Rain garden

FIGURE 3.4.21 Section2 of eEcological filter belt (Source: Made by author)

Vegetation retention zone with a certain width and slope can remove sediments, nutrients, organic matter and other substances in surface runoff and seepage through filtration, retention and absorption, so as to reduce the concentration and toxicity of pollutants entering the water body. It is the first barrier to intercept and purify rainwater in sponge green space. [Housing and Urban-Rural Development Department of Jiangsu Province.2018.].

FIGURE 3.4.22 Rain garden in site (Source: Made by author)

According to the different flooding conditions of the planting area in the rain garden, the planting area of the rain garden can be divided into the storage area, the buffer area and the edge area. The planting of the plants in these three areas should fully take into account the characteristics of different plants' tolerance to flooding and drought.

The requirement of submerging-resistance, pollution-resistance and purification ability of plant species in the water storage area is the highest, and at the same time, it is also required to have a certain early-tolerance ability in drought conditions without rainy season.

The buffer zone has a fixed volume of water storage, which requires the inundation tolerance of plants, drought tolerance and rainwater scouring resistance of plants.

The marginal area has no water storage capacity, and the plant species need to have strong early-tolerant ability, so there is no special requirement for the

submerging-resistant ability of the plants. The early-tolerant plants can be selected to connect with the surrounding plant landscape.

FIGURE 3.4.23 Rain garden in site

(Source:https://i.pinimg.com/originals/8a/e7/9d/8ae79dd6ff7e8269dd6944f4a2e4d95

4.jpg)

When planting plants, it is necessary to consider the matching of flowering date, color, shape, texture and season, so as to plant trees, shrubs and grass in layers to ensure the ornamental value of the rain garden.

(1). Priority should be given to native plants and exotic species

Rain garden generally choose water resistance, good moisture resistance, and plants beautiful shape of trees as common plants, easy to shape the landscape and management and maintenance.

(2). Choose plants with developed roots, luxuriant stems and leaves and strong purification ability

There are three main mechanisms for the degradation and removal of pollutants in rainwater. One is the absorption and utilization of nitrogen, phosphorus and other substances through photosynthesis. Second, oxygen is transferred to the substrate through the root system, and micro-processing units are formed around the root system to intersect the aerobic and hypoxic zones, so that aerobic, hypoxic and anaerobic microorganisms are in their proper position. The third is the interception and adsorption of plant roots to pollutants, especially heavy metals.

(3). Choose plants that can withstand both waterlogging and drought

Because the amount of water in the rain garden is closely related to rainfall, and there is an alternating phenomenon of full water period and dry water period, the plants planted should not only adapt to the aquatic environment, but also have a certain ability to resist early. So plants with strong roots, fast growth and large stems and leaves function better

(4). Choose plants that can be planted with each other to improve decontamination and appreciation

The reasonable combination of different plants can improve the water purification capacity. Plants with strong root oxygenation and weak root oxygenation can be mixed planted to form a compound plant bed, creating an environment where aerobic microzones and hypoxic microzones co-exist, thus conducive to the degradation of total nitrogen. Evergreen and deciduous herbs can be mixed to improve the water purification capacity of the garden in winter. Herbaceous plants and woody plants can be planted together to improve the structure of plant communities and ornamental.

(5). Use scented plants

Aromatic plants help to attract insects such as bees and butterflies, creating a better landscape effect.

FIGURE 3.4.24 Rain garden (Source: Made by author) 3.4.4.3.4 Ecological dry pond

FIGURE 3.4.25 Ecological dry pond in site (Source: Made by author)

FIGURE 3.4.26 Ecological dry pond in site (Source: www.yl1001.com)

3.4.4.3.5 Planting grass ditch

Planting grass ditch are made at the junctions between green space and hard pavement. The trenches are 1.8-3.0m in width, and the cross-section form is inverted parabolic line shape. The bottom width is 0.3-1.2m; 15 to 30 cm deep.

[Baidubaike.com]

The groove shape is smooth and natural, along the hard pavement edge in and out of the green space, in order to meet the functionality, but also increase its landscape, interesting. The main function of the planting ditch is to prevent rain erosion, carrying soil pollution of the road surface, square; The second is to collect and transmit rainwater, and plant ground cover in shallow gullies on the surface, and use the plants and soil in the gullies to infiltrate, intercept and purify rainwater runoff.

Planting grass ditch (Fig3.4.27) is an open green rainwater transmission channel covered with turf, which acts as infiltration, filtration, buffer and retention of rainwater during the transmission of rainwater runoff from upstream to downstream. As an alternative to the traditional grey concrete runoff ditch, it has many advantages, such as effectively reducing the peak discharge, postponing the peak and retaining the

sediment. When the sandbank is combined with the underground drainage ditch, the grass ditch can also effectively retain the rainwater and increase the infiltration of rainwater. It is a kind of high efficiency rainwater runoff transmission facilities, because of the variety of grass planting, grass planting ditch can play its due effect of

"sponge" but also provides people with different aesthetic taste, for the park a variety of creatures to provide a variety of living environment.

FIGURE 3.4.27 Section of Planting grass ditch Made by author

(Source:https://bbs.tianya.cn/m/post-worldlook-1643785-2.shtml)

FIGURE 3.4.28 Planting grass ditch

(Source: www.elalt.com) 3.4.4.3.6 Permeable pavement

The entire park is paved with permeable roads. Pervious paving (Fig3.4.29) is used as an alternative to hardened pavement paving, allowing rainwater to infiltrate to underground, supporting pedestrian and vehicular passage for visitors.

Generally permeable pavements contain a base pad composed of coarse aggregate for rainwater storage. Some foundation layers are composed of soil, gravel, and sand to increase stormwater storage and infiltration rate. Permeable pavement can remove precipitation and other pollutants in rainwater, disperse rainwater runoff, reduce flow and recharge groundwater. There are various types of permeable pavement, such as prefabricated modules, site pouring, permeable asphalt, gravel pavement, etc. The light-colored permeable pavement system with high reflectivity can also reduce the urban heat island effect to a certain extent, which conforms to the concept of sponge city.

FIGURE 3.4.29 Section of permeable pavement of park (Source: Made by author)

FIGURE 3.4.30 Permeable pavement of park (Source: Made by author)