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Landslide hazard analysis for Hong Kong using landslide inventory and GIS. 7099042005 鄭育騰 7099042023 何俊賢 7099042025 張台聖. Abstract. By using GIS and employing historical landslide data in Hong Kong to analyze where is the susceptible area.
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Landslide hazard analysis for Hong Kong using landslide inventory and GIS 7099042005 鄭育騰 7099042023 何俊賢 7099042025 張台聖
Abstract • By using GIS and employing historical landslide data in Hong Kong to analyze where is the susceptible area. • There are four main categories we consider as our parameters : • a. Terrain • b. Geology • c. Landslide • d. Environment • Each of those categories contains one or • more GIS layers.
Abstract • By using the "zonal statistics"and "raster calculator "we can obtain the correlation of each layer with the number of Landslide and the • hazard map. • Combining the hazard map with "Exposure Index" we can obtain the • risk map.
Geology and Climate of Hong Kong • Lithology : • a. volcanic rock(tuff) • b. intrusive rock(granite) • Deposit : • a. weathered from volcanic rock • b. the average thickness is 2m
Diurnal and seasonal distribution for landslides Diurnal distribution : • Landslides often occur during daytime • from 7 till 18 o’clock. • The peak hour is at noontime.
Diurnal and seasonal distribution for landslides Seasonal distribution : • The average monthly rainfall correlates • well with landslide occurrence . • EXCEPT MAY!!! • May has an abnormal high frequency of • landslides from 1991 to 1992.
Diurnal and seasonal distribution for landslides Seasonal distribution : • We delete the data of MAY and re-plot • the figure. • Clearly! We can observe the correlation • between rainfall and landslide.
Fatalities and injuries rate Cumulative casualties from 1948 till 1996 : • The total number of fatalities and • injuries are 556 and 570. • This data means that there are 23 • casualties per year.
Fatalities and injuries rate Cumulative casualties from 1948 till 1996 : • There are jumps in 1972. • In recent year , the casualties have decreased to 8 due to the LPM program.
Facilities risk rate Cumulative number of landslides facilities : • Double count of influences is allowed • in our analysis. • In resent years , landslides hazard on • squatter is dropping.
Facilities risk rate Cumulative number of landslides facilities : • Landslide hazard on road and footpath is increasing.
Facilities risk rate Percentage distribution of landslide on each facilities : • Only 1% of landslide hazards directly • hit on cars.
Landslide in different geological formations Percentage distribution of geological formation : • Volcanic formation : tuff. • Igneous formation : granite. • It is normally speculated that the • occurrence of landslide should depend • on the local geological formation.
Landslide in different geological formations Percentage distribution of landslide on soil types : • There seems no strong correlation • between landslide occurrence and • geological formation.
Frequency and volume relation of landslides Cumulative number of landslides per year & volume of landslide : • It is very unlikely that the data set for • small events is complete.
Landslide inventory Contour map and landslide data : • One way to generate hazard map is the • use of historical data. • We divide the Hong Kong map into • square grids .
Landslide inventory Contour map and landslide data : • Counting the number of landslides in each grid , using the curve to combine the grid with the same number.
Landslide inventory Contour map and landslide occurrence : • The six levels of contour lines are : • (1)0.25 (4)2 • (2)0.75 (5)4 • (3)1.25 (6)5
Using GIS to analyzing landslide hazard • The limitation of the hazard map • introduced just now is that only • landslide data has been used in • generate the map. • A useful hazard zonation map should • also depend on other factors . Such as • geology , geomorphology , hydrology , • vegetation and climate.
Using GIS to analyzing landslide hazard • Before combining those parameters , we • use zonal statistics in ArcGIS 8.2 to • generate the correlation of any two • layers. • These plots are useful for identifying the • important parameters affecting landslide • occurrence.
Using GIS to analyzing landslide hazard Zonal Statistics Raster Calculator • Seven layers of information have been • used in this analysis. • More layers can also be added to this • hazard analysis if their correlations with • landslide occurrences are clear and • measurable.
Conclusion • ArcGIS makes the landslide risk analysis • more efficiently and quickly. • There are things that we should bear in • mind : • a. Unreliable prediction on parameters • can lead to misleading hazard • estimation. • b. The Exposure Index we considered • should be more comprehensive.
