International Journal of Basic & Applied Sciences IJBAS-IJENS Vol:17 No:05 7 Micro-Zonation of Landslide Hazards Between City and , , , Using Geoinformatics

Ch.Udaya Bhaskara Rao1 and Rahul Verma2 1Department of Geography and Resource Management, , Aizawl-796004, 2 Department of Geology, Pachhunga University College, Aizawl-796001, Mizoram. Corresponding Author: [email protected]

Abstract-- Mizoram has highly undulating terrain with steep wedge failure is the prime cause of this slide. Massive slopes and deep valleys in its topographical set-up. As the terrain “Laipuitlang Slide” is a great example of human induced is of rugged nature composed of several unconsolidated factor (Verma, 2014). Still the area is lacking proper sedimentary formations, it is prone to frequent slope failures comprehensive studies at micro-level to understand the main causing massive landslides thereby disruption to traffic, damage cause in order to reduce the risk of this particular hazard at to property and loss of lives occurred at many sections in and places. GIS based landslide susceptibility mapping by around Aizawl city. An attempt has been made in this study to identify the areas of slope failure causing high magnitude heuristic and bivariate methods is useful to identify the areas landslides between Aizawl city and Lengpui airport by numerical prone to landslides more precisely (Prabhin Kayastha et al., rating scheme of landslide hazard evaluation factors (LHEF) 2013). Spatial probabilistic modeling for generation of slope with the help of the advanced tools of ArcGIS software. Five failure probability hazard map using geographical information zones of landslide hazards such as very high, high, moderate, low systems is much useful to identify the areas of slope failure at and very low have been identified along this road section. large scale (Zhou et al., 2003). The present study is an attempt in this part to prepare a micro hazard zonation map at large INTRODUCTION scale as per Bureau of Indian Standard, (1998) based on About 25% of the total geographical area of India is multi-criteria evaluation of the significant landslide causative in mountainous terrain prone to landslides mostly triggered by factors using GIS techniques. earthquakes and rainfall (Manik Das et al., 2011). A majority Study Area of landslides that occur in India particularly in the Himalayan It is a 35 km long the road section between Aizawl region are natural and catastrophic. Sometimes reservoirs also city and Lengpui airport. Topographically, it is a highly induce landslides with high magnitude (Singh et al., 2012). undulating terrain from the Aizawl city to Lengpui airport. Mizoram is also one of such highly undulating mountainous The relative relief of the area along the road ranges between terrains in the northeast India with steep slopes mostly linear, 85 and 866 m. The maximum relief of 866 m is found towards narrow and deep valleys. As the terrain is fragile, it is Hunthar Veng in the city and gradually decreases to 85 m subjected to frequent slope failures and subsequent towards village, and again rises up to 409 m towards topographic changes (Udayabhaskararao, 2014) causing Lengpui airport (Figure1). massive destruction to property and sometimes led to loss of Geology and Structure lives as happened several times in the past. Verma (2013) has The area is composed of sedimentary rocks such as outlined the prime causes of landslide in Aizawl township, in sandstones, siltstones and shales in alternate successions the light of aggravating factors. The human intervention in the belonging to Surma Group of Tertiary period (Ganju, 1975) in form of deforestation along with inappropriate land use its geological set-up. Most of the area except a few kilometers practices is also one the major causes for the frequent towards Lengpui airport is dominated by sandstone– occurrence of landslides in this mountainous region. A few siltstone/shale intercalation and prominently jointed in sets. studies of the road sections along north Tawipui –Thingfal, The regional dip is west ward with some local variations. The Hnathial-Hrangchalk, Hrangchalkawn-Rotlang and Roltlang- beds dip from moderate gradients of about 27o up to steep Tuichang in district of Mizoram have been carried gradients of 56o. The joints are mostly high dipping varying out by Tiwari et al. (1996, 1998 & 2001) based on facet wise from more than 50o to almost sub vertical trends. A majority validation of landslide hazard evaluation factors (LHEF) of the joints are dip type (Figure 2). rating scheme for computation of total estimated hazards Climate (TEHD). Similarly, a few detailed site specific studies have The area receives an average annual rainfall of about been carried out by Tiwari et al. (1996) and Tiwari and Kumar 2500mm. Most of the precipitation is received during (1997) at South Hlimen and Bawngkawn landslides in Aizawl southwest monsoon period between the months of May and district, Mizoram and suggested remedial measures to September. Temperature ranges between 20oC and 32oC. The minimize the adverse effects of slope failure. Verma (2014) area experiences humid sub-tropical climate. The entire area has studied the ‘Ngaizel landslide’ and revealed that the is covered by tropical semi-ever green forest with a wide

