Why is the water level of Poyang Lake rising fast?

　　As the last reservoir before the Yangtze River entered the lower reaches of the Yangtze River, Poyang Lake's water levels rose due to the convergence of many rivers and continuous heavy rainfall, and the water levels of multiple hydrological stations in the Lake District continued to exceed the warning line. According to monitoring data, at 18:00 on July 8, the main body of Poyang Lake and the surrounding water area reached 4,206 square kilometers, the largest in the past 10 years.

　　Experts said that maintaining the normal water level of Poyang Lake will play a role in flood storage in the Yangtze River, which is very beneficial to the Yangtze River and will also reduce the risks in the lower reaches of the Yangtze River.

　　1 Geographical reasons

　　Jiangxi Province is surrounded by mountains in the east, west and south, and the Poyang Lake Plain in the north. This topography caused most rivers in Jiangxi to eventually merge into Poyang Lake.

　　Xiushui, the five major water systems of Poyang Lake, the Gan River, Fu River, Xinjiang River and Rao River eventually flowed into the Yangtze River through Poyang Lake.

　　2 Reasons for rain

　　Since June 29, Jiangxi, Jiangxi, and Jiangxi have been hit by successive heavy rains. Among them, the average rainfall in Nanchang, Shangrao, and Jiujiang all hit record highs in the same period. In the meantime, there were 35 counties and cities in the heavy rainstorm in Jiangxi Province from 20:00 to 8:20 on July 7th, with a wide range of influence, the most since the complete meteorological records in 1961 (the original record was June 19, 2010, heavy rain The number of the above stations is 29). Continued heavy rainfall caused the water level of Poyang Lake to rise.

　　3 Causes of the Yangtze River

　　Cheng Xiaotao, a member of the Expert Committee of the National Disaster Reduction Committee and the former deputy chief engineer of the China Institute of Water Resources and Hydropower Research, said that Poyang Lake is one of the “reservoirs” of the Yangtze River, and its water level fluctuates synchronously with the Yangtze River. When "connected together". This year, due to continued heavy rainfall, the water level of the Yangtze River rose, and Poyang Lake was poured back.

　　In addition, the water channel connecting Poyang Lake and the Yangtze River is narrow, and the data shows that the narrowest point is only about 3 kilometers. In the case of a large flow of the Yangtze River, the flood discharge was not enough, causing the water level of Poyang Lake to continue to exceed the alert.

　　How important is Poyang Lake to flood control of the Yangtze River?

　　There are few tributaries in the rainy areas of the Yangtze River. As the last reservoir before the Yangtze River entered the downstream, Poyang Lake played a huge role in flood control in the lower reaches of the Yangtze River.

　　According to Cheng Xiaotao, if there is no Poyang Lake, the rivers such as Xiushui, Ganjiang, Fuhe, Xinjiang and Rao River in Jiangxi will directly flow into the Yangtze River, and the pressure of flood control downstream will be greater. Therefore, after the “Five Waters” are injected into the Yangtze River through the storage of Poyang Lake and then become relatively gentle, the downstream flood control pressure will be reduced. Therefore, maintaining the normal water level of Poyang Lake plays a role in the Yangtze River's flood storage, which is very beneficial to the Yangtze River and will also reduce the risk of the lower reaches of the Yangtze River.

　　Beijing News reporter Huang Zhecheng Deng Qi