三峡水库蓄水后荆江三口河道分沙量变化规律

Variation of sediment load diversion in the Three Outlets Channel of the Jingjiang River after the Three Gorges Reservoir impoundment

荆江三口河道是连通长江与洞庭湖的纽带,其水沙关系变化影响江湖关系的演变。基于三口河道2003-2020年的实测水沙数据,采用Mann-Kendall趋势分析法与水沙关系分析法,分析不同流量下三口河道分沙量变化趋势。研究表明,三峡水库蓄水后,三口河道年径流量和输沙量均为中等程度变异,输沙量变异程度高于径流量。藕池河康家岗站在年内前10%的高流量条件下输沙量为37.3%,其余各站在高流量条件下输沙量均超过50%,其中高流量对松滋河新江口站输沙的影响最为明显。在低于年平均流量情况下,各站输沙量仅占1.1%~11.4%,泥沙输移量可忽略。各站水沙关系曲线随时间趋于平缓,相同流量下输沙量大幅减少,在中高流量输沙量减少最为明显,9月输沙量受三峡水库汛后蓄水影响最明显。

The Three Outlets Channel(TOC)along the Jingjiang River is the link between the middle Yangtze River and Dongting Lake.The change of water and sediment affects the evolution of the river-lake relationship.Using the hydrological data(2003-2020)in the TOC,Mann-Kendall method and sediment rating curve method,the variation of sediment diversion in the TOC under different discharge levels is analyzed.After the impoundment of Three Gorges Reservoir,the change of mean annual runoff and sediment load in TOC are moderate,but the variation degree of sediment load is higher than that of runoff.Besides,about 37.3%of annual sediment flux is transported under high discharge conditions which occur only 10%of the year time in the Kangjiagang hydrological station,larger than 50%of the annual sediment load is transported under high discharge conditions in other hydrological stations,particularly in the Xinjiangkou hydrological station.At lower discharge conditions,only 1.07-11.4%of the annual sediment load is transported below the average discharge.There is almost no sediment load below the average annual discharge.The sediment rating curve in the TOC tends to flat since 2003,sediment flux decreasing largely under the medium and high discharge conditions,and the most significant impact occurred in September due to the initial impoundment of the Three Gorges Reservoir.