Because the underlying surface of the city is hard and cement is everywhere, the original natural ecological background and hydrological characteristics have been changed. Therefore, it is necessary to strengthen the infiltration of nature and put it in the first place. Its advantages are that it can avoid surface runoff, reduce the collection of cement ground and road surface pipe network, conserve groundwater, supplement the shortage of groundwater, purify water through soil and improve urban microclimate. There are many ways of rainwater infiltration, mainly changing various pavement and ground paving materials, transforming roof greening, adjusting the vertical direction of green space, and leaving rainwater from the source and then "infiltrating".
1 permeable landscape pavement
In the traditional urban development, the landscape pavement design of municipal public areas or residential areas mostly uses materials with poor water permeability, which leads to poor rainwater permeability. In this regard, rainwater infiltration can be achieved through permeable roads, or rainwater can be discharged to detention facilities near streets through canals and trenches.
2 permeable pavement
Roads occupy 10%-25% of the urban area in traditional urban development and construction, and traditional road paving materials are also one of the important secrets that lead to poor rainwater permeability. In addition to landscape pavement, rainwater infiltration can also be achieved through permeable pavement, and the pavement materials of parks, communities and parking lots are changed into permeable concrete to increase rainwater infiltration and reduce surface runoff. Infiltrated rainwater can be purified in underground storage tanks and then discharged into rivers or replenish groundwater, thus reducing direct discharge.
3 Green building
The construction measures of sponge city are not only the ground, but also the treatment of roof and roof rainwater. Building a green roof on a roof with load-bearing, waterproof and proper slope is beneficial to the emission reduction and purification of rainwater. For roofs that are not suitable for green roofs, rainwater can also be collected and guided through drains and rainwater chains for storage or infiltration.
For roofs that are not suitable for greening roofs, rainwater can also be collected and guided for storage or infiltration through drainage ditches and rainwater chains.
2 Sponge City-Storage
In other words, to leave rain, we must respect the natural topography and let the rain disperse naturally. Now, after man-made construction destroys the natural landscape, water will gather in one place in a short time, forming waterlogging. Therefore, it is necessary to regulate and store rainfall to realize peak regulation. At present, there are no fixed standards and requirements for water storage in sponge cities, and there are various underground water storage styles. There are two common forms: plastic module water storage and underground reservoir.
1 water storage module
Rainwater storage module is a new product, which can be used to store water without occupying space. With super pressure-bearing capacity; 95% of the hollow space can achieve more efficient water storage. Using waterproof cloth or geotextile can complete water storage and drainage, and at the same time, it is necessary to set the positions of water inlet pipe, water outlet pipe, water pump and inspection well in the structure.
2 underground reservoir
The rainwater collection tank consists of a tank body, an inlet settling well, an outlet well, high and low aeration caps, an inlet outlet pipe, an overflow pipe and an aeration system.
3 Sponge City-Stagnation
Its main function is to delay the rainwater runoff formed in a short time. For example, through the adjustment of micro-topography, the rainwater is slowly collected in one place, and time is used for space. The peak value of runoff can be delayed by "hysteresis" There are three specific forms: rain garden, ecological detention pond, infiltration filter and constructed wetland.
1 Rain Garden
Refers to the low-lying area where trees or shrubs are planted in the garden green space and covered by bark or ground cover plants. It can replenish groundwater by intercepting rainwater and infiltration, reduce the flood peak of surface runoff during rainstorm, and also reduce pollution by adsorption, degradation, ion exchange and volatilization. Among them, shallow pits can accumulate some rainwater, delay the time of rainwater collection, and soil can increase rainwater infiltration and alleviate the phenomenon of surface water accumulation. The accumulated rainwater can be used by plants, reducing the irrigation water for green space.
2 Ecological detention area
Conceptually, ecological flood detention area is a form of regulating and controlling runoff by using engineering soil and vegetation in shallow depression or landscape area. The control area includes grassland filtration, sand layer and puddle area, organic layer or covering layer, planting soil and vegetation. Ecological detention area is different from rainwater garden in soil requirements and engineering technical requirements, and its forms are also varied according to the location of the site, such as ecological detention area, detention tree pool and so on.
