Experts fear Kosi may have changed course

The surging waters that have flooded over 800 villages and displaced lakhs of people in Bihar after the Kosi breached its eastern embankment in Nepal could very well end up being the new course of the Kosi, its first eastward shift in recorded history, say experts who have long watched and studied the river.

The implications are crucial to deciding on the relief and reconstruction strategy. For, if this is the new course, nudging the river back to its original channel to the west, as is being planned now, could only be "postponing the problem."

The current flood zone, experts say, is in the "Dhusan channel" which the Kosi once occupied between 1921 and 1926. Before the breach last month, the Kosi was flowing down what is called the Sapt Kosi course, about 100 km west of the Dhusan channel.

"Left to its own devices, the Kosi probably wouldn't naturally re-occupy the Sapt Kosi course," says Neil A Wells, a geology professor at Kent State University and co-author (with University of Michigan's John Dorr) of a 1987 seminal paper on the Kosi's behaviour.

"If no one did anything, you would probably have Kosi flow down both the Sapt channel and the Dhusan for several months to several years. The Sapt channel will probably gradually fill in and the Dhusan channel (or more likely multiple interconnected channels) would be subject to a lot of diverse infilling, erosion, flooding, and shifting, until it established a new course," Wells said in an email interview with The Indian Express.

"So the fix should be perfectly fine for a few years if they do it right, barring exceptional rains and floods but it won't last forever. It will in no way be a 'solved problem' that people can ignore," said Wells.

This is echoed by Professor Emeritus B Prakash of IIT Roorkee who has worked on the Kosi since late '70s and Rajiv Sinha of IIT Kanpur, whose latest research is focused on flood-risk mapping of the Kosi basin.

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