Malappuram District

Home , Kottakkunnu, Malappuram, Malappuram district

MALAPPURAM DISTRICT

Geological Study and Action Plan Preparation for Protection of Kottakunnu Park

Report Submitted To

DISTRICT TOURISM AND PROMOTION COUNCIL – MALAPPURAM

Report Submitted by

Centre for Social and Resource Development (CSRD) 2nd Floor, Pulickan Hyper Bazar, Pudukad P O, Thrissur, Pin 680301 Ph: 04802756221, 9048435153,e-mail: [email protected]

ACKNOWLEDGEMENTS

We would like to take this opportunity to place on record our sincere gratitude to all those who have directly and indirectly helped us in the completion of this project.

First and foremost, we are grateful to the Malapuram district collector Mr.Jafar Malik IAS and Mr.Purushothaman P.N Deputy collector Disaster Management, Malappuram District for entrusting us with this work.

We wish to express our deep sense of gratitude to Mr.Binosh Kunjappan secretary DTPC Malappuram to give an opportunity to this project.

We would like to thank our guide Dr. Anto Francis. His timely advice, meticulous scrutiny, and scientific approach have immensely helped us to accomplish this task.

We are extremely thankful to Mr. Anwar, caretaker of Kottakunnu park and all the staff of the park for helping us throughout the work. We would also like to thank all the residents of Kottakunnu for their kind cooperation throughout the work especially Mr.Vinod municipal counselor of ward 17 Malappuram Municipality, Mr. Randeer & Mr. Nidheesh who provided us information about the region and helped us with the field work.

CONTENTS CHAPTER 1 ...... 5

INTRODUCTION ...... 5

ANATOMY OF SLOPE MOVEMENT ...... 6

TYPES OF MASS WASTING PROCESS ...... 8

TRIGGERING MECHANISM ...... 10

RAINFALL AND LANDSLIDES ...... 11

CHAPTER 2 ...... 13

STUDY AREA ...... 13

GEOLOGY AND GEOMORPHOLOGY...... 15

RAINFALL ...... 16

DRAINAGE ...... 18

KOTTAKUNNU LANDSLIDE 1 ...... 19

LANDSLIDE 2 ...... 20

TRIGGERING FACTORS FOR KOTTAKUNNU LANDSLIDES ...... 21

KOTTAKUNNU PRESENT SCENARIO ...... 26

CHAPTER 3 ...... 28

GEOTECHNICAL CHARACTERISITICS ...... 28

METHODOLOGY ...... 28

GEOTECHNICAL STUDIES ...... 29

ATTERBERG LIMITS ...... 31

SPECIFIC GRAVITY ...... 32

BULK DENSITY ...... 33

MOISTURE CONTENT ...... 34

PARTICLE SIZE DISTRIBUTION ...... 34

CHAPTER 4 ...... 35

LANDSLIDE HAZARD ZONATION MAPPING ...... 35

HAZARD, VULNERABILITY AND RISK ...... 35

EVALUATION FACTORS ...... 36

TRIGGERING FACTORS ...... 38

USES OF LANDSLIDE HAZARD ZONATION...... 38

ASSUMPTION FOR LANDSLIDE HAZARD ZONATION ...... 39

CHAPTER 5 ...... 40

LANDSLIDE HAZARD ZONATION OF KOTTAKUNNU AREA ...... 40

SLOPE ...... 40

ASPECT ...... 42

ROAD NETWORK ...... 43

DRAINAGE DENSITY ...... 45

PLAN AND PROFILE CURVATURE ...... 47

SOIL DEPTH/THICKNESS ...... 49

NORMALIZED DIFFERENCE VEGETATION INDEX (NDVI) ...... 51

TOPOGRAPHIC WETNESS INDEX (TWI) ...... 52

LAND USE LAND COVER ...... 54

DATA PROCESSING ...... 55

CHAPTER 6 ...... 58

THREATS AND PROBLEMS OF KOTTAKUNNU ...... 58

CHAPTER 7 ...... 66

RECOMMENDATIONS ...... 66

CHAPTER 8 ...... 68

ACTION PLAN ...... 68

DRAINAGE ...... 68

CONSTRUCTIONS & MODIFICATIONS ...... 73

RE-VEGETATION ...... 76

LANDUSE MODIFICATIONS ...... 77

CONCLUSIONS ...... 79

CHAPTER 1

INTRODUCTION

The Western Ghats, the most prominent orographic feature of peninsular India, occupies 47% of Kerala state, with a total area of 38,863 km2. Kerala is the third most densely populated (819 people/km2) state in the country. Even though the region once supported typical tropical forests and grasslands, substantially vast area has been cleared and converted into monoculture plantations and agricultural fields from the early 19th century onwards. All 13 of the 14 districts of Kerala except the coastal district of Alappuzha are prone to landslides. About 8% of area in The Western Ghats of Kerala is classified as critical zone for mass movements. The region experiences several types of landslides especially during the monsoon seasons. The prediction and mitigation of natural hazards is one among the most important part of sustainable development of a nation and its population. Along with the damage it causes to life a hazard also causes serious negative effects to the economy of the region where it occurs. Among these natural hazards, landslides are one of the frequent and are more disastrous event. Landslides being one of the major natural disasters that resulted into significant injury and loss of the human life, property and infrastructure throughout the world. The disaster management authority defines a landslide as the sudden downward/outward movement of earthen materials along a slope under gravity. The most common causes for the slope instability are intense and prolonged rainfall, earthquakes, snow melting, etc. Apart from these, the stability of the earthen slope also depends on the geotechnical properties of slope material, drainage pattern, land cover, slope gradient, etc. Landslides or slope failure occur when the gravity exceeds the resisting forces in the slope (Slope’s shear strength). Most of the devastating landslides were occurred in hill slopes >20º, except for the sea cliffs. The researches in Western Ghats says that the major trigger for landslides in these areas are associated with intense and/or prolonged rainfall causing relative pore pressure variations. The initiation points of most of the landslides are either a vegetation deficit area or those area having more number of shallow rooted trees. Another major factor that triggers the landslide are unscientific slope modification and overloading. Vegetation is having an integral role in the occurrence of slope failure. The ability of plants to intercept the rainfall, to control the soil moisture through evapotranspiration and enable slope stability through the roots makes it an important decisive factor. The shallow rooted plant cultivation along with unscientific land use practices are

5 catalyzing the slope failures in the hilly regions. Also the periodic felling or sometimes the uprooting of crops/plants after their lifespan, causes the loss of inherent cohesion of soil along with its exposure to the rainfall, makes the soil cover more vulnerable to erosion and slope failure. Even though it’s a fact that people are being given with guidance from various governmental bodies including Agricultural department, the practicing of slope terracing ignoring the natural drainage is a prevalent practice which is identified as a potential reason for an increase in number of slope failures/ landslides in the Western Ghats. This includes rock falls, rock slips, slumps, creeps, debris flows and in a few cases, rotational types of slides. The most prevalent, recurring and disastrous type of mass movements noted in Kerala are the ‘‘debris flows’’. They are called ‘‘UrulPottal’’ in the local vernacular. The characteristic pattern of this phenomenon is the swift and sudden down slope movement of highly water saturated overburden containing a varied assemblage of debris material ranging in size from soil particles to huge boulders destroying and carrying with it everything that is lying in its path. They are confined flows that affects the overburden weathered rock and soil, leaving the much stronger Precambrian crystalline basement intact.

