Our reporter Zhao Jueyun Shan Jie
Since my country entered the flood season in early June, many places such as Jiangxi, Anhui, Hubei, Hunan, and Chongqing have been hit by floods. As in previous years when faced with floods, China's largest water conservancy project-the Three Gorges Project on the Yangtze River has once again become the focus of attention at home and abroad. What role did the Three Gorges Project play in this year’s severe floods? Did the flood discharge of the Three Gorges Dam “do not help” and aggravate the floods in the middle and lower reaches of the Yangtze River? How much flood can the Three Gorges Project play a role in flood prevention? A few days ago, a reporter from "Global Times" interviewed the relevant person in charge of the Three Gorges Group Basin Hub Management Center and responded to many hot issues.
What role did the Yangtze River flood prevention and Three Gorges play this year
Global Times: During this round of flooding in the Yangtze River Basin, what were the main tasks of the Three Gorges Project in flood control? What role did it play?
Person in charge of the Three Gorges River Basin Management Center: The Three Gorges Reservoir is used in flood control strictly in accordance with the dispatching instructions of the Ministry of Water Resources and the Yangtze River Water Resources Commission. As of the 19th, the Three Gorges Project has been used for flood control 5 times in this flood situation, and the total amount of flood interception is about 14 billion cubic meters. On July 2, 2020, the Yangtze River No. 1 flood formed in the upper reaches of the Yangtze River, with a peak flow of 53,000 cubic meters per second (appearing at 14:00 on July 2). The Three Gorges Reservoir played the role of flood blocking and peak shaving, controlling the discharge flow of 35,000 cubic meters per second, and the peak shaving rate reached 34%. According to the calculations of the Yangtze River Water Resources Commission, the Three Gorges Reservoir was used alone to reduce the water level of Chenglingji by 0.2 meters, and the water level of Chenglingji was reduced by 0.8 meters through the joint operation of the upper Yangtze River water project (including the Three Gorges), avoiding Dongting Lake Chenglingji and Poyang Lake. The guaranteed water level in the mouth and the warning water level in Jingjiang Shashi have greatly reduced the pressure on flood control in the middle and lower reaches of the Yangtze River.
Affected by the significant increase in water inflow from the upper reaches of the Yangtze River and the Three Gorges section, the inflow of the Three Gorges Reservoir rose to 50,000 cubic meters per second at 10 o'clock on the 17th, and the Yangtze River's second flood of 2020 was formed. At 20 o'clock on the 19th, the inflow of the Three Gorges Reservoir was 46,000 cubic meters/second, which was 15,000 cubic meters/second lower than the current peak of 61,000 cubic meters/second. The No. 2 flood of the Yangtze River in 2020 passed the Three Gorges Dam smoothly.
How many years can the Three Gorges Project prevent floods?
Global Times: This year’s flood reminds many people of the 1998 catastrophic flood. If this flood did not exist for the Three Gorges Project, what kind of disasters and damage would it bring?
The person in charge of the Three Gorges Group Basin Hub Management Center: In 1998, the Yangtze River experienced a catastrophic flood, and the water level at the Shashi Station in the most dangerous section of the Yangtze River rose to 45.22 meters, exceeding the guaranteed water level by 0.22 meters. Jingjiang River was once faced with the choice of flood diversion, millions of soldiers and civilians The upper dike is strictly guarded, and the flood control situation is very severe. Through simulation calculations, if the Three Gorges Project had been completed at that time, the water level of the Shashi station in the Jingjiang section could not exceed 44.5 meters, and the flood distribution of Chenglingji would be reduced from 10.8 billion cubic meters to 3.5 billion cubic meters. The flood control pressure on the middle and lower reaches of the Yangtze River would be reduced. Greatly relieved. If there is no Three Gorges Project this year, the Chenglingji area of Dongting Lake and the mouth of Poyang Lake will exceed the guaranteed water level, and there will be part of the flood diversion and storage division. The water level at Hankou Station in Wuhan will be higher, and the flood control situation in the middle and lower reaches of the Yangtze River will be more tense.
Global Times: There are many online opinions on the flood control capacity of the Three Gorges Dam. Some say it can withstand the once-in-10,000-year flood, and some say it can prevent the once-in-a-year flood. What is the flood control capacity of the Three Gorges?
The person in charge of the Three Gorges Group Watershed Hub Management Center: Wanli Yangtze River is dangerously located in Jingjiang. The flood control function of the Three Gorges Project is mainly in the Jingjiang River section, which can make the Jingjiang River section encounter a once-in-100-year flood without flooding; in case of a once-in-100-year flood to a once-in-1000-year flood, including the 1870 flood in similar history, it can Controlling the flow of Zhicheng to no more than 68,000 cubic meters per second, coupled with the cooperation of flood diversion and storage areas, can prevent devastating disasters in the Jingjiang area.
