| Under the background of global climate change and urbanization development,urban flood has become one of the major natural disasters risking life-safety,social order,and economic development in urban areas.Risk assessment is the basis of risk response and management as well as technical support for disaster prevention and mitigation decision-making.Therefore,it is of great practical significance to analyze the causes and characteristics of urban flood,to conduct an in-depth study on risk assessment methods,and to carry out the risk assessment of urban flood disasters.Taking the Donghaochong(DHC)basin of Guangzhou city as study area,this thesis conducts a study on risk assessment based on relevant researches on urban flood disaster mechanism and risk assessment methods.The main research results of this thesis are as follows:(1)The research background and current situation of urban flood disaster were combed,and the application status,application scope,advantages and disadvantages of four flood disaster risk analysis methods were introduced including historical disaster statistics,remote sensing technology coupled with GIS technology,index system and scenario modeling.(2)Based on the natural and socio-economic data of Guangzhou City,the Mann-Kendall trend test method and linear estimation method were used for a quantitative or qualitative analysis of the impact mechanism of natural conditions and urbanization development on flood disaster in the context of a changing environment.The results revealed that the annual rainfall and average annual temperature had a clear upward trend,and a series of factors such as water system,outer river top trust,land use change,urban micro-terrain and economic development all increase the risk of urban flood disaster.(3)The basic concepts,assessment process,application of the index system method,the quantity and methods of zoning levels,and other aspects of urban flood risk assessment were systematically reviewed.The relationship among spatial resolution,human visual resolution,map scale and cartographic resolution was explored.And by taking the land use in the DHC basin as an example,an appropriate cartographic resolution was proposed to be between 0.10 mm to 0.20 mm.(4)The data from the DHC basin on drainage system,topographical distribution,land use and other aspects were collected.The water accumulation points were on-site visited to investigate the point distribution in the basin,and the causes of water accumulation was analyzed.In addition,an urban flood simulation model of the DHC basin was constructed based on InfoWorks ICM,and the simulation results of the model were analyzed through monitoring and investigation data.The results revealed that the urban flood simulation model had good accuracy and reliability.(5)Taking into account the natural and social attributes and index selection principles of flood disasters,the evaluation index system of the DHC basin was constructed from hazard and vulnerability,and the basic unit size of assessment and the weight of index were determined by combining the mapping resolution,hierarchical analysis and risk zoning.(6)An urban flood simulation model was constructed based on InfoWorks ICM to obtain disaster-causing factor data with a certain level of accuracy by simulating flood processes in situation of rainstorm return period being 1 a,5 a,and 50 a.In this study,the hazard-inducing environment,hazard-bearing body,and hazard prevention and mitigation capacity were analyzed and relevant index data were also obtained.Based on the evaluation index system and index weights,the urban flood risk assessment was carried out,and the flood risk-zoning maps under three situations were drawn.The risk-zoning maps showed that the distribution of hazard was closely related to the duration of inundation,and the distribution of vulnerability was closely related to population density.As the return period lengthened,both medium-high and high urban flood disaster risk areas increased significantly. |
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