16

CHAPTER 2

PHYSICAL SETTING OF THE STUDY AREA

2.1. GEOGRAPHIC SETTING

Idukki is the largest highland district of Kerala, and is covered with dense

tropical forests, plantations, scrublands and grasslands situated mostly in the lofty

hills of the western ghats. It is the second largest district in the state covering an

area of 4358 sq.km which constitutes 11.2 % of the total area of the state.

The district is located between North latitudes 9º16’ 30” and 10º21’00”,

East longitudes 76º 38’ 00” and 77º24’30”, and extends to about 115 km from

north to south and about 67 km from east to west. The district is included in the

Survey of India Topographical Maps (Scale 1:50,000 ) bearing Nos.58 B/16, 58

C/9, 58 C/13, 58 C/14, 58 C/15, 58 F/3, 58 F/4, 58 F/7, 58 F/8, 58 G/1, 58 G/2, 58

G/3, 58 G/5, 58 G/6, and 58 G/7. The district falls mainly within the highland

physiographic province of the state and is devoid of coastline or border with any

backwaters. The district is bounded on the north by Coimbatore and Dindigul

district of Tamil Nadu, and on the south by Pathanamthitta district, on northwest

by Ernakulam district, on the southwest by Kottayam district of Kerala and Theni

district of Tamil Nadu share the eastern border of the Idukki district. (Fig. 2.1)

The high land region, of western ghats which comprises of Idukki district has

unique and distinct geographical features.

Two National Highways namely NH-49 and NH-220, and twelve State

Highways pass through this district which facilitate significant communication

and transportation, but compared to the other districts the region exhibits poor

transport, communication, medical and educational facilities. Agriculture is the

main occupation of the people and most of the income is derived from agriculture

and allied occupations.

Idukki District was formed on 26 January 1972 as per the Government

notification No 54131/C2/71/RD dated 24th January 1972 carving out

Devikulam, Udumbanchola and Peermedu taluks of the erstwhile Kottayam

17

FIGURE 2.1

18

district and Thodupuzha taluk excluding Kalloorkadu village and portion of

Manjallore village included in Kallorkad and Manjalloor panchayats of the

erstwhile Ernakulam district. The jurisdiction was slightly altered by a subsequent

notification No.7754/C2/72/RD dated 14th February, 1972. As per G.O.(MS)

No.1026/82/RD dated 29th October 1982 wherein north Pamba valley and the area

around Sabarimala Sannidhanam in Milappra village of Peermedu taluk were

transferred to Pathanamthitta district. (Economics and Statistics, 2006). At present

the district consists of four taluks viz.,Devikulam, Udumbanchola, Thodupuzha

and Peermedu.

As per historical indications, Kuzhumur, the capital of Chera Kings of the

Sangam Age , is the present Kumily in Peermedu taluk of the district. It is

assumed that Nanthuzainad comprises of Devikulam, Udumabanchola, and

Peermedu taluks, Vempolinad and Manjunad of Kottayam district and

Kuzhumelainad of Thodupuzha taluk which was formed as part of the

Kulasekhara Empire (A.D.800-1102). By AD 1100, subsequently Vempolinad

was split up into Vadakkumkur and Thekkumkur and Karikkode in Thodupuzha

taluk became the capital of Vadakkumkur Rajas and Vadakkumkur was

subordinate to the Perumpadappu Swaroopam for a long period whereas

Thekkumkur was the most powerful Kingdom in those days. (Sreedhara Menon A,

1991)

The Modern history of the district started with the arrival of Europen

planters to this highland region. In 1877 Kerala Varma , the Raja of Poonjar

leased 227 square miles (590 km2) of Kannan Devan hills to John Danial Manroe,

a British Planter. The area was inaccessible and covered with virgin forest

wherein established the North Travancore Land planting and Agriculture society

to exercise their activities . The members of the society expanded their own

estates in various parts of the highland region through the construction of roads

along the forest region to promote transport network, development of settlements,

and factories for the production of tea in the preceding years. The Pallivasal

Hydroelectric Project, the first hydroelectric project of the State was initially

constructed by the tea companies for industrial use. Planters were the first

migrants to the high land region covered by dense forest. Deforestation process

19

FIGURE 2.2

Source: Survey and Land Records: Revenue Department

20

started in the highland region with the development of the plantation activities by

the end of the 19th century. Extensive areas of forest were cleared for construction

of Hydroelectric projects, factories, roads and settlement exclusively in Idukki

district.

2.2 ADMINISTRATIVE SET UP

There are four taluks in the district viz, Devikulam, Peermedu,

Udumbanchola, Thodupuzha, 52 grama panchayats, and eight community

development blocks. (Table 2.1) The community development blocks are

Adimali, Azutha, Devikulam, Elamdesom, Idukki, Kattappana, Nedumkandam

and Thodupuzha. The district headquarters is at Painavu, since June 1976, located

at ‘Kuyilimala’ a hill station surrounded by reserve forests in Thodupuzha taluk.

Thodupuzha is the only Municipality and township in the district and Munnar is a

census town. Kumily panchayat in the Azutha block is the largest in the district

and Edavatty panchayat in Thodupuzha block is the smallest. (Fig 2.2)

21

Table 2.1 ADMINISTRATIVE DIVISIONS

Source: Census Hand Book, Idukki District, 2011

COMMUNITY DEVELOPMENT BLOCKS/PANCHAYATS MUNICIPALITY

ADIMALI AZHUTHA DEVIKULAM ELAMDESAM IDUKKI KATTAPPANA NEDUMKANDAM THODUPUZHA THODUPUZHA

Adimali Elappara Chinnakanal Alakode Arakkulam Ayyappancoil Karunapuram Edavetty

Baisonvally Kokkayar Devikulam Karimannoor Idukki-Kanjikuzhi

Chakkupallam Nedumkandam Karimkunnam

Konnathady Kumily Kanthalloor Kodikulam Kamakshi Erattayar Pampadumpara Kumaramangalam

Pallivasal Peerumade Mankulam Kudayathoor Mariapuram Kanchiyar Rajakkad Manakkad

Vellathuval Peruvanthanam Marayoor Udumbannoor Vathikudy Kattappana Rajakumari Muttom

Vandiperiyar Munnar Vannapuram Vazhathope Upputhara Senapathy Purapuzha

Santhanpara Velliyamattom Vandanmedu Udumbanchola

Vattavada

22

2.3. PHYSIOGRAPHY

The physiographic framework of the study area is depicted in this section

in terms of relief and physiographic features. Idukki district comprises of many

topographical and geographical characteristics which extends across the

traditionally identified two physiographic divisions according to the PWD

classification of physiography, ie midland and highland. The altitude of the Idukki

district ranges from 20 m to more than 2600 m above mean sea level. Major part

of the area is covered by rugged mountain ranges, undulating hills, deep valleys

and forests. The midland portion of the study area constitute a minor portion to

form a narrow strip towards the west. Idukki district mostly falls in the highland

region (>80m above MSL) except the western parts of Elamdesom and

Thodupuzha blocks. Portion of the Thodupuzha block falls within the foot hill

zones of the Western ghats (KSLUB 1995). Central Ground Water Board (1999)

classified the highland into foot hills (80 to500 metre above MSL), plateau (500

to1500 metre above MSL) and high ranges (>1500 metre above MSL) as per the

difference in elevation of the respective regions. The foot hill region of Idukki

district is characterized by high drainage density and presents small hills with

steep slopes and deep cut valleys. Plateau region is another important

physiographic unit of the district, which is incised by a number of deep cut

streams and the north eastern part of the district is characterised by several rapids

and falls.

There are 14 peaks in the district which exceed a height of 2000 metres

above M.S.L. The highest peak in South India, Anamudi (2695 m) is located in

the north central part of the district, situated in the Adimali block.

2.4 LAND PATTERN

Major portion of the land area (56.23%) belongs to the western ghat high

range, occupying the central and southern portion of the district and altitude range

is in between 600-1200 metres. (Fig 2.3) This region exhibits varied structural

characteristics in Adimali, Idukki, Nedumkandam, Kattappana and Azutha block.

