Physical Features of Western Ghats- HIMALAI IAS
The river Pamba rises at an
altitude of 1650 m in the Peermade Plateau in the Idukki district of Kerala and
after traversing a distance of 176 km joins the Arabian Sea branching into a
number of channels. The basin extends over an area of 2235 km2. The entire
catchment area lies in Kerala state. The basin is bounded on the east by Western
Ghats and on the west by Arabian Sea. Manimala basin forms the northern
boundary of the basin while Achankovil basin forms southern boundary.
The river Achankovil rises south
of Devarmalai in the Western Ghats in the Pathanamthitta district of Kerala
at an elevation of 700 m. The Achankovil River after flowing for 128 km
joins the Pamba River at Veeyapuram. The basin extends over an area of
1484 km2 and lies entirely in Kerala State. The basin is bounded on the north by
Pamba basin and on the south by Kallada and Pallikkal basin. The Western
Ghats form eastern boundary of the basin while the Arabian Sea forms the
western boundary.
Major portion of the command area
lies in Vaippar basin. The total drainage area of Vaippar basin is 5255 km2.
The basin is bounded on the west by the Western Ghats, on the east by the
Bay of Bengal, on the north by the Vaigai basin and on the south by the
ridge line separating the Vaippar and other streams south of Vaippar. The
river Vaippar rises from the eastern slopes of the Varushanad hill range of the
Western Ghats at an elevation of about 1500 m near Sivagiri in the
Tirunelveli district of Tamil Nadu and flows generally in the easterly and south easterly
direction for a length of 140 km before joining
the Gulf of Mannar.
Topography of the basins,
reservoirs and command area
Like all the river basins in
Kerala, the Pamba and the Achankovil basins also can be divided into three natural
zones based on elevation, consisting of low land or sea-board, midland and
high land. The coast for a short distance along the borders of lakes is
flat, retreating from it the surface roughens up into slopes which gradually
combine and swell into mountains on the east. The low land area along sea coast
is generally swampy and liable to be flooded during monsoon
inundation. The plains/midlands succeed low land in gentle ascents and valleys
interspersed with isolated low hills. The high land on the eastern portion is broken
by long spurs, dense forests, extensive 1ravines and tangled jungles. Towering above
all their slopes are Western
Ghats that form eastern boundary
of the basins.
The Punnamedu dam lies in high
land region while the Achankovil Kal Ar and Achankovil dams are located in
midland regions. The main canal taking off from
the exit of tunnel from Achankovil Kal Ar reservoir pass through generally
gently sloping land, the slope generally lying in the range of 1 in 500 in the
initial reaches followed by more or less plains.
Geology of the basins, reservoirs
and command area
(i) Pamba Kal Ar
(i) Pamba Kal Ar
As per the Geological Survey of
India publication No. 30 the most prominent rock formation at the Punnamedu
dam site is of Archaean age Charnockites.Their colour varies from bluish
to dark. They are granulitic in texture. Charnockites with narrow bands of
pyroxene granulities, magnetite, magnetite quartz rock are the most wide
spread group of rocks in the area. The bed and banks of the river are of
rocky formation.
The Geological Survey of India
has conducted preliminary geo-technical investigation of Pamba Kal Ar dam
site. Fresh Charnockite gneiss with thin weathered layer is exposed in the
riverbed with the hill slopes on either banks covered by soil and scree
material. The riverbed is exposed with rock in blocky to massive, moderately
foliated joints.
(ii) Achankovil Kal Ar
The Achankovil Kal Ar dam site is
of Archaean aged Charnockites. Fresh magnetite with granulite /
amphilbolite rafts, Charnockites and intrusives of granite and pegmatite are exposed
in the riverbed at the dam axis. The rock exposures are confined to the
riverbed and the flanks and uphill side slopes are covered with soil and
boulders. The preliminary study indicates that the thickness of the overburden is
around 10-15 m at the lower levels and upto 25 m at higher levels.
