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Application of GIS on Landslide Susceptibility and risk mappingPradeep Paudyal[2009422004]Hydrogeology Lab.Department of Geology Kyungpook National UniversityLandslideA 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

CHINAINDIANEPAL

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 distributionS

Susceptibility parameter mapsSlope map

Aspect map

Hillshade map

Geological map

Distance to stream mapSlope mapSlope map comprises 6 classes of slopes measured in degree gradient

Areal distribution of slope map shows:

Slope (degree)Area (%)0 529.45 1517.915 2513.025 3519.035 4513.9More than 456.8Slope 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 classAspectNew class0 456180 225245 905225 270490 1353270 3155135 - 1801315 3606Aspect 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 AnalysisLandslide 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, andNpix (Ni) = total number of pixels in a certain parameter class.Methodology and AnalysisWeights obtained using LI method

AspectSlopeHillshadeClassValue (respect to N)weightclassValue (degree)weightclassDescriptionweight1(135 - 180)0.116706 1(0 - 5)-2.3003071highly sunny-1.2599182(180 - 225)-1.171285 2(5 - 15)-0.3232272Mod sunny-1.1853423(90 - 135)0.671444 3(15- 25)0.3762253sunny0.3985814(225 - 270)-1.444847 4(45 - 90)0.4055404little shaded1.0681265(45 - 90; 270 - 315)0.400887 5(35 - 45)0.3682295shaded0.9654776(315 - 45)0.116706 6(25 - 35)0.6084076Highly shaded0.930462Stream distanceGeologyclassDescriptionweightclassDescriptionweight1more than 150 m.-0.061381 1Lake sediments-1.0544852100 - 150 m.0.032283 2Sandstone-2.037765375 - 100 m.-0.316381 3Alluvial fans0.320249450 - 75 m.-0.177457 4slate-1.358030525 - 50 m.0.039331 5Limestone + slate-0.4261436Near than 25 m.0.217755 6Limestone1.003170ResultEach 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 susceptibilityThis categorization is in a subjective wayWeight= [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