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2 1.1 Slope failures or landslides Slope failures or landslides are short lived and abruptly occurring natural hazards in sloping terrains. They can cause extraordinary landscape changes and cause severe damage to life and property. Landslides are a form of mass movement, which can be described as a rapid down slope movement of soil, sediments and rocks due to gravity. It characteristically occurs along one or more discrete bounding slip surfaces (Hutchinson, 1988). Landslides include a broad range of mechanisms whereby the material is dislodged by sliding, flowing, spreading and toppling on account of gravity (Coates, 1981 ). Periods of intense rainfall and human intervention play an important role in triggering the process. This form of mass-wasting continues to be a concern for highway engineers, administrators, planners, geologists, land-managers and local dwellers in most of the hilly or mountainous tracts around the world. 1.2 Causes of slope failures Many complex variables contribute as a whole to cause a slope failure. These variables can be grouped into two categories which are intrinsic and extrinsic. The intrinsic variables include factors inherent on the terrain while the extrinsic variables include factors which trigger or initiate a failure. The intrinsic variables are slope gradient, relative elevation of the area, lithology and mineralogical composition of the rocks, structural features like the intensity of joints, their frequency, depth, length and attitude, geotechnical properties of rocks and soils like angle of internal friction, cohesion, bulk density, grain size and clay content, drainage characteristics, climate, antecedent moisture conditions of the stratum, vegetative cover and land use patterns. The extrinsic variables include high intensity rainfall, slope height, weight of the slope material, soil erosion, deforestation, construction of heavy structures, heavy vehicular traffic and seismic events. While these intrinsic variables make slopes susceptible to failure over a period of time, the extrinsic variables trigger the failure within a short span. Technically, landslide occurs when the average shear stress, acting on the potential failure plane within an inclined mass of particulate or rock material exceed the stresses that the material along the surfaces is capable of resisting (shear strength). The resisting forces are a function of the strength of the material in shear like cohesion & angle of internal friction between the grains (Chandler, 1986). Generally, the strength of materials depends on the lithology and antecedent moisture conditions. 14

3 1.3 Classification of slope failures Even though a number of classification schemes were attempted by several authors the most accepted classification schemes takes into consideration the kind of earth material, type and rate of movement, water content of slide material, and the failure plane characteristics. The earliest widely used classification is that of Sh arp e (1938). The more recent classification of landslides are those of Hutchinson ( 1968, 1978), Zaruba and Mencl (1969, 1982), Nemcok et al. (1972), Varnes (1978, 1984) and Coates (1977, 1981). Table 1.1 and Table 1.2 shows the most commonly used schemes of classification by V ames (1978) and Coates (1977) respectively. Table 1.1 Classifications of Landslides (Varnes, 1978) Type of Movement Type of Material Bedrock Soils Coarse Fine FALLS ROCK FALL DEBRIS FALL EARTH FALL TOPPLES ROCK TOPPLE TOPPLE TOPPLE Rotational Few units SLIDES Transnational Many units LATERAL SPREAD FLOWS COMPLEX SLUMP BLOCK- SLIDE SLIDE SPREAD FLOW {deep creep) SLUMP BLOCK- SLIDE SLIDE SPREAD FLOW Soil creep Combination of two or more types SLUMP BLOCK SLIDE SLIDE SPREAD FLOW Table 1.2 Classifications of Landslides (Coates, 1977) Type Type of Movement of Slide Material Rotational Planar Bed Rock Rock Slump Rock Slide Increasing Block Slide Rock coherence Flow (increasing Speed->) Rock avalanche Fall Rock fall Regolith Earth Slump Debris slide Soil fall Sediments Sediment Slump Loess Sand flow flow Sediment fall (increasing sediment size>) 1.4 Slope failures in the Indian context Among the natural hazards, earthquakes, slope failures, floods and cyclones are the major disasters affecting the Indian sub-continent. The destructive impact of landslides on 15

