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Snake River Flows Increased to Support Juvenile Salmon Migration by Staff Capital Press, May 18, 2021

The U.S. Bureau of Reclamation May 17 began increasing Snake River flows downstream of Milner Dam to provide more water in the Lower Snake basin below Hells Canyon Dam for juvenile salmon migration to the Pacific Ocean.

For more than a decade, a group that includes the Northwest states and tribes, the U.S. Army Corps of Engineers, the U.S. Environmental Protection Agency and Reclamation has coordinated annual flow increases for salmon.

This year's increase below Milner, in south central Idaho, is taking place earlier than usual amid dry conditions in much of the region.

Reclamation said in a release that recent flows of 3,000 cubic feet per second were initially projected to continue into early June. But agencies downstream requested the increase earlier to improve conditions for protected salmon populations.

Reclamation said flows from Milner were to increase to 4,000 cfs May 17 and to 5,000 cfs May 18. Flows are expected to stay at 5,000 cfs until May 24 and then start to decrease, stabilizing below 3,000 cfs a few days later.

This year's timing is "pretty much on par with what a dry year would look like with flows coming earlier in the spring," said Brian Stevens, water operations manager for Reclamation's Upper Snake Field Office in Heyburn, Idaho.

The volume of the total flow increase for salmon will be around 11,200 acre-feet -- Idaho Power's annual minimum of 5,000 acre-feet from Hells Canyon Dam, which the company owns, plus 6,200 acre-feet that will pass through from other sources upstream.

The Milner increase is above average, Stevens said.

Most outflows from Upper Snake River Basin dams are expected to be normal, he said. But inflows, which usually peak in early June, have been well below 2020 levels.

Stevens said natural inflows this winter will suffer, possibly leading to below-average storage in reservoirs, if the region does not get good precipitation this summer and fall.

Separately, Reclamation and the Corps announced they would increase Boise River flows downstream of Lucky Peak Dam May 17-19 to provide additional water for salmon migration in the lower Snake and Columbia rivers.

The Boise flows into the Snake near Parma, Idaho. It was flowing at 700 cfs at the Glenwood Bridge in the Boise-Garden City area in mid-May. The phased, three-day increase to about 1,900 is slated to last through May before flow returns to normal mid-summer irrigation levels of about 700.