The Northern Plains of India are composed up of the excellent silt called alluvium. The rivers bring it down from the Himalayas in the north and the peninsular plateau in the south. Such a plain is called an alluvial plain. If one takes a look at the delta of the Ganga-Brahmaputra, one will find that this act of deposition is still in the process. The Northern Plains are divided into two river systems- the Indus in the west and the Ganga-Brahmaputra in the east. Even on the contour map of India one can scarcely find any relief characteristic playing a potential water divide between the two river systems.

The Indus basin - Less than one-third of the Indus basin is located in India (Jammu and Kashmir, Himachal Pradesh and Punjab). The Indus is approximately 2900 km long. Its primary tributaries include the Satluj, Beas, Ravi, Chenab and Jhelum. One can take a look at the map to witness how these rivers unite together one by one before they eventually merge into the Indus. The slope of the Indus plain is pretty mild. The plain extends over 1200 km between the Arabian Sea in the south-west and foothills of the Western Himalaya in the north-east. Over this entire distance, the total descend of the plain is barely 300 metres. The rivers have turned the plain pretty productive and it now has one of the densest systems of canals for irrigation.

The Ganga basin - The Ganga has two primary origins in the Himalaya- the Bhagirathi and the Alaknanda. Both merge in Devprayag and flow as the Ganga subsequently. It enters the Northern Plains at Hardwar. The Yamuna joins it in Allahabad. Chambal, Sind, Betwa and Ken in turn join the Yamuna. They all stream through the Malwa plateau before entering into the plains. The Son is the only big river to join the Ganga straightaway from the southern plateau. Further east, the Damodar, irrigating the Chotanagpur plateau, joins the Hughli, a distributary of the Ganga. The big Himalayan Rivers uniting with the Ganga downstream of Allahabad from west to east comprise the Gomati, Ghaghara, Gandak and Kosi. The Ganga river system waters most of Haryana, southeast Rajasthan, northern Madhya Pradesh, Uttar Pradesh, Bihar and most parts of West Bengal. Ambala is located on the water divide between the Indus and the Ganga river systems. The plains from Ambala in the northwest to Sundarbans in the east extend over almost 1800 km. During its total broadening from Haryana to Bangladesh; there is a descend of barely 300 metres in its slope. The zig-zag or winding courses of the rivers prove how level the plains are. The Ganga is over 2500 km long.

The Brahmaputra valley - The Brahmaputra initiates in Tibet near the source of the Indus and Satluj. It transports a remarkable volume of water. The river is somewhat longer compared to the Indus, but most of its course lies in Tibet. It streams parallel to the Himalayan Mountains in Tibet, where it is called Tsangpo. When it takes a hairpin bend around Namcha Barwa (7757m), the undercutting done by this dominant river, is of the order of 5,500 metres. Here and in Arunachal Pradesh it is called Dihang. After the convergence of the Lohit, Dihang and Dibang, it is named the Brahmaputra. Leaving a huge volume of water, it also transports a gigantic amount of silt with it. In northern Bangladesh it is called Jamuna. In the central part after uniting with the Ganga, it is called Padma. Further south, the Meghna meets the main stream and the common stream is also called Meghna.

The Ganga-Brahmaputra delta - It is the largest and the fastest growing delta of the world. This is not only well-watered, but is also the most productive. Ganga and Brahmaputra divide into several distributaries in their lower courses. Due to the mild slope or gradient, the rivers become slow, and islands of silt and mud expand in their channel. To evade these obstacles, the rivers generally divide into a number of channels. The process is recurred various times to build up a classical delta. The lower part of the delta goes sloppy, where fresh water and sea water gets blended, because of high and low tides.