Research On Flood Risk Assessment And Risk Zoning In Coastal Mountainous And Hilly City

Coastal cities are not only regions with frequent natural disasters, but also important regions and strategic centers with high population density and highly-developed economy. Owing to the global warming, sea-level rising, and the interaction of land and ocean, the vulnerability and the natural disasters risk level of the coastal cities have remarkably increased, and the losses caused by natural disasters are enormous. Therefore, the research on the natural disaster risk of the coastal cities has become a focus owing to the importance and the high risk of the coastal cities exposure to natural disasters.Longwan District of Wenzhou City has seriously affected by flood disaster resulted from rainstorm of typhoon and storm surge. Beach aquaculture and fishery in Longwan District are well developed, but the annual typhoon flood season often results in casualties and great economic losses. Flood risk assessment and regionalization research in this region is not only able to make up inadequate study on flood risk in mountainous and hilly cities, but also able to enrich and develop the theories and methodologies of urban flood risk management.In this dissertation, the author establishes a theoretical framework and methodological procedure for assessment of flood risk in coastal mountainous and hilly cities. The research was supported by two foundations (key Foundation of National Natural Science of China"Scenario Analysis of Emergency Responses to Natural Disasters Risk in Coastal Cities" No: 40730526; National Natural Science Foundation of China "Study on Natural Disasters Risk Assessment System in Chinese Coastal Cities" No: 40571006). and the first-hand data obtained from the field studies and makes an overall risk assessment and regional study on flood risk in Longwan District, Wenzhou City, which shall be of scientific value and practical significance in construction of the flood risk management system with"risk prevention" as the core, safeguard of public safety and promotion of sustainable development strategy in coastal cities. The six main conclusions can be summed up as follows.Based on the overall consideration about the characteristics of the flood-causing factors, formative environment and hazard-affected bodies in the flood system, the author analyses the flood system risk in Longwan District discriminatorily. Flood disastrous factors are identified from three aspects: hydrometeorology, geographical position, and flood prevention and drainage facilities. Formative environment is analyzed from meteorology and underlying surface. Taking into consideration of rapid urbanization impact on flood disaster, types and characteristics of flood hazard-affected bodies are analyzed with different land use types. The correlation and spatial and temporal distribution of typhoons and rainstorms in Wenzhou are obtained by using the data on historical flood disasters caused by typhoons.Scenario-based studies on rainstorm flood risk assessment are especially carried out on the basis of mountainous and hilly region in medium-small watershed down streams and flooding scenarios at different return periods in Longwan District, Wenzhou. With the aid of self-compiled GIS program and flood scenario simulation on the basis of "precipitation volumetric method" , and taking consideration of natural factors such as surface runoff, topographic relief and infiltration, the author simulates flood surface level at different return periods, calculates respective flooding areas corresponded to different submerge depths range, and evaluates rainstorm flood hazard in Longwan District in terms of flood submerge depths. The author simulates typical flooding scenario caused by history-recorded typhoon rainstorms and evaluates the risk with the data observed when typhoon "Haitang" took place in Longwan District in 2005.The author establishes the classification scheme of different land use types flood vulnerability and assesses flood risk vulnerability on the basis of flood-resistance capability of various properties on different land use types and degree of flood losses. The author visually interprets aerial-images over Longwan District by ARCGIS software and determines flood vulnerability of different land use types in the study area. The results of the assessment on flood risk vulnerability in Longwan District reveal changes of flooding area in flood-vulnerable regions and area changes at various vulnerable degrees regions under different flooding simulation scenarios.Cost of different land use types and flood losses are evaluated in terms of foreign and domestic cost evaluation method for different land use types and social economic level of Longwan District. The following counties in Longwan District are sorted in descending order by flood losses at different return periods shown in the study: Yaoxi community > Shacheng community > Haibin community > Yongzhong community. Different land use types are sorted in descending order by flood losses at different return periods under simulated scenarios: industrial land > residential land > agricultural land > public land.The author constructs a method to compile flood risk zoning map in Longwan District by means of flood risk value as a regionalization indicator by means of GIS technology. The study shows that total flood risk areas are increasing while the frequency flood occurrence is decreasing from once in 5 years to once in 100 years. High risk regions are becoming medium risk regions and medium risk regions are becoming low risk regions. Additionally, the area of high risk regions is decreasing while that of low risk regions is increasing.In summary, this dissertation, on the basis of interdisciplinary studies, comprehensively analyzes flood risk system in coastal mountainous and hilly cities from various perspectives, makes a systematic research on flood risk assessment on coastal cities and takes a case study in Longwan District, Wenzhou. The author establishes a systematic flood risk assessment theory framework and methodological procedure for Chinese eastern coastal mountainous and hilly cities, which includes four parts: scenario-based flood hazard assessment, flood vulnerability-based flood vulnerability assessment, mesh-based flood losses assessment and flood risk assessment by correlation between flood losses value and occurrence frequency.Flood risk assessment study is an interdisciplinary research subject involving Disaster Science, Risk Science, Geography, Environmental Science, Meteorology, Hydrology and Hydro-dynamics, etc. Although the dissertation makes a partial useful exploration on flood risk assessment and risk zoning study in coastal cities, it is just at the threshold of the development of scientific theory in this study circle and solves actual problems. Flood risk assessment is a very complex work, and it shoud be further studied theoretically and practically.