4 people and their economic conditions are direct, and many fold, particularly in the mountainous regions of Himalayas and Western Ghats. The tropical climate, unstable land forms, deforestation and unplanned developmental activities make the hilly areas prone to landslides. Evaluation of the physiography of the Indian sub-continent shows four hilly regions that have all the innate characteristics favorable for slope failures. The four hilly regions are 1. Western Himalayas (Utter Pradesh, Himachal Pradesh and Jammu & Kashmir) 2. Eastern and NE Himalayas (West Bengal, Sikkim and Arunachal Pradesh) 3. Naga-Arakan Mountain belt (Nagaland, Manipur, Mizoram and Tripura) 4. Western Ghats including Nilgiris (Maharashtra, Goa, Karnataka, Kerala and TN The Landslide Hazard Zonation Atlas of India (Jan, 2004) presents the Geographical Information System (GIS) based landslide inventory map and landslide 0 20 SN AU81AN $U S I Fig.1.1. Geographical outline of the Western Ghats (after Tiwari, 1995) hazard zonation maps of India at the scale of 1 :6 million. This Atlas includes some of the worst landslides of India like Great Mal pa Rock Avalanche of 1998, the Alaknanda Tragedy of 1970 and Amboori landslide of Kerala of It is estimated that about 15% of the land area of Indian subcontinent poses terrain conditions favorable for generation of mass movements (Rao, 1989). The Himalaya mountain belts are comprised of tectonically unstable younger sedimentary rocks and are subject to severe seismic activity. This enhances the vulnerability of slopes and generation of massive slides in the Himalayas. Here the overburden along with the underlying lithology is displaced. Since the Western Ghats and Nilgiris are geologically stable and have uplifted plateau margins influenced by neo- tectonic activity, the slope failures are generally confined to the overburden without affecting the stable Precambrian rocks underneath, with rock falls along the cliff sections due to anthropogenic influence. 16

5 Situated in a humid and tropical climatic region the Western Ghats profoundly influences the regional climate on its eastern and western sides. The western slopes and plains receive an annual rainfall between mm, where as the eastern slopes getting between mm, represents a rain shadow region. The northern region of the western slopes enjoys very heavy precipitation for 3 to 4 months during the south-west monsoon with a clear dry spell for 6 to 7 months. In the extreme south, the rainfall is well distributed for a period of 7 to 8 months both by the south-west and north-east monsoons The Western Ghats or the Sahyadris run parallel to the Lakshadweep Sea constitutes a chain of hills and mountain ranges from the river Tapti in the north to Kanyakumari in the south for about 1600 km. The geographical outline of the Western Ghats (after Tiwari. 1995) is shown in Figure 1.1. The western slope is steep and usually terraced resembling stairs or steps (Ghats) from which it has acquired the name, Ghats (Pascoe. 1950). Anamudi the highest peak in Western Ghats is located in Kerala in the district of Idukki, has an elevation of 2694 meters. Slope failures along the Western Ghats of India have been studied by many. Vijith and Madhu (2008) assessed the susceptibility of landslides in paiis of Western Ghats, of Kerala using a geographical information system (GIS). Sharda (2008), Ganapathy et al., (2010), Iswar Das et al., (2010) and Pankaj et al., (2011) classified landslides into classes based on the landslide type, volume, scar depth, and run-out distance and a zonation map for landslide hazard for has been attempted based on Landslide Susceptibility Index (LSI) considering factors like lithology, slope angle, distance from major thrust/faults, landuse pattern and drainage density in relation to frequency of existing landslides. 1.5 Literature review on slope failures in the Kerala The Western Ghats of Kerala are highly fragile and are under repeated threats of landslides. Kerala is a narrow strip of land, of which 47% is occupied by the most prominent orographic feature of peninsular India - the Western Ghats. Every year with the onset of monsoon reports pour in from almost all the highland districts, about 'slope failures', 'landslides' and 'Urulpottal'. The characteristic pattern of this phenomenon is the swift and sudden down-slope movement of highly saturated overburden containing a variety of 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. In Malayalam. this phenomenon is known as 'Urulpottal'. Several workers have investigated occurrences of landslides in the Idukki district over the past few decades. The reported occurrences form only a part of the actual 17

