page 1 landslide hazard analysis for hong kong using landslide inventory and gis 7099042005...

Landslide hazard analysis for Hong Kongusing landslide inventory and GIS

7099042005 鄭育騰7099042023 何俊賢7099042025 張台聖

1. By using GIS and employing historical landslide data in Hong Kong to analyze where is the susceptible area.

2. 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

3. 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.

4. Combining the hazard map with "Exposure Index" we can obtain the

risk map.

Abstract

Geology and Climate of Hong Kong

名稱高度 (m) 行政區太平山 554 中西區柏架山 532 東區奇力山 501 中西區西高山 494 中西區歌賦山 479 中西區金馬倫山 439 灣仔區畢拿山 436 東區紫羅蘭山 433 南區渣甸山 433 灣仔區聶高信山 430 灣仔區歌連臣山 340 南區南朗山 284 南區摩星嶺 269 中西區龍虎山 253 中西區壽臣山 140 南區

3. Lithology : a. volcanic rock(tuff) b. intrusive rock(granite)

4. Deposit : a. weathered from volcanic rock b. the average thickness is 2m


Comprehensively consider the landslide hazard

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.


Seasonal distribution :

We delete the data of MAY and re-plot the figure.

Clearly! We can observe the correlation between rainfall and landslide.


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

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.

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.

Percentage distribution of landslide on each facilities :

Only 1% of landslide hazards directly hit on cars.


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.

Landslide in different geological formations

Cumulative number of landslides per year & volume of landslide :

It is very unlikely that the data set for small events is complete.

Frequency and volume relation of landslides

Frequency and volume relation of landslides

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 :

Landslide inventory

Counting the number of landslides in each grid , using the curve to combine the grid with the same number.

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

Landslide inventory

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.


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.


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.

Conclusion

Thank You For Listening

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