CHAPTER 2

GEO-ENVIRONMENT OF THE STUDY AREA

2.1 INTRODUCTION

The occurrence of landslide is mainly controlled by various geo-

environmental parameters of the terrain. Therefore, a detailed study of

different geo-environmental parameters viz., physiography, drainage

characteristics, and climatic conditions, intensity of rainfall, landuse /

landcover and seismicity pertains to Agumbe hill range is presented in

this chapter. However parameters like slope, geology and structure are

dealt in chapter 3 and chapter 4 respectively.

2.2 LOCATION AND ACCESSIBILITY

The Agumbe hill ranges which form the present study 8irea is

bounded by 13° 15' to 13° 40' N latitudes and 75° 00 ' and 75° 15' E

longitudes and falls in Survey of India Topo Sheets 4 8 0 / 2 , 4 8 0 / 3 {Fig

2.1). The area forms a part of Shimoga and Udupi districts of

Kamataka state covering about 1150 sq.km of Malnad region. It is

located at a distance of 320 km from Bangalore (the capital city of

Kamataka state), 70 km from Mangalore (the port city) and 80 km

from Shimoga (town, a cultural center).

This part of Western Ghats is very famous for tourism because

of its enchanting natural scenic beauty, including sunset viewpoint

and natural waterfalls in addition to a number of pilgrimage centers.

National Highway No. NH-13 passes through the Ghat section near

Agumbe and very well known as "Agumbe Ghat". It is connecting

Udupi, Mangalore and other coastal towns along the West Coast and

rest of the interior Kamataka. The most critical part of this national

high way is the Agumbe Ghat section where, the road comprising of

16

LOCATION MAP OF AGUMBE HILL RANGE

+

Fig 2.1 Location of Agumbe hill range

14 sharp Hairpin bends and steep westerly gradient restrict the

movement of long chasse and heavy vehicles.

2.3 PHYSIOGRAPHY

The Agumbe hill range runs in the NNW-SSE direction

coinciding with the general trend of Western Ghat scarp line. It is

characterized by immature and highly rugged physiography (Fig 2.2).

Geometrically, it displays asjnnmetrical ridge like structure having

steep western scarp and gentle eastward slope. The prominent

mountain peaks are Tulajankal Gudda with an altitude of 1426m

above MSL, Gangrikal -1423m and Ganga Mula -1189m., It is the

birthplace of River Tunga. The relative relief of different parts of the

study area exhibits the major breaks with steep slopes (>500m).

The Western Ghat scarp line forms water divide between the

east and west flowing rivers and also a major watershed of the

Peninsula. The rivers, which originate in the Western Ghats, show

comparatively young stage, marked by cascades and waterfalls, but in

plains they show maturity. This is thought to be, due to the

rejuvenation of the Ghats by an upward tilt connected in some way

with the faulting of the Arabian coast, and probably block uplift of the

region during the Middle Tertiaiy (Radhakrishna, 2001).

2.4 WEATHER AND CLIMATE

The Ghat represents the region of transition between hot and

humid coastal climate and that of the watered, more elevated, cooler

and not continuous humid zone. The area, which forms a part of the

popularly known "Malnad" and "Semi-Malnad" region, is representing

the tropical and sub-tropical type of climatic conditions. The terms

*Malnad' and *Semi-Malnad' - are regional terms mainly attributed to

the altitude, topography, rainfall and other unique climatological

17

Fig 2.3 : Digiotal Elevation Model (DEM) of Agumbe hill range

phenomenon. The area generally experiences agreeable warm and

himiid climate during summer, fo^y cold winter and receives heavy

precipitation during the rainy season. The maximum temperature

during summer is about 35° C and minimum during winter around

8°C.The minimum and maximum humidity is around 40% and 80%

during February and September months respectively. The length of

dry season estimated by water balance method varies from three to

four and half months and is shorter than the coastal region at the

same latitude.

2.5 INTENSITY OF RAINFALL

The Western Ghats forms strategic location and plays

significant role in checking the monsoon trade winds that carry clouds

and causing lot of rain to larger inland of Southern Peninsula.

Monsoon starts around 2^^ week of May with a minimum rainfall of

about 50nmi per day and attains a maximum rainfall of more than

300mm per day around Agumbe Ghats during the month of July.

Agumbe is the wettest place in the Southern Peninsula. Hence, it is

also called as "Dakshina Chirapunji", which is located at the central

part of the Agumbe hill range.

Perusal of the rainfall distribution patterns of the study area

(Table 2.1) reveals that western part of the study area on either side of

the scarp line, receives >2500 mm of annual rainfall therefore, the

region is commionly known as Malnad region. The eastern Semi

Malnad receives an annual rainfall between 1500-2 500mm which

gradually decreases to 1000 -1500mm in the Maidan region.

18

Table 2.1: Showing the monthly rainfall statement pertains to Agumbe region.

Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total

2002 "

4 "

50 205 1351 1483 1945

2001 ~ " ~ 185 205 2211 2183 1835 306 283 43 ~

2000 ~ * • * 15 219 2089 2004 2061 706 294 - 8

1999 " • "

3.6 577 1374 2327 1550 587 410 - - 7776

1998 - - - - 98.4 1997 3308 2144 1376 482 221 12.6 9639

1997 - - 0.4 24 53.4 1602 3094 2356 265 252 165 89.8 7900

1996 - 30.8 - 10.8 27.8 1757 2720 1853 767 246 66.0 - 7478.6

1995 1.0 - - 40.6 334.4 1022 3031 1846 886 201 33.0 - 7394.6

Table 2.2: Average monthly precipitation of rainy months

Sl.No Month Precipitation in mm

1 May 189

2 June 1682

3 July 2885

4 August 1975

5 September 749

6 October 345

7 November 215

19

2.6 DRAINAGE

The Agumbe hill range falls within the tectonically disturbed

zone of the Western Ghats and possess number of perennial streams

and drainage channels often associated with waterfalls. Tunga River

and Malathi Hole forms the east flowing drainage system. Whereas,

Sharavathi, Varahi, Sita Nadi and Yenne Hole, belongs to the west

flowing drainage system. The available evidences seem to indicate that

the Western Ghats owe their present elevation to uplifts along a fault

zone during Tertiary period (Radhakrishna, 2001). Easterly flowing

rivers, originating to the eastern plain in the western ghat scarp

contribute major portion of the water resources for irrigation, power

generation, domestic and industrial water supply etc., The marked

length of drainages of the easterly flowing rivers attribute to the

regional tilt of the Peninsula towards the east (Fig 2.3).

There are numerous waterfalls in the Western Ghats including

the world famous Jog Falls (252m), located in the north-western parts

of the study area. The Agumbe hill ranges comprises of four waterfalls

i.e., Kunchikal Abbi Falls (20m), Vanake Abbi Falls (15m) and Patali

Falls (25m) and are associated with west flowing streams. Suttinabbi

Falls (22m) is the only known east flowing stream in the area, and all

these falls are confined to Western Ghat scarp line.

2.6.1 Western Ghats scarp and drainage divide

The elevated portion of the terrain, which runs along the entire

stretch of the Western Ghat mountain chain, is known as Western

Ghat scarp line. This line serves as water divide for east and west

flowing rivers. The characteristic feature of this scarp line is the

frequent occurrence of numerous waterfalls. The net drop varies from

few meters to hundreds of meters and is mostly found to associate

with the west flowing streams. There are four waterfalls in the Agumbe

20

75°5' 75° 10'

§

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Fig. 2.3 Drainage network of Agumbe hill range overlay on FCC

Hill Range and all of them have originated in the vicinity of the

Western Ghat Scarp line. Among them, three are associated with east

flowing streams. The erosive power of the west flowing rivers are more

due to steep gradient this often leads to river captures of eastern

flowing rivers by west flowing rivers (Radhakrishna, 2001).

2.7 SOILS

Eastern part of the area comprises red loamy soils. The

thickness of soil varies from less than a meters to more than 10m

especially in the Western Ghat Scarp Line (WGSL), it is called a s hill

area soils. Whereas, the western part of WGSL is mostly covered with

lateritic soil and often occur as thick lateritic crust. Western part of

the area exhibits lateritization, either in the form of laterite cap-rock,

or iron rich laterite soils. The other type of soils noticed red sandy soil,

laterite gravelly soils, and hill area soils. Majority of the soils have

high water-holding capacity, which often exceeds lOOmjn.

2.8 FLORA AND FAUNA

The uniqueness of the Western Ghat in terms of habitat is the

richness of fauna and flora, which is generally measured through

various indices of biodiversity. The Western Ghat Mountains including

the Agumbe hiU ranges represent one of the very few "biodiversity

hotspots* of the world.

2.8.1 Flora

More than 75% of the study area is under forest cover. The

thick-forest cover over the r u ^ e d mountainous terrain is an

important element in terms of landscape of the region (Plate 2.1).

The geographic position, its altitude and warm humid climate

coupled with heavy precipitation, governs the wet evergreen, moist

deciduous, tropical and temperate forests. Multistoried canopies of

vegetation, viz., trees and shrubs, herbs, climbers, and epiphytes

21

characterize these forests. One of the significant features of the

biological spectrum of the Agumbe hill range is the presence of tall

trees with several useful timber species viz., teak, ebony, rosewood,

etc., besides, large variety of bamboos and large number of

medicinal plants which are of high conmiercial value grow naturally

in these forests.

The agricultural activity is mainly confined to valleys and hill

slopes, particularly in the eastern part of the western ghat scarp line.

The perennial crops like tea and coffee plantation are confined to hill

slopes whereas, areca nut, vanilla, banana and rubber plantations,

besides paddy, sugar cane, pepper, ginger and cardamom etc., are

grown in the valley portion of the study area.

2.8.2 Fauna

Besides rich flora, the western Ghat abounds in wild life with

amazing variety of species representing micro soil biota to large and

giant wild life like elephant that makes this region one of the very few

biodiversity hot spots of the world. The major animal fauna

representing this area are; elephants, lions, tigers, bears, foxes, wolf,

deers, rabbits, monkeys, pigs, and snakes besides varieties of birds

and insects etc.

