关键词: 荆江三口; 分洪能力; 分流量; 洞庭湖出流; 长江2020年洪水;

Abstract: During the flood season of 2020, there were 5 numbered floods in the Yangtze River Basin. The changes of flood diversion capacity of the three outlets on the Jingjiang reach and the outflow of Dongting Lake were directly related to the flood control safety of the middle reaches of the Changjiang River. Analysis based on the latest measured data was proposed and the following main understandings were obtained:(1) Affected by floods in the flood season of 2020, compared with the period of 2003～2018, the flood diversion of the three outlets on the Jingjiang River in July and August increased significantly; under the same large flow of Zhicheng Station, the three outlets divided flood volume of the Jingjiang River increased to a certain extent, among which the flood diversion volume of Songzi outlet increased significantly, the Ouchi outlet increased slightly, and the Taiping outlet decreased.(2) The diversion ratio of the three outlets was positively correlated with the flow of Zhicheng Station. In the flood season of 2020, the flow of Zhicheng increased to more than 38 000 m3/s, and the diversion ratio of the three outlets was basically above 20%. The diversion ratio of the three outlets was the largest at July 25, with a value of 26.1%, and the flood diversion capacity was as high as 11300 m3/s.(3) Compared with 2003, during the flood season of 2020, the water level under the same high flow of Luoshan Station all rose to varying degrees, which may be related to factor of the apparently large inflow of the downstream section. Before June 13, the change of flow ratio between the Chenglingji station and Luoshan station was mainly affected by the incoming flows from the Xiangjiang River, Zishui River, Yuanjiang River and Lishui River; while from June 14 to September 25, the flow ratio change was mainly affected by the change of the mainstream flow of the Yangtze River. When the flow at Jianli Station increased or decreased rapidly, the flow ratio changed oppositely. When the flow at Jianli Station changed slowly, the change of flow ratio was not obvious.

Key words: three outlets of Jingjiang River; flood diversion capacity; outflow of the Dongting Lake; Changjiang River flood in 2020;