Xinhua News Agency, Wuhan, July 29 - Title: flood take "two" with "three" flood also how to develop? ——The latest analysis of experts from the Yangtze River Committee
Xinhua News Agency reporter Li Siyuan
At 14:00 on the 28th, the inflow of the Three Gorges Reservoir has dropped from a peak of 60,000 cubic meters per second to 49,000 cubic meters per second. So far, the "2020 Yangtze River No. 3 Flood" has passed the Three Gorges Dam smoothly, evolving to the middle and lower reaches.
In July this year, the floods in the Yangtze River Basin were connected with "two" and "three", forming three numbered floods successively. How is the flood control situation of the Yangtze River? What benefits did the reservoir group including the Three Gorges play? How will the flood situation develop? The reporter interviewed the flood control experts of the Yangtze River Water Resources Commission of the Ministry of Water Resources to analyze the current flood situation in the Yangtze River.
After 3 rounds of floods, the Yangtze River flood control situation is grim but controllable
In the flood season this year, the Yangtze River Basin has continued to rain, and the flood control situation has gradually become tense.
On July 2, the "Yangtze River 2020 No. 1 Flood" formed in the upper reaches of the Yangtze River, and the lower reaches of Jianli in the middle and lower reaches of the Yangtze River subsequently exceeded the alarm. After the water level fluctuated slowly in the middle and lower reaches, on July 17, the "Yangtze River No. 2 Flood of 2020" was formed. Compared with "Flood No. 1", "Flood No. 2" has a high peak and large flood volume. The flow rate increased to 61,000 cubic meters per second at 8 o'clock on the 18th. The Three Gorges Reservoir blocked the flood and cut the peak, and the water level rose rapidly, rising to a maximum of about 164.5 meters, which exceeded the highest water level of 163.11 meters in the flood season since the construction of the Three Gorges Reservoir.
Affected by the recent heavy rainfall, the Minjiang River, Jialing River and the Xiangjiaba to Cuntan section, and the Three Gorges section of the upper reaches of the Yangtze River have significantly increased inflow. At 14:00 on the 26th, the inflow of the Three Gorges Reservoir reached 50,000 cubic meters per second, which once again reached the flood numbering standard. The "Yangtze River 2020 No. 3 Flood" formed in the upper reaches of the Yangtze River. After the formation of "Flood No. 3", its flow climbed all the way to 60,000 cubic meters per second, and began to recede around the early hours of the 28th.
Chen Guiya, deputy chief engineer of the Yangtze River Water Conservancy Commission, said that this round of floods smoothly passed the Three Gorges Dam and is evolving to the middle and lower reaches. After the three rounds of floods, the current water level in the mainstream of the middle and lower reaches of the Yangtze River is generally at a high level, but the slight fluctuations in the water level in the middle reaches are about to retreat, and the overall slow-down trend in the downstream will not change; the water level of the Three Gorges Reservoir has been slowly rising recently, reaching 162.79 meters at 14:00 on the 28th. The highest flood level reached on the 29th was close to 163.5 meters.
Chen Guiya said that "up and down strikes" made the Yangtze River flood control situation severe, but the overall situation was stable and controllable.
"As of 8 o'clock on the 28th, the remaining 18.78 billion cubic meters of flood control capacity of the upper reaches of the Yangtze River, including the Three Gorges, is indeed not'rich', but the controlling reservoirs of the Jinsha River and its upstream tributaries are for the defense of this river section and the large river basin. The flood protection storage capacity reserved by the flood has basically remained unchanged; the Three Gorges Reservoir will be gradually evacuated when the Yangtze River's main stream does not have much flood protection risk. Overall, it is fairly calm." Chen Guiya said.
The Three Gorges Project and other joint dispatching reservoirs to exert flood control benefits
Water conservancy and flood control experts said that since the main flood season, rainfall in the Yangtze River Basin has been significantly higher than that of the same period in normal years, and the rainfall has exceeded 1998. However, due to scientific flood regulation and other reasons, the current floods in the middle and lower reaches of the Yangtze River are smaller than in 1998.
