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Corps says Report on Greenhouse Gases from Lower Snake Reservoirs Misleading by Staff Columbia Basin Bulletin, April 5, 2024

'Relatively Clean Reservoirs in Columbia/Snake River'

The U.S. Army Corps of Engineers says that a report by a new group that recently asserted the four lower Snake River dams are a major source of greenhouse gases, particularly methane gas, largely used emission figures from dams and reservoirs outside of the Columbia and Snake river basins.

The report by Tell the Dam Truth, a group in favor of removing the Snake River dams, calculated that the four dams emit about 1.8 million metric tons of carbon dioxide equivalent every year. That, the group says in its report, is equivalent to almost 10,000 railcars worth of burned coal, or 405,000 gas-powered automobiles driven for one year, or 202,500,000 gallons of gasoline burned or 2,000,000 pounds of coal burned.

Instead of the green, zero-carbon source of energy that advocates for keeping the dams in place say, they instead are "a major source of the heat-trapping greenhouse gases causing the climate crisis. Compounding the problem, dams submerge and destroy natural carbon sinks that once grew under their reservoirs," a Tell the Dam Truth news release said.

See CBB, March 22, 2024, New Report by Group Favoring Breaching says Lower Snake Dams, Reservoirs Major Source of Greenhouse Gases

According to the Corps, the group's calculations and assertions are misleading and that there is more to the story.

"We're aware of the reported analysis of the lower Snake River dams carbon emissions," wrote Tom Conning, Public Affairs Specialist, Northwestern Division of the Corps. "While we have not seen the actual analysis, it is important to note that this study did not specifically measure emissions at these four federal dams. Instead, it uses pre-existing literature from the Columbia River System Operations Environmental Impact Statement to make a generalized claim.

"The U.S. Army Corps of Engineers advocates for transparency and public discourse; however, this evaluation and conclusion could be misleading without more context," he wrote.

He continued, writing that the federal government is following emerging scientific studies of greenhouse gas emissions (GHG) that result from all large bodies of water, including reservoirs and natural lakes.

"A review of the existing available scientific literature on GHG from reservoirs performed for the CRSO EIS concluded that methane gas is generally not an issue for the relatively clean reservoirs in the Federal Columbia River Power System; reservoirs with a higher concentration of decomposing debris see more methane," Conning wrote. "It is also important to note studies attributing some level of GHG to reservoirs have largely been conducted in tropical climates with environments vastly different from the Pacific Northwest. Even recent work by the Department of Energy's Oak Ridge National Laboratory to improve the accuracy of GHG measurements in reservoirs relies on a sampling pool of reservoirs in a cluster of southern states that do not reflect the environmental and temperature characteristics common to the FCRPS."

Appendix G, Sec. 5 of the Columbia River System Operation final environmental impact statement, discusses GHG emissions in the Columbia/Snake rivers, as well as the differences in those emissions between rivers in the Northwest and those elsewhere, particularly in warmer climates. That information can be found at Columbia River System Operation Final EIS.

In Appendix G's methane (CH4) emissions summary, the EIS says:

"The available data presented in this report on surface fluxes of CH4 emissions from diffusion for the Columbia River hydroelectric project reservoirs, particularly those located on the mainstem or in more arid terrain, demonstrate that the basin's overall contributions to global CH4 emissions are very small compared to other studies of comparable systems, although they can be quite high locally," Appendix G says. "The Columbia basin reservoirs produce CH4 in the range of one or two orders of magnitude less than current global estimates of surface emissions from reservoirs, even when only including hydroelectric reservoirs."

The EIS's Appendix G concludes that differences that contribute to the lower levels of methane emissions are the relatively cold water temperatures, the well-oxygenated conditions in most of the river and the "low water residence times prevalent throughout the basin" (the flow), according to the EIS.

The EIS says the Columbia and Snake river systems of dams and reservoirs are just a "modest" source of CH4 and worldwide a small source of GHG.

"Indeed, CH4 emissions from reservoirs compared to total global sources are quite small. In mean estimates of data from the 2000s, global reservoirs, including tropical locations, contributed about 4 - 5% of CH4 from anthropogenic sources, and of these, hydroelectric reservoirs contributed about 3 - 6% of CH4 emissions," the EIS concludes. "However, nontropical reservoirs have been shown to emit far less CH4 due to local regional features such as geology, climate, type of flooded soils and vegetation, and hydrologic regime." The EIS goes on to say that methane emissions from hydroelectric reservoirs in the Western U.S. "were reported to be the lowest of those on the continent, compared to eastern Canada and Central/South America."

Still, climate change may alter these findings, according to Appendix G: "Additionally, since increased GHG emissions is positively correlated with warmer temperatures, there will be an ongoing need to study the impacts of climate change on CH4 processes within temperate hydroelectric reservoirs," according to an International Panel on Climate Change study.

In a 2006 study, the IPCC noted that temperature is the main driver affecting reservoirs as a result of climate change and, among other impacts, will change oxygenation levels, lake stratification mixing rates and growth of biota.

The report by Tell the Dam Truth is here: "Estimate of Greenhouse Gas Emissions for the Lower Snake River Dams and Reservoirs using the All-Res Modeling Tool."

Related Pages:
Dam Accounting: Taking Stock of Methane Emissions from Reservoirs by Tara Lohan, The Revelator, 5/25/22

Related Sites:
Evaluating greenhouse gas emissions from hydropower complexes on large rivers in Eastern Washington US Department of Energy, Pacific Northwest National Laboratory. (2013)
Inventory of Greenhouse Gas Emissions and Sinks Environmental Protection Agency, 4/15/22