BONNEVILLE DAM — The U.S. Military Corps of Engineers is gutting and rebuilding a big part of Bonneville Dam’s fish ladder to make it simpler for Pacific lamprey to go the dam as they return from the ocean to spawn.
The venture comes as returns of the 450-million-year-old native fish species have shrunk to about 10 p.c of historic numbers following development of dams on the Columbia River, local weather change and different challenges.
The eel-like fish should go eight dams to entry a whole bunch of miles of historic spawning grounds alongside the Snake River. On the mainstem Columbia River, they have to traverse 9 earlier than they arrive on the unpassable Chief Joseph Dam.
Fish biologists with the Corps have estimated solely about half of the lamprey that attempt to make it previous every particular person dam truly succeed.
Work on the virtually 90-year-old Bonneville ladder began in December after years of strain by regional Native nations, environmentalists and fish biologists.
The fish ladder begins with a stepped climb up about 60 toes. That half will stay the identical.
After that, although, salmon, steelhead and lamprey have needed to navigate a winding sequence of 9 S-curves created by partitions on alternating sides of the roughly 20-foot circulation management channel.
These partitions at the moment are torn down and within the technique of being changed by new concrete partitions, this time extending throughout the channel aside from a small, angled break within the center. The brand new partitions may also have small holes on the underside sides.
“We had years of research showing that lamprey were struggling to pass this section. There was a real bottleneck,” Erin Kovalchuk, Corps venture supervisor for the renovation, mentioned whereas standing above the development and maintaining a tally of staff constructing frames for the brand new partitions.
The concept behind the renovation is to scale back the variety of sharp corners within the ladder, decrease the velocity water flows by way of it, reduce the general distance lamprey should journey and provides them locations to relaxation alongside the way in which.
As a result of the brand new concrete can also be easy and free from 90-degree angles, the change is predicted to permit lamprey to rely extra on suction from their hallmark “sucking disk” mouths to make it by way of the impediment, defined Tyler Ardent, a Corps park ranger on the dam.
The brand new ladder can be extra like what fish would have encountered on the river earlier than dams, when hundreds of thousands of lamprey would climb the slick, water-worn rocks of waterfalls together with Celilo Falls.
The Corps doesn’t but have knowledge on how a lot they count on passage numbers to vary, Kovalchuk mentioned. However the former fish biologist added {that a} related renovation at John Day Dam benefited salmon and lamprey, and that the Corps will conduct a two-year research to match passage earlier than and after the renovation.
Laurie Porter, the lamprey venture lead on the Columbia River Inter-Tribal Fish Fee, celebrated the development.
“We pushed hard for it, and it’s going to be beneficial to lamprey and salmon,” she mentioned.
The tribal fish fee’s venture, together with native restoration initiatives together with the Yakama Nation’s, have spent a long time working to revive populations of the culturally and ecologically important species.
The venture at Bonneville follows different modifications, together with the addition of a lamprey passage construction in 2013. The construction is an HVAC-like tube that lets the fish skip components of the fish ladder in favor of a journey that’s much less difficult.
The present renovations are anticipated to value about $8 million, Kovalchuk mentioned. The Corps couldn’t instantly present the entire sum of money spent on lamprey-related initiatives this yr or cumulatively.
The Corps expects the venture to be carried out by the primary week of March, when salmon passage begins.