GIS based post earthquake landslide hazard zonation mapping of Lachung Basin, Sikkim

International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 1, January 2014)

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GIS Based Post Earthquake Landslide Hazard Zonation

Mapping of Lachung Basin, Sikkim R Anbalagan

1, Rohan Kumar

2, Sujata Parida

3, K Lakshmanan

4

1Professor,

2,3,4Research Scholar, Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee-247667

(Uttarakhand), India

Abstract— Lachung basin is part of Sikkim Himalaya,

which was struck by a major earthquake on 18th September

2011. Earthquake resulted in many landslide incidents, which

caused great panic in the area. A landslide hazard zonation

map is prepared to assist mitigation planners in wake of

landslide trigger. In the present study pre and post

earthquake remote sensing data has been used to prepare

landslide inventory. Remote sensing data is further used to

delineate drainage pattern, photo lineaments, structural

features, lithologial features, and land/use land/cover type of

the area by applying digital image processing techniques.

Geological features are analyzed using criteria such as colour,

tones, topography and stream drainage pattern from the

imageries. Digital elevation model data is used to generate

primary topographic attributes namely, slope, aspect, and

relative relief. For landslide hazard zonation (LHZ) different

thematic maps such as land-cover map, slope map, relative

relief map, structural map, lithology map, lineament buffer

map, drainage buffer map, soil map, are assigned relative

weight on ordinal scale to obtain landslide hazard index

(LHI). Threshold values are selected according to breaks in

LHI frequency and a LHZ map is prepared which contains

very low hazard, low hazard, moderate hazard, high hazard

and very high hazard zones. Study suggests that landslides in

present area are influenced by the proximity to drainage,

lineament and topographic attributes.

Keywords— DEM, Earthquake, Landslide, Remote

Sensing, LHZ.

I. INTRODUCTION

Landslide is the result of a wide variety of geo-

environmental processes which include geological,

meteorological and human factors. The main factors which

influence land slide are discussed by Varnes and

Hutchinson [1], [2]. Generally the most important inherent

factors are bedrock geology (lithology, structure, degree of

weathering), geomorphology (slope gradient, aspect, and

relative relief), soil (depth, structure, permeability, and

porosity), land use and land cover (LULC) and hydrologic

conditions.

Landslides are triggered by many extrinsic causative

factors such as rainfall, earthquake, blasting and drilling,

cloudburst and flashfloods. Himalayan region has highly

undulating terrain which is a witness of ongoing orogeny

process. The region comes under major seismic zone.

These combined geo-environmental factors cause

numerous occasions of landslides and subsequently major

loss of life and property. The Himalayan landslides are

sometimes highly inaccessible and this gives planners a

major setback. But geospatial technique provides capability

of reaching every part of the inaccessible area, identifying

all types of landslides and determining landslide prone

zone on the basis of major causative factors. Remote

sensing and GIS based landslide hazard zonation is

suggested by several authors, such as Mantovani et al.,

Nagarajan et al., Gupta et al., Saha et al., Van Westen et al.

[3], [4], [5], [6], [7]. Landslide hazard zonation techniques

have been applied in Himalayan region by several authors

such as causative factor based hazard assessment done by

Anbalagan [8], Landslide hazard zonation based on

geological attributes by Pachauri and Pant [9], GIS based

landslide hazard zonation by Gupta et al. [5] and Saha et al.

[6]. In the present study spectral character of satellite

multispectral data are used to determine geology, structure,

photo lineament and drainage which are the major

parameters for Landslide Hazard Zonation. Digital

elevation model (DEM) of the area is used for terrain

parameter extraction. High resolution remote sensing data

is used for large scale landslide hazard zonation map.

II. STUDY AREA

The Lachung basin is located in the upper north-eastern

reaches of Teesta river in Sikkim state of India. It has

central longitude/latitude value of 88.65°E and 27.61°N.

The basin has temperate climate in the lower reaches of the

valley, where as high mountainous region in the north is

characterized by low temperature tundra type of climate.

The basin receives an average monthly rainfall of 52mm

and also snowfall in the month of December, January and

occasionally in the month of March (Fig. 1).

http://toolserver.org/~geohack/geohack.php?pagename=Lachung&params=27.61667_N_88.65_E_type:city_region:IN-SK

http://toolserver.org/~geohack/geohack.php?pagename=Lachung&params=27.61667_N_88.65_E_type:city_region:IN-SK



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FIGURE 1: LOCATION MAP OF LACHUNG BASIN.