174405-2323- IJBAS-IJENS @ October 2017 IJENS I J E N S International Journal of Basic & Applied Sciences IJBAS-IJENS Vol:17 No:05 8 variety of plant species.

Fig. 1. Location Map of the study area.

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Fig. 2. Lithology and Structures in the study area. MATERIALS AND METHODS geomorphic features and to map major land use/land cover Study area boundary, drainage network and pertinent units in the study area. Rainfall data for about 20 years (1997- topographic information have been obtained from the Survey 2017) from the two rain gauge stations located in Aizawl city of India topographical maps at 1:50,000 scale. Satellite and at Lengpui Airport has been collected to prepare rainfall imagery of IRS P6, LISS IV, MX at 5.8 x 5.8 m resolution of distribution map. Detailed field mapping has been carried out the year 2017 has been used to identify the prominent to map all litho-units and the structural features in and around

174405-2323- IJBAS-IJENS @ October 2017 IJENS I J E N S International Journal of Basic & Applied Sciences IJBAS-IJENS Vol:17 No:05 10 the area. Slope map has been prepared from digital elevation equal weightage along with the other factors considered for model of Cartosat-1 with 30 x 30 m pixel size (Resolution) validation. using the Spatial Analyst module tools of ArcGIS software. Relief and Slope Drainage density map has been prepared from the drainage Relief and slope are the most significant factors network of the area. ArcGIS software has been used to digitize which determine the degree and intensity of slope failure. As the thematic layers. The thematic layers have been edited to the area is of highly rugged nature, relief varies greatly even in remove common errors then cleaned and built for polygon a small area over a short distance. Relief in the area ranges topology for final data integration. The thematic layers have between 85 and 866 m (Figure 3). The maximum relief of been projected to polyconic coordinate systems then rasterized about 866 m is observed in the city towards Hunthar Veng for validation in order to generate landslide hazard zonation up to Rangvamual and gradually decreases to about 85 m map. Due weightages are assigned to each unit in the thematic towards Sairang village and again it rises up to about 409 m at layers as per Bureau of Indian Standards (1998). All the Lengpui village further north of the study area. thematic layers have been multiplied with the corresponding Similarly, the area exhibits a variety of slope classes ranging predetermined thematic weights for their integration with the from gentle to steep and very steep up to 90o. This layer has help of raster calculator in ArcGIS Spatial Analyst module to been classified into 5 major classes such as (i) less than 15o, generate a micro landslide hazard zonation map of the road (ii) 15o-30o, (iii) 30o-45 o, (iv) 45o- 60o and (v) more than 60 o section between Aizawl city and Lengpui airport. (Figure 3). Most of the area exhibits slope between 15o to 45o. Thematic Data Generation A few areas in the northern and southern parts particularly Seven thematic layers such as relative relief, slope, near Sairang and Lengpui villages are gently sloping. Some geotectonic features like faults and fractures, drainage density, plain land is also seen in these areas. The road section from lithology, rainfall distribution and land use/ land cover have Rangvamual to Sihhmui villages over a length of about 20 km been used for generation of the micro-hazard zonation map of exhibits steep to very steep slope ranging from 45o even up to the area. As drainage triggers landslides in this area due to 90o. Similarly, some parts bordering Aizawl city, north of sedimentary nature of the terrain, drainage density was given Hunthar and south of Lengpui are also steep to very steep.

