At that time, the Yangtze River basin was below Yichang, the main stream, and the flood volume of Dongting Lake system, Poyang Lake system and other important tributaries and lakes almost exceeded or approached the flood season of each water system. The flood peak discharge is extremely high, and the areas below Chenglingji have all broken through the historical measured records, which is the concentrated expression of each flood year since records began. For example, according to the frequency calculation results, the total flow of major control stations such as Yichang, Hankou and Datong in flood season is equivalent to 100, and the daily average maximum flow is once in Yichang every 20 years, once in Datong 167 and once in Hankou 1430. Therefore, the flood runoff in the middle and lower reaches of the main stream is large and concentrated, and the flood peak discharge is high. It can be said that this is a major feature of the Yangtze River flood runoff in 1954. ① The recurrence period of daily average maximum flow in Yichang, Hankou and Datong is limited by the data conditions at that time, and the estimation error is large.
1. 1954 comparison of floods above Yichang with flood years in previous years.
The annual runoff of Yichang Station 1954 in the main stream of the Yangtze River is higher than that of any flood year since the historical record (1965). The floods in April-10 and July-September were 497.5 billion m3 and 325.6 billion m3 respectively, accounting for 86.5% and 56.5% of the whole year, which fully showed that the flood season in April-10 was 49.5 billion m3.
2. Comparison between Sishui 1954 in Dongting Lake and floods in previous years.
The annual runoff of each station in Surabaya 1954 is slightly larger than that in flood years such as 193 1, 1935 and 1949. Although the flow data over the years are mostly interpolated figures, from the existing data, the water volume in flood season is still greater than that in other flood years.
3. 1954 Comparison between Hanjiang River flood and previous flood years.
The runoff above Xiangyang 1954 in Hanjiang River Basin is second only to 1938, but greater than 193 1, 1935, 1949. As for the flood runoff from July to September, it is less than 1949. The flood volume in flood season accounts for 60% of the whole year. This shows that Hanjiang river basin 1954 also belongs to the flood year.
4. Flow analysis of five rivers in Poyang Lake
The five rivers in Poyang Lake have a short discharge record year, and Nanchang Station in Ganjiang River has only seven or eight years (of which 1954 is poor), and the water level record at Poyang Lake mouth is also very scarce, so it is impossible to compare 1954 with previous years by runoff. However, according to the analysis of the rainfall data of Poyang Lake in that year, the abnormal rainfall generally exceeded the historical record. According to the comparison of water levels in Nanchang over the years, the highest water level 1954 is only a few centimeters lower than 1949, which can be indirectly quoted as a flood year.
The peak shape is huge and the flood lasts for a long time.
In the flood season of that year, the upper reaches of the Yangtze River were affected by the inflow of water from major tributaries such as Jinsha River, Minjiang River, Jialing River and Wujiang River, and with the influence of interval runoff, a tall flood peak was formed in Yichang, with an annual flow exceeding 40,000m3/s for 45 days, which was the longest lasting year since the station had a historical record.
The flood flows below Zhijiang, connecting Dongting Lake, Poyang Lake and Hanjiang River system. Affected by the natural regulation of lakes and depressions along the Yangtze River and the flood diversion and breach, a parabolic and long-lasting huge flood process is gradually formed below Chenglingji, the main stream of the Yangtze River. The whole flood period almost completely exceeds the hydrograph of each flood year and becomes the outsourcing line of each station over the years.
The upper, middle and lower reaches of the flood occurred simultaneously.
Judging from the start and end time of rainfall, generally speaking, the rainy season above Yichang in the upper reaches of the Yangtze River is from July to September, and the rainy season in the middle and lower reaches of the two lakes is from April to June, that is, the upper, middle and lower reaches are staggered in turn. Therefore, the main tributaries above Yichang and the four rivers of Dongting Lake and Poyang Lake produce water in July-September and April-June respectively, so as to reach the flood volume produced in the middle and lower reaches. The rainy season in the middle and lower reaches of this year has been postponed to July, which is about 1 month later than the normal year. The rainy season in the upper reaches appeared ahead of schedule, two months earlier than normal, which made the rainfall in the upper reaches overlap with the rainy season in the middle and lower reaches in May and June, and the rainfall in the middle and lower reaches overlapped with the rainy season in the upper reaches in July, which made the flood in the upper reaches occur ahead of schedule, and the flood peaks in the middle and lower reaches lagged behind, and the flood peaks of the main tributaries of the whole river overlapped and influenced each other, resulting in a catastrophic flood in the middle and lower reaches of the Yangtze River 1954.