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.