“The control reservoirs included in the joint operation of the Yangtze River Basin have played a positive role.” Chen Guiya said that in the process of defending against the three rounds of floods in July this year, if there is no interception and regulation of control reservoirs such as the Three Gorges, the flood peaks of the Chenglingji River section The water level will be about 0.8 meters, 1.7 meters, and 0.6 meters higher than the actual level. The flood peak water level of the Lianhuatang water level station will reach 35.14 meters, 36.09 meters, and 35.19 meters, respectively. The joint operation of the reservoir group has brought benefits, and has also lowered the flood peak water level of Hankou Station by 0.5 meters, 1.0 meters and 0.4 meters respectively.
According to reports, the "Flood No. 3" that just occurred reached a peak flow rate of 60,000 cubic meters per second at 14:00 on the 27th. At that time, the outbound flow from the Three Gorges Reservoir was strictly controlled at 38,000 cubic meters per second, and the flood interception rate reached 36. %. When the "Flood No. 1" occurred, the Three Gorges Reservoir "stepped on" five times and "brakes", the discharge flow decreased from 35,000 cubic meters per second to 19,000 cubic meters per second, and the maximum peak cut rate was 34%; At the peak of No. Flood, the maximum peak cut rate was 46%.
In addition, according to the latest statistics from the Yangtze River Committee, as of 14:00 on the 28th, the controlled reservoirs of the Yangtze River, including the Three Gorges Reservoir, had blocked approximately 30 billion cubic meters of floodwater during the three rounds of flooding in July this year.
According to Chen Guiya, according to the design, the Three Gorges Project mainly uses three methods of blocking floods, cutting peaks, and shifting peaks to play a flood control role. The flood control capacity of the Three Gorges Reservoir is 22.15 billion cubic meters, and the annual average runoff of the Yangtze River section where it is located during the flood season is about 300 billion cubic meters. Therefore, during the entire flood season, the Three Gorges Reservoir is in a state of holding floods at any time. However, once it is predicted that there will be a large inflow of water from the upper reaches of the Yangtze River or the flood control situation in the downstream will improve, the Three Gorges Reservoir needs to seize the favorable opportunity to increase the outflow flow and reduce the reservoir level.
"Only by continuously reusing the flood control storage capacity through'storage-control-discharge-storage' can the flood control function of the Three Gorges Project be fully brought into play." Chen Guiya said that flood control dispatch not only considers the present, but also considers the future. It is necessary to make reasonable and scientific decisions based on actual conditions and predictions, while the decision-making process in the face of real-time flood forecasting and dispatching is much more difficult.
Rainfall in the Yangtze River Basin will be transferred to the upper middle and lower reaches of the high water level operation will continue
The Yangtze River is in a critical period of "seven lower and eight upper" flood control. This year's floods have shown continuous and almost no intermittent characteristics. The Yangtze River also rarely experienced 3 rounds of numbered floods in July. Flood prevention experts said that as the western Pacific subtropical high rises westward and northward, after the 29th of this month, rainfall in the Yangtze River Basin will gradually shift to the upper reaches, and the middle and lower reaches will enter the midsummer season of sunny, hot, high temperature and little rain. At present, the Three Gorges Reservoir is ushering in a precious and short inflow of water. There will be many rounds of inflow in the foreseeable period; the water level in the middle and lower reaches will mainly recede, but the current situation of high-level operation will continue for a long time.
It is predicted that the Three Gorges Reservoir will usher in a round of water in the order of 40,000 cubic meters per second around August 2. According to the medium-term forecast by the Meteorological and Hydrological Department, the rainfall in the upper reaches of the Yangtze River is relatively large, and there will be at least two rounds of heavy rainfall in early and mid-August. The flood control situation on the Yangtze River is still severe.
Flood control experts said that although the overall risk this year is less than in previous years, the main and tributaries of the middle and lower reaches of the Yangtze River have been operating at high water levels for more than half a month. The dikes have been soaked in high water levels for a long time, and the risks of falling slopes, collapses, and piping are increasing and increasing. The trend. The most urgent task now is to do a good job in dike inspection and risk inspection. We must consolidate our responsibilities, promptly replace and enrich the front-line flood control force, further improve the professional level of disposal, strengthen the frequency of inspection and defense of key reservoirs, dikes, etc., to achieve early detection and early disposal of dangers. All localities and departments must get rid of the psychology of fluke, in accordance with the requirements of preventing and resisting major floods, do their best to prevent floods in the Yangtze River, and ensure the safety of people's lives and property.