However, high rate of endemism make the Western Ghats, a

highly sensitive ecological region at the national level. Due to the fact

that, increase in population density, large areas of forest have been

brought under cultivation (encroachment) especially by means of

"Malenadina Mannu Kadadi" a local terminology. It is one of the

methods of increasing the existing farmland into adjacent hill mass by

a typical way of excavation. This illegal removal of natural vegetation

and steep slope under cut without any plan/preventive measure

results in terrain instability.

22

There were many reported incidences of casualties/loss of lives

occurred during such operations of Malenadina Mannu Kadadi. The

destruction of forests resulted in pronounced imbalance in the

effectiveness of precipitation, maintenance of water table and

percentage of humidity and transpiration. Besides, the establishment

of Dams and Reservoirs, resulting in the submergence of river

catchment areas inhibited rich vegetation, has further accelerated the

regressive changes in bio-reserves of this part of Western Ghat region

Plate 2.1: A Panoramic scene from famous sunset viewpoint at Agumbe ghat

23

2.9 LANDUSE/LANDCOVER

Land use/land cover classes of the area show the spatial

distribution of land use practices, type of forests, cultivated area

and settlements, besides water bodies. Most of the agricultural

lands are located in valleys, at lower sloping grounds. The thick

forests, i.e. evergreen forests are found to occur along the crestal

portion of the Ghat regions, whereas the barren lands occupy the

moderately steep slopes. The terrain is characterized by high

frequency of slope instability in sparse forest area, less in barren

land and agricultural land, very less in moderate forest and dense

forest. Obviously the barren slopes produce frequent slope

instability due to lack of vegetal cover and greater erosion by

surface water. The instability of slopes is due to the slope

modifications a s well a s areas covered with less vegetation.

2.10SBISMICITY

The area falls in seismic zone III of the seismic zonation map of

India (Fig 2.5) as it is very close to Western Ghats fault scarp, which is

known to be geologically active. The area represents ample of

neotectonic signatures. Perusal of the seismic records of Kamataka

(Fig 2.5 & Table 2.3) indicates that early 1970 were an active period of

seismicity.

According to Radhakrishna (2001), there is a close relationship

between major lineaments and seismicity in the Western Ghats of

Kamataka. When the earthquake epicenter locations were integrated

with the lineament map, it is observed that large number of

earthquake epicenters (23 out of 33) fall either on major lineaments or

close to them.

24

Table: 2.3 Recorded earthquakes in Kamataka

SI. No. Year Latitude Longitude Magnitude Location

1 1828 13.0 75.0 5.7 Karkal 2 1829 13.0 77.6 4.3 BanRalore 3 1843 15.2 76.9 6.0 Bellary 4 1843 15.2 76.9 3.7 Bellary

5 1861 16.4 77.3 3.7 Raichur

6 1862 16.4 77 .3 3.7 Raichur 7 1865 12.3 76.7 3.7 Mysore

8 1882 13.0 77.5 3.7 Ban^dore

9 1889 12.87 74.8 3.7 Mangalore

10 1891 13.0 77.5 3.7 Bangalore

U 1916 13.0 77.5 5.0 Bangalore

12 1970 12.6 77.1 4.0 BangaloFe

13 1970 13.0 76.1 3.8 Hassan

14 1970 12.4 77.0 4.3 Mandya

15 1971 12.4 77.0 4.2 Manfya

16 1971 12.4 77.0 4.Z Mandya

17 1971 12.4 77.0 4.3 Mandya

18 1971 12.8 78.3 4.4 Kolar

19 1971 12.8 78.3 4.7 Kolar

20 1972 12.4 77.0 3.7 Mandya

21 1972 12.4 77.0 4.5 Mandya

22 1972 12.4 77.0 4.6 Mandya

2 3 1972 12.8 78 .3 3.7 Kolar

24 1973 17.0 76.3 4.3 Sindgj

25 1974 13.8 75.3 5.0 S h i m o ^

26 1974 12.8 78 .3 3.9 Kolar

27 1974 12.8 78 .3 4.1 Kolar

28 1975 15.0 76.0 5.0 Tungabhadra Res.

29 1980 15.27 76.1 3.5 Hospet

30 1982 12.8 78.3 3.7 Kolar

31 1993 17.37 77.47 5.0 ChinchoU

32 1997 17.44 76.06 4.6 Indi

25

13*40'0"N

13'30"0"N--

13^20'0"N

75'0

-13'40'O"N

-13^30•O••N

+

iJcmciKfs -13 20'0"N

LU.LCaASSES

I iBUltLBTll

^ 1 Forgsl^brtalbm

| [ | | HanlBtbni

H I B nvariTSmrnsk

I iRtxfcvlnoa

I \^ SoreBnw Land

{Vtaiorbaly

75"10'0"E

Landuse/Landcover classes of Agumbe hill range

26

IS I « 3 ( Part 1 ) : tHi

Fig 2.5 Seismic Zonation Map of India [After IS 1893 (Part 1): 2002]

27