Urban Waterlogging Simulation Based On SWMM And FVCOM Coupling Model

In the face of global warming,frequent occurrence of extreme weather and accelerated urbanization,the waterlogging problem in urban areas is becoming more and more prominent,and the phenomenon of "seeing the sea when it rains" in cities is becoming more and more serious,which has brought huge losses to the people and economy of China.How to effectively prevent and mitigate urban hydrological disasters in China has become a major problem that needs to be solved,and the effective prevention of urban waterlogging problems requires a comprehensive scientific and accurate simulation of urban hydrological processes.Based on this,this thesis takes the Three Gorges Vocational College area in Wanzhou District,Chongqing as the research object,and carries out the simulation study of urban pipe drainage system,two-dimensional surface diffuse flow model and hydrological reduction and control effect of sponge city by constructing a coupled model of one-dimensional SWMM pipe network and two-dimensional FVCOM surface diffuse flow,and grasps the pipe drainage capacity and urban waterlogging risk before and after sponge city transformation.The research results can provide theoretical basis and technical support for the accurate formulation of sponge city construction plans and scientific assessment of the hydrological reduction and control effects of sponge cities.The main research findings are as follows.(1)A one-dimensional SWMM pipe network model and a two-dimensional FVCOM surface diffuse flow model are constructed in the study area,and a coupled SWMM and FVCOM urban waterlogging model is proposed.The coupled models were parameterized and validated using measured data and pipe network-surface calculations,and the model results fit the measured values well,where the NSE values of the 1D model are as high as 0.76～0.87,and the maximum relative errors of the coupled models and the MIKE model in pipe flow and node water depth are only 2.31% and 4.49%,and the NSE values of the simulated results of surface water ponding at nodes are over 0.7,indicating that the coupled model has good reliability and stability.(2)Six rainfall scenarios with different recurrence periods were designed using the storm intensity formula and Chicago rain type in Wanzhou district,and the influence law of different rainfall recurrence periods on the drainage capacity of the pipe network and urban waterlogging process was simulated.The hydrodynamic simulation results of the pipe network show that the surface runoff volume,infiltration volume,check well overflow quantity and overflow volume in the study area show an increasing trend with the increase of rainfall recurrence period,while the runoff control rate shows a gradually decreasing trend,and the check well overflow status mainly depends on the rainfall recurrence period.The results show that the drainage capacity of the pipe network system in the study area is seriously insufficient,among which 86.99% of the pipe network drainage capacity does not meet the design standard of 5-year event or above,which is the main cause of urban waterlogging.The simulation results of surface water ponding show that the inundation area is mainly concentrated in the area with water depth greater than 0.5 m and less than 0.1 m,and is positively correlated with the rainfall return period,where the inundation area of low rainfall return period(P≤10 a)is mainly concentrated in the southwest side of the study area,while the high rainfall return period(P≥20 a)is concentrated in the northeast.The inundation risk level is mainly low and high risk,and the high risk range gradually expands with the increase of the rainfall return period.(3)The reduction and control effects of sponge city construction on urban waterlogging in the study area were investigated by adding a certain proportion of low-impact development(LID)facilities.The results show that LID facilities have good runoff reduction effects on the surface runoff volume,peak runoff volume,check well overflow quantity and overflow volume in the study area,but the runoff control ability gradually decreases with the increase of rainfall return period.At the same time,the installation of LID facilities can effectively reduce the surface water depth,water area and flood risk level,but the reduction and control ability are weakened with the increase of rainfall recurrence period,among which the reduction and control rate of LID facilities on water area can reach 55.84%～72.5%.The results confirm that the construction of sponge city can effectively mitigate the degree of urban waterlogging caused by low recurrence period rainfall(P<20 a).