Micro-Zonation of Landslide Hazards Between Aizawl City and …ijens.org/Vol_17_I_05/174405-2323-IJBAS-IJENS.pdf · 2017-11-12 · imagery of IRS P6, LISS IV, MX at 5.8 x 5.8 m resolution

International Journal of Basic & Applied Sciences IJBAS-IJENS Vol:17 No:05 7

174405-2323- IJBAS-IJENS @ October 2017 IJENS I J E N S

Micro-Zonation of Landslide Hazards Between

Aizawl City and Lengpui Airport, Mizoram, India,

Using Geoinformatics Ch.Udaya Bhaskara Rao1 and Rahul Verma2

1Department of Geography and Resource Management, Mizoram University, Aizawl-796004, 2 Department of Geology, Pachhunga University College, Aizawl-796001, Mizoram.

Corresponding Author: [email protected]

Abstract-- Mizoram has highly undulating terrain with steep

slopes and deep valleys in its topographical set-up. As the terrain

is of rugged nature composed of several unconsolidated

sedimentary formations, it is prone to frequent slope failures

causing massive landslides thereby disruption to traffic, damage

to property and loss of lives occurred at many sections in and

around Aizawl city. An attempt has been made in this study to

identify the areas of slope failure causing high magnitude

landslides between Aizawl city and Lengpui airport by numerical

rating scheme of landslide hazard evaluation factors (LHEF)

with the help of the advanced tools of ArcGIS software. Five

zones of landslide hazards such as very high, high, moderate, low

and very low have been identified along this road section.

INTRODUCTION

About 25% of the total geographical area of India is

in mountainous terrain prone to landslides mostly triggered by

earthquakes and rainfall (Manik Das et al., 2011). A majority

of landslides that occur in India particularly in the Himalayan

region are natural and catastrophic. Sometimes reservoirs also

induce landslides with high magnitude (Singh et al., 2012).

Mizoram is also one of such highly undulating mountainous

terrains in the northeast India with steep slopes mostly linear,

narrow and deep valleys. As the terrain is fragile, it is

subjected to frequent slope failures and subsequent

topographic changes (Udayabhaskararao, 2014) causing

massive destruction to property and sometimes led to loss of

lives as happened several times in the past. Verma (2013) has

outlined the prime causes of landslide in Aizawl township, in

the light of aggravating factors. The human intervention in the

form of deforestation along with inappropriate land use

practices is also one the major causes for the frequent

occurrence of landslides in this mountainous region. A few

studies of the road sections along north Tawipui –Thingfal,

Hnathial-Hrangchalk, Hrangchalkawn-Rotlang and Roltlang-

Tuichang in Lunglei district of Mizoram have been carried

out by Tiwari et al. (1996, 1998 & 2001) based on facet wise

validation of landslide hazard evaluation factors (LHEF)

rating scheme for computation of total estimated hazards

(TEHD). Similarly, a few detailed site specific studies have

been carried out by Tiwari et al. (1996) and Tiwari and Kumar

(1997) at South Hlimen and Bawngkawn landslides in Aizawl

district, Mizoram and suggested remedial measures to

minimize the adverse effects of slope failure. Verma (2014)

has studied the ‘Ngaizel landslide’ and revealed that the

wedge failure is the prime cause of this slide. Massive

“Laipuitlang Slide” is a great example of human induced

factor (Verma, 2014). Still the area is lacking proper

comprehensive studies at micro-level to understand the main

cause in order to reduce the risk of this particular hazard at

places. GIS based landslide susceptibility mapping by

heuristic and bivariate methods is useful to identify the areas

prone to landslides more precisely (Prabhin Kayastha et al.,

2013). Spatial probabilistic modeling for generation of slope

failure probability hazard map using geographical information

systems is much useful to identify the areas of slope failure at

large scale (Zhou et al., 2003). The present study is an attempt

in this part to prepare a micro hazard zonation map at large

scale as per Bureau of Indian Standard, (1998) based on

multi-criteria evaluation of the significant landslide causative

factors using GIS techniques.

Study Area

It is a 35 km long the road section between Aizawl

city and Lengpui airport. Topographically, it is a highly

undulating terrain from the Aizawl city to Lengpui airport.

