Clean Power

Published on August 9th, 2012 | by Katy Yan


Dam Drawdown an Overlooked “Global Warming Culprit”

August 9th, 2012 by  

While scientists have known for decades that tropical reservoirs are a significant source of greenhouse gas emissions, new research from Washington State University-Vancouver has revealed that temperate reservoirs can produce a significant surge in emissions during certain times in their operation. These periods are known as drawdown periods, when the water level in a reservoir drops rapidly, thereby exposing a “drawdown zone” of decayed plants that can be a continuous source of methane.

Drawdown area in the Three Gorges reservoir

Marshes in the drawdown area of the Three Gorges Reservoir could be a significant source of methane. Photo via Wikimedia Commons

Bridget Deemer, the researcher leading the study, measured dissolved gases in the water column of Lacamas Lake in Clark County and found methane emissions jumped 20-fold when the water level was drawn down. A fellow WSU-Vancouver student, Maria Glavin, sampled bubbles rising from the lake mud and measured a 36-fold increase in methane during a drawdown. Deemer and Glavin will present their findings at a poster session at the national meeting of the Ecological Society of America in Portland this week.

While emissions from drawdown regions have long been recognized by researchers and international research bodies like UNESCO (see UNESCO and International Hydropower Association’s Greenhouse Gas Measurement Guidelines), according to John Harrison, Deemer and Glavin’s advisor and an assistant professor of Earth and Environmental Sciences, this is the first study to actually demonstrate and quantify the relationship between water-level drawdowns and greenhouse gas releases.

Reservoir study area

Fallen tree at Lacamas Lake, Washington
Photo: Lonie Lougheed

This is also one of the few studies we’ve seen to actually examine drawdown zones in temperate reservoirs. Drawdown emissions have been studied and modeled in the tropical context (see Fearnside, 2009 and 2005) and to a limited extent at the Three Gorges Dam (see Chen, H. et al., 2009). In the case of Three Gorges, for instance, one-third of the reservoir is a drawdown region and given its massive size (its surface area is the size of Hong Kong) — that is no insignificant source of methane. While dam reservoirs cover a small portion of the earth’s surface, as Harrison notes, they harbor biological activity that can produce large amounts of greenhouse gases. When you think of the number of large dams in the world – more than 54,000 that are over 15 meters – and the countless others that are being proposed or are under construction, continuing to overlook reservoirs as a carbon source and treating dams as a “carbon neutral” energy source is no longer a viable option.

To fix this situation, an important first step is for governments and dam builders to recognize that dams have a carbon footprint (and a potentially significant one depending on where it’s located, its age, depth, and organic inputs). Next, countries must report their reservoir emissions in their national greenhouse gas inventories. However, since the requirement is that they follow IPCC guidelines, the IPCC must first adopt strong guidelines like those developed by UNESCO/IHA. Only then can we get a true accounting of a country’s overall carbon emissions.

On the project scale, this research could have important implications for how dam operators manage drawdowns, as emissions may be higher in summer months when warmer temperatures and low oxygen conditions in bottom waters stimulate the microbial activity that produces greenhouse gases. Managers can also consider the optimal time to take out a dam, according to Deemer. While a dam removal may lead to some greenhouse gas emissions initially, it will be a one-time occurrence, whereas emissions can recur with regular drawdowns. With this in mind, Deemer plans to look at three other reservoirs in Oregon and northern California’s Klamath basin, where a major dam decommissioning effort is underway.

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About the Author

I am the China Program Coordinator at International Rivers, an environmental and human rights NGO that seeks to protect rivers and defend the rights of communities that depend on them. I coordinate our activities around capacity-building of Chinese grassroots activists, manage our Intern and Volunteer Program, provide advocacy and analytical support to groups fighting destructive carbon-financed dams, and support our education and outreach efforts. On CleanTechnica, my blog explores dam-building in China and compliance carbon offsets.

  • hydropowerharmony

    I would like to see a study that compares the methane releases from rivers with no dams. Rivers fluctuate annually and naturally with snow melt, precipitation, and dry months. Seems far fetched to say that dams are the cause when this happens naturally. In fact, the Columbia River dams hardly fluctuate at all due to their regulations. This make me think that in same cases dams might be beneficial to climate change. Especially since dams can store water and use it for energy as needed. As the earth warms, we will be able to store cold snow-melt water deep in the reservoirs and access it later for the summer periods when the river would naturally be much warmer without them.