Top western ghat highland zone signifies a prominent sensitive zone occupies the

entire Devikulam block, reserved forest section of Azutha block with an area of

23

Fig 2.3

24

1043.89 sq.km (23.95%). Upland zone comprises 7.76% of the area of the district,

which is mainly found in the forested sections of Azutha block and in the

transition zone of Devikulam, Adimali and Elamdesom block. Mid upland portion

constitutes 4.98 % of total area of Idukki which spreads along Elamdesom block,

southern part of Thodupuzha block and western margin of Azutha block. Midland

occupies 7.07% of the total area mostly confined to the western part comprises

Thodupuzha, Elamdesom blocks and Thodupuzha municipality of the Idukki

district. ( Table 2.2 )

Table 2.2 IDUKKI DISTRICT- LAND PATTERN

Sl. No.

Altitude Land Pattern

Land Area in Sq.Km

Land Area

in % (Above Mean

Sea Level)

1 20m - 100m Midland 308.23 7.07

2 100m - 300m Mid – upland 217.14 4.98

3 300m - 600m Upland 338.13 7.76

4 600m - 1200m Western Ghat High Range 2450.61 56.23

5 Above 1200m Top Western Ghat High Range 1043.89 23.95

Source:- Agrarian Distress in Idukki, 2008

2.5. RELIEF

The elevation of study area increases towards north east and in the south

of Peermedu plateau reaching the maximum height in Devikulam block. The

average elevation increases from the west of the district to the east and reaches the

maximum at Tamil Nadu border in the east and then suddenly drops down

towards the vast plains of Tamil Nadu.

The Relief is the expression of the interaction of several different

phenomena and processes within the earth’s crust and on its surface. Its forms and

dimensions are primarily related to the geological units, and to the climate, both

past and present, which have either directly or indirectly acted upon these units.

(Daniel Berhane, 2000). The action of climate and the effects produced by the

nature of geological units on relief, occurs through the process of weathering and

soil formation, and through the influence of living organisms, including plants,

animals and man. Relief is therefore, intimately connected with many of the other

25

elements of landscape resources. However anthropogenic activities have a

significant role in the acceleration of land degradation (Olafsdottir, 2002).

Relief itself has strong influence on the process and phenomena related

with land and land degradation is strongly influenced by the size and shape of the

relief forms. The area wise distribution of elevation is given in the table 2.3.

Table 2.3

AREA DISTRIBUTION OF DIFFERENT ALTITUDINAL RANGES

Sl.No. Elevation in Metres Area in Sq.Km Area in % 1 0-100 308.23 7.07 2 100-200 129.58 2.97 3 200-300 87.55 2.01 4 300-400 80.62 1.85 5 400-500 98.10 2.25 6 500-600 159.40 3.66 7 600-700 199.14 4.57 8 700-800 370.67 8.51 9 800-900 519.28 11.92 10 900-1000 519.43 11.92 11 1000-1100 517.42 11.87 12 1100-1200 324.68 7.45 13 1200-1300 166.09 3.81 14 1300-1400 106.93 2.45 15 1400-1500 106.35 2.44 16 1500-1600 129.28 2.97 17 1600-1700 115.44 2.65 18 1700-1800 88.15 2.02 19 1800-1900 83.59 1.92 20 1900-2000 74.99 1.72 21 2000-2100 57.15 1.31 22 2100-2200 48.93 1.12 23 2200-2300 31.72 0.73 24 2300-2400 19.93 0.46 25 2400-2500 13.55 0.31 26 2500-2600 1.64 0.04 27 2600-2700 0.16 0.004

Source: Derived from ASTER data.

26

2.6. RELATIVE RELIEF

The relative relief gives an indication of the erosion potential and

associated indication of slope in the lofty areas. (Sooraj Kannan,.and Dr. Mathew,

2002). The study of relative relief depicts the relief of an area in relation to the

surrounding areas and it is one of the methods to depict the local relief of this

region. The empirical description of surface features is attained by the proper

analysis of altitude and its variation. Relative relief is an important morphometric

variable which signifies the morphological characteristics of terrain in highland

region. It represents actual variation of altitude in a unit area with respect to its

local base level. The relative relief map of the area gives a clear conception of the

nature and amount of local relief of Idukki district. The map shows three

categories of relative relief in this region

Table 2.4 IDUKKI DISTRICT- RELATIVE RELIEF

Sl.No. Relative Relief in

Metres Area in (Sq.Km) Area in (%)

1 <10 1516.41 34.80 2 10-20 1783.52 40.93 3 20-30 1058.07 24.28

Relative relief varies significantly in the high land region of Idukki, (Fig

2.4) with higher relative relief reveals steeper slopes and rugged topography. The

areas with higher relative relief on steeper slopes occupying 25% of total area

noted in Azutha, Devikulam, Adimali, and Idukki blocks. Major part of the study

area exhibit medium relative relief ( 41% ) (Table 2.4) and a low relative relief of

35% is confined to the western part of the district characterised by undulating and

gentle slope dominant in Thodupuzha, and Kattappana, and Nedumkandam

blocks.

2.7. GEOLOGY

The salient fact with regard to the geology of highland region of Kerala is

that it is composed of distinct units or earth features. The geology of a region

related with the event in nature and processes, has varied impacts on land

27

FIGURE 2.4

28

degradation. (Yanni Gunnell and David Harbor, 2008). The salient structural

features of the rocks of the ages have significantly influenced the

geomorphological evolution of the highland region. The geological formations are

the result of processes in the past geological time and the recent geological period

exhibits rock forms and structure of the land forms.

The geology of the area is quite diverse ranging from Archean to

Proterozoic, representing rocks of a wide range in age. The south Indian shield

comprises of various crustal blocks of Achaean to early proterozoic age separated

by shear zones. (Ajay Manglik, 2005). The shield exhibits significant diversity in

lithology, structural pattern, tectonics and metamorphism. Variation in the grade

of metamorphism in the south exhibits differential exhumation of these blocks

with granulites of Southern Granulite Terrain representing the deepest part of

continental crust. Together these blocks represent a complex tectonic frame work

and evolution of the region. The geological units exhibit a varied pattern from

west to east in the highland the region.

Geologically, Idukki is occupied by Precambrian crystallines, acid to ultra

basic intrusives of Archaean to Proterozoic age. (Table 2.5) The crystallines have

been extensively lateritised. The Precambrian crystalline rocks of Idukki are

chiefly metapelites, charnockites with associated gneisses and granulites,

schistose rocks which include the Peninsular gneisses and migmatites.. (Nambiar,

1996). Synthesis of data from different lineament or shear bound segments in

Idukki district indicates varying metamorphic conditions and that lifts up history.

It is also outlined that there is a progressive decline in the uplift of different

segments from north to south (Soman, 1997).

2.7.1. GEOLOGICAL SEQUENCE

Based on the studies by GSI, 2005 during the last three decades, the

following stratigraphic sequence has been identified in this region.

29

Table 2.5.

GEOLOGICAL SEQUENCE

Source: compiled from GSI, Part-IX, Kerala 2005.

2.7.1.1 THE ARCHAEANS

The archaens refer to the ancient rocks which were formed very long ago

covered by younger sediment either eroded or subsided. Rocks of Archaean Era

encompass a wide range rocks from, charnockite, khondalite gneiss and meta-

sedimentary rocks occupying the Western Ghats region of Idukki district that

includes the foothill region also.

2.7.1.1.1 Peninsular Gneissic Complex-I (PGC-I)

The rocks of Peninsular Gneissic Complex (PGC) comprise 17.44 %

(Table 2.6) of the study area and they consist of a heterogeneous mixture of

ERA PERIOD ROCK GROUP ROCK TYPE/LITHOLOGICAL

UNIT

Pre-

Cam

bria

n

Archaean

Peninsular Gneissic Complex (PGC I)

Foliated granite, hornblende gneiss, pink granite gneiss, biotite gneiss

Khondalite Group

Quartzite, mafic granulite, calc-granulite garnet-biotite-sillimanite-cordierite gneiss, garnet-biotitegneiss, leptynite

Charnockite(older) Mafic granulite, pyroxene granulite, Banded magnetite quartzite and gneissic charnockite

Arcahean to Lower Proterozoic

Vengad Group Quartz-mica schist and quartzite, conglomerate

Peninsular Gneissic Complex (PGC II) Migmatite/gneiss/older Ganitoid

Garnet-biotite-gneiss with associated migmatites, quartzo-felspathic gneiss, hornblende gneiss, hornblende-biotite gneiss, quartz-mica gneiss-mica schist and quartzite, conglomerate

Proterozoic Basic/Acidic Rocks Anorthosite and Gabbro/ Diorite/Seynite/Granite and Granophyre

30

FIGURE 2.5

Source: Geological Survey of India

31

granitoid materials. This includes hornblende-biotite gneiss (sheared), biotite-

hornblende gneiss, foliated granite and pink granite gneiss. Granite gneiss,mainly,

pink granite gneiss is widespread, and best developed in Devikulam block as a

whole except in central part (10° 04' 00": 77° 06' 30"), and the northern part of

Nedumkandam (10° 00' 00" : 77° 15' 00") block of Idukki District. It exhibits its

inherent character in Marayoor, Vattavada, Mankulam, Pallivasal, Bison Valley

and Chinnakanal Panchayats. (Fig.2.5)

2.7.1.1.2 Khondalite Group

The Khondalites are a distinct group of rocks comprises 0.80% of total

area which exhibits distinct regional character and it includes calc-granulites,

quartzite and para-gneisses of pelitic parentage. Calc-granulite and quartzite occur

as bands within the para-gneisses and amidst the Charnockite Group and

migmatitic gneisses. It is mainly found in a scattered manner in the entire

Thodupuzha block whereas it occurred as a single mass in the south of Munnar

panchayath. Traces of rocks belonging to this group are observed in the western

part of Azutha block also.

