Study Of Urban Stormwater Simulation In Typical Area Of Nanjing Based On SWMM

Urban storm water is a kind of overflow or even flood caused by storm when heavy rainfall overload the drainage system and exceeds the infiltration and storage.The stormwater model based on mathematical simulation is an effective method and have been widely used in different areas, such as rainfall forecasting, evaluation of urban flood control network measures and disaster assessment. Designing and optimizing quantitative evaluation model of the urban stormwater is beneficial to the construction and improvement of the city's waterlogging emergency mechanism. It also has a great significance on the city's disaster prevention s well as economic and social development.SWMM(Storm Water Management Model) model is a comprehensive urban runoff simulation system developed by the United States Environmental Protection Agency. The model considers several factors on rain and flood process, such as rainfall, infiltration, runoff and depression storage, network convergence and so on. It can simulate the city's hydrological process, water quality evolution and pipe network hydrodynamic process. SWMM is now widely used in the study of urban surface runoff and water quality simulation. This paper is supported by the scientific research project of mapping geographic information in Jiangsu province ( NO.JSCHKY201512) . In this paper, Xianlin Campus of Nanjing Normal University was taken as the study area. Remote sensing data, terrain data, land use data and other multi-source data were used in this study. We presents a distributed data modeling method considering the characteristics of surface buildings, underground pipe network, open channel and water. At the same time, we use SWMM model to make an empirical study on the simulation of typical storm flood events.The research contents and results of this paper are as follows:(1) This study explained the modeling mechanism of different modules in SWMM model (e.g. precipitation module, surface runoff module, ground confluence module, and pipeline transport routing module) based on analyzing the factors of stormwater characteristics of Nanjing city. we analyzed the design process of Keifer and Chu method, and then compared the principle and applicability of various surface runoff calculation and different pipe network convergence calculation method in different models. The analyses mentioned above provided us the basis for the selection of post simulation methods.(2)According to the regional characteristics, we designed an automatic flow direction model,and presented a modeling method considering both the surface drainage channel and network effect. Topological relation between the units of sub-basin spatial discretization of the basin according to the drainage system flow direction were established to build reasonable spatial discretization computing unit.The runoff coefficient was chosen as the calibration target to calibrate the model parameters in the absence of measured data.(3)This paper took the precipitation events on July 1, 2016 and October 26 as the study object, and verified the simulated results with measured data. We verified and briefly analyzed the simulation results through the observation overflow points. The results show that simulation effect goes well on the north of Xianlin Campus of Nanjing Normal University, but needs to be improved on the east-west. On this basis,this paper estimated the loading capacity of drainage system by analyzing the variation of rainfall-runoff, node flooding and conduit surcharge under different rainfall intensity which were setting in four return periods respectively. Finally,this paper simulated the ponding road of Xianlin Campus of Nanjing Normal University in rainfall of different return periods, and provided several suggestions for school staff going out on rainy days.