Assam floods

Subject: Geography

Context:

In Assam, over 24.68 lakh people affected and death toll rises to 102

Concept:

• Apart from incessant rainfall during the monsoon, there are many contributory factors to yealy floods in Assam
• Major cause is the very nature of the river Brahmaputra —dynamic and unstable.
• The Brahmaputra features among the world’s top five rivers in terms of discharge as well as the sediment it brings.
• At 19,830 cubic meters per second (cumec), it ranks fourth in discharge at the mouth, behind only the Amazon (99,150 cumec), the Congo (39,660 cumec) and the Yangtze (21,800 cumec).
• In terms of sediment yield, two spots along the Brahmaputa’s course were at second and third places in 2008. Brahmaputra’s annual sediment yield was 1,128 tonnes per sq km at Bahadurabad of Bangladesh, and 804 tonnes per sq km at Pandu of Guwahati.

Source: Indian express

• The vast amount of sediment comes from Tibet, where the region is cold, arid and lacks plantation. Glaciers melt, soil erodes and all of it results in a highly sedimented river.
• 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. The river’s channels prove inadequate amid this siltation, leading to floods.
• Again, because of the earthquake-prone nature of the region, the river has not been able to acquire a stable character.
• Besides these natural factors are the man-made ones habitation, deforestation, population growth in catchment areas which lead to higher sedimentation. For example, the sediment deposition itself creates temporary sandbars or river islands.