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Taming the meandering river once and for all is proving to be as difficult as it is essential. Experts talk to The Sunday Express about the need for desilting and channelising the river, afforestation and building strong embankments.

Written by Ravishtiwari |
September 7, 2008 11:34:26 am

Taming the meandering river once and for all is proving to be as difficult as it is essential. Experts talk to The Sunday Express about the need for desilting and channelising the river, afforestation and building strong embankments.
The wayward River of Sorrow has wreaked havoc, affecting over 35 lakh people and posing an engineering challenge that defies quick fixes. As in the course of the river, there are many twists and turns in the process of finding a sustainable solution. In the short run, fixing the breach and controlling the flood should minimise the misery of the affected, but finding a long-term answer to the problem is where the real challenge lies.

Says Neil A. Wells, 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, “Barring exceptional rains and floods, a fix at the breach site should be perfectly fine for a few years if they do it right, but it won’t last forever.”
Experts fear that Kosi’s new channel, which, as satellite images show, carries more water than the original channel, could well be the river’s new course. “Left to its own devices, the Kosi probably wouldn’t re-occupy the Sapt Kosi course,” says Wells.

So should the river be allowed to flow in the new channel or be brought into the original Sapt channel? “The new channel may take decades to stabilise, till which time the people living in the region will be in danger and may have to relocate constantly,” says Professor Nayan Sharma of the Department of Water Resources Development and Management at IIT Roorkee, who has worked on transboundary rivers like Brahmaputra, Mekong and Danube. Sharma is also a member of the high-level committee set up by the Government to suggest a long-term sustainable solution to the Kosi problem. He feels that given the high population density in the region, we cannot allow the infant channel free play. “We must make a serious attempt to bring the river back to the original channel,” says the professor.

When New Orleans was flooded after Hurricane Katrina hit the Mississippi River, breaching its embankments in August 2005, the administration repaired the breach to control the river. The Kosi, however, is a braided river—it forms multiple channels on its path—unlike the Mississippi, which is a controlled, single-channel river.

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What further compounds the problem is that the Kosi is heavily sediment-loaded, unlike the Mississippi, whose riverbed was stable. “While the deluge of New Orleans appeared more challenging because of Katrina, given Kosi’s fluvial hydraulic standpoint, our problem is more complicated,” says Professor Sharma. Professor Emeritus Brahm Prakash of IIT Roorkee, who has worked for two decades on the geology of the Kosi region, says, “Bringing the river back to the original channel without controlling the sedimentation is not going to solve the problem entirely. Due to heavy sedimentation, the entire riverbed between the embankments has gone up, so we have been raising the height of the embankments. We must acknowledge that this is not a solution as the riverbed is higher than the plains nearby. The water will always create heavy pressure on the embankments. These reparations are only postponing a bigger problem,” he points out.

While advocating a desiltation of the river by dredging the riverbed to bring its level below that of the surrounding plain, Professor Prakash also says that a sustainable solution must try to manage the discharge flow of the Kosi before it reaches the Shivalik range—from where it collects about 30 per cent of its sediment. He suggests reviving the High Kosi dam project with Nepal at Barahkshetra, upstream of the breach site. India can make Nepal a stakeholder in the project by signing a power purchase agreement and offering an inland navigation route till Haldia.

Besides, heavy afforestation must be undertaken in the Shivalik—or the lower Himalayan—range to hold together loose rocks and sand upstream of the Kosi to reduce the sediment load in the river. To bring the river to the original channel, the embankments must be “impregnable” on either side to avoid a breach in future, says Sharma, adding that measures should be adopted to minimise breading—division into multiple channels—in the Kosi and channelise its flow into the middle to avoid erosion and pressure on the embankments.

Making the embankments so strong is no mean feat, but Sharma cites the example of Holland, whose dykes keep the land from being washed away by sea currents, even though the country lies below the sea level. Using heavy ‘gabions’—rocks that are enmeshed into polymer/metal nets—and geotubes—sand-filled, heavy, geotextile tubes 120m long and with a 3m diameter which can withstand water pressure—can help, says Sharma. Sharma and Prakash agree that all these measures must be undertaken simultaneously to implement a sustainable solution.

“Given the nature of the challenge arising from the breach, the future management of Kosi embankments cannot be left to the agencies of the Bihar Government, which are burdened with several other tasks. There should be an exclusive Kosi Basic Authority, like the Tennessee Valley Authority or the Damodar Valley Authority, manned by experts and experienced engineers,” says Sharma.

While no repair of the breach for the long term can be undertaken in the next few months, till the volume of the water falls to below 50,000 cusecs, the authorities have come up with a strategy to divert water from the eastern embankment to the west. The slow progress of the short-term work on the breached site, though, is a matter for concern. The Sanyal Committee, constituted by the Bihar Government, has pointed out as much. Indeed, the Government is still looking for dredgers to dredge near the western embankment to divert the river back to the original channel.

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