Drainage

"If we look at the physical map we will notice that 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. This chapter will help us understand these phenomena in detail."

1.0Introduction

• Drainage : The term drainage is used to describe the river system of an area.
• Drainage basin : The area drained by a single river system is called a drainge basin.
• Water divide : An upland that separates the flow of two rivers or river system.
• River system : A river, along with its tributaries may be called a river system.
  

2.0Drainage systems in India

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 (ii) The Peninsular Rivers.

Apart from originating from the two major physiographic regions of India, the Himalayan and the Peninsular rivers are different from each other in many ways. 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 welldeveloped deltas

Some Features Made by 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 world's largest drainage basin is of the Amazon river

3.0The Himalayan River system

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 alongwith its tributaries may be called a river system.

(a) The Indus River System

• The Indus originates from the glaciers of the Kailash range in Western Tibet near Mansarowar Lake.
• It flows west and north west wards and enters Indian territory in Ladakh. It cuts through the mountains & forms a spectacular gorge. Several tributaries, the Zaskar, the Nubra, the Shyok and the Hunza, join it in the Kashmir region.
• It flows through Baltistan and Gilgit to finally emerge out of the hills at Attock. The Satluj, the Beas, the Ravi, the Chenab and the Jhelum join together to enter the Indus near Mithankot in Pakistan. The Indus flows south west across Pakistan to reach the Arabian Sea in 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 Ladakh, Jammu and Kashmir, Himachal Pradesh and Punjab and the rest is in Pakistan.
  
  Indus river basin

According to the regulations of the Indus Water Treaty (1960), India can use only 20 per cent of the total water carried by the Indus river system. This water is used for irrigation in Punjab, Haryana and the southern and the western parts of Rajasthan.

(b) 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, 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.
• These rivers cause floods in the parts of Northern Plains every year and cause damage to life and property whereas enrich soil for agriculture use.
• The main tributaries, which come from the peninsular uplands, are the Chambal, the Betwa and the Son. These rivers have shorter courses due to origination from semi arid areas.
  
  Ganga Drainage System
• 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 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 Sundarban Delta. (The Sundarban Delta derived its name from the Sundari tree, which grows well in marshy land. It is the world's largest and fastest growing delta. It is also the home of Royal Bengal tiger.)
• 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 meter for every 6 km . Therefore, the river develops large meanders.

(c) 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.
  
  Brahmaputra Drainage System
• Brahmaputra is known as the Tsang Po in Tibet and Jamuna in Bangladesh.
• 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 riverbed to rise. The river also shifts its channel frequently.

4.0The Peninsular Rivers

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 estuaries. The drainage basins of the peninsular rivers are comparatively smaller in size.

5.0The West flowing rivers

(a) The Narmada Basin

• This river originates from 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 pitcturesque 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.

(b) The Tapi Basin

• This river originates from Satpura ranges in 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. The main west flowing rivers are Sabarmati, Mahi, Bharathpuzha and Periyar.

6.0The East flowing rivers

(a) Godavari Basin:

(b) The Mahanadi Basin:

(c) Krishna Basin:

(d) The Kaveri Basin:

The river Kaveri makes the second biggest waterfall in India, known as Shivasamudram Falls. The hydroelectric power generated from the falls is supplied to Mysuru, Bengaluru and the Kolar Gold Field.

7.0Other East-flowing rivers

Beside three major rivers there are some smaller rivers flowing towards the east like the Damodar, the Subarnrekha, the Brahmani and Baitarni.

8.0Lakes

India has many lakes. These differ from each other in 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 lakes which are the result of the action of glaciers and ice sheets, while others have been formed by wind, river action and human activities.

• Freshwater lakes : Most of the fresh water lakes are in the Himalayan region. They are of glacial origin. The Dal lake, Bhimatal, Nainital, Loktak and Barapani are some of the fresh water lakes of India. Wular is the largest fresh water lake in India.
• Lakes of Tectonic origin : Folding and faulting produce hollows in the earth's crust. These hollows contain either salt or fresh water lake. The Wular lake in Jammu & Kashmir is the result of tectonic activity.
• Ox-bow and Lagoon Lakes: A meandering river across a floodplain forms cut-offs that later develops into ox-bow lakes. Spits and bars form lagoons in the coastal areas, e.g. the Chilika lake, the Pulicat lake and the Kolleru lake.
• Salt water 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.
• Man made 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).

71 per cent of the world's surface is covered with water, but 97 per cent of that is salt water. Of the 3 per cent that is available as freshwater, three quarters of it is trapped as ice.

Importance of Lakes

• A lake helps to regulate the flow of a river. During heavy rains, 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.
  
  Loktak Lake

Role of rivers in the economy

• Development of civilization: Rivers have played an important role in the development of civilization. Most of the ancient civilizations like Indus civilization, etc developed around the river.
• Development for agriculture: Rivers and their associated alluvial soils provide the most productive agricultural lands of the country.
• Settlement : Most of the large cities are located on the banks of a river. Not only these rivers provide water supplies but also they provide transportation.
• Industrial development : It has flourished along rivers. In many industries river water is used as a coolant and for the generation of hydroelectricity.
• Means of transportation : Rivers provide primary channel of inland transportation.

9.0River 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 is able to 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. Concern over rising pollution in our rivers led to the launching of various action plans to clean the rivers.

10.0National Rivers Conservation Plan (NRCP)

The river cleaning programme in the country was initiated with the launching of the Ganga Action Plan (GAP) in 1985. The Ganga Action Plan was expanded to cover other rivers under the National River Conservation Plan (NRCP) in the year 1995. The objective of the NRCP is to improve the water quality of the rivers, which are major water sources in the country, through the implementation of pollultion abatement work.

11.0Namami Gange Programme

Namami Gange Programme', is an integrated Conservation Mission, approved as 'Flagship programme' by the Union Government in June 2014 with budget outlay of RS. 20,000 crore to accomplish the twin objectives of effective abatement of pollution, conservation and rejuvenation of National river Ganga.

12.0Namami Devi Narmade

The Narmada River Conservation Mission has been undertaken by the government of Madhya Pradesh by a scheme named Namami Devi Narmade.

13.0MIND MAP