| dc.description.abstract | Earthquakes are one of the most destructive and dangerous of all natural phenomena as it could generate several fractures, cracks, and even co-seismic landslides that may cause havoc in mountainous regions. A number of debris flows during sequential rainfall mayalsooccurinanareawhichwasexposedtostronggroundshaking. Thisstudyfocuses on the sediment transportation and deposition evolution of watersheds with debris flow torrents,alongTachiaRiver. AerialphotoscoveringhazardssuchasChi-ChiEarthquake, Typhoon Toraji, Typhoon Mindulle, and Typhoon Aere, respectively, were mainly used. In this research, image analysis tool was also exploited to study the temporal and spatial morphologyofthesedimentsforthefourevents. Despitebeingseparatedforonly2.2km, two adjacent watersheds, DF025 and DF106, have different reactions to the earthquake and heavy rainfall events, thus sediment evolution analysis is approached differently for the two catchments. These differences could be attributed to different types of failure that occurred after Chi-Chi Earthquake- shallow landslides for DF025 while deep-seated landslide for DF106. The differences in source also translates to the type of basin in which DF025 could be categorized as supply-limited, while DF106 as supply-unlimited. Sediment-budget were estimated in the study where DF106 has an estimated deposition volume of 1.0 x 105 m3, 1.4 x 106 m3, and 1.1 x 106 m3 for Typhoon Toraji, Typhoon Mindulle, and Typhoon Aere, respectively. These deposits could travel downstream and create havoc to communities given the right conditions since only few debris reached Tachia River, same as DF025. The main objective of this research is to have a semiqualitative and semi-quantitative approach on the sediment evolution analysis on the watersheds with debris flow torrents along Tachia River.
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