2. 1 grass planting ditch
Planting shallow grass ditch has the functions of water transmission, sewage interception and purification. It is suitable for residential areas, industrial areas or commercial areas, parks, parking lots and both sides of public roads with small runoff and low population density, and can replace roadside drainage ditches or rainwater pipe systems. The top width of the grass planting ditch is 0.5~2m, the depth is 0.05~0.25m, the slope (vertical: horizontal) 1:3~ 1:4, and the longitudinal slope is 0.3%~5%. Can be set in front of rain gardens and concave green spaces as preventive treatment.
2.2 Rainwater Pool
Rainwater pond is a seepage pond, that is, a pond or depression built by nature or man-made for rainwater infiltration to supplement groundwater. Rainwater ponds can effectively reduce peak runoff. However, the rain pond slope protection needs to plant moisture-resistant plants. If the rain pond is deep (more than 60cm), low shrubs should be planted around the slope protection to form a low hedge to eliminate potential safety hazards. At the same time, the whole rainwater pond system needs to form microcirculation to prevent water from rotting.
2.3 Rainwater Wetland
Rainwater Wetland Artificial Rainwater Wetland is a comprehensive ecosystem. By using the principles of species regeneration and material circulation in the ecosystem, as well as the principle of structural and functional coordination, rainwater collected by rainwater gardens and ecological retention ponds is concentrated and purified. Moreover, it has the characteristics of large buffer capacity, good treatment effect, simple process, less investment and low operating cost, and is extremely suitable for more applications in sponge city construction.
4 sponge city network
Water quality can be purified through soil infiltration, vegetation, green space system, water body and so on. Therefore, it should be stored, purified and reused in cities. The rainwater purification system is equipped with different purification systems according to different regional environments. According to the present situation of the city, the regional environment can be roughly divided into three categories: rainwater collection and purification in residential areas, rainwater collection and purification in industrial areas and rainwater collection and purification in municipal public areas. According to the environment of these three areas, different rainwater purification links can be set up. At present, the familiar purification processes are divided into three links: soil infiltration purification, constructed wetland purification and biological treatment.
1 rainwater purification system three parts
Soil infiltration purification: most rainwater is collected, and soil infiltration purification is carried out at the same time, and the collected rainwater is discharged into the secondary purification tank through the perforated pipe or stored in the infiltration tank; The surface water that can't penetrate through the soil is filtered by aquatic plants and discharged into the primary purification tank.
Constructed wetland purification: it is divided into two treatment processes. One is the primary purification pond, which purifies rainwater without soil infiltration; The second is the secondary purification pool, which further purifies the rainwater discharged from the primary purification pool and the rainwater discharged through soil infiltration; The rainwater after secondary purification is discharged into the downstream clear water pool or directly lifted to the mountain water storage pool by the water pump. The water pump is used to circulate between the primary purification tank and the secondary purification tank and between the secondary purification tank and the clean water tank.
2 Three regional environments of rainwater purification system
Rainwater collection and purification in residential areas;
In the process of rainwater collection and purification in residential areas, due to the large construction area and green area of residential areas, a large number of water bodies can be collected through ecological detention areas, rainwater gardens and infiltration ponds after being washed by rainwater, and then filtered by soil into infiltration channel module reservoirs, so rainwater runoff is relatively small. Therefore, using the sponge city rainwater collection system to store, percolate and filter the rainwater, and then purify it by biotechnology, which can be used for greening irrigation, flushing toilets, washing cars and so on.
Rainwater collection and purification in industrial areas;
Different from residential areas, industrial areas have less green space, more hard sites and buildings, and the influence of industrial products is also greater. Therefore, in the rainwater collection and purification of sponge city, special attention should be paid to intercepting the infiltration rainwater. After industrial pollutants are filtered by garden facilities bearing the principle of sponge city, rainwater passes through the reservoir of soil infiltration channel module. The process is equipped with sewage interception treatment to purify the infiltration rainwater for the second time. After entering the modular reservoir, it is purified again by biotechnology, and then recycled for cooling water supplement, green irrigation, concrete mixing and so on.
