SEATTLE – Studies have shown it’s no easy task for juvenile salmon to make it through the Lake Washington basin to Puget Sound and one of the obstacles they must pass is the Hiram M. Chittenden Locks in Ballard.
Although salmon have been navigating the 100-year-old Locks for as long as it’s been operating, studies in the 1990s indicated they were having a difficult time. The Lock’s primary passage routes were deep in the water column, not easily found by juvenile salmon which stay closer to the surface.
The large lock filling culverts were a main route and contain sharp bends, fast moving water and barnacles. Together, these three hurdles likely injured salmon. To help them navigate the Locks, in 2000 the U.S. Army Corps of Engineers began installing smolt flumes every year on the Locks dam spillway.
The Muckleshoot Indian Tribe and King County partnered with the Corps to develop and build the flumes. Prototypes were first installed in 1995.
The flumes are stainless steel troughs with white metal tubes on the end that contain antennas, monitoring tagged salmon passing through. Mounted in the dam’s spillway, they provide a surface passage route readily found by the salmon. This limits the number going through the filling culverts.
”Water conservation is also an important benefit of the flumes,” said Dr. Scott Pozarycki, who oversees salmon migration and survival at the Locks. “Surface passage could be provided by simply opening a spillway gate, but that would use too much water during the spring and drop Lake Washington to unacceptable levels in summer and fall. The flumes use significantly less water allowing them to run for the duration of the juvenile migration season in most years.”
The current flumes are showing their age and monitoring equipment on the flumes is failing, according to Pozarycki. The Corps partnered with King County and West Fork Environmental to design a new prototype – a fiberglass smolt slide. It looks just like the name implies, a slide, with the small 4- to 6-inch fish gliding down from Lake Washington to Puget Sound. The slide’s integrated monitoring antennas are better, and the slide is easier and cheaper for the Corps to install and remove each year during the salmon out-migration.
The Corps conducted survival and injury testing of the prototype slide in April. Several hundred yearling coho salmon from the Issaquah Salmon Hatchery were used for the tests. The young coho were fitted with two inflatable balloon tags. One at a time, the tagged salmon were sent through a pipe which routed them into the slide.
“A couple minutes after their trip down the slide, the balloons inflated bringing the fish to the surface where three boat teams recovered and inspected them for injury,” Pozarycki said.
The recaptured fish were then transferred to 600 gallon pools and held for 48 hours to look for any delayed effects. ”The test indicates the new slide is safe for juvenile salmon,” said Pozarycki. The successful testing means the Corps will likely build two more of the slides to replace the remaining older flumes.
Even with the smolt flumes and slides, some will still end up going through the large lock filling culverts. To decrease possible salmon injury, each year during the annual maintenance pump out in November, Corps employees scrape the barnacles growing on the filling tunnel walls.
Slowing water velocity in the culverts would further reduce and possibly eliminate injury to salmon using that route, according to Pozarycki. The original, 100-year-old valves controlling water through the culverts need replacing and a nearly-complete new design will allow for much slower water velocities. Once design is complete, getting funding is the next step before the new valves can be installed.
“The new valves and smolt slides together, should allow safe passage to the vast majority of juvenile salmon transiting the Locks from the Lake Washington basin to Puget Sound,” said Pozarycki.
As part of the Lock’s Centennial events, the Corps is hosting a Fisheries Day 11 a.m. to 3:30 p.m., June 17. The Seattle Aquarium, NOAA Fisheries, National Wildlife Federation and Issaquah Fish Hatchery are just a few of the many agencies and organizations planning on providing information during the event.
For current information about activities at the Locks, visit the Locks’ Web site at http://bit.ly/BallardLocks or follow the Locks on Facebook and Twitter: www.facebook.com/chittendenlocks and http://twitter.com/ChittendenLocks.