IAS Prelims (GS) Preparation 2018
Day # 23 (April 15, 2017)
Topics of the day: Geography 9th NCERT chapter 3 key points
Chapter – 3
The term drainage describes the river system of an area.
The area drained by a single river system is called a drainage basin.
A mountain or an upland that separates two drainage basins is known as water divide.
The drainage systems of India are mainly controlled by the broad relief features of the subcontinent.
Accordingly, the Indian rivers are divided into two major groups:
i. the Himalayan rivers; and
ii. the Peninsular rivers
The Himalayan Rivers:
Most of the Himalayan rivers are perennial.
It means that they have water throughout the year.
These rivers receive water from rain as well as from melted snow from the lofty mountains.
The two major Himalayan rivers, the Indus and the Brahmaputra originate from the north of the mountain ranges.
They have cut through the mountains making gorges.
The Himalayan rivers have long courses from their source to the sea.
They perform intensive erosional activity in their upper courses and carry huge loads of silt and sand.
In the middle and the lower courses, these rivers form meanders, oxbow lakes, and many other depositional features in their floodplains.
They also have well-developed deltas.
The major Himalayan rivers are the Indus, the Ganga and the Brahmaputra.
These rivers are long, and are joined by many large and important tributaries.
A river along with its tributaries may be called a river system.
The Indus River System
The river Indus rises in Tibet, near Lake Mansarowar.
Flowing west, it enters India in the Ladakh district of Jammu and Kashmir.
Several tributaries, the Zaskar, the Nubra, the Shyok and the Hunza, join it in the Kashmir region.
The Indus flows through Baltistan and Gilgit and emerges from the mountains at
Attock.
The Satluj, the Beas, the Ravi, the Chenab and the Jhelum join together to enter the Indus near Mithankot in Pakistan.
Beyond this, the Indus flows southwards eventually reaching the Arabian Sea, east of Karachi.
The Indus plain has a very gentle slope.
With a total length of 2900 km, the Indus is one of the longest rivers of the world.
A little over a third of the Indus basin is located in India in the states of Jammu and Kashmir, Himachal Pradesh and the Punjab and the rest is in Pakistan.
According to the regulations of the Indus Water Treaty (1960), India can use only 20 per cent of the total water carried by Indus river system. This water is used for irrigation in the Punjab, Haryana and the southern and western parts of Rajasthan.
The Ganga River System
The headwaters of the Ganga, called the ‘Bhagirathi’ is fed by the Gangotri Glacier and joined by the Alaknanda at Devaprayag in Uttarakhand.
At Haridwar the Ganga emerges from the mountains on to the plains.
The Ganga is joined by many tributaries from the Himalayas, a few of them being major rivers such as the Yamuna, the Ghaghara, the Gandak and the Kosi.
The river Yamuna rises from the Yamunotri Glacier in the Himalayas.
It flows parallel to the Ganga and as a right bank tributary, meets the Ganga at Allahabad.
The Ghaghara, the Gandak and the Kosi rise in the Nepal Himalaya. They are the rivers, which flood parts of the northern plains every year, causing widespread damage to life and property but enriching the soil for the extensive agricultural
lands.
The main tributaries, which come from the peninsular uplands, are the Chambal, the Betwa and the Son. These rise from semi arid areas, have shorter courses and do not carry much water in them.
Enlarged with the waters from its right and left bank tributaries, the Ganga flows eastwards till Farakka in West Bengal. This is the northernmost point of the Ganga delta. The river bifurcates here; the Bhagirathi-Hooghly (a distributary)
flows southwards through the deltaic plains to the Bay of Bengal. The mainstream, flows southwards into Bangladesh and is joined by the Brahmaputra. Further down stream, it is known as the Meghna. This mighty river, with waters from the Ganga, and the Brahmaputra, flows into the Bay of Bengal. The delta formed by these rivers is known as the Sunderban delta.
The length of the Ganga is over 2500 km.
Ambala is located on the water divide between the Indus and the Ganga river systems.
The plains from Ambala to the Sunderban stretch over nearly 1800 km, but the fall in its slope is hardly 300 metres. In other words, there is a fall of just one metre for every 6 km. Therefore, the river develops large meanders.
The Sundarban Delta derived its name from the Sundari tree which grows well in marshland.
It is the world’s largest and fastest growing delta. It is also the home of Royal Bengal tiger
The Brahmaputra River System
The Brahmaputra rises in Tibet east of Mansarowar lake very close to the sources of the Indus and the Satluj.
It is slightly longer than the Indus, and most of its course lies outside India.
It flows eastwards parallel to the Himalayas.
On reaching the Namcha Barwa (7757 m), it takes a ‘U’ turn and enters India in Arunachal Pradesh through a gorge. Here, it is called the Dihang and it is joined by the Dibang, the Lohit, and many other tributaries to form the Brahmaputra in Assam.
In Tibet the river carries a smaller volume of water and less silt as it is a cold and a dry area.
In India it passes through a region of high rainfall. Here the river carries a large volume of water and considerable amount of silt.
The Brahmaputra has a braided channel in its entire length in Assam and forms many riverine islands.
Every year during the rainy season, the river overflows its banks, causing widespread devastation due to floods in Assam and Bangladesh.
Unlike other north Indian rivers the Brahmaputra is marked by huge deposits of silt on its bed causing the river bed to rise. The river also shifts its channel frequently.
Brahmaputra is known as the Tsang Po in Tibet and Jamuna in Bangladesh.