  • katyyan

    Some perspective:

    Based on research from the Intergovernmental Panel on Climate Change, over the last 20 years, the warming impact of annual large dam methane emissions is equivalent to 7.5 billion tonnes of carbon dioxide. By comparison:

    Global CO2 emissions from fossil fuel burning (2004): 26.6 billion tonnes

    US CO2 emissions from fossil fuel burning (2005): 6 billion tonnes

    EU-15 emissions from fossil fuel burning (2003): 3.3 billion tonnes

    Global CO2 emissions from coal (2003): 9.6 billion tonnes

    US CO2 emissions from coal (2005): 2.1 billion tonnes

    US CO2 emissions from road transport (2005): 1.7 billion tonnes

    Global CO2 emissions from aviation (2002): 0.5 billion tonnes

    • Bob_Wallace

      Katyyan – I’m bothered. I’m concerned that we might have a group of researchers who have started out to prove a preconceived point rather than do real science.

      I checked Google to see if there was anything unusual about Lacamas Lake, perhaps it was newly constructed and was cooking off submerged vegetation. Here’s what I found on Wiki –

      “The 43,000 acres (174 km²) around these lakes collect precipitation and form the Lacamas Creek which feeds into both lakes. This area is mostly large open fields and private farm or ranch land. The resulting runoffcontains high levels of fertilizers which leads to nutrient abundance in both lakes. This nutrient abundance has caused plant overgrowth and algaeproblems. Consequently only a few fish species are able to live in either lake ( brown trout, rainbow trout, largemouth bass, bluegill, crappie, yellow perch, catfish and sturgeon). The government considers the lake to be eutrophic.”

      Now, how unique might that lake be? Is that a specific piece of data from which we want to build a large general case.

      I recall the noise coming from the anti-dam folks who were using a very shallow lake in South America which had covered up an immense amount of vegetation for the amount of water it held.

      I recall one person claiming that large amounts of vegetation grows back on reservoir banks when the water level drops and is then drowned when the water rises. That does not happen in North America, top soil is generally lacking so plants have very poor growing conditions.

      I worry that some people are taking extreme examples and trying to apply them broadly.

      • katyyan

        Hi Bob_Wallace. You are right to be vigilant about the scientific integrity of studies, but I think in this case, the case study may be more the norm than the exception. Most of the reservoirs that I’ve monitored for reservoir emissions research are highly eutrophic – think Three Gorges – and have a large amount of pollution inputs upstream from point and non-point sources. A lot of the research on reservoir emissions is on eutrophic reservoirs these are more likely to be significant sources of reservoir emissions. The question in these cases isn’t are they or aren’t they carbon emitters, but how much do they emit (and ideally, what’s the net emissions). I think the researchers of this study would agree that more research needs to be done at other sites on draw-down zones in order to get the full picture on this particular topic.

  • If we just get rid of all the water on the planet, maybe that will solve the problem.

  • Bob_Wallace

    Could  you give us some context here?  How much methane are we talking about?  How much compared to the fossil fuel generation this technology replaces?

    Lifetime data please.  Not initial year data when flooded vegetation is cooking off.

    • katyyan

      Thanks Bob for your interest – all excellent questions. They won’t be publishing their final results until later this year. I will definitely circulate them one they do. The emissions from drawdown zones will probably look minimal compared to fossil fuel generation (and there’s still the entire carbon budget of the reservoir to consider over a longer timespan as you indicate), but that is not where the significance of the study lies. It’s interesting because it helps to elucidate the role of drawdown zones and clarifies one more piece of the overall reservoir emissions puzzle. 

      • Bob_Wallace

        I think it very important to put things into perspective. Sometimes a number standing alone might be taken to mean something different than what it actually means.

        There are no 100% clean ways to harvest energy. The cleanest, solar panels for example, require mining and refining to produce the glass, silicon and aluminum needed to make panels. Wind turbines need concrete, steel, copper and they kill a few birds.

        The alternatives: No electricity or very damaging fossil fuels (which actually kill more birds per kWh than does wind).

        We should be critical of dams, certainly of shallow reservoir dams. But put that criticism in the context of other ways to generate and store power.
        Think medicine:

        This pill will make you feel lousy. But it will also save your life.

        Maybe later we’ll invent a pill that both cures you and makes you feel great. But for now….

  • OMG what about Tides? Man its not the oil and gas industry after all, its water. Yea man, water rising and lowering. Whew, for a while I suspected carbon emissions, fossil fuels, deforestation.

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