ANATOMY OF SLOPE MOVEMENT

Various terms are used to describe the features associated with the slope movement Crown: The practically undisplaced material still in place and adjacent to the highest parts of the main scarp. Depleted mass: The volume of the displaced material, which overlies the rupture surface but underlies the original ground surface. Depletion: The volume bounded by the main scarp, the depleted mass and the original ground surface. Displaced material: Material displaced from its original position on the slope by movement in the landslide. It forms both the depleted mass and the accumulation. Flank: The undisplaced material adjacent to the sides of the rupture surface. Compass directions are preferable in describing the flanks but if left and right are used, they refer to the flanks as viewed from the crown. Foot: The portion of the landslide that has moved beyond the toe of the surface of rupture and overlies the original ground surface. Head: The upper parts of the landslide along the contact between the displaced material and the main scarp.

Main body: The part of the displaced material of the landslide that overlies the surface of rupture between the main scarp and the toe of the surface of rupture. Main scarp: A steep surface on the undisturbed ground at the upper edge of the landslide, caused by movement of the displaced material away from the undisturbed ground. It is the visible part of the surface of rupture. Minor scarp: A steep surface on the displaced material of the landslide produced by differential movements within the displaced material. Original ground surface: The surface of the slope that existed before the landslide took place. Surface of rupture: The surface which forms the lower boundary of the displaced material below the original ground surface. Surface of separation: The part of the original ground surface overlain by the foot of the landslide. Tip: The point of the toe farthest from the top of the landslide. Toe: The lower, usually curved margin of the displaced material of a landslide, it is the most distant from the main scarp. Toe of surface of rupture: The intersection (usually buried) between the lower part of the surface of rupture of a landslide and the original ground surface. Top: The highest point of contact between the displaced material and the main scarp.

TYPES OF MASS WASTING PROCESS

The various types of mass wasting process can be differentiated by the kinds of material involved and the mode of movement.(Table.1.1) Mass movements or landslides are generally classified on the basis of three major criteria:-

(1) Rate of movement (rapid or slow) (Table.1.2)

(2) Type of movement (primarily falling, sliding, or flowing) and

(3) Type of material involved (rock, soil, or debris)

Table.1.1: Types of landslides

Table.1.2: Types of landslides (Rate of movement)

TRIGGERING MECHANISM

It is found that in many instances it is not a single factor that causes the slope failure but cumulative effect of the factors leads to the disaster. (Table.1.3) Intense rainfalls for several hours or moderate intensity lasting several days trigger most landslides. Rapid infiltration of rainwater, causing soil saturation and a temporary rise in pore-water pressures is the mechanism by which most shallow landslides are generated. Rapid melting of a snow-pack caused by sudden warming spells or by rain falling on snow can add water to hillside soils. Rain- on-snow commonly reduces the water content of the snow pack and adds sufficient water to soils, thus triggering landslides. The sudden lowering of the water level (rapid draw down) against a slope can trigger landslides in earth dams, along coastlines and on the banks of lakes, reservoirs, canals and rivers. Deposition of loose volcanic ash on hillsides is followed by erosion and mud or debris flows triggered by intense rainfall. Strong ground shaking during earthquakes also triggers rock falls, soil slides and rockslides in steep slope. Landslides involving loose saturated, cohesion less soils on low to moderate slopes commonly occur due to earthquake-induced liquefaction, where, shaking temporarily raises pore-water pressure and reduces the soil strength. Anthropogenic factors for landslides includes human activities like construction of buildings, dams and bridges, quarrying and blasting, deforestation, blocks of natural drainage channels and damming of water in hill slopes. Toe cutting of hill slopes is the main reason for slope failure. The external factors that cause slope failures are quarrying, deforestation, water leakage, land use change and wrong water management practices.

GEOLOGICAL MORPHOLOGICAL PHYSICAL HUMAN CAUSES CAUSES • Weak material • Slope angle • Intense rainfall • Excavation • Sensitive materials • Uplift • Rapid snow melt • Loading • Weathered • Rebound • Prolonged • Drawdown materials • Fluvial erosion • precipitation • Land use • Sheared materials • Wave erosion • Rapid drawdown change • Jointed or fissured • Glacial erosion • Earthquake • Water • materials • Erosion of lateral • Volcanic eruption • management • Adversely margins • Thawing • Mining orientated • Subterranean • Freeze-thaw • Quarrying • discontinuities erosion • Shrink-swell • Vibration • Permeability • Slope loading • Ground water • Water leakage contrasts • Vegetation change changes • Deforestation • Material contrasts • Soil pore water • Rainfall and snow • pressure fall • Surface runoff • Seismic activity

Table.1.3: Causes of Landslides

RAINFALL AND LANDSLIDES

Rainfall is recognized nationally and internationally as a major triggering factor for the initiation of slope instability and the initiation of landslide movement. Such movement may range from subtle, minor displacements to catastrophic scale movements in terms of velocity and travel distance. Landslides are very common occurrence during a long period of heavy rainfall and occur every year in many parts of the world, especially in environments that provide a prolonged and intense

11 rainfall, steep slopes, sparse vegetation and an abundant source of incoherent fine-grained soils, including colluviums and residual soils. These landslides are common sights in tropical countries, and in some cases, in temperate regions where residual soil prevails. In a tropical region like Kerala, most landslides occur annually between June and September, in which period the frequency and intensity of rainfall is higher than any other months. The climate of Kerala in particular is dominated by the monsoon circulation. During one half of the year the wind blows from the oceans to the south of the Asian land mass, while during the other half there is a seasonal wind blowing from the Asian landmass to the oceans to the south. There is a spectacular reversal of pressure and wind patterns between these two six-month periods. The gradual rise in temperature through spring to summer does not happen, due to the onset of the south-west monsoon. Temperatures drop sharply in June. The usual classification into spring, summer, autumn and winter is therefore not adopted in the state. January and February is winter season, March to May is the pre-monsoon season, June to September is the south-west monsoon season and October to November is the post- monsoon season.

