Our reporter Li Jie                       

  After the flood season this year, the Yangtze River Basin experienced frequent rainfall and the flood control situation was very severe.

For many "Three Gorges people", this is a "big test".

  The Three Gorges Reservoir is the core of the upstream cascade reservoirs and the "master switch" for controlling the inflow of water from the middle and lower reaches.

  From July 2nd to August 17th, more than a month, 5 times of flooding were entered into the storage.

The flood interval is short, continuous and multi-peak, and accompanied by the largest flood peak of 75,000 cubic meters per second, the Three Gorges Project is facing the biggest test since the construction of the reservoir.

  Precise forecast and scientific dispatch!

In the vast Yangtze River basin, the Three Gorges Project is like a "copper wall and iron wall" across the river. Sometimes it opens up, intercepts floods and cuts peaks, sometimes opens sluices to drain waves, and releases flood reservoirs. In the game with the floods, it is defending. The downstream main stream flood prevention safety.

  To protect the Yangtze River.

After this battle, people have re-understood the Three Gorges Project, a major national weapon.

Panorama of the Three Gorges Project on the Yangtze River in China.

Photo by Zheng Jiayu

  Historical level response

  ——Refreshing many records since the construction of the Three Gorges Project: the largest flood peak, the largest flood storage capacity, and the first orange flood warning

  75,000 cubic meters per second!

At 8 o'clock on August 20, the largest flood peak since the construction of the reservoir in 2003 arrived at the Three Gorges Project.

  In the forecast analysis room of the Yangtze River Electric Power Dispatching Center of the Three Gorges Group, the data from each station is still streaming continuously, flashing in the computer.

The forecasters breathed a sigh of relief: it is no different from the forecast result!

The scheduling plan can be implemented smoothly.

  Affected by the continuous heavy rainfall from August 15 to 17, many tributaries such as the Minjiang, Tuojiang, and Fujiang tributaries in the upper reaches of the Yangtze River have historically ranked peak discharges.

At 20 o'clock on the 17th, the Three Gorges Project ushered in the Yangtze River's No. 5 flood in 2020, and the peak discharge exceeded the maximum since the construction of the Three Gorges Reservoir.

  What is the concept of 75,000 cubic meters per second?

According to calculations, the same flow will fill a West Lake in about 3 minutes, and fill a Taihu Lake in about 16 hours.

In the 1998 catastrophic flood, the maximum peak flow rate was 63,300 cubic meters per second, which was about 80% of the peak of "Flood No. 5".

"Without the Three Gorges Project, the pressure and tension in the middle and lower reaches of flood control would be unimaginable." said Gao Yulei, a senior engineer at the Three Gorges Group Basin Hub Operation Management Center.

  In order to withstand the flood peak of 75,000 cubic meters per second and reduce the flood control pressure in the middle and lower reaches of the Yangtze River, the Three Gorges Project played a role of blocking flood peaks, opening 10 deep flood discharge holes and 1 drift hole to control the discharge flow at 49,200 cubic meters per second .

  Lasts up to 10 hours!

From 18:00 on August 20, the inflow of the Three Gorges Project began to slowly decrease, marking the Yangtze River's No. 5 flood peak in 2020 smoothly passing through the Three Gorges.

  The flood process also refreshed many records since the construction of the Three Gorges Project: the largest flood peak, the largest flood retention capacity, and the first orange flood warning.

  According to hydrological restoration calculations, if the upstream reservoir group centered on the Three Gorges does not block the flood peaks, the Jingjiang flood diversion area must be opened, 600,000 people in the flood diversion area will be transferred, 493,000 mu of arable land and more than 100,000 mu of aquaculture area will be submerged .

  "Flood peak height is large, continuous and multi-peak", this is a feature frequently mentioned by the staff involved in flood control in interviews.

From July 2 to August 17, the Three Gorges Reservoir had five times of numbered floods entering the reservoir in more than a month, of which the interval between the fourth and fifth floods was only 80 hours.

Since the flood season, the Three Gorges Reservoir has successfully responded to 12 floods of the order of more than 30,000 cubic meters per second, ranking first since the construction of the reservoir.

  "This year's flood situation is the most tense since the construction of the Three Gorges Project, and the difficulty of dispatching has also greatly increased. However, the joint dispatch of the Three Gorges, Xiluodu, Xiangjiaba, Wudongde and other reservoir groups has effectively guaranteed the flood control safety of the middle and lower reaches of the Yangtze River. "Gao Yulei said.

