Urban waterlogging simulation and rainwater pipe network system evaluation based on SWMM and SCS method
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Abstract:
With the acceleration of urbanization,the underlying surface of a city has undergone tremendous changes.The area of bare vegetation has been reduced,and the area of construction roads has increased.This has significantly increased the impermeability of urban areas,reduced the amount of rainwater infiltration,and condensed the drainage system.Surface rain can not be discharged quickly,and urban flood disasters occur frequently.To change the urban waterlogging problem ,the improvement and transformation of urban rainwater pipe network systems are the key points.However,most cities in China have low design standards for rainwater pipe network systems and can not cope with extreme rainstorms with high return periods.Since the 1980s,with the development of remote sensing technology and geographic information system and its wide application in hydrology,significant progress has been made in urban hydrology research.Many urban hydrological models have been developed and applied in urban hydrology.The model performs urban waterlogging simulation and rainwater pipe network system analysis can provide solutions for improving urban waterlogging problems. SWMM (storm water management model) is a dynamic precipitation-runoff simulation model,which is mainly used to simulate a single precipitation event or long-term water quantity and water quality simulation in a city.Its runoff module part comprehensively handles precipitation,runoff,and pollution load in each sub-basin.The confluence module part transmits water volume through pipe networks,channels,water storage and treatment facilities,water pumps,and regulating gates.The model can track and simulate the water quality and quantity of runoff produced by each sub-basin at any time with different time steps,as well as the flow,depth and quality of water in each pipeline and river.Likewise,the SCS model is developed by the Bureau of Water and Soil Conservation belonging to the United States Department of Agriculture in 1954.It is widely used in watershed hydrological simulations.The runoff curve number method (SCS-CN) has a simple calculation process,few parameters required,easy access to data,and consideration of the characteristics of the underlying surface of the region. The surface runoff continuity errors of the simulation results obtained by inputting three spots of rain with different recurrence periods are all 0,and the continuity errors of flow calculation are -0.43%,-0.24%,and -0.18%,respectively.Using the comprehensive runoff coefficient method,the comprehensive runoff coefficients of the measured rainfall data are 0.658,0.667,and 0.682 in sequence.The pipe network is analyzed:when the rain return period is 1 a,the full pipe rate of the pipe section is 4.4%,and the pipe section overload rate is 4.4%.When the rain return period is 2 a,the full pipe section rate is 24.53%,and the pipe section overload rate is 24.53%.The return period of rainfall increased to 5 years,the full pipe section rate was 33.96%,and the pipe section overload rate was 32.08%.The main influencing factors of pipeline overload are the overload of upstream and downstream pipelines,the accumulation of water at both ends,the impermeability of the surrounding catchment area and its total area.The nodes are analyzed: when the rainfall return period is 1 a,8 nodes generate water,when the rainfall return period is 2 a,37 nodes generate water,and when the rainfall return period is 5 a,60 nodes generate water.The main influencing factors of node stagnant water are the impermeability of the catchment area,the CN value,the total area,and the density of the city and the pipeline network. The model can simulate the urban rainstorm and waterlogging in Zhengzhou Hightech Zone,but the rainwater pipe network system in the high.tech zone can not well cope with the heavy rain in the design return period in the drainage code of Zhengzhou City.The overload pipe section and stagnant water of the drainage pipe network of Zhengzhou High.tech Zone have different nodes,but the two have a close positive correlation.The nodes at both ends of the overloaded pipe section are more prone to overflow,thus forming four obvious flood.prone areas.
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