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Spring Spill begins facilitating fish passage at Snake and Columbia river dams

Published April 21, 2021
Spill through two raised spillway weirs (right) and conventional spillways at McNary Dam on the lower Columbia River improves downstream passage survival for juvenile salmon and steelhead.

Spill through two raised spillway weirs (right) and conventional spillways at McNary Dam on the lower Columbia River improves downstream passage survival for juvenile salmon and steelhead.

Federal water managers have begun the annual spill of water past hydroelectric dams on the Columbia and Snake rivers to help juvenile salmon and steelhead migrate to the ocean this spring. The spill began April 3 on the lower Snake River and April 10 on the lower Columbia River.

Spill for juvenile fish passage helps reduce the proportion of juvenile fish that pass dams through the turbines and helps reduce passage delay at each dam, thereby shortening their travel time through the Snake and Columbia rivers.

The specific “Flex Spill” operations at each dam are outlined in the U.S. Army Corps of Engineers’ 2021 Fish Operations Plan and in NOAA Fisheries’ 2020 Columbia River System biological opinion.

This year’s spill operations again include juvenile fish passage spill at performance standard levels for eight hours each day when energy demand and electricity prices tend to be higher, then spill up to the maximum amount allowed by state water quality standards for the other 16 hours a day when electricity prices are lower.

“The continued trial of flex spill will help us assess both short and longer-term benefits to fish while also providing flexibility to balance clean power generation with the needs of fish as we operate the system,” said Tim Dykstra, senior fish program manager for the USACE’s Northwestern Division.

Federal agencies briefed the Northwest Power and Conservation Council on results of flex spill operations in 2020. The spill helped carry juvenile salmon to the estuary faster and with high survival, as hoped. The most important measure of success will come in two to five years when fish that migrated downstream begin to return, revealing whether the higher spill also increases adult returns as some have projected.

“We need to keep asking the question, ‘How can we do this better,’” said Michael Tehan, Assistant Regional Administrator for the Interior Columbia Basin in NOAA Fisheries West Coast Region. “This is an important opportunity to test the projections for what higher spill may do for fish.”

And the early results?

“The early results have been promising, with the increased generating flexibility in the summer successfully offsetting the negative impacts of reduced flexibility in the spring,” said Kieran Connolly, BPA’s vice president of Generation Asset Management. “Given that water conditions and emerging power markets are very dynamic, we will need to evaluate this innovative approach for multiple years to confirm that these preliminary results hold up over time. Ultimately, flexibility for power generation allows us to keep power costs affordable while also playing a critical role in regional efforts to manage power reliability and carbon emissions.”

Water managers expect spill levels in 2021 to resemble last year, when they increased up to the state water quality standards of 125% total dissolved gas at many dams. The increased spill is above the 120% TDG spill levels that were last implemented in 2019.

Cooler spring temperatures have slowed runoff this year, leaving river flows too low to reach those high spill levels. However, flow and spill volumes will increase as snowmelt increases in coming months. Water managers at USACE and the Bureau of Reclamation balance water storage with releases as spring flows increase to benefit fish and agriculture. For example, they hold cold water in Dworshak Reservoir for later release to cool the rivers during the heat of the summer.

Continuing spill of water past dams throughout the juvenile salmon and steelhead migration is one of a series of comprehensive steps to benefit fish affected by federal dams on the Columbia and Snake Rivers. NOAA Fisheries recovery plans outline an even broader range of actions necessary for the species to fully recover.

USACE will also operate Lower Granite Dam to temporarily hold water to a higher level when flows are low to maintain the federal navigation channel, until sediment can be removed. The district continues to develop plans to perform work to remove sediments that is impacting the Federally authorized navigation channel. USACE will also hold water to a higher level behind John Day Dam from April 10 to June 1 to discourage nesting of Caspian terns that prey on juvenile salmon and steelhead.

Matt Rabe

Release no. 21-019