摘要荖濃溪集水區2009年受莫拉克颱風連續三天的豪雨肆虐下，造成 河水暴漲及大規模的崩塌，嚴重危害民眾生命財產及聚落安全。為萃取集 水區於極端事件下，深層崩塌發生之區位，本研究以荖濃溪集水區為樣區， 利用危害度及脆弱度乘積的正規化值，作為集水區崩塌風險度指標；其中 危害度採用莫拉克颱風三日降雨量；脆弱度採該集水區鄰近雨量站莫拉克 事件前200年重現期距之三日降雨量、植生綠劣指標(iNDVI)、道路密度及 空間離散度、距河道距離等作為脆弱度因子。崩塌規模潛勢係以植生覆蓋 指數(mNDVI)、地形濕潤指數(TWI)、河道凹岸指標、河道向源侵蝕指標等 四項作為推估因子。結果顯示，集水區已崩塌區位中，風險值較大之區位 集中於集水區下游處，其主要受莫拉克颱風降雨空間分布特性及道路開發 影響；而規模大之區位則多位於源頭區位。另未崩塌區位中，崩塌規模大 且風險大之區位，主要位於集水區出口鄰近之源頭集水區，將來遭逢極端 降雨事件發生大規模崩塌可能性較高，必須特別留意。

Recently, it has been widely reported that the duration and intensity of the most extreme rainfall events is increasing and consequently large-scale landslide, debris flow and river sediment occurred more severe in Taiwan. Such events caused catastrophicdisaster which damage infrastructures, properties and human living.Laonong River watershed devastated by Typhoon Morakot was selected to assess the risk and scale of landslide potential. The landslide risk estimated from the multiplication of the hazard and vulnerability which required the relevant normalized factors i.e. rainfall return period, 3-day rainfall accumulation of 200-year return period, road density, Normalized Difference Vegetation Index (NDVI), and Spatial Dispersion Index (SDI). The landslide scale was derived from the combination of NDVI, Topographic Wetness Index (TWI), river curvature, and headwater erosion. Results show that the low risk areas with large-scale landslide occurred at the concave of upstream, whereas the sites nearby watershed outlet respond to high risk level. In addition, the non-failure areas located at the downstream and the upstream should be paid more attention due to highly potential landslide risk in probability and scale