都市化對都會地區淹水程度及洪災損失之衝擊評估─以臺中都會區為例

Abstract

近年來受都市化及氣候變異導致災害頻繁的影響，都會地區淹水災害不斷。本研究以臺中都會區為研究對象，探討其土地利用變遷過程對淹水程度及災害損失之影響。為反應都會區複雜之水理特性，本研究針對都會地區之區域排水系統、雨水下水道系統與地表逕流整合模擬，以整合演算法透過一維變量流模式、雨水下水道模式與二維地表漫地流模式之銜接，建構都會地區淹水模擬模式。模式中除考慮都會區地表曼寧糙度係數與入滲容量等因素，亦加入建蔽率對通水面積之反應。模式以2008年卡玫基颱風之淹水事件進行模式之檢定驗證，透過實測淹水資料之範圍比對，其模式之趨勢大致吻合。 本研究對於淹水模式中影響都會地區淹水之都市化因子(地表曼寧糙度、入滲及通水面積折減)分別進行探討與分析。藉由分析結果，延伸討論在土地利用變遷中，依據國土利用資料及臺中市政府公告之都市計畫內容，架構1997年、2007年及未來2017年等都市化程度之情境。研究中以1997年都市化程度為基準，探討都會區內於都市化前後淹水程度之衝擊評估，再以地表集水區劃分流域空間分布，並深究土地利用變遷中，都市化因子對各流域間的交互影響。最後，本研究應用地理資訊系統整合土地利用與各情境之淹水模擬結果，量化評估災害損失。都市化使都會區內建築物密集程度增加，進而影響淹水模擬結果，其研究結果顯示都市化對流域中下游的反應為明顯。以衝擊評估量化之結果中看出，在評估都市化效應時，災害損失增加幅度較淹水程度更具指標性，可用以提供未來規畫者決策參考。

Recently, flooding hazard in urban areas becomes progressively serious due to climate variations and urbanization. In this work, Taichung metropolitan is selected to be a study area and the flood degree and damage are investigated according to its land-use change processes. The simulation model, coupled the 1-D river routing model, the storm water management model and 2-D inundation routing model, to study the interaction of regional drainage, sewerage and surface runoff. Besides the urbanization factor of Manning’s n value considering in the above model, the other factors (i.e. infiltration and building blockage effect) are also introduced in the model. This present model is validated based on the data of Typhoon Kalmaegi flooding event in 2008. The simulated results have good agreement with the measured data. In this work, to quantitatively evaluate the effect of inundation on the urban area, the urbanization factors such as Manning’s n value infiltration and building blockage effect are conducted in the present model. Three different land-uses of Taichung metropolitan (i.e. the scenarios of land-use in 1997, 2007 and 2017 for future urbanization) are introduced to further discussion. According to the urbanization of 1997 scenario, the impact assessments on flood degree and flood damage losses are investigated. Furthermore, the entire catchment basins (i.e. Fa-Tzu River and Hann Creek basin) are divided based on the spatial distribution of land-use into several sub-basins for discussing the flood hazard under different urbanization factors. Finally, the simulated results in the present work are presented by using geographic information system. The quantitative assessments of flooding losses are displayed. The simulated results show that the downstream area of catchment basin not only suffers large damage but also becomes the major area where is impacted by flooding inundation. In addition, the density of building construction plays an important role to affect the evaluation of the impact of urbanization. Under the quantitative results of impact assessment, the change of flooding losses is more sensitive than flood degree. Thus, the index of flooding losses is more representative in predicting the flooding hazard.