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Big Snowpack Boosts Snake River Water Release to Aid Fish by Brad Carlson Capital Press, June 21, 2023

The Snake River is the largest tributary to the Columbia.

Upper and middle Snake River flows sent downstream to benefit migrating juvenile salmon and steelhead are expected to exceed last year's total.

"We have had higher releases for a longer period than usual due to above-normal snowpack," said Ryan Hedrick, water operations specialist at the U.S. Bureau of Reclamation's Snake River Area Office in Boise. "The last time we were up this high for a while was 2019."

Under a 2008 biological opinion from National Oceanic and Atmospheric Administration Fisheries, Reclamation each year provides up to 487,000 acre-feet per year of water, known as flow augmentation, to aid migrating salmon and steelhead in the lower Snake and Columbia rivers, according to the bureau.

The opinion applies to the Snake River Basin above Brownlee, the farthest downstream of the Snake storage reservoirs. The annual targeted minimum is 427,000 acre-feet.

This year's systemwide total is on track to be 445,000 acre-feet, up 18% from last year, Hedrick said.

Low carryover storage, dry conditions and many reservoirs not filing factored into the 376,893-acre-foot total for last year, according to Reclamation's 2022 report on the flow augmentation program. It was the only year since 2004 that the bureau was not able to provide at least 427,000.

Water for flow augmentation comes from Reclamation's own supply and water it rents from irrigation districts' available supplies. Flood-control releases cannot be used for flow augmentation.

On the Boise River, "as flood control nears its end, we transition into flow-augmentation flows," Hedrick said.

Boise flow augmentation started in mid-June and is expected to conclude around the second week of July. After these releases are completed, flows will be at normal summer levels to meet irrigation demand, he said.

Reclamation plans to start flow augmentation by late June in the Payette Basin, Hedrick said. Those releases, from Cascade and Deadwood reservoirs, will continue through August.

The Boise and Payette are tributaries to the middle Snake River. The Snake River is the largest tributary to the Columbia.

Related Pages:
Power from River Flow by Idaho Power & BPA, Energy Info Administration
Flow Augmentation on Lower Snake River Spreadsheet 1987-2014, Idaho Department of Water Resources
Flow Augmentation: Does or Doesn't Help by N.S. Nokkentved, Times-News, 12/14/00