台灣地區因為地形陡峭、地質破碎、豪雨集中，加上山坡地之過量開發，近年來極端降雨事件造成環境劇烈變化，土砂災害發生的頻率與規模也隨之增加。2009年8月Morakot颱風帶來驚人雨量，嘉義縣、高雄縣、屏東縣山區累積最大降雨量高達2,900 mm以上，而南投、臺南及屏東三縣亦超過1,500 mm，因此造成嚴重山崩、土石流、堰塞湖、洪患與土砂災害。本研究將以曾文水庫集水區為研究區域，以HEC-RAS 4.1及FLO-2D數值模式模擬集水區在重現期距25年、50年、100年與莫拉克颱風下之洪峰流量，對河道沖淤位置之變異及對河川高階地之影響範圍，進一步評估茶山部落之安全性。本研究成果可提供給相關單位做防救災體系架構與運作改善之參考依據。

As a result of heavy rainfall, steep topography, young and weak geological formations, earthquakes, loose soils, slope land cultivation and other human disturbance, much area in Taiwan are prone to the occurrence of disastrous mass movements such as landslides and sediment disasters. During recent years, the extreme rainfall events brought huge amounts of rainfall and triggered severe changes in watershed environments. Typhoon Morakot in August 2009 brought amazing rainfall, cumulative Chiayi County, Kaohsiung County, Pingtung County mountainous maximum rainfall of up to 2,900 mm or more. Nantou, Tainan and Pingtung three counties rainfall over 1,500 mm, thus causing severe landslides, debris flow, flooding and sediment related disasters were induced by this heavy rainfall event. In this thesis, the study area is the Zengwen reservoir watershed. The study will use HEC-RAS 4.1 and FLO-2D numerical model to find the separating location between erosion and deposition, evaluate influence area of riverbank evaluation, and analyze the safety of Cha-San Village under peak flow of 25-year, 50-year, 100-year return period and Typhoon Morakot. The results show that the simulation can provide some guideline for designing evacuation route and prevention facilities.