| With the rapid development of urban construction,a large number of urban green spaces are replaced by impervious surface.This phenomenon leads to the decrease of groundwater recharge and change of urban hydrological cycle characteristics.At the same time,the high runoff coefficient of impervious surface increases greatly the rainwater confluence speed,which makes the city flood peak appear earlier,and increases greatly the total runoff and peak flow.Low impact development is a source control management measure,which simulates natural hydrological condition through infiltration,filtration,evaporation and other ways.Low impact development makes hydrological characteristic unchanged,realizing runoff decrease,pollution load reduction and protecting receiving water.First of all,this paper choosed two kinds of low impact development technique,namely green roofs and bioretention facilities.This paper carried out the study of runoff influence factors and water quantity optimization research of green roof,and carried out the study of runoff control of modified bioretention facility and service life of bioretention facility.Secondly,on the basis of green roofs,bioretention facilities and other conventional low impact development technologies,this paper developed rainwater system pollution producing and collecting model based on low impact development which suitable for building and community.After that this paper carried out demonstration projects in the residential building in Shenzhen,and changes of water quantity and water quality of the community were verified using the above model.The main results are as follows.?1?This paper studied the influence of matrix thickness,matrix type and vegetation type on water quantity and water quality in different rainfall,respectively.The increase of matrix thickness could improve the runoff reduction rate,and the corresponding total runoff reduction rate were 18.94%,25.46%and 32.55%,respectively.The influence of perlite modified substrate on the runoff reduction rate was better than recycled brick modified substrate and garden soil substrate,and the corresponding total runoff reduction rate were 18.94%,12.41%and 9.17%,respectively.The influence of ophiopogogon japonicas on the runoff reduction rate was better than shortleaf lilyturf,and the corresponding total runoff reduction rate were 18.94%and 13.84%,respectively.The increase of matrix thickness could enhance the anti erosion ability of rainstorm,and the corresponding EMC value of suspended solid were 11-122,11-51 and 13-39 mg/L,respectively.Recycled brick modified substrate could improve the removal efficiency of organic matter by void structure and viscidity,and perlite modified substrate could improve the chemical phosphorus removal by aluminum oxide.The root system of ophiopogogon japonicas was better than shortleaf lilyturf in absorbing nitrogen.?2?Through the use of flat roof rainwater pipe technology in building and community,this paper carried out the influence of concrete roof height,area ratio,rainfall return period on peak discharge and rainwater pipe diameter to slove the status of the existing green roof matrix layer thickness was small.When the concrete height increased from 1cm to 5 cm,the peak discharge reduction rate increased from 15.62%to 36.98%,and rainwater pipe diameter decreased from 1300 mm to 900 mm.When the roof area ratio increased from 10%to 25%,the peak discharge reduction rate increased from 15.74%to 41.88%,and rainwater pipe diameter decreased from 1300 mm to 900 mm.When the rainfall return period increased from 0.5 a to 5 a,the peak discharge reduction rate increased from 36.43%to 23.29%,and rainwater pipe diameter increased from 800 mm to 1200 mm.?3?This paper adopted three stage wetland to carry out the study of runoff control of modified bioretention facility,and analyzed water quantity and water quality in different rainfall.This bioretention facility had significantly delayed action on runoff peak,and the delay time in different rainfall was 6-12 min.The runoff peak reduction rate in different rainfall was 40.5%-100%.The runoff volume reduction rate in different rainfall reached 26.78%-100%.The overflow effluent TN and NH3-N concentrations of bioretention facility were less than 15 and 5 mg/L,which satisfied ornamental waterscape class water quality requirement of“landscape water quality of city wastewater reclamation”.The permeate effluent SS,TN and NH3-N concentrations of bioretention facility were less than 10,15 and 5mg/L,which satisfied ornamental waterscape class water quality requirement.?4?This paper adopted bioretention facility to study the influence of soil layer thickness,aquifer height and permeability coefficient on different fillers adsorbing total phosphorus,and then calculated the service life of the corresponding bioretention facility.When the service area ratio and effluent TP concentration were 1:2 and 0.3mg/L,the service life of three fillers all exceed 1 year with soil layer thickness of 20 cm or more.When the service area ratio and aquifer height were 1:2 and 5 cm,the service life of activated alumina exceed 2 years with effluent TP concentration of 0.1 mg/L or more.When the service area ratio and permeability coefficient were 1:2 and 5*10-6 m/s,the service life of activated alumina exceed 3 years with effluent TP concentration of0.3 mg/L or more.?5?Based on the characteristics of spatial and temporal distribution dispersion of runoff and pollutant and diversity of transmission path in building area,low impact development rainwater system model was developed based on GIS platform.This model had LID visualization design and SWMM dynamic wave hydraulic automatic design,which was suitable for building residential scale.This model inherited characteristics of distributed hydrological model of SWMM and advanced computing function of whole rainfall runoff analysis.In addition,this model had powerful geographic data extraction,spatial analysis and spatial analysis function of GIS,and this model could be seamlessly connected with the commonly used CAD system.?6?This paper carried out demonstration projects in the residential building in Shenzhen,and changes of water quantity and water quality of the community were verified using the above model.The runoff volume reduction rate of this community increased by 36.92%47.78%,and the reduction rate of SS,COD,TN,TP,NH3-N increased by 52.50%54.68%,69.78%69.99%,73.60%74.06%,47.37%48.39%,44.00%47.22%.The rainwater system pollution producing and collecting model based on low impact development could better predict the water quantity and water quality of actual rainfall.According to rainfall data of Shenzhen city in 2016,this model calculated the total annual runoff control and SS load reduction can reach 72.8%,69.5%. |
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