Regarding the flood control compensation dispatching method of the Jingjiang section, the focus is on preventing the catastrophic upstream flood, which is the most basic dispatching method and flood control function formulated in the preliminary design of the Three Gorges Reservoir. Later, after more than ten years of research and practice, it was proposed that the Chenglingji flood control compensation and dispatching method should be reasonably considered under the premise of ensuring the safety of the dam of the pivot and not reducing the Jingjiang flood control standard.
Global Times: If the current flood situation continues, will the Three Gorges still have sufficient capacity to continue regulation?
Person in charge of the Three Gorges River Basin Hub Management Center: I need to remind everyone that the Three Gorges Project mainly intercepts the incoming water from the upper reaches of the Yangtze River, focusing on ensuring the flood control safety of the Jingjiang River section and taking into account the flood control requirements of the Chenglingji area. Through the preliminary storage, the water level of the Three Gorges Reservoir rose from 145 meters to 155 meters, and 5.6 billion cubic meters of water was stored. The flood control storage capacity of the Three Gorges is 22.15 billion cubic meters. At present, there is still nearly 17 billion cubic meters of storage space left, which has sufficient capacity to deal with the next wave of floods. The regulation and storage of the Three Gorges Project is mainly to solve the flood control problem of the mainstream of the Yangtze River. Even if the Three Gorges Reservoir discharges flood, it must not exceed the flood control compensation standard of the downstream flood control objects, and will not add additional flood control pressure to the downstream. However, if the heavy rains are concentrated below the Three Gorges Dam in the later stage, regional floods occur in the middle and lower reaches of the Yangtze River, floods occur in tributaries, or the city itself suffers serious waterlogging, the city's own drainage facilities must be used to solve the problem. However, the Three Gorges Reservoir can reduce the discharge flow by blocking upstream floods as much as possible, minimizing the water level of the downstream mainstream, helping downstream cities to drain waterlogging and disaster relief, and greatly alleviate downstream pressure.
Is there any risk of "deformation" of the Three Gorges Dam
Global Times: Every year, some overseas media hype up alarmist remarks such as the "deformation" of the Three Gorges Dam and the "risk of dam failure". What is the current safe operation status of the Three Gorges Dam? Has there been any so-called "deformation" or other risks recently?
Person in charge of the Three Gorges River Basin Hub Management Center: Currently, the Three Gorges Dam is operating in good safety. There has not been any so-called "deformation" or other risks recently, and the Three Gorges Project is not as "fragile" and vulnerable as some people think.
In order to grasp the operation status of the Three Gorges Dam in real time and accurately, the safety monitoring project, as part of the main Three Gorges project, began to bury safety monitoring instruments as early as 1994. As of the end of June 2020, more than 12,000 instruments have been installed in the Three Gorges Dam. Supports and instruments are distributed throughout all permanent buildings, foundations and slopes of the Three Gorges Project. Monitoring items include special monitoring of deformation, seepage and seepage pressure, stress and strain, strong earthquakes, hydraulics and dynamics. In addition to professional monitoring based on advanced technology and equipment, manual inspections were also carried out. Rumors such as the "deformation" of the Three Gorges Dam and the risk of "dam failure" are alarmist talkers. Any speculation without scientific and careful monitoring data is unscientific, irresponsible, layman, or even with ulterior motives.
Global Times: Some people believe that the Three Gorges Dam has continuously discharged floods this year, which has aggravated the flooding in the middle and lower reaches. How do you respond to this statement? How much does the situation in the Poyang Lake water system have to do with the flood discharge of the Three Gorges?
Person in charge of the Three Gorges River Basin Management Center: Reservoir flood discharge is only a form of discharge from the reservoir through flood discharge facilities. Generally speaking, the outflow from the reservoir is given priority to passing through the unit, and only when the outflow flow exceeds the capacity of the unit. The use of deep hole, surface hole and other flood discharge channels, but the flood discharge of the reservoir does not mean that the reservoir has not played the role of flood control. For example, at 14:00 on the 2nd of this month, the flood peak flow of the Three Gorges Reservoir reached 53,000 cubic meters per second. According to the dispatching instructions of the Yangtze River Water Resources Commission, the outflow flow of the Three Gorges Reservoir should be controlled at 35,000 cubic meters per second. At this time, the full capacity of the 34 units of the Three Gorges Power Station is about 31,000 cubic meters per second. Therefore, the remaining flow of about 4000 cubic meters per second needs to be discharged through the flood channel. Although the Three Gorges is discharging floods, the total flow out of the reservoir is 35,000 cubic meters per second, which is still smaller than the inbound flow of 53,000 cubic meters per second, and it is still playing a role in preventing floods. The flood interception of the Three Gorges Reservoir reduced the flood control pressure of Poyang Lake and prevented the Poyang Lake Hukou Station from exceeding the guaranteed water level.