Dam Scam?

Dams are just plain awesome. Forged from tons of rock, stone, or concrete, a dam's giant wall straddles river valley to help prevent flooding and churns water to produce hydroelectric power (electricity generated by water-run turbines). "Some even have gated waterways called locks that raise and lower ships," says mechanical engineer Neil Norman.

In fact, dams have proven so valuable to modern civilization that over 60 percent of the world's rivers feature at least one. In the last 50 years, more than 45,000 large dams--at least 15 meters (49 feel) tall--have been erected.

But a new report from the World Commission on Dams (WCD)--the first worldwide assessment of dams--shows the giant structures may cause more damage than benefit. Not only do they strain dam-builders' pockets, but the environment as well.

A dam works as a barrier to cut off a river's natural flow, pooling water into a reservoir (artificial lake) behind the wall. Then collected water gates redirected for usage. "Dams have been used since the dawn of agriculture to irrigate fields," says Norman. And they help contribute up to 16 percent of the world's food source. But ironically WCD found the mega-structures have also driven between 40-80 million people worldwide--mostly farmers--off their lands.

Many communities become displaced when rerouted water supply starves their fields of water, minerals, and nutrients. "Rivers carry natural nutrients downstream," says Norman. Some farmlands depend on these nutrients to stay fertilized, but some dams cut off the nutrients' flow downstream. "That happened in Egypt and hurt many farms by the Nile River," adds Norman. Worse, the WCD found most displaced farmers have never been compensated for their losses, resulting in economic hardship.

Changes in a river's water flow also impact its teeming life. The WCD reports that large dams have endangered or caused extinction to over 20 percent of the world's 9,000 freshwater fish species.

In the U.S., one hotly debated issue concerns the dams of the Columbia and Snake rivers in Oregon and Washington, and the rivers' salmon population. Conservationists are alarmed over the fish's dramatic decline. Once 16 million strong, the rivers' salmon numbers have fallen to a mere 1 million today. One factor: Salmon spawn (reproduce) in freshwater upstream and make their way downstream to live in salty seawater--before swimming upstream again to spawn. "Dams block salmon from swimming upstream," says Norman. "Yet the dams generate a lot of very cost-effective power for the people in the U.S."

While large dams provide 19 percent of the world's electricity, the WCD claims one fifth of dams generate less than 75 percent of their electrical potential. And one quarter of water supply-dams deliver only half their capability. No, the world can't do away with dams. But the WCD hopes its report will spur more thorough studies and better community understanding before breaking soil for new dams.

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