Quartzite exists as linear lines amidst the khondalitic gneiss, charnockite

and migmatitic gneisses that spread along the western region.

2.7.1.1.3 Charnockite Group

Charnockitic rocks usually show spatial association of rocks and have

great diversity in lithology and are composed of metamorphosed types and have

wide distribution and importance in the district. Charnockite and charnockitic

gneiss are larger in number as compared to other crystalline rocks, covering

43.48% of the total study area. The charnockites are well-exposed in the high–

hills of western ghat mainly in Idukki district. It is also observed in the eastern

stretch of Udumabnchola and the western margin of Thodupuzha taluk

.(Vidyadharan et.al, 1978).

2.7.1.2. ARCHAEAN TO PALEO PROTEROZOIC

2.7.1.2.1. Vengad group

The Vengad Group comprises of basal conglomerate, quartzite and quartz-mica

32

schist occupies a small portion of 0.03 % area in Peermedu and Kumily

panchayats in Peermedu taluk.

2.7.1.2.2 Migmatite/Gneiss/ (PGC-II)

Migmatite is a rock at the frontier between igneous and

metamorphic rocks occupies 34.41% of the study area. It consists of variety of

gneissic rocks which form charnockite as a dominant litho-

assemblage.(Nageswara Rao et.al,1970).

Table 2.6

IDUKKI DISTRICT- ROCK GROUPS

Sl.No. Rock Group Area ( Sq.Km) Area( %) 1 Acidic rocks 47.58 1.09 2 Basic Rocks 13.35 0.31 3 Charnockite group of rocks 1894.78 43.48 4 Khondalite Group of rocks 34.72 0.80

5 Migmatite Complex (PGC II) 1499.44 34.41

6 Vengad 1.11 0.03

7 Penisular Gneissic Complex (PGC I ) 760.00 17.44

8 Waterbody 107.02 2.46 Source: Derived from Geology Map of Kerala, 2005

In Idukki district, Garnet-biotite gneiss is widely seen as light grey, pink

garnet-bearing biotite gneiss which is a gneissic granulite. The presence of biotite

and concentration of garnet in layers gives the rock a banded appearance.

(Geological and mineral map of Kerala, 1995). These rock types occur within the

migmatites and are associated with charnockite and are found mainly in the blocks

of Elamdesom, Thodupuzha and Thodupuzha Municipality. The naming is purely

based on the preponderance of the minerals in the corresponding area and these

rocks occur in the Periyar valley area in the east of Thodupuzha.(Nair et.al,1976).

The composition of migmatite is spread in a varied manner along the blocks of

Devikulam, Nedumkandam, Kattappana and Azhutha. Younger granites and its

variants occur around Munnar in Idukki district, and many of these granites occur

along crustal fractures and faults.

33

The Munnar (10° 05' 00" ; 77° 05' 00") granite with an areal extent of 50

sq km is an E-W bearing irregular body displaced within the migmatite and

apophyses extend into the surrounding gneisses. The granite dated to be 740 ± 30

m.y (Odom, 1982)

2.7.1.3. PROTEROZOIC

During the Proterozoic, larger continental landmasses continued to form

by the accretion of smaller ones, which often caused extensive mountain-building.

(Radhakrishna and Mathew Joseph, 1993)

In this basic dyke position within the Archaean crystalline rocks of

Western Ghats are spread throughout the entire length and breadth of the Idukki

district. Among the rocks the basic rocks are hard and massive plutonic rocks of

basic composition which constitute 0.31% of the total area observed in

Kumaramangalm, Karimanoor, Udumbanoor, Alakode, Manacaud and Purapuzha

panchayats of Thodupuzha taluk. Whereas the acidic rocks are hard and massive,

plutonic rocks of granitic / acidic composition which comprise 1.10% of the area

are found mainly in Devikulam block and other areas which are spread along the

eastern margin of Nedumkandam and Kattappana block of Idukki district.

2.8. GEOMORPHOLOGY

The major geomorphic features present in the study area are Denudation

hills, dissected plateau, Lateritic plateau, Valleys and River channel. The

mountain chain of the Western Ghats in Idukki is older than Himalayan mountains

and it represents geomorphic features of immense importance with unique

processes. (UNESCO World Heritage Centre, 2012)

The landforms in the Idukki district are dynamic because the relief,

climate and lithology perform major role in their development by the process of

weathering and erosion. Landform is important because the shape of the land is an

important determinant of the uses that can be made of the land. The configuration

of the surface is significant in the study of land degradation because the resulting

34

FIGURE 2.6

35

features due to construction of landforms are the principle consideration of the

geographer.

The study area have the landscapes which are evolved by a combination of

fluvial, denudation and tectonic processes to make patterns over the centuries. The

landforms are fragile and sensitive and become vigorous when it is influenced by

geomorphic system.

Tectonic movements have a great influence upon the intensity of

denudation process. Denudation and the movements of the earth’s crust are

interconnected with each other and they provide the direction of topographic

development. The processes of fragmentation and denudation generally govern

the highlands, consequently a gradual lowering of the absolute and relative

elevations take place which modifies the relief. Subsequently the enduring

processes of denudation give rise to transformation of the entire highlands into

rolling denuded plains and other surfaces.

The aerial extent and percentage of the total area of different geomorphic

units identified in the study area are tabulated in Table No 2.7

Table 2.7 IDUKKI DISTRICT – GEOMORPHOLOGY

Sl.No. Units Area( Sq.km) Area( %)

1 Denudational Hills 2754.71 63.21 2 Dissected Middle Plateau 844.50 19.38 3 Lower Plateau [Lateritic] 211.40 4.85 4 Reservoir Islands 2.09 0.05 5 River Channel 12.67 0.29 6 Valley 225.71 5.18 7 Valley [Denudational Hills] 211.79 4.86 8 Water Body 95.13 2.18

2.8.1. Denudational Hills

Denudational hills are the remnants of the natural dynamic process of

denudation and weathering. The geomorphic forms of denudational hills occur as

exfoliation domes, bornhardts, linear ridges, mesas, low mounds and erosional

hills at the foot of the hills. The shape of the denudational hills are controlled by

36

lithology, and spacing by joints and fractures occurring in them. The

denudational hill features are classified into a) hills in granites, gneisses and

migmatites, b) hills in schistose formations and c) hills in basic intrusive (dykes).

Of these, the denudational hills in granites, gneisses and migmatites are the most

extensive and occur in the study area. (Fig. 2.6)

Denudational hills occupy a major part of the study area constituting 63 %

from north to south in Devikulam, Adimali, Elamdesom, Idukki, Kattappana and

Azutha block. Series of denudational hill ranges found in the study area in association

with reserve forest are locally known by different names with varying altitudes.

The occurrence of residual mounds and denudational hills indicates that

the tectonic activity (upliftment) which has taken place in the north western region

of the study area has resulted in the development of these land forms.

A complex erosional process shapes the structural hills predominantly by

erosion, circumdenudation, weathering and mass wasting. The dip of the bed

controls the rate of denudation in structural hills which are linear to arcuate with

exhibiting definite trends composed of varying lithology .( Jasrotia,et al, 2012)

2.8.2. Plateau

The foot hill in the study area is a narrow strip of land where midland

region grades geographically into the plateau form. The elevation of this plateau

region ranges from 80 to 500 m from the mean sea level and has a slope from 30

to 50% and occasionally up to 80%, and the width of the foot hill ranges between

2 to 8 km. Plateau region with varying nature is another important physiographic

unit of the district characterised by a moderately sloping land mass with a slope of

less than 30 % and an elevation of less than 1500 m from mean sea level. Major

part of the district except a small portion along the west and north fall in this

region which is incised by a number of deep cut streams. (Ground water

information booklet of Idukki district,2008).

