Simulation And Evaluationof Waterlogging In Sponge City Based On SWMM Model

In recent years,with the rapid development of social economy,the acceleration of urbanization and the increase of urban surface hardening rate,the risk of urban waterlogging has greatly increased,and urban non-point source pollution has intensified,so it is urgent to improve the living environment.Taking Miaotouyong drainage area in Guangzhou as the research area,a numerical model of urban waterlogging was established based on urban rainwater management model(SWMM),and the model was calibrated by using historical data.For the model with verified accuracy,rainfall with return periods of 1a,2a,5a,10 a,20a,50 a and 100 a is taken as the input condition of the model,and low-impact development(LID)measures such as permeable pavement,rain garden and green roof are respectively arranged for the model,and the impacts on runoff and pollutants before and after the LID arrangement are compared and analyzed.Finally,the comprehensive benefits of each scheme are evaluated by the improved fuzzy evaluation method.The conclusions are as follows:(1)Based on the principle of regional generalization,the urban waterlogging model is established by studying the actual situation of regional drainage network and considering the main roads and land use types in the region.Six measured rainfall and runoff data were selected to adjust the parameters of the model,and the six Nash coefficients(NSE)were all greater than 0.75,which ensured the accuracy of the model.(2)Different LID facilities have different effects on flood peak reduction.The effect of combined LID facilities on flood peak reduction is obviously better than that of single LID facilities.From the total amount of runoff and the effect of flood peak control,the order of LID facilities is: permeable pavement+rain garden+green roof > permeable pavement+green roof > permeable pavement+rain garden > rain garden+green roof >permeable pavement > rain garden.The delay effect of single LID facilities on flood peak is not obvious,but the occurrence of flood peak is delayed by 5-15 min after different combinations of LID facilities are deployed compared with those without LID facilities.(3)Different LID facilities have different impacts on water environment.Different pollutants increase rapidly with the increase of flow in the early stage of rainfall,and decrease with the increase of flow after reaching the peak.The combination scheme has the best effect on reducing three kinds of pollution: permeable pavement+rain garden+green roof,which can reduce the total amount of suspended solids(TSS)by70.34%-65.68%,the total amount of chemical oxygen demand(COD)pollutants by61.82%-58.73%,and the total amount of total nitrogen(TN)pollutants by 62.36%-55.52%.(4)Different spatial locations of LID have different effects on urban waterlogging and water environment.LID was laid in the upper,middle and lower reaches of the study area,and the reduction rate of total runoff by adding permeable pavement in the lower reaches was higher than that in the upper and middle reaches.The effect of TSS peak reduction rate is the best in the middle reaches,and the effect of COD and TN peak reduction rate is the best in the downstream.The increase of reduction rate decreases with the increase of recurrence period,and the order of increase is: downstream > midstream >upstream.(5)Based on the characteristics and reality of the study area and the applicability of LID facilities,a multi-index evaluation system of LID in the central city of Guangzhou is constructed from three aspects of economy,environment and society,and the comprehensive benefits of LID facilities in Miaotouyong area of Guangzhou are evaluated by improved fuzzy evaluation method.It is concluded that in the construction of sponge city in Miaotouyong drainage area of Guangzhou,permeable pavement should be given priority when laying single LID facilities;When laying two kinds of LID facilities,permeable pavement and green roof should be given priority.