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

174405-2323- IJBAS-IJENS @ October 2017 IJENS I J E N S International Journal of Basic & Applied Sciences IJBAS-IJENS Vol:17 No:05 11 Drainage Density geological set-up. The thickness of these units, vary at places Tlawng is the only main river along with its from a few centimeters to several meters (Table.1 and Plate 1). tributaries flowing towards north in the area. A majority of the Most of area along this road except the southern parts of 1st and 2nd order streams occupy higher elevations ranging Lengpui airport is dominated by sandstone–siltstone/shale from 600 to 800 meters. A few 3rd order streams are found intercalation which is prominently jointed in sets which shows particularly at lower elevations mostly flowing along the different patterns of lithology and structures. The thickness of structural valleys. The main course of Tlawng river is rock exposures at Hunthar Veng is 24 m which decreases up structurally controlled by active faults at several parts in the to 5 m at nearly 11 km from station 1 (Table 1). The area. The drainage density of the area has been divided into thickness of the exposure is about 93 m at Phunchawng (8.1 five major classes such as very low, low, moderate, high and km from station 1). At several places along this 45 km long very high based on the network of the channels (Figure 4). road section the rock exposures of about 60 to 100 m thick Faults and Fractures (Geotectonic features) are found. After the Phunchawng locality (12 km from Faults and fractures are considered to be one of the station 1), the thickness of exposures range from 5 m to a most significant geotectonic factors which have strong control maximun of 24 m (at 8.3 m from station 1),where massive on slope failure. The degree and extent of slope failure is sandstones with huge joints are exposed. The dominent mainly based on the presence of active faults and fractures. As lithology of sandstone, shale and siltstone intercalation all the area is tectonically active, quite a good number of faults along the road section shows varying dips with the minimum and fractures are seen in this part cutting across several rock of 27o is recorded at Shihmui (22.4 km) and the maximun of formations even at higher elevations. In addition, weak and 56o at Phunchawng localitiy (12 km from Station.1). The weathered bedding planes also play a vital role in slope failure strata at many locations is intersected by cross-cut high angle as seen at many parts along the road section. A majority of and sub vertical joints with joint angles varying from 57o to the streams which flow at higher elevations are controlled by 85o. Some joints with lower angle are found ranging between fractures as seen on the satellite image. The faults and 18o and 42o. A majority of the joints are dip type. Many parts fractures identified in the area are oriented in almost all of the road sections have mild to intense shears. The regional directions. In fact, the main course of the river Tlawng is dip is westward with some local variations (Figure 2). The guided by several active faults in this area. beds dip from moderate to quite steeper gradients (27 o - 56o). Lithology The joints are mostly high dipping varying from more than 50o The area is composed of sedimentary rocks of sandstones, and exhibit almost sub vertical trends. siltstones and shales in alternate successions in its regional

174405-2323- IJBAS-IJENS @ October 2017 IJENS I J E N S Table I International Journal Field of Data Basic Sheet & of Applied the Study SciencesSection (Hunthar IJBAS-Lengpui-IJENS Road). Vol:17 No:05 12

Source: Field Survey (2016-2017) Rainfall Land Use/ Land Cover The area receives an average annual rainfall of about Land use and land cover is also one of the 2500 mm. The area towards the Aizawl city receives more determining factors in landslide evaluation. Built-up areas than 2500 mm of rainfall and the area beyond Sihhmui and with settlements are most distressed by landslides as they are Sairang up to Lengpui airport receives less than 2500 mm compact. Most of the area is covered by dense forest except a of rainfall (Figure 5). As a whole, rainfall decreases towards few patches of degraded forest particularly at Lengpui the plain area where Lengpui airport is located. 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

174405-2323- IJBAS-IJENS @ October 2017 IJENS I J E N S International Journal of Basic & Applied Sciences IJBAS-IJENS Vol:17 No:05 13 exceeding more than 45o. Wet-rice cultivation is practiced whereas a small extent of 0.30km2 area of shifting cultivation only in medium extent of 1 km2 only in and around Sairang is found at Phunchawng village. Exposed barren rocky areas village mostly along the left bank of the river Tlawng 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.

