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Understanding Assam Floods

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July 19, 2019

What is the issue?

  • Assam is in the grip of yet another flood, with lakhs of people displaced and some killed, besides hundreds of animals.
  • In this context, here is a look at why Assam has traditionally been flood-prone and an assessment of the measures taken.

Why are floods so destructive in Assam?

  • Apart from heavy and constant rainfall during the monsoon, there are many contributory factors, both natural and man-made that make floods so destructive in Assam.
  • Brahmaputra - The very nature of the river Brahmaputra is 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.
  • Tibet is a cold and arid region, and lacks plantation. Glaciers melt, soil erodes and all of it results in a highly sedimented river.
  • On the other hand, Assam primarily comprises floodplains surrounded by hills on all sides.
  • So, by the time the Brahmaputra enters Assam, i.e. from a high slope to a flat plain, its velocity decreases suddenly.
  • This results in the river unloading the sediment.
  • Also, following the devastating earthquake of 1950, the level of the Brahmaputra rose by two metres in Dibrugarh area in eastern Assam.
  • Because of the earthquake-prone nature of the region, the river has not been able to acquire a stable character.
  • So the river’s channels prove inadequate amid the siltation, in turn, leading to erosion and floods.

  • Man-made factors - Besides the natural factors are the man-made ones which lead to higher sedimentation.
  • These include habitation, deforestation, population growth in catchment areas (including in China), etc.
  • For instance, the sediment deposition itself creates temporary sandbars or river islands.
  • It is common for people to settle in such places, which further restricts the river flowing space.
  • When rainfall is heavy, it combines with all these factors and leads to destructive floods.

How effective are the flood control measures?

  • Dams - In its master plan on the river in 1982, the Brahmaputra Board had suggested that dams and reservoirs be built to mitigate floods.
  • However, the idea of dams has traditionally been a double-edged sword.
  • One of objectives of dams is to regulate the release of flood waters.
  • But, the release, when it comes, can sometimes be beyond the capacity of the channels downstream, further leading to floods there.
  • In the Brahmaputra basin, there were protests against dam-building plans on grounds of displacement and destruction of ecology.
  • All these prevent the plans from moving forward.
  • Embankments - Given the above, the government has been using only one approach towards floods, which is building embankments on the river.
  • Embankments were proposed only as an interim and ad hoc measure for short-term mitigation and thus, they lack durability.
  • Since they were temporary measures, the government did not spend on high-specification embankments, and so, are weak and are regularly breached.
  • Dredging - The government also considered dredging (digging up the riverbed and making the river deeper).
  • However, this is not a wise idea given the fact that Brahmaputra sediment yield is among the highest in the world.
  • Even if the silt is taken out this year, more silt will be deposited the following year, making the very expensive effort futile.
  • Overall, most of the government’s measures have been piecemeal and short-term, and the problem is not addressed at the source.

What could a sustainable solution be?

  • Addressing the issues only in Assam, when the flood strikes, could not be long-term solution.
  • There has to be a “basin-wide approach” to the flood problem of Assam.
  • An “integrated basin management” system should ideally bring in all the basin-sharing countries on board.
  • The countries should come to an understanding about taking measures in the catchment areas.
  • For this, the inter-state relationships, political cooperation and the role of the government are important.
  • Flood-plain zoning is another measure in which depending on the vulnerability of the area it is divided into different categories.
  • Accordingly, certain activities such as farming, building a house, etc are banned.


Source: Indian Express

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