6 incidences. The incidences are normally investigated upon and reported only when it affects the local inhabitants in the form of losses to life and property. Much of the mass movements taking place in the forest land causing irreversible damage to the forest environment goes unnoticed and hence is not documented. Seshagiri et al., (1982) carried out the first landslide hazard zonation of a segment of the Nilgiri plateau. The work clearly indicates that the multiple slides recorded in the high sloping areas fringing the Nilgiri plateau are of the type described as debris flows affecting the cover material on the slopes. The event was triggered by the high intensity rains over saturating the cover material. Krishnanath et al., (1985, 1993, 1996), Krishnanath and Sreekumar (1996), Sreekumar (1998), Sreekumar and Krishnanath (2000) studied a number of profiles along the communication arteries and river channels within Idukki and Pathanamthitta districts and identified a number of profiles which are at the geotechnical threshold. Kandaswamy et al., (1985) recorded mass movements in the district of Wayanad in Kerala within Kabani basin at Thariode and Brahmagiri in 1960, Chembara peak estate in 1980 and found that the unfavorable geologic conditions, such as thick lateritic cover, tampering of the natural drainage network, large scale deforestation and intense rainfall close to the divide within the first order sub basin, were the causes for the massmovements. Sankar ( 1991) described the rock fall in Chengodumala, Kozhikode district, along a steep slope of +25 and stated that deforestation leading to removal of vegetative cover contributing to the absence of root bolting had resulted in the major rock fall. In 1992 a landslide occurred in Elichiavali village of Palakkad district which is located in the low level terraces of Bhavani river. Officers of Geological Survey of India reports that 317 mm ofrain fall took place between 12th and 18th of November, 1992 and debris material from middle slope area moved down along a tributary breaching the flanks up to its confluence with Bhavani river affecting two housing colonies. The investigators suggested stream training measures as long term mitigatory measure. Thampi et al., (1992) reports land disturbances in the form of landslides and subsidence due to piping from the Palakayam area of Manarghat taluk of Palghat district. The mud flow of Bison Valley village of Idukki district had initiated at a height of 1100 meter on a slope of+ 30. Thampi et al., (1994, 1995) envisaged this as the result of anthropogenic activities resulting in the artificial steepening of the slopes and withdrawal of the toe support resulting in slumping and sliding of the upper hard laterite as blocks. The Center for Water Resource Development and Management studied the instability patterns of the communication arteries in the Lakkidi area of Kozhikode district 18

7 and suggested surface drainage corrections and structural measures like buttressing as mitigatory measures to prevent failure along the road sections (Narashima Prasad et al., 1995). The natural disaster that had occurred in 1984 at Mananthavady, Mundakai, Meppadi and Vaithiri of Wayanad districts, was the result of the regionally unfavorable geologic structural trends together with the complementary high monsoon rainfall causing localized infiltration resulting in high pore-water pressure within the overburden material (Muraleedharan, 1995). Thampi et al., (1994, 1995) reported landslide occurrences in the flat topped, porous vesicular laterite crested hills (slope +20 ) that stand out as Mesas on the sandy costal tracts at Ezhom and Cherukunnu panchayats of Kannur district. Earnest et al., (1995) had studied the landslides that occurred at the Kallumala area of Attappady block in Palakkad district during the monsoons and predicted the ground water movement as the triggering mechanism. Biju Abraham et.al (1996) studied the lithological and structural properties of the rocks with differing moisture contents and mineralogy along the Thodupuzha-Munnar road and concluded that the percolating water acts as a triggering force for the onset of mass wasting. Massive slides in the sub-catchment of Chaliyarpuzha, near Kodaranji in Koilandi taluk of Calicut district during July 1991 claimed four human lives. The slopes are very steep and under cultivation of seasonal crops warranting severe tilling of ground. The steep slopes are meticulously contour bunded blocking all small seasonal drainage channels. The blockage of drainage channels during rains caused over saturation of the overburden on steep slopes resulting in debris flows. Thampi et al., (1997) reports similar failures caused by blockage of surface drainage on high-sloping terrain from Kurachundu in Calicut district during October It may be noted here that the cause attributed to both of the above failures are the saturation of the overburden caused by practices of improper landuse adopted on high-slope terrains. Sreekumar (1998) developed a landslide hazard zonation map along Kottayam Kumili road. He studied the chemical and mineralogical variations along lateritic slopes indicating extreme interactive complexity of these processes resulting in the heterogeneity of the weathering profiles. Land disturbances in the form of debris flows, debris topple and mud slides had occurred in parts of Chittar and Sitatodu Panchayats of Pathanamthitta district. Severely affected localities include Kochukoikkal, Mundampara, Seethakuzhi and Munnukallu in Sitatodu panchayat and Minkuzhi in Chittar panchayat on 13th July,

