| Summary: | 碩士 === 國立成功大學 === 地球科學系碩博士班 === 98 === In this study, by using the concept of stream order and working in the platform of geographic information system (GIS) ,four periods of FORMOSAT 2 images taken from 2008 to 2009 that covered three typhoon events are used to identify landslides and debris flows in the Chishan River watershed. In the images taken after the Typhoon Kalmaegi in 2008, 727.25 hectares landslides have been recognized. Additionally, 566.07 hectares landslides are triggered by the Typhoon Sinlaku in 2008 and 3239.60 hectares landslides are induced by the Morakot in 2009.
For debris flows triggered by the Kalmaegi and Sinlaku in 2008, there are 17 debris flows in gullies with a stream order 1, 17 in gullies with a stream order 2, 9 in gullies with a stream order 3, and 2 in gullies with a stream order 4. 90% of debris flows occurred in gullies with a stream order 1 have landslide density over 2.04%, Additionally, 90% of debris flows occurred in gullies with a stream order 2 and 3 have landslide density over 1.3% and 0.55 %, respectively.
For the Typhoon Morakot, there are 161 debris flows to be recognized in gullies with a stream order 1, 106 in gullies with a stream order 2, 42 in gullies with a stream order 3, and 12 in gullies with a stream order 4. 90% of debris flows occurred in gullies with a stream order 1 have landslide density over 4.08%, In addition, 90% of debris flows occurred in gullies with a stream order 2 and 3 have landslide density over 2.47 % and 1.96 %, respectively.
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