Rainwater collection and purification in municipal public areas;
Compared with the first two areas, rainwater collection and purification in municipal public areas have different aspects, such as large green area and different mountain heights in different areas, resulting in different runoff and large rivers and lakes. Therefore, it is the most important problem to slow down the impact damage of rainwater scouring on the mountain surface and the direct pollution of water sources. As far as the above problems are concerned, the maintenance of mountains and the filtration of rivers and lakes by ecological detention areas and plant buffer areas should be considered in rainwater collection for rainwater purification in urban areas. In terms of rainwater storage, water storage tanks are mainly used to store infiltration rainwater. On the one hand, the purified water is used for municipal greening and toilet flushing; on the other hand, it is discharged into rivers and lakes to replenish Shui Yuan, thus solving the water shortage problem.
5 Sponge City-Use
Use rainwater purified by soil infiltration, constructed wetland and biological treatment as much as possible, and strengthen the utilization of rainwater resources in both water-rich and water-deficient areas. Not only can the flood disaster be alleviated, but the collected water resources can also be used, such as collecting and purifying the rainwater in the parking lot for car washing. We should conserve water by infiltration, keep water in place by storage, and then use it in place by purification.
Collect rainwater for building construction
Collect rainwater for greening irrigation.
Collect rainwater for car washing.
Collect rainwater for the toilet.
Collect rainwater for fire fighting.
Collect rainwater for landscape water.
6 Sponge City-Pie
It is the combination of urban vertical and engineering facilities, drainage and flood prevention facilities with natural rivers, surface drainage and underground rain water pipes and canals to realize the general and excessive discharge of rainwater and avoid disasters such as waterlogging. In some cities, excessive rainfall leads to floods. It is necessary to take artificial measures to drain rainwater.
When the peak value of rainwater is too large, surface drainage is combined with underground rainwater pipes and canals to realize the general and excessive discharge of rainwater and avoid disasters such as waterlogging. Part of the rainwater stored after purification in rainwater garden, ecological detention area and infiltration filter is used for greening irrigation and daily life, part of it is reinjected into groundwater through infiltration, and the rest is discharged into rivers through municipal pipe network. It not only reduces the probability of water accumulation when the peak rainfall is too high, but also reduces the direct pollution to the water source at the first time.
Sponge city refers to a city with good "elasticity" in adapting to environmental changes and responding to natural disasters like a sponge. It absorbs water, stores water, seeps water and purifies water when it rains, and "releases" the stored water for use when necessary.
The construction of sponge city should follow the principle of ecological priority, combine natural channels with artificial measures, maximize the accumulation, infiltration and purification of rainwater in urban areas, and promote the utilization of rainwater resources and ecological environment protection on the premise of ensuring the safety of urban drainage and waterlogging prevention. In the process of sponge city construction, it is necessary to coordinate the systematicness of natural precipitation, surface water and groundwater, coordinate all aspects of water supply and drainage, and consider its complexity and long-term nature.
There are several ways to build a sponge city. The first is to protect the original ecosystem of the city. Protecting the original water ecological sensitive areas such as rivers, lakes, wetlands, pits and ditches is the basic requirement of sponge city construction. Maximize and leave enough woodland, grassland, lakes and wetlands to conserve water and cope with heavy rainfall, and maintain the natural hydrological characteristics before urban development.
The second is ecological restoration and restoration. Under the traditional extensive urban construction mode, the natural environment such as damaged water bodies is restored and repaired by ecological means, and a certain proportion of ecological space is maintained.
The third is low-impact development. According to the concept of development and construction with the lowest impact on urban ecological environment, the development intensity should be controlled reasonably, enough ecological land should be reserved in the city, and the proportion of urban impervious area should be controlled to minimize the damage to the original water ecological environment of the city. At the same time, properly excavate rivers and lakes according to the demand, increase the water area, and promote the accumulation, infiltration and purification of rainwater.