8 In a study on the environmental set up of the Neyyar Catchment Area in Trivandrum district Suresh Babu et al., (2000) describes seven slope failures happening within 120 Sq. kms. of uninhabited forest area. High gradient, thick overburden, deterioration of natural vegetation along with high precipitation was identified as the causative factors. Apart from these soil creep in the interjunction zone of slopes and valley floor is a common feature noted within the N eyyar wild life sanctuary area. A devastating landslide occurred on August 2004 in the Nittukotta Mala near Pasukadavu in the Marudhonkara Panchayat of Calicut district claiming ten human lives apart from damaging agricultural fields. Field studies indicate that the slope modification and drainage diversion were responsible for the failure (Sankar and John Mathai, 2004). Many recent landslides like the Amboori slide of 2001 in Trivandrum district which claimed 39 lives and almost all the slide occurrences in Munnar area during 2005 and series of small incidences in Vadakara, Koilandi and Kuttiyadi during 2005 are due to human interference in the form of recent developmental activities without any consideration of the fragility of the terrain. Thampi (2006) while attempting a regional zonation of Western Ghats based on geomorphology found that an area of approximately 1500 sq. kms falling within the highland region of Kerala is likely to be landslide prone and suggests that it needs detailed studies to identify the critical zones. 180 slides were recorded from the upper catchment area of Minachil and Manimala rivers. A landslide Hazard Zonation of this area was attempted based on the characteristics of these slides. In high sloping areas (>20 slope) the construction of contour bunds across natural hollows often disrupts the natural drainage and triggers debris flows. Apart from the debris flow that is prevalent in the Western Ghats landslides also happen in the midland and coastal region mainly due to the engineering practices without any consideration for the geological and hydro geological set up of the terrain. The extensive landslides along the Trivandrum - Kanyakumari railway line in 1997 which had resulted in closing of this line for a long period is an excellent example (Thampi, 2006). In regions where landslide investigation is a young discipline, the analysis of historical documents can provide important information about the type and the temporal and spatial distribution of landslide events (Devoli et al. 2007). A detailed description of the history and chorology of landslide prone areas of the state is given by Kuriakose et al., (2009). Sreekumar and Aslam (2010) states that structural features, slope conditions, anthropogenic and climatic factors play a key role in slope failures of Western Ghats in Idukki district. 20

9 A study by CESS reveals that 1848 km 2 or % of Kerala is under high landslide hazard category and 3759 km 2 or 9.77% under low hazard category. Devikulam, Vythiri, Nilambur, Mannarkad and Ranni are the most landslide prone taluks in the state. It states that Sq.Km or 8.9% of land area in Idukki district is prone to high landslide hazard risk and Sq.Km or 20.02% of land area as low land slide hazard risk area (CESS, 2010). Table 1.3 gives the details the locality, date of occurrence, type of failures and the extent of reported damage due to landslides in the Kerala region of Western Ghats from 1958 to 2010 reported by the news media. Sreekumar and Arish Aslam (2011) concluded that 17.30% of grama panchayat of Devikulam, Munnar, Elappara, Peruvandanam, Kumili and Kakkayar comes under critical and highly unstable categories based on micro zonation using landslide susceptibility index. SI. No. Table 1.3 Details of landslides occurrences in the Kerala region of Western Ghats Locality Date of Occurrence Type of Failure Reported Damage I Todupuzha, Arakkulam, Erumeli, Rock slide & debris 24 persons killed, Thousands of houses 2, Aug,1958, ldukki Ost. flow washed away 2 Moozhiyar 20, July 1968 Debris flow Destroyed the Sabarigiri hydroelectric project area 3 Kattippara, Idukki Ost. 1st & I Ith July 1968 Debris flow 2 children died 4 Adimali, Idukki Ost. July 26, 1974 Rocks & Debris 33 persons killed a lot of wild elephants Slide & animals were killed Kodancheri - Eeramthodu of Calicut 5 Ost. July 27, 1974 Debris flow 3 died 6 40 places in Anakkampayal, Calicut Rock slides & Total wreckage of the agrarian July 28, 1974 Ost. Debris flow economy 7 ValiakaYu - Mathaichira & Pattikkadu, Debris & rock July 25, 1976 Trichur Ost. slides 16 persons of two family killed 8 Anakkampayal, Calicut Ost. July 12, 1978 