LANDSLIDE LITERATURES

Slope stability problems have received worldwide attention. In order to provide a systematic approach to study the landslides, Varnes (1984) defines various types of landslides. Einstein (1988) explained a theoretical concept regarding danger, hazard, and risk. Landslides have been correlated with extended (weekly, monthly or seasonal) periods of rainfall by Hutchinson (1970), Krishnanath (1985), Biju Abraham, et.al (1996) and Sampath, et.al (1995). They have observed that the high intensity rainfall is one of the major triggering mechanisms of landslides. According to Sreekumar and Krishnanath (1995), Storms that produce intense rainfall for periods as short as several hours or have a more moderate intensity lasting several days have triggered number of landslides. Tan Wenhui et al.,(2011) describes the rainfall infiltration is the important factor affecting the slope surface

CHAPTER 2

STUDY AREA

The study area falls between 11°2'59.85"N to 76°4'35.89"E and 11°2'56.26"N to 76° 5'15.08"E Geographic coordinates (Figure.2.1)

Kottakunnu is a laterite hillock in the heart of the Malapuram town, it is a recently developed tourist spot in the district run by DTPC, Kottakkunnu derives its name from an old fort, which was built by the Zamorins of Kozhikode is the highest point in Malappuram town with maximum elevation of 132m . It was the campsite of British military when it reached there in 1921 in large numbers to quell an uprising of Muslim peasants. The British authority used it as a firing range and many rebels were killed here by them. After freedom of India it is used Indian military as firing range. So it is of great historical significance named as Kottakkunnu grounds.

FFigur e 2.1. Study Area

Figure 2.2. Satellite Image of Study Area

The top portion of Kottakunnu is bounded on the south & west portions by a boundary wall which is of about 1m high. Walkway is built encircling the top portion. Several buildings for leisure is constructed in the top portion. Kottakunnu has two entrances one at the southern bottom region and another at the top north corner.

GEOLOGY AND GEOMORPHOLOGY

Kottakunnu is a flat topped hill, the flat top portion is about 11acre in area. The region is a denudational terrain characterised by flat-topped laterite capped flats, mesas, interfluves, hills, mounds and spurs interspersed by narrow valleys as well as wide alluvial valleys and flood plain. Geomorphological studies in this region have brought out remnants of palaeoplanation surfaces having extensive and plateau-type remnants with thick laterite profile. The study area mainly consists of lateritic soil. The depth to bedrock in the study area varies highly from about 2m to about 12m. Charnockite group of rocks forms the bed rock in the study area.(Figure.2.3)

FiFgure. 2.3. Geomorphology

RAINFALL The area has more or less the same climatic conditions prevalent elsewhere in the State viz. dry season from December to February and hot season from March to May, the South-West monsoon from June to September and the North-East monsoon from October to December. The normal rainfall of the district is 2793.3 mm. Out of this, major rainfall contribution is from SW monsoon followed by the NE monsoon. The South West monsoon is usually very heavy and nearly 73.5% of the rainfall is received during this season. NE monsoon contributes nearly 16.4% and March to May summer rain contributes nearly 9.9% and the balance 0.2% is accounted for during January and February months. (Table.2.1) (Figure.2.4)

KERALA AGRICULTURAL UNIVERSITY

RAIN FALL DATA AT AGRICULTURAL RESEARCH STATION, ANAKKAYAM, MALAPPURAM DT. 2014 2015 2016 2017 2018 2019 Month Rain fall Rain fall Rain fall (mm) Rain fall Rain fall Rain fall (mm) (mm) (mm) (mm) (mm) January 0.00 0.00 0.00 0.00 0.00 0.00 February 0.00 0.00 0.00 0.00 0.00 0.00 March 0.00 6.80 4.6 6.6 0.00 0.00 April 45.40 128.60 0.00 15.6 48.8 26.8 May 157.00 236.90 65.4 99.2 169 7.4 June 417.20 434.00 494.6 372.6 675.8 307.4 July 770.80 265.60 342.3 329.6 733.4 558 August 506.50 245.60 161.7 423.1 567 803.7 September 250.40 190.00 62.6 445.6 79.8 214 October 276.00 181.20 44.2 116 89.1 498.2 November 99.60 106.80 24.8 57.6 72.6 December 27.00 21.40 3.2 5.8 0.00

Table.2.1. Rainfall data

Figure.2.4. Rainfall Data Source: AGRICULTURAL RESEARCH STATION, ANAKKAYAM, MALAPPURAM DT

DRAINAGE

Being the highest point in the town Kottakunnu is said to be the major source for many of the streams that provided freshwater to the town and nearby areas, Parachola, Kottapanchola, Valavilchola, Chakkichola, and Thekepuramchola were all small streams that received water from Kottakunnu. The drainage network was created using GIS Hydrology tools, for obtaining precise data 1m contour was used to generate the streams and hence streams show higher order. (Figure.2.5.)

Figure.2.5. Drainage

KOTTAKUNNU LANDSLIDE 1

Location : 11° 2'50.43"N-76° 4'54.39"E

The first landslide occurred on the southwestern slope of Kottakunnu on 9/08/2019 at about 1.30 PM. (Figure.2.6) A portion of the slope along with trees and the walkway remnants and decoration light posts came down the slope with the debris covering chola road, destroying a house and killing 3 people including an infant. The slope mainly has lateritic soil. The area does not have a well- developed soil profile. The sediments are loose and the rocks a highly weathered. The crown areas have an overburden of about 2.5m gradually increase about the bottom. The runoff of debris is about 160 m length. Streams where formed by the excessive rain. This along with the overburden (constituting weathered rock and lateritic soil) came down and caused the disaster. The crown portion is at about 80m from MSL the total width of the crown portion 27m, the tail region is about 155m from the crown overburden thickness observed in the region is 2.75m. Cracks were formed in the region above the crown of this landslide extending in an accurate manner in both directions.

Figure.2.6. Landslide location 1

LANDSLIDE 2

Location: 11° 3'1.87"N - 76° 4'54.33"E

The second slide occurred in the northwest slope of Kottakunnu in the Cherattukuzhy area. (Figure.2.7.) The crown portion is at an elevation of 62m, the total width of the slide is 30m and the tail portion is 80m from the crown. The slide occurred on 9-08-2019 a portion of the slope along with trees came down destroying 2 houses partially, first order stream has formed after the slide in the area.

