Research On Stormwater Runoff Control Effect Of Road Low Impact Development Measures

Increases in impervious land area resulting from urban development can have enormous repercussions on the subsidence of groundwater level,urban road waterlogging and corresponding water quality.As typical road Low Impact Development(LID)measures,permeable asphalt pavement system and bioretention facility system can be applied to urban roads and urban districts Sponge City construction because of their good source stormwater runoff treatment performance.With the continuous progress of Sponge City-Low Impact Development construction,they have good application prospect.At present,there are still some limitations in the study on the stormwater runoff control effect of road LID measures,and there are few studies on the combination effect of road LID measures and pipe system.For this purpose,the following works were carried out:The essence of the stormwater runoff control effect of road LID measures is based on the effective infiltration of rainfall.In this thesis,starting from the study of rainfall infiltration process of road LID measures(permeable asphalt pavement system and bioretention facilities),by building an indoor road LID measures rainfall infiltration simulation system,real-time monitoring of road LID measures rainfall infiltration response can be achieved.The unsaturated hydraulic parameters of road LID materials were inverted by means of road LID rainfall infiltration response(bottom outflow)and HYDRUS software.Meanwhile,the process of rainfall infiltration of permeable asphalt pavement system was analyzed.After that SWMM was used to establish a road chachment scale stormwater model,to simulate and analyze the stormwater control effect of road LID measures transformation schemes under different rainfall conditions,and the life cycle benefit-cost of each scheme was implemented.Finally,the urban chachment scale SWMM model including urban roads and urban districts area was established,and the stormwater runoff control effect of road LID measures at the urban chachment scale was simulated.Among them,this thesis focuseed on the mitigation effect of road LID measures on urban road water logging and hydraulic load of dranige pipe system,and also analyzed the combination effect of road LID measures and pipe system.The main research results were as follows:(1)The indoor LID measure rainfall infiltration simulation system was used to monitor the road LID measure rainfall infiltration response,and combined with the HYDRUS inversion module to invert the unsaturated hydraulic parameters of permeable asphalt mixture and bioretention facility medium filler.The results showed that the variation of VG-α and n of different permeable asphalt mixtures was small,and the recommended values were 2.3 and 2.0,respectively.For bioretention facility medium filler,the input parameters of SWMM model of medium fillers were obtained by using the unsaturated hydraulic parameters: Wilting point and Field capacity,and the selection of medium fillers for bioretention facility system was based on the permeability and Available Water Capacity.The simulation results of permeable asphalt pavement system rainfall infiltration showed that the rainfall intensity and the antecedent moisture content have a greater impact on the rainfall infiltration response(outflow time,outflow peak,retention rate)of the permeable asphalt pavement.The amount of rainwater retention in the permeable asphalt pavement system was mainly determined by the sand cushion,and the water storage capacity of the permeable asphalt pavement system can only be exerted when the "excess infiltration runoff" occurs in the sand cushion.(2)The application of road LID measures on the scale of road project can significantly improve the stormwater runoff control indicators of road area(annual runoff volume control rate,total field surface runoff reduction rate,outflow time delay rate,peak time delay rate,etc.).The higher the application ratio of road LID measures in road area,the better the runoff control effect would be.In the actual project,the annual runoff control rate was suggested to be simulated by multi-year and long-duration rainfall.The rainfall recurrence period has a great influence on the stormwater runoff control indicators of the design rainfall event of road LID measures,and the control indicators decreased when the rainfall recurrence period increased.However,the stormwater runoff control indicators of the transforamation scheme(scheme 4)with a higher proportion of road LID measures is stable.The overflow of bioretention facility system would significantly reduce the overall stormwater runoff control effects of the road LID measures transformation schemes.In actual projects,special attention should be paid to the overflow design.(3)The application of road LID measures at the urban chathment scale was similar to the stormwater control effect of the road project scale,which can significantly reduce the surface runoff in the urban area.However,the reduction effect of the total amount outflow from the drainage outlet was small.The application of LID measures in urban roads and urban districts(scenario 3)can significantly alleviate the waterlogging of urban roads and the hydraulic load of the pipe system.While the mitigation effect of applying LID measures only in urban road areas(scenario 2)was relatively small.Under the condition of high rainfall recurrence period(10a),the combination of road LID measures and pipe system("grey-green")can significantly improve the road waterlogging reduction capacity and pipe system hydraulic load reduction capacity,and the pipe diameter optimization was achieved.(4)The life cycle benefit-cost results of the road LID measures transformation schemes on the road project scale showed that: the life cycle benefit-cost of annual runoff volume control rate of the bioretention system construction in road green belt(scheme 2)was the highest,followed by scheme both the non motor vehicle lane and green belt road transformed by LID measures(scheme 3);The life cycle benefit-cost of the design rainfall event stormwater control indicators of each transformation scheme decresed with the increase of rainfall recurrence period.However,the scheme with higher proportion of road LID transformation(scheme 4)was relatively stable,and the benefit-cost was relatively better when the rainfall recurrence period was higher.