A Washington State University professor who was among the first to sound an alarm about methane emissions from hydroelectric reservoirs says, in his opinion, "the jury is still out on the extent to which Columbia River reservoirs are significant greenhouse gas sources."
And while a new study on methane emissions from 1,500 hydroelectric facilities worldwide includes several from the Columbia Basin, it doesn't shed significant new light on how the Columbia's facilities measure in that regard. That's partly because most of the Columbia Basin's reservoirs haven't been measured for methane emissions. The new study uses modeling to estimate worldwide emissions, and even its authors acknowledge uncertainties due to the many factors that determine whether an individual reservoir has the conditions to generate large amounts of methane.
Methane is a greenhouse gas with 34 times the warming potential of carbon dioxide over 100 years, and 84 times the potential over 20 years, according to the Intergovernmental Panel on Climate Change. It is produced by decaying organic material in the sediment trapped behind dams when oxygen is not present.
John Harrison, researcher and professor at WSU's School of the Environment, co-authored a large-scale study in 2016 that estimated the world's reservoirs are emitting 25 percent more methane than previously thought—the equivalent of roughly 1 gigaton of carbon dioxide a year, or 1.3 percent of greenhouse gases produced by humans.
His research, which measured actual methane generated, found high emissions in the Columbia Basin's Lacamas Lake and Foster Reservoir, and lower emissions from reservoirs behind Cle Elum, Kachess and Keechelus dams in Washington's Yakima River basin.
A new study by the Environmental Defense Fund also found large variations in methane production at hydroelectric reservoirs. The study evaluated GHG emissions from 1,500 hydropower facilities now operating in more than 100 countries, which together generate nearly half of the world's hydroelectric power.
The study, "Climate Impacts of Hydropower: Enormous Differences among Facilities and over Time," was published Nov. 13 in Environmental Science & Technology. It notes that the magnitude of greenhouse gas emissions depends on several factors, and varies greatly, even within the same basin. "Studies to date show that individual hydropower plants have greenhouse gas emissions that vary across several orders of magnitude, some can even be a carbon sink, while others can have emissions greater than those from coal-fired power plants on a per unit [of] power generated basis."
The study focused on plans for new hydroelectric generation to replace fossil fuels, and urged careful consideration and evaluation before new dams are built. It noted hydropower now comprises two-thirds of all renewable electric generation, and that hydroelectric power is expected to grow by between 45 and 70 percent over the next 20 years. "The underlying message that hydropower is not universally beneficial to the climate needs to be more widely understood if the global commitment to reduce global warming rates are to be met," it concluded.
A news release on the study from the Environmental Defense Fund said, "If minimizing climate impacts are not a priority in the design, construction and geographic placement of new hydropower facilities, we could end up generating electricity that yields more warming—especially in the near-term—than fossil fuels."
Ilissa Ocko, who co-authored the study, told NW Fishletter that while some parts of the world are gearing up to build more hydroelectric dams, not a lot of expansion is expected in the U.S., where some dams are being removed.
However, she said, even for facilities that generate more GHG emissions compared with coal, "I wouldn't necessarily suggest we want to close them. There are options for capturing methane emissions, which would be my first approach."
Ocko noted that overall, hydropower in the U.S. is fairly low when it comes to greenhouse gas emissions, compared to warmer climates such as Africa and South America.
Her analysis found that more than 200 of the 1,500 hydroelectric facilities analyzed contribute more to global warming than coal or natural gas in the first five to 10 years after they were built, including 42 in the U.S., or 12 percent.
One of those—Albeni Falls in Idaho—lies in the Columbia Basin. Greenhouse gas emissions were evaluated in the study using a model, and were not actually measured. Ocko said her study used data for hydroelectric reservoirs gathered for another study, and whether any emissions from any of the individual facilities are accurate depends largely on whether the model estimates are accurate. She said the high emissions estimated for Albeni Falls stem from the large surface area of Lake Pend Oreille behind the dam, and that the model needs to be confirmed before that specific facility is singled out. However, according to the U.S. Army Corps of Engineers, Lake Pend Oreille is one of the largest and deepest natural lakes in North America, and was made only slightly larger by the dam, which would likely change how the facility rates in Ocko's model.
In addition to estimating methane emissions through modeling, the study also accounts for the difference between the net carbon balance of the land before and after development of the reservoir—which would likely be a carbon sink in a terrestrial landscape, and a carbon source in peat lands or swamps.
Also using modeling, 10 other Columbia Basin hydroelectric facilities were analyzed as part of Ocko's study, including Grand Coulee, Libby, Hungry Horse, Dworshak, Bumping, Detroit, Cougar, Dexter, Oxbow and Brownlee dams. All of them except Grand Coulee and Libby rated significantly lower for GHG emissions compared with the average of all U.S. hydroelectric facilities. Bumping, Detroit, Cougar, Dexter and Oxbow projects rated comparable or lower in GHG emissions than wind power, which is nearly four times less GHG-emitting than solar, according to the modeling.
In an interview with NW Fishletter, Steve Juul, water quality lead at the Corps' Walla Walla District, said many different characteristics determine which reservoirs emit methane. "I think the only way to find out would be to actually go out and take the measurements," he said, He said he's unaware of any plans to study methane emissions from Columbia Basin reservoirs, and does not think the agency has the funding to conduct them.
Juul said he's unfamiliar with the model used in Ocko's study, but in terms of singling out any projects, "My preference is we get the data first. Unless the model's been verified for all of these—perhaps it's OK, but I suspect with a large range of conditions, I doubt whether a model can cover all of those."
When Harrison's study came out in 2016, the Corps issued a short paper about why the agency believes methane production isn't an issue in the Federal Columbia River Power System.
"Ultimately, it depends on the following factors: location, water temperature, water flow, depth, nutrient concentration, amount of plant growth, climate in the region, and the process that uses dissolved oxygen," the Corps paper said. "For the relatively clean reservoirs of the Federal Columbia River Power System, which include the lower Snake River dams, conditions for low dissolved oxygen concentrations are not prevalent, thus methane gas is generally not an issue."
Corps spokesman Joseph Saxon told NW Fishletter that, in addition, the lower Snake and Columbia River dams are run-of-river reservoirs, where water is not held behind dams for long periods, and where reservoirs are unlikely to produce appreciable amounts of methane because oxygen is present throughout the reservoirs' depths.
Harrison said that the important factor is whether oxygen is present in sediments behind a dam, which is where methane is mainly produced. He concluded, "Without taking measurements, it's impossible to say whether the specific systems are significant sources of methane."
Since his 2016 study, Harrison has been working with an internal group at the IPCC, and learned in late November an IPCC committee voted to include methods he helped develop to complete national inventories for methane produced at reservoirs.
"Going forward, countries are going to be evaluating the greenhouse gas footprint of reservoirs as part of their national greenhouse gas inventories," he said, adding, "That wasn't the case before."