Figure.2.7. Landslide location 2

TRIGGERING FACTORS FOR KOTTAKUNNU LANDSLIDES

RAINFALL

From the rainfall data obtained from Agricultural research station at Anakkayam, the slides had been triggered by heavy rainfall of 115mm. The top portion of the region is flat and as a result a rain of 115mm could generate about 51,19,225 liters of water. Without proper measures to drain this massive amount of water, all this water flowed out through unstable regions and caused the slides. As per the local information large quantities of warm muddy water flowed downhill in both the landslide locations prior to the sliding incidents. So it can be concluded that the intensive rainfall is the main factor for the slides in both the cases. (Table.2.2) (Figure.2.8)

August, 2019 Rain (mm)

1 0.00 2 0.00 3 3.4

4 0.00 5 55.4 6 12.2 7 76.4 8 30.6 9 115.2 10 84.4 11 143.4 12 27.8 13 36.4 14 40.4 15 10.4 16 12.2 17 5.4 18 0.00 19 0.00 20 0.00 21 0.00

22 8.8

23 0.00 24 4.6 25 6.4 26 22.4 27 28.5 28 20.4 29 9.2 30 32.6 31 17.2

803.7 Table.2.2. Daily Rainfall Data

Figure.2.8.Daily rainfall data August 2019 (Star denotes landslide event)

HUMAN INTERVENSION

As mentioned earlier Kottakunnu had been the source of water for many downhill streams that flows in to the Machingalthodu and nearby paddy fields. But the unscientific construction practice in the region has reduced the amount of water flow into these streams. The southwestern slope of Kottakunnuu has been barren for many years with large boulders of laterite. As a part of Kottakunnu master plan the slope was modified and walkways were constructed without considering the natural drainage of the region, the large boulders were crushed and trees were planted in these modified slopes. An old reservoir was buried during the process of modification of the park which acted as a collection point of most of the streams in the southwestern slope. This reservoir was used by the locals for their daily needs. On the flat top of Kottakunnu there existed two wells about 30m apart and which were connected by tunnels that were remains of Tippu’s military assault was also buried for the construction of helipads. Recently a road has been constructed on the private land on the top portion of Kottakunnuu, close to the lateritic scarp cutting laterite 3-4 meters in several areas. All these factors together increased the impact of a rainfall induced landslide. (Figure 2.9)

Figure.2.9.Road cut cliff

KOTTAKUNNU PRESENT SCENARIO

Presently Kottakunnu has no proper drainage system to bring down the water that gets collected on the top portion. The western side of the top flat region is bounded by 1m high boundary wall which blocks the free flow of rain water down slope. There is no proper facility to drain the rain water from this area and during the last monsoon, the accumulated rain water had overflows the boundary wall at several points. At the north western side channel is constructed for draining water. Due to unscientific construction of this water flows directly to the nearby private a land. This also has created a problem for the residents of the northern slope. The road to Kottakunnu top also has no gutter for the water to reach downhill. Several construction activities have been done on the fragile western slope of Kottakunnu. Most of these activities are done unscientifically. Construction activities are vigorously carried out on the flanks and top portion of Kottakunnu. These construction activities can cause a serious threat to Kottakunnu and its residents. The 1m tall boundary wall constructed along the northern edge of the flat top portion without any provision for drainage is quite detrimental. The construction activities along the slopes like roads and walkways block the natural drainage. The construction of a private road at the base of the laterite scarp at the top is another problematic construction. The road is constructed unscientifically by cutting laterite to about 5m and also without considering the drainage and slope properties. As this road is deeper than the adjoining areas, it acts as a drainage channel. As this road is incompletely constructed water flowing down along this road flows out and spreads on to the slope. The end point of this road is only few meters upslope of the landslide location. The construction of this road by the cutting of large massive laterite blocks has made these structures more vulnerable to weathering caused both by the roots of plants and also running water. As a result large fractures are seen on the laterite blocks which in future could lead to rock falls and similar disasters. Rainy season brings about a great fear in the minds of the residents of Kottakunnu. About 32 families in the flanks of Kottakunnu have been shifted to relief camps or have moved to their relative’s houses during the past monsoon season. So a proper decision making and construction processes must be done immediately on the slopes of Kottakunnu in order to reduce the hardships of these people.

Area of land owned Number of Families <25cents 44 25-50 cents 5 50-100cent 3 >1acre 2

From the table it can be seen that most of the residents of Kottakunnu owns less than 25 cent of land, if the slope stabilizing construction activities are to be done on household basis it would be difficult for each of this families and would not yield a good result. So the construction activities recommended must be done on a ward basis incorporating it with central or state government schemes and funding.

Total dimension of house Number of houses <500 sq.ft 4 500-1000 sq.ft 16 1000-1500sq.ft 9 1500-2000 sq.ft 5 >2000 sq.ft 1

Year of construction Number of houses Before 1990 27 1990-2000 14 2000-2010 17 2010-2015 10 After 2015 12

Number of households owing ancestral property 30 Number of households who bought land & settled in 25 the region

Number of households owning well 22+1 (Dugwell+Borewel) Number of households doing agriculture & 17 common crops Cocconut,Plantain,Vegetables, Areca nut

CHAPTER 3

GEOTECHNICAL CHARACTERISITICS

Geotechnical characteristics of the material play an important role in deciding the factor of safety of slopes. Geotechnical properties such as liquid limit, plastic limit, shrinkage limit, optimum moisture content, maximum dry density, texture, specific gravity, cohesion and internal friction angle have been determined using standard procedures, in the geotechnical lab.

METHODOLOGY

SAMPLE COLLECTION Samples for the geotechnical studies were collected from different locations within the boundary of Kottakunnu where landslides occurred in August 2019. The samples were taken by using a core having a length of 1 feet and a diameter of 4 inch. Total of 7 samples were collected from the landslide locations. (Figure3.1)

Sample No: CH1, CH2, S1, S2, S3, S4, S5.

S - Represents the samples taken from Landslide Location 1.

Samples S3,S4,S5 were taken from the upslope regions and samples S1 & S2 were taken from the down slope region

CH – Represents the samples taken from Landslide Location 2.

Sample CH1 was taken from the down slope portion and sample CH2 was taken from the upslope portion

These samples were examined in geotechnical lab of Govt. engineering college Thrissur.