The Peninsular Rivers
A large number of the Peninsular rivers are seasonal, as their flow is dependent on rainfall.
During the dry season, even the large rivers have reduced flow of water in their channels.
The Peninsular rivers have shorter and shallower courses as compared to their Himalayan counterparts.
However, some of them originate in the central highlands and flow towards the west.
Most of the rivers of peninsular India originate in the Western Ghats and flow towards the Bay of Bengal.
The main water divide in Peninsular India is formed by the Western Ghats, which runs from north to south close to the western coast.
Most of the major rivers of the Peninsula such as the Mahanadi, the Godavari, the Krishna and the Kaveri flow eastwards and drain into the Bay of Bengal.
These rivers make deltas at their mouths. There are numerous small streams flowing west of the Western Ghats.
The Narmada and the Tapi are the only long rivers, which flow west and make esturies.
The drainage basins of the peninsular rivers are comparatively small in size.
The Narmada Basin
The Narmada rises in the Amarkantak hills in Madhya Pradesh.
It flows towards the west in a rift valley formed due to faulting.
On its way to the sea, the Narmada creates many picturesque locations.
The ‘Marble rocks’, near Jabalpur where the Narmada flows through a deep gorge, and the ‘Dhuadhar falls’ where the river plunges over steep rocks, are
some of the notable ones.
All the tributaries of the Narmada are very short and most of these join the main stream at right angles.
The Narmada basin covers parts of Madhya Pradesh and Gujarat.
The Tapi Basin
The Tapi rises in the Satpura ranges, in the Betul district of Madhya Pradesh.
It also flows in a rift valley parallel to the Narmada but it is much shorter in length.
Its basin covers parts of Madhya Pradesh, Gujarat and Maharashtra.
The coastal plains between Western Ghats and the Arabian sea are very narrow.
Hence, the coastal rivers are short.
The main west flowing rivers are Sabarmati, Mahi, Bharathpuzha and Periyar.
The Godavari Basin
The Godavari is the largest Peninsular river.
It rises from the slopes of the Western Ghats in the Nasik district of Maharashtra.
Its length is about 1500 km.
It drains into the Bay of Bengal.
Its drainage basin is also the largest among the peninsular rivers.
The basin covers parts of Maharashtra (about 50 per cent of the basin area lies in Maharashtra), Madhya Pradesh, Odisha and Andhra Pradesh.
The Godavari is joined by a number of tributaries such as the Purna, the Wardha, the Pranhita, the Manjra, the Wainganga and the Penganga.
The last three tributaries are very large. Because of its length and the area it covers, it is also known as the ‘Dakshin Ganga’.
The Mahanadi Basin
The Mahanadi rises in the highlands of Chhattisgarh.
It flows through Odisha to reach the Bay of Bengal.
The length of the river is about 860 km.
Its drainage basin is shared by Maharashtra, Chhattisgarh, Jharkhand, and Odisha.
The Krishna Basin Rising from a spring near Mahabaleshwar, the Krishna flows for about 1400 km and reaches the Bay of Bengal.
The Tungabhadra, the Koyana, the Ghatprabha, the Musi and the Bhima are some of its tributaries.
Its drainage basin is shared by Maharasthra, Karnataka and Andhra Pradesh.
The Kaveri Basin
The Kaveri rises in the Brahmagri range of the Western Ghats and it reaches the Bay of Bengal in south of Cuddalore, in Tamil Nadu.
Total length of the river is about 760 km.
Its main tributaries are Amravati, Bhavani, Hemavati and Kabini.
Its basin drains parts of Karnataka, Kerala and Tamil Nadu.
The river Kaveri makes the second biggest waterfall in India, known as Sivasamudram. The hydroelectric power generated from the falls is supplied to Mysore, Bangalore and the Kolar Gold Field.
Beside these major rivers, there are some smaller rivers flowing towards the east.
The Damoder, the Brahmani, the Baitarni and the Subarnrekha are some notable examples
LAKES
Most lakes are permanent; some contain water only during the rainy season, like the lakes in the basins of inland drainage of semi-arid regions.
There are some of the lakes which are the result of the action of glaciers and ice sheets, while the others have been formed by wind, river action, and human activities.
A meandering river across a flood plain forms cut-offs that later develop into oxbow lakes.
Spits and bars form lagoons in the coastal areas, eg the Chilika lake, the Pulicat lake, the Kolleru lake.
Lakes in the region of inland drainage are sometimes seasonal; for example, the Sambhar lake in Rajasthan, which is a salt water lake. Its water is used for producing salt.
Most of the fresh water lakes are in the Himalayan region. They are of glacial
origin. In other words, they formed when glaciers dug out a basin, which was later filled with snowmelt.
The Wular lake in Jammu and Kashmir, in contrast, is the result of the tectonic activity. It is the largest freshwater lake in India.
The Dal lake, Bhimtal, Nainital, Loktak and Barapani are some other important fresh water lakes.
Apart from natural lakes, the damming of the rivers for the generation of hydel power has also led to the formation of Lakes such as Guru Gobind Sagar (Bhakra Nangal Project).
A lake helps to regulate the flow of a river.
During heavy rainfall, it prevents flooding and during the dry season, it helps to maintain an even flow of water.
Lakes can also be used for developing hydel power.
They moderate the climate of the surroundings; maintain the aquatic ecosystem, enhance natural beauty, help develop tourism and provide recreation.