Apart from incessant rainfall during the monsoon, there are many contributory factors, natural and man-made. At the crux is the very nature of the river Brahmaputra —dynamic and unstable.
Its 580,000 sq km basin spreads over four countries: China, India, Bangladesh and Bhutan, with diverse environments.
The Brahmaputra features among the world’s top five rivers in terms of discharge as well as the sediment it brings.
The vast amount of sediment comes from Tibet, where the river originates. “That region is cold, arid and lacks plantation. Glaciers melt, soil erodes and all of it results in a highly sedimented river.
By the time the river enters Assam — a state comprising primarily floodplains surrounded by hills on all sides — it deposits vast amounts of this silt, leading to erosion and floods. “As the river comes from a high slope to a flat plain, its velocity decreases suddenly and this results in the river unloading the sediment
because of the earthquake-prone nature of the region, the river has not been able to acquire a stable character. Following the devastating earthquake of 1950, the level of the Brahmaputra rose by two metres in Dibrugarh area in eastern Assam.
Besides these natural factors are the man-made ones — habitation, deforestation, population growth in catchment areas (including in China) — which lead to higher sedimentation. For example, the sediment deposition itself creates temporary sandbars or river islands.
