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Fish Ladder Construction - An Engineering Spectacle

Hagerman Valley Chamber 07/17/19

By Virginia Hutchins (view original article here)

During Idaho Power’s 2005 dam relicensing, state and federal wildlife agencies wanted to restore that life history. A fish ladder finished in 2008 — at Idaho Power’s diversion for its Lower Malad hydro plant — reconnected the lower two miles of the Malad River.

On average, about 2,500 trout pass upstream through that ladder each year, said Steve Brink, senior fisheries biologist for Idaho Power. Something between 1,000 and 8,000 trout head downstream through it each year.

But until now, the mile of river between Idaho Power’s upper diversion and the Devil’s Washbowl waterfall at Malad Gorge park has remained isolated.

Planning of the upper fish ladder — another requirement of the same 30-year federal relicensing — has been in the works for years, in consultation with Idaho Department of Fish and Game, U.S. Fish and Wildlife Service and other state and county entities. And Brink has been a key player since Idaho Power began researching Malad River fish passage in 1996.

“I have quite a bit of attachment to these things finally getting built,” Brink said, visiting the Upper Malad project site in late June.

Researchers mapped more trout-spawning habitat above the upper diversion than in either of the lower reaches of the Malad. It’s not easy walking along the bank through the stinging nettle and poison ivy that line the Upper Malad forebay, but some anglers did anyway.

“This has been a good fishery for a select few locals who know how to get in here,” Brink said.

Building fish ladders for upstream passage, Brink said, has been well mastered elsewhere. But Idaho Power spent the extra time and money to figure out downstream passage in the Malad River; its Lower Malad ladder to date has passed at least twice as much downstream fish traffic as upstream.

Now, at the Upper Malad, it wants to recreate that success.

To best intercept trout heading downstream, Idaho Power’s team developed a 3-D flow model for the Upper Malad forebay. The answer: Position the new fish ladder in the southwest corner of the canyon’s tight turn, where 600 to 650 cubic feet per second of spring water enters the river.

“That spring water is excellent trout habitat,” Brink said.

The ladder’s system of slots and pools needs only 14 cfs of water. But to better attract fish, the ladder will pull in about 64 cfs. The extra 50 cfs will be screened, then piped to the bottom to rejoin the water that runs through the ladder.

Through a window in the ladder’s fish-viewing vault, Idaho Power must count the fish that pass through. It’ll use the automated video imaging software it spent years developing at the Lower Malad ladder — able to recognize each fish’s species and record its length and direction of travel — but in hardware that incorporates the camera and computer into something the size of a pop can.

That full automation is a victory that frees up a lot of labor — particularly for a biologist in Brink’s office who has been processing partially automated fish-count data from Lower Malad.

“He’s been looking at fish TV,” Brink said, “for nine years.”