Heavy rainfall caused floods and the Three Gorges Project did not help? The fact is just the opposite!

　　The Three Gorges Project did not help? The facts are just the opposite

　　Our reporter Ji Leilei

　　Since June, frequent and continuous heavy rainfall in the Yangtze River Basin has caused floods in Hubei, Chongqing, Jiangxi and other places. As a key water conservancy project in the Yangtze River Basin, the role of the Three Gorges Project in preventing floods has once again become the focus of attention. However, some people think that the flood discharge of the Three Gorges Project "does not help." On the contrary, the Three Gorges Project is a key factor in controlling risks in the Yangtze River Basin.

　　Since the main flood season this year, there have been 9 significant rainfall processes in the Yangtze River Basin, and the overlap of rain areas is high, and the rainfall is basically non-stop. In terms of rainfall, this year’s rainfall is 40% more than normal, and the middle and lower reaches of the Yangtze River are 60% more than usual. Especially in the first ten days of July, heavy rains were frequent. Ten-day rainfall in the middle and lower reaches of the Yangtze River was 1.6 times higher than the average over the same period, and the 10-day rainfall in Poyang Lake system was 3.1 times higher than the average over the same period. Among them, the Poyang Lake area was 4.3 times more than the same period.

　　Affected by concentrated heavy rainfall, on July 2nd, the upper reaches of the Yangtze River, the Wujiang River, the Three Gorges section, and the Dongting Lake water system experienced a significant water increase process. The Three Gorges reservoir's inflow flow increased rapidly. At 10 o'clock that day, the Three Gorges Reservoir ushered in the No. 1 Yangtze River in 2020. The flood peak at 14 o'clock reached 53,000 cubic meters per second.

　　At the same time, the water levels of many rivers and lakes in the Yangtze River Basin have continued to rise. The water levels of the Yangtze River from Jianli to Jiangyin, Dongting Lake and Poyang Lake have exceeded the flood control warning level. Some lakes and dams have exceeded the guaranteed water level. The downstream flood control situation is very severe.

　　Faced with severe flood control pressure in the middle and lower reaches, can the Three Gorges Reservoir not discharge flood? This has to start with the basic “rules” of the Three Gorges’ flood blocking and storage, and the exchange of space for time to ensure safety: flood blocking, peak cutting, and peak shifting should be carried out alternately in a smooth and orderly manner, instead of always keeping the flood in the reservoir.

　　The flood control capacity of the Three Gorges Reservoir during the flood season is 22.15 billion cubic meters, and it is mainly used for flood control in three ways: one is to intercept floods, that is, to intercept floods that exceed the safe discharge of the middle and lower reaches of the river to ensure the safety of flooding in the Yangtze River below the Three Gorges Project; It is peak reduction. When the downstream flood control situation is tense, the large flood peak from upstream is reduced, the outflow of the reservoir is reduced, and the downstream flood control pressure is relieved; the third is peak shifting to prevent upstream and downstream flood peak encounters and increase downstream flood control pressure. Once the downstream flood control situation improves, it is necessary to seize the favorable opportunity to increase the flow out of the reservoir and lower the water level of the reservoir to free up the storage capacity.

　　The prerequisite for flood prevention is to ensure its own safety. During the flood season each year, the upper reaches of the Yangtze River will have many flood peaks, and the total amount of floods formed greatly exceeds the flood control capacity of the Three Gorges. In order to be able to meet a new round of floods at any time, the Three Gorges cannot store water to an excessively high water level at one time, let alone fill the reservoir at once. The Three Gorges Dam must not only cut down the turbulent natural flood peaks, but also ensure that there is a safety margin in the main stream of the middle and lower reaches of the Yangtze River in terms of the timing and amount of discharge.

　　For example, in response to the development of the No. 1 flood of the Yangtze River in 2020, the Three Gorges Reservoir "slips on" five times and "brakes" the discharge rate from 35,000 cubic meters per second to 19,000 cubic meters per second. The maximum peak cutting rate is 34%; at the peak of the No. 2 flood of the Yangtze River in 2020, the maximum peak cut rate was 46%. Up to now, the Three Gorges Reservoir has successfully responded to five floods since the flood season this year, with a total water storage capacity of 14.6 billion cubic meters, which is equivalent to "pocketing" 3.3 Taihu Lake water.

　　Therefore, the flood discharge of the Three Gorges Reservoir is scientific and orderly. It is precisely through this process of continuously reducing flood peaks and regulating the flow of floods from the Three Gorges Reservoir, which effectively reduced the speed and magnitude of the rise of water levels in the middle and lower reaches of the Yangtze River, and eased the pressure on flood control in the middle and lower reaches of the Yangtze River.

　　It is worth noting that after years of construction, the Yangtze River Basin has basically formed a comprehensive flood control system based on dikes, the Three Gorges Reservoir as the backbone, and other main and tributary reservoirs, flood storage and detention areas, river improvement and other engineering measures that complement non-engineering measures for flood control. At present, the reservoirs in the upper and middle reaches of the Yangtze River still have a flood control capacity of 21.1 billion cubic meters. After the combined use of the upper and middle reaches of the reservoir group, there are still 32.5 billion cubic meters of excess floods in the middle and lower reaches that require reasonable arrangements with other engineering measures. Controllable state.

　　However, in the process of flood control and flood control, the backbone water conservancy projects represented by the Three Gorges Project are only part of the Yangtze River flood control system and are not omnipotent. How to play the role of reservoirs, dikes, and embankments for flood storage, and to minimize the water level of the Three Gorges Reservoir and the water level of the control stations in the middle and lower reaches is the current difficulty in flood control.

　　Up to now, floods in most areas of the middle and lower reaches of the Yangtze River are less than in 1998, but this does not mean that vigilance can be relaxed. According to the latest hydrometeorological forecasts, affected by a new round of heavy rainfall, the inflow of the Three Gorges Reservoir in the upper reaches of the Yangtze River will increase, and the middle and lower reaches of the Yangtze River will maintain high water levels. Combining the current flood situation and subsequent forecast analysis, preliminary judgment is that the flood situation in the Yangtze River Basin may still develop further, and the future flood control situation is still severe. It is necessary to attach great importance to the real-time changes of the flood situation in the river basin, strengthen the rolling flood forecast and early warning, and further strengthen the flood control projects in the river basin. Comprehensive use of non-engineering defense measures.