The relationships between sediment discharge and landslide-induced by typhoon and earthquake along the Chenyoulan River
|Keywords:||陳有蘭溪;山崩;輸砂量;The Chenyoulan River;landslide;sediment discharge||Issue Date:||2005||Abstract:||
Examining the effects of four events -- typhoon Herb, 921-earthquake, typhoon Toraji and typhoon Mindulle -- along the catchments of Chenyoulan River, we found that newborn landslide rate increased to 70%, while the reactive landslide rate decreased to 40%. Regression exponent results show that the landslides associated with these four events were all greater than 1.5, indicating that the landslides in Chenyoulan watershed are dominated by small landslides, which tend to be less than 2000m2. Probability distribution in the upslope area at the lower most point reached by landslides shows that 90% of the landslides remained confined to hillslopes after 921-earthquake. In addition, the post-earthquake average sediment discharge was 37 Mt/yr, some 13 times the pre-earthquake amount. The post seismic unit sediment concentration also increased by 4 times in the Chenyoulan River.
The post-earthquake landslide rate for Nanchuang formation increased 17times. In contrast, the landslide rate for Hoshe formation only increased 3.4 times, and the metamorphic formation only increased 4.8 times. These results reveal that the rock strength of Nanchuang formation was smaller than that of Hoshe formation and metamorphic formation. The post-earthquake reactive landslide rate for Nanchuang formation and Hoshe formation decreased to 25%, but at the same time the metamorphic formation decreased only 6%. The controlling factor came from the discontinuities distribution, because the joints sets for Nanchuang formation and Hoshe formation were only 2/3 of the metamorphic formation.
Analysis of the correlation between landslide distribution and distance from the Chelungpu fault revealed that the 921 co-seismic landslide rates decayed more rapidly after 20 km; landslide effects of typhoon Toraji indicated similar results. The relation between accumulated rainfall and landslide rate display that during typhoon Herb the landslide rate increased with the accumulated rainfall, and the correlation coefficient reached 0.99. But during typhoon Toraji and Mindulle the landslide rate didn’t have good relation with the accumulated rainfall, the landslides during typhoon Toraji and Mindulle maybe affected by 921 earthquake.
|Appears in Collections:||地質科學系|
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