Debris flow 4 members of a family killed 9 Ootty, Nilgiri hills Dec O 4, 1978 Debris flow 75 persons killed IO Valara, Idukki Ost. July 1976 Rock falls 4 persons were killed II Adimali, Idukki Ost. Nov 03, 1977 Soil slip IO killed underneath 12 Kumali, Kollam - Pattada area July 14, 1983 Soil and Debris Slip 2 children killed 13 Puthuppady,Waynad Ost. June 15, 1984 Debris flow 8 persons killed Debris & rock 15 persons killed, devastated 70 acres slides ofland 15 Koompanpara, Muthuvankudi, Rock slide & 30 persons killed 26,27 June 1985 Keerithodu, Arakkulam, Idukki Ost. Debris Flow Acres of land destroyed 16 Kalpetta - 9th Hairpin bend at Wayanad Ghat road July 14, 1984 Rock slide Traffic obstruction for two weeks 17 Vimalagiri - Tadianpadu road, Rock slide & complete destruction of road & Panamkutty, Adimali, Keerithodu, Aug 18, 1986 Debris flow agricultural land Idukki Ost. 14 Mundakkal, Waynad Ost. July 01, Thakarappadi road, Wayanad Ost. June 23, 1986 Rock mass slide complete destruction of the road 19 Kalpetta - 9th Hairpin bend at Wayanad Ghats road Sept 25, 1986 Road slided road destroyed 20 Umgathiri Panchayat, Vettilappara Sept 21, acres of agricultural land completely Debris flow chelakkulam mala, Malappuram Ost. destroved. 21 Kalpetta 9th Hairpin bend at Wayanad rock slided on to the road from a height Oct 07, 1987 Rock slides Ghats road of200' 22 Attappady - churam road in Wayanad Rock & debris Oct 19, 1987 Ost. Slides Loss of life and property 23 Adakkakundu, 8 km from I 00 acres ofland completely destroyed June 04, 1988 debris slide Kaliamkunnu, Malappuram Ost. 50 lakhs loss 24 Pulluppara, Idukki Ost. June 27, 1988 Debris flow 4 killed 25 Kalpetta 8th Hairpin bend at Wayanad Ghats road July 19, 1988 Rock Slide Road completely blocked for 2 days 26 Kodancheri taluk July 20, 1988 Debris flow 200 acres of land lost 21

10 27 Ambukutti, Sultan battery July 20, 1988 Rock slide Rs I cores loss A side of mountain slided down 28 Poovaranthodu, Calicut Dst. July 19, Rock & Debris 1988 Bridge linking Kodancheri - Mullupara slide was washed off 29 Karuvarakundu, Malappuram Dst. Aug 23, 1988 Debris flow 150 acres ofland destroyed 30 Koorkunnu, near Kanjirapuzha dam, Sept 14, 1988 Debris & Rock Palghat Dst. slide 3 killed 31 Asramam area, nr. Mulamattom Power house, ldukki Dst. Sept 14, 1988 Debris flow IOO's of houses destroyed 32 Irumbakamchola, Trichur Dst. Sept 14, 1988 Debris flow 3 killed, 31 houses damaged Koompanpara, ldukki Dst. July 27, 1989 Rock slide 9 killed, a house humed, acres of land destroyed Nadukanimala, Mulamattom, ldukki ROCK & Debris Dst. July 28, 1989 Slide 9 killed Todupuzha & Minachil Taluks, ldukki 35 19th & 20th Sept 25 landslides & Dst rock slips 50 houses damaged Ramapuram, Palai Sept 29, landslides in a Road wounding the hill vanished single night without a trace Kurachundu, Calicut Dst. June 26, 1990 Debris flow 38 Umakkunnu, Quilon Dst. June 25, 1990 Debris flow 39 Thakarappadi, in Tamarasseri Ghat Rock & Landslip June 26, 1990 road, Waynad Ost. Loss of property 40 Mangakkadavu & Kandalad hills in Landslides and Kodaranji Nayadumpullu road was June 08, 1991 Calicut Ost. debris flow destroyed 41 Kodaranji- in Koilandi, Kozhikode 4 deaths July 01, 1991 Debris flow Dst. Kodikutti & Ettadu near Mulamattom Debris & Rock 30 acres of flourishing agricultural land Oct 14, 1991 in Idukki Ost. slides lost 42 Pasukadavu, Calicut Dst. June 19, 1992 Rock slides 5 acres of land devastated 43 Kappikalam - (Padinjarethara) June 19, 1992 Rock & Debris 11 killed, accumulation of 40' height of Banasuran mala, Vaithiri taluk, Early morning flow mountain soil on the road Waynad Dst. Thakarappadi in Tamarasseri Ghat June 20, 1992 Boulder falls on to road, Waynad Dst. night the road 7 landslides occurred. Road damaged Meghamalai, in Madurai - Cumbum Landslip at 25 Nov 14, 1992 road places in the area 37 persons killed, I 00 dwellers missing. 46 Sanghili forest in TVPM Dst. Nov 15, 1992 Landslip 16 persons missing 47 Idukki Ost. Nov 15, Rock and Debris 1992 falls Many roads damaged 48 Karuvarakundu, Malappuram Ost., Crops worth Rs 4 crore lost,35 Oct 07, 1993 Palakkayam in Palakkad Dst. Debris flow houses destroyed Adivaram, Peringalam, & Kottackal, Rock and Debris Roads & bridges destroyed. One Death Oct 08, Waynad Dst falls. I 00 slides reported 50 Marappalam near Coonoor in The Ghat road & mountain railway Boulders, and soil Nov 11, 1993 line was washed off along with vehicles Mettupalayam - Ootty Ghat road slip & structures. Melattur, Malappuram Dst. Jan 17, 1994 Debris flow One Killed 52 Bison Valley, Munnar,Idukki Dst. July 13, Debris & Rock 1994 slides 7 killed, acres ofland destroyed 53 Pallivasal near Munnar,Idukki Ost. July 13, 1994 Rock & debris Disrupted traffic in Kochi - Madurai slides NH-49 Rock & debris Disrupted traffic in Kottayam Kumili