Can we refuse to "see the sea" this summer? Construction | Management | City
For the Jiangnan region, including Shanghai, there is a rainy season before July and a typhoon season afterwards. Rainwater and flood management is an important part of urban planning and construction. From a global perspective, how to avoid extreme weather causing "urban inland seas" has become a challenge faced by many countries and regions.
In recent years, many international metropolises have suffered from urban waterlogging, resulting in heartbreaking losses of life and property.
In 2011, in Copenhagen, continuous rainstorm triggered floods that destroyed many infrastructures, resulting in sky high insurance compensation. In 2016, London was hit by rainstorm, and many roads became waterways, which is still fresh in the memory of many people.
In cities, high precipitation and prolonged rainfall are the causes of waterlogging. On the one hand, the drainage systems in some areas are not up to standard or aging; On the other hand, during the rapid expansion of cities, the natural systems that originally had the function of water storage, flood control, and peak shifting were destroyed.
As the frequency of extreme weather increases, the impact of rainwater further intensifies, such as shortened convergence time and increased peak flow, leading to frequent disasters and the loss of rainwater resources that could have been recycled. How to be proactive? Each country has its own unique focus based on local conditions.
The concept of "low impact development"
Practice in multiple countries
In recent years, countries such as Europe and America have been exploring solutions centered around "low impact development". In the 1990s, this concept was born in Maryland, USA, but it took root in Europe.
The core of low impact development is to reduce the impact of urban development and construction on rainwater. Most of the implementation forms are imitating the local runoff cycle and natural hydrological cycle, mainly through infiltration, storage, groundwater evaporation, replenishment, retention, transpiration, etc., in order to minimize the interference of artificial construction on urban rainwater, with a focus on the decentralized utilization and control of the source system.
The related technologies are constantly developing and iterating. Currently, while reducing the generation of urban rainwater runoff, it can also reduce flood peaks and runoff volumes, allowing the region to retain most of the rainwater runoff in place without freeing up large areas of land resources, replenishing groundwater, and preventing urban flooding disasters can be a win-win situation.
Some countries and regions, such as Germany and the United States, ensure and promote the control and utilization of rainwater in urban low impact development facilities through laws, regulations, and policies, and promote the optimization of water resource management through multi-party coordination.
The development of rainwater utilization technology in Germany has become quite mature. Here, the most basic rainwater utilization unit is residential buildings. Through careful design in the early stage, roof rainwater can be collected and treated through rainwater drainage pipes for flushing toilets and greening irrigation. This mode is called roof rainwater collection system.
At the 1867 Paris World's Fair, architect Rabiz Carl exhibited his "Roof Garden" model, and more and more green roof technologies were applied in Germany in various forms. For example, rooftop lawns, sky gardens, and hybrid types of both require careful selection of plants and soil thickness. Scientists have also developed lightweight matrix materials specifically to reduce roof loads. The large-scale use of these technologies plays an important role in reducing rainstorm runoff and beautifying the city.
It is worth mentioning that in recent years, "Green Roof 2.0" has emerged - hybrid photovoltaic cells have been added to green roof systems. The principle is that the lower the ambient temperature, the better the performance of the photovoltaic cell. Compared to other traditional roofs, the transpiration potential of green roofs significantly cools the roof surface, thereby improving the performance of photovoltaic cells. At the same time, photovoltaic panels also shield some of the roof surface, reducing sunlight exposure and reducing evaporation rate on green roofs.
In Spain, engineers completed a pilot scale photovoltaic roof greening experiment and found that the power generation efficiency of hybrid photovoltaic green roofs with chrysanthemum plants and hybrid photovoltaic green roofs with Sedum plants was 1.29% and 3.33% higher than that of gravel roofs, respectively. They also used models to simulate green roofs in the UK and Denmark respectively, evaluating their optimal environment and potential to achieve sustainable development and maximum utilization.
The ecological community rainwater utilization system is a comprehensive rainwater utilization technology that emerged in Germany in 1990. One typical example is the Wallstadt residential community located in Mannheim. The rainwater in this residential area flows into the open channel through a wide and shallow channel with a certain shape on the ground. The open channel is constructed in imitation of natural rivers, with springs or shaped buildings built in certain areas, and aquatic plants planted along the channel. The bottom of the open channel is treated with anti-seepage to maintain the stability of the water surface. If the water volume is too large, it will automatically overflow through the anti-seepage layer to replenish groundwater. The construction of ecological communities relies on the natural purification effect of aquatic plant systems or soil, combining rainwater utilization with landscape design to achieve control and utilization of rainwater within the community through forms such as rooftop gardens, water features, infiltration, and reuse of reclaimed water.
In some cities in the United States, the concept of low impact development has been implemented in the construction process of "green streets". The urban road ecological drainage system in the United States integrates road greening into the management of street rainwater. Its core is the management and utilization of rainstorm runoff. Typical cases include the green street project on the 12th Avenue in the southwest of Portland, and the green street and parking plan in San Mateo County, California. The Green Street project has transformed some parking spaces on the roadside into an ecological treatment system that integrates rainwater collection, regulation, and treatment. In actual operation, the street's runoff can be controlled almost throughout the year through this ecosystem.
