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River Basin in India
   A River basin is the portion of land drained by a river and its tributaries. It encompasses all of the land surface dissected and drained by many streams and creeks that flow downhill into one another, and eventually into one river. The final destination is an estuary or an ocean. As a bathtub catches all the water that falls within its sides, a river basin sends all the water falling on the surrounding land into a central river and out to the sea.
Depending upon basin area Indian rivers have been divided into three categories:

Categories of Indian River Basins


 River Basin





Equal to or more than 20,000




Between 2000 to 20,000




Less than 2000


Source: Central Pollution Control Board, Delhi.

Major Basins
Out of 13 Major river basins, three are international and ten are interstate. The three international basins; the Ganga, the Brahamputra, the Indus have snow –fed rivers originating in the Himalayas whereas the interstate basins have rivers originating either in Central India or peninsular regions. Following is the distribution of river basins among the States:

1.       Maharastsra has five river basins 
2.       Karnataka, Gujarat and Rajasthan has four each
3.       Andhra Pradesh, Bihar and Orissa three each
4.       Haryana two

West Bengal, Kerala, Tamil Nadu, Assam, Sikkim, Arunanchal Pradesh, Nagaland, Uttar Pradesh, Punjab, Delhi, Jammu & Kashmir and Himachal Pradesh one each. 
For detailed  Database on major river basin click here

Though the Ganga is only the third longest river flowing through India(Indus & Brahamputra are the longest)yet the Ganga River basin,  is  largest  in India, occupying approximately 25 percent of the nation's area. It is bounded by the Himalayas in the north and the Vindhya Range in the south. The Ganga has its source in the glaciers of the Greater Himalayas, which form the frontier between India and Tibet in northwestern Uttar Pradesh. In the northern part of the Ganga River basin, practically all of the tributaries of the Ganga are perennial streams. However, in the southern part, located in the states of Rajasthan and Madhya Pradesh, many of the tributaries are seasonal. The Ganga, the Yamuna, the Ghagra, Gantak & Kosi are the main constituents of the Ganga river basin.

The Second largest river basin is that of Godavari and the third is being the Krishna basin. The Mahanadi transverse through this basin. The Narbada, Tapti & the Pennar basins are smaller though they have immense agricultural importance.

Medium Basins 
Medium river basins occupy 8% of total basin area and about 119940 million cubic water flows through them. Out of forty-five Medium river basins, four are international and eleven are interstate. A total of seventeen rivers having a combined basin area of 63500 square kilometers join the Arabian Sea, while other 24 having a combined basin area of 210596 square kilometers fall in the Bay of Bengal. Rest four rivers originate in India and ultimately cross the national boundary.
For detailed database on Medium Basins click here

Minor Basins
The total area of minor basins is 9% of total basin area of Indian rivers while runoff is 127 MCM.There are fifty-five Minor river basins having a combined basin area of about 2 lakh square kilometers. Most of them originate from Eastern and Western Ghats. In addition to these there are few desert rivers too, which flow for some distance and get lost in the deserts.

Ground Water potential of Basins in the Country
Graph 1 represents comparison between total available replenishable ground water and ground water balance left in the basins for exploitation after being used for irrigation, industrial, domestic & other uses.It has been reported that Ganga basin possesses maximum amount of 170.99 cubic km/year of total available replenishable ground water & 96.37 cubic km/year is left for exploitation. Further, Subarnrekha basin possess minimum amount of of 1.82 cubic km/year of total available replenishable ground water & only 1.4 cubic km/year is the balance of ground water available for exploitation/future use. 

Graph 1: Total available replenishable ground water and ground water balance left in the basins for Exploitation

Source: Data from Ministry of Water Resources.

Graph No. 2: The average annual runoff and utilizable flow of rivers

Source: State of India's Environment, CSE, 1999

The data indicates that the Ganga river basin has maximum value of estimated utilizable flow of surface water i.e.50% approximately out of the average annual runoff of 501.643 cu Km (which is second largest among the listed river basins in the graph 2 ) whereas the the Brahamputra with   the largest average annual runoff of 537.067 cu.Km contributes only 4% of utilizable flow of surface water. Also it shows that the river Sabarmati with minimum average annual runoff of 3.812 cu.Km also contributes 50% of its runoff towards utilizable flow.

The issues or the problems related to quality & quantity of water within the river basins are the result of prevailing climatic and hydrological conditions alongwith with demographics In spite of high average annual rainfall factors like higher mean temperatures, high evaporation rates, and the seasonal nature of major rivers contribute to various problems in primary river basins in the country.

            The quantity & quality of water in the river basin also varies, as they are spread all over the country. Their natural state has been disturbed due to factors like industrialization, urbanization and population growth. The flow of almost all the major rivers is restricted due to construction of barrages, dams and reservoirs. This affects mean annual flow and increased quantity of water in a river at a particular time

            Restricted rainfall of three months in most parts of the country leads to drying of rain-fed rivers during summer & late winters and ultimately lower stream density & water scarcity as an emerging constraint. On the other hand this period of monsoon is also cause of floods and accumulation of sand, silt & other materials & hence siltation. Siltation rate in India is among the highest in the world. Indian rivers contribute 35% of the sediments to the world ocean water as compared to water flowing through the rivers of the world which is 5% only .It has been estimated that about 135 thousand million metric-tones of sediment load and 32 thousand million tones of soluble matter enter into ocean through various rivers in our country which is 90% of the total solid waste going into the ocean & causing pollution.

Pollution is also one of the major problems associated with the river basins within India.  e.g. The Ganga river basin  being the largest in length and basin area (approx. 34.39% of the total basin area of all the major basins) contains many highly populated cities in it. The discharge of pollutants from domestic & municipal sources (80%) and industrial effluents (20%) from these cities gets accumulated due to very less flow in summer & this deteriorate the quality of the Holy Ganga water

               Immediate actions are required to have balance between population growth & the water capacity of the hydrological basins to satisfy the water demand. This requires a proper river basin management system to have sustainable water availability. This could be achieved by proper planning, management & operations in river basin framework.

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