Physiography: Northern Plains

The Indus–Gangetic plains, also known as the "Great Plains", are large floodplains of the Indus, Ganga and the Brahmaputra river systems. The major rivers of this system are the Ganga and the Indus along with their tributaries; Beas, Yamuna, Gomti, Ravi, Chambal, Sutlej and Chenab.

Extent

The northern plains are formed by the alluvial deposits brought by the rivers – the Indus, the Ganga and the Brahmaputra. These plains extend approximately 3,200 km from east to west. The average width of these plains varies between 150-300 km. The maximum depth of alluvium deposits varies between 1,000-2,000 m.

They run parallel to the Himalaya mountains, from Jammu and Kashmir and Khyber Pakhtunkhwa in the west to Assam in the east and draining most of Northern and Eastern India. 

The Indo-Gangetic Plain is divided into two drainage basins by Delhi Ridge;

  • western part drains to the Indus, and 
  • eastern part consists of the Ganga–Brahmaputra drainage systems. 

This divide is only 350 metres above sea level, causing the perception that the Indo-Gangetic Plain appears to be continuous from Sindh in the west to Bengal and Assam in the east.

Three Zones of the Plains

From the north to the south, these can be divided into three major zones: the Bhabar, the Tarai and the alluvial plains. The alluvial plains can be further divided into the Khadar and the Bhangar.
  1. Bhabar: It is a narrow belt ranging between 8-10 km parallel to the Shiwalik foothills at the break-up of the slope. As a result of this, the streams and rivers coming from the mountains deposit heavy materials of rocks and boulders, and at times, disappear in this zone. It is not suitable for crops and is forested.
  2. Terai: South of the Bhabar lie the grasslands of Terai and Dooars. Tarai belt has an approximate width of 10-20 km where most of the streams and rivers re-emerge without having any properly demarcated channel, thereby, creating marshy and swampy conditions known as the Tarai. This has a luxurious growth of natural vegetation and houses a varied wildlife. 
  3. New alluvial deposits: The south of Tarai is a belt consisting of old and new alluvial deposits known as the Bhangar and Khadar respectively. 
    • Khadar: Close to the rivers is Khadar land of new alluvium that is subject to flooding. 
    • Bhangar: Above the flood limit, Bhangar land is older alluvium deposited.

Features of the Northern Plains

  • The states of Haryana and Delhi form a water divide between the Indus and the Ganga river systems. 
  • Northern plains have features of mature stage of fluvial erosional and depositional landforms such as sand bars, meanders, oxbow lakes and braided channels. 
  • The mouths of these mighty rivers also form some of the largest deltas of the world, for example, the famous Sunderbans delta. 
  • Otherwise, this is a featureless plain with a general elevation of 50-150 m above the mean sea level. 
  • The Brahmaputra plains
    • These are known for their riverine islands and sand bars
    • Most of these areas are subjected to periodic floods and shifting river courses forming braided streams
    • Brahmaputra river flows from northeast to southwest direction before it takes an almost 90° southward turn at Dhubri before it enters into Bangladesh. 
  • These river valley plains have a fertile alluvial soil cover which supports a variety of crops like wheat, rice, sugarcane and jute, and hence, supports a large population.

Significance

The Indus-Ganga belt is the world's most extensive expanse of uninterrupted alluvium formed by the deposition of silt by the numerous rivers.
  • The plains are flat and mostly treeless, making it conducive for irrigation through canals
  • The area is also rich in ground water sources. 
  • The plains are the world's most intensely farmed areas
  • The main crops grown are rice and wheat that are grown in rotation. Others include maize, sugarcane and cotton. 
The Indo-Gangetic plains rank among the world's most densely populated areas with a total population exceeding 400 million.