圖書典藏及影音數位平台

透過整合型研究，以水文地文區域化之觀點，針對過去西南沿海地區經常遭受淹水之區域進行探討及研究，探討沿海淹水敏感區近年來受氣候變異之災害衝擊評估，徹底瞭解並解決西南沿海淹水敏感區受水文及地文之影響為重心，乃為現階段洪災科技發展之重點課題。

The purpose of this project is to develop an inundation risk assessment framework for the southwest coastal area, Taiwan. This framework enables the determination of inundation risk with the consideration of hydrologic and topographic uncertainties. Furthermore, based on the results of inundation risk assessment, this project will propose an optimal groundwater pumping strategy which simultaneously considering the inundation risk and water demand. This study will be carried out in two years. This report presents results of the first year and has already completed the development of inundation risk assessment framework. In the developed inundation risk assessment framework, the inundation risk is defined as the product of inundation hazard and vulnerability. The inundation hazard is the probability density function of inundation depth while the vulnerability is the relationship between damage and inundation depth. After the inundation risk was defined, the global sensitivity analysis was applied to find the most sensitive variables in inundation simulation. The results showed that the uncertainties of digital elevation model (DEM) and precipitation under a specified return period are the most sensitive input for estimating the inundation depth. The developed framework was applied in the study area (Erlin and Yuliao drainage system in Changhua County and the drainage system in the northern Yunlin County) to assess the inundation risk under present condition. Besides, the spatial distribution of accumulative land subsidence between 2012 and 2021 was predicted by a one-dimensional land subsidence model. The DEM and channel geometry in 2021 were produced based on the predicted land subsidence field along with the present topography data. Thus, the inundation risk in the study area after ten years land subsidence was also predicted. Finally, the effects of land subsidence on the freeboard and inundation depth were analyzed based on the results of inundation risk assessment before and after ten years land subsidence. The analysis of freeboard showed that except the extremely low-lying area where the elevation is lower than the spring high tide level, the change of freeboard after ten years land subsidence is mostly influenced by the spatial variation of land subsidence field. Higher change rate of the land subsidence field along the channel direction induces more significant change of freeboard. Besides, the freeboard at a cross section tends to decrease after ten years land subsidence when the land subsidence decreases in the channel downstream direction. The spatial variation of land subsidence field also significantly influences the change of inundation depth outside the extremely low-lying area after land subsidence. The inundation depth at a computation grid tends to increase after ten years land subsidence when the land subsidence at this grid is greater than that at its neighbor grids. Unlike the change of freeboard and inundation depth outside the extremely low-lying area, the freeboard and inundation depth within the extremely low-lying area are always decreased and increased respectively after ten years land subsidence. Furthermore, the decreased freeboard at a channel cross section is typically 0.8 to 1.0 times the magnitude of land subsidence at the same cross section. This study showed that for a coastal area with potential land subsidence problem, the spatial distribution of future land subsidence should be quantified and incorporated into the flood management.