A Mega-Dam Dilemma in the Amazon

A huge dam on Peru’s Inambari River will bring much-needed development to the region. But at what cost?

The dam, to be built at the confluence of the Inambari and Araza rivers, is one of dozens expected to power South America's economic ascent. (Ivan Kashinsky)
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Lula reduced Brazil’s poverty rate from 26.7 percent in 2002, when he entered office, to 15.3 percent in 2009—accounting for some 20 million people. Peru has done almost as well: it has reduced its poverty rate from 50 percent to 35 percent, a difference of about four million people. But farming and resource extraction require lots of land and energy, which is why Brazil is expected to need 50 percent more electricity in the next decade, and Peru at least 40 percent more. In the short term, both countries will have to keep pushing deeper into the Amazon to generate electricity.

Meanwhile, they are under pressure from trading partners and finance organizations such as the World Bank to manage their growth with less environmental damage. Brazil has a bad reputation for its decades of rain forest destruction; it has little interest in becoming known as a polluter, too. With the world’s focus on limiting fossil-fuel consumption, hydropower has become the easy answer.

Until recently, Brazil had focused its hydropower construction within its own borders. But a hydropower facility works best near a drop in elevation; gravity pushes water through its turbines more quickly, generating more electricity—and Brazil is almost completely flat. Which is why, over the past decade, Brazil has underwritten mega-dams in Bolivia, Paraguay and Peru.

In 2006, Brazil and Peru began negotiating an agreement to construct at least five dams throughout Peru, most of which would sell power to Brazil to feed the growth in its southwestern states. Those negotiations produced the deal that García and Lula signed last summer.

Although Peru relies primarily on fossil fuels for its energy, Peruvian engineers have been talking about a dam along the Inambari since the 1970s. The momentum of the rivers coming down from the Andes pushes an enormous volume of water through a narrow ravine—the perfect place to build a hydropower plant. The problem was simply a lack of demand. The region’s recent growth took care of that.

But there are risks. By flooding 155 square miles of land, the proposed dam will wipe out a big chunk of carbon-dioxide-absorbing forest. And unless that forest is thoroughly cleared beforehand, the decay of the submerged tree roots will result in massive releases of methane and CO2. Scientists are still divided over how to quantify these side effects, but most acknowledge that hydropower is not as eco-friendly as it might appear. “It’s not by definition cleaner,” says Foster Brown, an environmental geochemist and expert on the southwestern Amazon at the Federal University of Acre, in Brazil. “You cannot just say it’s therefore a better resource.”

What’s more, the dam may kill much of the aquatic life below it. On my trip along the river with Nathan, he explained that freshwater fish are particularly sensitive to variations in water and sediment flow; they do most of their eating and reproducing during the dry season, but they need the high water levels of the rainy season to have room to grow. The dam, he said, will upset that rhythm, releasing water whenever it runs high, which could mean every day, every week or not for years. “Shifting the river’s flow regime from annual to daily ebbs and flows will likely eliminate all but the most tolerant and weedy of aquatic species,” Nathan said.

And the released water may even be toxic for fish. Most dams release water from the bottom of the reservoir, where, under intense pressure, nitrogen has dissolved into it. Once the water heads downriver, however, the nitrogen starts to slowly bubble out. If fish breathe it in the meantime, the trapped gases can be deadly. “It’s the same as getting the bends,” said Dean Jacobsen, an ecologist on Nathan’s team.

Others point out that if the fish are full of mercury, the local people may be better off avoiding them. In the long run, a stronger economy will provide new jobs and more money, with which locals can buy food trucked in from elsewhere. But such changes come slowly. In the meantime, the people may face massive economic and social displacement. “Locally, it means that people won’t have enough to eat,” said Don Taphorn, a biologist on the team. As he spoke, some fishermen were unloading dozens of enormous fish, some weighing 60 pounds or more. “If this guy didn’t find fish, he can’t sell them, and he’s out of a job.”

Brack, however, says the benefits of the dam—more electricity, more jobs and more trade with Brazil—will outweigh the costs and in any case will reduce the burning of fossil fuels. “All the environmentalists are crying out that we need to substitute fossil-fuel energy with renewable energy,” he said, “but when we construct hydroelectric facilities, they say no.”


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