Chapter - 3 Drainage

The term drainage describes the river system of an area. Small streams flowing from different directions come together to form the main river, which ultimately drains into a large water body such as a lake or a sea or an ocean. The area drained by a single river system is called a drainage basin. Any elevated area, such as a mountain or an upland, separates two drainage basins. Such an upland is known as a water divide.

DRAINAGE SYSTEMS IN INDIA

The Indian rivers are divided into two major groups:

• The Himalayan rivers; and
• The Peninsular rivers.

Himalayan rivers

• They 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.
• 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. They have cut through the mountains making gorges.
• They 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.

1.  THE INDUS RIVER SYSTEM

• Origin -The river Indus rises in Tibet, near Lake Mansarowar. Flowing west, it enters India in the Ladakh district of Jammu and Kashmir. It forms a picturesque gorge in this part.
• 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.

2.  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.
• Tributaries- Yamuna, the Ghaghara, the Gandak and the Kosi. The river Yamuna rises from the Yamunotri Glacier in the Himalayas. The Ghaghara, the Gandak and the Kosi rise in the Nepal Himalaya. The main tributaries, which come from the peninsular uplands, are the Chambal, the Betwa and the Son. These rise from semi-arid areas.
• 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 downstream, 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.

3.  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.

Peninsular rivers

• They are seasonal, as their flow is dependent on rainfall.
• They have shorter and shallower courses as compared to their Himalayan counterparts. 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. The Narmada and the Tapi are the only long rivers, which flow west and make estuaries. The drainage basins of the peninsular rivers are comparatively small.

1.  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 can be observed.
• 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.

2.  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. Find out the states in which these rivers drain the water.

3.  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, Madhya Pradesh, Odisha and Andhra Pradesh. The Godavari is joined by many 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’.

4.  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

5.  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 Maharashtra, Karnataka and Andhra Pradesh.

6.  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.

Lakes

India has many lakes. These differ from each other in the size, and other characteristics. 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-off that later develop into ox-bow lakes. Spits and bars form lagoons in the coastal areas, e.g. 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. The Wular lake in Jammu and Kashmir is the largest freshwater lake in India. The Dal lake, Bhimtal, Nainital, Loktak and Barapani are some other important fresh water lakes.
• 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).

Lakes are of great value to human beings.

• 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

ROLE OF RIVERS IN THE ECONOMY

Water from the rivers is a basic natural resource, essential for various human activities. Using rivers for irrigation, navigation, hydro-power generation is of special significance – particularly to a country like India, where agriculture is the major source of livelihood of most of its population.

RIVER POLLUTION

The growing domestic, municipal, industrial and agricultural demand for water from rivers naturally affects the quality of water. As a result, more and more water is being drained out of the rivers reducing their volume. On the other hand, a heavy load of untreated sewage and industrial effluents are emptied into the rivers. This affects not only the quality of water but also the self-cleansing capacity of the river. For example, given the adequate streamflow, the Ganga water can dilute and assimilate pollution loads within 20 km of large cities. But the increasing urbanization and industrialization do not allow it to happen and the pollution level of many rivers has been rising.

SOME IMPORTANT FACTS

• The world’s largest drainage basin is of the Amazon river
• The ganga basin is the largest basin in India.
• 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.
• The kunchikal Falls is the biggest waterfall in India.