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Wikipedia contributors, "Doab," Wikipedia, The Free Encyclopedia, (accessed June 20, 2011).
Doab (English: //) is a term used in South Asia for the "tongue," or tract of land lying between two converging, or confluent, rivers. It is similar to an interfluve. In the Oxford Hindi-English Dictionary, R. S. McGregor defines it as "(Persian do-āb: a region lying between and reaching to the confluence of two rivers (esp. that between the Ganges and Yamuna)."
The Doab designates the flat alluvial tract between the Ganges and Yamuna rivers extending from the Sivalik Hills to the two rivers' confluence at Allahabad. The region has an area of about 23,360 square miles (60,500 square km); it is approximately 500 miles (805 km) in length and 60 miles (97 km) in width.
Currently the following states and districts form part of the Ganga Doab:
Central or Middle Doab
The Punjab Doabs
Each of the tracts of land lying between the confluent rivers of the Punjab region of Pakistan and India has a distinct name, said to have been coined by Raja Todar Mal, a minister of the Mughal emperor Akbar. The names (except for 'Sindh Sagar') are a combination of the first letters, in the Persian alphabet, of the names of the rivers that bound the Doab. For example, Jech = 'Je'(Jhelum) + 'Ch'(Chenab). The names are (from west to east):
Sindh Sagar Doab
The rivers flowing through the Malwa region, covering current states of Madhya Pradesh and parts of north-eastern Rajasthan, also has doab region such as Upper Malwa doab and Lower Malwa doab.
The Raichur Doab is the triangular region of Andhra Pradesh and Karnataka states which lies between the Krishna River and its tributary the Tungabhadra River, named for the town of Raichur.
Khadir, bangar, barani, nali and bagar
Since North India and Pakistan are coursed by a multiplicity of Himalayan rivers that divide the plains into doabs (i.e. regions between two rivers), the Indo-Gangetic plains consist of alternating regions of river, khadir and bangar. The regions of the doabs near the rivers consist of low-lying, floodplains, but usually very fertile khadir and the higher-lying land away from the rivers consist of bangar, less prone to flooding but also less fertile on average.
Khadir is also called Nali or Naili, specially in northern Haryana the fertile prairie tract between the Ghaggar river and the southern limits of the Saraswati channel depression in that gets flooded during the rains.
Within bangar area, the Barani is any low rain area where the rain-fed dry farming is practiced, which nowadays are dependent on the tubewells for irrigation. Bagar tract, an example of barani land, is the dry sandy tract of land on the border of Rajasthan state adjoining the states of Haryana and Punjab. Nahri is any canal-irrigated land, for example, the Rangoi tract which is an area irrigated by the Rangoi channel/canal made for the purpose of carrying flood waters of Ghagghar river to dry areas.
Historically, villages in the doabs have been officially classified as khadir, khadir-bangar (i.e. mixed) or bangar for many centuries and different agricultural tax rates applied based on a tiered land-productivity scale.