Landslide hazard zonation (LHZ) mapping on meso-scale for systematic town planning in mountainous terrain

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1 Journal of Scientific & Industrial Research 486 Vol. 67, July 2008, pp J SCI IND RES VOL 67 JULY 2008 Landslide hazard zonation (LHZ mapping on meso-scale for systematic town planning in mountainous terrain R Anbalagan*, D Chakraborty and A Kohli Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee Received 27 July 2007; revised 29 February 2008; accepted 09 May 2008 Planning and execution of development schemes in Himalayan terrain is always challenging because of inbuilt fragile nature of mountain ecosystem. Landslide hazard zonation (LHZ mapping on meso-scale (1: ,000 may guide planners to choose suitable locations for urbanization and expansion in hills. In present work, scope of regional scale LHZ mapping technique has been increased to accommodate more detailed aspects of inherent causative factors responsible for slope instability. This technique also incorporates effects of external causative factors such as seismicity and rainfall as correction ratings. This technique has been effectively applied to prepare a LHZ map on meso-scale in Nainital area. It will be useful for town planners to plan civil constructions in relatively safe zones. In addition, environmentally unstable slopes can be given adequate attention by planning suitable control measures. Keywords: Hazard classes, LHZ mapping, Meso-scale, Nainital, Planning in hilly terrains Introduction The fast rate of construction practice often overlooks adverse geological features that are inherently present in a mountain ecosystem. Lack of proper geological and geotechnical investigations in planning stage has adversely affected existing geo-environmental condition in the Himalaya leading to increased incidences of hill slope instability. So there is an urgent requirement for a landslide hazard evaluation technique, which shall be adopted in the planning stage so that major problems related to slope instability (SI can be avoided during implementation of these projects or even after their completion. In this context Landslide Hazard Zonation (LHZ mapping on meso-scale is one such hazard evaluation technique, which may find application for systematic town planning and expansion of urban settlements in hilly terrains. LHZ Mapping Technique LHZ mapping on meso-scale is an empirical approach, which demarcates hill slopes into zones of varying degree of stability on the basis of their relative hazards. Mapping scale is 1:5,000 1:10,000. The *Author for correspondence anbaiitr@gmail.com smallest unit of study while carrying out meso-scale LHZ mapping is a slope facet, which is that part of hill slope having similar slope characteristics (same amount of slope inclination and direction with a maximum variation of ± 20 for both and is usually bordered by natural features (ridges, spurs, gullies, depressions, streams and rivers. This technique accounts for inherent causative factors (whose effect in inducing instability can be studied or assessed on slope responsible for SI and accordingly rates them depending on their influence in inducing instability. These include geology of slope material comprising: a lithology; b structure; c slope morphometry; d relative relief; e land use and land cover; and f hydrogeological conditions. Hazard probability of a facet usually depends on combined effect of all inherent parameters, which can vary from facet to facet 1,2. However, this approach also incorporates effect of external parameters (whose effect cannot be assessed/ studied on the slope facet like seismicity and rainfall, as separate correction parameters. This map provides useful information to town planners in following ways: i It indicates nature of instability of hill slopes that can be suitably accounted in site selection; ii It indicates potentially unstable slopes which require further detailed studies following analytical techniques to assess their status of stability;