III. GEOLOGICAL SETTING

In the present study, geological setting is derived from

works of several authors like Ray, Acharya & Shastry,

Sinha-Roy, Neogi et al. and Catlos et al. [10], [11], [12],

[13], [14] (Fig. 2). Rock types of Lachung valley belongs to

the Chungthang Formation and Kanchenjunga gneiss of

Central Crystallines of Higher Himalaya. Chungthang

Formation comprises of quartz biotite schist, calc-silicate

rocks and graphite schists. The quartzites at places have

intrusions of amphibolites and pegmatite veins. These

rocks are seen in Chungthang area at the mouth of the

basin.

In the Lachung area the Kanchanjunga Group of rocks

comprising gneisses are exposed. These rocks are hard,

compact and well jointed and at places intruded by

tourmaline granites and pegmatites. The rock types are

represented mainly by high grade metamorphics of central

crystalline gneissic complex. The contact between the two

is reported to be thrusted [11], [10], [12] (Table I). Due to

complex folding gneissic and schistose bands are intricately

folded with meta-sedimentary units. In general, the rock

type trends in NW-SE to N-S direction dipping towards

northeast to east direction.



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The implications of tectonics and lithological attributes

have been considered in formulating concepts as regards to

landslides in Sikkim Himalayas.

IV. DATA USED

Topographic map of the survey of India of 1:50000

scale

Geological and Structural map representing lithology

and structure

Soil Map

Satellite sensor data of ASTER (VNIR Band - visible

and near-infrared), IRS LISS-IV and ASTER DEM

Field data involving GCP of landslide occasions.

To process these data ERDAS 9.2, ENVI 4.5 and Arc-

GIS 9.3 software are used.

FIGURE 2: REGIONAL GEOLOGICAL MAP OF SIKKIM HIMALAYA [11],

[10], [13].

TABLE I

STRATIGRAPHIC SUCCESSION PRESENT IN LACHUNG BASIN [10], [11]

Group Lithology

Recent Sediments Alluvial and fluvio-glacial deposits

consisting of boulders and pebbles

Gondwana Grit, pebbles, boulder beds and

carbonaceous shale with occasional coal

seam, pegmatite, quartzite

Daling Interbedded quartzite and chlorite sericite

phyllite/schist

Chungthang Interbedded quartzite and garnetiferous

quartz biotite schist, garnet-kynite-

sillimanite-biotite-quartz schist

Central Crystalline

Gneissic Complex

Banded gneiss with augen gneiss and

quartz-biotite gneiss

V. METHODOLOGY

Raw remote sensing multispectral data is processed in

ENVI 4.5 software, different bands are extracted and

georeferenced to UTM WGS 1984 Zone 45 projections.

VNIR band of the data is selected for the study. These data

are coregistered and subtracted according to the area of

study. Topo-normalization is performed on the basis of

digital elevation model. Normalized difference vegetation

index (NDVI) of the data is extracted and on the basis of

that 8 land/use land/cover classes are categorized. ASTER

DEM data is downloaded from the NASA website. Some

DEM enhancement techniques are performed such as DEM

fill, Sink removal etc. From the DEM data slope, aspect,

relative relief, hill shade and drainage maps are prepared.

Photo-lineaments are also extracted from DEM by using

Laplace Edge enhancement filter. These lineaments are

compared with lineaments prepared from IRS (Indian

Remote sensing Satellite) LISS-IV multispectral data by

onscreen digitization. Corrections are made in the

lineament. Ancillary data such as geological map, soil map,

etc are digitized and georeferenced in GIS environment.

Landslide inventory map is prepared on the basis of data

collected from field and satellite imageries. Each thematic

layers are assigned relative weight on ordinal scale to

obtain landslide hazard index. Landslide hazard index is

further used to generate landslide hazard zonation map

(Fig. 3).



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VI. DATA LAYERS

Following data layers are prepared for Landslide Hazard

Zonation

a) Land use/Land cover map

b) Slope map

c) Relative relief map

d) Drainage buffer map

e) Lineament buffer map

f) Soil map

g) Lithological Map

VII. DRAINAGE PATTERN

The river bed gradient from inception of the river to the

upstream of Lachung where the river takes a turn towards

south to south westerly direction is of very high order. The

fall in elevation being 2100m over a distance of 21km, the

gradient is 100m/km. On the other hand the river bed

gradient further downstream of Lachung is less as

compared to the upper portion. The fall in elevation up to

Chungthang is 1016m over a distance of 17km with a

gradient of 60m/km. Further downstream of Chungthang

the river bed gradient is conspicuously low falling around

30m/km or less. The general pattern of drainage is a

complicated aspect as the dominant pattern is not very

clear. In the higher reaches close to the ridge the first order

streams cluster to form second and third order ones

indicating a dendritic or tree type drainage pattern. Further

down the streams in the middle reach, where the slopes are

moderate to steep form third or fourth order drains, though

the fifth order is very rare. It is common to notice that the

streams joining the river on the right bank and in parts of

left bank takes deflection towards downstream before

joining the main river. These drainage networks have

compelling relation with the landslides. During the field,

study majority of landslides are found nearer to the

drainage area.

