Since the flood season this year, from south to north, Changsha, Nanchang, Chengdu, Hangzhou, Wuhan, Nanjing, Beijing and many other cities have been embarrassed by heavy rainfall, showing severe waterlogging. "On rainy days, I went to see the sea" and "the car became a submarine", which became a popular ridicule for netizens.
Many talk articles argue that China should learn from Western countries and build large drainage pipes underground to allow the rapid accumulation of rainwater in urban areas to drain to rivers. Environmental education scholar Li Hao believes that many cities in developed countries now begin to pay attention to the use of rainwater resources to make up groundwater, and the method of treating rainwater has changed radically. The overall idea is to change "drainage" to "retained water". This is completely consistent with the planning thinking of trying to retain rainwater resources when building cities, gardens or houses in ancient China.
Environmental education scholar Li Hao recently observed in Germany and the United States how the cities there deal with rainwater discharge. She believes that managing the danger of urban waterlogging can be accomplished by changing the ground plan. These successful practices from ancient China and the modern West have a good effect of eliminating accumulated water, simple methods, and can be continued, which are beneficial to environmental protection and the use of rainwater resources. The accumulation of water in many cities is not only a problem of the underground pipe network, but the large-scale hardening of the city is also an important reason.
Reporter: Recently, many cities in China have experienced heavy rain or waterlogging. The first is that the underground pipe network standard is too low. Is it still composed of large-scale laying of hardened ground and cement in the city?
Li Hao: After the onset of waterlogging in Beijing on June 23, I went to Exit D of Taoranting Subway and the Lotus Bridge on the West Third Ring Road to observe the cause of the stagnant water caused by the heavy rain. The situation seen is that the main reasons for the occurrence of stagnant water in these areas are ground hardening, oasis ridges, no drainage holes on the road baffles, and no lowlands that absorb rainwater. Recently, cities in the north and the south are showing "heavy rain is flooding." I think that the problem of water accumulation in many cities is not just a problem of underground pipe networks. An important reason is the severe urban hardening phenomenon. There is a big misunderstanding in many cities. : Hardening is modernization. Modernization requires leaving the land, turning the land into concrete, and seeking luxury and beauty, which has brought severe environmental problems. After the city has hardened on a large scale, rainwater can only flow to low-lying places, and the road becomes a drainage ditch. Underneath the overpass and the tunnel, there is a simple accumulation of water, which constitutes urban waterlogging. Many urban planners did not consider the issue of rain and water when they were planning on the ground. Concrete floors are everywhere, and there is a seam between the bricks, which is impervious to water. After the "skin" of the earth hardens, the sky and ground are not connected with each other, resulting in high temperatures in the city, nowhere to rain, and floods. Underground pipe networks are not the trend of modern city construction in the world. Paris built a large underground pipeline more than 100 years ago to drain rainwater into urban rivers, and it is no longer doing so. Many studies in the 1970s in Europe and the United States have shown that the pollution of surface runoff caused by rainwater becomes a serious problem. Rain falling on the hardened ground of the city will be polluted by daily waste, car exhaust emissions, grease, heavy metals, pesticides and other dirty things, including even carcinogens. If drained into the underground pipe network and walked into the river, it will constitute a very serious problem. Large sewage discharge has severely affected river water quality and ecological environment. The drainage of many rainwater will also cause the groundwater in the city not to be recharged, which will cause water shortage.
These lessons were presented decades ago in developed countries, and now they are correcting this huge mistake, parting from hardened urban construction forms to reduce flooding. This is a serious change in the thinking of architectural planning in Western countries. Now in Germany, the proportion of urban permeable ground is required to be at least 60% and ideally more than 80% to ensure that waterlogging prevention and groundwater levels do not drop. Cities that can continue to develop in the 21st century can no longer harden the land on a large scale. The rainwater is dew, which is the water resource provided by God. Do n’t think about draining it immediately, you should try to keep it.
Reporter: Many ways to talk about the article are just one way out: China should learn from western countries more than 100 years ago, build large drainage pipes underground, and let the urban water accumulated in the rain quickly drain into the river. Your opinion seems to be different?
Li Hao: The old Western method of directly discharging surface runoff containing pollutants into rivers will pollute clean rivers. Repairing such a pipe network is not being initiated. Rainwater is dew, which is the water that God gave to the earth, and we should try to keep it. Change the method, let the rainwater flow into some artificial lakes, and store the water into water resources that are conducive to urban development. When the rain comes, the best way is to go underground and turn into underground water resources.
