Study On Theory And Practice Of Ecological Rainwater System In Sponge City

Based on SWMM model,this text made simulation and analysis on parameters of different structures in a rain garden,such as different soil types and different ratio of soil of planting soil,drainage layer thickness and volume fraction of aquifer plants,taking a district in Wujiang as the research object so as to research on the influences of these parameters on the rain garden runoff control and pollutant removal.Through simulating the effects of rainwater garden on runoff control and pollutant removal in different recurrence periods,this paper determined the recurrence period when the runoff control of rainwater garden reached the maximum load.Finally,the paper introduced the sponge city reconstruction project of water town garden center square in Wujiang,and made a analysis and evaluation on the actual operation effect of rainwater garden.This paper contrasted areas of research runoff control effect and pollutant removal efficiency of seven different soil in the rain garden,including sand,loam and clay,loamy sand,silty loam,sandy clay,sandy clay loam and so on.The result showed that what has the best runoff control effect is sand,and clay is the worst.What has the best pollutant removal effect is the sand,and clay is the worst.This paper contrasted runoff control effect and pollutants removal efficiency of 15 different ratios of planting soil in rain garden,the results showed that the runoff control effect and the pollutant removal effect of the rainwater garden 3(the ratio of sand,loam and clay is 5%,15% and 80%)are the best,and in direct proportion to the ratio of sand,suggesteing ratio of sand and clay is over 70% and between 5%~10%,respectively.The best proportion of the rainwater garden planting soil is 80% sand,5% loam and 15% clay,respectively.The paper compared runoff control effect and runoff pollutants removal efficiency of different rain garden vegetation coverage and different drainage layer thickness.The results showed that the rainwater garden vegetation volume should not be too small or too big.If vegetation volume is to small,the rain garden landscape effect will be affected,If vegetation volume is to big,the function of the rain garden will be directly affected.The optimal value of vegetation volume fraction was about 0.3.The drainage layer thickness has little effect on runoff control effect and runoff pollutant removal efficiency.The paper conpared that the runoff control effect,pollutant removal effect and pipe flow reduction effect of rainwater garden at different rainfall recurrence periods.The results showed that the runoff control effect,pollutant removal effect and pipe flow reduction effect are inversely proportional to recurrence period.When the rainfall recurrence period is P=5a,the rainwater garden reaches the maximum bearing capacity,and when rainwater garden exceed the maximum bearing capacity,the runoff control effect,pollutant removal effect and pipe flow reduction effect of the rainwater garden start to be significantly reduced.Using rainwater garden can effectively reduce the pipeline flow in the study area and increase the maximum bearing capacity of the pipeline.Therefore,the rainwater pipe diameter can be appropriately reduced in the area where rainwater garden LID is set.Rain water garden center square garden of catchment area has a better removal effect of pollutants,of all,removal rates of SS,TN,TP and COD were 74.99%,68.68%,52.21%,and 53.84%,respectively.And the concentration of four kinds of pollutants in rainwater garden outlet reached to Ⅳ class standard of surface water in 150 min.Rainwater garden is an effective measure to control hydrology and pollution in sponge city.