| Under the background of global warming,extreme rainfall events occur frequently.With the acceleration of urbanization and the continuous increase of urban area and population,the original green vegetation in various places is greatly reduced,and the water permeability of the underlying surface becomes worse."Waterlogging in every rain" has become a persistent disease of the city,which has not only caused great losses to the national economy,but also seriously endangered the personal safety of the general public,Therefore,how to predict and prevent urban waterlogging has become a social hot topic.Taking a community in Linwei District,Weinan City,Shaanxi Province as the research object,this paper establishes the urban waterlogging model by establishing one-dimensional pipe network and two-dimensional overflow model.Analyze the surface runoff condition,drainage capacity of rainwater pipeline and overflow quantity of inspection well in the study area under different design return periods,and divide the waterlogging risk level based on inundation depth and time.Through the evaluation of the current rainwater pipe network,the scheme of transforming the regional rainwater pipe network is put forward to improve the rainwater drainage capacity;By adding lid facilities to weaken rainwater runoff,it provides a theoretical basis for urban flood prevention and disaster reduction.The main conclusions are as follows:(1)Combined with the precipitation characteristics of the study area,the rain flood model of urban community is constructed,and the variation coefficient is controlled within±5%by using the runoff coefficient method.The parameters of the model are calibrated to obtain the impervious coefficient of each underlying surface,the initial loss of rainfall 0.7mm,the hydrological attenuation coefficient 0.9 and other parameters.(2)Simulating the current rainwater pipe network under different rainfall return periods,it is found that the pipes with drainage capacity less than 1-year return period account for 42.1%of the total length,and 53%of the pipes with drainage capacity within 1-2-year return period;The inspection wells overflowing under the rainfall conditions of la,2a,3a and 5a account for 24.1%,45.8%,60.2%and 72.3%of the total number.Through comprehensive analysis,the rainwater drainage system in the study area can not meet the rainfall of 1-year return period,and the overall drainage capacity is poor.(3)Simulate the ponding situation in the study area under different return periods,and use the waterlogging evaluation method based on ponding depth and time to classify the waterlogging risk level of the study area under 20 years of rainfall.The analysis shows that the waterlogging range of risk level Ⅰ accounts for 67.4%of the ponding range,and the road ponding reaches more than 75%.The low-lying areas in the West and southeast of the study area are prone to serious waterlogging.(4)According to the analysis results of the current pipe network,two reconstruction schemes are designed.The simulation shows that the two schemes have different improvement effects on the drainage capacity of the study area.The improvement rates of scheme Ⅰ and scheme Ⅱ under 1a～5a rainfall conditions are 7.2%～18%and 10.5%～52.5%respectively.When the rainfall return period is large,the improvement effect of scheme Ⅱ is significantly better than that of scheme Ⅰ.(5)Taking the annual runoff control rate of 85%as the target,the deficient volume of the study area is calculated to be 541.7m3.By optimizing the setting of lid facilities,the utilization rate of facilities reached 92.4%,the cumulative surface runoff decreased by 24.7%,and the peak surface runoff decreased by 38.1%,which greatly weakened the surface runoff in the study area.The waterlogging in the study area under simulated rainfall conditions for 20 years shows that the ponding range is reduced by about 33.7%,and the ponding on the road is also reduced by about 30%.The transformation effect is remarkable. |
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