THE DALLES, Ore. (AP) - Smolt have a rough life.
Their perilous journey from birthplace to sea is
fraught with deadly barriers. A new project at
The Dalles Dam is designed to help the young
fish slip past predators after they make it past the
formidable dam.
Young salmon make their way
through the dam in one of three ways. About 10
percent go through the powerhouse and turbines.
Another 10 percent travel through the blasting water
of the ice and trash sluiceway that flows out of the
south side of the dam.
The remaining 80 percent are the focus of the $45
million spill wall project. They make their way
through the spillways from April through August when
the dam is spilling water for fish.
"The dams are required to spill 40 percent of the
river," said Lance Helwig, the U.S. Army Corps of
Engineers project manager for the spill wall. The
requirement is part of the rules in force for salmon
protection under the Endangered Species Act.
The idea behind the spill wall is simple: Fish
that come through the fast-flowing waters of the
spillway are disoriented and easy prey for predator
fish like northern pikeminnow and smallmouth bass
that lurk in the shallows just beyond the dam.
At present, the water from the spillway disperses
the little fish toward those shallows. When the
spill wall is done, it will direct those young
salmon toward a deep, swift-running channel known as
a thalway that runs downriver below the surface near
the northern riverbank.
Predator fish don't like the fast, deep water, so
the idea is that diverting the juveniles to the
channel will help them regain their natural defense
mechanisms before being faced with predators.
The spill wall is shaped like a giant hockey
stick that stretches past a stilling basin and
across the natural shelf that extends beyond it,
directing water toward the thalway.
Studies performed on a scale model of the dam
indicate that guiding juvenile salmon to the
deepest, fastest part of the river will likely
improve survival rates for yearly chinook and
steelhead by 4 percent to 98 percent for fish that
travel over the spillway.
"It doesn't sound like much, but 3 or 4 percent
makes a big difference when you're talking about
tens of millions of fish," Helwig said.
"We've spent quite a bit of time studying The
Dalles and we're confident this may be the solution
to get us up to survival targets," Helwig said.
Once the wall is completed in 2010, more fish
studies will take place to gauge the success of the
project.
The spill wall takes up more than half of the
annual $80 million to $90 million budget for fish
mitigation that is split between the Portland and
Walla Walla U.S. Army Corps of Engineers districts
that oversee the dams on the Columbia and its
tributaries.
General Construction Contractors of Poulsbo,
Wash., won the contract for the project. The company
has worked on a variety of fish mitigation projects
on the big Corps dams, including Bonneville, John
Day and Ice Harbor.
"We've been working on the Columbia for several
decades," said Dan Proctor of General Construction
Contractors.
Workers have been on site since summer,
precasting the heavy pillars that will fit together
to make the wall.
The tallest of the pillars is about 37 feet tall
and weighs about 200 tons. The anchor tendons - 118
feet in length - will be drilled deep into the
bedrock below to hold each piece of the wall in
place.
Precasting work on the pillars has been under way
at the dam since summer, but in-water work had to
wait for the six-month window of time from Oct. 1 to
April 1, when most of the migratory fish have made
their way through the river.
The contractor will build the first 300 feet of
wall - the part before the hockey-stick angle -
during the current in-water work period. They will
continue to cast the pillars on shore until the
pieces for the entire wall are completed.
The remainder of the wall will be placed and
completed between October 2009 and April 2010, in
time for the annual spill season, when the largest
number of juvenile fish migrate downstream.
The finished wall will be 10 feet wide and about
830 feet long, with the first 200 feet being 43 feet
high and the remainder being between 25 and 30 feet
high.
