CASE STUDY OF LAND SUBSIDENCE AT WESTERN GHATS

Visvesvaraya Technological University Belgaum, Karnataka-590014

A PROJECT REPORT ONCASE STUDY OF LAND SUBSIDENCE AT WESTERN GHATS

Submitted in partial fulfillment of the award of degree ofBACHELORE OF ENGINEERING in CIVIL ENGINEERING

By PRITHVIRAJ.K.PATIL 1DS11CV077 MEGHANA.U.K 1DS11CV050 MRUTHUNJAYA.A 1DS11CV053 SAHYADRI.H.N 1DS11CV092

Under the guidance ofDr.A.R.RAJENDRAProfessor and Examination DeanDept. of Civil Engineering,D.S.C.E

Carried out at

2014-2015DEPARTMENT OF CIVIL ENGINEERINGDAYANANDA SAGAR COLLEGE OF ENGINEERINGBANGALORE-560078

CASE STUDY OF LAND SUBSIDENCE AT WESTERN GHATS

Dayananda Sagar college of Engineering, Civil DepartmentPage 49

DAYANANDA SAGAR COLLEGE OF ENGINEERING BANGALORE-560078 DEPARTMENT OF CIVIL ENGINEERING

2014-2015 CERTIFICATEThis is to certify that the Project Work entitled CASE STUDY OF LAND SUBSIDENCE AT WESTERN GHATS is a bonafide work carried out by Prithviraj.K.Patil (1DS11CV077), Meghana.U.K (1DS11CV050), Mruthunjaya.A(1DS11CV053) and Sahyadri (1DS11CV092) in partial fulfillment of requirements for Bachelor of Civil Engineering, Visvesvaraya Technological University, Belgaum during the year 2014-2015. This Project Report satisfies the academic requirements in respect of project work (10CV85) prescribed for the award of Bachelor of Civil Engineering Degree.

Signature of Guide Signature of HOD Signature of PrincipalDr. A.R.Rajendra Dr.H.K.Ramaraju Dr.K.KaribasappaDept. of Civil EngineeringDept. of Civil Engineering Dayananda Sagar College of Engineering

Name and signature of Examiners:1.

2.

ACKNOWLEDGEMENT

Naming all the people who have helped us in achieving this goal would be impossible, yet we attempt to thank a selected few who have helped us in diverse ways.

We would like to express our immense gratitude to Dr.H.K.Ramaraju Head of the Civil Engineering Department, for his constant support, motivation and encouragement to come up with this work.

We express my warm thanks to our guide Dr.A.R.Rajendra, Professor and Dean of Examination, Department of Civil Engineering, and Dr.Ramesh, Professor, DSCE and Mr.Senthil, Senior Geologist, Geological Survey of India, Bangalore for their skillful guidance, constant supervision, timely suggestion and constructive criticism in successful completion of my seminar in time.

Finally we also take this opportunity to thank Mr.Venkatesh, Mr.Samarth, Mr Mr.Vinay and all the staff members of Department of Civil Engineering, who have rendered their whole hearted support at all the time for successful completion of the project We also express our gratitude towards the people of Basarikatte for their corporation and support in completion of this projectABSTRACT A large scale landslide and subsidence is reported at various locations of Western Ghats this occurs at the end of rainy season every year to different scales One such location is Basarikatte, in Chikmagalur District of Karnataka State, India. It is located 58 KM towards west from District headquarters Chikkamagaluru. 292 KM from State capital Bangalore Basarikatte receives high rainfall of more than 3000 mm/year Total population of Basarikatte is 1333, living in 289 houses. Total area of Basarikatte is 428 hectares Four years back a small land subsidence was observed near one of the charitable hostel with complete infrastructure, this landslide/subsidence increased subsequently over four years considerable amount of soil has moved in and moved out has reported by local people The main objective of this study is to ascertain whether it is a case of Land subsidence or landslide The reasons for land subsidence/slide To study further possibility of land dislocation Possible remedial measures A site visit was arranged (April02-04) to study the soil properties and physical properties of slope, disturbed and undisturbed soil samples were collected and tested in laboratory for various parameters Detail study was carried out in the laboratory for the soil properties which are helpful for the stability analysis, the soil slope was found to be 38o which is quite steep with the natural moisture content at the time of visit was at liquid limit (36.5%) The stability analysis was carried out and the factor of safety against failure is found to be 0.989 it is advised that the slope is bound to fail has the factor of safety against failure is close to 1.As the slope is in at unstable state dumping of soil to bridge the connectivity may accelerate slide, hence it is suggested not to dump soil They have constructed concrete retaining wall which would not prevent the sliding because the soil may flush out during rainy season because there is no retention of soil between hard rock and beam of retaining wall