The relative relief of the area along the road ranges between

85 and 866 m. The maximum relief of 866 m is found towards

Hunthar Veng in the city and gradually decreases to 85 m

towards Sairang village, and again rises up to 409 m towards

Lengpui airport (Figure1).

Geology and Structure

The area is composed of sedimentary rocks such as

sandstones, siltstones and shales in alternate successions

belonging to Surma Group of Tertiary period (Ganju, 1975) in

its geological set-up. Most of the area except a few kilometers

towards Lengpui airport is dominated by sandstone–

siltstone/shale intercalation and prominently jointed in sets.

The regional dip is west ward with some local variations. The

beds dip from moderate gradients of about 27o up to steep

gradients of 56o. The joints are mostly high dipping varying

from more than 50o to almost sub vertical trends. A majority

of the joints are dip type (Figure 2).

Climate

The area receives an average annual rainfall of about

2500mm. Most of the precipitation is received during

southwest monsoon period between the months of May and

September. Temperature ranges between 20oC and 32oC. The

area experiences humid sub-tropical climate. The entire area

is covered by tropical semi-ever green forest with a wide



variety of plant species.

Fig. 1. Location Map of the study area.



Fig. 2. Lithology and Structures in the study area.

MATERIALS AND METHODS

Study area boundary, drainage network and pertinent

topographic information have been obtained from the Survey

of India topographical maps at 1:50,000 scale. Satellite

imagery of IRS P6, LISS IV, MX at 5.8 x 5.8 m resolution of

the year 2017 has been used to identify the prominent

geomorphic features and to map major land use/land cover

units in the study area. Rainfall data for about 20 years (1997-

2017) from the two rain gauge stations located in Aizawl city

and at Lengpui Airport has been collected to prepare rainfall

distribution map. Detailed field mapping has been carried out

to map all litho-units and the structural features in and around



the area. Slope map has been prepared from digital elevation

model of Cartosat-1 with 30 x 30 m pixel size (Resolution)

using the Spatial Analyst module tools of ArcGIS software.

Drainage density map has been prepared from the drainage

network of the area. ArcGIS software has been used to digitize

the thematic layers. The thematic layers have been edited to

remove common errors then cleaned and built for polygon

topology for final data integration. The thematic layers have

been projected to polyconic coordinate systems then rasterized

for validation in order to generate landslide hazard zonation

map. Due weightages are assigned to each unit in the thematic

layers as per Bureau of Indian Standards (1998). All the

thematic layers have been multiplied with the corresponding

predetermined thematic weights for their integration with the

help of raster calculator in ArcGIS Spatial Analyst module to

generate a micro landslide hazard zonation map of the road

section between Aizawl city and Lengpui airport.

Thematic Data Generation

Seven thematic layers such as relative relief, slope,

geotectonic features like faults and fractures, drainage density,

lithology, rainfall distribution and land use/ land cover have

been used for generation of the micro-hazard zonation map of

the area. As drainage triggers landslides in this area due to

sedimentary nature of the terrain, drainage density was given

equal weightage along with the other factors considered for

validation.

Relief and Slope

Relief and slope are the most significant factors

which determine the degree and intensity of slope failure. As

the area is of highly rugged nature, relief varies greatly even in

a small area over a short distance. Relief in the area ranges

between 85 and 866 m (Figure 3). The maximum relief of

about 866 m is observed in the city towards Hunthar Veng

up to Rangvamual and gradually decreases to about 85 m

towards Sairang village and again it rises up to about 409 m at

Lengpui village further north of the study area.

Similarly, the area exhibits a variety of slope classes ranging

from gentle to steep and very steep up to 90o. This layer has

been classified into 5 major classes such as (i) less than 15o,

(ii) 15o-30o, (iii) 30o-45 o, (iv) 45o- 60o and (v) more than 60 o

(Figure 3). Most of the area exhibits slope between 15o to 45o.

A few areas in the northern and southern parts particularly

near Sairang and Lengpui villages are gently sloping. Some

plain land is also seen in these areas. The road section from

Rangvamual to Sihhmui villages over a length of about 20 km

exhibits steep to very steep slope ranging from 45o even up to

90o. Similarly, some parts bordering Aizawl city, north of

Hunthar and south of Lengpui are also steep to very steep.