Plateau section in the study area is further divided into dissected middle

plateau and lateritic lower plateau. Dissected plateau region constitute 19% of the

total area and is mostly confined to middle part of the highland region.

37

Nedumkandam and Kattappana block exhibit vast extension of dissected topography.

In addition to this, northern part of Ranni reserved forest section in Azutha,

Mannankandan reserved forest section in Adimali, a linear stretch between

Mannankandam and Thodupuzha reserved forest section, south of Mannavan chola

and the area surrounded by Nanchivayal in Devikulam block have a dissected

topography. Lateritic plateau encompasses 5% of the area towards the west of

Thodupuzha forest with few outliers in Elamdesom and Thodupuzha block.

2.8.3. Valleys

The major rivers and streams in Idukki are encircled by valleys associated

with denudational hills composed of reserved forest which occupy 5% of the

study area whereas low lying valleys comprise 5% in the western part of the

region in Thodupuzha, Kattappana Adimali, and Devikulam block.

2.8.4. River Channel

River channel is recognized as a significant geomorphological feature with

0.3% of the area primarily associated with river Periyar which exhibits the largest

network of streams.

2.8.5. Reservoir Island

Reservoir Island constitutes a minor feature with 0.05% of the study area

found in the midst of Idukki reservoir.

2.9 CLIMATE

The United Nations Convention to Combat Desertification (UNCCD)

states that land degradation results from various factors including climatic

variations and human activities. (UNCCD, 2005)

Climatic change is one of the major component contributing to or even

trigger to land degradation. To assess viable land management practices, the

climatic effects and the peril of climate-related factors in a region must be known.

The interaction between land surface and the atmosphere involves multiple

processes all of which vary simultaneously. Hence land surface is an important

part of the climate system. Fragmentation of landscape can affect convective flow

38

regimes and rainfall patterns locally and globally. Land use and land cover

changes influence land-surface characteristics and, indirectly, climatic processes.

( Mahmood et. al 2009)

The weather and climate of Idukki is characterized by the presence of

monsoon winds. To understand the characteristics of climate, knowledge of

physiography is very important. The movement of monsoon current is normally

blocked by the orientation and elevation of mountain ranges. Consequently

uplifting and condensation of air takes place which provide rainfall on windward

side and scarcity of rainfall on the leeward side. Orographic precipitation is

responsible for most of the rains in Idukki and the precipitation varies in different

altitudinal ranges and is subject to fluctuation of wind, orientation of hill, slope

etc. The plantation and agriculture economy which is the back bone of Idukki

flourish with the availability of seasonal rainfall. Though Idukki receives nearly

nine months of rainfall, the fluctuation from the normal position is less compared

to other areas. The climatic conditions in the mid lands, plateau regions and hill

ranges of the district have wide variations. An understanding of the climatic

characteristics helps us to analyse the nature of land use activities in this district.

Since contrasts in climate are experienced in different physiographic regions, land

use activities also differ accordingly. Generally climate varies from east to west

with the descending elevation of landscapes. On the basis of weather and climatic

situation in Idukki, the year is broadly divided in to four seasons.

Winter ( January-February)

Hot Weather Period (March-May)

South West Monsoon (June-September)

North East Monsoon (October-December)

Among the periods, the south west monsoon season provides major share of

the rainfall in Idukki. This is the main rainy season with seasonal and regional

variations in different areas whereas the north east monsoon season constitute

secondary monsoon accounted in retreating phase. In hot weather period instability

occurrs with the high temperature and humidity accompanied by thunderstorms

whereas winter season is experienced by minimum rainfall and cloudiness.

39

As all the physiographic regions in Idukki do not have full fledged

climatic stations, the details incorporated in this work are mainly based on the

mean values from all the available meteorological stations from 1901 onwards.

2.9.1 RAINFALL

Rainfall and temperature are the prime factors in determining the climate

and its variability; and the extremity of rainfall can lead to soil erosion and land

degradation. The area receives rainfall both from south west monsoon and north

east monsoon. The district receives an average rainfall of about 2800 mm. The

rainfall increases towards the ghats with maximum rainfall in the western slope of

Munnar plateau. From there, the rainfall decreases towards east into the rain

shadow region of the Western Ghats. The major rainfall contribution is from south

west monsoon from June to September which contributes 60.4% of the total

annual rainfall. The North East monsoon from October to December contributes

24.4% of the annual rainfall and the balance 15.2% during the period January to

May (CGWB,2008). The table shows the normal seasonal rainfall in Idukki

during the year 2008.

Table 2.8.

RAINFALL IN IDUKKI

Rainfall Normal

Rainfall (mm) Normal Rainy

Normal Onset

Normal Cessation

days

(number)

SW monsoon (June-Sept)

987.6 73 June 1st week

Sep 1st week

NE Monsoon 506.57 32 October 1st November 3rd (Oct-Dec): Week week

Winter 85.54 6 (Jan- Feb)

Summer 203.6 16 (Mar - May)

Annual 1783.31 (Actual 08-09)

Source: Agriculture Contingency Plan, Idukki district, 2008

40

According to the rainfall data received from available stations from 1999-

2007 (Table 2.9) the annual rainfall is maximum in 2005 (5757 mm) and

minimum in 2003 ( 3152 mm ); and the highest negative change (-1582 mm )

occurred in 2006 and the lowest of -209 mm in 2003. Highest positive change

occurred during the year 2005 whereas lowest in 2007. The general trend shows

that an alternative change happened during these periods. (Fig.2.7)

Table 2.9 ANNUAL RAINFALL IN IDUKKI (1999-2007)

Annual Rainfall 1999-2007 (In Millimetres)

Year Annual rainfall Variation

1999 3833

2000 3225 -608 2001 3686 461

2002 3361 -325 2003 3152 -209

2004 3835 683

2005 5757 1922

2006 4175 -1582

2007 4500 325

Source: Economics and Statistics, Government of Kerala, 2009

Fig 2.7

41

Seasonal distribution of rainfall shows (Table 2.10) that the quantity of rainfall is

maximum in south west monsoon season. In the period from 1999-2007,

maximum rainfall of 4378 mm has been received in 2005 and minimum in 2002

during this season. North east monsoon rainfall comes second with a maximum of

923 mm at the beginning of the period itself and minimum occurred in the

following year. Summer rain also contributes a major share along the rainy

seasons in Idukki and the lowest amount is provided during the winter season.

Table 2.10

SEASONAL RAINFALL IN IDUKKI (1999-2007)

Seasonal Rainfall 1999-2007 (In Millimetres)

Year Seasons

Winter Hot Weather SW Monsoon NE Monsoon 1999 49 786 2074 923 2000 105 313 2540 267 2001 32 379 2648 627 2002 4 687 1894 776 2003 39 445 1904 764 2004 11 862 2499 463 2005 41 614 4378 724 2006 10 985 2514 666 2007 9 444 3443 604

Source: Economics and Statistics, Government of Kerala, 2009

Fig 2.8

42

The normal monthly rainfall in mm at various rain gauge stations for the period

1901 to 1999 is given below. Rainfall data shows a general variation in stations

which comprise of the regions from west to east. (Table 2.11 ) Peermedu

experienced maximum normal rainfall, whereas medium is in Munnar,

Thodupuzha and minimum is in Vandanmedu in these years. Monthly maximum

rainfall recorded in June at Munnar and Peermedu, minimum in Thodupuza and

Vandanmedu. (Fig 2.9) The highest normal rainfall is experienced at Munnar

(1098.2 mm) in July and least amount at Vandanmedu in February (14 mm). The

spatial distribution of variability of annual rainfall over Idukki ranges from 24%

to 28 %.

