The Study Of Simulation And Planning Program Of Sponge City Construction Measures Based On SWMM Model

In the process of rapid urbanization process in China,the type of urban underlying surface has changed greatly,the original vegetation and soil is replaced by the building district and the road square.The increase of the water infiltration area caused by the increase of the impermeable area ratio leads to the loss of the rainwater infiltration,which causes the people’s life and property to suffer loss.Through the construction of the sponge city can effectively reduce the adverse effects of the urbanization process on the original ecological environment,reduce the surface runoff,realize the benign hydrological cycle,and maximize the protection of the urban ecosystem.At present,the research of sponge city construction is in full swing in China,but the systematic study and concrete plan of the effect of LID measures in mountainous cities are not complete.This paper combines the terrain and landform of the mountain city,aiming at the special layout of the mountain city in the construction of the sponge City,using the SWMM model to simulate the effect of the rain and flood control of the LID measures,and provide the technical support for the construction of the spongy city in the mountain city.Taking Chengnan New District of Youyang County as the research area,and taking Rain Water runoff simulation of LID measures as the target,the hydrological analysis model of typical mountainous cities is established in this paper.Then according to the rainfall data of the study area,the rainfall law is analyzed,and the formula of rainstorm intensity in the region is calculated.At the same time,the sensitivity of the model parameters is obtained by the natural conditions of the study area and the present situation of development.On the basis of sensitivity analysis,the model parameters are adjusted to determine the model parameters,and the model simulation process after the parameter rate determination is compared with the actual rainfall process.The SWMM model can be used to simulate the actual region.Secondly,the model was used to simulate the hydrological reduction effect of the green roof,the low elevation greenbelt,the permeable pavement and the grassed swales with the same area ratio,under seven different rainfall recurrence periods.In order to better control the total runoff,peak runoff and delayed peak time,based on the simulation results of different LID measures,the four measures were combined to simulate the rain flood control effect under the 2-hour rainfall duration of 1-100 years rainfall recurrence period.Finally,according to the actual situation of the underlying surface in the study area,the LID program under different influencing factors is calculated by using the SWMM model.At the same time,the reduce effect of LID measures,the effect of operation t and the cost of building installation are taken as energy efficiency analysis indexes.The energy efficiency of three different programs is analyzed by AHP,and the best LID program in the research area is determined.Based on the above research findings:(1)Using the P-III curve for line fitting analysis and using the least square method to solve the regional rainstorm intensity formula,the formula is as follows:(1429.8658x(1 +0.972×log(p)))·(2)The q =(1429.8658×(1+0.972×log(p)))/(t+11.1217)0.6728 ·(2)The sensitivity parameters of SWMM model for total runoff are N-Imperv,D-Imperv,N-Perv and N-Perv.The sensitivity parameters of SWMM model for runoff peak value are D-Imperv,N,N-Imperv.(3)For the green roof,the low elevation greenbelt,the permeable pavement and the grassed swales with the same area ratio,the order of the total runoff reduction effect under the rainfall same recurrence period is as follows:the low elevation greenbelt>the permeable pavement>the green roof>the grassed swales.For the control effect of runoff peak value,the control effect of four LID measures decreases with the increase of rainfall intensity.The runoff peak value of the low elevation greenbelt and the grassed swales was higher than that of the traditional development model due to the runoff discharge with impermeable area.For the delay of peak time,there is still a delay of 5min during the 100-year rainfall process in the low elevation greenbelt.The other measures,due to their structural characteristics,have not delay the peak time in high intensity rainfall.(4)Combination of the low elevation greenbelt and the permeable pavement(combination 1),the green roof and the permeable pavement(combination 2),the green roof and the grassed swales(combination 3),the low elevation greenbelt and the green roof and the permeable pavement(combination)4)in the process of rainfall with different intensity,all of them can effectively control the total runoff volume.In the case of once in 100 years,the total runoff reduction rate is still 24.1%,14%,11.9%and 26%.For the reduce effect of runoff peak,the control effect of combination 1 and combination 4 is basically the same in the same rainfall reproduction period.For delayed peak time,combination 2 was the first to fail,followed by combination 3.Combination 1 and combination 4 maintained the control effect of delayed peak 5min for high intensity rainfall.The order of rain flood control effect considering LID combination is as follows:combination 4>combination 1>combination 3>combination 2.(5)The total annual runoff control rates of LID programl,2 and 3 are 75.55%,75.99%and 76.06%.The layout area of the green roof,the low elevation greenbelt,the permeable pavement and the grassed swales in program 1 is 24658.74 m2,57301.14 m2,738.61 m2,16543.32 m2.The layout area of program 2 is 23318.49 m2,560 49.21 m2,69887.16 m2,31048.22 m2.The layout area of program 3 is 24658.74 m2,57301.14 m2,738.61 m2,16543.32 m2.(6)Based on the reduce effect of LID measures,the effect of operation t and the cost of building installation,the energy efficiency of three sets of sponge city development program in Chengnan New District are compared.Through calculation and test,the weight of the three programs to the best LID program is 0.247,0.533,0.22,which indicates that the first choice of the LID program in the study area is program 2.