Why Kosi changed from cat to tiger - warning against plugging breach

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By G.S. MUDUR in Delhi
  • Published 12.09.08
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New Delhi, Sept. 12: The proposed repair of the breach in the Kosi that has submerged northern Bihar will leave vast areas still vulnerable to intense flooding, environmental activists and engineers have warned.

Water resources ministry officials had last week hatched a plan to plug the breach using boulders, polypropylene sheets and sandbags after slightly diverting the river’s flow to allow the repair work.

But experts cautioned that creating a short segment of new embankment at the site of the breach would only leave long stretches of aging embankments on both sides of the river as vulnerable to future floods as before.

“A river such as Kosi with an enormous volume of water cannot be tamed with embankments,” said Rajiv Sinha, professor of engineering geosciences at the Indian Institute of Technology, Kanpur. The volume of water in the Kosi in the months after the monsoon is sometimes 40 times its discharge before the monsoon, Sinha said.

The embankments built on either side of the Kosi during the 1950s and 1960s to protect several thousand square kilometres of northern Bihar and Nepal had a typical lifespan of 25 or 30 years, Sinha said. “They were never envisaged as a long-term solution.”

The Kosi also carried such high loads of sediments that at some points along the embankment, they had raised the riverbed even higher than the adjoining land, according to a fact-finding team that had visited stretches of the Kosi in Bihar in March this year. Instead of protecting the land from floods, these embankments contributed to increasing the flood-prone area in Bihar from 2.5 million hectares in the 1950s to 6.8 million hectares now, the team said in a report released today.

Experts said the embankments and the rising sediment levels had combined to dramatically reduce the space for water, increasing the chance of breaches at dilapidated points along the embankments. “Caging Kosi has made a tiger out of a cat, making the river ferocious and unpredictable,” the report by environmental activists Gopala Krishna and Sudhirendar Sharma, two members of the fact-finding team, said.

The embankments had prevented the Kosi from distributing its annual silt load of about 92 million cubic metres into areas on either side of the river and improving soil fertility there. Instead, they contributed to waterlogging in the low-lying areas on the two sides of the river by preventing natural drainage from the area.

“The embankments have had a disastrous impact. The breaches cause floods, and even when there’s no flood, there’s permanent waterlogging in the low-lying areas on the sides of the river,” Krishna said.