Research On The Effect Of LID Measures On Flood Of Town District Based On SWMM

Plot B-6 in Shahe Town,Changping distract Beijing which used to be farmland was chosen as study area.Based on Storm Water Management Model,consulting the parameters in Storm Water Management Model User’s Manual,the hydrological model of Plot B-6 was established.The model was used to compare the influences on the flood of study area of traditional urbanization and urbanization with single LID measures(permeable pavement,low elevation greenbelt)and different combined measures.The results and conclusions showed as follows:(1)the traditional way of urbanization in the study area led to a significant increase of impervious area.It resulted in the peak flow discharge and volume of runoff increased,reaching peak flow earlier.(2)The Storm Water Management Model has great practicality and convenience in the construction of flood impact assessment,which can provide reference for the planning and design of the construction area.(3)Low elevation greenbelts and permeable pavement can reduce volume of runoff and peak flow discharge.Low elevation greenbelts can delay the peak flow but permeable pavement can’t.However,in different proportions and different rainfall frequency conditions,there are different effects of flood control.Low elevation greenbelt:1)The lower the rainfall intensity,the greater the peak flow reduction rate;when p=5%,what’s more,a bigger area of one sunken lawn can result in greater peak reduction rate.2)p=5%、p=10%,the peak flow can be delayed,but peak flow delay has not increased significantly with the increase of low elevation rate.3)p=5%、p=10%,the runoff coefficient had a linear reduction with increase of sunken lawn area;p=20%,sunken lawn rate 50%,the reduce effect of runoff coefficient becoming worse.Permeable pavement:1)The smaller the rainfall intensity,the greater the peak reduction rate.Under the three kinds of rainfall intensity,it all showed best reduction effect of peak flow discharge when the permeable pavement rate of 50%-75%.2)permeable pavement can’t delay peak flow.3)Under the three kinds of rainfall intensity,the effect of reducing the runoff coefficient has not much difference,and under one kind of rainfall intensity,the runoff pavement rate of about 75%,the effect of reducing the runoff coefficient is best.(4)The combined LID of permeable pavement and sunken lawn can reduce flood peak,delay flood peak and reduce runoff coefficient,and the effect of rainwater stagnation is better than that of single LID.Different propotions different effects.1)The ratio of the sunken lawn and the pavement should only meet the requirements(50%,70%),the effect of reducing the peak、the runoff coefficient can achieve a good one.On this basis,The decrease rate can not be significantly increased with the greening rate or the pavement rate increasing;2)Under p=5%,p=10%scenario,the peak can be delayed to a certain extent,but when p=20%,there is no effect of delaying the peak.And p=5%,the greater the sunken lawn rate,the more obvious the role of delayed flood peak,but even if the sunken lawn rate of 100%,peak delay time is only 98s.Therefore,the combination of measures in the delay peak effect is not very significant,so that the combination of the two measures can not replace reservoir.