CASE STUDY OF LAND SUBSIDENCE AT WESTERN GHATS

CONTENTS

Chapter 1 Introduction 08Chapter 2 Methodology 30Chapter 3 Study Area 33Chapter 4 The Problem 34Chapter 5 Observation, Conclusion and Recommendations 51

LIST OF FIGURESPlate1: Map of Western Ghats 08Plate2: Landslide Hazard Zone Mapping 27Plate3: Study Area- Basarikatte 31Plate4: Picture of shree sadguru bhraman charitable hostel, Basarikatte 35Plate5: Picture of uprooting of trees in the study area 36Plate6: Picture of destroyed house, Basarikatte 37Plate7: Picture of concrete retaining wall constructed, Basarikatte 39FigureA: Slope stability analysis for Slope 42o 40FigureB: Slope stability analysis for Slope 30o 40Figure1: Average Rainfall variation for past four years44Figure2: Annual Rainfall variation for past four years44Figure3: Monthly variation of rainfall for the year 201045Figure4: Monthly variation of rainfall for the year 201145Figure5: Monthly variation of rainfall for the year 201246Figure6: Monthly variation of rainfall for the year 201346Plate7: Lineament Map of study area 47Plate7: Geomorphology Map of study area48 Plate7: Land Use Pattern Map of study area49

LIST OF TABLESTable A: Causes of Landslide 20Table 1: Case history of Land Subsidence in other countries 29 Table2: Soil testing results38Table3: Water test results 42Table4: Rainfall data of the study area-basarikatte 43

CHAPTER: 01INTRODUCTION

Western Ghats is a chain of mountains running parallel to the West coast of Peninsular India. The range starts from the mouth of river Tapti and extends southwards up to Kanniyakumari (Cape Camorin) through the states of Gujarat, Maharashtra, Goa, Karnataka, Kerala and Tamil Nadu. The continuous chain of mountains has a major discontinuity in the Palghat gap thus separating the Nilgiris from the Anamalais. Western Ghats lie between 8 20' - 20 40' N and 73 - 77 E and is approximately 1,600 km long (Nair and Daniel, 1986) and covers an area of 1,60,000 km2 . The average elevation is around 900 m and the highest mountain peak is Anaimudi (2695m). Western Ghats lies towards the western edge of Deccan plateau and separates the plateau from the narrow coastal zone of the Arabian Sea. It is surrounded by the Arabian Sea towards the west, the arid Deccan plateau towards the east and the Vindhya-Satpura ranges in the north.

Western Ghats are characterised by conical as well as flat topped hills interspersed with valleys and spurs (Vajravelu and Vivekananthan, 1996). Along the Western side there are steep ravines and canyons and towards the eastern side there are the flat topped spurs intersected by valleys (Subramanyam and Nair, 1974). The mountain chains of Western Ghats are steep on the windward side and sloping towards the Deccan plateau on the leeward side in the state of Maharashtra whereas the range south of Palghat is sloping towards the windward side in Kerala and steep towards the leeward side in Tamil Nadu (Nayar, 1996).

The hills north of the Krishna basin (largely Maharashtra and Gujarat) are with fragile basaltic rocks. South of the Krishna basin is the region of Precambrian archean crystalline hard rock's (nearly 2000 million years old granites, schists, gneisses, quartzites, etc).