2 ANBALAGAN et al: LANDSLIDE HAZARD ZONATION MAP ON MESO SCALE IN NAINITAL AREA 487 iii If potentially unstable slopes become unavoidable during planning stage, suitable precautionary measures can be taken up in potentially unstable slopes before starting excavation; iv If unstable zones are located close to important engineering structures, urbanized colonies or other important installations, it may be essential to monitor slope to understand time dependent deformation behavior of the slope. Accordingly, instrumental slope monitoring can be carried out on these slopes; and v The data available on meso-scale can be used as an input data for risk assessment. Landslide Hazard Evaluation Factor (LHEF Rating Scheme LHEF rating scheme, which also follows an empirical approach, takes into consideration individual and net effect of all inherent causative factors responsible for SI (Table 1. Inherent factors 3 are used for preparation of LHZ mapping on macro-zonation approach. Maximum value of ratings for individual parameter is awarded keeping in mind its estimated significance in causing SI and also to represent overall field conditions. External parameters (seismicity and rainfall are also incorporated in LHEF rating scheme, apart from six inherent parameters. Various causative factors and their corresponding LHEF rating values are as follows: Lithology a Rock Slopes Lithology or rock type is an important factor in controlling slopes stability, and hence maximum LHEF rating of 2 is given. It controls the nature of weathering and erosion for a rock slope and this point is taken care of while awarding the ratings. Under this parameter, rocks are broadly classified into three categories (Table 2. Type-I rocks consist of crystalline rocks (igneous and Causative Factor Inherent factors Table 1 Maximum LHEF rating for different causative factors Maximum LHEF rating Geology 1 Lithology Structure Slope morphometry Relative relief Land use and land cover Hydrogeological conditions 1.0 Total LHEF Rating 10.0 Correction due to external factors a Seismicity & b Rainfall 1.0 (to be added separately to the total of LHEF Corrected LHEF Rating 11.0 Table 2 Ratings for rock types Category Rock types Ratings Type-I Basalt, quartzite and massive limestone & dolomite 0.2 Granite, gabbro and dolerite 0.3 Granite gneiss and metavolcanics 0.4 Type-II Well-cemented terrigenous sedimentary rocks (dominantly sandstone with 1.0 minor beds of clay stone and Gneissic rocks Poorly-cemented terrigenous sedimentary rocks (dominantly sandstone with 1.3 intercalations of clay or shale beds Type-III Well foliated gneiss 1.0 Shale, slate, phyllite and other argillaceous rocks like siltstone, mudstone and claystone 1.2 Schistose rocks 1.4 Shale with inter-bedded clayey rocks (siltstone, mudstone, etc. 1.8 Weathered shale and other argillaceous rocks, phyllite and schistose rocks 2.0

3 488 J SCI IND RES VOL 67 JULY 2008 Table 3 Correction factors for weathering Weathering Description Rating condition Rock type-i Rock type-ii Completely Rock totally decomposed/ disintegrated to C 1 = 4.0 C 1 = 1.5 weathered soil, no or minor existence of initial rock structure (Correction factor C 1 Highly weathered Rock totally discolored, discontinuity C 2 = 3.5 C 2 = 1.35 planes show weathering products, rock structure altered heavily with minor soil formation near surface (Correction factor C 2 Moderately Rock prominently discolored with remnant C 3 =3.0 C 3 =1.25 weathered isolated patches of fresh rock, weathering and alteration prominent along discontinuity planes, considerable alteration of rock structure (Correction factor C 3 Slightly Rock partially discolored along C 4 =2.5 C 4 = 1.15 weathered discontinuity planes indicating weakening of rock mass, rock structure is slightly altered (Correction factor C 4 Faintly weathered Rock slightly discolored along discontinuity C 5 =2.0 C 5 =1.0 planes which may be moderately tight to open in nature, intact rock structure with or without minor surface staining (Correction factor C 5 Description Table 4 Ratings for soil types Rating Older well compacted fluvial fill material (alluvial 0.8 Clayey soil with naturally formed surface 1.0 Sandy soil with naturally formed surface (alluvial 1.4 Debris comprising mostly of rock pieces Older well compacted 1.2 mixed with clayey or sandy soil Younger loose material 2.0 metamorphic along with massive calcareous rocks, which suffer less erosion resulting in steep slopes. Type- II rocks mainly comprised of well and poorly cemented terrigenous sedimentary rocks. Type-III category consists of soft argillaceous rocks, their low grade metamorphic equivalents and well foliated gneissic rocks. Soft rocks (claystone, siltstone, mudstone, shale, schist, phyllite and other such rocks erode faster and are easily weathered close to surface. Moreover, phyllite, schist and gneissic rocks have well developed foliation plane along which act as weak plane for sliding to take place. In LHEF rating scheme, weathering of fresh rocks is also included as a correction factor (Table 3, which is to be multiplied with corresponding rating of Type-I and Type-II rocks. Type-III rocks usually have an inbuilt higher rating, for which there is as such no requirement to multiply with correction factor. But depending on weathering condition, rating can be suitably modified to represent the field condition. Maximum value for Type III can be increased to 2 as the worst possible condition. b Soil Slopes Some hill slopes may be composed of mainly loose soil and debris overburden, where genesis and