Table 2.11

RAINFALL IN IDUKKI AT GUAGE STATIONS (1901-1999)

Month

Rainfall (mm) at various rain gauge stations (1901 – 1999)

Thodupuzha Peerumedu Vandanmedu Munnar

January 25 16.7 26.8 16.1

February 33.1 36.2 14 23.7

March 82.6 56.3 42.5 39.3

April 204.8 135.1 107.6 146.9

May 333.2 313 145.5 252.2

June 735.6 927.7 360.8 743.4

July 785.9 1080.6 466.3 1098.2

August 557.1 639.8 310.8 702.8

September 337.1 429.6 188.4 341.7

October 433.7 466.4 229.6 263.1

November 244.5 211.8 157.4 136.3

December 59.5 57.9 57.9 39.6

Source: Ground Water Information Booklet, Idukki, 2008

43

Fig 2.9

Table 2.12

SEASONAL RAINFALL AT WEATHER STATIONS (1901-1999)

Rainfall (mm) at various rain gauge stations (1901 – 1999)

Season Thodupuzha Peerumedu Vandanmedu Munnar

SW Monsoon 603.93 769.43 331.58 721.53

NE Monsoon 245.9 245.37 148.3 146.33

Winter 29.05 26.45 20.4 19.9

Hot Weather 206.87 168.13 98.53 146.13

(Derived from CGWB data,2008)

44

Fig 2.10

The seasonal normal rainfall values recorded at different stations indicate

that annual rainfall variability is larger than seasonal rainfall variability. (Table

2.12) A minimum rainfall of 19.90 mm during winter and maximum of 769.43

mm is distributed in south monsoon season at Munnar and Peermedu. Generally

the rainy season contribute maximum rain in all the regions except in

Vandanmedu. The second share of rain is derived from north east monsoon

distributed equally in Thodupuzha, Peermedu, Vandanmedu and Munnar. During

hot weather season sufficient normal rainfall is experienced in all the stations

except Vandanmedu. Uniform distribution of rains occurs during winter in all the

regions of study area. (Fig.2.10)

2.9.2 TEMPERATURE

Generally temperature varies between 21 0 C to 27 0

C from east to west

with a minimum seasonal variation in the district. But in eastern highland the

temperature seasonally varies between -1 0 C to 15 0

C from November to January

and 15 0 C to 200

C during March/April. The temperature is high during the

months of March to May and is low in January and February. The mean monthly

45

maximum temperature ranges from 25.1 0C to 31.5 0C and minimum temperature

from 18.6 0C to 14.0 0 C.

It is observed from the average values of temperature ( 1901-2002) taken

from the weather stations in the study area that mean annual temperature is

maximum in April and minimum in December. The hottest months are April and

May, thereafter temperature declines up to the month of December. Again an

increasing trend is seen in January and February and it reaches its maximum in

April and May.

Table 2.13

MEAN ANNUAL DIURNAL TEMPERATURE 1901-2002

Mean Annual Diurnal Temperature Season Month Temp 0 C

Winter ( January-February) 9.28 Hot Weather (March-May) 8.14 South West Monsoon (June-September) 6.35 North East Monsoon (October-December 7.57

(India Meteorological Department, Thiruvananathapuram)

The diurnal and seasonal variation of temperature is uneven in the district.

(Table 2.13) The seasonal mean diurnal temperature shows maximum (9.28 0C)

during winter season and minimum in south west monsoon rainy period.

Fig.2.11

46

2.9.3 POTENTIAL EVAPOTRANSPIRATION

Evapotranspiration is the transfer of moisture from the surface of the earth

to the atmosphere through the process of evaporation and transpiration. But the

rate of evapotranspiration has temporal and spatial variations because of weather,

landuse, soil characteristics etc. Potential evapotranspiration refers to the water

loss from the vegetation areas because of climate and other factors.(Table 2.14)

The mean annual potential evapotranspiration values show a maximum of

6.19 mm in March and 4.76 mm in July. The seasonal variability ranges from 4.89 in

the rainy season to more than 5 in other seasons. By using the average of available

stations the potential evapotranspiration is 26 % in winter, 28 % in Hot weather and

23 % each during south west monsoon, north east monsoon seasons. The highest

values is during hot weather period whereas lowest is in both rainy seasons.

Table. 2.14

POTENTIAL EVAPOTRANSPIRATION (1901-2002)

Potential Evapotranspiration during 1901-2002

Season Month In mm %

Winter ( January-February) 5.67 26

Hot Weather (March-May) 5.95 28

South West Monsoon (June-September) 4.89 23

North East Monsoon (October-December) 4.89 23

(India Meteorological Department, Thiruvananathapuram)

2.10 GROUND WATER

Ground water resource of highland region in Idukki is the part of

hydrological cycle which acts as a reservoir of water for drinking and other uses.

It is uncontaminated than surface water, and it occurs under water table conditions

in laterites and weathered mantle of crystalline rocks. The rock formations from

Archaean to Proterozoic, which control occurrence and movement of ground

water, generally vary in composition and structure. Groundwater systems are

dynamic and water is continuously slow in motion in down stream from areas of

recharge to areas of discharge. (UNEP 2003) Ground water is usually held in

47

FIGURE 2.12

48

porous soils or rock materials under topographic conditions. The water table

varies according to the surface conditions influenced by rainfall pattern showing

regional variation. The rise and fall of water table occurs in accordance with the

variability of climate.

Laterites occur mainly in Thodupuza and western parts of Elamdesom,

Adimaly, Nedumkandam and Kattappana blocks in the gentle slopes and valleys.

Extensive laterite aquifers are also found in panchayats of Kumaramangalam,

Muttom, Edavetty, Mannarkkad, Kodikulam, Karimannoor ,Adimali, Rajakkad,

Nedumkandam, Kattappana, Chakkupallam, and Vandanmedu. The thickness of

the laterite varies from 0.5 to 4 Metres. The topography of the region influences

sub surface flow of water and its levels in various regions. In highland and in

steep slopes, the dug well tapping laterites get recharged fast and the recharged

water is escaped as sub surface flow, consequently the level of water falls in the

wells located in these areas. The depth of water table varies in laterite hillock,

ridges and gentle slopes. Most of the lateritic area is underlaid by weathered

crystalline rocks which forms aquifer throughout the district. The thickness of

weathering ranges from less than 2.0 to around 20 meters. Weathered thickness is

mainly found in granite terrains occurring in parts of Devikulam, Adimali and

Nedumkandam blocks. The deep fractured crystalline aquifers are harnessed for

bore wells for home purposes, agriculture as well as for providing water.

The depth of water table fluctuates widely since the district belongs to

monsoon regime. During the period of pre monsoon and post monsoon the

groundwater level in wells fluctuates in east and west of the region. The analysis

of rainfall data done by CGWB, 2008, during the pre monsoon period between

1997-2006 shows that 65% of the wells have shown a rising trend in water level

in western part of the district whereas in the post monsoon period about 70 % of

the wells show falling trend in water level and it is maximum in eastern highland

portion of Idukki. Though there is a large ground water development in some

areas, the water level is getting regenerated in the succeeding rainy season.

However a falling trend is noticed in the eastern part of the district.

49

There is a direct human intervention in this region over the years which

have led to reduction in ground water recharge. The landscape has changed

drastically over the years due to deforestation, plantation agriculture, destruction

of traditional water systems, destruction of local water systems, and stoppage of

river flows by the construction of dams and other river projects. Since the

intervention increases widely, that has affected the groundwater recharge systems

in the study area.

The following categories have been evolved to describe the ground water

characteristics of various geomorphological areas occurring in the study area.

Table. 2.15

GROUND WATER

Ground water condition Geomorphology Area

(Sq.Km) Area (%)

Very good Denudational Hill 212.31 4.87

Very good to good Plateau 226.3 5.19

Moderate Plateau 214.52 4.92

Moderate to Poor Plateau 846.68 19.43

Poor Denudational Hill 2750.35 63.11

Water body Waterbody 107.84 2.47

(Derived from ground water map, 2000)

The table shows that very good water condition occurs in 4.87% of the

area mainly in denudation hills of Peermedu, Udumabnchola, Thodupuzha and

Devikulam. (Table 2.15) .Very good to good, Moderate, Moderate to poor ground

water potential is experienced in Plateau region comprising Udumabanchola,

Peermedu and Thodupuzha covering an area of 5.19%, 4.92% and 19.43

respectively. (Fig 2.12) Major part of the area experiences poor groundwater

occurrence in Devikulam, Peermedu, eastern portion of Thodupuzha and in

Udumabanchola .

2.11 WATERSHED

The river system is spatially and temporally hierarchical in nature

(Schumm and Lichty1965) and explained in terms of integrated set of independent

and dependent variables which shape and control watershed characteristics over

50

time and space. Highland region represents one of the largest fluvial hierarchy

influenced by definite patterns of variables like geology, climate, land use, soils,

and potential natural vegetation. Watersheds are often formed as a single eco

region and therefore have properties that are indicative of land degradation. The

hydrological unit consists of basin, catchment, and watershed which fluctuate

according to spatial and temporal aspect. Although these terms have identical

implication in prominent sensibility, scientifically they are distinct. Size of a

watershed is driven by the size of the stream occupied by it. (Watershed Atlas of

India, AISLUS, 1990) It may be difficult to delineate small sized watersheds

whereas in undulating and hilly terrains smaller sized watersheds could be easily

delineated. Watershed morphology varies within the study area in terms of quality

of stream resources which is influenced by relief, drainage density etc.

