In order to alleviate urban waterlogging and optimize urban environment, the concept of sponge city has been favored by many urban planners and builders. Sponge city is a city that can drain, absorb and store water like a sponge. In addition to good flexibility, such cities can better adapt to environmental changes, effectively alleviate urban water resources problems, and enhance the city's ability to cope with natural disasters and its own defense capabilities.
1 project overview
When a city comprehensively improves Husha Port and its surrounding environment, the focus is on drainage. On the basis of the development of surrounding areas, the waterfront landscape resources should be scientifically utilized and further utilized. The main purpose of this project is to better control the black and odorous water body of the harbor canal, improve the drainage capacity of the canal, and build a comprehensive park integrating sponge landscape recreation, education and popular science. Park planning is based on the landform where the project is located. A comprehensive sponge system is established in various ways, and rainwater treatment facilities are combined with urban landscape to realize the mutual combination of landscape and flood control work, so that the park is not only rich in landscape, but also the waterfront space can extend in depth.
2 sponge city construction planning and design points
The specific ways of rainwater treatment are as follows: after the rainwater falls on the roof, it needs to be collected in high-rise flower beds and rain buckets by initial abandonment, and then it needs to overflow and collect in low-potential green spaces, in which the rainwater in the rain buckets can be thrown into green water; Rainwater falling on the ground can be purified and absorbed by rainwater gardens, low-potential green spaces or infiltration pavements, and other rainwater exceeding the standard needs to be discharged into rainwater pipes. In order to reduce the impurity content in the rainwater pipeline, various interception devices can be hung at the rainwater outlet, such as cyclone precipitation or sewage interception hanging basket. After treatment, part of the rainwater can be discharged into the rainwater pipeline for indirect use, and the rest can flow into the landscape water body or rainwater pool for storage, filtration and disinfection, and then concentrated water distribution, and then put into road sprinkling, greening irrigation and landscape water body water replenishment. Because it is difficult for the park itself to absorb all the rainwater, too much rainwater can be discharged to other parks and squares around the park. The application process of rainwater in the park is shown in figure 1.
3 sponge city construction planning and design technology
3. 1 permeable paving method When using permeable paving method, the following two aspects should be considered: when paving, there should be a wider joint gap area between materials, thus enhancing the water permeability of the gap; When selecting materials, we should choose those with higher water permeability. Laying method of gap permeable underlying surface. When paving bricks are spliced, there will be a certain gap between bricks, which can be filled with fine sand, ceramsite or pebbles. In this paving system, because the paving brick material itself has no water permeability, the leakage rate of precipitation can only be ensured through the reserved gaps between bricks. Common paving methods are grass brick paving and bread brick paving. Laying technology of self-infiltration underlying surface. Because the underlying surface of this pavement structure is a complete block.
3.2 Rainwater Collection System
System layout design. Rainwater collection system has many functions, such as reducing flood peak, storing rainwater and treating water quality, so as to achieve the purpose of storing, purifying and reusing rainwater. In addition, the rainwater collection system can also form an excellent landscape, attracting more animals and plants to inhabit and grow here. When arranging the rainwater collection system, it is necessary to scientifically design the ecological detention facilities and concave green space structure to form an effective circulation system with the park landscape water system project. The rainwater in the green space can flow naturally through the terrain, permeate, purify and filter in turn by using ecological detention facilities, and then enter the green water body. If it is difficult for rainwater to be discharged by itself, it is necessary to arrange corresponding ecological detention facilities, such as rainwater outlets, rainwater purification ponds, rainwater open ditches, etc., to transmit rainwater and finally make it flow into the landscape water system in the green space. However, in order to ensure the cleanliness of the whole water system, the water system in the green space should be connected with the urban rivers to form a circular flow. When arranging concave green space, it is necessary to scientifically determine the elevation of green space so that it is lower than the appropriate elevation of the surrounding ground, so that the rainwater collected on the surrounding ground can flow into the green space smoothly.
Generally speaking, in the design of concave green space, the slope should be kept at about 2%, and it should be 50~ 100mm lower than the surrounding squares or roads, so that rainwater can be collected more quickly. Rainwater runoff collected by sidewalks and roads will first enter the set ecological detention area. It is necessary to design ecological detention facilities. When designing the park, we can design water-resistant and moisture-proof plants in low-lying areas in a planned way to form grass ditches, rainwater dry streams and rainwater purification infiltration pools with ecological and landscape functions at the same time, so as to quickly absorb the rainwater generated by itself and its surrounding areas, so that the rainwater can temporarily stay and slowly penetrate into the soil. Generally speaking, biological detention facilities can be roughly divided into complex and simple types, and can be divided into ecological tree ponds, high flower beds, biological detention areas and rainwater gardens according to their different locations. Infiltration well is also a device to promote rainwater infiltration, mainly to improve rainwater passing through the seepage velocity of the shaft wall and bottom hole. When arranging seepage wells, it is necessary to ensure that rainwater has been pretreated before entering the seepage wells; The elevation of the inner bottom of the outlet pipe of the seepage well should be higher than the elevation of the inner top of the inlet pipe, but not higher than the elevation of the outlet pipe of the upstream adjacent well. When the storage capacity of the seepage well is insufficient, horizontal seepage pipes can be connected around the seepage well to form a radiation seepage well. Seepage well structure is shown in Figure 2.
3.3 Ecological detention facilities
Ecological retention ditches can be divided into ecological grass planting ditches and landscape dry streams. Among them, when designing landscape dry streams, plants with high humidity tolerance can be selected, and pebbles and Shi Jing can be used to form a landscape stream with high ornamental value, and this stream can be connected with green water bodies. From the functional point of view, we can use landscape dry streams to collect rainwater, fully collect natural precipitation, and then put it into the supplement and construction of landscape water bodies, so as to reduce artificial water supply as much as possible and better cope with seasonal changes. As shown in figure 3. Generally, landscape dry streams can be arranged around all kinds of hard spaces, and the collection speed of rainwater can be accelerated by using the terrain, so that the rainwater can be preliminarily purified and filtered, and at the same time naturally infiltrated. Functionally, the ecological grass planting ditch is similar to the landscape trunk stream, which usually needs to be designed beside the park road. By setting more natural surface ditches and wet herbs, ecological grass planting ditches can collect, permeate and filter rainwater better. After rainwater is absorbed and biodegraded by plants, the pollutant content will be greatly reduced, thus achieving the effects of runoff pollution control and rainwater collection and utilization. Park landscape water system is an indispensable part of the whole ecological detention facility. The final landscape space for rainwater collection needs to be interconnected with urban rivers to ensure its cleanliness. In addition, many aquatic plants need to be planted in riparian areas, and nutrients in water can be preliminarily purified through biological action.
4 conclusion
The application of sponge city has very important practical significance, which can effectively alleviate the harm of rain and flood, reduce the drainage pressure, purify and reuse the collected water, greatly improve the utilization efficiency of water, and play a role in saving resources and protecting the ecological environment. However, the construction of sponge city is not accomplished overnight, and every detail should be strictly checked, including scientific selection of permeable pavement technology, reasonable collection and reuse of rainwater, ensuring the correctness of the layout of ecological detention facilities and greatly improving the construction effect of sponge city.
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