In recent years, with the global climatechange, extreme weather such as heavy rains and typhoons around the world haveled to more and more frequent "flooding" incidents. The sewers havebeen praised by Hugo as “the conscience of the city.” In this issue, let ustake a look at how foreign cities have created green drainage to prevent urbanshackles.
No one in Japan throws things at the sewer
Japan is surrounded by the sea, there aremany inland rivers and their branches on the land, and there are many mountainsand the ground is undulating, which makes it easy to accumulate water in thelower part. Therefore, Japan has experienced many severe storms and floods.
After the floods, Japan tried to buildurban flood drainage facilities. Today, Japan generally relies on a wide rangeof sewers, urban drainage ditches, and collecting rainwater to solve stagnantwater. In Tokyo, the sewer network extends in all directions, with a totallength of about 16,000 kilometers. These sewers allow the rainwater that fallson the road to drain quickly. As long as it is not a torrential rain, there isvery little water in Tokyo. Office workers only need to wear a pair of ordinaryleather shoes in the rainy days to ensure that the shoes and socks are not wet.There are many ditches for flood drainage in Japanese cities. Some of theseditches are branches of inland rivers, and some are dedicated to drainagechannels. Although the city is full of gold, the government has never buriedthe drainage ditch in order to build commercial facilities, and does notarbitrarily change the direction of the ditch.
The Japanese have a strong sense ofprotecting the sewers and have strict management of the use of sewers. The Lawon the Prevention of Water Pollution is formulated. In ordinary Japanesehouseholds, the sink has a large drain, but it must use a special mesh with avery fine mesh, so there is almost no big thing to enter the sewer; in thebathroom and the washroom, it is not allowed to directly pour the hair into thebathroom. Sewer; Japan also stipulates that it is not possible to pour oil intothe sewer. The Tokyo Metropolitan Sewerage Bureau advocates that people shouldwipe it with waste paper before washing the dishes or the oil pan, and thenwash it with water to prevent the oil from entering the sewer and solidifying,causing obstruction. The Tokyo Metropolitan Sewerage Bureau also emphasizedthat if oil and hair are directly washed into the sewer, it may be directlywashed into the river by heavy rain and pollute the environment. In addition,Japan also has waste cooking oil coagulants, special cleaning agents for sewerpipes, etc., which are used to protect the drainage system from blockage. Theapartment where the author resides is directly contracted by the property andthe waterway cleaning company. The semi-annual use of high-pressure water forfree cleaning of the sink, bathroom and washing machine drains for theresidents, so there has never been a sewerage in the past 10 years. More importantly,Japanese residents are more conscious of not throwing things into the waterway.This is the most important factor for the Japanese drainage system to maintainefficient and smooth flow. ▲
600 years artificial river protection Seoul
As a peninsula country, South Korea isconducive to rapid drainage from a geographical perspective, but large amountsof precipitation in a short period of time may still cause local flooding.Every time the flooded city was flooded, the South Korean government and citymanagers continued to “reinforce the dead”, and now the casualties and propertylosses caused by heavy rain in South Korea are gradually decreasing.
The Qingxi River reconstruction in thecenter of Seoul is a typical case of the combination of urban environmentaltransformation and flood control. Cheonggyecheon was an artificial riverexcavated by the Joseon Dynasty to exclude water from the city of Seoul morethan 600 years ago. From 1937 to 1978, Cheonggyecheon was covered with cementslabs and became an invisible underground river. Later, the mayor of Seoulrushed to discuss the ecological restoration of Qingxi River and thesurrounding environment reconstruction project. In the past two years, the5.8-kilometer Qingxichuan Road and the viaduct covered on it were demolished,and the waterfront ecological landscape was constructed. Free time. The projectwas completed in October 2005, and Cheonggyecheon reappeared as a city centerlandscape in the lives of Seoul citizens. In addition to greening and improvingthe small environment of the city center, an important consideration in thedesign of the Cheonggyecheon Rehabilitation Project is urban drainage, which isdesigned to withstand floods once in 200 years. Usually, people can go down tothe hydrophilic platform and get close contact with Cheonggyecheon. Once thereis strong precipitation, Cheonggyecheon will seal the river, and the mainfunction will be turned into urban drainage. The rainwater flows intoCheonggyecheon through the various drainage outlets in the center of Seoul.After the facilities of the pool, you can return to the Han River. It is withthe city's drainage artery in Cheonggyecheon that the main business district ofSeoul can be shocked during the torrential rains. ▲
US water accumulates on the spot
Hurricane Katrina, which took place in NewOrleans, USA in 2005, reminds me of it. At that time, 70% of New Orleans'cities were flooded, and a beautiful tourist city turned into a vast ocean. Afriend lived in the flood-stricken area at that time. After the embankmentcollapsed, her house was not flooded, and the home that she struggled for morethan a decade was turned into nothing. In 2015, I came to the area where NewOrleans once suffered floods. The district is still under construction, and thenew housing foundation is a whole higher than the first floor.
