A winter upgrade to Foster Dam’s fish weir is
expected to provide a safer passage over the dam for juvenile salmon and
But first, the U.S. Army Corps of Engineers
needs to remove a large crane from the dam’s upper deck that was once used for
collection and passage over the dam of adult fish. That requires the Corps to
close the road on top of the dam December 4 through 29, to all traffic in order
to remove the crane.
Foster Dam is located on the South Santiam
River, a tributary of the Willamette River, near Sweet Home, Oregon.
Once the crane is removed and out of the way,
the Corps will install a newly-designed fish weir this winter, which the agency
says should increase the cushion in the spillway for juvenile fish migrating
downstream. The new weir will be taller than the existing weir and wouldn’t
allow for Corps staff to place or remove it if the crane remained in place.
According to a Corps news release, a fish weir
is a structure that is placed in a dam's spillway to manage water for juvenile
fish passage. The weir constrains the release of water to maintain flow
requirements, provides attraction for fish (stream-like flow from the surface
of the reservoir) and creates a 'cushion' of water when landing on the
spillway. This cushion makes the fall from the reservoir less harmful for the
“The new weir is expected to effectively
improve attraction, passage and survival of juvenile chinook salmon and
steelhead,” said Jeffery Hicks, a Corps Portland District structural engineer.
“It will do this, while minimizing impacts to other benefits of Foster Dam,
such as flood risk management, hydropower generation and recreation.”
The Corps had been using the crane and
elevator system, which it says was innovative for its time, for adult fish
collection and passage over Foster Dam; however, the equipment wasn't fully
successful in moving fish above the dam in an efficient manner. Corps
biologists concluded there were better options.
"We found that transporting fish directly
to the South Santiam allowed the fish to spawn more successfully," said
Greg Taylor, Portland District fisheries biologist. "The crane became
obsolete once we upgraded the fish facility."
Currently, the Corps partners with the Oregon
Department of Fish and Wildlife to move fish above the dam after the fish climb
a fish ladder to a collection facility, also known as 'trap and haul.' The
crane is now in the way of Corps efforts to pass juvenile fish downstream of
the dam, which is a requirement of the Willamette Valley Biological Opinion.
Photos are at: http://www.nwp.usace.army.mil/news/article/Article/1379478/ongoing-improvements-for-fish-passage-at-foster-dam-to-close-road/
The Corps announced a new facility at the dam
in early 2015 that ensures fish can bypass the 126-foot flood control structure
in better condition as they migrate upstream, improving the odds they reach
their spawning grounds high in the South Santiam basin.
When Foster Dam was constructed in the 1960s,
an adult fish collection system was included in the original design. The system
included a ladder that guided fish into a holding pond and processing area
adjacent to the spillway. From there, the fish were directed into a hopper
basket, manually netted, placed into a truck, and transported upstream for
The new facility has several upgrades,
including improved flows that attract salmon and steelhead to the base of the
fish ladder more effectively, as well as larger holding pools that will
minimize stressful overcrowding conditions.
Direct contact between fish and humans is
significantly limited. Fish are sorted using a system that includes PIT tag
detectors, hydraulic gates, and flumes (or chutes) that guide fish into holding
pools or return them to the river. The fish collected in holding pools are
transported to a truck using a new water-to-water transfer system that
eliminates the need to dewater or capture fish in nets. The truck transports
the fish upstream of the dam so they can spawn in the South Santiam River and
--CBB, September 23, 2016, “Trucking Spawning
Salmon Above Willamette Dam Showing Success In Offspring Survival, Adult
--CBB, October 30, 2015, “Mortality For
Transported Willamette Spring Chinook Declines When Held In Cool, Pathogen Free
--CBB, February 6, 2015, “Upgrades At Oregon’s
Foster Dam (South Santiam) Fish Passage Facility Aimed At ESA-Listed