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GIS
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Identification and Prediction of Dip Slope by API and GIS Approach
3-2 Lincoln Vila -The Most Famous Case of Dip Slope Hazard
After the attack of Typhoon Weny on 18 August 1997, Lincoln Villa, a famous residential area on sloping lands near Taipei City, encountered a catastrophe of a damage of 100 houses and a casualty of 100 people ( figure 3) (Chi et. Al., 1998; Tian,1998). This is a typical dip slope hazards as ever seen in Taiwan due to inappropriate site selection and site treatment.
Figure 3. Dip Slope Hazard of Lincoln Vila Catastrophe on 18 August 1997.
3-3 Unstable Dips Slopes Processing Approaches and Results
for the study area in San-Guang of Tauyen Country, a DTM dataset was obtained by simply subsetting the Taiwan DTM, which is a 40 meters DTM covering whole Taiwan Island, created by Agriculture and Forestry Survey Team. This dataset was used to derive slope direction and slope angle of the study area. in the mean time, a dataset for deriving dip direction and dip angle of bedding planes was created by digitizing the geological map of the study area. The dip slope area can be generated by comparison between slope direction and dip direction. In this study, the slopes with a difference of less then 22.5 degrees between theses two directions are assumed dip slopes. subsequently, the dip slope area are further divided into stable and unstable sub-areas by comparison of dip angle and slope angle and slope angle, as discussed on paragraph 3-1. figure 4a shows the areas of dip slopes. figure 4b shows the areas where dip angle is less than slope angle. by overlaying these two datasets, unstable areas can be obtained by looking at dip slopes with enlighted bedding planes ( figure 4c and 4d). figure 4c is an aerial photo taken in 1990 overlaid by e unstable polygons whereas Figure 4d is an aerial photo taken in 1997. the results proved a large scale dip slope hazard such as the one near the center of the aerial photos with 200 meters in length can be predicted as shown in Figure 4c and Figure 4d.
Figure 4 Results of unstable dip slope processing
Conclusion
The highly fractured nature is a major cause of hazardous landslides in Taiwan. After a severe damages caused by Typhoon Herb in 1996, it was recognized critical to conduct a general survey of existing landslides of he whole island. A aerial photo-interpretation was applied due to the advantage of bird-view and the stereoscopic capability. And, GIS is adopted to establish a landslide database.
One of the major types of the landslide hazards is the dip slope failure. With the processing of database of DTM and rock formations, the areas prone to dip slopes hazards can be predicted. And, this is further compared with the landslides interpreted form aerial photographs to verify the prediction. the case form Tauyen Country of northern Taiwan proves that unstable dip slope cab be predicted.
References
- Chi J.J., Lin C J and Kiu H J (1998) A Study on the Causes of Lincoln Vila Catastrophe. Ti-Chi, V.18, no. 1, P. 43-58, ISSN: 0303-092X. June, 1998. ( in Chinese )
- Liu Jin-King (1985 a ) Remote Sensing for Landslide Identification and prediction -cases form Taiwan. Proceedings of Advanced Technology for Monitoring and Processing Global Environmental Data, Convened in the University of London by the Remote Sensing Society, UK and CERMA, USA, 10-12 September 1985. P.223-232.
- Liu Jin-King (1985 b) Remote Sensing for Identifying Landslides and for Checking Landslide Prediction. MSc. Theses, University of London, July 1985. 164p
- Liu JK, Wu C N and Chuang M Y (1983) Relations between Lineaments, Joint Patterns, Seismicity and Techtonic Stresses in Taiwan Island. Proceedings 17th Intl. Symp. Remote Sensing of Environment, Ann Arbor, Michigan, may 9-13, 1983.
- Liu J K, Wong S C, Wu S M, Huang J H, Huang C T and Wong W N (1998) A Preliminary Study on te Identification of Various Landslide Types Using Panchromatic and Color Aerial Photographs. Proceeding s of Airborne Remote Sensing Symposium, Convence in Industrial Technology Research Institute, by Remote Sensing Promotion Committee of Agriculture Council and ITRI, 23-24 April 1998. P.199-208 ( in Chinese)
- Tinan Y M (1998) Case History of Linclon Vila Catastrophe. Ti-Chi, V.18, No.1, P.59-82 IISN: 0303-092. June, 1998. ( in Chinese )
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