Drainage System in India
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Basic concepts of
drainage
Question: What are ‘drainage systems’
and the geographical factors affecting a drainage system?
Answer: The flow of water through well-defined channels
is known as ‘drainage’ and
the network of
such channels is called
a ‘drainage system’.
The
drainage pattern
of an area is the outcome of or
depends upon:
· the geological time period
·
nature and structure of rocks
· topography
· slope
· amount of water flowing and the periodicity
of the flow
Ø Catchment
Area: A river drains the water collected
from a specific
area, which is called
its
‘catchment area’.
Ø Drainage basin: An area drained
by a river and its tributaries
is called a drainage basin.
Ø
Watershed: The boundary
line separating
one
drainage
basin from
the
other
is
known
as
the
watershed.
Ø Water divide: The geographical boundary separating two drainage systems
is called water divide.
Ø River Regime: The pattern of
flow of water in a river channel
over a year
is known as its
regime.
Note: The catchments of large rivers are called river basins while those of small rivulets and rills are often
referred to as watersheds. There is, however, a slight difference
between a river basin
and a watershed. Watersheds are
small in area while the
basins cover larger areas.
Important Drainage Patterns
1. Dendritic pattern:
The drainage pattern resembling the branches of a tree is known as “dendritic” the examples of which are the rivers of northern plain. It is the most common form of drainage system. In a dendritic system, there are many contributing streams (analogous to the twigs
of a
tree), which are then joined together into the tributaries of the main river (the branches and
the trunk of the tree, respectively).
They develop where the river channel follows the slope of the terrain.
2. Parallel drainage pattern:
A parallel drainage system
is a
pattern of rivers caused by steep slopes with some relief.
Because of the steep slopes, the streams are swift and straight, with very few tributaries, and all flow in the same direction. This system forms on uniformly sloping surfaces, for example, rivers
flowing southeast from the Aberdare Mountains in
Kenya.
3. Radial Pattern:
When the rivers originate from a hill and flow in all directions, the drainage pattern is known as
‘radial’. The rivers originating from the Amarkantak range present a good example of it.
4. Trellis Pattern:
When the primary tributaries of rivers flow parallel to each other and secondary
tributaries join them at right angles, the pattern is known as ‘trellis’. The geometry of a trellis drainage
system is similar to that of a common garden trellis used to grow vines.
As the river flows along a strike valley,
smaller tributaries feed
into it from the steep slopes
on the sides
of mountains. These
tributaries enter the main
river at approximately 90 degree angles, causing a trellis-like appearance of
the drainage system. Trellis drainage is
characteristic of
folded mountains.
5. Centripetal Pattern: When the rivers discharge their waters from all directions in a lake or depression,
the pattern is known as ‘centripetal’.
Consequent and Subsequent rivers
Ø A river system that follows a normal downhill pattern along a pre-existing land surface is said to be
consequent (the consequence of original slope). This
pattern can be altered by mountain uplift,erosion around resistant rock units, etc. When
altered, this is called subsequent (subsequent to the
original pattern).
Ø Occasionally a
river may erode its bed into the path
of
another and capture
it. This is called
stream capture or piracy. When this happens, the downstream portion
of the captured river dries up
and is said to be beheaded.
Antecedent and Superimposed Rivers
Ø The case of rivers cutting right through mountain ranges is especially intriguing. Two models have
been given serious consideration. The first, called ‘antecedent’, postulates that the river has stayed
more or
less in its original position as slow uplift of the region has taken place.
Ø As long as uplift is slower than the erosional capability of a river, the river can maintain its normal
position
and
grade (slope) across uplifting regions.
Ø Its position being antecedent to uplift,
the
sequence is appropriately
referred to as antecedent drainage.
Ø The river Arun, which crosses the Himalayas a few dozen km east of Mount Everest through deep and
almost impassable gorges, is considered to be antecedent. The second model to explain rivers cutting through mountain
ranges are called ‘superposed’,
a contraction of superimposed.
Ø In this model the pattern of a river from a higher level is superimposed on the present topography.
The mountain ranges are assumed to have already been there but buried in sediments and the rivers flow
on the surface of
the sediments
that cover these ranges.
