1. Application of GIS on Landslide Susceptibility and risk mapping
Pradeep Paudyal
[ ]
Hydrogeology Lab.
Department of Geology
Kyungpook National University

2. Landslide
A generalized / collective name for mass movement activities on the earth surface
Slide (rock slide, soil slide, mud slide)
Fall (rock fall, soil fall)
Topple
Flows (debris flows, mud flows)

3. Causative factors for Landslide
Natural causes:
Slope of terrain
Faces of sloped surface (aspect)
Direction to the sun (hillshade)
Rock /soil type and depth
Intensity of rainfall
River works and drainage pattern, etc.
Anthropogenic causes:
Road cut / quarrying on mountain terrain
Changing land use pattern and deforestation, etc.

4. Landslide susceptibility
Landslide susceptibility is defined as a possibility of occurrence of landslide in a particular area once upon a time in future
Landslide susceptibility mapping delineates the hazardous zones due to occurrence of landslides
The present study is focused on preparation of landslide susceptibility map with an application of geographic information system (GIS)

5. Study area Southwest part of Kathmandu (capital of Nepal)
It covers some part of middle mountains and flat land of Kathmandu valley
CHINA
INDIA
NEPAL

6. Physiography

7. Distribution of Landslides
About 125 landslides are mapped to prepare the landslide susceptibility map.
Landslides only greater than 25 m x 25 m dimension are considered
Most of landslides are distributed on the north-faced slope of hilly terrain

8. Landslide distribution

9. Susceptibility parameter maps
Slope map
Aspect map
Hillshade map
Geological map
Distance to stream map

10. Slope map
Slope map comprises 6 classes of slopes measured in degree gradient
Areal distribution of slope map shows:
Slope (degree)
Area (%)
0 – 5
29.4
5 – 15
17.9
15 – 25
13.0
25 – 35
19.0
35 – 45
13.9
More than 45
6.8

11. Slope map

12. Aspect map
Aspect map is a measure of slope faces reference to the north direction
Aspect map comprises 10 classes including flat land as aspect zero.
The aspect map was reclassified into 6 classes as:
Aspect
New class
0 – 45 6
180 – 225 2
45 – 90 5
225 – 270 4
90 – 135 3
270 – 315 1
315 – 360

13. Aspect map

14. Hillshade map
Hillshade map is a measure of direction and altitude of sun to the sloping face
It reflects a gradient value of hillshade, which is later categorized into 6 classes during map analysis

15. Hillshade map

16. Geological map
Due to very high importance of rock type in occurrence of landslide, a geological map of study area has also been considered
The geological map shows 6 different rock units:

17. Geological map

18. Distance to stream map
Streams have also vital role on inducing landslides; close to a stream has a high possibility of landslide occurrence
Streams are buffered and classified into 6 classes:

19. Distance to stream map

20. Methodology and Analysis
“Landslide Index Method” is used to calculate the respective weights for landslide susceptibility mapping
wi = weight given to a certain parameter class,
Dense class = landslide density within the parameter class,
Dense map = landslide density within the entire map,
Npix (Si) = number of pixels containing landslide in a certain parameter class, and
Npix (Ni) = total number of pixels in a certain parameter class.

21. Methodology and Analysis
Weights obtained using LI method
Aspect
Slope
Hillshade
Class
Value (respect to N)
weight
class
Value (degree)
Description 1
( )
(0 - 5)
highly sunny 2
( )
(5 - 15)
Mod sunny 3
( )
(15- 25)
sunny 4
( )
( )
little shaded 5
( ; )
( )
shaded 6
( )
( )
Highly shaded
Stream distance
Geology
more than 150 m.
Lake sediments m.
Sandstone m.
Alluvial fans m.
slate m.
Limestone + slate
Near than 25 m.
Limestone

22. Result
Each parameter maps are overlaid and the respective weights are summed up as:
A resultant landslide susceptibility map is obtained with a range of value, which is categorized into 3 classes: High, Medium, and Low susceptibility
This categorization is in a subjective way
Weight= [Wslope + Wasp +Whillshade + Wstreamdis + Wgeol ]

23. Landslide susceptibility map

24. Validity Test
About 25% of landslides were separated for validation test of the prepared landslide susceptibility map.
The test shows 18 landslides out of 25 lie in the high hazard zone, while rest 5 landslides lie in the moderate and 2 lie in the low hazard zone respectively.

25. Validity Test

26. Risk assessment Risk is a measure of loss of life and properties.
By crossing the layer of landslide susceptibility and settlement, about 250 residential houses are under high hazard zone.
Considering information about average household size of 10 person per house, 2500 people are under high vulnerable zone due to landslides.

27. Settlement under risk

28. Conclusions
GIS is very useful tool that can be applied in building a statistical model in the field of natural science too if spatial information are available.
GIS can link the socioeconomic and demographic attributes to the spatial information that becomes helpful in policy making and planning.

29. Thank you