(iii) Achankvoil river
Moderately weathered to fresh
garnetiferous biotite gneiss is exposed in the bed of Achankovil river on the
right bank. Some foliation joints are also noticed along east-west
direction.
(iv) Interconnecting tunnel
The inlet of the Pamba Kal Ar -
Achankovil Kal Ar interconnecting tunnel is located on the left bank of
Chellikkal Ar, a tributary of Pamba Kal Ar. Moderately weathered to fresh
Charnockites are exposed in the riverbed at the site. Foliations in
north-east and south-west direction are noticed at the site. The tunnel traverses across
the ridge between Pamba and Achankovil basins. Outlet of the tunnel is
located on the right flank of Muthuvantodu, tributary of Achankovil Kal Ar.
At the outlet point soil and scree material and weathered charnockite exposures
are existing nearby.
(v) Achankovil Kal Ar – Tamil
Nadu tunnel
The inlet point of the tunnel is
located on the left bank of Achankovil Kal Ar River near Pulikkayam. Massive
charnockite gneiss is exposed at the inlet location. Foliation is trending
in northeast to southwest direction with vertical dip and is near normal to
sub-normal to the tunnel alignment. The tunnel outlet is located near Mundal Ar
in Tamil Nadu side. The site is exposed with massive Charnockites and have
sufficient rock cover above the tunnel.
(vi) Command area
The command area lying in the
Tirunelveli, Virudhunagar and Tuticorin districts is predominantly
covered by Peninsular gneisses, granites and other sedimentary and metamorphic rocks
with two third area comprising rocks of Archaean origin of igneous
metamorphic/ other intruded rocks and remaining area covered by rocks of
sedimentary origin. There are two main groups of rocks in the area viz.
Charnockites and the Khondalites. Charnockites and associated migmatites occupy the
western parts of Sankarankovil taluk but occur only as thin bands and
lenses in the other parts of the basin. The Khondalite group with ferrous
zilmanite graphite gneiss with the associated migmatite exists in the southern
and western parts of the Tirunelveli district and garnetiferrous biotite
gneisses and quartz feldspathic gneisses with their migmatitic derivatives exist in
the Tuticorin district, southern parts of Virudhunagar district and
northern parts of the Tirunelveli district. Thin bands of quartzite and crystalline
limestone are associated with the Tirunelveli and Kovilpatti taluks.
The soils in the command area can
be broadly classified as Grayish brown clayey soils, Yellowish brown to
reddish brown soil and grayish brown to light brownish grey soils. Grayish brown soil extends over 65%
area of the project command and are developed from
weathered classic gneiss and schist’s. Texture of this soil varies from
sandy loam to sandy clay loam and sandy clay 3loam to clay loam in surface, clay loam to
clay in sub-surface horizon. Yellowish brown to reddish brown
soils are derived from weathered quartzite
gneisses. Texture of the soil is
mostly coarse loam in surface and sub-surface is sandy clay to gravely clay.
Grayish brown to light brownish grey soils are developed from calcareous
quartzite gneiss and cover 16% area of command.
River system and Basin
characteristics:
Basins
(i) The Pamba
The Pamba is the third longest
river in Kerala. It is formed by the confluence of Pamba Ar, Kakki Ar, Arudai Ar,
Kakkad Ar and Kall Ar. The Pamba Ar in turn is formed by several streams
having their origin in the Pullichimalai, Nagamalai and Sundaramalai in the
Peermade plateau at an altitude of +1650 m. The river flows downwards in a
north-westerly direction till it receives some more streams from
Maruvattapara Malai. It then flows in southwesterly direction till its confluence
with Kakki Ar. The Pamba after receiving Kakki Ar
flows in a westerly direction
till Arudai Ar joins it near Udumpara Malai. The river then flows in a
southwesterly direction till Ponachi and in southeasterly course until the Kakkad Ar joins
the river near Perunad. The river then flows in a southern direction upto
Vadasserikkara where it is joined by the Kall Ar.
