Scientific risk avoidance during flood season is crucial. The Haihe River basin is crucial
Recently, affected by the adverse factors such as typhoon "Dusurai", the Haihe River Basin has experienced heavy to rainstorm, local extremely heavy rainstorm, and many places have suffered disasters. The Beijing Tianjin Hebei region has repeatedly issued a red rainstorm warning, closed the scenic spot, and reminded citizens not to go out unless necessary. At the beginning of the rainstorm, some people questioned whether the closure of scenic spots in Beijing was "making a mountain out of a molehill" on the social platform, and others were puzzled about the use of flood storage and detention areas. In fact, the closure of scenic spots and the use of flood storage and detention areas during the flood season are scientific risk avoidance measures taken after expert analysis by meteorological and water conservancy departments. They are aimed at maximizing the safety of people's lives and property, and are not a big deal.
From the precipitation of Haihe River basin in this round of rainstorm, it is imperative to open the flood storage and detention area. From July 28th to 11:00 on August 1st, the average rainfall in the basin reached 129 millimeters, with a total precipitation of over 40 billion cubic meters. How big is 40 billion cubic meters? The largest reservoir in China is the Three Gorges Reservoir in the Yangtze River Basin, with a total capacity of 39.3 billion cubic meters, including a flood control capacity of 22.15 billion cubic meters. This wave of precipitation has exceeded the total storage capacity of the Three Gorges Reservoir.
The average annual precipitation in the Haihe River Basin is far less than that in the Yangtze River Basin. Although the People's Republic of China attached great importance to water conservancy and built a large number of large, medium, and small reservoirs, it was not able to stop such extreme precipitation. This round of rainfall is the highest recorded rainfall in 140 years by instruments in the Beijing area. After the arrival of the flood, the water conservancy department finely adjusted the reservoir to intercept and reduce the peak, reducing the downstream flood control pressure. All 155 large and medium-sized reservoirs in the Haihe River Basin have been put into flood control.
Reservoirs and flood detention areas are important components of the flood control system. Flood storage and detention areas are low-lying areas and lakes outside river embankments that temporarily store floods. They are mostly places that have been submerged by river floods in history. When floods are too severe, using flood storage and detention areas to divide and store floods and reduce flood peaks can minimize disaster losses, which is a scientific and effective method in global flood control practice to reduce flood hazards.
According to the Revised List of National Flood Storage and Detention Zones, China has established a total of 98 national flood storage and detention zones, including 28 in the Haihe River Basin. Eight flood storage and detention areas have been successively opened in Haihe River basin due to this rainstorm flood. As of August 3rd, Hebei Province has transferred over 1.2 million people, including over 850000 people from flood storage and detention areas. Looking back at historical data, from 1950 to 2021, 66 out of 98 national flood storage and detention areas were put into use 424 times, with a cumulative flood storage and detention capacity of over 140 billion cubic meters.
From the historical experience of flood control and flood fighting, the weakening of rainfall does not mean that the danger is far away. After the rainstorm, the public still needs to pay attention to the meteorological warning and evacuate in time.
On the one hand, geological disasters have a lag effect. Rockfall is prone to occur along roads in mountainous areas after rain, and landslides and subsidence may occur after prolonged soil soaking. Especially in the western and northern parts of Beijing, as well as the western part of Hebei province, which have accumulated a large amount of rainfall, they are still in a period of geological hazard danger. In the next two to three weeks, the public should try to minimize their entry into mountainous areas and stay away from geological hazard points.
On the other hand, water flows from mountainous areas into plains, and the risk of flooding in low-lying areas remains high. In August 1963, the Haihe River Basin also experienced a rare extremely heavy rainstorm. After the rainstorm, the water level in the downstream river reaches the highest point two days after the rain stops, and the water flow returns to the river after the rain stops for 7 to 12 days. The ponding in the plains and depressions basically subsides until September, and Tianjin in the downstream fought against the flood for a month. Currently, the staggering rainfall of over 40 billion cubic meters is converging into floods that rush out of mountainous areas and into plains, posing a serious threat and requiring the use of flood storage and detention areas. The use of flood storage and detention areas requires the prior transfer of personnel within the area, which should be fully evacuated and must be evacuated.
From a long-term development perspective, the construction of China's disaster prevention system still needs further improvement. Taking flood storage and detention areas as an example, it can be considered to increase the construction of wetland parks that also serve as flood storage and detention areas. It is strictly prohibited to build houses on dry river beds. At the same time, compensation work should be carried out in accordance with laws and regulations for the flood storage and detention areas that have been put into use to help residents rebuild after disasters and restore normal living order as soon as possible after water withdrawal. Floods have no lovers and emotions, and disaster prevention and reduction require scientific strategies and concerted efforts.