4 ANBALAGAN et al: LANDSLIDE HAZARD ZONATION MAP ON MESO SCALE IN NAINITAL AREA 489 Table 5 LHEF rating for relationship between structure and slope Condition Rating Total rating of all conditions 1 Parallelism between slope and discontinuity Relationship between slope inclination and dip/ plunge of discontinuity Dip of discontinuity/ plunge of wedge line 0.5 Table 6 Ratings for relationship of parallelism between slope and discontinuity Category Difference in angle of parallelism Rating Slope condition 1 Plane: (α j - α s 2 Wedge: (α i - α s 3 Topple: (α j - α s ± 180 or (α j - α s I > Very favorable II Favorable III Fair IV Unfavorable V Very unfavorable Where α j = Dip direction of discontinuity, α i = Direction of plunge of the line of intersection of two discontinuity surfaces and α s = Direction of slope inclination Note: For slopes falling in category I in Table 6, the ratings for structure as awarded in Tables 7 and 8 will not be applicable and hence a rating of zero may be awarded relative age are considered as the main criteria, while awarding ratings (Table 4. Older alluvial soil is generally well compacted and characterized by high shear strength and also resistant to weathering. On the other hand, younger colluvial soil is loose or incompact in nature, soil for which they generally have low shear strength parameters. Structure a Rock Slopes Stability of hill slopes consisting of in situ rocks is largely dependent on relationship between slope orientation and attitude of dominant discontinuities. Structures include both primary and secondary discontinuities like bedding, foliation, schistosity, joints, shear zones and other such features. In this connection, failure modes taken into account are namely plane, wedge and toppling. For individual failure modes, following three types of conditions (Table 5 exist between slope and the most unfavorable discontinuity plane or wedge: i Parallelism between slope and discontinuity Extent of parallelism between inclination direction of slope and dip of discontinuity plane or the plunge ii iii of line of intersection of two such planes is considered here. With increasing parallelism, the chance of failure increases. In LHEF rating scheme, maximum rating given for this condition is 0 50 (Table 6. Relation between inclination of slope and amount of dip of discontinuity/ plunge of wedge line The differences in dip amount of slope and discontinuity plane or plunge of line of intersection of two such planes are taken into consideration. If slope is steeper than discontinuity surface or line of intersection of planes (day lighting condition, the slopes become vulnerable to plane or wedge failure modes. For toppling failure, dip of unfavorable discontinuity is added to inclination amount of slope. Most unfavorable situation appears when the added value exceeds 160. Maximum rating for all these cases are given as 1 00 (Table 7. Amount of dip of discontinuity/ plunge of wedge line With increasing amount of dip of discontinuity plane or the amount of plunge of line of intersection of two such planes, the material may cross angle of friction of rock mass constituting the slope leading to its instability. Steeper the slope angle more is the chance of slope failure. Maximum rating for this

5 490 J SCI IND RES VOL 67 JULY 2008 Table 7 Ratings for relationship between amount of dip/ plunge of discontinuity and that of slope inclination Cate- Difference in angles Rating Sum of angles Rating Slope condition gory 1 Plane (β j - β s & 3 Topple 2 Wedge (β i - β s (β j + β s I > < Very favorable II Favorable III Fair IV 0 ( Unfavorable V > > Very unfavorable Where β j = Dip amount of discontinuity, β i = Amount of plunge of line of intersection of two discontinuity surfaces and β s = Amount of slope inclination Table 8 Ratings for amount of dip of discontinuity Category Dip amount Rating Dip amount Rating Slope condition 1 Plane (β j 3 Topple (β j 2 Wedge (β i I < < Very favorable II Favorable III Fair IV Unfavorable V > > Very unfavorable Where β j = Dip amount of discontinuity and β i = Amount of plunge of line of intersection of two discontinuity surfaces relation, as awarded in the rating scheme, is 0.50 (Table 8. b Soil Slopes In case of slope facets consisting of overburden soil and debris material, assumed depth of overburden is considered for awarding ratings (Table 9, as the mode of failure changes with increasing depth of overburden. Slope Morphometry Slope morphometry maps for meso-zonation purpose are prepared after getting slope angle from sections drawn through slope facet along the direction of inclination incorporating highest and lowest contours passing through it. For meso-zonation purpose, an average slope angle for the whole facet is judiciously selected. If there is a significant variation (>20 along slope profile, it is better to study that slope, making a separate facet. Finally, all slope angles are categorized into six different classes, with a maximum rating of 2.0 (Table 10. Table 9 Ratings for depth of soil cover Depth of soil, m Rating Probable mode of failure < Dominantly Talus Talus & sometimes Circular Circular & sometimes Talus Dominantly Circular > Dominantly Circular Note: When depth of soil cover is <5m, then put rating of 1 if the slope angle is more than 35. Relative Relief Relative relief represents maximum height of a facet, from bottom (valley floor to top (ridge/ spur along slope direction. Relief of a facet can simply be calculated by counting difference between elevations at bottom most point of a facet to top most point of the same, along slope direction. For meso-zonation purpose, five classes of relief are considered. Maximum rating under this parameter is 1.0 (Table 11.