Figure3.1.Sample collection

GEOTECHNICAL STUDIES The collected samples from the core was taken out first and let it for air dry for 24 hours and later oven dry for another 24 hours in the geotechnical lab. Then the soil sample is analyzed to get the shear strength parameters such as the angle of internal friction and cohesion. Other engineering properties such as grain size, specific gravity, liquid limit, plastic limit, shrinkage limit, optimum moisture content (OMC), maximum dry density (MDD). The obtained results are given in the Table 3.1

Table.3.1. Results

ATTERBERG LIMITS Consistency is the term used to describe the ability of the soil to resist rupture and deformation. It is commonly described as soft, stiff or firm, and hard. Water content greatly affects the engineering behavior of fine-grained soils. In the order of increasing moisture content, a dry soil will exist into four distinct states: from solid state, to semisolid state, to plastic state, and to liquid state. The water contents at the boundary of these states are known as Atterberg limits. Between the solid and semisolid states is shrinkage limit, between semisolid and plastic states is plastic limit, and between plastic and liquid states is liquid limit. Atterberg limits, are water contents at critical stages of soil behavior. They, together with natural water content, are essential descriptions of fine-grained soils. Liquid Limit, LL Liquid limit is the water content of soil in which soil grains are separated by water just enough for the soil mass to loss shear strength. A little higher than this water content will tend the soil to flow like viscous fluid while a little lower will cause the soil to behave as plastic. Plastic Limit, PL Plastic limit is the water content in which the soil will pass from plastic state to semi-solid state. Soil can no longer behave as plastic; any change in shape will cause the soil to show visible cracks. Shrinkage Limit, SL Shrinkage limit is the water content in which the soil no longer changes in volume regardless of further drying. It is the lowest water content possible for the soil to be completely saturated. This is the point in which soil will pass from semi-solid to solid state. The plastic limit for different soils has a narrow range of numerical values. Sand has no plastic stage, but very fine sand exhibits slight plasticity. The plastic limit is an important soil property. The range of the plastic state is given by the difference between liquid limit and plastic limit and is defined as the plasticity index. The plasticity index is used in soil classification and in various correlations with other soil properties as a basic soil characteristic. With the increase of sand content plasticity index of soil decreases, which might be due to decrease of inter molecular attraction force. Due to decrease of attraction force, liquid limit of the soil decreases and accordingly plasticity index decreases. But as the clay content increases inter molecular attraction force increases and liquid limit increases. (Table.3.2)

Plasticity Index (%) Soil Type Degree of Plasticity Degree of Cohesiveness

0 Sand Non-plastic Non-cohesive

<7 Silt Low plastic Partly cohesive

7-17 Silt clay Medium plastic Cohesive

>17 Clay High plastic Cohesive

Table.3.2. Plasticity Index

The finer the particles of the soil, the greater are the amount of shrinkage. the value of shrinkage limit is used for understanding the swelling and shrinkage properties of cohesive soils. The plasticity index of the soil in the study area varies from 4-9. So they belongs to low plastic and medium plastic soil. So they are essentially silt to silty clay type of soil.

SPECIFIC GRAVITY Specific gravity of soil solids is the ratio of the weight in air of a given volume of dry soil solids to the weight of an equal volume of distilled water. The term specific gravity of soil actually refers to the specific gravity of the solid matter of the soil, which is designated Gs. A soil’s specific gravity largely depends on the density of the minerals making up the individual soil particles. It is an important index property of soils that is closely linked with mineralogy or chemical composition and also reflects the history of weathering. It is relatively important as far as the qualitative behavior of the soil is concerned and useful in soil mineral classification, for example iron minerals have a larger value of specific gravity than silicas. It gives an idea about suitability of the soil as a construction material; higher value of specific gravity gives more strength for roads and foundations. It is also used in calculation of void ratio, porosity, degree of saturation and other soil parameters. Higher the specific gravity, higher will be the load carrying capacity of soils. (Table.3.3)

Table.3.3. SPECIFIC GRAVITY The specific gravity of samples studied varies from 2.67 to 2.73. So three samples with specific gravity less than 2.7 are silty sand while those with 2.71-2.73 contain inorganic clays.

BULK DENSITY Bulk Density reflects the soil’s ability to function for structural support, water and solute movement, and soil aeration. High bulk density is an indicator of low soil porosity and soil compaction. It may cause restrictions to root growth, and poor movement of air and water through the soil. Compaction can result in shallow plant rooting and poor plant growth, influencing crop yield and reducing vegetative cover available to protect soil from erosion. By reducing water infiltration into the soil, compaction can lead to increased runoff and erosion from sloping land or waterlogged soils in flatter areas. In general, some soil compaction to restrict water movement through the soil profile is beneficial under arid conditions, but under humid conditions compaction decreases yields. (Table.3.4.)

Soil Texture Ideal bulk densities for Bulk densities that restrict plant growth (g/cm3) root growth (g/cm3)

Sandy <1.60 >1.80

Silty <1.40 >1.65

Clayey <1.10 >1.47

Table.3.4. BULK DENSITY

Bulk density of the samples studied from 1.496 to 1.661. Presence of silt and fraction is evident from the bulk density values

MOISTURE CONTENT The soil moisture content of soil is the quantity of water it contains. Moisture may be present as adsorbed moisture at internal surfaces and as capillary condensed water in small pores. Moisture may be present as adsorbed moisture at internal surfaces and as capillary condensed water in small pores. At low relative humidity’s, moisture consists mainly of adsorbed water. At higher relative humidity’s, liquid water becomes more and more important, depending on the pore size. The higher moisture content of the soil can result in the higher chances of slope failures.

PARTICLE SIZE DISTRIBUTION The percentage of different sizes of soil particles is determined by sieve analysis. It gives an idea regarding the gradation of the soil i.e. it is possible to identify whether a soil is well graded or poorly graded. The particle size also helps to identify the amount of different soil particles present in the soil, usually the very fine particles of soil tend to get easily eroded by water, the behavior of soil to particular situations like rains also is affected by the particle size distribution of the soil. The sieve analysis uses different sieves to classify soil particles into gravel, sand, clay and silt based on their size range. Information obtained from particle-size analysis can be used to predict soil-water movement

Two samples from Cheratukuzhy area have high values of silt and clay fractions (combined) 58.5 & 61.90%, while rest of the samples have low clay content varying from 25.3 to 36.3%. The low clay content soil contains relatively higher percentage of sand and gravel. The presence of coarser gains in soil increases the permeability of the soil making them more prone to landslides. This is further evident from the plasticity index and bulk density values.