Plate1: Map of Western Ghats (Source: IIRS Publication, June 2002).Soils vary from humus rich peat in the montane areas to laterite in the lower elevation and high rainfall belts. Soils are generally acidic. The Western Ghats sector receives rains from the southwest monsoon. It rains all the year round in southern parts while in the areas in the north remain dry for 8 9 months. The average annual rainfall in the Western Ghats region is 2500 mm. Rainfall is as high as 7600 mm in localities such as Agumbe (Daniels and Vencatesan, 2008).The climate is generally warm and humid but becomes hot in summer and cold in winter months. Mean temperature ranges from 18 to 24 C, rises beyond 30 C in summer season and sometimes down up to 0 C in winter season in places of high altitudes. There are 38 east flowing and 27 west flowing major rivers in the Western Ghats. The rivers which originate in the west in the Western Ghats drain into the Arabian Sea while the three major rivers in the Western Ghats Kaveri (Cauvery), Krishna and Godavari flows eastwards into the Bay of Bengal (Murthy et al., 1996).

Champion and Seth (1968) classified the vegetation of Western Ghats into four major types:1. Moist tropical forests (Tropical evergreen forest, tropical semi evergreen forest, tropical moist deciduous forest, and littoral and swamp forests).2. Dry tropical forests (tropical dry deciduous forests, tropical thorn forests)3. Montane subtropical forests (subtropical broad leaved hill forests)4. Montane temperate forests (montane wet temperate forests)

Apart from the above mentioned vegetation types different types of vegetation occurs along the Western Ghats. This includes scrubs, sholas, montane grasslands, tropical moist deciduous forest, tropical dry deciduous forest, peat blogs, Myristica swamps, tropical evergreen forests, semi-evergreen forest and lateritic rocky plateaus.

Evergreen forests: These forests occur along the windward side at an altitude of 200- 1,500 m with 2,500 - 5,000 mm rainfall. The canopy is dense with trees which are up to 60 m high. Evergreen forests are found in the western slopes of the Western Ghats in Kerala and Karnataka (Nair and Daniel, 1986; Daniels and Vencatesan, 2008).

Semi-evergreen forests: Semi-evergreen forests occur in the Western Ghats of Maharashtra, Goa, Karnataka and Kerala within an elevation range of about 300-900m.

Moist Deciduous forests: Moist deciduous forests occur between 500 900 m. Altitudes where the rainfall is 2,500 mm to 3,500 mm. Trees are as high as 60 m but the canopies of the trees in these forests are not as dense as the ones in the evergreen forests (Nair and Daniel, 1986; Daniels and Vencatesan, 2008).

Dry Deciduous forests: Dry Deciduous forests are confined to areas with an elevational range of 300 900 m with 1000 2000 mm mean annual rainfall (Nair and Daniel, 1986; Daniels and Vencatesan, 2008).

The Sholas (Grasslands): In the Western Ghats natural grasslands are found above 1,500 m with 2500 5000 mm rainfall in Bababudangiris, Kudremukh, Nilgiris, Anaimalais, Palnis and Cardamom hill ranges. The grasslands which are also called as shrub savannas or the sholas are characterized by number of herbaceous and shrubby species mixed with grasses (Nair and Daniel, 1986; Daniels and Vencatesan, 2008).

Rocky lateritic plateaus: Undulating lateritic plateaus occur along the west coast of the Western Ghats. These harbour herbaceous vegetation. These are commonly found in the Northern and Central Western Ghats (Nair and Daniel, 1986).

Myristica swamps: These are located at the bottom of valleys which are covered with water during the greater part of the year. These are found in southernmost part of Kerala, Tamil Nadu, Karnataka and Goa. These occur up to 600 m altitude in areas with medium to high rainfall (Nair and Daniel, 1986).

Scrub forest: Scrub jungles are located in areas between 200-500 m elevation with 300-600 mm of annual rainfall. This vegetation type is dominated by short trees which are 15-20 m high (Nair and Daniel, 1986; Daniels and Vencatesan, 2008).

Savannas: Savannas are seen in areas between 1,700-1,900 m in elevation with 2500 3500 mm rainfall (Nair and Daniel, 1986; Daniels and Vencatesan, 2008). Pascal (1988) categorized Western Ghats into three regions: the Northern Western Ghats, the Central Western Ghats and the Southern Western Ghats. The geographical area of present study is restricted to the Northern Western Ghats and the Central Western Ghats (up to the political boundary of Karnataka).