To make the proper assessment of landslides drainage

buffer map with buffer distance 50m, 100m, 150m, 200m

are prepared.

VIII. TOPOGRAPHIC ATTRIBUTES

From the DEM data it has been observed that the upper

portion of the Lachung basin is aligned in NW-SE

direction, while the lower portion is aligned in NE-SW

direction. The basin shows large variations in slope angles.

The areas just adjoining river bed are generally very gentle

(<10˚). The debris cones present in the vicinity of the river

bed have gentle slope angles (<20˚) which is also seen in

upper levels in certain patches. Similarly on the southeast

side and downstream of Lachung, gentle slopes can be seen

on high levels on left bank. These gentle slopes are often

intercalated with slopes of moderate angles (20˚-40˚). The

fairly steep (30˚-40˚) to steep slopes (40˚-50˚) are seen

profusely in the middle portions on both sides of the valley.

Particularly these slopes are conspicuously seen on the

right bank side. The very steep (50˚-60˚) to extremely steep

slopes (>60˚) are seen close to the top of the ridge. The

basin shows well distributed pattern of varying categories

of slope aspects. The left bank predominantly shows west

and south-westerly slopes in the upper portion of the basin

with less south and south easterly slopes. On the other hand

in the lower reaches, north and north-easterly slopes are

dominantly present with east west and south-westerly

slopes. On the right bank easterly and north-easterly slopes

are present in large numbers with less northerly slopes in

the upper portion of the basin, while in the lower reaches,

south and easterly slopes are dominantly present. In

general, the trends of slope aspects are perpendicular to the

flow direction of the river in different locations. Relative

relief is found to be varying between 0 to 320 meters.

Relative relief map is generated from the DEM data by

applying 3x3 grid matrix filter.



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FIGURE 3: METHODOLOGY FLOWCHART OF THEMATIC LAYER GENERATION

Topographic Map Digitized and subtract Multispectral image, DEM

Regional Geological Map

Base Map

Subtract

DEM Image

Geological Map Drainage Buffer Map Lineament Buffer Map

LULC Map

Slope Map Drainage Map Lineament Map

Relative relief Map

Buffering Buffering

Surface Analysis Drainage Analysis Edge Detection Focal Range

NDVI Supervised Classification



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IX. LINEAMENT PATTERN

The overall lineament pattern of Lachung basin shows a

nearly similar trend as that of drainage pattern. A cluster of

lineaments close to the ridge line coincides with the barren

rock exposures. In the middle reaches a series of nearly

parallel lineaments are seen. They are nearly perpendicular

to the river flow direction locally. The structure controls in

the stream flow direction is clearly substantiated by the

lineament map. Distance from these structural features

have relative influence on the landslide [5], accordingly

buffer map is prepared for landslide hazard zonation.

X. LAND USE LAND COVER

Image classification resulted into 8 land/use land/cover

classes such as dense vegetation, sparse vegetation, lake,

drainage, settlement, cloud-cover, fallow/barren land, and

snow cover. It is found that basin in general has a good

vegetation cover with thick vegetation covering an area of

about 98 sq km. It is mainly concentrated on the left bank

of the Lachung river in the lower reaches between

Chungthang and Lachung. On the right bank the thick

vegetation is seen adjoining to the river upto Lachung with

patches of sparse vegetation and barren land. A part of

middle and top slopes close to the ridge are generally

barren in nature due to snow cover. On the left bank the top

slopes close to the ridge are barren in the upper reaches of

the basin. Sparse vegetation is seen as patches and well

distributed within the basin.

XI. LANDSLIDE INVENTORY

Landslide inventory map is prepared from satellite

imageries and field investigations. Temporal ASTER and

IRS LISS-IV remote sensing data of pre and post

earthquake is used to map the landslides. Based on the size

they have been divided visually into large, medium and

small. These landslides are shallow in nature. Since the

depth of the slides is limited to few meters it is mainly

affecting the overlying debris materials and a small part of

the rocks below which seems to be intact. The resultant

debris can be seen lying on the slope below. A few medium

size slides are seen mainly in the middle portions of the

valley.

The small landslides are commonly seen in many places,

though they seem to be concentrated in the lower reaches

where the debris cone materials are present. Moreover,

debris materials are consistently present on either side of

the river. Hence wherever the river takes sharp turns locally

the toe erosion had resulted in a series of shallow landslides

by the side of the river on either bank. Landslide data is

used for the validation of landslide hazard zonation map

(Fig. 4).

