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Research Article Volume 6 Issue No. 7 Landslide Hazard Zonation (LHZ) Of Saiha District, , Using Remote Sensing and GIS Lalrokima Chenkual1, Lalbiakmawia, F2 Laltanpuia, Z D3 Disaster Management Centre, Administrative Training Institute, , Mizoram, India1 Public Health Engineering, Aizawl, Mizoram, India2 Directorate of Science & Technology Aizawl, Mizoram, India3

Abstract: Saiha district, Mizoram is prone to natural hazards like landslide, earthquake, etc. Landslide is one of the natural disasters, which involves sliding of mass of earth or rock down the slope along a definite zone or surface. Landslide Hazard Zonation may be defined as a technique of classifying an area into zones of relative degrees of potential hazards by ranking various causative factors operative in a given area based on their influence in initiation of landslides. Landslide Hazard Zonation map is prepared based on the integration of data acquired from various geo-environmental thematic databases. Combining various controlling parameters by giving different weightage value for all the themes, the final map is derived in a GIS environment on 1:50,000 scale. The area and the map is then classified into Very high, High, Moderate, Low and Very low hazard zones. Very High Hazard Zone constitutes an area of 138.44sq. km and forms 9.89% of the total district area and High Hazard Zone occupies 340.85sq. km which is 24.35% of the total district area while Moderate Hazard Zone constitute an area of about about 598.07sq. km and occupies 42.72% of the total district area; Low Hazard Zone extends over an area of about 279.47sq. km and forms 19.96% of the total district and Very Low Hazard Zone covers an area of about 31.1sq km and forms 2.22% of the total district area

Keywords: Landslide, Hazard Zonation, Geo-environmental Parameter, Geological features, Thematic layers

Introduction: Landslide Hazard Zonation may be Saiha District is located to the south- defined as a technique of classifying an area into zones of eastern part of Mizoram between 22o38E 01.19o and 21o56E relative degrees of potential hazards by ranking various 22.20o N Latitudes and 92o49E 21.37o and 93o12E 10.550 causative factors operative in a given area based on their Longitudes. It is bounded to the north & north west by influence in initiation of landslides. Thus, the LHZ of an district (62 kms) and west by district (73 area aims at delineating the landslide potential zones and kms) and on the south and east by Myanmar (159 kms long). ranking them in order of the degree of hazard from The District is surrounded by the river Kolodyne landslides. LHZ maps are very helpful for planners, (Chhimtuipui or Beina) on the three sides- east, north and engineers, etc, in identifying and delineating unstable west. The total geographical area of Saiha district is 1399.00 hazard-prone areas, selecting viable sites for carrying out sq. km. Saiha district falls in the Survey of India Topo sheet developmental schemes and evolving database for the risk Nos. 84 B/14, 84 B/15, 84 B/16, 84 C/13, 84 F/2, 84 F/3, 84 analysis of landslides in the area. F/4 and 84 G/1. The study area i.e., Saiha district is Saiha district is prone to various natural characterized by the presence of several lineaments, both hazards like landslide, earthquake, wind & cyclone and major and minor faults oriented in different directions, and cloudburst. Various geological and geophysical settings, steep slopes. The lithology is mainly represented by soft climatic, meteorological and hydrological condition of the sedimentary rocks, such as shale, silty shale, sandstone and area induces the occurrence of these natural hazards. their admixture in varying proportions. Besides, loose and Anthropogenic processes such as developmental activities unconsolidated sediments form a dominant composition on i.e, construction of buildings, roads and other infrastructures the exposed surface, particularly in built-up areas. This, can influence the natural forces to manifest as hazards. together with the aforesaid factors makes it susceptible to Landslide is one of the natural landslides. Therefore, overcoming the problem of this geo- disasters, which involves sliding of mass of earth or rock hazard is essential for the safety of life and property and down the slope along a definite zone or surface. Landslides hence hazard zonation is necessary for the district. attain specific significance because of their widespread occurrence resulting in great loss to public due to both direct 1.2 Methodology and Data used and indirect consequences. Their occurrence becomes more Landslide Hazard Zonation map is vexatious because of its unpredictability in both time and prepared based on the integration of data acquired from space. Hence, due attention should be given in combating various geo-environmental thematic databases. Of the this natural hazard. Preparation of Landslide Hazard several methods, Qualitative method is found suitable and Zonation (LHZ) map is one of the first steps in this direction. has been employed for carrying out LHZ mapping. A

