The relationships between geological environment and landslides-induced by typhoon and earthquake along the Tachia River
Date Issued
2005
Date
2005
Author(s)
Chuang, Shan-Chieh
DOI
zh-TW
Abstract
This study focused on the effects of four events including typhoon Herb in 1996, 921-earthquake in 1999, typhoon Toraji in 2001, and typhoon Mindulle in 2004 along the catchments of Tachia River between Techi Dam and Ma-an Dam.
We used SPOT satellite images and air photos to map landslide and analyzed the landslide data with GIS program. The measurement data of suspended-sediment load was conducted to estimate the annual sediment discharge and comparison of the unit sediment discharge before and after 921-earthquake. The result of rock strength test was used to discuss the relationships between geological environment and landslides-induced by typhoon and earthquake along the Tachia River.
From the result of landslide mapping, we found the newborn landslide rate was 88% in 921-earthquake, 47% in typhoon Toraji, and 49% in typhoon Mindulle. The newborn landslide areas were 14 and 19 square kilometers in typhoon Toraji and Mindulle, respectively. It indicated that the completeness of formation was destroyed by 921-earthquake, so the landslide areas were increased. Besides, the reactive landslide rates were 51% in 921-earthquake, 59% in typhoon Toraji, and 66% in typhoon Mindulle. And the reactive landslide areas were 15 and 19 square kilometers in typhoon Toraji and Mindulle, respectively. It implied that the landslide induced by 921-earthquake was reacted more easily in consequent torrential rain events.
According to rock strength test, the average uniaxial compressive strength of the Paileng Formatiom, Chiayang Formatiom and Tachien Sandstone were 107, 129 and 137 MPa. The average volumetric joint counts were 11.6, 10.9 and 12, respectively. The 48 % landslides induced by 921-earthquake in the Paileng Formation was higher than others. The landslide rate of the Chiayang Formation and the Tachien Sandstone were increased 5 and 11 times than that in typhoon Herb, respectively. It indicated that the high rock strength of formation with dense discontinuities was especially easily collapsed during the earthquake event.
According to the data of the sediment discharge in typhoon Herb and Toraji, we found that the rainfall and total water discharge during typhoon Herb were 1.8 times than that during typhoon Toraji, but the sediment discharge during typhoon Herb was less 50% than that during typhoon Toraji. If we compared the data of suspended-sediment load, we found that the unit sediment discharge ratio was all greater than 1 before and after 921-earthquake. This result indicated that unit sediment discharge in the post-earthquake was greater than that in the pre-earthquake, so the ratio of unit sediment discharge raised in multiple times with the increasing of water discharge.
Subjects
山崩
重現率
輸砂量
敏督利颱風
大甲溪
landslide
reactive rate
sediment discharge
Typhoon Mindulle
Tachia River
Type
thesis
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