BONNEVILLE DAM — The U.S. Army Corps of Engineers is gutting and rebuilding a large section of Bonneville Dam’s fish ladder to make it easier for Pacific lamprey to pass the dam as they return from the ocean to spawn.
The project comes as returns of the 450-million-year-old native fish species have shrunk to about 10 percent of historic numbers following construction of dams on the Columbia River, climate change and other challenges.
The eel-like fish must pass eight dams to access hundreds of miles of historic spawning grounds along the Snake River. On the mainstem Columbia River, they must traverse nine before they arrive at the unpassable Chief Joseph Dam.
Fish biologists with the Corps have estimated only about half of the lamprey that try to make it past each individual dam actually succeed.
Work at the almost 90-year-old Bonneville ladder started in December after years of pressure by regional Native nations, environmentalists and fish biologists.
The fish ladder starts with a stepped climb up about 60 feet. That part will remain the same.
After that, though, salmon, steelhead and lamprey have had to navigate a winding series of nine S-curves created by walls on alternating sides of the roughly 20-foot flow control channel.
Those walls are now torn down and in the process of being replaced by new concrete walls, this time extending across the channel except for a small, angled break in the middle. The new walls will also have small holes on the bottom sides.
“We had years of research showing that lamprey were struggling to pass this section. There was a real bottleneck,” Erin Kovalchuk, Corps project manager for the renovation, said while standing above the construction and keeping an eye on workers building frames for the new walls.
The idea behind the renovation is to reduce the number of sharp corners in the ladder, lower the speed water flows through it, cut the overall distance lamprey must travel and give them places to rest along the way.
Because the new concrete is also smooth and free from 90-degree angles, the change is expected to allow lamprey to depend more on suction from their hallmark “sucking disk” mouths to make it through the obstacle, explained Tyler Ardent, a Corps park ranger at the dam.
The new ladder will be more like what fish would have encountered on the river before dams, when millions of lamprey would climb the slick, water-worn rocks of waterfalls including Celilo Falls.
The Corps doesn’t yet have data on how much they expect passage numbers to change, Kovalchuk said. But the former fish biologist added that a similar renovation at John Day Dam benefited salmon and lamprey, and that the Corps will conduct a two-year study to compare passage before and after the renovation.
Laurie Porter, the lamprey project lead at the Columbia River Inter-Tribal Fish Commission, celebrated the construction.
“We pushed hard for it, and it’s going to be beneficial to lamprey and salmon,” she said.
The tribal fish commission’s project, along with native restoration projects including the Yakama Nation’s, have spent decades working to restore populations of the culturally and ecologically essential species.
The project at Bonneville follows other modifications, including the addition of a lamprey passage structure in 2013. The structure is an HVAC-like tube that lets the fish skip parts of the fish ladder in favor of a journey that’s less challenging.
The current renovations are expected to cost about $8 million, Kovalchuk said. The Corps could not immediately provide the total amount of money spent on lamprey-related projects this year or cumulatively.
The Corps expects the project to be done by the first week of March, when salmon passage begins.