slides road 55 Chappattu, Idukki Dst. July 13, 1994 Rock & debris Disrupted traffic in Elappara - slides Kattapana Adimali,Idukki Dst. July 13, 1994 Rock & debris slides 8 houses completely destroyed Pattarpattakunnu, in Nilambur,Idukki 5 killed, Acres of high yielding July 15, 1994 Debris flow Dst. agricultural land destroyed 58 Valankollimala in Kuruvalangadu, Idukki Dst. July 15, 1994 Mountain slide Heavy rainfall Vallokmala in Tinur Village, Calicut Ost. July 29, 1994 Debris flow 100 families shifted 60 Kuttiyadi in Marudhonkara village, Calicut Ost. July 29, 1994 Debris flow Acres of agricultural land devastated 61 Pasukadavu, Calicut Dst. July 29, 1994 Debris flow Acres of high yielding agricultural land destroved 62 Akamalavaram, Paruthipara, Kallamala, Palghat July 29, 1994 Debris flow Loss of property 63 Menamkulam, Akamala,Tvm Ost. July 25,1995 Debris flow Loss of property 64 Ezhom, Kannur Dst. July 26, 1995 Debris flow Loss of property 65 Talanadu, Kottayam Dst. July 21, 1997 Debris flow Loss of property 66 Padi, Kasargod Dst. July 20, 1997 Debris flow Loss of property 67 Pazhampallichal, Idukki Ost. July 20, nos of Deep to 16 deaths blocked the NH-49 at several Shallow soil and places for I month. Bridge at NH Vandiperiyar, ldukki Dst. July 13,

11 rock slides was washed off 68 Ozhuvathadam in Devikulam Taluk, Idukki Ost. July 21, 1997 Debris flow Two death reported 69 Valara in Devikulam Taluk, ldukki Ost. July 21, 1997 Rock Slide One death reported 70 Cheeyappara in Devikulam Taluk of Idukki Dst. July 21, 1997 Debris flow One death reported Three deaths reported. Trivandrum- 71 Idichakkaplamoodu, Trivandrum Ost. Nov 15, 1998 Rock Slide Nagercoil railway line blocked by debris 72 Pamba in Pathanamthitta Ost. Jan 15, 1999 Rock Slide Twenty Five deaths reported 73 Periyanmala in Kottayam Ost. Jan 16,1999 Debris flow No death toll reported 74 Chundakkadu in Palakkad Ost. Aug 25, 2000 Debris flow One death reported 75 Udumbannoor near Thodupuzha in The dead included three members of a July 9, 2001 Debris flow Idukki district. family. 76 Mankulam in ldukki, July 9, 2001 Debris flow One person missing in a landslide at Mankulam in Idukki Todupuzha-Idukki road Minmutty, Roads and communication network July 9, 2001 Debris flow Idukki district. destroyed 78 Vandiperiyar town, Idukki Ost. July 9, 2001 Debris flow Kottayam- Kumali route blocked Udumbannoor, Venniyani Mala near Thodupuzha in Idukki Ost. July 9, 2001 Debris flow 4 people died. 80 Thrissur July 8, 2001 Debris flow 3 persons died people were killed. Four houses on Amboori, Trivandrum Nov 9, 2001 Debris Slides the upper part of the rocky 'kurisumala' Poochamukku in Neyyar dam came down 82 Munnar, Vandiperiyar & Kumili in Vehicular traffic disrupted and Idukki Ost., Erattupeta & Wagaman in Oct 07, 2003 Debris slide hours. communication network paralyzed. Kottavam district. 83 East Field Estate at Mekkad in the 600 m of a hill tract with a rubber Oct 07, 2003 Rock Slide Aryankavu in Kollam district. plantation washed away. 84 Munnar, Devikulam, Koompanpara, Ten people killed. Road traffic and Vandiperiyar, Elappara & Kuttikanam. July 24, 2004 Debris flow telecom net works destroyed., ldukki district in Kerala 85 Kottiyur in Kannur district. Aug 04, 2004 Debris flow Three members of a family including two children died. 86 Kuttiyadi in Kozhikode Ost. Aug 04, 2004 Debris flow Claimed 9 lives 87 Kulamavu in Idukki Dst. Aug 04,2004 Debris flow 5 members of a family killed when a check dam collapsed 88 Munnar in ldukki Ost. Aug 12, 2004 Debris flow 8 lives lost. 20 roads destroyed. 89 Nittukottamala in Kozhikode Aug 10,2004 Debris flow Ten Deaths reported 90 Mulliyar village, Atta Pamabu, in Kasargod district April 26, 2005 Debris flow 10 people killed and 13 injured Devikulam-Munnar Road Complex Slide persons killed. The entire Munnar 91 Munnar-Marayur and Munnar-Adimali July 25, 2005 spots in Munnar town remains inundated and cut off roads town slided. from other areas 92 Vallamthodu in Wayanad Ost. June 6, 2007 Debris flow Four Deaths reported Koodaranchu Anayodu and Two persons were dead. Extensive July 16, 2007 Debris flow Vettilappara in Malappuram district damage to crops Kairadi in Palakkad Ost. July 17, 2007 Debris flow One Death reported 95 Panakkachal in Kozhikode Dst. July 17, 2007 Debris flow One Death reported 96 Mysoorpetta in Kozhikode Dst. July 17, 2007 Slump One Death reported 97 Kavalupara in Palakkad Ost. July 17, 2007 Rotational Slide One Death reported 98 Edavanna in Malappuram Dst. July 17, 2007 Rotational Slide Two Deaths reported IOI At Nondimedu on the Ootty-Coonoor Oct 26, 2007 Debris flow Loss oflife and property NH road Udhagamandalam, Thekkalla area of Traffic was totally stopped on the June 24, 2008 Debris flow Gudalur-Kerala NH National Highway Udumbanchola taluk ofldukki district, Aug 30, 2008 Debris flow Loss of property Kerala, India. 102 Sabarimala, Pathanamthitta Ost. Sept 4, 2008 Debris flow Washed offchandranathan road. 103 Kalikavu Panchayat, Malappuram district Sept 5, 2008 Debris flow One Person dead and 15 houses were destroyed. 104 Vellamunda and Muppanad 16 July 2009 Panchayat, Wayanad Ost. Debris flow 14 landslides being reported in One person was killed 105 A fatal landslide in Puchappara, near Vellimattam, Idukki district. Oct 27,2009 Debris flow Seven people died. 23