Table 2.16

IDUKKI DISTRICT - WATERSHED

Sl.No. Watershed Name Area (Sq.Km) Area (%) 1 Manimala 107.19 2.46 2 Meenachil 5.28 0.12 3 Muvattupuzha 615.56 14.12 4 Pambar 384.33 8.82 5 Pamba 202.20 4.64 6 Periyar 2968.27 68.11

Periyar is the largest watershed in Idukki which covers two third of the

total area (68 %) covering most of the areas of Azutha, Nedumkandam,

Kattappana, Idukki, Adimali and Devikulam blocks. (Table 2.16) The streams

drain through the denudational hill section scattered in this region. The

Muvattupuzha watershed constitute the second largest watershed with 14% area of

the district covering entire Elamdesom, Thodupuzha block and Thodupuzha

municipality. Pambar the interstate watershed between Kerala and Tamil Nadu

covers 8.82% area of the district in northern part of Devikulam block, occupied by

Kudakkad and Chinnar reserved forest hills. Pambar, the inter district watershed

between Pathanamthitta and Idukki extends along the southern border in Azutha

block covers an area of 4.64% of the district. (Fig.2.13).The inter district

Manimala watershed borders with Kottayam district covering an area of 2.46 % of

51

FIGURE 2.13

52

the Idukki district occupied the western part of Azutha block. The smallest

watershed Meenachil borders along the western portion of Elappara, Arakulam

panchyats in Azutha and Idukki block.

2.12 DRAINAGE

The drainage network of the study area is significant because land

transformations and land use activities change the course of rivers and this lead to the

deterioration of streams. The exploitation of highland for plantation and other

activities affect the river basin system and the downstream regions. The drainage

system reveals the origin and development of streams over different geological

periods. The origin and subsequent evolution of drainage system is determined and

controlled by nature of surface, slope and geologic structure. ( Strahler A.N, 1969)

The Western ghats, running through the Idukki district, plays a significant

role in determining the uniqueness of this morphogenetic region. The study area

falls in this typical morphogenetic region is characterized by the presence of a

number of tributaries.

Human interference with the river systems has affected the natural flow of

rivers in a number of ways. Construction of dams and barrages on the major rivers

has affected the entire river system and its effects will be manifested as

aggradation or degradation in certain reaches and alteration of natural ecosystem

due to the changes in the supply of nutrients and sediments. Illegal deforestation

of the dense forests on the western ghat and plantation activities has resulted in

concentrated overland runoff and erosion.

The drainage is structurally controlled and most of the streams are flowing

through deep gorges with steeply sloping valleys.

Idukki district is drained mainly by three west flowing rivers namely Periyar,

Thodupuzha and Manimala and one east flowing river, the Pambar. (Fig.2.14)

Out of these, the major part of the district is drained by Periyar and its tributaries..

2.12.1 PERIYAR RIVER

Almost 80% of the district is drained by the river Periyar which originates

from Sivagiri hills in the south eastern part of the study area and takes a north

53

FIGURE 2.14

54

westerly course through the entire region. It is harnessed for electricity and irrigation

at various parts on the course of the river. Mullaperiyar dam, Idukki hydro electric

project, Idamalayar hydro electric project are constructed along its course of river

Periyar. Kundala Dam, Mattupetty Dam, Munnar head works, Ponmudi Dam, and

Kallarkutty dam are constructed across the various tributaries of river Periyar.

After it flows through the Peermedu, Udumbanchola and Devikulam

taluks, enters into the neighbouring district of Ernakulam. It flows through steep

valleys, with cascade, waterfalls and gorges and it also receives tributaries. The

tributaries confluence into Periyar lake and there after the river takes a roughly

north western course up to Ayyappan Kovil and then a northern course for about

20 km till Kumbalankudi. From there on, the river takes almost a straight line

course roughly in a North Western direction. The important tributaries of Periyar

river in the district are Mulla river, Pannar, Puyankutti Aru, Muthirapuzha Aru

and Perinjamkutti Aru. The Periyar River and its tributaries have good structural

control and are aligned along major fracture zones.

In Azutha block, river bed is rocky and sand deposits are found as sporadic

patches and the sands found here are coarse to medium grained with pebbles and

cobbles. Slumping of river banks and changes in the river bed configuration are

noticed in this area. In Kattappana block, river bed is rocky and sand deposits are

found all along the channel.

2.12.2. MULLA RIVER

It flows in the east west direction in the southern part of the district in

Azutha block at elevation ranges between 1020-1000 Metres. It originates at

Kottamalai peak in the Periyar Tiger Reserve. After flowing through the forest

section in the west, it joins with the Periyar at Mullakudy, just at the beginning of

the Periyar Lake formed by the Mullaperiyar dam.

2.12.3. PANNIAR

Panniar, the tributary of river Periyar flows in the east west direction in

Udumbancola taluk and merges with the Ponmudi reservoir. In Konnathady

55

panchayat of Udumbanchola taluk, the river channel is composed of crystalline

rocks and experiences less channel degradation. Sand deposits are found in

patches on the rocky river bed.

2.12.4. AZUTHA RIVER

Azhutha river which is the tributary of Pamba river flows along a tiny area

in south of the study area.

2.12.5. THODUPUZHA RIVER

The Thodupuzha river, a tributary of Muvattupuzha originates from the

Tangakkanam hills at an elevation of 1096 m above mean sea level. It mainly

flows through the Thodupuzha taluk in Idukki district and is observed that the

river bed is rocky and is composed of crystalline rocks and is very resistant to

channel degradation. Sand deposit is medium to coarse grained with gravel rich

and there sand deposits are found as sporadic patches along the river channel.

Some portion of the river bank exhibit slumping.

2.12.6. KALIYAR PUZHA

Kaliyar puzha which runs parallel to the Thodupuzha river in Thodupuza

taluk originates from Thodupuzha forest division at Chelakkadu at an elevation of

987 metres. It receives a tributary from the right known as Kannadi Aru at

Machani hills. In Elamdesom block the river stretch has been degraded

considerably due to indiscriminate sand mining activities. Consequently carving

of river banks, slumping, lowering of river channel and changes in river bed

configuration are seen in the area. River bed is rocky and sand deposits are

present as discrete patches in the course of Kaliyar puzha.

2.12.7. KARINTHIRI RIVER

Karinthiri river drains through Mankulam panchayat in Devikulam block

of the study area receives two tributaries in its left and right. The left bank

tributary is known as Metakadu Aru and in Mankulam panchayat of Devikulam

block, the river bed is rocky and the river flows through very steep valleys. Sand

deposits are found as patches on the rocky river bed and the sand is coarse to

medium grained with appreciable quantities of pebbles and cobbles. In Marayoor

56

panchayat of Devikulam block, the river bed is composed of hard crystalline

rocks; and the river stretch at many places is generally inaccessible as the river

flows through deep valleys.

2.12.8. MANIMALA RIVER

Manimala river flows through a small portion along the boundary with the

Kottayam district near Mundakkayam. River bed is composed of mainly

crystalline rocks. Sand and gravel deposits area are found as sporadic patches

along the river channel and the river bank on either side is covered with vegetative

growth.

2.12.9. MUTHIRA PUZHA

Muthira puzha flows through the central part of Idukki district along the

taluk boundary of Udumbanchola, Thodupuzha and Devikulam. It is a

continuation of river Periyar which joins with Idukki reservoir in south and

Ponmudi reservoir in north. In Bison valley panchayat of Adimali block, the

river channel is composed of crystalline rocks and experiences less degradation.

Sand deposits are also found in extensive patches along the river bed except close

to the Ponmudi reservoir.

Pamba river flows through the southern portion of the border line with

Pathanamthitta district in an east west manner.

