Federal agencies are winding down their annual spring juggling act of water, fish and power, as this year's spring spill operations featured a record of amount of water spilled over federal dams on the Columbia and Snake rivers.
The sophomore season of the flexible spill regime will end June 15 on the Columbia River and June 20 on the Snake River.
The flexible spill agreement was signed in 2018 by Northwest states, tribes, BPA and its federal partners, and offered a three-year truce in litigation while providing assurances BPA's total spill costs won't cost ratepayers more than operations ordered by courts in 2018, or approximately $40 million, BPA said.
It's also a chance to test scientific modeling that indicates juvenile salmon and steelhead benefit from higher spill levels (see story).
This year's runoff got off to a slow start, as cold temperatures kept lots of water frozen in the mountains through most of April and May. With low river flows, managers struggled to meet minimum flow requirements for fish and power in most of April.
But by late May, more springlike temperatures across the region brought high flows to both the Columbia and Snake basins.
"In the past we'd see flows come up and then recede a little, then come back up," Pam Van Calcar, manager of generation scheduling at BPA, told Clearing Up. "We kept waiting for the water to come, then it finally showed up. It was a little more compacted this year than in the past."
Historically, the Snake River basin starts melting before the Columbia Basin, Van Calcar said. But this year, flows in the two basins "moved closer together" than in past years.
By mid- to late April, federal agencies had enough water to spill to 125 percent total dissolved gas levels. And by the end of May and early June, both rivers were ripping and federal agencies were spilling water at a record level.
This year for the first time, dam managers spilled water to 125 percent TDG levels at federal dams to help push migrating juvenile fish downstream. That meant hydro generation dropped to the lowest levels possible during much of the day, while a record amount of water was spilled.
When river conditions allowed, the four dams on the lower Snake River were spilling approximately 80 to 90 percent of the water that flows downriver, depending on the facility. On the lower Columbia, dam operators were spilling approximately 40 to 75 percent of the passing water, depending on the dam, BPA said recently.
Even with hydro generation limited, BPA had a hard time finding loads for power in early June. Spring is shoulder season in the Northwest, a time when most thermal generation goes off line or is dialed back substantially to make way for abundant carbon-free hydroelectricity.
With thermal units in the region backing down, BPA asked Energy Northwest to adjust output from the 1,207 MW nuclear Columbia Generating Station.
The plant returned to service at around 6 p.m. June 10, after a 41-hour maintenance outage that began around 12:30 a.m. June 9.
CGS, located in Richland, Wash., entered the outage after a period of load-following for BPA that started May 30 in response to generation oversupply amid high river flows (CU No. 1956 ). CGS generation dropped to 25 percent on June 6, before the plant went off line for maintenance.
The plant is now running at 40 percent, and it is expected to stay at that level through June 24 as it continues to help BPA with load shaping, Carla Martinez, spokeswoman for CGS owner and operator Energy Northwest, told Clearing Up.
For the first time since 2018, BPA declared an oversupply event on June 1 and curtailed 3,054 MWh of wind energy in the region (CU No. 1956 ). Van Calcar said the oversupply event was based more on the shape of the runoff, rather than on water volume.
"If the water would have come off as it normally does, we may have been able to avoid an oversupply event," she said.
The flex spill agreement calls for decreasing summer spill this year in mid-August, or about two weeks earlier than in past years, to allow BPA to recoup power sales lost during the spring.
"The last two weeks of August are usually hot and dry with lots of regional power demand and a volatile power market," Peter Williams, BPA operations research analyst, said in a prepared statement.
"By agreeing to spill more water for fish in the spring, we can spill less in late summer, and there's usually high-power demand with high prices that could make up for the revenues lost in the spring," Williams said.