Abstract: This paper introduces the Sustainable Urban Drainage System (SUDS), discusses the prospect of its promotion and application in China, and puts forward ideas with reference value.
Key words: sustainable drainage system, urban drainage, rainwater utilization, eco-city
In recent years, we often see news about heavy rains causing urban water logging and traffic jams. A sudden rainstorm often causes traffic jams in many places in the city, and even causes casualties. This exposes many problems in the process of urbanization in our country. In terms of drainage, our country has lagged behind developed countries in Europe and the United States for more than a decade, and there is still plenty of room for improvement. This article aims to introduce the urban sustainable drainage system that developed countries are developing and popularizing in recent years.
Functions of urban sustainable drainage systems
Sustainable Urban Drainage Systems (Sustainable Urban Drainage Systems, referred to as SUDS), sometimes referred to as sustainable drainage systems, is a new type of drainage concept, which takes overall consideration of urban drainage systems and introduces the concept and measures of sustainable development. Based on the idea of trying to replicate natural ecological drainage systems, SUDS uses low-cost, low-environmental impact methods to clean, purify and recycle rainwater and surface water by collecting, storing and using technical and engineering means to reduce flow rates. This idea was first applied to urban drainage systems in England, but its development was not limited to urban limits.
The SUDS aims to systematically reduce the likelihood of urban water logging. It increases the utilization rate of surface water such as rainwater, take into account the reduction of river pollution, and improve water quality. It designs and manages water resources to meet current and future societal needs while maintaining ecological, environmental and hydraulic integrity.
In a natural environment, part of the rainwater that falls to the surface percolates into the ground through a percolation process, and the other part forms surface runoff that follows rivers back to the sea. But in many areas, especially urban areas, most of the ground surface is made of buildings and sealed concrete pavement, which largely limits the natural infiltration of rainwater. Traditional urban drainage systems consist mainly of pipes and culverts that uniformly collect surface water and transport it to an underground network of pipes. Eventually, the water will be discharged into natural bodies of water such as rivers, making the collection and circulation of surface water much faster than natural water infiltration processes.
Drawbacks of traditional urban drainage systems
The core design concept of the traditional urban drainage system is to lead the surface water to the discharge point of the water body as quickly as possible. However, during a heavy rain, the large amount of rainwater that collects quickly not only increases the pressure of the drainage system sharply, leading to urban water logging, but also may cause a series of ecological problem.
First, heavy rain will cause the water level and flow velocity of rivers to rise sharply, which will increase the risk of flood disasters in the downstream. Pipelines are discharged into the river. Second, in the long run, the water quality of the river and groundwater will deteriorate, which will affect the ecological environment of the surrounding areas. Third, most rainfall is channeled directly into piped drainage systems to drain along water bodies, reducing the chance of infiltration to recharge groundwater reserves during droughts. The rainwater use is not very sufficient.
In response to the disadvantages of traditional drainage systems, SUDS aims to reduce the impact of drainage systems in one area on another area by minimizing the amount of drainage, and to improve water quality. It also has the functions of flood control, rainwater recycling and pollution reduction, which fully reflects the diversity of water systems. Not only can it reduce the possibility of urban flooding during extreme rainstorms, but it also has many other benefits, such as: minimizing the spread of pollution, maintaining or restoring natural water flow, improving water quality and beautifying the environment. In addition to its functional advantages, its overall cost is lower than that of traditional drainage systems. Practice shows that it can save up to two-thirds of the cost.
Application of sustainable urban drainage systems
The United Kingdom is one of the countries that are greatly affected by surface water flooding such as urban water logging, and heavy rainfall is the main cause of urban water logging. Its government continues to explore and optimize flood prevention and management methods, forming an urban water logging prevention system with timely early warning and scientific drainage as the main features. At the same time, it vigorously promotes the use of advanced SUDS technology to manage surface and groundwater, and requires all new development and redevelopment. All regions should seriously consider building a sustainable drainage system that can reduce drainage pressure and be environmentally-friendly.
