Novel spiral water slide system to let juvenile fish head downstream
Slightly more than 10,000 adult sockeye salmon just arrived in Lake Cle Elum, their upstream migration diverted by a tanker truck ride courtesy of Yakama Nation Fisheries.
By introducing the fish to an area that has been blocked for a century by a dam, tribal biologists hope to rebuild a healthy population. These adults will spawn and their surviving offspring will migrate to the ocean and back, returning to help the population grow.
It’s a good plan, but there’s a big hurdle. The Cle Elum Dam doesn’t just hold back water, it holds back salmon.
The reservoir’s fluctuating levels make it impossible to use the types of fish passage typically found on the Columbia River’s hydroelectric dams, where water levels stay relatively stable.
After years of work, Bureau of Reclamation engineers are finalizing a first-of-its-kind design for a system to let juvenile fish head downstream, regardless of reservoir level. The plans will be ready for construction next year, but federal funding for the $100 million project, a key part of the Yakima Basin Integrated Plan for water management, still needs to be authorized before work can begin.
“There’s nothing like this anywhere,” said Jason Wagner, an engineer at Reclamation’s technical center in Denver. “It’s very new. It’s kind of exciting.”
The passage has three parts: a stepped inlet to let fish swim in at varying water heights, and a spiral water slide that quickly lowers the fish to a tunnel past the dam that delivers them to the river.
Plans for getting returning adults upstream are far less high-tech. Fish will be trapped below the dam, be driven around the dam in a tanker truck and then dumped in the lake.
For Wagner, the most exciting part is the novel design for the downstream passage, which he believes can be used at other storage reservoirs in the region. For Brian Saluskin, fish passage biologist for the Yakama Nation, it’s the critical step to eventually restoring self-sustaining runs of salmon and steelhead to the Yakima River’s upper tributaries, where they have been largely shut out for a century.
“With fish passage, you are opening up 41 miles of pristine habitat above Cle Elum,” Saluskin said. “We’d like to see this happen as soon as it can.”
Saluskin said the Yakama Nation wants to see the Bureau of Reclamation build fish passages at all five of the region’s storage dams, but efforts started with Cle Elum because it offered the most upstream habitat.
Before spending millions to build fish passage for a reservoir with no fish, Reclamation and the Yakama Nation decided to make sure that salmon could still use the habitat that had been empty for so long. The Yakamas began reintroducing sockeye salmon in 2009, with adults transplanted from the upper Columbia River.
In preparation, they built a temporary fish slide down the dam’s face in 2005 and tested it with leftover hatchery fish. It’s definitely better than nothing, Saluskin said, but the fish can only access it when the reservoir is full and water is spilling over.
When the reservoir fills up varies from year to year, depending on when snow melts. In drought years, the lake may never reach maximum height, said Joel Hubble, a Reclamation fish biologist. That makes things difficult for the juvenile fish, who have a specific migration window for heading downstream, he said.
This spring, for example, the juvenile sockeye were ready to leave the reservoir in April, swimming back and forth in front of the dam, Hubble said, but they couldn’t use the slide until mid-May.
Waiting can mean the fish miss their window and decide to stay in the lake or face higher temperatures in the lower Yakima River, which reduces survival, Hubble said.
“They all have their own time they want to leave; it depends on weather and temperature,” ....
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