Pros And Cons For Thousands Of Big Dams Coming Online In Next 20 Years

by Michael Keller
Pros And Cons For Thousands Of Big Dams Coming Online In Next 20 Years

In Brazil’s Amazon basin, engineers are busy building a new dam that stretches 5 miles across the Madeira River. When it’s complete in 2015, the project’s 50 turbines will transform the river’s flowing waters into 3,750 megawatts of electricity. The reservoir that trails behind the dam will submerge up to 42 square miles of land. It’s a big project, and one of 34 hydroelectric dams that will be built by 2021 to help the country meet growing energy demands.

In China, more than 100 projects representing some 120 gigawatts of power are planned to be under construction by the end of 2015. The building frenzy, in a country wherehydropower already accounts for 22 percent of total capacity, is being spurred on to meet ambitious electricity production targets while fighting the choking pollution the country has been enduring.

Hydropower is booming, and development plans are particularly intense around the developing world. Flowing water already accounts for 80 percent of the global electricity production from alternative energy sources. And increasing demand for alternatives to fossil fuels means 3,700 major dams might be built in the next two decades, according to a new University of Copenhagen study.

“Hydropower is an integrated part of transitioning to renewable energy and currently the largest contributor of renewable electricity,” said Christiane Zarfl, an assistant professor for environmental system analysis at Germany’s Tübingen University. Her team’s study is being published in the journal Aquatic Sciences.

[Global spatial distribution of future hydropower dams, either under construction (blue dots; 17%) or planned (red dots; 83%). Courtesy of Aquatic Sciences.]

When they eventually come online, the construction projects will double hydroelectric production. But such developments, though helping the world diversify its energy production portfolio, are not without their problems. Zarfl’s analysis showed that dam-building plans would reduce the world’s remaining large free-flowing rivers by as much as 20 percent.

The creation of reservoirs, the alteration of flow volume, velocity and path, and the roads, equipment and materials needed to build these behemoth structures impact nearby and downstream human, flora and fauna populations. They can also alter the ecological services the unobstructed system provides.

“It is vital that hydropower dams do not create a new problem for the biodiversity in the world’s freshwater systems, due to fragmentation and the expected changes in the flow and sediment regime,” Zarfl continued.

Like all of the world’s energy sources, the costs of hydropower are being weighed against its benefits. It is currently the most abundant source of alternative energy, now producing 4,000 terawatt-hours of electricity around the globe. And with the international mission set to reduce fossil fuels’ output of gases that cause harmful pollution and climate change, the International Energy Agency (IEA) has set an ambitious goal of 7,000 terawatt-hours of hydropower generation by 2050.

“Regardless of whether they are large or small, or associated with a reservoir or run-of-river, hydropower projects must be designed and operated to mitigate or compensate for impacts on the environment and local populations,” Maria Van Der Hoeven, the IEA’s executive director, said in an interview with the International Hydropower Association. Still, “if we are going to try to put the world on a more sustainable energy future, then the use of hydropower will have to expand.”