The relationship between vegetation and landslide-induced by typhoon and earthquake along the catchment of Chenyoulan River

• Main Authors: I-Hui Chen, 陳宜徽
• Other Authors: 陳宏宇
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/90242729964064028293

碩士 === 國立臺灣大學 === 地質科學研究所 === 93 === In the study, we are trying to find out the relationship between landslide distribution and vegetation along the catchments of Chenyoulan River from 1996 to 2004. We use SPOT satellite imagines and air photos to map the landslide and analysis the Normalized Difference Vegetation Index of typhoon Herb, 921-earthquake, typhoon Toraji and typhoon Mindulle. We use both the Experimental Forest of NTU and Taiwan Forestry Bureau’s data to estimate the biomass. Using the data from the test of geomaterial to discuss relationship between lithology and landslides. In general, the NDVI values of landslide area are between -0.2 to 0.2, and biomass is between 50t/ha to 350t/ha. When NDVI increases 0.1, vegetation cover rates will add 20%, and elevation increase 1000 meters, biomass add around 80t/ha to 100t/ha. It means when NDVI values increase and vegetation cover rates will add in the same time in this study area. From the mapping of the landslide, we found that in 1999 921-earthquake’s landslide areas are 2.6 times, flux biomass is 3.4 times, and NDVI values decrease 0.08 than typhoon Herb’s. In 2001, typhoon Toraji’s landslide areas are 2.1 times, flux biomass is 1.6 times, and NDVI values decrease 0.04 than 921-earthquake’s. In 2004, typhoon Mindulle’s landslide areas are 1.1 times, flux biomass is 1.2 times, and NDVI values decrease 0.09 than typhoon Toraji’s. It is say that landslide areas have the negative relation with NDVI. From the result of rock strength, sonic wave test and vegetation, we can find out metamorphic rock strength is between 100MPa to 150MPa. Rock strength and sonic wave test are 2 and 1.5 times than Nanchuang formation. Discontinuities and NDVI values are 2 and 0.5 times than Nanchuang formation. According to the result, NDVI values have negative relation with rock strength, sonic wave test and discontinuities. In several typhoon events, sediment discharge is from 0.3Mt to 28.7Mt and biomass is from 9.4kt to 97.4kt. It means in rainfall most sediment is from the geomaterial rather than vegetation. Because vegetation is only 0.36% of sediment discharge.