Development of a risk evaluation model for rainfall-induced flood hazard based on hydrologic frequency analysis and fragility curves

In Taiwan, the hillside is about over 70% of the total area. These areas also have steep topography and geological vulnerability. However, when an event of torrential rain comes during a typhoon, the flood disasters usually occur at the low elevation areas due to the long duration and high intensity of rainfall. Therefore, a design which considers the flood management model has become an important issue in Taiwan. In this study, a outcomes of quantitative precipitation estimation for Flood Fragility Curve (FFC) was developed, based on the geomorphological, land use map, drainage area map and population density condition factors using disaster management at the Taichung in Taiwan, during over 20 years ago rainfall events. This study addressed an effective flood hazard assessment process, linking together the outcomes of quantitative precipitation estimation by hydrologic frequency analysis data for FFC model. The Physiographic Drainage-Inundation model (PHD-model) method was used to determine the rainfall indicates (R, I) for numerical analysis. Land use map from digital aerial images were applied to analyze the relationship between flood area and property loss. Land use map from digital aerial images were applied to analyze the relationship between flood area and property loss. The 5-M DEM (digital elevation model) was used for slope variation, elevation and river distance analysis in the study site, and the curve fitting model of power function was conducted to determine the proposed empirical FFC model. The model can express the flooded area ratio a damage state for a certain classification (or conditions) of flood disasters by considering a specific hazard index for a given event. Finally, these results can be used to assess the property loss from land use, and, in the future, to manage the risk of flood in the watershed for disaster victims.