CHAPTER 4

LANDSLIDE HAZARD ZONATION MAPPING

Landslide hazard zone is commonly shown on maps, which display the spatial distribution of hazard classes (Landslide Hazard Zonation). Landslide hazard zonation refers to “the division of the land in homogeneous areas or domains and their ranking according to degrees of actual / potential hazard caused by mass movement”. Landslide failures have caused untold number of causalities and huge economic losses. In many countries, economic losses due to landslides are great and apparently are growing as development expands into unstable hillside areas under the pressure of expanding populations. In spite of improvements in recognition, prediction, and mitigation measures, worldwide landslide activity is increasing. The factors causing this expected augmented activity are • Increased urbanization and development in landslide prone areas. • Continued deforestation of landslide prone areas • Increased regional precipitation caused by changing climate patterns. At least 90% of landslide losses can be avoidable if the problem is recognized before the development or deforestation begins. Hence, there is a big need for identification of existing and potential unstable slopes.

HAZARD, VULNERABILITY AND RISK It is important to distinguish between the terms disaster and hazard. A potentially damaging phenomenon (hazard), such as earthquake, landslide by itself is not considered a disaster when it occurs in uninhabited areas. It is called a disaster when it occurs in a densely populated area, and results in a large destruction.

NATURAL HAZARD (H): the probability of occurrence of a potentially damaging phenomenon within a specified period of time and within a given area.

VULNERABILITY (V): the degree of loss to a given element or set of element at risk resulting from the occurrence of a natural phenomenon of a given magnitude. It is expressed on a scale from 0 (no damage) to 1 (total loss).

SPECIFIC RISK (RS): the expected degree of loss due to a particular natural phenomenon. It may be expressed by the product of H and V.

ELEMENT AT RISK (E): the population, properties, economic activities, including public service, etc., at risk in a given area.

TOTAL RISK (RT): the expected number of lives lost, persons injured, damage to property, or disruption of economic activity due to a particular natural phenomenon. It is therefore the product of specific risk (Rs) and elements at risk (E) gives the total risk as given in equation

EVALUATION FACTORS When assessing the probability of land sliding within a specified recognition of the conditions that caused the slope to become unstable and the processes that triggered the movement is of primary importance. If is well known that many factors play an important role in creating slope failure, the thematic inputs which determine the probability of land sliding for a particular slope or an area may be grouped into two categories called the preparatory factors and the triggered factors The preparatory factors, which make the slope susceptible to failure without actually initiating it and there by tending to place the slope in a marginally stable state, such as geology, structures, slope and aspect, relative relief, geomorphology, soil, The triggering factors shift the slope from a marginally stable to an unstable state and thereby initiating failure in an area of given susceptibility, such as heavy rainfall and earthquake.

SLOPE The topographical parameters like slope, aspect and relative relief play a significant role in landslide. Slope maps define slope categories on the basis of the frequency of particular angles of slope. The distribution of the slope categories is dependent on the geomorphologic history of the area. The angle of slope of each unit is a reflection of a series of localized processes and controls, which has been imposed on the facet. It is observed that slope greater than 25° is significant for the landslide.

ASPECT Aspect identifies the down-slope direction of the maximum rate of change in value from each Cell to its neighbors. (Aspect can be thought of as the slope direction). The values of the Output raster will be the compass direction of the aspect.

LANDUSE AND LAND COVER The present day land use has an important bearing for landslide hazard zonation and mitigation measures. Land cover is an indirect indication of the stability of hill slopes. Barren and sparsely vegetated areas show faster erosion and greater instability as compared to reserve or protected forests, which are thickly vegetated and generally less prone to mass wasting processes. Forest cover, in general, smothers the action of climatic agents on the climatic agents on the slopes and protects them from the effects of weathering and erosion. A well-spread root system increases the shearing resistance of slope material. Agriculture, in general, is practiced on low to very low slopes, though moderately steep slopes are not spared at places. However, the agricultural lands represent areas of repeated water charging for cultivation purposes and as such may be considered stable. Satellite data has the capability to directly record these features from the ground. The different density of vegetation, the rocky exposures, agricultural lands etc is mapped from the high resolution satellite data.

STRUCTURE The geological structure plays a crucial role for landslides. Geological structures play a major role in the occurrence of landslides. Bedding planes, joints, foliations, faults and thrusts are the discontinuities associated with the incite rocks over hill slopes. These structural discontinuities in relation to the slope inclination have greater influence on slope instability Hence, lineaments and faults in general, are considered as significant geological structures for landslide hazard zonation.

HYDROGEOLOGICAL CONDITIONS The presence of streams, rivers, underground water, saturation state of rocks/soils, and drainage pattern control the hydrological properties of an area and play a vital role in slope failure. In hilly terrain, the groundwater flow is irregular along structural discontinuities of rocks. Presence of water generally decreases shear strength of slope forming material and increases the probability of slope failure.

GEOMORPHOLOGY Geomorphology depicts the present morphological set-up. This is very important since some of the important geomorphic elements give us a clue for the future landslide in that area. The Dissection pattern of hills likes the highly dissected hill, moderately and low dissected hills helps in understanding the denudation chronology of the area. The role of denudation process in the landslide is very well known. The toe cutting by the river is important denudation process, which triggers landslide.

TRIGGERING FACTORS In addition to inherent causative factors, external factors like periodic seismic shocks, heavy rainfall and anthropogenic activities are triggering the landslides. Stable existing slope conditions get disturbed or become unstable if it falls in higher seismic zones and may lead to the landslide phenomenon. Likewise, zones of high annual rainfall are problematic due to sudden increase in pore water pressure in slope after a heavy rainfall. Mudslides, debris flow always get associated with high instantaneous rainfall. When considering landslides in Kerala rainfall comes in the first place for triggering landslides than seismicity.

USES OF LANDSLIDE HAZARD ZONATION The Landslide hazard zonation maps have multi uses, some of which are listed below. • The landslide hazard zonation maps identify and delineate unstable hazard-prone areas, so that environmental regeneration programs can be initiated adopting suitable mitigation measures. • These maps help planners to choose favorable locations for sitting development schemes such as townships, dams, roads and other developments. • Providing general awareness to local people about the vulnerable regions so as to reduce loss of human life • General purpose master plans and land use plans. • Discouraging new development in hazard prone areas. • Choice of optimum activity pattern based on risk zones. • Discouraging anthropogenic triggering factors in high hazard zones, like quarrying blasting etc. • Quick decision making in rescue and relief operations. Even if the hazardous areas cannot be avoided altogether, their recognition in the initial stages of planning may help to adopt suitable precautionary measures, and there by create strategies for the mitigation of the disaster and also reduce the overall loss that might occur due to the event. Hazard zonation map forms the base of all types of disaster management programs.

