| Summary: | 碩士 === 長榮大學 === 土地管理與開發研究所 === 94 === The characteristics of the mountain in Taiwan are steepness; and it is located at the subtropical area of western Pacific and on the path of typhoons. As the result, the frequent earthquake, typhoon, and torrential rain cause the instable slope to have sand and soil disaster easily. The watershed of reservoir often located at mountain area where it has precipitous landforms and poor geology condition; the damage to slope happens frequently. The damage of slope or landslides will not only cause the soil to run off, the collapsed soil will also enters the reservoir with river and silt up. The amount of water a reservoir can store will decrease so the functionality will drop as well. The landslides caused by rainfall is the main source of soil that causes reservoir to silt up; in order to effectively prevent the disaster from happening again, the investigation of collapsed area is important preparation work to adequately grasp the characteristics of watershed collapse. It can provide a reference for reservoir management plan. Though the long-term investigation and analysis on the environmental sensitive area of environment, we can understand more about the characteristics of disaster and the cause. Therefore, this research first use SPOT satellite images to determine and analysis the new collapsed area during typhoon period due to rainfall, and trace the transition over time. Second, perform correlation between the determination result of new collapsed area and geology, direction of slope, and rainfall characteristics of reservoir to analysis the element that causes collapse to occur.
From the satellite image, we discovered that there is an obvious difference in the rainfall of Typhoon and space distribution, number of collapse, and seriousness of collapse. The collapses caused by Mindulle typhoon mainly take place at center of watershed. Nari and Haitang typhoon show a more average distribution of space and collapse area. Also, with the correlation of water environment analysis of collapse area and watershed, we discovered that the collapse often occurred where the steepness of the slope is between 20°~40°. For geology properties, Tapang formation and the Nanchuang formation is the main layer for collapse. The collapse often happened where the slope is facing southeast. Under the effect of rainfall, when the slope and geology properties meet the description above, the potential of collapse during the center of typhoon torrential rain will increase. It shows that the characteristics of collapse still have tighter relation with the rainfall. Therefore, rainfall has great affect on the collapse location, scale, and number. In other words, the scale and intensity of rainfall is an important element that affects the collapse.
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