International Journal of Engineering Science and Computing, July 2016 8724 http://ijesc.org/ qualitative approach essentially depends on expert opinion in use/land cover were first mapped from satellite imagery and dividing an area into different zones of varying landslide other ancillary data using visual interpretation techniques. susceptibility. The methodology involves several steps Geological features like faults, lithology and lineaments which includes detailed geological survey of the area from were extracted from satellite imagery using basic principles satellite imagery, SOI topographic maps and also from the of image interpretation involving color, tone, texture, ground. It is well known that the occurrence of landslide is pattern, shape, size and association. The different thematic mainly governed by the geo-environmental factors of the layers are then subsequently integrated using Arc Info GIS terrain. As such, these geo-environmental parameters, viz., Software. The table indicating the weightage value (on the lithology, geological structures like lineaments and faults, scale of 1-10) of parameters for landslide is shown in Table soil type, drainage density, geomorphology, slope and land No 1.1

Table No 1.1 : Ratings for parameters and categories

Parameter Category Weight

Sandstone 4 Siltstone & Shale 8 Lithology Shale & Siltstone 9 Crumpled Shale 10

Heavy Vegetation 3 Light Vegetation 5

Land Use / Land Cover Scrubland 6 Barren land 7

Built-up 8 0 - 15 1

15-25 3 25-30 4

Slope Morphometry 30-35 5 (in degrees) 35-40 6

40-45 7 45-60 8

> 60 5 Structure Length of Buffer distance on either 8 (Faults and Lineaments) side High Structural Hill 4

Medium Structural Hill 3 Geomorphology Low Structural Hill 2

Valley Fill 0

Each individual thematic layer is carefully location of both old and active landslides, dip amount and analysed so as to establish its relation to landslide dip direction of the rock beds are also considered. susceptibility. For example, in lithology layer, the crumpled Combining all the above controlling parameters by giving shale unit offers more chance of slope failure than the hard different weightage value for all the themes, the final map is and compact sandstone unit. Similarly, areas located within derived in a GIS environment on 1:50,000 scale. The map is the vicinity of fault zones and other geological structures are then classified into Very high, High, Moderate, Low and more vulnerable to landslides and other mass movements. Very low hazard zones. The area statistics of the landslide For this, areas of 100 m on both sides of all the lineaments hazard zones of Saiha district is given in Table No 1.2. The including faults are buffered. Likewise, due considerations Landslide Hazard Zonation map of Saiha district is shown in are given for the relation between landslides and other Figure No 1.1. thematic layers. In addition, proximity to road cutting,

International Journal of Engineering Science and Computing, July 2016 8725 http://ijesc.org/ Result and Discussion From the analysis, area statistics of Landslide Hazard Zonation of Saiha district can be shown as follows :- Hazard Class Area (Sq. Km) % Very High 138.44 9.89 High 340.85 24.35 Moderate 598.07 42.72 Low 279.47 19.96 Very Low 31.1 2.22 Water Body 11.97 0.86 TOTAL 1399.90 100.00 Table No 1.2: Area statistics of LHZ of SaihaDistrict

