Author(s): Zican He; Juanjuan Fang; Geng Qu; Tianyin Sun; Hualong Luan; Chunyan Deng
Linked Author(s): Zican He, Geng QU
Keywords: No Keywords
Abstract: The Ma’anshan Reach, ranging from DongLiang Mountain to CiMu Mountain, is located in the lower reach of the Yangtze River. As a critical reach of the Yangtze River, the evolution of the Ma’anshan Reach has received attention in the fields of geography, river ecology, and engineering. Since 2003, the completion of the Three Gorges Dam (TGD) has decreased more than 95% of the sediment supply, the clear erosive water causes significant riverbed erosion below the TGD. However, Ma’anshan Reach exhibited a continuous deposition from 2003~2016, as opposed to the general scour trend. To explain this special phenomenon, we combined observation field data and a 2D morphological model, determined the spatial and temporal riverbed adjustments of the Ma’anshan Reach in the last twenty years, analyzed the sediment dynamic during low flows and flood flows, and assessed the factors that caused the continuous deposition. The results show that: (1) After 2003, nearly 95% of the suspended sediment has been cutoff, and both the incoming flow frequency distributions and seasonal distribution of sediment transport rate have been centralized in the lower Yangtze River. Due to the sediment supply provided from the upstream riverbed erosion and bank collapse, the sediment concentration of the the Ma’anshan Reach had restored to 30% of the original value in the pre-TGD period. (2) In response to the altered flow-sediment regime, the Ma’anshan Reach exhibited a continuous deposition from 2003~2016, with an accumulated deposition volume of 0.63 billion m3. The sediment deposition was concentrated in the Niutun Bar near the left bank and the channels between the Xiaohuang Island and the Lower Hejia Bar, with deposited sand thickness up to 10m. (3) The morphological characteristics of widening in the middle and narrowing in the inlet and outlet generated several slow-flow regions, creating a condition for coarse sand from upstream to settle down; The increase in lower flow duration induced by TGD operation promoted the sediment deposition; The upstream reach adjustments caused the rightwards of the mainstream lines, leading to the lateral extension of the slow-flow region. In addition, the continuous deposition was still a natural evolutionary.
Year: 2024