3.2.3. The Brahmaputra River System

The Brahmaputra rises in Tibet east of Mansarowar lake very close to the sources of the Indus and the Satluj. It is slightly longer than the Indus, and most of its course lies outside India. It flows eastwards parallel to the Himalayas. On reaching the Namcha Barwa (7757 m), it takes a ‘U’ turn and enters India in Arunachal Pradesh through a gorge. Here, it is called the Dihang and it is joined by the Dibang, the Lohit, and many other tributaries to form the Brahmaputra in Assam.

The Brahmaputra River starts in Tibet, near Mansarowar lake. It flows towards the east, closely following the Himalayas. Upon reaching Namcha Barwa, a tall mountain, the river makes a U-turn, entering India through Arunachal Pradesh. In this region, it is referred to as the Dihang River, and merges with several notable tributaries like the Dibang and Lohit, which contribute to forming what we know as the Brahmaputra in Assam.

Think of a large water slide that starts in a playground (Tibet) and then winds its way down toward the pool (India). It takes a sharp turn near a big set of stairs (Namcha Barwa) before diving into the water (the river merging with its tributaries). The tributaries, like friends joining the fun, make the water experience larger and more exciting.

In Tibet, the river carries a smaller volume of water and less silt as it is a cold and dry area. In India, it passes through a region of high rainfall. Here the river carries a large volume of water and considerable amount of silt. The Brahmaputra has a braided channel in its entire length in Assam and forms many riverine islands.

As the Brahmaputra flows through Tibet, it experiences less rainfall, resulting in a smaller water volume and less silt in its flow. However, when it enters India, the scenario changes dramatically due to abundant rainfall in the region. This leads to an increase in both the water volume and the amount of silt that the river carries. In Assam, the river exhibits a braided pattern because of the way it divides around islands, creating many smaller waterways.

Imagine a sponge that can absorb a lot of water. In dry conditions (Tibet), the sponge (river) holds only a little water. But when it's soaked (high rainfall region in India), the sponge can hold so much more, creating a mess of intertwining paths (braided channels) as it expands and covers the ground.

Every year during the rainy season, the river overflows its banks, causing widespread devastation due to floods in Assam and Bangladesh. Unlike other north Indian rivers, the Brahmaputra is marked by huge deposits of silt on its bed causing the riverbed to rise. The river also shifts its channel frequently.

In the rainy season, the Brahmaputra often overflows, which leads to significant flooding in areas like Assam and Bangladesh. This is due to the large amounts of water it carries, especially after heavy rains. Moreover, the river is consistently depositing silt onto its bed, which can cause the riverbed to elevate over time. Additionally, because of these sediment deposits, the river's course can change frequently, which presents challenges for the communities living near its banks.

Think of a river as a large water balloon. As you fill it with more water (rain), it may start overflowing (flooding). As you add sand to the balloon (silt), the base of the balloon rises, and when you squeeze it, it can change shape easily (river shifting course), which can lead to water spilling out in different areas.

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