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

Physiography

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

Landslide distribution

S

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

Slope map

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

Aspect map

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

Hillshade map

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:

Geological map

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:

Distance to stream map

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 ]

Landslide susceptibility map

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.

Validity Test

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.

Settlement under risk

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.

Thank you