Optimization And Effect Evaluation Of LID Combination Scheme Based On SWMM Model

With the acceleration of urbanization,the proportion of impermeable urban underlying surfaces has increased,and problems such as urban waterlogging disasters and water environment pollution have become increasingly prominent,seriously endangering the safety of residents’ lives and property.In this context,China has proposed the concept of sponge city construction based on the excellent foreign rainwater and flood management system-Low Impact Development(LID).By arranging LID facilities,we can control rainfall runoff and purify water quality.Taking a newly established sports development company in Wuxi as the research object,a rainfall runoff model was constructed using SWMM(Storm Water Management Model)software to simulate and analyze the hydrological effects of the study area under conventional development modes.Three different LID combination schemes were designed,and the Analytic Hierarchy Process was used for comprehensive benefit comparison and optimization.Six different rainfall return periods were selected,Simulate and analyze the hydrological and water quality effects of the LID combination scheme with the highest comprehensive benefits,and explore its improvement effect on surface runoff control and water quality regulation in the research area,providing reference for the construction of sponge cities in similar research areas.The main research results of this article are as follows:(1)The SWMM rainwater management model in the study area was constructed.The variation coefficients of the simulated runoff coefficient and the actual runoff coefficient under the four rainfall return period scenarios of P=2,3,5 and 10 years were all within10%,indicating that the model has good accuracy and applicability in this area.(2)The simulation analysis results of hydrological effects under conventional development models indicate that the size of rainfall peak coefficient is an important factor affecting the design of drainage pipelines,the size of rainfall return period is an important standard for measuring the drainage capacity of pipeline networks,and the impermeability rate of the underlying surface is an important factor determining the occurrence of urban waterlogging.Improving the water permeability of urban underlying surfaces is the most effective way to alleviate urban waterlogging,so arranging LID facilities can effectively solve urban water environmental problems.(3)By comparing the applicability of LID facilities and taking into account the actual situation of the study area,three different LID combination schemes were selected,consisting of permeable pavement,biological retention ponds,sunken green spaces,and grassy ditches.On the basis of meeting the target of 75% annual total runoff control rate for the construction of sponge cities in the region in all three schemes,an optimization model for comprehensive benefit comparison based on environmental,economic,and social benefits was constructed using Analytic Hierarchy Process(AHP).The results showed that the comprehensive benefit of LID combination scheme 2 was the highest at0.4585,and it was determined to use 13076 square meters of permeable pavement The combination plan of 1364 square meters of biological retention pool and 1940 square meters of sunken green space is the best sponge layout plan in the research area.4)After the arrangement of LID combination facilities,the surface runoff control and water quality control capabilities of the study area are greatly improved.Compared with the traditional development model,the surface runoff reduction rate was 50.11%-64.81%,the peak runoff reduction rate was 54.67%-62.04%,and the emission reduction rate at the discharge outlet was 26.87%-43.87% under the six different rainfall recurrence periods P=2,3,5,10,20 and 50 a.The reduction rate of peak discharge is 37.58% ～ 66.53%,and the reduction rate of total discharge of four pollutants(SS,COD,TN and TP)is 31.60% ～65.74%.With the increase of surface infiltration,the phenomenon of pipeline and node overload is significantly reduced,and the beginning time of surface runoff,peak flood discharge and peak SS concentration are delayed somewhat.However,LID facilities’ functions of promoting infiltration,retention and storage of rainfall runoff,peak cutting and emission reduction,delaying peak time and pollution interception and purification will reach the limit value with the increase of rainfall intensity.The effect of runoff control and water purification is weakened.When P=2a,that is,when the return period is low,the control effect of surface runoff and water quality is the best.Figure [42] Table [67] Reference [116]...