Very High Hazard Zone: This zone is Low Hazard Zone: This includes areas highly unstable and is at a constant threat of landslides, where the combination of various controlling parameters is especially during and after an intense spell of rain. This is unlikely to adversely influence the slope stability. In other because the area forms steep slopes with loose and words, this zone comprises areas where the chance of slope unconsolidated materials. Besides, it includes areas located failure is low or unlikely to occur. Vegetation is relatively near faults and tectonically weak zones. It also includes dense, though some areas may not have vegetative cover. areas where unplanned quarrying, road cutting and other Although some of the areas may be covered with soft and human activities are extensively undertaken. The vegetation unconsolidated sediments, the slope angles are generally is generally sparse. The exposed rocks are characterized by low, about 30 degrees or below. This zone extends over an numerous bedding and joint planes which facilitate the area of about 279.47sq. km and forms 19.96% of the total chance of sliding down along the slope. Therefore, it is district area. recommended not to established any developmental work in Very Low Hazard Zone: This zone this zone as far as possible, except if unavoidable. This zone mainly comprises vegetative areas and is located away from constitutes an area of 138.44sq. km and forms 9.89% of the human settlement. As such, it is assumed to be free from total district area. present and future landslide hazards. The dip and slope High Hazard Zone: It includes areas angles of the rocks are fairly low. Although the lithology where the probability of sliding debris is at a high risk due to may comprise soft rocks and overlying soil debris in some weathered rockand soil debris covering steep slopes which areas, the chance of slope failure is minimized by low slope when disturbed are prone to landslides. Most of the pre- angle and vegetation present within its vicinity. This zone existing landslides fall within this category. This zone covers an area of about 31.1sq km and forms 2.22% of the comprises areas where the slope aspect and dip direction of total district area. the rocks, which are usually very steep, (about 45 degrees or Apart from the various hazard classes, more) are parallel to each other. This makes them some areas are covered by water bodies which are not susceptible to slide along the slope. Several lineaments, included in the hazard classes. Such water bodies cover an fractured zones and fault planes also traverse the high hazard area of 11.97sq. km which is 0.86% of the total district area. zone. Areas which experience constant erosion by streams From the above, it can be easily calculated because of the soft nature of the lithology and loose that Very High Hazard and High Hazard Zone constitutes an overlying soil, fall under this class. Vegetation is generally area of 479.29 sq. km and forms 34.24% i.e more than one either absent or sparse. Owing to the above reasons, this third of the total district area. Moderate Hazard Zone zone is also geologically unstable and preferably be avoided. constitute an area of 598.07 sq. km and forms 42.72% i.e This zone occupies about 340.85sq. km which is 24.35% of almost half of the total district area clearly indicating the the total district area. vulnerability of the district to landslide Moderate Hazard Zone: This zone is generally stable, though it may contain unstable zones in Conclusion: some areas. Moreover, seismic activity and continuous Being a hilly terrain, the area is prone to heavy rainfall may reduce its stability. Though this zone may landslides and every year a number of landslides are reported include areas such as cliffs that have steep slopes (more than from various localities. These cause a lot of problem to 45 degree), the orientation of the rock bed and absence of public, resulting in loss of life and property, disruption of overlying loose debris and human activity make them less communication network, and also cause economic burden to hazardous. In general, this zone comprises areas that have the society. Landslide incidents are more prominent during moderately dense vegetation, moderate slope angle and the rainy/monsoon season as the soil structure gets soften by relatively compact and hard rocks. This zone is heavy and continuous downpour, especially in high degree predominantly high in terms of areal extend. It spreads over of slope. It is suggested that microzonation of the district an area of about 598.07sq. km and occupies 42.72% of the may be undertaken to map in a smaller scale. It is expected total district area. that various line governmental departments must carefully

International Journal of Engineering Science and Computing, July 2016 8726 http://ijesc.org/ go through the paper for developmental planning process, Mathur V.K, Sarkar.S (2004), Recent trends in Landslide selection of sites for installation of assets and infrastructure Hazard Zonation and Risk Assesment : An overview, initiatives so that vulnerability to landslide is reduce; prevent Landslide Disaster 97 – 103p loss of lives and property and attain sustainable developments. MIRSAC (2006) Natural Resources Mapping of Mizoram, Saiha District using Remote Sensing & GIS (Unpbl. Project Acknowledgement : Report), Mizoram State Remote Sensing Application Centre, The authors thanks the Department of Disaster Science, Technology and Environment, Planning Management & Rehabilitation, and Department. their respective Departments. MIRSAC (2011) Atlas of Landslide Hazard Zonation of References Mizoram (Unpbl. Report), Mizoram State Remote Sensing Anbalagan R et al., (2007), A field Manual for Landslide Application Centre, Science & Technology, Planning Investigations, DST 1- 153pp Department, Aizawl, Mizoram.

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International Journal of Engineering Science and Computing, July 2016 8727 http://ijesc.org/ Figure No. 1.1. Landslide Hazard Zonation Map of Saiha District

International Journal of Engineering Science and Computing, July 2016 8728 http://ijesc.org/