12 106 Puthuppady, Balussery in Kozhikode district Oct 3, 2009 Debris flow damage to crops and houses Thalayad near T amarasseri in blocked Thalayad-Kakkayam road and 107 Kozhikode district, Oct 3, 2009 Mudslides destroyed 'Jalanidhi' water supply system 108 Thumpichil mala, Puchappara in ldukki district Oct27,2010 Debris Slide 3 death tolls reported 109 Vanchuvathu near Palode, Trivandrum A 20' road cut cliff slipped down into Nov 21,2010 Debris Slide district the Shenkotta road llo Vithura - Ponmudi road Nov 21, 2010 Debris Slide 13 debris slide occurrence in, NedumcU?.adu - Ponmudi road Ill Nandiyoodu, Trivandrum district Nov 21, 2010 Debris Slide Debris slide on to a house 1.6 Study area The study area forms part of the Western Ghats in Idukki district, Kerala State, and 1s located along Todupuzha- Idukki- Adimali -Munnar road (TM - road). The road comprises part of two highways namely, state highway No.33 from Todupuzha to Adimali and the national highway No.49 from Adimali to Munnar (Fig 1.2). The road is a 123 km stretch of winding course linking the town of Todupuzha through Arakkulam, Kulamavu dam, Painavu, Karimpan, Panamkutty and Adimali to Munnar, a renowned tourist destiny in Kerala. To study the factors determining the area of influence of the slopes along TM road, the adjacent areas of the road stretch are also included in the study, comprising a total area of 438 Sq.Km. The study area is located within Latitude 9 46' & 10 05'N and Longitude 76 45' & 77 05'E falling in the Survey of India topographic sheet Nos. 58 C/13, 58 C/9, 58 F/4. Idukki district was formed on 26 th January Administratively the area comes partly under Kottayam and partly under Idukki districts. The district head quarters at Painavu, finds its place in the southern part of the study area at an elevation of about 850 m above mean sea level. The district's name, 'Idukki' is derived from the Malayalam word 'Idukku' which means a narrow gorge. Periyar, the largest river of Kerala, flowing through the gorge formed between two mountains - 'Kuravanmala' (839 meters) and 'Kurathimala' (925 meters) formed the site for 'IDUKKI DAM' which is Asia's biggest Arch Dam of 555 feet height. This prestigious project of India is situated in south eastern part of the study area. Its underground Power House is located at Mulamattom which is about 19 kms from Todupuzha ( The area has all the features of a highland terrain, with its picturesque landscape of denudational hills, deeply dissected valleys and dissected plateaus. Several slope failures have been reported from this segment and hence is considered as an ideal terrain for the study of slope failures Significance of the Study With the onset of monsoon, reports pour m from different parts of the state especially from the highland districts of Kerala about slope failures/landslides causing 24

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14 severe damage to life and property especially along the slopes and communication lines in ldukki district. These recurring disastrous events warrant a detailed study on the slope stability of those areas to identify and propose suitable remedial measures that can be adopted by planners and administrators. Among all the natural hazards, slope failures are most amenable to corrective measures aimed at prevention. The present research proposes to undertake a detailed investigation of the slope stability problems along and around Todupuzha- Idukki- Adimali -Munnar road in ldukki district, Kerala. 1.8 Objectives of the Study The main objectives of this study are: 1. To identify and locate unstable slope profiles along Todupuzha- Idukki - Adimali- Munnar road in ldukki district, Kerala state, India, (TM road). 2. To identify the different types of slope failures that may occur along the TM road, by looking at their nature and reasons for failure. 3. To evaluate the geological, geotechnical, meteorological, anthropogenic and geomorphic factors responsible for past and present occurrences. 4. To define a rainfall intensity threshold value for the triggering of landslides in the study area. 5. To integrate the data on a GIS platform for assessing the terrain adjoining the TM road, in terms of its fragility and to classify the entire terrain into various stability categories based on the fragility index and to prepare a fragility index map of the study area. This evaluation will help in identifying areas which are stable and where infrastructure could be established without any threat to the terrain system. 