XII. WEIGHT ANALYSIS

Weighted rating system is based on the relative

importance of various causative factors derived from field

knowledge [5]. Input data layers such as soil map,

lineament buffer map, slope map etc. are assigned

weightage (out of total 100%) factor according to their

corresponding impact on the landslide triggers. Different

classes of input layers are given rating on the scale of 1 to

10 where 1 stands for the class which has minimum impact

on landslide (Table II).

XIII. LANDSLIDE HAZARD INDEX

Landslide Hazard Index is prepared by assigning

influence/weight to factor and rating to different classes.

Weight factor of the input layer is multiplied by the

corresponding rating given to that particular class on pixel

basis. Finally summation of each layer is done.

LHI = Σ Weight/influence of factors× ratings of

classes/attributes

In present study LHI is found varying between the

ranges of 2 to 8 out of maximum 10.

XIV. LANDSLIDE HAZARD ZONATION

For landslide hazard zonation, threshold value of 2, 3, 5,

7 has been used from the frequency break in LHI. Using

reclassification operation a landslide hazard zonation map

is prepared which contain five zones such as, very low

hazard, low hazard, moderate hazard, high hazard, very

high hazard. Majority filter function of Arc GIS 9.3 is used

to make the map smooth (Fig. 5). The Pi chart indicates the

percent distribution of different landslide hazard zone

(Fig. 6).



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FIGURE 4: POST EARTHQUAKE LANDSLIDE INVENTORY MAP OF LACHUNG BASIN.



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TABLE II

SUMMERY OF ASSIGNED WEIGHT AND RATING

Thematic Raster Layer Weight (%) Field Rating

Soil Type 10 Loam/sand 5

Rock/ Loam 2

Loam/Rock 4

Permafrost 2

Sandy loam 6

Sandy/Clay loam 7

Sandy loam/Rock 5

Geology 20 Quartzite/Garnet schist 6

Permafrost 2

Migmatite/Biotite schist 5

Slope 15 Very Low 1

Low 3

Moderate 5

Moderately High 6

High 7

Very High 9

Land Cover 20 Water Body Restricted

Snow Cover 2

Dense vegetation 2

Sparse vegetation 5

Settlement 6

Fallow Land 8

Drainage Buffer 10 0 – 50m 9

50 – 100m 7



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100 – 150m 5

150 - 200m 3

>200m 1

Lineament Buffer 15 0 – 50m 9

50 – 100m 7

100 – 150m 5

150 - 200m 3

.>200m 1

Relative Relief 10 Very Low 2

Low 3

Moderate 5

High 7

Very high 9

XV. VALIDATION OF LANDSLIDE HAZARD ZONATION

CLASSES

Validation of landslide hazard map is performed on the

basis of collected field data and landslide incidents

observed from the IRS LISS IV data of 20th November

2011. Field study was performed during the month of

March 2012. Altogether 85 landslide incidents have been

delineated which are of varying size. Most of the slide are

small and found adjoining to the drainage. Landslide data is

overlaid on the landslide hazard zonation map.

Landslide percentage in each LHZ class (in percentage)

is compared (Fig. 7). Landslide is found in three classes

like low hazard, moderate hazard and high hazard zones.

Low hazard zone comprise 17.7% of the total area in which

6% of total landslide has been found. 74% area is

comprised by moderate hazard zone which contains 42% of

the total landslide observed. High hazard zone accounted

6% of the total area, in which 52% of the total observed

landslide are present. Very low hazard and very high

hazard zones accounted no landslide occasions.



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FIGURE 5: LANDSLIDE HAZARD ZONATION MAP OF LACHUNG BASIN.



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FIGURE 6: PI CHART SHOWING THE DISTRIBUTION OF LANDSLIDE

HAZARD ZONE CLASSES.

FIGURE 7: BAR CHART SHOWING THE LANDSLIDE OCCURRENCE IN

RELATION TO LANDSLIDE HAZARD ZONE CLASSES.

XVI. CONCLUSION

Present study suggests that the distribution of landslides

is influenced by a combination of factors such as proximity

to the lineament, presence of weathered metamorphic

rocks, barren or less-vegetated areas, as well as other

factors. It is observed that south aspect of slope faces are

more prone to get rainfall and henceforth supports thick

vegetation cover which makes them less vulnerable to mass

movements. Another phenomenon observed is that the

south aspect coincides with barren land. In this case due to

rainfall, barren land cover becomes more prone to

landslide. It is inferred that the presence of terrain

conditions such as slope and relative relief lead to landslide

susceptibility of the area. Local influence such as relative

relief, proximity to drainage and proximity to lineament are

very important for landslide trigger.

Thus the geospatial methodology for integration of

various topographic, geological, and structural, land

use/land cover and other datasets seems to be quite suitable

for determining terrain parameters and landslide hazard

zonation.

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Documents

GIS based post earthquake landslide hazard zonation mapping of Lachung Basin, Sikkim