It then flows in northwest upto
Panni before taking southwestern course. The river is known as Panni Ar here.
The river flows in western course upto Kuriannur and in southern
direction upto Kozhencherry and takes a westerly direction upto Pandanad. The
river splits into two branches near Pandanad. One branch flows in southwesterly
direction and is joined by a branch of Achankovil River. The Manimala
River joins the Pamba near Nirettupuram. The river thereafter flows northward
and falls into Vembanad lake. The Pamba Kal Ar on which the
Punnamedu dam is located originates from Peermade plateau in Idukki
district at an altitude of +1050 m. The river flows for about 67 km in northwesterly
direction before joining Pamba near
Vadasserikkara.
(ii) The Achankvoil
The Achankvoil River is formed by
joining of several small streams originating from the Pasukida Mettu, Pamakkal
Teri and Rishi Malai at altitudes ranging between +700 m and +160 m. The
river follows a north westerly course till Kumbazha and in this portion it
is joined by Kal Ar about 1 km upstream of Turai forests. The river follows
a generally western direction till Idappamon. Here it turns northwest upto
Thazakkara and thereafter flows westwards. At Tharaimukku, the Kuttenperoor
canal branches from the main river and joins
4Pamba. The river then splits up in several
branches and the main branch flows in a north westerly direction to
join Pamba river near Veeyapuram.
The Achankovil Kal Ar on which the
Achankovil Kal Ar dam is located rises in Western Ghats near Devarmalai at
an elevation of +1200 m and flows for 30 km in generally east-west
direction before taking southern turn to join Achankovil river.
Basin characteristics
(i) Rainfall
Like many parts of India, the
Pamba and Achankovil basins receive major portion of rainfall during
south-west monsoon period (June – September). The south-west monsoon forms
around 80 per cent of annual rainfall. The north-east monsoon constituting
remaining portion of rainfall strikes in October and continues till
November.
The rainfall distribution in the
Pamba basin is mainly influenced by the geographical disposition and the
physical features of the area within the basin. The Western Ghats forming
eastern boundary of the basin receives fairly high rainfall ranging from
4307 mm to 3659 mm. The areas west of Western Ghats receive lesser
rainfall with the increasing distance from Western Ghats. The average annual
rainfall down of Western Ghats ranges from 3324 mm in the reaches near
Western Ghats to 2900 mm near coast. The rainfall in Achankovil basin
on the other hand is distributed fairly uniformly through out the basin
varying from 3346 mm to 2317 mm except for an isolated case of 6556 mm.
The average annual rainfall of the Pamba Kal Ar and Achankovil Kal Ar
catchments is around 2600 mm.
The command area receives major
portion of the rainfall during north-east monsoon i.e., during
October-December. The average rainfall in the command area is 772 mm. This area
experiences a maximum and minimum of 184 mm and 14.5 mm so far
during November and June in monsoon period.
(ii) Climate
Both the Pamba and Achankovil
basins enjoy tropical climate without much variation in temperature. Good
rainfall, moderate temperature and a humid atmosphere throughout the year
are the characteristic features of these basins. The climate along the
coastal areas of the basin is generally hot with a high degree of humidity. The
temperatures in the mountainous regions are generally low. The south-west
monsoon which is dependable, sets in June and lasts till September. The north-east
monsoon which is uncertain sets in October and continues till
November.
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HIMALAI IAS - ALL CORNERS OF BANGALORE & DELHI, ALL DIRECTIONS OF KARNATAKA, ALL REGIONS OF INDIA - FREE FOR JAMMU & KASHMIR ASSAM, SIKKIM, NAGALAND, ARUNACHAL PRADESH, MEGHALAYA, MANIPUR, NEPAL, BHUTAN - FOR PASSING EXAM, VISIT - www.himalaiiasclasses.com, Email: iashimalai@gmail.com, Contact: 11:00am to 8:00pm - 91- 9740346715/ 91-9844609250.