Environment & the World

Wednesday, December 6, 2006

Hydropower – not so clean after all?

Filed under: Climate Change, Energy, Water — Cathy @ 7:18 pm

I have never been a fan of large dam projects.  In the United States, dams have decimated salmon populations, reduced the Colorado River to a trickle by the time it reaches the Pacific, and otherwise transformed the ecology of our western rivers.  And in many developing countries, dam projects displace hundreds of thousands of people, often without giving them adequate compensation.  Large popular movements have arisen against major dam projects like the 3 Gorges Dam in China or the Narmada River dams in India.

But dam proponents have argued that dams don’t emit carbon dioxide, so they must still be better than coal, right?  Well, perhaps not, at least in tropical regions.  A recent article in the journal Nature (“Methane quashes green credentials of hydropower”, Nature 444(30): 524-525, 2006) highlights recent research suggesting that “the global-warming impact of hydropower plants can often outweigh that of comparable fossil-fuel power stations.”  How?  When land is flooded to create the reservoir, a large amount of organic matter is trapped underwater, and more organic matter flows in over time.  In warm tropical waters, this organic matter decays into methane and carbon dioxide.  Since methane is a 20 times more potent greenhouse gas than CO2, these reservoir emissions can be quite significant.  Indeed, the article cites an example of Brazil’s Balbina Dam, whose construction caused the flooding of 2500 square kilometers of rainforest; it is now accepted that a coal plant would have been better for the climate!

The article notes that the debate over the magnitude of reservoir emissions is not yet settled, largely due to a lack of data on dam methane emissions.  However, by some estimates, counting the methane emitted by dams (95-120 million tons per year) would represent a 20% increase in global methane emissions!  This is a large enough number, and enough is known about dam methane emissions, to make many scientists want to start acting now on this problem. 

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6 Comments »

  1. This issue of large-scale hydropower you bring up is really an important one. Hydropower in and of itself seems like a wonderful idea given that, when done right, it results in no emissions and is a renewable resource. Taken to the extreme, though, hydropower is not necessarily so wonderful and environmentally benign.

    Like you mentioned, massive projects can flood vast areas of land, displacing at times hundreds of thousands of people, and destroying important ecosystems, etc. Disruption of fish movement and silt deposition are also problems, as well as the schistosomiasis-carrying snails which can accumulate in the dam lakes. Since dams hold back silt, the water released from the dams carry less of it and erode downstream banks more quickly. Also, the silt that came from the annual floods of the Nile, for example, served as a natural fertilizer for many farmers in the region, who must now rely on fertilizers.

    The thought of dams causing greenhouse gas emissions never really crossed my mind, but it makes a lot of sense considering how wetlands can also be sources of methane. If all the of the other disadvantages to large-scale hydro weren’t enough to make us reconsider how we go about it, maybe the rising tide of concern about global warming will. That being said, I don’t think it’s necessary to abandon hydropower all together. In fact, microhydropower and and other small scale systems can be built with all the benefits of clean renewable energy and with fewer drawbacks. I hope we continue to harness the power of water, just in a wiser way.

    Comment by Amir — Friday, December 8, 2006 @ 1:54 am

  2. Thanks for your comments, Amir. I should have been more clear, I think. I also have no problem with “micro-hydro” projects that harness some of the energy in the water without completely blocking the flow of the river. My opposition to hydropower is really an opposition to the large-scale mega-dams that cause all the problems that you articulated in your comment.

    Comment by ckunkel — Saturday, December 16, 2006 @ 1:11 am

  3. And there are lots of places where run of the river hydropower, tidal power, wave energy capture and so on can tap into the energy of falling water without the need for large scale dams. In many places we will also be needing flood protection barriers (on the Thames in London one appeared 20 years ago) and again these can be combined with electricity generating capacity. In BC the existing dams could produce more power. Revelstoke for instance has space and infrastructure for two more turbines. And in Vancouver water is spilled most of the winter from the dams that provide us with water for domestic use

    Comment by Stephen Rees — Wednesday, December 20, 2006 @ 12:41 pm

  4. thats good information, thanks

    Comment by boni — Sunday, November 15, 2009 @ 5:52 am

  5. CSIRO, through the Water for a Healthy Country Flagship, is undertaking research to underpin the effective management of water quality in the Great Barrier Reef.

    Comment by Water Barrier — Friday, November 20, 2009 @ 5:24 am

  6. OMG enjoyed reading your article. I submitted your rss to my google reader.

    Comment by fetetrimi — Friday, December 11, 2009 @ 9:57 am


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