2.12.10. PAMBAR RIVER

Pambar is one among the three east flowing rivers in the state. The river

originates in Devikulam taluk at an altitude of 1950 m above mean sea level. In its

initial reaches, it is locally called Thalayar. The river crosses into Tamil Nadu

State after covering a course of about 25 km within the Kerala State ( Kerala State

Gazetter 1986). The main tributaries of Pambar are Iravikulam, Myladi,

Thirthamala, Chengalar and Thenar. The Thenar has a 12 km course in Kerala and

joins Pambar after crossing the borders to form the Amaravathi river, a tributary

of Cauvery. The total catchment area of Pambar including that of Thenar within

Kerala State is 384 km2. The river exhibits a dendritic drainage pattern. The river

is having steep gradient and hosts several waterfalls (CGWB, 1999). Pambar and

57

Iravikulam diversion schemes are the two major commissioned projects in the

river (CWRDM, 1995). In Munnar panchayat of Devikulam taluk, the river

stretch is dominated by rocky substratum and sand deposits are found as patches

within the river channel. Sand is medium to coarse grained with appreciable

quantities of gravel. River banks are blanketed with tea plantations and forest.

2.12.11. PAMBA RIVER

Pamba river rises at an altitude of 1650 metre in Peermedu plateau of the

Azutha block in Idukki district and flows in a east west direction. It extends about

0.32 sq.km from Anavattam in east and flows towards west along the southern

boundary of the study area.

In addition to the river systems, the reservoirs found in this district are

Anayirangal, Idukki, Mattupetty, Mullaperiyar, Ponmudi, and Sethuparbatipuram

2.13. STREAM ORDERING

Stream ordering refers to the determination of the hierarchical position of

streams within a drainage basin. A river basin contains its definite branches or

segments having different positions in the basin area and they have their own

morphometric characteristics. Therefore it is necessary to locate the relative

position of a segment in the basin, so that the ranked system of stream segments is

visualised. Thus, stream order is the measure of the position of a stream in the

hierarchy of tributaries. (L.B.Leopold, 1969)

Table 2.17 IDUKKI DISTRICT - STREAM ORDER

DISTRIBUTION OF STREAMS

Stream order Stream length in Km

Stream number

1 8762 16480

2 2372 7332

3 1221 3803

4 573 1909

5 118 375

6 20 69

58

FIGURE 2.15

59

The following relationships are generally noted between stream length and basin

orders. (Table)

1. Total length of the given order is inversely related to stream order ie, total

stream length decreases from the lower order to successive higher orders.

2. There is positive relationship between mean stream length and basin order

ie, mean length increases with successive increasing orders.

The drainage pattern of Idukki displays both dendritic and trellis pattern

and slope failures are more frequent in first, second and third order

streams.(Fig.2.15) First order streams occupy a major part of the study area with a

length of 8762 Km and their concentration is least in Thodupuzha block where the

topography is lateritic in the dissected lower plateau and eastern portion of

Chakkupallam, Vandanmedu and Karunapuram panchayat exhibit denudational

structural hills.(Table 2.17) Second order streams are noticed in all the area with

a length of 2372 Km and is absent in Thodupuzha Municipality. Third order

streams spread in the area with a length of 1221 Km and is absent in Manakkad,

Kumaramangalam, Kodikulam panchayats of Thodupuzha, Elamdesom block and

Thodupuzha Municipality. Though the fourth order streams come with a length of

573 Km and are found in all taluks, their concentration is minimum in Idukki and

central part of Azutha block. Fifth order stream passes through the region with a

length of 118 Km mainly in Devikulam and Azutha block. The sixth order stream

is having a minimum length of 20 Km only in the Munnar and Marayoor

panchayaths of Devikulam block.

2.14. NATURAL VEGETATION

The highland region of Idukki is characterised by a high landscape

complexity with advantages of monsoon rainfall, and ideal soil conditions.

Variation of rainfall and altitude contribute natural vegetation mainly different

types of forests like tropical, evergreen, semievergreen and moist deciduous

forests. (Fig. 2.16) Major part of the study area is under forest cover confined to

south, central, north east and northern part occupying Azutha, Devikulam, Idukki,

Elamdesom and Adimali blocks of the study area. Major trees found in this region

are teak, rosewood, ebony, irul, white cader, and maruthu. The forest cover of

60

FIGURE 2.16

61

Idukki district extends through the forest divisions of Kottayam, Munnar,

Marayoor, Kothamangalam, , Thekkady (WL), Munnar (WL), Peermedu (WL),

Mankulam special division and Idukki (WL).(Forest Statistics, 2009)

2.15. SOIL

Soil is a natural resource and non renewable in a short term as it takes

between 200 and 1000 years for 2.5cm of topsoil to form (Piementel et al.,

1995).There are four major soil types identified in the district- forest loam, laterite

soil, brown hydromorphic soil and alluvial soil (CESS, 1984). A major portion of

the district is covered by forest loam which is the product of weathering of the

rock characterized by a surface layer rich in organic matter. They are generally

acidic, high in nitrogen content and poor in bases, due to heavy leaching and they

are dark reddish brown to black with a texture of loamy to silty loam. In highland

region where the denudation has occurred, leaching and deposition of humus is

common. The lateritic soil is the next prominent category and is seen in the

midland regions, particularly in Elamdesom and Thodupuzha blocks of the

district. It is well drained and is low in plant nutrients and organic matter. The

fertility of the soil is generally poor with low availability in nitrogen and

phosphorous. The brown hydromorphic soils are confined to valleys formed as a

result of transportation and sedimentation of materials from the adjoining hill

slopes. Alluvial soil is seen as narrow strips and is common along the banks of

Thodupuzha river and is fertile in nature.

2.15.1. SOIL TEXTURE

Soil texture is a permanent characteristic of the soil. It has an important

role in crop production from the stage of growing seeds up to the maturing of

crops. The surface soil textural class provides a guide to the understanding of soil

water retention and availability, workability of soil, infiltration and drainage

conditions, and suitability for specific crops. (Agboola et.al. 2000). Soil texture is

the coarseness or fineness of the soil determined by the relative proportion of the

various sizes of soil particles. Hence it is an indicator to analyse primary products

with various size in the soil mass. It is also an indicator of other soil properties,

but used alone, it has a limited predictive value of these other properties. Texture

62

FIGURE 2.17

63

indicates the ease with which a soil may be cultivated and it guides us to

understand the soil water retention and availability, workability of soil, infiltration

and drainage condition, crop suitability etc.

Table 2.18

IDUKKI DISTRICT- SOIL TEXTURE

Sl.No. Categories Area ( Sq.Km ) Percentage

1 Clay 3714.70 85.24

2 Gravelly Clay 280.60 6.44

3 Gravelly Loam 223.01 5.12

4 Loam 31.86 0.73

5 Water bodies 107.84 2.47

Source: Values derived from Soil Texture Map

Four broad textural groups are identified in the region, such as clay,

gravelly clay, gravelly loam and loam soil. Table 2.18 and Figure 2.17 shows the

distribution of soil in the study area as per the surface textural classes. The largest

part of about 85.27% study area is covered by the clayey soil found in all regions

of Idukki district excluding western half of Thodupuzha block, Peruvanthanam

and Kokkayar panchayaths of Azutha block and the central part of Marayoor and

Kanthalloor panchayat in Devikulam. Gravelly clay (6.44%) occurs in Adimaly

panchayat in the southern portion of Devikulam, and Manakkad, Purapuzha,

Karimkunnam, and Thodupuzha. The Highland series of gravelly loam consists of

moderately deep, well drained soils that are formed in colluviums on back slopes

from 15 to 50 percent of mountains. It covers an area of 5.12% and is found in

Arakkulam, Kudayottoor, Velliamatom,Vannapuram; and Adimaly panchayat in

Thodupuza and Devikulam block. The southern portion of the district mainly in

Kokkayar and Peruvanathanam panchayat in Azutha also have this soil. Loam

soils constitute less than 1% of the area covering Marayoor, Kanthalloor and

Vannapuram in Devikulam and Thodupuzha block.

2.15.2. SOIL DRAINAGE

The air and water movement within the soil profile is governed by internal

soil drainage. Drainage capacity of each soil profile is governed by soil texture,

64

FIGURE 2.18

65

landform characteristics, and depth of ground water table which has an influence

on erosion and cropping etc.(.Zotaj et.al. 2006) The growth of vegetation depends

upon drainage condition which prevails within the soil. The colour of soil profile

and their distribution is an indicator of the average drainage conditions of several

seasons.

