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Improper plugging of diversion tunnel blamed for dam failure

Owner of one of the world's largest dams, the 202m tall Campos Novos Dam in southern Brazil, this week played down the sudden, unplanned loss of its impounded water, late last month.
The partially filled reservior fell by 53m, completely emptying, over two days on 20-21 June. The unplanned event sent water cascading downstream.Campos Novos Dam is a concrete faced rockfill structure. The $671M (£376M) was completed last year by a consortium led by Brazilian construction giant Camargo Corrêa and consultant Engevix. Client is Enercan, a joint venture between Brizilian energy company CPFL Energia and aluminium smelter CBA.Aerial photographs taken on 22 June showed large cracks in the concrete, upstream face of the dam.But Camargo Corrêa president Enio Schneider said that the cracks were not structural. He claimed that the water loss had occurred through a river diversion tunnel created as part of the temporary works during construction of the dam. The tunnel had been improperly backfilled, and had reopened, allowing the water release, he said.But US-based environmental group the International Rivers Network said that local residents are worried about the integrity of the dam itself.They says that water has been seeping through the dam ever since inpoundin of water started in February.A UK-based geotechnical engineer said that if the content of the reservior had been lost through the dam wall itself the structure would have suffered significant damage, which would be visible in photographs.The released water raced down a parched riverbed and into the reservoir of a dam downstream that was almost empty due to a severe regional drought.

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