三峡工程后长江口徐六泾入海水沙特征变化研究

Characteristics of hydro-sediment changes in Xuliujing of Yangtze River Estuary after the Three Gorges Project operation

基于2004-2019年长江口徐六泾断面观测数据,分析了三峡工程修建以来长江入海水沙特征和变化过程。结果表明,三峡水库修建后入海流量年内分配在2010年后出现显著改变,洪季期间的7月流量增大17%,9月减小22%,枯季各月流量升高15%以上。徐六泾多年垂线平均含沙量为0.09 g/L;2010年是徐六泾表层含沙量减少的拐点,减少幅度达50%。2014年以后,徐六泾表中层含沙量呈新一轮下降进一步减少,底层含沙量从2016年开始有所升高,入海含沙量减少趋势放缓。入海泥沙多年平均中值粒径为6.5μm,2016年以前黏土与粉砂含量之比约为4∶6,砂含量低,之后含砂量平均占比由2%上升到10%,入海悬沙粗化。建坝对入海水通量的年内分配有重要影响,入海泥沙特征变化则受建坝与中下游河流自适应调整的双重影响。

Based on the field data collected at Xuliujing in the Yangtze Estuary from 2004 to 2019, the characteristics and processes of hydro-sediment flux into the sea since the construction of the Three Gorges Project(TGP) were analyzed. Results show that after the Three Gorges Project operation the annual runoff distribution had changed significantly since 2010. The runoff increased by 17% in July, decreased by 22% in September and increased by more than 15% in the dry season. The temporospatial averaged suspend sediment concentration(SSC) at Xuliujing was 0.09 g/L. SSC reduction aggravated after 2010 when SSC of the surface layer experienced a decrease of 50% in this year. After 2014, the SSC in the surface and middle layers at Xuliujing showed a new round of downward trend. However, the SSC in the bottom layer began to increase from 2016 and the decreased rate of the entire SSC into the sea was slowed down. The temporal average median particle size of sediment into the sea was 6.5 μm. The sediment consisted of clay(40%) and silt(60%) with very low sand composition before 2016. However, the average content of sand increased from 2% to 10% and the suspended sediment into the sea coarsen after 2016. It can be concluded that the dam construction has an important influence on the annual distribution of water flux, while the variation of sediment characteristics is affected by both the dam construction and the adaptive adjustment of the river.