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Fig. 6. Major Litho-units and Land use/land cover in the study area. Multi-Criteria Evaluation and Micro-Hazard Zonation distribution (Figure 7) were classified as per the values The different units in each of the seven layers such as obtained and assigned due weightages to all landslide hazard relief, slope, drainage density, lithology, land use/land cover, evaluation factors (LHEF) according to the estimated geotectonic features like faults and fractures and rainfall priority in the hazard zonation (Table.2).

174405-2323- IJBAS-IJENS @ October 2017 IJENS I J E N S International Journal of Basic & Applied Sciences IJBAS-IJENS Vol:17 No:05 15 Table II Weightages of Landslide Hazard Factors.

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

The thematic layers, thus generated have been Rangvamual and Phunchawng falls under ‘very high to rasterized for validation using raster calculator. All the raster moderate hazard zone’. layers have been reclassified and assigned thematic weights The severity in this section reflects the adverse as fixed with the help of 3D analyst module to generate final impact of dense urbanization on the waning slopes due to landslide hazard zonation map. The thematic layers have been improper sewerage and practically uncontrolled and multiplied with the corresponding predetermined thematic unmonitored constructions. Similarly, the section between weights for their integration as shown here. Phunchawng to Sairang is relatively less hazardous which ([Relief*0.15] + [Slope*0.20] + [Geotectonic features*0.10] reflects the reduced load of urbanization as this part has less + [Drainage density*0.15] + [Lithology*0.15] + [Land use density of human settlements. The remaining part of the road *0.15] = [Rainfall*0.10]) section of Sairang-Sihhmui-Lengpui is relatively safer as the Based on the multi-criteria analyses of various zone is falling in ‘very low-low-moderate hazard’. However, causative factors, the micro-landslide hazard zonation map of the section around locally known as ‘elephant rock’ (Plate 2) the area has been prepared. The map shows five distinct is a very high hazard zone due to presence of huge jointed classes of intensity of landslide hazards such as very high, blocks of massive sandstones with the overlying shales. As a high, moderate, low and very low along the study section whole there are 9 prominent landslide hazard zones of various (Figure 7). The road section from Hunthar Veng to intensities have been identified along the study section (Plate 3).

