Flood risk assessment of coastal community: A case study in Longwan District of Wenzhou City
沿海城市社区暴雨洪水风险评价——以温州龙湾区为例

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 studies on flood risk in mountainous and hilly cities, but also able to enrich and develop the theories and methodologies of urban flood risk management. Scenario-based studies on rainstorm flood risk assessment are especially carried out on the basis of mountainous and hilly regions in mediumand small watersheds down streams and flooding scenarios at different return periods in Longwan District, Wenzhou. By calculating the frequency of precipitation of heavy rain in Longwan District of Wenzhou City, the different precipitation and flow depths of different return periods were obtained. 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, this article simulates flood surface level at different return periods, calculates respective flooding areas corresponded to different submerge depths range, and evaluates rainstorm flood risk in Longwan District in terms of flood submerge depths. The paper simulates typical flooding scenario caused by history-recorded typhoon rainstorms and evaluates the risk with the data observed when typhoon "Haitang" occurred in Longwan District in 2005.