What does it mean that "the water level in the Three Gorges Reservoir exceeds the flood control limit by nearly 2 meters"? Zhang Boting explained his doubts

  Surging News Reporter Yang Yang

  "Due to the recent heavy rainfall, the water level in the Three Gorges Reservoir area has continued to rise. At present, the water level in the reservoir area is close to 147 meters, which exceeds the flood control limit by nearly 2 meters." On June 21, a report from CCTV Finance and Economics attracted network attention. Due to the recent occurrence of over-alarm and above floods at multiple tributaries and multiple stations in the Yangtze River Basin, some netizens expressed concern that the Three Gorges “exceeded the flood control limit by nearly 2 meters”: does this mean that the reservoir is unsafe?

  This is not the case. "Flood limit water level is the sign that the reservoir has the largest flood control capacity, and it is completely different from the concept of warning water level that will cause a flood hazard once it is exceeded." Zhang Boting, deputy secretary general of China Hydropower Engineering Society, accepted the surging news (www.thepaper.cn ) Explained in the interview that the so-called flood limit water level is actually the water level where the reservoir has the largest flood control capacity.

  Generally speaking, during the non-flood season, the reservoir maintains a high water level for functions such as water supply, power generation, and irrigation. But before the flood season comes, the reservoir must lower the water level to the flood control limit level to free up the reservoir capacity to meet the coming flood. The normal storage level of the reservoir of the Three Gorges Project is 175 meters, and the corresponding storage capacity is 39.3 billion cubic meters. During flood season, flood control limits the water level to 145 meters, and the flood storage capacity is 22.15 billion cubic meters. In the report on June 21, the water level in the reservoir area "close to 147 meters" and the 175-meter water level still have more than 20 billion cubic meters of flood storage capacity.

  According to Zhang Boting, in the past, due to the insufficient development of science and technology and information technology, people's forecasts of long-term weather were not very accurate. Therefore, in order to ensure that the reservoir plays a good role in flood control, the reservoir is generally required during the flood season to operate at the flood-limiting water level with the largest flood control capacity.

  According to previous news released by the Three Gorges Group, in December 2019, the Three Gorges Reservoir started this round of pre-flood decay work, with an initial water level of 174.79 meters. At 17:00 on June 8 this year, on the eve of the main flood season of the Yangtze River, the upstream water level of the Three Gorges Dam had dropped to the flood control limit level-an elevation of 144.99 meters, 22.15 billion cubic meters was vacated in advance, equivalent to more than 1,550 West Lakes. All flood storage capacity. The Three Gorges Reservoir began to enter the flood control operation stage.

  According to the above-mentioned news, “According to the relevant dispatching regulations, in principle, the water level of the Three Gorges Reservoir will be controlled and operated according to the flood control limit water level of 145 meters in order to ensure sufficient flood storage capacity. Using the flood storage capacity vacated in advance, the floods will be stored in the reservoir; after the floods recede, the Three Gorges Reservoir will gradually lower the water level to 145 meters under the premise of ensuring the safety of the downstream and the stability of the reservoir bank. Possible floods."

  Including the Three Gorges Reservoir, according to the Ministry of Water Resources, as of 18:00 on June 8th, the controlled reservoir group included in the joint operation has vacated about 56 billion cubic meters of flood control capacity, and some reservoirs have 21.7 billion cubic meters below the flood limit. The storage capacity can be adjusted by 40 meters. The 40 controlled reservoirs have a total storage capacity of 77.7 billion cubic meters.

  The Yangtze River Water Resources Commission of the Ministry of Water Resources requested on June 22 to strengthen the management and management of controlled reservoirs, scientifically dispatch the reservoirs such as the Three Gorges and Danjiangkou, and block flood peaks to ensure the safety of flood control and water supply.

  For many years, the operation of reservoirs in flood seasons in our country has basically adopted a fixed-time and fixed-flood water level scheduling method. Taking into account factors such as joint operation of upstream reservoirs, power generation, shipping, and flood control, Zhang Boting suggested that it is more scientific to change the current fixed and static flood limit water levels to dynamic indicators.

  Zhang Boting told Peng Mei News that with the development of science and technology, modern long-term weather forecasts have been quite accurate. In addition, many cascade reservoirs have been built in various watersheds in my country. The flood control effect of a single reservoir does not always have to be the best. "Each year when the water level of the Three Gorges Reservoir increases by one meter, it is estimated that about 500 million kilowatt-hours of electricity can be added. More importantly, in the year of extreme drought, maintaining the flood-limiting water level may also cause huge water loss. For example China’s large reservoirs such as the Three Gorges and Longtan have all experienced water shortages due to the extreme drought in autumn, affecting the supply of water resources throughout the dry season."

  With the development of modern science and technology, developed countries have adopted more scientific dynamic flood limit levels. "No longer pursue a single reservoir, we must reduce the water level to the flood limit water level during the flood season. Instead, we will implement dynamic flood limit water level management based on the forecast of the water regime and the comprehensive flood control capacity of the cascade reservoir group. On the premise of ensuring the safety of flood control In order to maximize the benefits of the reservoir’s water resources."