Built-up Area Low-impact Development Plan Selection And Runoff Flow And Water Quality Simulation Evaluation Based On SWMM

In this paper,a Built-up area in Nanning,Guangxi is taken as the study area.By understanding the operating principle of the SWMM model and generalizing the study area,the SWMM model of the rainwater system in the study area is constructed and the hydrological,hydraulic,and water quality parameters of the model are determined.Two different rainwater runoff control schemes were designed based on the current status of the study area and the features of low-impact development facilities.The first scheme is a combination of three low-impact development facilities with lower economic costs,namely sunken green spaces,permeable pavement and shallow vegetation;The second scheme is the three facilities with better landscapes,sunken green spaces,green roofs and shallow vegetation ditch;The third scheme is a combination of four low-impact development facilities with better overall performance,namely Sunken green spaces,permeable pavement,green roofs and reservoirs.Analysis of Economic Benefits of Three schemes Through Life Cycle Costing.in the return periods P=la,P=2a,P=3a,Comparing the total runoff reduction rate,peak discharge reduction rate,SS,COD,TN,TP reduction rate,The highest economic benefit of Scheme 3.Therefore,the LID combination scheme of scheme 3 is selected to be deployed in the research cell.In the case of different rainfall returns,the changes in runoff flow and water quality in the study area were simulated.Under the six different rainfall conditions,the rainfall return periods were 0.25a,0.5a,la,2a,3a,and 10a.The total runoff reduction rate of LID facilities to the system was 24.6%,23.9%,24.4%,23.1%,22.3%,21.0%,respectively.The reduction rate of discharge peak was 28.4%,27.0%,26.9%,30.6%,26.7%,24.3%respectively;The reduction rate of LID facilities to SS was 44.4%,35.0%,29.4%,24.2%,21.8%,17.5%,respectively;to COD was 36.2%,31.6%,29.1%,26.5%,25.8%,24.8%,respectively;to TN was 28.7%,24.1%,20.2%,15.8%,13.3%,13.2%,respectively;to TP was 55.0%,51.9%,49.2%,45.6%,41.0%,37.9%,respectively.With the increase of the return period of rainfall,the total amount of runoff and the reduction rate of flood peak flow showed a general downward trend.In addition,the runoff start time and the peak occurrence time of the systems using the LID facilities are lagged behind those of the systems not using the LID facilities.Therefore,it can be shown that the LID facility has a declining effect on rainfall and runoff.It can be seen that LID has a good removal effect on various pollutants.There is a certain degree of similarity in the variation trend of the concentrations of various pollutants,and with the increase of the return period of rainfall,the total load reduction rate of pollutants tends to decrease.