Fig. 3. Topgraphic Relief and Slope in the study area.



Drainage Density

Tlawng is the only main river along with its

tributaries flowing towards north in the area. A majority of the

1st and 2nd order streams occupy higher elevations ranging

from 600 to 800 meters. A few 3rd order streams are found

particularly at lower elevations mostly flowing along the

structural valleys. The main course of Tlawng river is

structurally controlled by active faults at several parts in the

area. The drainage density of the area has been divided into

five major classes such as very low, low, moderate, high and

very high based on the network of the channels (Figure 4).

Faults and Fractures (Geotectonic features)

Faults and fractures are considered to be one of the

most significant geotectonic factors which have strong control

on slope failure. The degree and extent of slope failure is

mainly based on the presence of active faults and fractures. As

the area is tectonically active, quite a good number of faults

and fractures are seen in this part cutting across several rock

formations even at higher elevations. In addition, weak and

weathered bedding planes also play a vital role in slope failure

as seen at many parts along the road section. A majority of

the streams which flow at higher elevations are controlled by

fractures as seen on the satellite image. The faults and

fractures identified in the area are oriented in almost all

directions. In fact, the main course of the river Tlawng is

guided by several active faults in this area.

Lithology

The area is composed of sedimentary rocks of sandstones,

siltstones and shales in alternate successions in its regional

geological set-up. The thickness of these units, vary at places

from a few centimeters to several meters (Table.1 and Plate 1).

Most of area along this road except the southern parts of

Lengpui airport is dominated by sandstone–siltstone/shale

intercalation which is prominently jointed in sets which shows

different patterns of lithology and structures. The thickness of

rock exposures at Hunthar Veng is 24 m which decreases up

to 5 m at nearly 11 km from station 1 (Table 1). The

thickness of the exposure is about 93 m at Phunchawng (8.1

km from station 1). At several places along this 45 km long

road section the rock exposures of about 60 to 100 m thick

are found. After the Phunchawng locality (12 km from

station 1), the thickness of exposures range from 5 m to a

maximun of 24 m (at 8.3 m from station 1),where massive

sandstones with huge joints are exposed. The dominent

lithology of sandstone, shale and siltstone intercalation all

along the road section shows varying dips with the minimum

of 27o is recorded at Shihmui (22.4 km) and the maximun of

56o at Phunchawng localitiy (12 km from Station.1). The

strata at many locations is intersected by cross-cut high angle

and sub vertical joints with joint angles varying from 57o to

85o. Some joints with lower angle are found ranging between

18o and 42o. A majority of the joints are dip type. Many parts

of the road sections have mild to intense shears. The regional

dip is westward with some local variations (Figure 2). The

beds dip from moderate to quite steeper gradients (27 o - 56o).

The joints are mostly high dipping varying from more than 50o

and exhibit almost sub vertical trends.



Source: Field Survey (2016-2017)

Rainfall

The area receives an average annual rainfall of about

2500 mm. The area towards the Aizawl city receives more

than 2500 mm of rainfall and the area beyond Sihhmui and

Sairang up to Lengpui airport receives less than 2500 mm

of rainfall (Figure 5). As a whole, rainfall decreases towards

the plain area where Lengpui airport is located.

Land Use/ Land Cover

Land use and land cover is also one of the

determining factors in landslide evaluation. Built-up areas

with settlements are most distressed by landslides as they are

compact. Most of the area is covered by dense forest except a

few patches of degraded forest particularly at Lengpui

airport. Settlements are located along the road in a linear

form except the major settlements like Aizawl city and

Lengpui airport which are compact (Figure 6). Except

Lengpui all other settlements are located over steep slopes

Table I Field Data Sheet of the Study Section (Hunthar-Lengpui Road).



exceeding more than 45o. Wet-rice cultivation is practiced

only in medium extent of 1 km2 only in and around Sairang

village mostly along the left bank of the river Tlawng

whereas a small extent of 0.30km2 area of shifting cultivation

is found at Phunchawng village. Exposed barren rocky areas

are seen all along the entire 45 km long road section.

Fig. 4. Drainage density and Geotectonic features in the study area.

