A sustainable engineering disaster
Dinesh Kumar Mishra looks back at the history of floods in North Bihar and wonders what this year has in store
Had the Kosi river not breached its eastern embankment at Kusaha last year, 2008 would have gone down as a drought year in North Bihar. The rains were scanty and there was virtual drought after the breach occurred. That is why the Kosi hit only 3.3 million people across five districts, 35 blocks, 993 villages and an area of 368,000 hectares (ha) and 527 people were killed.
Among Bihar's rivers, the Kosi's sediment load is high and it meanders. It was embanked in late 1950s and made to flow in a channel so that 214,000 ha outside the embankments could be spared the seasonal flood. These embankments are nearly 125 km long on either side and are spaced at an average width of 10 km apart. A barrage was constructed to regulate water for irrigation and the embankment was extended upstream.It is in these extensions, called afflux bundhs, that the breach happened last year.
The embankments were to stop spilling of floodwater, but they also prevent the sediments from escaping. This has raised the riverbed, forcing the embankments to be raised accordingly. But there is a limit to raising and maintaining embankments. The riverbed rises an average of 10 cm each year, where the breach took place. It was flowing five metres higher than the level at the time the river was embanked--this makes for an unstable river that can easily breach embankments, which also prevent rainwater from draining into the river, causing water logging outside. On August 18, 2008, that's what happened for the eighth time (see list on map).
And this was when the amount of water in the river was less than a sixth--15 per cent--of the flow that the embankments were designed to endure. After the breach, nearly 90 per cent of the water flowed through a new course the river had carved for itself outside where it had been engineered to flow.
"Nothing short of immediate plugging of the breach was acceptable to the people hit by the floods who were living in the new floodplain of the river," said Gautam Chaudhary, a resident of Birpur on the protected countryside of the eastern embankment. "They were not used to such floods after the embankments were built. The boats are not there because they were not needed; people have forgotten how to swim."
Had the Kosi not breached its sides and run through its designated course, it would have inundated 414 villages (34 of them in Nepal) that live within the embankments. When the river was engineered, it was assumed these villages would get rehabilitated in the land freed from the Kosi's seasonal floods, but they would be able to cultivate their lands within the embankments during the lean season. This did not prove very practical; most residents returned to their ancestral homes.
"Punarwas to banwas hai" (Rehabilitation is exile), said Manoj Chaudhary of Saharsa district's Murali village, located within the Kosi embankments. People choose to stay where they can earn a living. Most migrate seasonally for supplementary income.
The river has three distinct reaches. The lower reaches were embanked in the 1950s and the upper reaches in the 1970s. The middle was left untouched because the river was said to be unstable here. In 2006, out of the blue, the current government criticized its predecessor and talked of providing succour to the people of the middle Bagmati basin. It decided the river had matured here, and started building embankments.
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