6 ANBALAGAN et al: LANDSLIDE HAZARD ZONATION MAP ON MESO SCALE IN NAINITAL AREA 491 Table 10 Ratings for slope morphometry Slope type Slope angle Probable type of failure Rating Escarpment / Cliff > 65 Falls & topples 2.0 Very steep slope Falls & topples 1.8 Steep slope Slides 1.6 Moderately steep slope Slides 1.3 Gentle slope Slides with creep movement 0.8 Very gentle slope < 15 Slides with creep movement 0.5 Table 11 Ratings for Relative relief Land Use and Land Cover Land use and land cover pattern is one of the important parameters governing slope stability. Vegetation has major role to resist slope movements, particularly for failures with shallow rupture surfaces. A well spread network of root system increases shearing resistance of slope material due to natural anchoring of slope materials, particularly for soil slopes. Moreover, a thick vegetation or grass cover reduces action of weathering and erosion, hence adds to stability of the slopes. On the other hand, barren or sparsely vegetated slopes are usually exposed to weathering and erosion, thus rendering it vulnerable to failure. Additional water for agriculture purpose recharges slopes in agricultural fields, apart from receiving natural precipitation. Similarly, a populated land on a very gentle slope (slope angle 15 under normal circumstances is least expected to suffer from SI, which is also induced because of anthropogenic activities, like urbanization, particularly on higher slope angles (>30. It not only removes vegetation cover but also adds to the natural weight of the slope as surcharge due to weight of civil structures. In a hill slope with higher slope angle, buildings are usually located by constructing local cut slopes and flat terraces. With this concept, urbanization is broadly classified into three categories: i A sparsely urbanized slope is one where construction terraces are located far apart (more than 15m of horizontal spacing providing a considerable distance between two terraces along the slope; ii A moderately urbanized slope is characterized by comparatively closer location of construction terraces but leaving an optimal horizontal spacing of 5-15m between individual terraces; and iii In a heavily urbanized slope construction terraces are located very close to each other ( 5m horizontal spacing in such a way that successive terraces almost touch each other at places. With increasing urbanization, water due to Relief classes Relative relief (m Rating Very low < Low Medium High Very high > domestic usage may be released on the slope surface wherever the drainage measure is inadequate. This water may get added up to the subsurface water and may develop pore water pressure, leading to SI. Similarly, barren land affected by anthropogenic activities is also most vulnerable to landslides. The maximum rating for this parameter is 2.0 (Table 12. Hydrogeological Conditions Presence of water generally decreases shear strength of slope forming material and thereby increasing the probability of slope failure. Since it is difficult to assess subsurface flow of groundwater quantitatively for entire facet, visual estimation of field condition have been considered as an alternative measure to award the ratings. For better representative groundwater condition assessment, it is advisable to take field data after monsoon. Maximum rating for this parameter is 1.0. The qualitative hydrogeological conditions of facets are rated as follows: flowing, 1.0; dripping, 0.8; wet, 0.5; damp, 0.2 and dry, 0. Correction Parameter Incorporating Effects of External Factors External factors like seismicity and rainfall may initiate slope movements and are accordingly called as triggering factors. Seismically, India is divided into four major seismic zones where Zone-II represents an area of minimum seismic intensity while Zone-V indicates maximum intensity of seismicity. Intensity of ground shaking increases proportionately from Zone-II to Zone-V. So a slope, which is critically stable under

