The four lower Snake River dams have long been an important source of power for the Pacific Northwest.
Story and photos by RYAN HALL | RURAL MONTANA EDITOR
The four lower Snake River dams have long been an important source of power for the Pacific Northwest. That hasn’t changed, but the amount of power they are able to produce for the up to nine months each year that fish pass through the dams has, and that impacts electric cooperatives in western Montana.
The lower Snake River dams are made up of Ice Harbor, Lower Monumental, Little Goose and Lower Granite dams. Each one has six turbines, though they vary slightly in age, style and output. Combined, the four dams are capable of producing enough electricity to power all of Montana and Wyoming, according to Paul Ocker, chief of operations and maintenance for the Walla Walla District of the Army Corps of Engineers, which manages the dams.
Ocker said the mission of the dams has changed since they were built in the 1960s and ‘70s.
“The main reason they were built was for navigation,” he said, noting that hydropower was later added to the dams. Staff at Lower Granite and Ice Harbor dams said that all four dams were built with fish ladders for returning adult fish. Additional fish-passage measures for juvenile fish were added later.
Ocker said that in his 24 years with the Army Corps of Engineers, he has seen power take a backseat to fish considerations.
“The focus is even greater on fish than when I first got here,” he said. “For the Snake River dams, I think we are reaching the limit of what we can do.”
In 2022, the four lower Snake River dams produced 6.6 million megawatt hours of power, or enough to provide electricity for about 600,000 homes. That’s a lot of power, but it’s a lot less than it used to be — and could still be.
“In the last 25 years, we are producing a lot less power than we used to,” Ocker said. “We are spilling a lot of water for fish migration — a lot more than we used to.”
He explained that in the past, each of the four dams on the lower Snake River would typically run five turbines. This spring, with low flows and a new court settlement and biological opinion dictating spillage, the dams typically ran one turbine, and often at minimum generation.
“We don’t make a decision without considering fish,” said Brian Vorheis, operation project manager for Ice Harbor Dam.
Rob Lustig, operation project manager at Lower Granite Dam, said that’s the case there as well.
“A lot of things we are doing differently are related to that biological opinion,” he said. “Here, hydro is not king.”
For example, on May 23, Ice Harbor dam spilled 69,000 cubic feet per second (cfs) of water through the dam’s spillways — think of each cfs as being about the size of a basketball. The dam used just under 10,000 cfs of water to generate what dam officials call “min-gen,” or minimum generation — about 75 megawatts (MW). That means roughly seven times the amount of water being used for generation was spilled — without going through the powerhouse — to aid juvenile fish migration.
A day earlier, Lower Granite had one turbine running at min-gen, producing 85 MW. Turbines at Ice Harbor can produce up to between 102 MW and 111 MW each, while Lower Granite turbines each produce up to 135 MW.
“Normally this time of year we had three, four, five, even six” turbines running at up to max output, Lustig said.
“How much we generate right now is dictated by a settlement agreement that is overseen by the courts,” Ocker said. “It is the desire of the environmental groups and the plaintiffs to have all fish pass by a non-powerhouse route.”
He said that typically, the fish survival rate through a turbine is about 90 percent, while it’s 98 percent through other passage routes, such as the spillway, or being diverted around the turbines by fish screens.
Ocker noted that the new turbines at Ice Harbor have a fish survival rate between 96 and 98 percent.
He said that prior to the settlement agreement, a biological opinion issued by the National Oceanic and Atmospheric Administration, would dictate how much the dams could generate.
“What are the loads and how much electricity we had to make at the time,” Ocker explained. “We spilled excess water if there was not enough demand.
“Now we spill specifically for fish eight or nine months out of the year,” Ocker said. “As the Corps of Engineers, what we are required to do is balance what the people need and what the environment needs.”
Vorheis said that once Ice Harbor reaches the 10,000 cfs inflow it needs to run one turbine at min-gen, it must spill the next 110,000 cfs to meet the current operating plan under the settlement, before it can generate any more power. Vorheis said that without a mandated spill, 96,000 cfs would be enough to generate at maximum power. The plan requirements mean that it would now take a river flow of 206,000 cfs to be able to run all six turbines at maximum output.
“I don’t know if we will ever see all six lights on again,” Vorheis said, referring to the lights on each turbine that show it is running. “Four years ago, we were running all six units. Since spill kicked off in April (2024), we’ve been running one unit at min-gen.”
Brad Sharp, chief of operations at Lower Granite Lock and Dam, said that since 2020, the total project generation has decreased by between 20-25 percent, with a majority of that coming in the spring salmon run of April until mid-June.
Sharp noted that generation is variable based on snowpack each year, but the five-year averages show a trend. From 2015 to 2019, Lower Granite Dam produced an average of 307,930 megawatt hours (MWh) in April. From 2020-2024, the five-year average for April was 91,224 MWh. For May, the average dropped from 385,103 MWh to 202,691 MWh over the same timeframes.
One key element that remains, even with the fish passage plan, biological opinions and court settlement, is that hydropower stands at the ready should a power emergency occur, where demand outpaces supply.
“There’s still the availability component. That availability is still important to the reliability of the grid,” said Harold Wentworth, chief of operations for Ice Harbor. “If an emergency were to happen, we would deviate from the fish passage plan with appropriate coordination.”
He said that if the Bonneville Power Administration were to call for more power, which could occur if intermittent generators such as wind or solar were to stop producing, there has to be backup power that is “already spinning” and ready to ramp up.
“In this region, that is primarily hydropower,” Wentworth said.
“Our projects fill that gap,” Lustig added.
Ice Harbor Dam is capable of producing an additional 100 MW in 2-3 minutes, and can be at full power within 8 minutes, Wentworth said.
“We just come up,” he added.
The same is true up and down the Snake River, including at Lower Granite Dam.
“In 6 minutes, we can go from not generating anything to powering a city the size of Portland,” Lustig said.
Republished with permission from Rural Montana Magazine, the magazine of Montana’s Electric Cooperatives Association (MECA).
Read this article in the July edition of Rural Montana: Rural Montana Magazine | July 2024 (PDF)
