| Summary: | 碩士 === 國立臺灣大學 === 土木工程學研究所 === 104 === Large-scale landslides triggered by rainfall or earthquake often caused much loss of lives and property, thus landslide susceptibility assessment plays an important role in hazard mitigation. The study focused on the geo-environmental characteristics before the large-scale landslide occurrences including morphological, geological and hydrological features and the differences between landslide and non-landslide distributions. The Qishan River basin in Namashia District, Kaohsiung County, Taiwan, with 57 events of large-scale landslides during Typhoon Morakot in 2009 were used as study area. With application of slope-units, environmental landslide potential has been estimated by statistical methods and rainfall condition has also been discussed.
Slope-units mapped by ArcGIS tools were used to extract the morphological, geological, watershed and rainfall factors. By conducting the hypothesis test and discriminant analysis in SPSS, significant factors correlated to landslides were found and selected to form the potential analysis model. It was found that slope-units mapped according to watershed and 4 reclassified aspects, fitted the range of large-scale landslides better. Under the principal of landslide area ratio more than 30% as a landslide unit, 6 factors including: slope type, standard deviation of slope degree above half ramp, types of formations, distance to geological structural line, watershed width and unit drainage density, all display significant differences between landslide and non-landslide groups with physical meanings and low correlation to one another. The overall accuracies of discriminant analysis model for fitting and prediction were 70.3% and 75.8%. Gradual addition of these factors helps to separate groups and discriminant function to concentrate within each group.
Concerning rainfall factors, the relation and the correlation with environmental potential to landslides were analyzed. It was discovered that rainfall increased with higher elevation. Long-term rainfall had better correlation with large-scale landslides. If the discriminant function Z score is higher than 0.15, it was classified as a potential landslide unit. It was suggested that the accumulative rainfall in 48 hours with 1,000 mm may be used as an alert rainfall threshold to large-scale landslides.
|
|---|