The employees of the Three Gorges Power Plant are inspecting the jacking equipment of the Three Gorges plant.

Photo by Jiang Yu

  "Everything is based on forecasts"

  ——The peak value of 75,000 cubic meters per second of "Flood No. 5", which is predicted 48 hours in advance

  Rain and water conditions change rapidly. The Yangtze River Basin involves a wide range of areas. In the face of unknown floods, how much and how long will the flood discharge be, and how can it be scientifically controlled?

  "It can be said that everything is based on forecasting." said Guo Le, director of hydrological forecasting of the Yangtze River Power Station Dispatching Center of the Three Gorges Group.

The flood peak value of 75,000 cubic meters per second of "Flood No. 5" was predicted 48 hours in advance.

  The meteorological and hydrological forecasting department is known as the "staff" of flood control and the "clairvoyance" of water and rain conditions. It is an important guarantee for the development of flood control, power production, and engineering construction.

  Precise forecasts come from hard-core technology support.

In the forecaster's computer, there will be such a water and rain information system in the Yangtze River Basin, which is full of scattered telemetry stations.

Key data such as rainfall, water level, and flow rate can be transferred to the forecasting system every 10 minutes.

There are more than 11,000 telemetering stations connected to the system in this way, of which 642 are self-built telemetering stations belonging to the Three Gorges Group, which are equivalent to independent "weather stations."

  In addition to the collection of information, forecasting systems and models are equally critical.

Last year, the Ladder Dispatch Center began to produce refined numerical forecast products, which effectively improved the flow forecast accuracy and forecast period.

"We use a grid-based forecasting model, which is equivalent to dividing the Yangtze River basin into many small grids, which are getting smaller and smaller in space and more frequent in time, which promotes the continuous refinement of rain and water regime forecasts." Guo Le said.

  Accurate forecasts also come from the team's coordinated operations.

Hydrological forecasting depends not only on the support of hard data, but also on forecasters' judgment on the actual conditions of the Yangtze River Basin, and continuous manual interaction and data correction. Experience and continuity are both important.

"Since the flood season entered this year, the floods have continued to peak, and it is even more necessary to maintain continuity of work. Almost everyone is spinning." Guo Le said that even when the shift is arranged, it is like a 400-meter relay race, requiring a forecaster. For a period of "accompaniment run", it was transferred to the "next club".

  In order to calculate the most accurate flow rate, the forecasting team worked hard to "rush forward", adopting the hard-core model of "two main values, one sub-value, basin coordination, full check, and 24-hour duty", nailing itself like a nail In the post.

The picture shows the Three Gorges Dam, which is opening a deep hole for flood discharge on August 19.

Photo by Zheng Jiayu

  "Find the optimal solution for scheduling"

  ——Dynamic flood control, through scientific formulation of dispatching plans, to make the Three Gorges Project "live"

  "The flood conditions in the middle and lower reaches of the Yangtze River are severe. May I ask whether the value of the reservoir flow reduction of the Three Gorges Reservoir has been determined tomorrow. Our suggestion is..." The most anxious July and August, the duty room of the Yangtze River Electric Power Distribution Center often heard such dialogues. On the other side of the phone, the staff on duty are often in intense discussions.

  Since the flood season this year, Yangtze Power has received and implemented 57 orders from the Yangtze River Commission, issued more than 2,400 cascade power station gate opening and closing instructions, and the total storage of cascade reservoirs was 34.865 billion cubic meters.

  With the forecast of water and rain conditions, it is also necessary to formulate a scientific dispatch plan to make the Three Gorges Project "live".

  Gao Yulei introduced that the Three Gorges Dam is for dynamic flood control, rather than keeping the floodwater in the reservoir.

Before the general flood, the water level should be lowered to free up the storage capacity; when the flood enters the reservoir, the upstream and downstream situation should be combined to release the flood to ensure that the water level of the downstream control station is kept within a safe range; after the flood passes, once the downstream flood control situation improves, seize Favorable opportunity to lower the water level of the reservoir and free up storage capacity for the next flood.

  Although the Three Gorges Reservoir is large, its total storage capacity only accounts for 8.7% of the annual runoff at the Three Gorges dam site compared with the water volume of the Yangtze that goes to the east. Therefore, the inflow of the Yangtze River upstream of the reservoir can only be adjusted between seasons. Seasonal regulation reservoir.

