The characteristics of topography and occurrence of hillslope debris flows in Shitou area

• Main Authors: Lung-Chang Wang, 王隆昌
• Other Authors: Ching-Weei Lin
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/79138556635060010825

碩士 === 國立成功大學 === 地球科學系碩博士班 === 93 === 　Taiwan results from collision of Eurasian plate and Philippine Sea plate, orogeny produces steep topography and short and rapid rivers; in addition, rainfall frequently focuses on summer season producing slope instability such as rock falls, debris slides and debris flows. After 921 earthquake, the disaster of landslides and debris flows often occur in Taiwan central mountain area during rainfalls or typhoons, especially during Typhoon Toraji and Nari in 2001.In all kinds of numerous disasters ,some debris flows occurred on steep slope and gully topography were unapparent, were named hillslope debris flows. 　This study collects aerial photos and 5 X 5m DEM of Shitou area after typhoon Toraji and Nari to identify channelized and hillslope debris flows. Geography information systems (GIS) is used to determine their topographic parameters, such as length, average slope, watershed area and the form factor of the watershed. According to the topographic parameters, the distributions of them and the relationships between them of channelized debris flows are compared with hillslope debris flows. Besides, this study choose five factors, such as slope, the area of landslides, the maximum precipitation brought by Typhoon Toraji, 921 horizontal peak ground accelerations, to determine the occurrence conditions of hillslope debris flows. 　Hillslope debris flows, originating on steep slopes have the short gully length, small watershed and the narrow shape of the watershed of the topographic characteristics and gully length is related to watershed area. Channelized debris flows, originated on gully have the long gully length, large watershed and the wide shape of the watershed of the topographic characteristics and gully length is related to watershed area ,average slopes of bed. Average slopes of bed are related to watershed area. From the result of factor analysis, landslides triggered hillslope debris flows may influence by 921 earthquake. The materials of landslides will start moving along hill slope and mix with water in full to initiate hillslope debris flows on proper slopes, distance of mass movement, and rainfall conditions.