Download - Pradeep Paudyal [2009422004] Hydrogeology Lab. Department of Geology Kyungpook National University
Application of GIS on Landslide Susceptibility
and risk mapping
Pradeep Paudyal[2009422004]Hydrogeology Lab.Department of Geology Kyungpook National University
LandslideA generalized / collective name for
mass movement activities on the earth surface
Slide (rock slide, soil slide, mud slide)Fall (rock fall, soil fall)ToppleFlows (debris flows, mud flows)
Causative factors for LandslideNatural causes:
Slope of terrainFaces of sloped surface (aspect)Direction to the sun (hillshade)Rock /soil type and depthIntensity of rainfallRiver works and drainage pattern, etc.
Anthropogenic causes:Road cut / quarrying on mountain terrainChanging land use pattern and deforestation, etc.
Landslide susceptibilityLandslide 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)
Study areaSouthwest part of Kathmandu (capital of
Nepal)It covers some part of middle mountains
and flat land of Kathmandu valley
CHINA
INDIA
NEPAL
Distribution of LandslidesAbout 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
Susceptibility parameter mapsSlope map
Aspect map
Hillshade map
Geological map
Distance to stream map
Slope mapSlope 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
Aspect mapAspect map is a measure of slope faces
reference to the north directionAspect map comprises 10 classes
including flat land as aspect zero.The aspect map was reclassified into 6
classes as:
Aspect New class Aspect New class
0 – 45 6 180 – 225 2
45 – 90 5 225 – 270 4
90 – 135 3 270 – 315 5
135 - 180 1 315 – 360 6
Hillshade mapHillshade 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
Geological mapDue 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:
Distance to stream mapStreams 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:
Methodology and Analysis“Landslide Index Method” is used to
calculate the respective weights for landslide susceptibility mapping
)(/)(
)(/)()(
NiNSiN
NiNSiNLn
mapDense
classDenseLnwweight
pixpix
pixpixi
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.
Methodology and AnalysisWeights obtained using LI method
Aspect Slope Hillshade Class Value (respect to N) weight class Value (degree) weight class Description weight
1 (135 - 180) 0.116706 1 (0 - 5) -2.300307 1 highly sunny -1.259918
2 (180 - 225) -1.171285 2 (5 - 15) -0.323227 2 Mod sunny -1.185342
3 (90 - 135) 0.671444 3 (15- 25) 0.376225 3 sunny 0.398581
4 (225 - 270) -1.444847 4 (45 - 90) 0.405540 4 little shaded 1.068126
5 (45 - 90; 270 - 315) 0.400887 5 (35 - 45) 0.368229 5 shaded 0.965477
6 (315 - 45) 0.116706 6 (25 - 35) 0.608407 6Highly shaded
0.930462
Stream distance Geology class Description weight class Description weight
1 more than 150 m. -0.061381 1 Lake sediments -1.054485
2 100 - 150 m. 0.032283 2 Sandstone -2.037765
3 75 - 100 m. -0.316381 3 Alluvial fans 0.320249
4 50 - 75 m. -0.177457 4 slate -1.358030
5 25 - 50 m. 0.039331 5 Limestone + slate -0.426143
6 Near than 25 m. 0.217755 6 Limestone 1.003170
ResultEach 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 ]
Validity TestAbout 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.
Risk assessmentRisk 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.
ConclusionsGIS 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.