‘Flip-Flop’ a Boon to Salmon, Rafters in Yakima River Basin

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The federal Bureau of Reclamation’s annual Yakima River Basin “flip-flop,” in which reservoir flows are manipulated to adjust river levels, should be complete sometime next week.

The late-summer project, which reduces flow in the upper Yakima, Cle Elum and Bumping rivers while increasing flow in the Tieton and Naches rivers, is designed to help salmon spawn and stabilize irrigation water supply. That’s done by slowly reducing flows out of the Keechelus and Cle Elum reservoirs and increasing flows from Rimrock Reservoir.

“It allows the salmon to spawn at lower levels, more natural levels,” said Chris Lynch, a hydrologist with the bureau.

The rates by which the flows are reduced and increased are determined by many factors, including irrigation water demand, he said. It was “a nice gradual descent” through the first half of August, with the flip-flop getting more significant and noticeable starting around Aug. 27.

The bureau has undertaken the flip-flop each year since 1981. Lynch expects the process will conclude and the river levels will be settled by next Wednesday or so — Monday at the earliest, Sept. 15 at the latest. Exactly when is hard to predict because rivers are dynamic and affected by outside factors such as weather.



“It’s kind of fine-tuning by the tail end,” he said.

The change is significant, though. At the beginning of August, flows out of Cle Elum Reservoir were as high as 3,650 cubic feet per second. By the end of the flip-flop next week, that number will be reduced to 220 cubic feet per second.

Flows out of Rimrock Reservoir, around 1,000 cubic feet per second at the start of September, will increase to between 1,800 and 2,400 depending on irrigation demands and weather.

The change in flows creates outstanding whitewater rafting on the Tieton River, Lynch said. That was never part of the bureau’s reasoning behind the program, but outdoor enthusiasts certainly appreciate it.

“It plays right into the recreation,” Lynch said. “It’s a nice little side-effect.”