(Economic Observation) Authoritative interpretation: What is the serious waterlogging in Zhengzhou?
China News Service, Beijing, July 22. Title: Authoritative interpretation: What is the reason for the serious waterlogging in Zhengzhou?
Author Pang Wuji Lei Xiaolin
Heavy rains in Henan led to serious water accumulation and waterlogging in Zhengzhou.
Many local trains and buses were trapped, the subway was flooded, and cars were washed away in many streets.
Zhengzhou City has become a pilot project for the construction of sponge cities in Henan Province in 2016. Previously, it also proposed to invest 53.48 billion yuan (RMB, the same below) to build sponge cities.
People may wonder, after 5 years of sponge city construction, why can't we prevent waterlogging?
Data map: On July 21, 2021, heavy rain caused serious water accumulation in the urban area.
Photo by Wang Zhongju, published by China News Agency. Image source: CNSPHOTO
Not ordinary waterlogging
What is waterlogging?
Wang Jiazhuo, Dean of the Ecological Municipal Institute of the China Planning and Design Institute (Beijing) Planning and Design Company, said in an interview with a reporter from China News Agency that it mainly refers to cities where strong rainfall occurs locally that cannot be discharged, and it is accumulated locally and reaches a certain depth, causing certain harm. disaster.
Jia Haifeng, a professor at the School of Environment of Tsinghua University, also told a reporter from China News Agency that urbanization is one of the main reasons for the formation of urban waterlogging.
Some impervious constructions interfere with the water cycle and generate relatively large runoff.
Studies have shown that under the same rainfall, the runoff generated by highly urbanized areas can reach about 5 times compared with natural areas.
However, this time Zhengzhou is not ordinary waterlogging, Wang Jiazhuo said, but the flood and waterlogging are intertwined.
It can be seen from the video that rapid-flowing floods have formed on many roads in Zhengzhou, far exceeding the limits of urban water storage and drainage.
Jia Haifeng also believes that the main reason for the serious accumulation of water in Zhengzhou this time is the excessive rainfall under the global climate change.
This is a waterlogging caused by extreme events, which is actually a natural disaster.
Should Sponge City "back the pot"?
After years of sponge city construction, why is the waterlogging in Zhengzhou still serious this time?
Wang Jiazhuo pointed out that the construction of sponge cities is certainly effective, but it takes a long time and cannot be accomplished overnight, and the construction of sponge cities can only cope with rainfall within the flood protection standard.
Visually speaking, if a local bridge with a maximum load-bearing capacity of 50 tons is designed, and the bridge has not yet been completed, a 200-ton truck will arrive and collapse the bridge. “Can you tell that the bridge is not working? Useless conclusion?"
Jia Haifeng also said that when Zhengzhou was piloting a sponge city, it only selected a specific area in the city (according to national requirements, an area of more than 15 square kilometers).
For a city that is often thousands of square kilometers, a dozen square kilometers is very small.
And every system has its limits. People often say that the sponge city is "no waterlogging in heavy rain, no water accumulation in light rain, and no black and smelly water", but it does not mean that all the problems of waterlogging will be solved after the sponge city is built. It is also unrealistic.
Zhang Chen, a Chinese survey and design master and chief engineer of Shanghai Municipal Engineering Design and Research Institute (Group) Co., Ltd., told a reporter from China News Agency that how to resolve disasters caused by extreme climates is still a difficult problem both in China and internationally.
The recent heavy rain in Germany has caused huge disasters in North Rhine-Westphalia and Lai Fah. Hundreds of people in Germany have been killed due to urban flooding, mountain floods and mudslides.
Beyond the engineering fortification level
In April of this year, the General Office of the State Council issued the "Implementation Opinions on Strengthening Urban Waterlogging Control", which stated that by 2025, cities will basically form urban drainage with "source emission reduction, pipe network emission, storage and drainage simultaneously, and emergency exceeding standards" according to local conditions. Waterlogging prevention engineering system.
Wang Jiazhuo explained that these four stages can be said to cooperate with each other and each perform its duties.
Source emission reduction is mainly aimed at small and medium rainfall. For example, when the rainfall is below 20-30 mm per day, this part of the rainfall is absorbed on-site through permeable bricks and sinking green spaces.
When the rainfall is 30 mm/day to 30-50 mm/hour, the baton will be handed over to the pipe network for discharge.
When the rainfall reaches 50-70 mm per hour, drainage often needs to be dealt with by pumping stations, regulating storage and other facilities. This stage is called simultaneous storage and drainage.
Finally, when the rainfall exceeds 70-80 millimeters per hour, it is generally necessary to enter the emergency phase of exceeding the standard, because it is an extreme event and exceeds the level of engineering fortification.
The heavy rain in Henan Province has entered the emergency phase of exceeding the standard.
According to the China Meteorological Administration, the 1-hour rainfall in Zhengzhou, Kaifeng and other places from 8:00 on the 17th to 6:00 on the 21st exceeded 100 mm, of which the maximum hourly rainfall at the Zhengzhou Meteorological Observatory reached 201.9 mm (16:-17 on the 20th) , Breaking through the historical extreme value of hourly rainfall in mainland China.
Wang Jiazhuo explained that the surrounding rivers and lakes are also full, and there is no place to drain it. The drainage system can no longer solve it.
How to manage urban waterlogging?
In response to waterlogging caused by extreme weather, Wang Jiazhuo said that extreme weather cannot be avoided and prevented, but some measures can be taken to reduce disaster losses.
First of all, we must not have a fluke mentality, and we must increase emergency response efforts, including strengthening the prediction of disasters, clarifying the connotation of each early warning level, and improving emergency plans.
It is also necessary to strengthen publicity and public education to raise the public’s awareness of taking the initiative to avoid disasters.
At the same time, investment should be increased to improve facility standards.
In addition, in the process of urban development and construction, Wang Jiazhuo said that more measures should be taken to "leave white and increase green" and leave more space for water in order to mitigate disasters.
Jia Haifeng believes that we should attach importance to the construction of resilient cities so that we can quickly restore urban functions while ensuring safety when encountering similar extreme rainfall.
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