In Australia, urban planners and engineers conduct extensive cutting-edge research and interdisciplinary discussions around the technological core of low impact development. The Melbourne Edinburgh Rainwater Garden has effectively solved the local drought problem for many years. Rainwater gardens, as a low impact development facility with simple structure, low cost, easy maintenance, and good rainwater purification effect, are widely used. The principles of Mariwood Rainwater Gardens and Burton Forest Rainwater Gardens in Oregon, USA are the same.
Japan strengthens non-technical means
Singapore launches ABC program
Japan, which is located in Asia with our country, also faces the challenge of rain and flood disasters year-round due to its specific climate and terrain conditions.
Japan is located on the eastern edge of the Asian monsoon climate zone, with high annual precipitation intensity and concentrated rainfall time. The data shows that its annual rainfall is twice the global average annual rainfall. Every year, the rainfall period here is mainly concentrated from June to August, when the rainy season and typhoon season alternate. Summer often experiences heavy rainfall, making it the season with the highest risk of rain and flood disasters throughout the year.
From a geographical perspective, Japan is a mountainous country, with mountainous and hilly areas accounting for over 80% of its land area, far higher than the 20% -40% level of European countries. The steep terrain of the mountains results in fast rainfall runoff rate and short catchment time, which places particularly high demands on the immediate drainage capacity of urban areas. Many cities in Japan are concentrated at low-lying sea entrances, and heavy rainfall has caused many flood disasters.
When it comes to urban flood control and disaster prevention in Japan, the most distinctive feature is its multifunctional rainwater regulating pool. On the basis of traditional and single function rainwater regulation ponds, Japanese urban management departments have developed multifunctional regulation and storage facilities, which have the characteristics of high design standards, large scale, and high efficiency investment. In the non rainy season or in the absence of heavy rainstorm, the multi-functional storage facilities can also fully or partially play a variety of functions such as urban landscape, parking lot, sports ground and entertainment place.
In addition to specific technical means, the policies and regulations in the urban rainwater and flood management guarantee system in Japan are gradually improving, becoming the key to non-technical disaster prevention.
Looking back on its development path - in response to the increasingly frequent floods, Japan promulgated the River Law in 1896, which was a milestone in Japan's flood control policy. According to the bill, Japan has carried out large-scale flood control engineering construction on major rivers. Afterwards, flood disaster prevention and control, mainly focused on river flood control, became the main purpose of river management. From 1911 to 1920, Japan implemented its first National Flood Control Master Plan, launched modern flood control projects, and applied them to 65 river basins throughout the country. While emphasizing "water management", "mountain management" is also being coordinated and promoted. The "Emergency Measures Law for Mountain and Water Management" was promulgated in 1960.
In 1977, the national level "comprehensive flood control measures" were launched, which promoted the construction of urban rainwater infiltration and storage facilities on the basis of regulating land development and utilization. In 1997, Japan amended the River Law, which explicitly stated that environmental protection should be considered while developing and regulating rivers, based on disaster prevention and water resource development. Participatory planning and corresponding management principles were also included. The Basic Law on Water Cycle in Japan, promulgated in 2014, aims to promote the healthy and healthy development of water cycle systems through various measures.
In encouraging citizens to participate in rain and flood disaster management, Japan adopts a combination of economic subsidies and risk education. In order to improve the efficiency of river management in urban areas, the Japanese Ministry of Land, Infrastructure, Transport and Tourism launched a registration system called the "100mm/hour Safe Rainfall Plan" in 2013. This is a comprehensive management platform mainly focused on risk information sharing, runoff information recording, and management information integration. The central government provides financial subsidies to various regions through information registered with municipal authorities, encouraging citizens to carry out corresponding rainwater and flood management work. At the same time, the registration system also records the incentive measures taken by various regions. Among them, some regions provide direct economic subsidies for private construction of rainwater storage facilities, while others provide economic assistance for citizens' environmental protection activities. In addition, many regions also provide assistance such as tax reduction and environmental risk education.
In Southeast Asia, Singapore, as an island country, does not have a natural groundwater reservoir. Although it is located in a tropical region with abundant rainfall, there is limited land available for collecting and storing rainwater. Therefore, the country solved the problem with a comprehensive plan called "ABC Urban Design".
In the context of ABC urban design, the local water department launched the "Urban Water Landscape Design Certification System" in 2010. Projects that incorporate ABC design concepts can apply for certification. The evaluators score from four dimensions: vitality, aesthetics, cleanliness, and innovation, with multiple specific scoring items detailed for each dimension. Taking "cleanliness" as an example, the purpose of this standard is to ensure the water environment and review the overall effectiveness of rainwater and flood management. The scoring items included include: treatment or retention of runoff from more than 35% of the catchment area, rainwater collection and reuse, and whether rainwater collection is integrated with the ABC water landscape design.
Jialenghe Bishan Park is one of the classic cases. There are three adventure parks, two restaurants, and a large waterfront entertainment area in the park. The original Jialeng River in the park was 2.7 kilometers long and was a straight concrete drainage channel. When the park was renovated, it was transformed into a 3-kilometer long canal that mimics natural ecology, winding and flowing through the entire park. At the same time, soil biotechnology was used to reinforce the riverbank and prevent erosion.
The park land near the Jialeng River has been carefully designed, and when heavy rain comes, it becomes a drainage channel to receive more rainwater into the river and be treated as needed. The park has its own ecological water purification system - four stepped circular wetlands, with various wetland plants planted from top to bottom to filter rainwater. The filtered water will be stored and transported to the hydrophilic entertainment area for recycling.
