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Do massive dams ever make sense?

A new report from researchers at Oxford University argues that large dams are a risky investment – soaring past projected budgets, drowning emerging economies in debt and failing to deliver promised benefits . Do they ever really make sense?

A peek over the edge of the Hoover Dam’s 60-storey wall is enough to send shivers down anyone’s spine. Constructed from enough concrete to pave a motorway from New York to San Francisco – this colossal barrier is touted as a symbol of man’s mastery over nature and a marvel of 20th Century engineering. The dam was credited with helping jump-start America’s economy after the Great Depression, reining in the flood-prone Colorado River and generating cheap hydroelectric power for arid south-western states. Even more miraculously, the Hoover Dam was completed two years ahead of schedule and roughly $15m (£9m) under budget.

But for megadam critics, the Hoover Dam is an anomaly. The Oxford researchers reviewed 245 large dams – those with a wall height over 15m (49ft) – built between 1934 and 2007. They found that the dams ran 96% over their approved budgets on average – Brazil’s Itaipu dam suffered a 240% overrun – and took an average of 8.2 years to build. In the vast majority of cases, they say, megadams are not economically viable.

BBC article