Northern Western Ghats (Tapti to Goa): The northern Western Ghats are popularly known as Sahyadris. It starts from the mouth of river Tapti and extends 750 km in length up to Goa. The altitudinal range is between 300-1500 m msl excluding high crests (Karthikeyan, 1996). Along the Northern Western Ghats isolated, conical, flat-topped hills occur with steep sides which are marked with distinct striations. The major peaks in Northern Western Ghats (Sahyadris) are Kalsubai (1645m), Mahableshwar (1438m) and Harishchandragad (1424m).

The main groups of soils found along the Northern Western Ghats are high and low level laterites, red loam, medium black soil, red gravelly soils and mixed red and black soil. Medium black soils are found on flat hill tops while the valleys have deep red gravelly soils with good humus content (Karthikeyan, 1996).

The South west monsoons bring heavy rains in the Northern Western Ghats. The rainy season begins in early June and ceases off during September. The mean annual rainfall varies from 2000 - 7000 mm. The humidity is 70 - 90% during the monsoons and 10 - 30% during dry periods. The mean annual temperature varies from 20 - 24C. Mean daily temperature in the coldest months (December - January) ranges between 18 - 24C while the absolute minimum temperature is 6 - 15C in different places of Northern Western Ghats (Karthikeyan, 1996).The vegetation occurring along the Northern Western Ghats can be classified as: scrub forest, dry deciduous forest, moist deciduous forest, montane subtropical evergreen forest (Karthikeyan, 1996).

2) Central Western Ghats (South of Goa up to Palghat gap): Central Western Ghats starts from south of Goa up to the Palghat gap. However, due to logistic reasons, in the present study the area is restricted up to the political boundary of Karnataka. This region is approximately 320 km long (Kamath, 1982). The ghats in this section rise sharply to form unbroken and uneven rampart averaging an altitude of 900 m. In the study area of Central Western Ghats, Kudremukh (1892 m) is the highest peak followed by Thadiandamol (1745 m) and Pushpagiri (1713 m). The Western Ghats in this section are very close to the coast and at several places touches the shore.

The main groups of soils found along the Central Western Ghats are lateritic soil, red soil, mixed red and black soil, red loam and brown clay. Lateritic soils occur in the coastal regions of Uttara Kannada, Dakshina Kannada, Shimoga and Hassan districts. Red soils occur in Shimoga, Hassan and Chikmagalur districts.

Western Ghats in Karnataka though receive rainfall from the south west monsoons also receive rains from the north east monsoons during October to January. Annual rainfall varies from 4000 mm to 8000 mm. Annual rainfall is highest in the Western Ghats section and lowest in the eastern parts of Chitradurga towards the leeward side. Agumbe receives highest rainfall (8270 mm) in this sector followed by Bhagamandala (6032 mm).

The mean annual temperature varies from 18 - 20C. Mean daily temperature ranges between 20 - 24C. The humidity is 90% during the monsoons in the month of July and August. The vegetation occurring along the Central Western Ghats can be classified as: tropical evergreen forest, semi-evergreen forest, moist deciduous forest and the sholas.

ABOUT CHIKMAGALUR DISTRICT:

Chikmagalur is known as- A gateway to Western Ghats. The district is the very heart and soul of Malnad. The breath taking beautiful Sahyadri hill ranges; the land scape; the rivers; the flora and fauna; the lush green coffee estates and the rich heritage of the district all add to the importance and glamour of this place.

Chikmagalur district has got a geographical extent of about 7200 sq.kms, out of which about 40% of it is covered by forest area, between 120551 and 130541 north latitudes and 7551 and 760221 east longitudes. Shimoga bound the district in the north. District shares its boundaries with Chitrdurga, Tumkur and Hassan towards south, it is bounded by Hassan district on the south west and the west, and the Western Ghats constitute a natural barrier which separates it from the Dakshina Kannada district. Many parts of the district are situated in heavy rainfall zone. However 2 talukas Kadur and Tarikere are located towards the east comprising more or less level lands and partake the features of maidan areas.

The district presents a college of different and diverse colours of nature. On the one hand eastern talukas of Tarikere and Kadur are dry falling in the maidan areas, on the other western parts of the district i.e. Chikmagalur, Narasimharajpura, koppa, Sringeri and Mudigere constitute western ghats and are extremely important from geological point of view.The climate of the district is agreeable and cool throughout the year. Though March, April and May are regarded as summer months, during this period the maximum day temperature stays around 30c and the night temperature however around 19c.The average annual rainfall of the district is 1990mm. The eastern belts receive a rainfall of about 600mm/yr only, while the western belt receiving around 3000mm/yr.

