Research On The Rainstorm Runoff Effect Of Mountainous City And Measures Of Ecological Reconstruction Based On SWMM

In recent years, flood disaster caused by storm water happened at home andabroad not only threat the people’s life and property safety, but also cause hugeeconomic loss to countries and individuals. Therefore, preventing flood disaster hasbecome the vital importance of city flood control. At present, the land use layout has afundamental change caused by the high level urbanization greatly changed the watercycle model, and led to the increase of the total amount of runoff, the peak of therunoff and the runoff coefficient. Thus this phenomenon not only threats the citydrainage pipeline safety operation, but also has already become the cause of the cityflood disaster. This phenomenon is particularly prominent in the rapid development ofthe mountainous city. Therefore, it is necessary to research on the rainstorm runoffeffect under different land use layout in mountain city which can provide importanttechnical support to the city flood control and the drainage pipe network securityoperation. The paper adopted the SWMM model to research the rainstorm runoff effectin the mountain city for the first time, and launched the systemic research of rainstormrunoff effect in mountainous city based on the rainstorm runoff characteristic underdifferent land use layout scenarios.The paper selected University City of Chongqing as the study object. EstablishSWMM model of the post-development land use layout scenario, and adopt therecommended values as the model parameter calibration. Then use the Nash-Sutcliffeefficiency coefficient and B%MSSE index to verify the accuracy of the model.Through flow meter observation sequence values and model simulation sequence valueof each rainfall, we calculated the Nash-Sutcliffe efficiency coefficient and B%MSSEindex which can meet the accuracy requirement of the model. The research region hasan area of76900m~2. The pervious area ratio of the pre-development andpost-development land use layout scenario is91%and35%respectively. Based on theimpervious area ratio greatly reduced, we researched the runoff discipline underpre-development and post-development land use layout scenario in the condition ofdifferent rainfall return period (2a,5a,10a,20a). We also research the effect of thefront peak type, the middle peak type and the last peak type to the post-developmentland use layout scenario, and the gradient’s effect to the post-development land use layout scenario. In view of the runoff effect of the post-development, we adopted theLID and BMPs to improve the post-development land use layout scenario. Theresearch shows that:①The accumulation rainfall runoff coefficient, duration of the runoff, the peakof the runoff, the total amount of the runoff of the post-development land use layoutscenario can be7.01times,2.28times,6.98times and7.06times to thepre-development land use layout scenario.②The effect of the front peak type, the middle peak type and the last peak typeto the post-development land use layout scenario is that with the increase of the rainfallpeak coefficient, the runoff duration and the total amount of the runoff increase.③The gradient’s effect to the post-development land use layout scenario is thatwith the increases of the gradient, the duration of the runoff decrease. The peak of therunoff increases with the increases of the gradient.④LID has a double peak and total amount reduction effect. The LID1land uselayout scenario can reduce the peak of runoff, the total amount of the runoff of thepost-development land use layout scenario reached to48%and25%respectively, andthe peak of runoff, the total amount of the runoff is3.62times and5.30times to thepre-development land use layout scenario.The LID2land use layout scenario canreduce the peak of runoff, the total amount of the runoff of the post-development landuse layout scenario reached to79%and81%respectively, and the peak of runoff, thetotal amount of the runoff is1.27times and1.30times to the pre-development land uselayout scenario.⑤The BMPs land use layout scenario cannot reduce the total amount of runoff,but it can regulate the process of the runoff. It can extend the duration of the runoff andalso reduced the peak runoff of post-development land use layout scenario reached to65%. It’s peak of runoff is2.66times to the pre-development land use layout scenario.⑥The LID2+BMPs land use layout scenario can reduce the peak of runoff, thetotal amount of the runoff of the post-development land use layout scenario reached to90%and81%respectively. The peak of runoff, the total amount of the runoff is65.32%and1.3times to the pre-development land use layout scenario.⑦The combined LID and BMPs technology is the best measure to deal with thestorm water runoff effect because of the perfect practice to reduce the peak of runoffand the total amount of the runoff than the separate LID or BMPs.In view of the big rise of the slope in mountain city and the frequent status of rainstorm, we research the effect of the different rainfall intensity and different slopeon the instant rainfall runoff coefficient. The results show that:①In the same rainfall intensity, the higher gradient, the shorter the steady valueof the instant rainfall runoff coefficient. The instant rainfall runoff coefficient is thesame under different gradient.②In the same gradient, the bigger the rainfall intensity, the shorter the changetime and the steady value time of the instant rainfall runoff coefficient.