The Brahmaputra River is one of the youngest major rivers in the world from a geological perspective. Originating in the young Himalayan range, it flows through Tibet and India before reaching its delta in Bangladesh. At its mouth, the river fans out into numerous channels, resembling the intricate roots of a vast banyan tree as it merges with the Bay of Bengal.

The Brahmaputra River is one of the youngest major rivers in the world geologically. It is also often described as a "moving ocean" due to its magnanimity. The Brahmaputra originates at an altitude of 5,300 meters about 63 kilometers southeast of Lake Mansarovar in Tibet. In Sino-Tibetan region, the Brahmaputra is known as the Tsangpo. The river flows eastward across the Tibetan plateau for 1,625 kilometers before entering a deep, narrow gorge at Pe on the Namcha Barwa peak on the Himalayas (3,500 meters). The river bends here what is known as the Great Bend of the Yarlung Tsangpo River as the river enters its notable gorge across the Himalayas. It then continues southward through the east-west trending ranges of the Himalayas, including the Greater Himalayas, Middle Himalayas, and the Sub-Himalayas.

Upon crossing the Indo-China border near Pasighat, the river is referred to as the Siang or Dihang. The Siang is joined by two major tributaries, the Dibang and the Lohit, just upstream of Kobo, combining to form the Brahmaputra River. Flowing westward through Assam for approximately 700 kilometers from Dhola to downstream of Dhubri, the river then abruptly turns south and enters Bangladesh.

The gradient of the Brahmaputra varies significantly along its course. In the upstream gorge section near Pasighat, the gradient is steep, ranging from 4.3 to 16.8 meters per kilometer. However, it flattens to as little as 0.1 meters per kilometer near Guwahati. This dramatic reduction in slope as the river exits the Himalayas and flows into the Assam plains results in a sudden dissipation of its enormous energy and a substantial unloading of sediments downstream.

Over its 2,880-kilometer journey, the Brahmaputra receives contributions from 22 major tributaries in Tibet, 33 in India, and 3 in Bangladesh. The tributaries on the northern bank typically flow through shallow braided channels, have steep slopes, carry heavy sediment loads, and are characterized by their flashy nature. In contrast, the southern bank tributaries have flatter gradients, deeper meandering channels with fine alluvial soils, and lower sediment loads.

The Brahmaputra valley and its surrounding hill ranges are seismically unstable due to the collision between the Eurasian (Chinese) and Indian tectonic plates. The 1897 and 1950 earthquakes, both of Richter magnitude 8.7, are among the most severe in recorded history, causing extensive landslides, rock falls, subsidence, and changes in the river’s course and tributary configurations.

The drainage basin of the Brahmaputra covers approximately 580,000 square kilometers, spanning longitudes from 82°E to 97°50' E and latitudes from 25°10' N to 31°30' N. The basin includes 293,000 square kilometers (50.51%) in Tibet (China), 45,000 square kilometers (7.75%) in Bhutan, 194,413 square kilometers (33.52%) in India, and 47,000 square kilometers (8.1%) in Bangladesh.