Floods are one of the most serious naturaldisasters in the United States. River water levels, increased rainfall, andhurricanes can all pose flood risks. Although the United States does not have aunified flood control bill, the states will decide according to the actualsituation. In addition to traditional dams, concrete buildings are used todefend against floods. In the rainy season every year, many places in NewOrleans will still have internal entanglement. Since the whole city is about 3meters below sea level, the water is extremely difficult to discharge. Whenwater is accumulated, people will pump the water out, but the effect islimited. Later, the city government selected one of the districts forexperiments to re-inject the stagnant water into the marshes and soil. Theurban environment has a more benign cycle, which has played a very importantrole in improving the entire ecology. It not only solves the problem of wateraccumulation, but also protects the land and improves the air quality. Theproject is now in beta and will be rolled out to other regions and cities inthe future.
The weather is unpredictable, the flood isruthless, even in developed countries, it is also facing the risk of guilt, andneeds to be improved with climate change. Preventing in advance is far moreimportant than post-disaster reconstruction. ▲
German drainage, eight-pronged
Germany is a country with frequent floodsand floods, especially in the basins such as the Elbe River and the DanubeRiver. It is often threatened by floods. To this end, cities across Germanyhave built drainage systems consisting of urban sewers, reservoirs,depressions, and beaches to keep the city as far away as possible.
Sewer system. Germany is the first countryin Europe to establish a sewer system. As early as 1842, Hamburg built acity-wide drainage system. In 1867, Frankfurt built the first systematic modernsewer system. At present, the German public drainage pipeline has reachednearly 600,000 kilometers, which can prevent urban floods and accumulaterainwater.
Depression - seepage system. This is a newtype of rainwater treatment system that has been promoted in Germany in recentyears, including the installation of depressions and seepage channels. Thesefacilities are connected to drains with holes to form a distributed rainwatertreatment system. Through the short-term storage of rainwater in low-lyinggrassland and long-term storage in the seepage, it is guaranteed that as muchrainwater as possible will be infiltrated. At the same time, the system delaysthe rainwater flooding time, reduces the burden of the drainage pipeline, andplays an important role in disaster prevention and mitigation. In addition, dueto the timely replenishment of groundwater, land subsidence can be prevented,thus creating a virtuous circle of urban hydrological ecosystems.
River beaches and ecological fields. “Therelationship between flood control and natural river beaches is very close.”Destel, director of the Institute of River and Beach Research at KarlsruheUniversity of Technology in Germany, said that the government is now mainlyadopting engineering and technical measures such as building flood walls andincreasing dams. These measures are not enough. River beaches and ecologicalfarmland should be restored to improve water storage capacity. Below the floodcontrol levees of cities such as Cologne, Germany, there is a wide river beach,and the flood can temporarily serve as a diversion.
Large area city park. Many urban centers inGermany have large urban parks. For example, the British garden in Munichcovers an area of about 410 hectares. The Tiergarten park in the center ofBerlin covers an area of about 210 hectares. After many large buildings aredeactivated or abandoned, the German government will consider planning it as acity green space or park. A huge "reservoir".
Green roof. It can not only control thetemperature rise through evaporation of water, but also absorb more rainwaterand reduce the pressure on urban pipelines under heavy rainfall. Expertsbelieve that if the roof greening work can reach a certain density, at least60% of the rainfall can be retained.
Permeable pavement. Since the 1960s,Germany has been working on the development of various rainwater infiltrationdevices. At present, many urban areas such as sidewalks, bicycle lanes, andsuburban roads are subject to water-permeable floor tiles, leaving a gapbetween bricks and bricks to allow water to pass through. There are also someroads paved with fine gravel or fine cobblestones. The permeable pavement notonly solves the problem of water accumulation, but also balances the urbanecosystem.