1. Flood process
From June12 to 27, affected by heavy rain, the Poyang Lake water system broke out, and the water levels of Fuhe, Xinjiang and Changjiang successively broke through the highest water levels in history. Floods have also occurred in Zishui, Yuanjiang and Xiangjiang rivers of Dongting Lake system. The floods from the two lakes merged into the Yangtze River, which caused the water level below Jianli in the middle and lower reaches of the Yangtze River to rise rapidly, and gradually exceeded the warning water level from June 24.
From June 28th to July 20th, the main rain area moved to the upper reaches of the Yangtze River. The first flood peak appeared in Yichang on July 2, with a flow of 54,500 cubic meters per second. The water in Jianli, Wuxue and Jiujiang hydrological stations exceeded the highest water level in history on July 4. The second flood peak occurred in Yichang in July 18, with a flow of 55,900 cubic meters per second. During this period, the water level of the main stream in the middle and lower reaches of the Yangtze River once dropped, because the inflow of Dongting Lake and Poyang Lake was small.
From July 2 1 day to July 3 1 day, a large-scale heavy rainfall occurred again in the middle reaches of the Yangtze River. On July 2 1 ~ 23, heavy rain fell in Wuhan and its surrounding areas. On July 24th, there was a big flood in Yuanjiang and Lishui of Dongting Lake system, among which the peak flow of Shimen Hydrological Station in Lishui 19900 cubic meters per second was the second largest flood in this century. At the same time, major floods occurred in Xinjiang and Le 'an rivers of Poyang Lake system. The third flood peak occurred in Yichang on July 24, with a flow of 5 1700 m3/s. The water level in the middle and lower reaches of the Yangtze River rises rapidly. After July 26th, the water levels in Shishou, Jianli, Lianhuatang, Luoshan, Chenglingji and Hukou once again exceeded the highest level in history.
In August, the water levels in the middle and lower reaches of the Yangtze River and the two lakes remained high, and there were five flood peaks in the upper reaches of the Yangtze River, including three from August 7 to 17 10, which led to the continuous rise of the water level in the middle reaches. The fourth flood peak occurred in Yichang on August 7, with a flow of 63,200 cubic meters per second. At 4 o'clock on August 8, the water level in Shashi reached 44.95 meters, which was 0.28 meters higher than the flood diversion level of 1954. The sixth flood peak in Yichang occurred in August 16, with a flow of 63,300 cubic meters per second, which was the largest flood peak in 1998. In the process of flood peak advancing to the middle and lower reaches, it meets the floods of Qingjiang River, Dongting Lake and Hanjiang River, and the hydrological station in the middle reaches reaches the highest water level in mid-August. The flood peak water levels of Shashi, Jianli, Lianhuatang and Luoshan hydrological stations in the main stream are 45.22m, 38.3 1m, 35.80m and 34.95m, respectively, which are 0.55m, 1.25m, 0.79m and 0.77m higher than the historically measured high water levels. On 20th, the highest water level at Hankou Hydrological Station 1998 was 29.43m, which was the second in history, only 0.30m lower than that at 1954. The seventh and eighth flood peaks in Yichang are smaller than the sixth flood peak.