Relationships between landslide and river chemistry after Bei-Nan earthquake in Lu-Ye River, Taitung
Date Issued
2009
Date
2009
Author(s)
Shih, Tsun-Ying
Abstract
This study focus on the relationships between landslides and stream chemistry in Lu-Ye river catchment after Bei-Nan earthquake (Mt = 6.2) and subsequent typhoon events. The result shows that the landslide ratio was 1.3% before Bei-Nan earthquake. It rose to 1.7% after the earthquake, 2.3% after typhoon Chan-Chu, 1.9% after typhoon Wipha. The annual sediment discharge in 2006 is 27 Mt/y which is 2.3 times of the mean value (12Mt/y) of past decade. These results indicate that the consolidation of bedrocks in Lu-Ye catchment was getting weaker when they underwent strong shaking movement after Bei-Nan earthquake. The following Chan-Chu typhoon resulted in heavy rainfall (276mm/day) and triggered the slope failure, and the landslides material was flushed into river channel. The main factors controlled landslide distribution are rock strength and joint number. The rock strength in Bilushan formation (29.4MPa-26.7MPa) is weaker than Dananao formation (53.6MPa-61.6 MPa), and the joint number in Bilushan formation is higher than Dananao formation. These factors caused the higher landslide ratio in Bilushan formation (3.6% in Bilushan formation and 1.4% in Dananao formation). he major dissolved ions in river water were getting higher after the earthquake and typhoon Chan-Chu but showed no remarkable trend after typhoon Wipha. This result indicate that the earthquake and Chan-Chu typhoon not only resulted in huge amount landslide and sediment delivered to the river , but also affect the river water chemistry. The rising ion concentration may be attributed to the minerals (feldspars, micas and clay minerals) in rock. The particulate carbon experiment result showed that the percentage were lower in wet seasons and increased 4 times in dry seasons. The rising of particulate organic carbon was due to plants decomposing on catchment slope.
Subjects
landslide
typhoon
earthquake
river chemistry
Type
thesis
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