristics of sediments can be partly reflected by the critical diameter to distinguish wash load and bed material load (WAB) and the ratio of wash load to suspended sediment (WTS). However, the WAB and WTS of the Yangtze River(YR) have not been fully investigated. In this study, data of sized suspended sediment and bed material at four stations in the middle and lower YR were collected to calculate the WAB and WTS, using the most-curvature method. The variations were then analyzed. The results suggest that the WAB and WTS of Yichang station varied greatly before the impoundment, while that of other stations were in small fluctuations. After the impoundment, the WAB of Yichang station increased dramatically to 1.856 mm, and the growth rate of the WAB at Jianli and Hankou stations were 1.0% and 4.1%, respectively (compared with WAB in 2002), while that of Datong station was -8.4%. Comparing with the rising WAB, the WTS of Yichang station continued to rise until it was close to 100%. However, the WTS of other stations decreased overall (30%-40% in Jianli and Hankou, and 8% in Datong).