Alluvial plains are large depositions of sediment by river systems in flood basins. They are found in great numbers all over the world within the boundaries of the river water shed.
Alluvial plains are formed in several ways, i.e. by flooding, prolonged weathering, ground water sapping etc. The northern plains are the largest depositories of rich alluvium in India. These plains were deposited by the three mighty rivers, i.e., The Indus, Ganga and Brahmaputra.
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.
Bhabar 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.
South of the Bhabar is the Tarai belt, with an approximate width of 1020 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.
The south of Tarai is a belt consisting of old and new alluvial deposits known as the Bhangar and Khadar respectively.
The Brahmaputra plains 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.
The mouths of these mighty rivers also form some of the largest deltas of the world, for example, the famous Sunderbans delta.
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.
