Snake River Juvenile
by Josh Babcock
MOSCOW, Idaho - Lower Granite Lock and Dam has collected a little more than 2 million fish and transported 904,000 below Bonneville Dam so far this year - a far cry from the 6.68 million collected and more than 4 million transported in 2014.
Elizabeth Holdren, supervisor and fisheries biologist at Lower Granite, described this year as "not typical," but said there is still time this summer for those numbers to jump. She said low flow and an early spring run are two contributors to the low numbers of fish collected and transported at Lower Granite.
Although there usually would have been a peak by now, she said, in April hundreds of fish were seen jumping in the Lower Granite forebay and it's likely many of those fish were spilled over the dam and thereby not collected or transported.
In 2014, Holdren said, there were 26 days at Lower Granite that flows exceeded 100 kilo cubic feet per second, all of which came before mid-June. This year there have been zero days that exceeded 100 KCFS. Holdren said the highest flow day this year has been 74 KCFS.
According to the Columbia Basin Bulletin, Lower Granite, which is the first dam juveniles encounter as they swim to the ocean, handles the most fish out of all eight dams in the Columbia and Snake River dam system.
To improve the survivability of juvenile salmon, Lower Granite offers a number of routes fish can take.
The first and most popular option for fish is surface spill.
To spill those fish near the surface over the dam, Lower Granite uses a removable spillway. One of the dam's spillway gates is lifted and a spillway weir is used to allow some water through, creating a waterslide for fish to glide through the dam.
According to the U.S. Army Corps of Engineers, the first removable spillway weir was installed at Lower Granite in 2001 and it has a survival rate that exceeds 95 percent.
Holdren said while most salmon like to swim near the water's surface, the dam's configurations cause some fish to dive 50 to 60 feet to find their passage routes. For those fish that swim away from the forebay and surface spillway and at lower depths to navigate the dam, Holdren said, multiple 45-degree angle fish screens are used to help guide the fish into a bypass channel where juveniles are attracted to 12-inch orifices by bright LED lights.
John Bailey, fisheries biologist for the Corps, said 14-inch orifices are being constructed to replace the 12-inch orifices to attract more juvenile fish to the collection channel, which is part of the Corps $50 million juvenile bypass upgrade.
Once juveniles reach the collection channel they make their way outside of the dam into a 1,800-foot pipeline that routes them underground to the Juvenile Fish Facility (JFF). Some fish are rerouted right back into the Snake River and the others continue their trek and wind up at the JFF.
Once juveniles arrive at the JFF they reach a slotted-grate, where only juveniles are small enough to fall through.
Holdren said from there those fish will reach the raceways, an area of the JFF that has multiple rectangular-shaped tanks that are about 15 to 20-feet long and a few feet deep.
The only other route of passage for salmon is through the powerhouse where the dam's turbines are located. Bailey said only about 5 percent of fish travel through the turbines and of those fish about 96 percent survive.
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