Research On The Technique Of Concave Green Space With High Permeability

With the continuous growth of urban development,impermeable surface replaces the original farmland,green land and other water permeable ground,which leads to the rapid increase of rainfall surface runoff.At the same time,the increase in population and density has brought about a large accumulation of pollutants.These pollutants were washed away by Rain Water and diverted into urban rivers,The phenomenon of black and bad rivers has become very universal.As an important part of the urban ecosystem,urban green space can not only reduce surface runoff,delay flood peak,but also absorb some pollutants carried by runoff.It is great significance to urban pipeline network decompression and urban river water quality improvement.Now most of urban green spaces are convex green space and common concave green space.And the research of domestic concave green space mainly focuses on the laws of water retention and seepage ability of natural concave green space,flood peak reduction capability and pollution interception ability and so on.There is little research on optimizing the structure of concave green space and improving the seepage capacity of water storage.In order to further improve the water storage and water seepage capacity of the concave green space,a high permeability concave green space was developed by embedding high permeable materials in the green space which strengthening the water storage and seepage capacity of the green space.Three kinds of concave green space with high permeability were designed and developed,which include.horizontal high permeable green space,vertical high permeable green space and combined high permeable green space by data collection and experimental research.By simulating rainfall production and abortion sewage pilot plant,the runoff reduction effect and runoff pollution reduction ability are evaluated,comparing with traditional convex green space and common concave green space,which provides theoretical basis for urban green space planning and construction.The main conclusions of this paper are as follows:In order to further improve its water storage and seepage capacity,the internal structure was optimized,and three types of concave green space were designed:horizontal high permeable green space,vertical high permeable green space and combined high permeable green space.A gravel ridge with a depth of 0.5m and a width of 0.3m was planted under the middle ground of the horizontal high permeable green space,surrounded by geotextile;Three gravel piles with a diameter of 0.15 m were driven under the vertical high permeable green space,which deep 1.5 m;buried Stone Ridge and three crushed Stone piles are combined,which buried under the ground of the combined high permeable green space.In addition,adding permeable layer of coal slag composite soil over the underground structure of green space to improve the infiltration rate of rain water.The structure of three kinds of concave green space is shown in fig.2-1 and 2-8.Under the conditions of Chicago design rainstorm with rainfall duration of 1?10a and 30?120min duration,the total runoff of common concave green space is reduced by 23.14%-67.04%,and the runoff coefficient is 0.29?0.69,comparing with convex green space;the total runoff of horizontal high permeable green space is reduced by 50.26%?100%,and the runoff coefficient is 0.00-0.46;the total runoff of vertical high permeable green space is reduced by 37.66%?93.46%,and the runoff coefficient is 0.06?0.57;the total runoff of combined high permeable green space is reduced by 56.24%-100%,and the runoff coefficient is 0.00?0.40.The larger the rainfall,the smaller the runoff reduction rate.Compared with convex green space,in the rainfall experiment of a homogeneous rainfall model with less rainfall intensity,the reduction rate of rain water runoff of combined high permeable concave green space is 100%;the reduction rate of horizontal high permeable green space and vertical high permeable green space are 90.67%?100%,82.98%?100%respectively;.The reduction rate of common concave green space is 50.39%?100%.Compared with convex green space,every concave green space has different extent to reduce the runoff pollutant of rain water,the bigger the rainfall intensity,the smaller the reduction range.Reduction rate of COD are 38.55%?90.96%,80.40%?100%,62.63%?96.11%,86.75%?100%;Reduction rate of SS are 78.75%?91.48%,90.25%?100%,85.26%?98.67%,92.49%?100%;Reduction rate of TN are 22.50%?87.45%,70.08%?100%,52.98%?97.74%,79.41%?100%;Reduction rate of TP are 50.62%?79.17%,75.33%?100%,64.27%?96.71%,82.95%?100%,by common concave green space,horizontal high permeable green space,vertical high permeable and combined high permeable concave green space.In the year of natural rainfall runoff records,runoff reduction rates of common concave green space,horizontal high permeable green space,vertical high permeable and combined high permeable concave green space are 59.05%,83.84%,77.16%,87.79%,compared with the upper convex green space;runoff reduction rates of horizontal high permeable green space,vertical high permeable and combined high permeable concave green space are 60.53%,44.22%,70.18%,compared with common concave green space.Annual total runoff control rates of convex green space common concave green space,horizontal high permeable green space,vertical high permeable and combined high permeable concave green space are 42.44%,76.43%,90.70%,86.85%,92.97%.In the process of simulating rainfall and natural rainfall,,the plants planted in the concave green space need to have strong waterlogging resistance,and the wet plants such as Yellow iris and Cyperus alternifolius are selected.In order to keep the soil permeability and avoid the formation after long-term operation of green space,it is necessary to take some corresponding measures,which can keep the volume weight of green land around 1.2g/cm3,so as to ensure the effect of continuous permeable flood storage.