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South Fork Necanicum Diversion Project

Waterways Consulting led the design effort for fish passage improvements and modification of the intake structure at the City of Seaside’s South Fork Diversion.  Construction of the fish passage improvements were completed in August 2012 with the remaining elements to be completed over the next several months.

By NANCY McCARTHY
The Daily Astorian | Posted: Friday, July 6, 2012 10:24 am
SEASIDE — When Seaside city officials were offered the opportunity to make their water delivery
system more efficient and also improve fish habitat, they expressed interest.
When they were told that all they would have to do was contribute a portion of time spent by the city’s
public works director, they said, “OK.”
Well, actually, they said more than that.

“It’s beyond great that we’re all together in this,” said Mayor Don Larson when he first learned of the
project. “It’s a partnership. ... It couldn’t have been easy.”
Several agencies, including the Necanicum Watershed Council, Oregon Watershed Enhancement
Board, U.S. Fish and Wildlife Service, Oregon Department of Fish and Wildlife, the National Oceanic
and Atmospheric Administration, Longview Timber and volunteers, are contributing funds and services
to complete the $724,508 project.
On July 16, crews will begin work on the project to improve the efficiency of the city’s reservoir at
Peterson Point and enhance salmon habitat at the water diversion dam in Seaside’s watershed. The dam
is on the south fork of the Necanicum River 1.5 miles upstream from the confluence with the
mainstream Necanicum.
The project calls for reducing the size of the dam, strengthening an area where it appears to be
crumbling and constructing a new diversion building to house electric stream screens and a generator.
More screens, as well as efficient pumps that will enable operators to regulate water levels also will be
installed at Peterson Point.
When the project is done, “The city can say its water is fish-friendly,” said Melyssa Graeper, director of
the Necanicum Watershed Council.
At the focus of the project is an 8-foot-high diversion dam that crosses the south fork of the Necanicum.
Originally constructed in 1926, the dam was 6 feet high. It was designed by L.C. Rogers, who also
designed Seaside’s promenade and seawall.
In 1951, the dam’s height was increased to 8 feet after debris built up and raised the water level.
But the added height makes it difficult for adult fish heading upstream to jump over the dam during
low-water periods, and a fish ladder, also installed in 1951, is inefficient. Juvenile fish have trouble
making the leap even during the high water season.
The dam also disrupts the natural flow of wood and gravel downstream, and that affects the quality of
fish habitat below the dam.
“It has been identified as a fish passage barrier by the Oregon Department of Fish and Wildlife for a
long time, said Graeper. The council applied for grants to conduct the project and is coordinating it.
“But nothing was broken. It’s not illegal. The water is being diverted (to Seaside’s water reservoir) just
fine.
“But the fish needed to be helped,” Graeper said.
The salmon that did make it over the dam could find a nice habitat waiting for them. Large pieces of
wood, placed in the south fork of the Necanicum River by Longview Fibre, provide pools for the salmon
to spawn in.
It was that effort that sparked the dam project, said Graeper.
A notch will be carved into the center of the dam to reduce it to the original 6-foot height, and the
cutting will be feathered out to the edges, which also will be lowered. Water then will run over the dam
year-round, Graeper said.
In addition, the streambed will be graded to reduce the steep drop from the top of the dam to the water
so juvenile fish heading upstream won’t have to jump as high.
During low water season, the water coming from the south fork is diverted at the dam, gravity fed to the
city’s reservoir at Peterson Point about five miles south of Seaside. At times of low water during dry
years, no water goes into the south fork, and that disrupts fish habitat. But the city doesn’t have the
ability to control the intake of water at the diversion site.
“You don’t think about conserving water when you live on the coast,” Graeper said.
But on summer days fish habitat can suffer when the water is low, and if that happens, the local
economy could be affected, she noted.
“Here in Oregon and on the coast, salmon are such a large part of the economy, and the south fork is
providing wild coho habitat,” she said. “If we did nothing, everyone would go on until the dam fails.
The city would be left with a big mess…the city would have to come up with the money from
somewhere.”
If the dam did fail and water could no longer be diverted to the reservoir in the summer, that could
affect residents and visitors, she said.
When the reservoir is full, the water spills into the main stem of the Necanicum. But outdated World
War II-era pumps operated by the city don’t allow operators to efficiently regulate how much water
goes into the reservoir. In addition, the current fish screens often don’t prevent the deaths of younger
fish.
“When we do the new diversion, there will be controls to allow operators to manage how much water
enters the stream,” Graeper said. “Both systems will be screened, and it will be safe for fish.”
An added bonus is that much of the money spent on the project will go to local contractors and
businesses, Graeper said. The bidding form used by the watershed council asks how local resources will
be used.
Seaside Public Works Director Neal Wallace praised the watershed council’s work, along with the U.S.
Fish and Wildlife Service.
“This project will improve the flow of sediment going into the streambed and will allow us to take less
water from the diversion when the things are more critical. We will be taking some of the load off of the
south fork,” Wallace said.
He noted that the city already supplies all of the drinking water that residents and visitors need
year-around.
“This project,” he said, “is all about the stewardship side of things.”


Link to Original Article....

 

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