| Summary: | 碩士 === 國立中興大學 === 水土保持學系所 === 95 === Abstract
With the properties of steep topography couples with slope land exploitation and unusual high rainfall events occurred, Shihmen reservoir watershed usually suffers problems of turbidity in water supply at the typhoon and/or storm seasons. To study factors which affect watershed landslide and put some countermeasures into practice can help this reservoir watershed for sediment control effectively.
Three severe landslides at Shihmen reservoir watershed caused by typhoon Wayne, Huber and Elle in 1986, 1998 and 2005; respectively. GIS technology is applied to extract and analyze the relevant factors that affect watershed landslide. Watershed thematic maps such as: slope, aspect, altitude, geology, soil, road, river and land use are employed to establish the database of susceptibility factors, which most affect watershed landslide. In addition, watershed landslide susceptibility value of each factor is derived using instability index method. The deviation coefficient for the percentage of landslide is used to calculate the weight of each factor and to delineate the spatial distribution of landslide susceptibility areas at the Shihmen reservoir watershed.
Environment factors only and man-made disturbance factors added are separately discussed in this study. The environment factors consideration shows that the watershed landslide susceptibility value is 3.21, 4.79 and 3.89 for the year of 1986, 1998 and 2005; respectively. If man-made disturbance factors added, the watershed landslide susceptibility value will drop to 2.97, 4.76 and 3.88 for the corresponding years. The man-made disturbance factors significantly lower the watershed landslide susceptibility value and increase areas of the watershed landslide susceptibility. By summarizing the weight of each factor, the main susceptibility factors that affect watershed landslide are soil and geology. In 1986 and 1988, it shows that the weight of soil factor is 0.2911 and 0.3050 respectively, which is higher compared to the other factors. While the weight of geology factor becomes the highest (0.3448) in 2004, the reason may conclude as the effects of the 921 earthquake which occurred in 1999. This shows that the 921 earthquake caused fragile geology, which results in higher weight of geology factor.
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