Modeling And Risk Assessment Of Coastal Urban Flooding Based On Combined Rainfall And Tide Scenarios

In recent years,influenced by global climate change and urbanization,extreme rainfall events and urban flooding disasters have occurred frequently in China,especially in coastal areas affected by both rainfall and tide levels,urban flooding problems are more prominent.Coastal cities are the most densely populated and economically dense areas in China,and flooding has seriously affected the public safety and economic and social development of cities.The study of flooding simulation and risk assessment under rain and tide encounter scenarios can provide a scientific basis for relevant departments to formulate disaster prevention and mitigation strategies,and has important engineering practical significance.This paper takes the independent river area in Haizhu District of Guangzhou City as an example,constructs a 1D-2D coupled flooding model,carries out flooding simulation and risk assessment under different scenarios,analyzes flooding distribution characteristics and change patterns,draws flooding risk maps,and carries out research on flooding prevention and control measures based on the analysis results.The main research results are as follows:(1)In order to simulate and analyze rain and tide encounter scenarios,a 1D-2D coupled flooding model based on the SWMM(Storm Water Management Model)model and the LISFLOOD-FP model was constructed,and the model was validated using historical measured data.(2)Different rainfall and tide encounter scenarios were set according to the characteristics of the study area,and the flooding simulations under different scenarios were carried out based on the constructed coupled model,and comprehensive analyses were conducted on the load status of pipe sections,nodal overflow,ponding depth and ponding area.The results show that rainfall and tide level are the common causative factors of flooding in the study area,and the increase of rainfall return period and tide level will cause the increase of flooding in the study area.Spatial distribution shows that the northern riverine areas of the study area are more susceptible to tide levels than the western riverine areas.The degree of influence by tide level in the area is related to various factors such as rainfall recurrence period,tide level,distance from the outer river,and surface elevation.(3)Considering the natural and social attributes of flooding hazards,nine risk assessment indicators characterizing hazard and vulnerability were selected to form the flooding risk assessment index system,and the weights were calculated by using hierarchical analysis method,and the comprehensive risk values were calculated by applying Arc GIS spatial overlay analysis function and weighted comprehensive evaluation method to draw the flooding risk map of the study area under different scenarios.The results show that the overall flooding risk distribution in the study area is high in the middle and low in the periphery when it is not influenced by tide level,and the area of low risk area accounts for the largest proportion;when it is influenced by tide level,the overall flooding risk distribution is high in the north and low in the south.The distribution of high-risk flooding areas in the study area has common characteristics,and they are all located in the vicinity of old neighborhoods and roads with low-lying terrain.The risk level of flooding in Sushe Street is the highest affected by the rainfall tide level,and the flooding prevention and control work should be carried out as a priority.(4)According to the results of the scenario simulation and risk assessment,green measures are carried out to retrofit the high-risk areas of flooding and gray measures are carried out to retrofit the overflow nodes,both of which can mitigate the overflow phenomenon of the nodes to different degrees.The combination of green measures and gray measures can effectively mitigate the waterlogging situation in the study area.