Experimental Study On Rainwater Infiltration And Purification Of Urban Greenland Runoff Based On SWMM

With the acceleration of urbanization,the continuous expansion of hardened pavement areas has changed the original hydrological characteristics of cities and towns and caused serious urban waterlogging disasters.At the same time,a large amount of pollutants carried by surface runoff are directly discharged into the receiving water body without treatment,which makes the water environment increasingly worse.Taking the concept of sponge city construction as the main direction,adopting low-impact development(LID)measures is an effective way to solve this problem.Based on the analysis of runoff rainwater and soil characteristics of different types of green land in Qijiang District,Yangzhou City,this paper evaluates the infiltration and purification effect of green land soil after infiltration and improvement.Combined with the rainwater management model SWMM,taking the peak runoff reduction rate and runoff pollution control rate as the control targets,the effect of the reconstruction of runoff water quantity and runoff water quality under different rainfall recurrence periods in Sanwan Park was evaluated.First,we collected runoff rainwater and soil samples from five different functional green areas:wetland park green space,residential area green space,industrial area green space,campus green space,and national road green space.The pollution degree of runoff rainwater was analyzed,and the physical and chemical characteristics of the soil after being washed by runoff rainwater were tested.The physical and chemical properties of different types of green space soil are not obvious,and the characteristics of the four nutrients are quite different from each other;according to the soil comprehensive quality coefficient p,the grade of the five types of green areas is divided.Then select several better soil improvement materials,and mix them with different ratios of single and mixed,and analyze the improved soil permeability.It was found that under the same water flow conditions,the stable infiltration rate of the soil mixed with sand and chaff only increased compared with the original soil;The permeability of sand and chaff mixed is better than that of single sand or chaff;the structural modifier desulfurized gypsum can effectively increase the soil permeability.And using the mercury intrusion method to analyze the pore characteristics of the improved soil,it was found that the pore characteristics of the improved soil had a significant effect on the infiltration capacity.Secondly,the purification capacity of the improved soil with different proportions was analyzed.It was found that when sand and chaff are mixed into the soil alone,the larger the proportion of sand and chaff,the better the purification effect.The purification effect of sand and chaff mixed is better than that of single sand or chaff.Adding desulfurized gypsum when mixing sand and chaff alone can achieve better purification effect,and adding desulfurization gypsum and PAM when mixing sand and chaff is better.At last,based on the previous research results,four Low-Impact-Development measures were added to Sanwan Park:permeable pavement,sunken green space,green roof,and artificially improved soil infiltration.Using the storm management model SWMM,with the peak runoff reduction rate and runoff pollution control rate as the control targets,the change pattern of runoff water quantity and runoff water quality in Sanwan Park under different rainfall recurrence periods after the transformation was studied.The research results can alleviate or solve the problems faced by the current urban stormwater management,and can also provide valuable reference for China’s runoff rainwater pollution control,rainwater utilization and sponge city construction.