ASSUMPTION FOR LANDSLIDE HAZARD ZONATION Landslide Hazard Zonation has been actively pursued for the last two decades and various methodologies are still being refined. Varnes (1984) has outlined three assumptions that form the basis of landslide hazard zonation.

• It is considered that future slope failures are most likely to occur in geologic, geomorphologic and hydrologic situations that have led to past failures. • In a given study area the factors that cause landslides can be rated or weighted. • If conditions that promote instability can be identified, it is often possible to estimate their relative contribution and assign them some spatial quantitative index.

Thus, the degree of potential hazard in the area can be estimated depending on the number of failure inducing factors present in a given locality.

CHAPTER 5

LANDSLIDE HAZARD ZONATION OF KOTTAKUNNU AREA

Different factors are used to prepare the landslide zonation map of the study area.

SLOPE The slope is the degree of steepness of a terrain. The slope is classified here into seven different classes 0-1º, 1-3º, 3-5º, 5-10º, 10-15º, 15-25º, >25º.(Figure 5.1) The slope was extracted from DEM created form contour using GIS surface tool. Slope plays an important role in determining the landslide in an area most slides occur within the range of 25-40º.The steep slopes are a one of the important factor for causing landslides, in the study area the north western slope has the maximum slope. (Table5.1) (Figure.5.2)

SLOPE ( In degrees) AREA ( In Acres )

0 to 1 ( flat to nearly level ) 12

1 to 3 ( very gently sloping ) 53

3 to 5 (Gentle sloping ) 57

5 to 10 ( Moderately sloping ) 48

10 to 15 ( Strongly sloping ) 33

15 to 25 (Moderately steep to steep ) 15

>25º (Steep ) 3.7

Table.5.1. Slope Classification

Figure.5.1 Slope Classification

Fig 5.2. Slope Map

ASPECT Aspect is the slope orientation with respect to north. Aspect map of the area was prepared using DEM and was divided into nine classes namely, flat (-1), north (0° – 22.5° and 337.5°-360°), northeast (22.5°-67.5°), east (67.5°-112.5°), southeast (112.5°-157.5°), south (157.5°-202.5°), southwest (202.5°- 247.5°), west (247.5°-292.5°) and northwest (292.5°-337.5°).

Aspect (slope orientation) affects the exposure to sunlight, wind and precipitation thereby indirectly affecting other factors that contribute to landslides such as soil moisture, vegetation cover and soil thickness. Here the first landslide took place in the Western slope and the second one near Cheratukuzhy was in Northwestern Slope.(Figure5.3)

Figure.5.3. Aspect Map

ROAD NETWORK Unscientific Modification of slope, in which road plays a crucial role, is considered as the major cause of most of the landslides. The road map was made using the data obtained from Google earth and field survey and tools in GIS. The main roads in the study area are

• Cherattukuzhy Road • Kottakunnu Road • Chola Road • Manjery Road And an unmetalled road. (Figure.5.4.)

Figure.5.4. Road Map

ROAD BUFFER Road buffer is an important factor in analysis of the property damage caused by landslides. The unmetalled road constructed recently creates major problems for the region. Buffer distance is used to determine the distance from the road. Buffer distance used was 5m, 10m.15m. (Figure.5.5)

Figure.5.5. Road Buffer Map

GEOLOGY (LITHOLOGY)

The lithology of an area has a greater influence on the stability of its slopes. The nature of the rock including its vulnerability to weathering process, structural control (joints, fractures etc), porosity and permeability are the major factors of slope failure. The main rock type found in the region was charnockite. As only one rock type is found it cannot be used as an evaluation factor for the zonation mapping. Geologic structures like joints were also not seen exposed for evaluation.

DRAINAGE DENSITY Rivers and its distributaries mainly carry out the natural method of landscaping of a region in Western Ghats. The running water is a very important geological agent in effecting transportation of the weathering product from an elevated area to lowland area. Therefore it is necessary to evaluate the drainage characteristics of the terrain. An understanding of the drainage network helps us to learn how this factor involved in land degradation. The initial fingertip tributaries are called the first order streams when two first order streams join a second order stream and two second order stream join to form a third order and so on. The number, length, gradient etc of streams can be evaluated in terms of total drainage density. Drainage density is defined as the ratio of the total length of streams to the total area. High drainage densities are indicative of impervious strata, high rainfall, and little vegetation and active stream incision all of which may be associated with mass movement. But in the high density expected regions of Kottakunnu the amount of water was found to be very less than the obtained value, this suggest that the natural drainages which drained water to these regions had been blocked and would have infiltrated to the slopes.(Figure 5.7.) Probably, this condition causes high pore pressure from surface down and also creates differential pressure gradient between the top weathered zone and bed rock and reduction in shear strength of the top material. Therefore, heavy precipitation creates a zone of high pore pressure in the weathered zone or in the thick soil cover above the sound bed rock that results in slope failures. (Table.5.2) (Figure.5.6).

DRAINAGE DENSITY AREA ( In Acres )

HIGH 98

MEDIUM 115

LOW 10 Table.5.2. Classification of drainage distribution

Figure.5.6. Classification of drainage distribution

Figure 5.7. Drainage density Map

PLAN AND PROFILE CURVATURE Curvature is the second derivative of a surface, or the slope of the slope. It is the curve in the slope surface. Curvature is mainly classified into two Profile curvature and Plan curvature. Profile curvature is parallel to the direction of the maximum slope. The negative value (Figure 5.8 A) of the profile curvature represents the convex upward surface. The positive profile (Figure.5.8 B) value represents concave upward surface. Zero value represents linear surface (Figure.5.8.C) Profile curvature influences the acceleration and/or deceleration of flow across the surface. (Figure.5.10)

Figure.5.8.Profile Curvature

Plan form curvature (commonly called plan curvature) is perpendicular to the direction of the maximum slope. The positive value (Figure.5.9.A) represents sideward convex surface. A negative plan (Figure.5.9.B) represents sideward concave surface. Zero value represents linear surface (Figure.5.9.C.) Profile curvature relates to the convergence and divergence of flow across a surface.(Figure.5.11) Curvature maps were prepared using GIS software.

Figure.5.9.Plan Curvature

Figure.5.10. Profile Curvature Map

Figure.5.11. Plan Curvature Map

Both profile and plan curvatures affect the susceptibility to landslides. Profile curvature affects the driving and resisting stresses within a landslide in the direction of motion. Plan curvature controls the convergence or divergence of landslide material and water in the direction of landslide motion. The sign of the curvature value is important for determining concavity or convexity of the curve. In both profile and plan curvature maps, concave and convex surfaces are represented by the respective negative and positive values. Based on the plan curvature hill-slopes can be subdivided into hollows, noses and relatively planar regions. Hollows are regions in which the plan curvature of the contours is concave in the down slope direction and where surface water would converge as it moves down slope. Noses or coves are regions where the plan curvature of the contours is convex in the down slope direction and the surface water will diverge. Relatively planar regions have plan curvature values around zero. Hollows concentrate groundwater and the concentration of groundwater probably leads to increased landslide activity.