FORESTS IN CHIKMAGALUR DISTRICTThe west of the district is covered with some of the best forest in the country. Throughout the Jagra valley (Bhadra wild life sanctuary). Mudigere, Koppa, Sringeri, N.R. pura and parts of Chikmagalur taluks was earlier a continuous stretch of highly valuable forests, densely clothing the hillsides. During the years since this tree growth gives valuable shelter to coffee plantations, most of it has been converted into large and extensive coffee estates, so much so that Chikmagalur district has become the foremost among coffee growing districts in the country today. Tea and other plantation. Crops have also claimed large chunk of pristine forests. The district is unique in having diverse kinds of forests, which are as follows:

1) Scrub type forest: Found in drier tracts in Kadur and Tarikere taluks these are degraded kind of forests where vegetation is thorny type and bushy. Main converted into plantations of eucalyptus, cassia siamea, Acacia auriculiformis etc, by the forest department.

2) Thorny dry deciduas forest: Found in those areas having lesser rainfall. Abounds in deciduous tree species, which shed their leaves during summer months.

3) Moist deciduous forest: These occur in those areas having better rainfall. Leaf shedding takes place during summer months. Teaks, Rosewood, Nandhi, and terminalias are the conspicuous species.

4) Semi evergreen forests: These are the forests occurring in areas receiving good rainfall. They have a mix of tree species form moist deciduous and evergreen forest. Rich bio diversity is found in them.

5) Evergreen forests: Found in the region of very high rainfall these are treasure houses of medicinal plants. The forests of Bhagavathi valley in Kudremukh National Park and Balur state forest in Mudigere range are the examples. They support huge tree with high and almost closed canopy. They are rich in canes.6) Shoals forests: Sholas are one of the wonders of nature they occur as patches in the depressions and hollows of the high peaks like Baba Budans, Kudremukh rumbling along the slopes. A typical undisturbed shoal forest has got closed canopy, so that even sunrays may find it difficult to pass through. Soil is very rich in humus. These are rich in humus. These are the harbingers of natural water streams. Invariably shoals occur as an oasis in grasslands. During summers grasslands are under intensive threat of fire. This fire also takes its toll on shoals leading to their continuous shrinking although they occur as small expanses of forest only in the crevices or depressions but we have a huge shoal forest by name shankar shoal near Kemmanagundi. The area of shankar shoal is few hundred hectares.

7) Grass lands: A very important feature of the hills of Chikmagalur district is the existence of grassland. These appear like a velvety green spread covering the entire hillocks. It is so enchanting and soothing to see them during rainy season when the new grass is coming up. Although they may look like vast expanses of land having only dense growth of coarser grass interspersed with shrubby plants here and there, they are treasure houses of very important herbaceous medical plants. They also act as live sponges to soak the rainwater to recharge the water table. These grasslands are the climatic climax and by carbon dating they are found to have exited for millions of years. They have been assigned a very important function by nature and they have to be allowed to remain there. They are very valuable grazing meadows for herbivores like Gaurs, In fact, in the past whenever it has been tried to convert them into some plantations by been so encouraging.

However since there are invaluable grazing grounds, large numbers of cattle so grazing on them. Because of this in order to have better and tender grass during rains, villages usually burn them during summers. This fire is also at times spreads to intervening shoals and is a cause of destruction of shoals too. Due to such burning the hillocks get charred and become sooty black during summers.