Fig. 5. Rainfall Distribution in the study area.



Fig. 6. Major Litho-units and Land use/land cover in the study area.

Multi-Criteria Evaluation and Micro-Hazard Zonation

The different units in each of the seven layers such as

relief, slope, drainage density, lithology, land use/land cover,

geotectonic features like faults and fractures and rainfall

distribution (Figure 7) were classified as per the values

obtained and assigned due weightages to all landslide hazard

evaluation factors (LHEF) according to the estimated

priority in the hazard zonation (Table.2).



Table II

Weightages of Landslide Hazard Factors.



Fig. 7. Micro Landslide Hazard Zonation Map of the study area.

The thematic layers, thus generated have been

rasterized for validation using raster calculator. All the raster

layers have been reclassified and assigned thematic weights

as fixed with the help of 3D analyst module to generate final

landslide hazard zonation map. The thematic layers have been

multiplied with the corresponding predetermined thematic

weights for their integration as shown here.

([Relief*0.15] + [Slope*0.20] + [Geotectonic features*0.10]

+ [Drainage density*0.15] + [Lithology*0.15] + [Land use

*0.15] = [Rainfall*0.10])

Based on the multi-criteria analyses of various

causative factors, the micro-landslide hazard zonation map of

the area has been prepared. The map shows five distinct

classes of intensity of landslide hazards such as very high,

high, moderate, low and very low along the study section

(Figure 7). The road section from Hunthar Veng to

Rangvamual and Phunchawng falls under ‘very high to

moderate hazard zone’.

The severity in this section reflects the adverse

impact of dense urbanization on the waning slopes due to

improper sewerage and practically uncontrolled and

unmonitored constructions. Similarly, the section between

Phunchawng to Sairang is relatively less hazardous which

reflects the reduced load of urbanization as this part has less

density of human settlements. The remaining part of the road

section of Sairang-Sihhmui-Lengpui is relatively safer as the

zone is falling in ‘very low-low-moderate hazard’. However,

the section around locally known as ‘elephant rock’ (Plate 2)

is a very high hazard zone due to presence of huge jointed

blocks of massive sandstones with the overlying shales. As a

whole there are 9 prominent landslide hazard zones of various

intensities have been identified along the study section

(Plate 3).



CONCLUSION

The study is first of its kind to generate large scale

micro-hazard zonation map of the road section between

Aizawl city and Lengpui airport. The map shows five distinct

classless of landslide hazard zones. The road section from

Hunthar Veng to Rangvamual and Phunchawng falls under

very high-high-moderate hazard zones mostly due to dense

urbanization on the waning slopes as there is no proper

sewerage and no monitor of heavily loaded constructions. The

road section between Phunchawng to Sairang is relatively less

hazardous as there is relatively less urbanization. Similarly,

the road section of Sairang-Sihhmui-Lengpui is relatively

safer as the zone is falling in ‘very low-low-moderate hazard’

due to less topographic elevation. The area needs proper

monitoring for construction of heavily loaded structures over

precipitous slopes to mitigate the intensity of landslides

thereby to reduce the risk of damage.

ACKNOWLEDGEMENTS

The authors are thankful to Department of Science

and Technology, Govt. of India, New Delhi for providing

financial assistance by granting a major research project to

conduct the present study. The second author is thankful to the

Principal, Pachhunga University College, Aizawl, for

providing necessary facilities to carry out this work.

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PLATE-1

PLATE-2

About 11 metres thick huge jointed blocks of massive sandstone with overlying shales around locally called

‘elephant rock’ at about 24 km from Aziawl city.

Sandstone–shale intercalations at bottom and massive

sandstone at top within the 11 metres thick sandstone

unit at about 24.2 km from Aizawl city

Sub-vertical joints within the 6 metres thick

sandstone at 12.3 km from Aizawl city.



PLATE-3

The prominent Landslides between Aizawl city and Lengpui Airport.

Documents

Micro-Zonation of Landslide Hazards Between Aizawl City and …ijens.org/Vol_17_I_05/174405-2323-IJBAS-IJENS.pdf · 2017-11-12 · imagery of IRS P6, LISS IV, MX at 5.8 x 5.8 m resolution