Ø
The sedimentary layers over and around the mountain ranges are then eroded with time and the river cuts
down through them including the buried ranges.
With
either model one ends up with the same final
result. This makes it more difficult to tell which really
occurred.
INDIAN DRAINAGE SYSTEM:
Indian drainage system may be divided on various bases.
A. On the
basis of discharge of
water (orientations to the sea), it may be grouped
into:
1. The Arabian Sea drainage
2. The Bay of Bengal drainage.
They are separated from each other through the Delhi ridge, the Aravalis and the Sahyadris. Nearly 77 per cent of the drainage area consisting of the Ganga,
the Brahmaputra, the Mahanadi, the Krishna, etc. is oriented towards the Bay of Bengal while 23 per cent comprising the Indus, the Narmada, the Tapi, the Mahi and the Periyar
systems discharge their waters in the Arabian Sea.
B. On
the basis of the size of
the watershed, the
drainage basins of
India are grouped
into three categories:
i. Major river basins with more than 20,000 sq. km of catchment area. It includes 14 drainage basins such
as the Ganga, the Brahmaputra, the Krishna, the Tapi, the Narmada, the Mahi, the
Pennar, the Sabarmati, the Barak, etc.
ii. Medium river basins with catchment area between 2,000-20,000 sq. km incorporating 44 river basins such as the Kalindi, the Periyar, the Meghna, etc.
iii. Minor river basins with catchment area of less than 2,000 sq. km include fairly good number of
rivers flowing in the area of low rainfall.
C. On
the basis of the mode of
origin, nature and characteristics, the Indian drainage may also be
classified into:
i. The Himalayan drainage
ii. The Peninsular drainage.
Although it has the problem of including the Chambal, the Betwa, the Son, etc. which are much older in age and origin than other rivers that have their
origin in the Himalayas,
it is the most accepted basis of
classification THE HIMALAYAN DRAINAGE Ø The Himalayan drainage system has evolved through a long geological history Ø It mainly includes the Ganga, the Indus and the Brahmaputra river basins. Since these are fed both by melting of snow and precipitation, rivers of this system are perennial. |
Ø The various
geographical features made by the Himalayan rivers are:
· In upper reaches (Youthful stage): Gorges, V-shaped
valleys, rapids,
waterfalls, truncated spurs etc.
· In plane areas or middle part (Mature stage): While entering the plains, they form depositional features like flat valleys, ox-bow lakes, flood plains,
braided channels, and deltas near the river
mouth. Over the plains they display a strong meandering tendency and shift their courses frequently.
The major river systems of Himalayan drainage are
1. The Indus system
2. The Ganga system
Note: Discuss their life from their birth
to
death i.e. from source to mouth.
Major features
if they make,
their
importance etc.
THE PENINSULAR DRAINAGE SYSTEM
Ø
The Peninsular drainage system is older than the Himalayan one. This is evident from the broad, largely-graded shallow valleys, and the maturity of the rivers.
Ø The Western Ghats running close to the western coast act as the water divide between the major
Peninsular Rivers, discharging their water in the Bay of Bengal and as small rivulets joining the Arabian
Sea.
Ø Most of the major Peninsular Rivers except Narmada and Tapi flow from west to east. The Chambal, the
Sind, the Betwa, the Ken, the Son, originating in the northern part
of the
Peninsula belong to the
Ganga river system.
Ø The other major river systems of the peninsular drainage are – the Mahanadi the Godavari, the Krishna
and
the Kaveri. Peninsular rivers are characterized by fixed course, absence
of meanders and non-
perennial flow of water. The Narmada and the Tapi
which flow through the rift valley are, however, exceptions.
Note: Regarding evolution of Himalayan drainage and Peninsular drainage system: A story could be told to
make it interesting.
Comparison between the Himalayan River system and Peninsular River system:
Small Rivers flowing West
River
|
Origin
|
Shetruniji
|
Amreli district
|
Bhadra
|
Rajkot district
|
Dhadhar
|
Panchmahal district
|
Vaitarna
|
Nasik district
|
Kalinadi
|
Belgaum district
|
Sharavati
|
Shimoga district
|
Other important west flowing rivers are: Sabarmati, Mahi, Periyar,
Bharatpuzha, Dhandhar etc.
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