Details Of Forest lands In The District Excluding Private ForestDivision Forest land in hectaresChikamagalur 77154Koppa 113810Bhadra wild life 49246Karkala wild life part 35411Bhadravathi part 24990Total 300611

LANDSLIDESLandslides occur when masses of rock, earth or debris move down a slope. Mudslides, debris flows or mudflows, are common type of fast-moving landslides that tend to flow in channels. These are caused by disturbances in the natural stability of a slope, which are triggered high intensity rains. Mudslides usually begin on steep slopes and develop when water rapidly collects in the ground and results in a surge of water-soaked rock, earth and debris. Causes may be of two kinds: 1. Preparatory causes & 2: Triggering causes. Preparatory causes are factors which have made the slope potentially unstable.. The triggering cause is the single event that finally initiated the landslide. Thus, causes combine to make a slope vulnerable to failure, and the trigger finally initiates the movement. Thus a landslide is a complex dynamic system. An individual landslide characteristically involves many different processes operating together, often with differing intensity during successive years. The main trigger of landslides is heavy or prolonged rainfall. This could be either an exceptional short lived high intensity event, or of a long duration rainfall event with lower intensity, lasting several days, such as the cumulative effect of monsoon rainfall. In the former case it is usually necessary to have very high rainfall intensities, whereas in the latter the intensity of rainfall may be only moderate - it is the duration and existing pore water pressure conditions that are important.

Table A: Causes of Landslide

Gravity caused slope instability occur naturally due to earth quakes, etc. Slope failures are also triggered by high degree of human impact on the environment. Land use changes may lead to land degradation, and make hillslopes more susceptible to instability (or mass movement). The past several decades have witnessed intense disruption of forest cover, for alternative land uses (mining, quarrying, monoculture plantations, agriculture, human settlements, roads, railways etc.) or for biomass needs, in the mountains and hills of India. In such events when extreme meteorological events, such as heavy rainfall happen landslide episodes, have increased causing human and cattle deaths and destruction of property and livelihoods. Susceptibility to landslides may be considered as a natural, tangible process in a landscape, taking into account the rainfall history, as well as the geological and geomorphic setting of the area. Risk levels increase drastically in landslide prone areas whenever human pressures increase.

In addition to rainfall, several factors probably contribute to slope failure. These include:i) Geological structures like shattered, fragmented and highly jointed rocks and topography like steep slopes, interacting to provide the geometry favouring landslides.ii) Prolonged rainfall certainly produces abnormally high antecedent groundwater levels, more so in places where the ground water level is already high due to the nearness of rivers or estuaries or other water bodies. It is the collective rainfall of many days that enhances the pore water pressure.iii) Poor drainage network in the hillocks due to changes in land cover (removal of vegetation or obstruction of drainage channels) alters the drainage.iv) Steep slopes cut for pathways and residential buildings near the base of the slope further destabilizes the slope by removing the basal support.

Landslides are classified by causal factors and conditions, and include falls, slides and flows, which are described below. There are many attributes used as criteria for identification and classification including rate of movement, type of material and nature of movement. A combination of characteristics can also contribute to anincreased risk of landslide hazards.

a. Falls: Falls are abrupt movements of rocks and boulders i.e., masses of geologicmaterials that become detached from steep slopes or cliffs. Movement occurs byfree-fall, bouncing, and rolling on separation along discontinuities such as fractures, joints, and bedding planes. Gravity, mechanical weathering, and the presence of interstitial water strongly influence falls.In falls, material is detached from a steep slope or cliff and descends through the air by free fall or by bouncing or rolling down the slope. Rock fall, the most common type, is a fall of detached rocks from an area of intact bedrock.

b. Topples: The end-over-end motion of rock down a slope. Under the actions of gravity and forces exerted by adjacent units or by fluids in cracks toppling occurs. Toppling failures are distinguished by the forward rotation of a unit or units about some pivotal point, below or low in the unit.

c. Slides: Even though the term slide used in general for any landslide it has more restrictive use of the term refers only to mass movements, where there is a distinct zone of weakness that separates the slide material from more stable underlying material. Slides include rockslides the down slope movement of a rock mass along a plane surface; and slumps the sliding of material along a curved (rotational slide) or flat (translational slide) surface. Slow-moving landslides canoccur on relatively gentle slopes, and can cause significant property damage, but they are far less likely to result in serious human casualties.

d. Flows: Flows are plastic or liquid movements in which mass (e.g., soil and rock) breaks up and flows during movement. Flows are typically rapidly moving and also tend to increase in volume as they scour out the channel.a. Debris flow: A debris flow is a form of rapid mass movement in which a combination of loose soil, rock, organic matter, air, and water mobilize as slurry that flows downslope. Debris flows include