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People believe hydroelectric dams provide clean energy. It’s not true.
I don’t blame the public or the media for making this false claim—I’ve heard it come out of the mouth of the biggest dam operator in the Southwest U.S. (see CRWUA presentation, Dec. 2013, slide 13), and the media often repeats it (see E&E article June 30). Unfortunately, it was further repeated in a horribly misguided “study” put out by the U.S. Dept of Energy in April.
But when I heard it quoted three months ago in this May 12 New Yorker story out of the mouth of Mark Tercek who is CEO of The Nature Conservancy to rationalize his organization’s support of new dams in Columbia, I knew it’s time to once-again address this disastrous myth.
Tercek is quoted as saying: “Environmentalists generally hate dams, even though they’re clean energy.”
- Organic material—vegetation, sediment and soil—flows from rivers into reservoirs and decomposes emitting methane and carbon dioxide into the water and then the air throughout the hydro-electric generation cycle. Studies indicate that where organic material is the highest (in the tropics or in high sediment areas) hydro-electric dams can actually emit more greenhouse gases than coal-fired powerplants. (See this report from International Rivers, this peer-reviewed article reported in Science Daily, this news report on Nature World News and this report about the Belo Monte dam). These methane emissions are not limited to tropical areas; they occur in the U.S. too. “Methane springs” are widely reported on the mud flats of Lake Powell which is a reservoir behind Glen Canyon Dam on the Colorado River (Living Rivers, slide 41), and “trains” of “methane bubbles” have been reported floating on Lake Powell (High Country News, page 5, May 17, 2011). As far back as 1948, the U.S. Geological Survey examined what they then called “gas pits” in the mud flats of Lake Mead which is a reservoir behind Hoover Dam on the Colorado River (USGS, page 162 and 180). As a real conversation ender, Brazil’s National Institute of Space Research estimates that “dams are the largest single [human-caused] source of methane, being responsible for 23 percent of all methane emissions due to human activities.”
- Large dams contain enormous amounts of cement which during the construction process uses massive amounts of energy that emits greenhouse gas emissions. For one medium-sized dam project proposed for the Cache la Poudre River in Colorado, it is estimated that the construction would emit 218,000 metric tons CO2-equivalents which equals the emissions from almost 46,000 automobiles on the road for one year. Larger dams, such as Hoover Dam which contains 4.36 million cubic yards of concrete, would have exponentially higher climate change impacts from construction. The largest hydro-electric dam on the planet—the Three Gorges Dam in China—contains 27.15 million cubic meters of cement.
- Dams that divert water out of rivers may have significant additional climate change impacts because they drain and dry up downstream wetlands that are “carbon sinks” holding vast amounts of greenhouse gases in soils. This draining and dry-up causes carbon and methane to be released and emitted into the air. A proposal for a dam on the Cache la Poudre River in Colorado would dry up 1,700 acres of wetlands thus emitting about 7,000 metric tons of CO2 equivalents. As just one more example, when the Colorado River was diverted and drained, the dams and diversions dried up about 2 million acres of wetlands in the former Colorado River Delta—the climate change impact of destroying those wetlands was likely staggering.
- Some dams, like the proposed massive ecosystem-wide Belo Monte dams on the Amazon River in Brazil, also include massive deforestation plans on areas that will be flooded by behind the reservoirs. The deforestation itself would release enormous amounts of greenhouse gas emissions.
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