The Brahmaputra System

The Brahmaputra is one of the largest rivers in the world, and its story is one of changing names, national borders, and enormous sediment loads. It begins not in India, but high in the Tibetan plateau, and its behaviour downstream — especially the flooding and erosion it causes — is a direct consequence of its geography and the sheer scale of its tributaries.

The river has its origin in the Chemayungdung glacier of the Kailash range, near the Mansarovar lake. From this source, it flows eastward for nearly 1,200 km through a dry and flat region of southern Tibet. Here it is known as the Tsangpo, a name that means 'the purifier'. In this Tibetan stretch, its major right bank tributary is the Rango Tsangpo.

After this long, relatively gentle journey across the plateau, the river's character changes completely. It carves a deep gorge through the Central Himalayas near Namcha Barwa (7,755 m) and emerges as a turbulent, dynamic river. Once it reaches the foothills, it is known by two names — the Siang or the Dihang. It enters India west of Sadiya town in Arunachal Pradesh.

Flowing southwest from there, the river receives its main left bank tributaries — the Dibang (also called Sikang) and the Lohit. It is only after the confluence with these rivers that it becomes known as the Brahmaputra.

The Brahmaputra then travels roughly 750 km through the Assam valley, and along this stretch it receives numerous tributaries. Its major left bank tributaries are the Burhi Dihing and the Dhansari (South). On the right bank, the important tributaries are the Subansiri, Kameng, Manas, and Sankosh. Among these, the Subansiri is notable: it originates in Tibet and is an antecedent river — meaning it existed before the Himalayas were fully uplifted and has maintained its course by cutting through the rising mountains.

The river enters Bangladesh near Dhubri and flows southward. In Bangladesh, the Tista joins it on the right bank, and from this point the river is called the Jamuna. It eventually merges with the river Padma, which falls into the Bay of Bengal. …