Investigation of Landslides and Debris Flows in Tachia Watershed Between Maan Dam and Techi Dam

Abstract

The Chi-Chi earthquake and subsequent typhoon events induced severe landslides and debris flows in the watershed of Tachia river. It inflicted severe damage to the power generation facilities and highway links. For the rehabilitation planning, quantitative assessment of landslides, debris flows and river deposits were conducted by using aerial photos and satellite images obtained at six stages of earthquake and typhoon events. The future trends of landslide and debris flow were also investigated by using empirical models. The long-term deposition or scouring was also conducted by numerical simulation. The results show that over 50,000,000 to 70,000,000m3 of sliding volume were induced in the Chi-Chi earthquake and subsequent typhoon events during 1999 to 2005. By conservative estimation, 60% of the debris still remain in the watershed, which will cause silting of the main river channel in the future. The deposition in the main river channel will increase with decreasing rate in the future, and river channel scouring is not expected to occur in the future 20 to 30 years

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