7 492 J SCI IND RES VOL 67 JULY 2008 Table 12 Ratings for land use and land cover types Land use & land cover types Rating Agricultural land or populated flat land ( < Thickly vegetated forest area 0.80 Moderately vegetated area 1.20 Sparsely vegetated area with thin grass cover 1.50 Sparsely urbanized 1.20 Moderately urbanized 1.50 Heavily urbanized With proper surface and/ or subsurface drainage measures no wet patches on slope 1.60 Inadequate drainage wet patches observed on slope 1.70 Barren land 1.80 Barren land with slope excavation (cut slopes for road construction, mining 2.00 activities, etc Table 13 Ratings for external factors Seismic zone Rating Average annual rainfall of the area Rating II 0.2 < 50 cm 0.2 III cm 0.3 IV cm 0.4 V 0.5 > 150 cm or history of cloud burst 0.5 existing slope conditions, may become unstable if it falls in higher seismic zones and may result landslide phenomenon. Similarly, zones of high annual precipitation are also problematic as there are always chances of sudden pore water pressure built up in slopes following a heavy spell of rain and this may also induce slope instability. Ratings for these two factors shall be given separately and shall be added to the total estimated hazard (TEHD values as a correction parameter (Table 13. Calculation Of Total Estimated Hazard (TEHD From LHEF Ratings TEHD is calculated by adding LHEF ratings obtained for individual inherent parameters and later applying suitable corrections for external parameters (rainfall and seismicity. Depending upon the location of study area, correction parameters may vary widely (Table 13. The final TEHD value indicates overall condition of instability and shall be calculated facet wise by adding all values of inherent and external parameters as Total Estimated Hazard (TEHD = Ratings for (lithology + structure + slope morphometry + relative relief + land use and land cover + hydrogeological conditions + Correction for external parameters (seismicity and rainfall LHZ map on meso-scale of an area is prepared from corrected TEHD values of the facets. On the basis of range of TEHD values, all slope facets in an area can be categorized into five classes of relative hazard zones (Table 14. A LHZ map on meso-scale will show spatial distribution of these hazard zones and accordingly help town planners to select relatively safe areas for future development. For town planning and construction purposes, slope facets, which fall, in VLH and LH zones are Table 14 Landslide hazard zones based on corrected Total Estimated Hazard Hazard Range of zone corrected TEHD value Description of zone I TEHD < 3.5 Very low hazard (VLH zone II 3.5 TEHD < 5.0 Low hazard (LH zone III 5.0 TEHD 6.5 Moderate hazard (MH zone IV 6.5 < TEHD 8.0 High hazard (HH zone V TEHD > 8.0 Very high hazard (VHH zone

8 ANBALAGAN et al: LANDSLIDE HAZARD ZONATION MAP ON MESO SCALE IN NAINITAL AREA suitable. Slopes falling in HH and VHH are unfavorable and may be avoided as far as possible. In comparison to VHH and HH facets, slopes falling in MH class are considered relatively safer for construction practice, but may contain local areas of instability. If constructions are to be carried out in HH and VHH slopes, then suitable control measures should be taken up prior to construction. Preferably, these facets shall be studied in detail on 1:1000-1:2000 scale incorporating analytical and observational techniques in order to understand status of stability and to plan suitable control measures. Similar approach can be adopted for MH slopes to identify the unstable pockets and accordingly reduce the probability of hazard. Landslide Hazard Zonation Mapping of Nainital on Meso-Scale A Case Study Nainital (Lat: N N29 24 and Long: E E79 28 is located in Kumaun Lesser Himalaya. The study area is approx. 8 km2 and falls in Survey of India Toposheet No. 53 O/7 (1:50,000. Nainital lake is located within a saucer shaped depression, bounded by hills from all sides. The lake is fairly elliptical (eye in shape with a maximum length of approx. 1 km along NW-SE direction and maximum width of about 500 m. Highly urbanized Sher-ka-danda hills are located to E and NE of Nainital lake. It merges with Naina Hills in the north. The lake is bounded by Ayarpatha-Deopatha hills in W and SW directions. It is surrounded by Lesser Himalayan hills from all sides, 493 except in S-SE direction, where from Balia ravine, the only outlet of lake, emerges and passes through Kailakhan area, before descending into the plains to meet Gola River near Kathgodam. Nainital is facing hill slope instability problems for over a long period. Earliest reported incidence of landslides dates back to 18th century. Since then, the landslide problems were being reported intermittently causing damages to civil structures. In view of this, a LHZ map of Nainital has been prepared on meso-scale (1:5,000 to study landslide hazard probability of town area surrounding the lake. Geology of Study Area Geologically, the area is represented by rocks of Infra-Krol, Krol & Tal Formations of Proterozoic age4,5. Dominant rock types include grey slates and phyllites (Lower Krol Formation, calcareous slates (Middle Krol Formation, massive limestones and dolomites with minor slates (Upper Krol Formation and quartzites with intercalated sandstones of Tal Formation (Fig. 2. Sher-ka-danda hills located on the easterly direction to lake are made up of slates and phyllites of Lower Krol Formation. These slopes often show manifestation of creep movements such as tension cracks, tilting of trees and other such features. Meso-scale LHZ Map of Nainital For preparation of LHZ map of Nainital town on meso-scale, initially a slope facet map (Fig. 1 of Fig 1 Slope facet map of study area