Table 2.19 IDUKKI DISTRICT - SOIL DRAINAGE

Sl.No Categories Area ( Sq.Km ) Area (%)

1 Imperfectly Drained 57.64 1.32 2 Moderately well Drained 58.97 1.35 3 Well Drained 4241.39 97.32

Idukki district is identified as well drained (97.32%) because of the

availability of water with the presence of network of streams and preservation of

humidity by the vegetation (Table 2.19). In a well drained soil, the drainage water is

removed readily but not rapidly from soils which consequently are dry for a

significant part of the time although they commonly retain near optimum amounts of

moisture for lengthy periods. Well drained soils are commonly intermediate in

texture, although soils of other textural classes may also be well drained. (Fig 2.18)

Moderatly well drained soils constitute only 1.32% of the study area

occurring in Idavetty and Kodikulam panchayaths of Thodupuza and Elamdesom

block. In this drainage, water is removed from the soil slowly, so that the profile is

wet for a small but significant part of time. These soils have a slowly permeable

layer within or immediately beneath the solum, with relatively high water table,

addition of water through sweepage, or some combination of these conditions.

In an imperfectly drained soil, water is removed from the soil slowly

enough to keep it wet for significant periods but not all the time. It occupies an

area of 1.3% in the Marayoor, Kanthalloor, Munnar, Devikulam, Konnathady

panchayaths of Devikulam and Adimali block.

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2.15.3. SOIL SLOPE

Formation of soils on side slope is influenced by the configuration of the

land from east to west in this region as it controls surface run-off and erosion.

Since the area experience variation in climate with respect to rainfall, it influences

the rate of run-off through the area. The relationship of soil slope to soil properties

varies due to the intensity and nature of the other soil forming factors. Within the

region the properties are commonly found to be relief related; thickness and

organic content, depth of the colum and other characteristics of the materials. In

humid highland regions where the soils are on nearly low relief tend to have

thicker solum than those found on slopes. The involvement of other soil forming

factors makes it difficult to isolate the influence of slope on soils. Certainly it is

not possible to find one type of soil on steep slopes and another on level ground.

However, if the soil type is uniform, then quality of soil is better on level ground

than on steep slope.

Table 2.20

IDUKKI DISTRICT - SOIL SLOPE

Sl.No. Categories Area (Sq.Km) Area ( % ) 1 Very Gentle 21.7 0.50 2 Gentle 218.8 5.02 3 Moderate 618.8 14.20 4 Moderately Steep 3167.8 72.69 5 Steep 223.0 5.12 6 Water bodies 107.84 2.47

Table 2.20 shows the distribution of soils in the region according to their

slope class and Figure 2.19 shows that the soil slope is moderately steep about

72.69% of the study area in all the blocks. This character is found mainly in

Nachivayal, Kodikulam, Idavetty, Purapuzha, Kumaramangalam, Kodikulam,

Karimanoor , Alakkode and Thodupuzha Municipality. Steep soil slope (5.12%)

extends in Arakulam, Kudayattoor, Velliayamattam, and Vannapuram, Kokkayar,

and Peruvanthanam panchayaths. Moderate situation (14.20%) is mostly confined

to Vandiperiyar, Kumily,Vandanmedu, Vazhathope, Kanchiyar, Muttom,

Senapathy, Chinnakanal, Adimaly, and Munnar panchayaths.

67

FIGURE 2.19

68

FIGURE 2.20

69

2.15.4. SOIL DEPTH

Soil depth is an important parameter which determines the types of vegetation

and its performance. The occurrence of soil layer in this area need special attention

because of plantation and other related activities.( Kosmas, et.al. 1999). The depth

of the soil suggests the volume of soil, in which the plant root can obtain nutrients and

water for its growth. Deeper the soil, more chance for the trees to get nutrients and

water for plants. Therefore deep soil has more advantage over the shallow soil. Deep

soil indicates that the soil has been through a longer time for its formation from the

parent material. Spatial pattern in soil depth arises from complex interactions of

surface elements of the region.

Soil depth provides an indication of the available water capacity, which in

turn affects evapotranspiration. Consequently accurate representation of soil depth at

scales relevant to these processes is increasingly important in land degradation

studies.

Table 2.21 IDUKKI DISTRICT - SOIL DEPTH

Sl.No Categories Area ( Sq.Km ) Area ( % )

1 Deep 131.81 3.02

2 Very Deep 4118.35 94.50

3 Waterbody 107.84 2.47

Table 2.21 and Fig 2.20 shows the distribution of land according to soil

depth classes. About 95 % of the total area in the district is having very deep soil

except a small portion of western margin; and the deep soil areas ( 3.02%) are

found in the western margin mainly in parts of Adimali, Vannapuram, Muttom,

and in small linear stretches of Kumily and Peruvanathanam panchayaths.

2.16 EROSION PRONENESS

Soil resource is significant to preserve the productivity in high

mountainous region. Sustainable use of highland depends upon conservation and

potential use of soil and water resources (Sushil Kumar, et.al. 2002). Land

70

degradation, especially soil erosion is a severe and sweeping problem in many areas

of highland region of India. An erosion prone area varies in accordance with the

physical configuration of the land and is subjected to the variables acting upon it.

Assessment and mapping of erosion prone area is necessary for the conservation of

soil and thereby land quality (Kalpana O. Bhaware, 2006). Various anthropogenic

activities agitate the highland ecosystem and thereby activate serious diversification

of natural erosion rates. Accelerated soil erosion has negative economic and

environmental impacts and it initiates on-site and off-site effects on productivity due

to decline in land and soil quality (Shrestha 1997).

The Idukki highland region of Western Ghats has been experiencing soil

erosion in different levels from time immemorial. Susceptibility to erosion is the

prime concern for determining the vulnerability to land degradation in the terrain.

Assessment of the terrain provides the status of erosion in land system with

respect to physical components exerting their role upon them (Moench, 1991). In

this study the components taken for evaluation are slope, drainage density and

vegetation cover and the layers are overlaid by giving weightage to derive the

erosion prone area into four classes.

Table 2.22 EROSION PRONENESS

EROSION PRONENESS

Categories Area in Sq.Km Area in %

Low 712.40 16.35 Moderate 1164.79 26.73 High 1443.53 33.12 Very High 1037.28 23.80

It is noticed from the table 2.22 that major part of the study area

experienced high erosion proneness of 33.12% is evident in the blocks of

Azutha, Devikulam, Adimali, Idukki and Kattappana where the impact of

drainage, slope and vegetation cover is high. Very high situation of 23.80% is

observed in the blocks of Devikulam, Azutha and part of Idukki and Elamdesom.

Moderate erosion proneness predominantly found in Azutha , and some of the

71

FIGURE 2.21

72

sections in Devikulam and Nedumkandam blocks. Erosion proneness is low

(16.35%) mostly towards the west comprises of Thodupuzha block and

municipality area. (Fig.2.21)

2.17 SOIL EROSION

Soil erosion is a common and unavoidable process but it can be turned to

be a severe environmental and economic problem when it is accelerated by human

activities. (Tania Del Mar Lopez et al, 1998). Process involved in soil erosion is

complex in nature, influenced by topography, soil characteristics, climate and land

use. In highland region where topography, soil and climate are akin, the rate of

erosion and their variation are connected with the prevailing land use in the

region. Land use practices which change the landscape is notable in highlands and

it leads to deterioration of land by way of declining productivity. Soil erosion

varies within and among the land uses due to the human activities such as

farming, mining and tourism etc.

In developing countries like India, soil erosion has accelerated due to

demographic, socio-economic factors and limited resources (Bayramin et.al,

2002). The highland ecosystem exhibits diverse land use practices, and poor land

management that leads to soil erosion and the farmers are incapable of

maintaining soil fertitility.

Table 2.23

IDUKKI DISTRICT- SOIL EROSION

Sl.No. Categories Area ( Sq.Km ) Area %

1 Moderate Erosion 2451.20 56.25

2 Moderate to Severe Erosion 1694.04 38.87

3 None to Slight Erosion 21.70 0.50

4 Severe and Rockland 79.51 1.82

5 Severe to Moderate Erosion 3.70 0.08

6 Water bodies 107.84 2.47 Source: NBSS&LUP, Bangalore

73

FIGURE 2.22

74

Among the different classes of soil erosion more than half of the area exhibit

moderate erosion (56%) and this is found in the blocks of Azutha, Kattappana,

Nedukandam, Elamdesom, Thodupuzha, Devikulam and Thodupuzha

municipality. (Table 2.22) Moderate to severe erosion (39%) has occurred from

north to south in Devikulam, Adimali, Idukki and Azutha block. Severe and

rockland(1.82%) is found in two sections of Adimali and Thodupuzha blocks

which comprises of open forest and mixed crops with settlement. (Fig.2.22).