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CONCLUSION susceptibility mapping procedures in Kulekhani water shed, Nepal. The study is first of its kind to generate large scale Journal of Geological Society of India, 8, pp 219-231. [6] Singh, Y., Bhat, G.M., Vinay Sharma, Pandita, S.K and Thakur, micro-hazard zonation map of the road section between K.K. (2012), Reservoir induced landslide at Assar, Jammu and Aizawl city and Lengpui airport. The map shows five distinct Kashmir: A Case Study. Journal of Geological Society of India, classless of landslide hazard zones. The road section from 80, pp 435-439. Hunthar Veng to Rangvamual and Phunchawng falls under [7] Tiwari, R.P., Sharma, B.L. and Singh, B. (1996), Geotechnical appraisal of Bawngkawn landslide, Aizawl, Mizoram, Proceedings very high-high-moderate hazard zones mostly due to dense of International Conference on Disaster Mitigation, Madras urbanization on the waning slopes as there is no proper 1(A):A4, pp 125-131. sewerage and no monitor of heavily loaded constructions. The [8] Tiwari, R.P., Lanuntluanga,F., Kachhara, R.P. and Singh, road section between Phunchawng to Sairang is relatively less B.(1996), Landslide hazard zonation along Hrangchalkawn- Roltlang road section, Lunglei, Mizoram, Journal of Engineering hazardous as there is relatively less urbanization. Similarly, Geology, XXV(1-4), pp 257-269. the road section of Sairang-Sihhmui-Lengpui is relatively [9] Tiwari, R.P. and Kumar, S. (1997), South Hlimen landslide in safer as the zone is falling in ‘very low-low-moderate hazard’ Mizoram-A pointer, Envis Bulletin Himalayan Ecology & due to less topographic elevation. The area needs proper Development, 5(2), pp 12-13. [10] Tiwari, R.P., Lannuntluanga, F. and Kachhara, R.P. (1998), monitoring for construction of heavily loaded structures over Landslide hazard zonation- A case study along Hnathial- precipitous slopes to mitigate the intensity of landslides Hrangchalkawn road section, Proceedings of International thereby to reduce the risk of damage. Conference on Disaster Management, Tejpur, pp 461-478. [11] Tiwari, R.P., Lannuntluanga,F. and Kachhara, R.P (2001), Landslide hazard zonation along north Tawipui-Thingfal road ACKNOWLEDGEMENTS section, , Mizoram, Pre-Seminar volume of The authors are thankful to Department of Science National Seminar on Geotechnical & Geological Hazards in the and Technology, Govt. of India, New Delhi for providing Indian Context. Jour. Geological Survey of India, Shillong, pp financial assistance by granting a major research project to 231-226. [12] Udayabhaskararao, Ch. (2014), Topographic changes in Aizawl conduct the present study. The second author is thankful to the city and its surroundings during 1973-2013: A digital terrain Principal, Pachhunga University College, Aizawl, for analysis through remote sensing and GIS techniques. Geographic, providing necessary facilities to carry out this work. 9, pp 19-26. [13] Verma, R. (2013). Landslide hazard in Aizawl Township, Mizoram" in Edited Vol. Landslides and Environmental REFERENCES Degradation in Hilly Terrains. Editor. R.A.Singh, ISBN. No. [1] Acho-Chi. (1998), Human interference and environmental 81085097-90-9 Gyanodaya Publication, Nanital, Uttarakhand, pp instability: addressing the environmental consequences of rapid 11-21. urban growth in Bamenda, Cameroon. Environment and [14] Verma, R. (2014). Ngaizel Landslide, Aizawl, Mizoram, India: A Urbanization, 10 (2), pp 161-174. Case of Wedge Failure; Asian Academic Research Journal, Vol.1, [2] Bureau of Indian Standard (1998), Indian standard: preparation of Issue.22, June 2014, ISSN.2319-2801, pp. 422-429. landslide hazard zonation maps in mountainous terrain; Guidelines [15] Verma, R. (2014). Landslide Hazard in Mizoram: Case Study of Part.2: Micro Zonation, 17 p. Laipuitlang Landslide, Aizawl. International Journal of Science [3] Ganju, J.L. (1975), Evolution of orogenic belts of India. and Research (IJSR), ISSN (Online): 2319-7064, Impact Factor Geological Mineralogical Meteorological Society of India, 4, pp (2012): 3.358; June 2014. 17-26. [16] Zhou, G., Esaki, T., Mithani., Y., Xie, M. and Mori, J. (2003), [4] Manik Das, A., Sankar Kumar, N. and Soumay Kanti, M. (2011), Spatial probabilistic modeling of slope failure using an integrated Landslide hazard and risk analysis in India at a regional scale. GIS Monte Carlo simulation approach. Engineering Geology, 68, Disaster Advances, 4 (2), pp 26-39. pp 373-386. [5] Prabhin Kayastha, Megh Raj Dhital, and Flormond De Smedt. (2013), Evaluation and comparison of GIS based landslide

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PLATE-1

Sandstone–shale intercalations at bottom and massive Sub-vertical joints within the 6 metres thick sandstone at top within the 11 metres thick sandstone sandstone at 12.3 km from Aizawl city. unit at about 24.2 km from Aizawl city

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.

174405-2323- IJBAS-IJENS @ October 2017 IJENS I J E N S International Journal of Basic & Applied Sciences IJBAS-IJENS Vol:17 No:05 19 PLATE-3

The prominent Landslides between Aizawl city and Lengpui Airport.

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