| In order to alleviate the problems of water shortage and flood caused by urbanization,China builds "Sponge City",and the concave green space is proposed to collect and utilize rainwater.The concave green space is a form of green space lower than the surrounding ground,the ability of traditional concave green space in rainwater detention,retention and reuse needs to be improved.In this article,the bioretention with the strongest regulating capacity in concave green space was selected as the research object,the traditional design from top to bottom is ponding layer,vegetation layer,soil layer,filter layer filled with sand and water storage layer filled with gravel.In this article,a new structure of concave green space was designed,the gravel was emptied to increase the water storage space and a perforated partition and hollow columns were set to support the upper soil.The perforated partition makes rainwater seep naturally from the soil layer to the storage layer,the hollow columns have holes in the lower part of the tube wall and are filled with water-absorbing material to supply rainwater from the storage layer to the upper plant growth.According to the structure of traditional and new concave green space,the model experiment methods were developed to carry out rainfall and evaporation experiments.In the rainfall experiment,the ponding duration of the two model boxes was almost the same.In terms of runoff delay time,flood peak delay time,peak reduction rate and water retention rate,the model experiment values of the new concave green space were 21.5 h,22.5 h,94.7% and 91.4%,which were all greater than the 11.8 h,13.5 h,93.6% and 48.7% of the traditional concave green space.Therefore,under the premise of not reducing the permeation effect,the detention and retention effect of the new concave green space is better than that of the traditional concave green space.In the evaporation experiment,the two model experiments evaporated together for 10 days firstly.In the early stage of evaporation,the water content of the traditional concave green space was slightly larger,but at this time,the water content of the new concave green space was maintained at a high level,which could support plants to grow well;in the later stage of evaporation,the water content of the new concave green space was larger,while the water content of the traditional concave green space wa s at a low level,which was unfavorable for plant growth.After that,the water level of the storage layer of the new concave green space was lowered to the vicinity of the hole s of the water-absorbing column.During the three days of evaporation,the wate r level dropped continuously,indicating that the new structure can still absorb water upward through the suction column under the condition of low water level.The evaporation experiment shows that the new concave green space is better than the traditional one in rainwater reuse.Based on the experiments,the numerical models of the new and traditional concave green space were established,and the reliability of the numerical models was verified by comparing with the experimental results of rainfall and evaporation.By numerical simulation,the rainfall condition of different rainfall durations in different recurrence periods was applied,the result was that the new concave green space model was greater than the traditional concave green space model in terms of runoff delay time,flood peak delay time,peak reduction rate and water retention rate,it shows that the new concave green space has a better effect on runoff regulation;the climatic condition of Shenzhen for one year was applied,the result was that the water content of the new concave green space model at the soil depth of3.5 cm,13.5 cm and 23.5 cm was suitable for grass root growth for 259 days,311 days and 317 days,which were all greater than the 214 days,239 days and 242 days of the traditional concave green space model,it shows that the new concave green space has a better effect on long-term service. |
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