9 494 J SCI IND RES VOL 67 JULY 2008 Fig 2 Geological map of study area Fig 3 Slope morphometry map of study area

10 ANBALAGAN et al: LANDSLIDE HAZARD ZONATION MAP ON MESO SCALE IN NAINITAL AREA 495 Fig 4 Relative relief map of study area Fig 5 Land use & land cover map of study area lake catchment was prepared from SOI toposheet (1:5,000. Altogether, 29 slope facets were identified for the purpose of LHZ mapping. Slope morphometry and relative relief maps were also prepared from toposheet. The condition of all inherent parameters was actually examined on slope facets in order to assign suitable LHEF ratings and to prepare various thematic maps (Figs 2-6. As the study area falls in seismic zone IV with an average annual precipitation of the order of cm, adequate correction ratings for external parameters were also added. Thus, LHEF ratings obtained for individual facets were added up to get the facet wise corrected TEHD value. On the basis of these values, various hazard classes were determined (Fig. 7. Hazard Classes Meso-scale LHZ map (Fig. 7 indicates that hill slopes on E and NE side of the lake forming part of

11 496 J SCI IND RES VOL 67 JULY 2008 Fig 6 Map of hydro-geological condition in study area Fig 7 Landslide hazard zonation (LHZ map of study area Sher-ka-danda hill and Naina hill fall dominantly on HH and VHH zones. Slopes of Ayarpatha-Deopatha hills, bordering SW flanks of the lake, fall dominantly in MH zone with small pockets of HH and VHH zones. The concentration of urbanization on Sher-ka-danda hill is generally of high order, particularly in the lower levels close to lake. Similarly, high urbanization is also seen in foothill region of Naina hill. The constructions in these areas are steadily growing without taking into consideration existing instabilities. This may add to natural unstable

12 ANBALAGAN et al: LANDSLIDE HAZARD ZONATION MAP ON MESO SCALE IN NAINITAL AREA 497 conditions and may aggravate overall stability of these hill slopes. This fact has been validated by detailed stability analysis of HH and VHH slopes taking into account the mode of failure, shear strength parameters and slope geometry. Analysis indicates stable slope condition when dry, but becomes unstable under water saturation. Hence, it is time to control unplanned constructions on these hill slopes, which may help to protect existing geo-environmental balance of Nainital. Conclusions The Himalaya represents one of the most fragile mountain ecosystems of the world, where systematic planning is a must for successful implementation of developmental schemes. LHZ mapping on meso-scale (1:5,000-10,000 may guide town planners to identify relatively safe areas for future constructions and town expansion. Meso-scale LHZ mapping is an empirical approach, which takes into, account both inherent and external parameters responsible for slope instability. Stable zones like VLH and LH are considered safe for civil constructions. Hill slopes falling in MH class are also safe for construction practice, but may contain local pockets of instability, which should be suitably accounted during constructions. For slopes falling in HH and VHH classes, it is always advisable to avoid constructions. If unavoidable, detailed study on 1: scale shall be done to evaluate the status of stability of these slopes. Suitable control measures shall be identified before taking up constructions in order to minimize geo-environmental hazards. As a case study, a meso-scale LHZ map of Nainital town was prepared, which indicates about 40% falling in HH class and about 25% falling in VHH class. The conditions of these potentially unstable hill slopes were also validated by detailed stability analysis and shall be suitably accounted during civil constructions. References 1 Anbalagan R, Singh B, Chakraborty D & Kohli A, A Filed Manual For Landslide Investigation (DST, Govt. of India, New Delhi 2007, 153p. 2 Anbalagan R, Landslide hazard evaluation and zonation mapping in mountainous terrain, Engineering Geology, 32 (1992, BIS 14496, Preparation of Landslide hazard Zonation Maps in Mountainous terrains Guidelines, Part 2 Mcro-zonation (BIS, New Delhi Valdiya K S, Geology and Natural Environment of Nainital Hills, Kuamun Himalaya (Gyanodaya Prakashan, Nainital 1988, 155p. 5 Valdiya K S, Geology of Kumaun Lesser Himalaya (Wadia Institute of Himalayan Geology, Dehradun 1980, 291p.