| Summary: | 碩士 === 國立屏東科技大學 === 水土保持系所 === 100 === Construction of Tseng-Wen reservoir is to solve the problem of lack of water resources in order to supply for the Chia-Nan plain region, because of the intense rainfall events such as typhoons and heavy rainfall, makes a large amount of landslides occurred in the upstream areas of the reservoir watersheds, causing the sediment siltation serious, reduce storage capacity and shorten the life of a reservoir. Therefore, It is an important work at understand characteristics of Landslides and landslide potential of Tseng-Wen reservoir watershed, help improve within sediment prevention benefits in the watershed and extend the operating life of the reservoir. Therefore, this study collect the landslides at 10 games of the typhoon and torrential rain between 2001~2010 to analysis the spatial and temporal variations of landslides. and using GIS technique to build the landslides database, Explore the Effects of the landslide of by potential factor (slope, aspect, elevation, geology, soils, land use) and triggering factors (rainfall). In addition, we also using the dangerous value method to discussed the landslide potential in the study.
Result shows that the spatial and temporal variations of landslides in the Tseng-Wen reservoir watershed. Before Typhoon Morakot, the landslide rate is remain below 1%, after Typhoon Morakot, makes a large amount of landslides occurred in the watershed, cause the landslide rate increased to 3.07%. Then, there are continue to decrease year by year trend. Result shows that the magnitude and frequency distribution of landslides, there are in line with the exponential relationship. By contrast, the frequency of small-scale landslides occurred more than the large-scale landslides, and lead to large-scale landslides occurred mainly by rainfall. The results show that the landslide caused in mainly take place in the upstream areas of the watersheds, it mostly happened at the height of 500~1,250meters, and the slope grade is at 27°~43°, and with increasing slope landslide rate is also enhanced. In addition, a large number of landslides also occurred in the enlarged area of former landslide zone and the headward erosion zone.
Result shows that the characteristics of landslides and rainfall. After Typhoon Morakot, the rainfall conditions induced collapse due to the Slope Stability reduce both collapse more, should be followed downward correction as appropriate. This research use Daogi formula to estimate the landslide rate in this watershed. It is advice may be given the average rainstorm of one day replace the average accumulated rainfall of watershed, and the critical rainfall may be given 130mm~250mm. This result is more in line with the characteristics of the watershed and the typhoons rainfall.
The dangerous value method to analyst the weights of landslide factors are land use, soil, slope, geology, rainfall, elevation and aspect respectively. The results show that the reasonable land use can reduce the possibility of landslide. A simple test result shows that the dangerous value method can predict landslide well. By using the multi-tempral landslide layers, the accuracy of the landslide potential maps can be compared, The analytical results show the predict landslide precisely where 70.48% landslide fall on the high susceptibility zone. Finally the analytical results can effective application to watershed management planning and preliminary forecast of disaster prevention.
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