1.9 Methodology The present study requires a multi-disciplinary approach. In order to accomplish the objectives of the study the following methodology is adopted. 1. This research work is a continuation of the project entitled 'Slope processes along river channels and communication arteries in Idukki and Pathanamthitta districts ofkerala' by Prof. R Krishnanath (1984). Hence relevant data from the project are incorporated in this study. Literature review on slope processes and past occurrences of slope failures examined through scanning the news media and existing literature for the study area and adjoining areas. Details of the locality, date of occurrence, type of failures and the extent of reported damage 26

15 due to landslides in the highland region of Kerala Western Ghats from to 2010 are collected to compare the extent of the past landslide occurrences and their localization. 2. Preparation of a base map of the study area using survey of India toposheets of 1 :50,000 scale (58 C/13, 58 C/9, 58 F/4) with field survey, to locate the palaeo as well as potential landslide occurrences in the study area. 3. Detailed geological field investigations and mapping of various profiles in TMroad for identifying potentially unstable profiles along with the preparation of a geological map of the study area. The profiles are divided into various subsectors for detailed investigations. Reconnaissance survey and scanning of slopes is conducted along predetermined transects. Details of lithology, fracture pattern, structure, general mode of failures, regolith characteristics, groundwater conditions, vegetation, height, slope and width of the road cutting along the high-way-side profile has been documented. Emphasis was given only to potentially dangerous slopes. 4. Collection of oriented block samples of cover material from the profiles for determining the geotechnical properties such as the grain size, specific gravity and the shear strength parameters such as angle of internal friction and cohesion etc. at the Engineering geology laboratory of College of Engineering, Trivandrum. 5. The rainfall data from available ram gaugmg stations m the study are statistically analyzed to indentify the influence of rainfall on slope failure and to derive a possible rainfall intensity threshold value for triggering failure. 6. Graphical analysis (Markland's projection techniques) of structural elements recorded from various profiles along the TM-road is attempted to identify the different modes of failure and their influence on slope failures. 7. Based on the structural analysis (Kinematic analysis) and geotechnical properties, estimation of factor of safety (Kinetic analysis) of the various sectors in individual profiles along the TM-road, in dry and wet conditions estimated. Based on these data preparation of a geotechnical landslide hazard zonation map of the area is prepared. 8. Geospatial analysis is attempted using various factor maps prepared on a GIS platform (scale 1 :50,000) pertaining to the study area using Survey of India topo-sheets and remote sensing. A fragility zonation study helped to integrate the thematic I factor maps to produce the fragility map of the study area.. Based on the map the fragile zones are identified and have been compared with 27

16 geotechnical hazard zonation map. A summation of all parameters generated through terrain evaluation is used to estimate. the fragility of the terrain. Data integration involves dividing the study area into square grids of dimension 1 cm. This grid is overlaid on each factor map and respective weight of each factor map is allotted for each grid and the cumulative weight value for each grid of the study area is arrived at. Based on the cumulative weight value of all factors the grids are categorized into highly fragile, fragile, moderately fragile and stable. In addition to getting an overall fragility picture of the segment the output will give the individual hot spots as far as terrain stability is concerned on a scale 1 :50,000. To calculate the overall terrain fragility of a segment the following formula is used. Overall terrain fragility of a segment = W /G, Where, G - is the total number of grids falling within the segment W - is total weight of all grids falling within the segment The hot spots or highly fragile areas are to be evaluated further for evolving mitigation strategy needed to avoid calamities during infrastructure development. 9. Based on the degree of fragility the required guidelines for future development could be formulated to maintain the road ecosystem alongtodupuzha- Idukki - Adimali - Munnar road. 28