Specifically, SUDS includes a range of technologies for the sustainable management of surface and groundwater. Stormwater is often mixed with unnatural pollutants, which results in high treatment costs. But SUDS insists on using natural means to remove stormwater as much as possible, and not just relying on the pipe system to remove it. For example, in the upstream sub-basins of the drainage system, rainwater is infiltrated into the ground on the spot, or its discharge time is prolonged, or temporarily stored. In this way, it will achieve the effects of peak reduction, flow reduction, surface water runoff purification, and groundwater storage. Its engineering facilities include seepage ponds, underground seepage canals, surface permeable pavements, controlled rainwater discharge outlets, various dry or wet ponds, small reservoirs, etc.
SUDS adopts measures to dispose of rainfall runoff nearby by increasing ground infiltration capacity to recharge groundwater, delaying confluence time, and reducing storm runoff. The frequency of floods is reduced, and the diameter of downstream urban drainage pipe networks and pumping stations are reduced. SUDS aims to protect and improve water quality, coordinate the relationship with the environment, and at the same time consider the needs of local residents. Taking measures to deal with stormwater flow nearby can control the current and future flood problems from the source. It starts from point source pollution and non-point source pollution to protect water resources.
General principles:
It can be concluded that the three principles followed by SUDS are:
1. Diversification of drainage channels. It helps to avoid the traditional drainage pipes being the only outlet.
2. Drainage incorporates filtration to reduce discharge of pollutants into waterways.
3. Recycle surface water such as rainwater where possible.
SUDS also recommends that existing combined and divergent sewerage systems need to be refined and developed without large-scale conversion of one form to the other. In specific operations, the drainage system to be used is determined by the specific geographical conditions and environment, and sometimes it is necessary to combine multiple drainage technologies. As for what method to take, it varies with terrain and population density.
Prospects for sustainable urban drainage systems
SUDS controls and utilizes rainwater from the source, which can not only ensure the natural hydrological cycle of the urban water system, maintain the needs of the natural living environment of animals and plants, but also create a rich natural hydrological environment on the basis of ensuring flood control safety. It fully reflects the sustainable concept of water system. Its application in urban planning will help the concept of sustainable development be reflected in urban construction. But the application of SUDS is also restricted by many factors, such as laws and regulations, management system and so on.
Abroad, many countries and regions have formulated a series of laws and regulations on rainwater utilization, giving strong support to rainwater utilization. For example, some developed countries have to design rainwater utilization facilities before building new communities. Without these measures, the government will levy rainwater discharge fees and facility fees. However, in our country, there is currently a lack of mandatory legal regulations on rainwater harvesting.
It is possible to retain and transform the original relatively complete confluence system, or to adopt a new hybrid system or incomplete diversion system, etc. At the same time, investment benefits must be considered. Among them, the diversion system costs a lot of money, and the transformation from the combined system to the diversion system has a large impact range and takes a long time. It is technically insufficient to effectively prevent the continuous pollution of urban rainwater runoff to water bodies. Therefore, the implementation of SUDS is an inevitable requirement for the sustainable development of our country’s economy and society. In addition, it is an inevitable requirement for solving the shortage of water resources and controlling water pollution, and the basis for building a circular economy in our country.
The promotion and implementation of SUDS
The promotion and implementation of SUDS is a huge and complex system project. And it is also a long-term task, which requires the active cooperation of laws and regulations, systems, administration, management, education, publicity, technology, finance, etc. In view of the current specific situation, it is suggested that future work should focus on the following:
(1) Formulate and promulgate laws and regulations related to SUDS. Among them, the government should be the main undertaker for the promotion and implementation of this work. It must establish corresponding management departments and pass necessary legislative and administrative means to implement a series of strategies for the implementation of SUDS.
(2) Carry out relevant publicity and education work and strengthen the public’s understanding of the SUDS concept. Let people know more about the current situation and existing problems of the domestic drainage system, and further gain the understanding and support of the society.
(3) Establish demonstration projects corresponding to SUDS, conduct case studies, accumulate experience, and provide better reference for realizing larger-scale SUDS.
(4) Formulate planning and design standards corresponding to SUDS. National SUDS planning should be formulated on the basis of the watershed, fully considering the current status of the existing water supply system, drainage system and flood control system. And at the same time, it combines the water demand of industry and agriculture in the watershed. The detailed development goals and ideas should be formulated.
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