  Blocking floods, cutting peaks, and staggering peaks are the main ways the Three Gorges Reservoir plays its role in flood control.

Flood interception means intercepting 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; peak cutting means reducing the large flood peaks from upstream and reducing the outflow of the reservoir when the downstream flood control situation is tense. Relieve downstream flood control pressure; peak shifting means to prevent upstream flood peaks from encountering downstream flood peaks and increase downstream flood control pressure.

  The truth seems uncomplicated, but behind every scheduling, not only is the time and situation, precise calculations, but also a balancing technique that is considered by multiple parties.

"It is necessary to make a comprehensive judgment on the Yangtze River Basin and the Three Gorges Project. It is necessary to consider not only the safety of the pivotal dam, but also the shipping, power generation and other factors, and at the same time coordinate the layout. This is a complex, systematic, Scientific decision-making process." Gao Yulei said.

  Flood is the order.

As early as the end of last year, the Three Gorges Reservoir started to fade before the flood, and prepared for the flooding of the reservoir in advance. Since the flood, all parties have been waiting for it.

"From once a day to three meetings a day, four or five sets of plans are presented each time. The work intensity and density are much higher than in the past, in order to report accurately and calculate carefully, find the optimal solution, and ensure the safety of the Yangtze River." Three Gorges Flood Control People rush to the front line.

  Good operation indicators of the dam

  ——The current performance of the dam is better than expected and design standards in all aspects. In mid-September ushered in a 175-meter experimental water storage

  “Colleagues of the flood season department conduct daily inspections, with a cumulative trip of more than 100 kilometers, and the total number of floors climbed up and down is about 600 floors." At the beginning of the flood season, Peng Liangliang, the duty officer of the Three Gorges Power Plant, and his colleagues started the daily inspection during the flood prevention period. mode".

Once the inbound flow reaches 30,000 cubic meters per second, they will guard key parts such as the flood discharge dam section for 24 hours to ensure the safe and stable operation of equipment and facilities.

  The safety of the Three Gorges Project is the basis of dispatch and operation, and it is also a topic that the society pays close attention to after flooding.

  "On the basis of doing a good job in the daily monitoring of the Three Gorges Project, we strengthened the flood season observations. On the one hand, we conscientiously do a good job in data collection, and conduct real-time assessment of the safety status of the dam based on the monitoring data; on the other hand, technicians are on duty at the construction site 24 hours a day And intensify on-site inspections and inspections.” said Geng Jun, a senior engineer at the Monitoring Center of the Three Gorges Group Watershed Hub Operation Management Center.

  In order to comprehensively, accurately, and timely grasp the working behavior and safety status of each building and its foundation, in the early stage of construction, the safety monitoring of the Three Gorges Project was included in one of the eight major technical designs of the Three Gorges Project, and the layout covered all Complete monitoring system for buildings, foundations and engineering slopes.

  "From our monitoring results of key indicators such as dam stability, stress and strain, the monitoring values ​​are all within the design allowable range." Geng Jun said, "It can be concluded that since the flood season this year, the Three Gorges Hydropower Project has Industrial buildings and flood discharge facilities are in normal operation, and the dam's various operational indicators are good."

  Practice shows that the Three Gorges Project has withstood the most severe flood test since the construction of the reservoir.

"The construction of the Three Gorges Project is a millennium plan. The Three Gorges Project has undergone a large amount of scientific research, engineering practice, and data monitoring for decades from demonstration to construction to operation. This work tells us an indisputable fact that the current aspects of the Three Gorges Dam The behavior is better than expected and design standards." said Fan Xiaxia, member of the Party Group and deputy general manager of the Three Gorges Group.

  But at the same time, the Three Gorges Project cannot be labeled "all-round."

  "It needs to be emphasized that the Three Gorges Project is a key backbone project in the flood control system of the Yangtze River, but not all of it. For the Yangtze River Basin, flood control projects should be done in all river sections and tributary water systems. The complexity of the Yangtze River flood control problem It determines the arduousness and long-term nature of the flood control of the Yangtze River," said Lei Mingshan, chairman of the Three Gorges Group.

  September 10 is approaching, and the Three Gorges Reservoir will usher in a new task: 175 meters of experimental water storage.

Historically, the possibility of flooding in September cannot be ruled out, but the reservoir has now vacated enough storage capacity.

The current work is being carried out in an orderly manner in the coordination of flood control and water storage.

The great power will continue to benefit the national economy and people's livelihood in the game with water.