SOIL DEPTH/THICKNESS It is the measure of thickness of unconsolidated or weathered soil above the hard rock.. It is observed that the thickness is one among the major contributor of slope failures throughout the study area. The measurement was taken from the surface to the contact between soil and hard rock during the field study. The data was obtained by field study about 20 locations were taken for the data the contact zone between hard rock and overburden was found mainly from the wells and was processed using the interpolation techniques in GIS. Soil depth is a very important factor which controls landslide. When the thickness of soil is low it indicates a very poorly formed soil profile and also high infiltration. The chances for slides at these sites are very high. In the first landslide location of Kottakunnu the soil thickness was found to be very low, in certain places near the crown it was found to be less than a meter. When the natural drainage at this region is blocked, the water easily infiltrates through this thin layer of soil to the weathered rock horizon. As the water cannot move downwards due to the impervious layer it gets accumulated there increasing the pore pressure and providing an upward buoyant force. This upward force can finally cause slope failures. The weathered rock fragments.(Figure.5.12) which are found abundant in the first landslide debris point out to such a type of slope failure.(Figure.5.13)

Figure.5.12 Weathered Rock fragments at landslide location 1

Figure.5.13. Soil Depth Map

ollur

NORMALIZED DIFFERENCE VEGETATION INDEX (NDVI) The most important biophysical indicator to landslide is the vegetation cover. The normalized difference vegetation index (NDVI) is a measure of the amount of greenvegetation cover on the surface. The formula can be expressed as: NDVI = (NIR – red) / (NIR + red) The formula suggests that the difference in spectral reflectance between Near Infrared (NIR) and red gives the vegetation index. NDVI values range from -1.0 to 1.0 with higher values indicating green vegetation and bare soils being represented by values which are closest to 0. Water bodies show negative NDVI values NDVI values of the study area were derived from Sentinel 2 imagery acquired for the area in the month April 2019. (Figure.5.14) c=e^ ([-α NDVI/ (β - NDVI)]) ,Where, α, β are unit less parameters and it determines the shape of curve relating to Normalised Difference Vegetation Index (NDVI) and C factor. Values provided are 2 and 1. Estimated NDVI values are in the range of 0.04-0.68.

Figure.5.14. NDVI Map (Band 8) and (Band 4) of Sentinel 2 Imagery were used for extracting the Vegetation Index of the study area, since most of the study area has higher value , it indicates good vegetation cover is found

51 all over Kottakkunnu. Under normal conditions landslides are initiated at regions of lower vegetation. But at both landslide locations of Kottakunnu slides were initiated at regions with vegetation, which attributes other factors for causing slides.

TOPOGRAPHIC WETNESS INDEX (TWI) The topographic wetness index (TWI), also known as the compound topographic index (CTI), is a steady state wetness index. It is commonly used to quantify topographic control on hydrological processes. The index is a function of both the slope and the upstream contributing area per unit width orthogonal to the flow direction. The index was designed for hill slopes. Accumulation numbers in flat areas will be very large, so TWI will not be a relevant variable. (Figure.5.15).The index is highly correlated with several soil attributes such as horizon depth. Methods of computing this index differ primarily in the way the upslope contributing area is calculated. It can be calculated using formula: TWI = TWI = ln / Ø in which stands𝑎𝑎 for𝑡𝑡𝑎𝑎𝑛𝑛 catchment area and tanØfor slope gradient. TWI is associated with flow accumulation at the given terrain. It is effectively used to understand the soil moisture condition and 𝑎𝑎 other related phenomenon. TWI was computed using GIS software.(Table.5.3)(Figure5.16)

Figure.5.15. TWI Map

Figure.5.16 TWI Classification Table

TOPOGRAPHIC WETNESS INDEX AREA (In acres )

<6 24

6 to 10 90

10 to 15 95

>15 13

Table.5.3.TWI Classification

LAND USE LAND COVER Land use Land cover pattern is one of the key factor responsible for slope failures. In the study area presence and absence of vegetation is one of the important factor that decides slope stability. In the vegetated area depth to which roots of the trees are penetrating are also a factor that decides slope stability. The LULC pattern was generally classified in to following Agriculture, Built up (Cities/Town/Villages). The study area being very close to the town does not have much diversity in the land use. (Figure.5.17) There is no plantations along the slopes of Kottakuunu and apart from the western slope no change in natural vegetation pattern is observed. On the western slope in the property owned by DTPC natural vegetation of short grasses were removed and trees were planted. The large roots of these trees also might have disturbed the shallow soil in this region and caused failure. Of the total study area of 225acres about 12% i.e. 27.51acre of land forms the builtup area.

Figurer.5.17. Landuse and Landcover Map

DATA PROCESSING The Zonation map was prepared using the GIS weighted sum overlay. This process overlay several rosters using a common measurement scale and weights each according to its importance. The layers are then overlaid together based up on these weights and ranks assigned to them. And the landslide susceptibility map of the area was obtained. In the map the red colored areas mark the zones of high risk of landslides, (Figure.5.18)

Figure. 5.18.Landslide Susceptibility Map Of Kottakunnu area

Of the total study area of 225 acre.

• 9% of area falls under the high landslide prone area. (20 acres)

• 26% medium vulnerable area (57 acres)

• 37% low vulnerable area (81 acres)

• 28% stable area (60 acres). (Figure.5.19)

Some buildings are located in the high vulnerable regions of Kottakunnu. Most regions of the park come under low and stable region. But it is clear from the map that the western and northwestern slopes are highly prone to landslides (Figure.5.20)

Figure.5.19. Classification Of study Area

Landslide susceptibility maps describe the relative likelihood of future land sliding based solely on the intrinsic properties of a locale or site. The map overlaying the built up regions over the susceptible areas gives an idea for the governing bodies about the critical zones of future landslides. The medium and high zones in the map mark the regions with higher risk of landslides due to their intrinsic properties. The high risk zones are at critical equilibrium of slope failures and could be initiated with very small triggers. The medium zones are also at critical state and any future unscientific modifications in this region could change the medium zones to high risk zones. So government interventions must be done to prevent such practices in the medium and high vulnerable regions.

Figure.5.20 Buildup Overlay On Susceptibility Map of Kottakunnu