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Impact of Chi-Chi earthquake on the occurrence of landslides and debris flows: example from the Chenyulan River watershed, Nantou, Taiwan

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Title: Impact of Chi-Chi earthquake on the occurrence of landslides and debris flows: example from the Chenyulan River watershed, Nantou, Taiwan
Authors: Lin, Ching-Weei1,2 chingwee@dprc.ncku.edu.tw, Shieh, Chjeng-Lun2,3, Yuan, Bee-Deh4, Shieh, Yeou-Chung2, Liu, Shou-Heng1, Lee, Sen-Yuan2
Source: Engineering Geology. Jan2004, Vol. 71 Issue 1/2, p49. 13p.
Subjects: Earthquakes, Landslides, Aerial photographs
Geographic Terms: Taiwan
Abstract: The Chenyulan River watershed in central Taiwan was chosen for evaluating the impact of the Chi-Chi earthquake on the occurrence of landslides, and for exploring the initial conditions triggering debris flows. Interpretations of aerial photographs and SPOT images as well as field investigations were used to identify landslide and debris flow occurrences. Precipitation data were then utilized to investigate critical conditions leading to the debris flow.Comparison of five SPOT images taken between June 1996 (before the July 1996 Typhoon Herb) and September 1999 (before the Chi-Chi earthquake) shows that the landslide area increased from 7.1×106 to 7.5×106 m2 during that time. However, by January 2000 (after the Chi-Chi earthquake), the landslide area almost tripled to 20.8×106 m2. Measurement of images taken in March and August 2001 reveals that the landslide area had further expanded to 24.2×106 and 27.5×106 m2, respectively.Significant differences before and after the earthquake are also noticed in (1) the intensity and amount of precipitation required for triggering debris flow, (2) the size of contributing drainage basin in which debris flows occurred, and (3) the frequency of debris flows. After the Chi-Chi earthquake, maximum hourly rainfall intensity and critical accumulated precipitation necessary to initiate debris flow reduced to as low as 1/3 of the pre-earthquake figures. Prior to the Chi-Chi earthquake, most debris flows occurred in gullies with slopes greater than 10°, and in drainage basins larger than 0.1 km2. Conversely, after the earthquake, debris flows were observed even in gullies with effective drainage area smaller than 0.03 km2. Furthermore, before the earthquake, the debris flow recurrence time in the study area was greater than 5 years, whereas six debris flow events have been observed in the 2 years since the earthquake. [Copyright &y& Elsevier]
Copyright of Engineering Geology is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Database: Engineering Source
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  Data: Impact of Chi-Chi earthquake on the occurrence of landslides and debris flows: example from the Chenyulan River watershed, Nantou, Taiwan
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  Data: <searchLink fieldCode="AR" term="%22Lin%2C+Ching-Weei%22">Lin, Ching-Weei</searchLink><relatesTo>1,2</relatesTo><i> chingwee@dprc.ncku.edu.tw</i><br /><searchLink fieldCode="AR" term="%22Shieh%2C+Chjeng-Lun%22">Shieh, Chjeng-Lun</searchLink><relatesTo>2,3</relatesTo><br /><searchLink fieldCode="AR" term="%22Yuan%2C+Bee-Deh%22">Yuan, Bee-Deh</searchLink><relatesTo>4</relatesTo><br /><searchLink fieldCode="AR" term="%22Shieh%2C+Yeou-Chung%22">Shieh, Yeou-Chung</searchLink><relatesTo>2</relatesTo><br /><searchLink fieldCode="AR" term="%22Liu%2C+Shou-Heng%22">Liu, Shou-Heng</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Lee%2C+Sen-Yuan%22">Lee, Sen-Yuan</searchLink><relatesTo>2</relatesTo>
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  Data: <searchLink fieldCode="JN" term="%22Engineering+Geology%22">Engineering Geology</searchLink>. Jan2004, Vol. 71 Issue 1/2, p49. 13p.
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  Data: <searchLink fieldCode="DE" term="%22Earthquakes%22">Earthquakes</searchLink><br /><searchLink fieldCode="DE" term="%22Landslides%22">Landslides</searchLink><br /><searchLink fieldCode="DE" term="%22Aerial+photographs%22">Aerial photographs</searchLink>
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  Data: The Chenyulan River watershed in central Taiwan was chosen for evaluating the impact of the Chi-Chi earthquake on the occurrence of landslides, and for exploring the initial conditions triggering debris flows. Interpretations of aerial photographs and SPOT images as well as field investigations were used to identify landslide and debris flow occurrences. Precipitation data were then utilized to investigate critical conditions leading to the debris flow.Comparison of five SPOT images taken between June 1996 (before the July 1996 Typhoon Herb) and September 1999 (before the Chi-Chi earthquake) shows that the landslide area increased from 7.1×106 to 7.5×106 m2 during that time. However, by January 2000 (after the Chi-Chi earthquake), the landslide area almost tripled to 20.8×106 m2. Measurement of images taken in March and August 2001 reveals that the landslide area had further expanded to 24.2×106 and 27.5×106 m2, respectively.Significant differences before and after the earthquake are also noticed in (1) the intensity and amount of precipitation required for triggering debris flow, (2) the size of contributing drainage basin in which debris flows occurred, and (3) the frequency of debris flows. After the Chi-Chi earthquake, maximum hourly rainfall intensity and critical accumulated precipitation necessary to initiate debris flow reduced to as low as 1/3 of the pre-earthquake figures. Prior to the Chi-Chi earthquake, most debris flows occurred in gullies with slopes greater than 10°, and in drainage basins larger than 0.1 km2. Conversely, after the earthquake, debris flows were observed even in gullies with effective drainage area smaller than 0.03 km2. Furthermore, before the earthquake, the debris flow recurrence time in the study area was greater than 5 years, whereas six debris flow events have been observed in the 2 years since the earthquake. [Copyright &y& Elsevier]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Engineering Geology is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1016/S0013-7952(03)00125-X
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      – Code: eng
        Text: English
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      – SubjectFull: Landslides
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      – SubjectFull: Aerial photographs
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      – SubjectFull: Taiwan
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      – TitleFull: Impact of Chi-Chi earthquake on the occurrence of landslides and debris flows: example from the Chenyulan River watershed, Nantou, Taiwan
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              Text: Jan2004
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