Our ancient people did just that, so that rainwater could go underground and enter the cycle of nature. In ancient Chinese villages, gardens, ancient temples, and imperial palaces, the proportion of permeable ground was mostly above 80%, which is the case of the Forbidden City. The Forbidden City has been built for more than 500 years, and there has been no record of flooding in ancient times. However, this year, netizens released photos of the water accumulation in the Taihedian Square of the Forbidden City caused by heavy rain in Beijing. I was not surprised to see that, because of the overhaul of the Forbidden City, the ancient floor tiles were changed to harden the past permeable ground. Distressed.
Now, in some communities in Germany, there is a rule for building new houses. The ground must be laid with permeable bricks, Dutch bricks, or green plants to allow rainwater to enter the site. If it is drained into the floor drain network, sewage charges must be paid. This represents the future trend of rainwater treatment. On June 23, the average rainfall in Beijing was about 50 millimeters, and Beijing's area was 16,700 square kilometers. Even if we counted it, about 800 million tons of water were dropped this time. Beijing now has 9.5 billion to 10 billion tons of precipitation a year. If such precious water resources can be retained, Beijing's water shortage can be alleviated.
Pay attention to above-ground planning: lay the permeable ground so that rainfall directly enters the ground; the oasis should be concave
Reporter: Laying permeable ground and increasing the area of oasis can help us retain the rain in the sky. What are your specific claims?
Li Hao: Recently, I took the opportunity of visiting Germany and the United States to investigate carefully how rainwater discharge is handled there. Some of their practices are worth learning.
Spread more water on the ground so that the rain falls directly into the ground. Flooring methods include the use of high-load non-sand concrete flooring, hole flooring, gravel flooring, brick or stone seam-type flooring, permeable brick flooring, and grid flooring. The permeable ground can filter surface pollutants, purify water quality, and let rainwater directly make up for groundwater. The area in the city that can be transformed into permeable grounds includes motor vehicle roads, pedestrian paths, squares, parking lots, construction sites, communities, schools, sports fields, and so on. If the city has wild vegetation zones, rainwater should be discharged into these areas, and the wild vegetation developed root systems should be used to transport rainwater into the ground. The surface ecology of wild vegetation areas is very active, which can well differentiate or remove various pollutants contained in surface runoff. Artificial oasis is also a good place to absorb surface runoff. As long as the height of the oasis is lower than the road surface to become a concave oasis, the oasis can fully receive surface runoff, obtain sufficient rainwater, and reduce the need for sprinkler water. Many oasises in Beijing have been built into high-topped oasis, but no concave oasis has been built. In China's ancient gardens and homes, the oasis planning is simply concave. In modern western countries, there is no calculus between the oasis and the road. When it rains, surface runoff can flow into the oasis and be absorbed by the soil. In addition, in order to improve the ability to absorb rainwater, the organic matter in the garden can be covered to increase the looseness and water retention of the soil. On the closed overpass, there should be more drainage holes at the baffle; grass side trenches and artificial lakes should be planted to collect rainwater.
Reporter: What else can be done to change the ground plan for controlling the danger of waterlogging?
Li Hao: On closed overpasses, there should be more drainage holes at the baffle. The density of the holes is approximately every 95 cm, and the width of the holes should be greater than 12 cm. These data come from the drainage hole plan of the stone railing base of the Forbidden City. These holes ensure that the abutment of Taihedian never accumulates water. The ground under the platform is a permeable ground composed of bricks and mud. Therefore, the water discharged from the holes can be absorbed on the ground without standing water. In the United States, well-drained overpasses have the same dense, larger-diameter rainwater straight drain holes, and the ground under the overpass is covered with stones and other methods to maintain good water permeability. This can prevent the accumulated water on the pavement of the overpass from converging under the bridge during heavy rain, which will cause waterlogging problems.
危险，在改动地上规划上还有哪些可做的工作？ Reporter: What else can be done to change the ground plan for controlling the danger of waterlogging ? These successful methods in ancient China and the modern West have a good effect of eliminating accumulated water, and the methods are simple and sustainable. They are beneficial to environmental protection and the use of rainwater resources. The tradition is there, the lessons are there, and in the face of the impact of waterlogging, we should calm down and find out the cause of waterlogging in our cities, find a new road, catch up with the trend of the world, choose the most economical and environmentally friendly methods to avoid standing Disasters, and turned heavy rain into a city's precious water resource.