The $50 million faucet.
Byline: Mike Stahlberg The Register-GuardBLUE RIVER - On the upstream side of Cougar Dam, workmen put in two shifts a day in their push to complete construction of a towering 350-foot-high concrete monolith, most of which will be under water in a few months.
Just downstream of the dam, spring chinook salmon chase each other and stir up gravel in an ancient reproductive ritual that has been on hiatus in the South Fork McKenzie River for 40 years.
The spawning of those big fish provides a vivid reminder of why the U.S. Army Corps of Engineers is spending $52 million on that concrete structure taking shape on the other side of the dam.
The big tower is, in effect, a giant faucet that will allow the Corps to correct water temperatures thrown out of balance when it built the dam. It's an elaborate and expensive attempt to fix a temperature imbalance that helped push native spring chinook salmon to an endangered species listing.
Water temperatures have been all wrong on the South McKenzie - and on a sizeable stretch of the mainstem McKenzie - since 1963, the year Cougar Dam was completed and ice-cold water began flowing through turbines at its base.
Drawn from the depths of the reservoir, the water in the summer and early fall was simply too cold for salmon. The fish wouldn't even swim into the South Fork McKenzie, much less spawn there.
Then in late fall, when the reservoir was emptied in preparation for the winter flood-control season, warm water that had been near the surface of the reservoir all summer surged through the outlets and into the river.
That unseasonable warmth triggered premature hatching of any salmon eggs buried in the gravel over which it flowed. Fish fry emerged in November and December, when there was little insect life on which to feed. Their survival rates were poor.
All that changed in the spring of 2002, when a contractor blew a hole through the concrete "plug" in a diversion tunnel at the base of Cougar Dam, allowing the reservoir to be drained and providing construction crews access to the base of the dam.
There, over the past two-plus years, crews from Wildish Sand and Gravel have been at work - first demolishing half of a round fish-passage tower (that never worked properly), then fitting a 70-by-80-foot rectangular addition to the remaining half of the original tower. All of that was topped by a "mechanical building" that will house the machinery needed to operate the new facility. When complete, the entire structure will include 13,500 cubic yards of concrete.
Originally budgeted at $41 million in 1998, the temperature control project grew in cost due to inflation and the need to beef up the original design to comply with newer seismic standards. Not all of the money went toward design and construction of the concrete tower. Opening the tunnel used to drain the reservoir was a $12 million contract. An extensive environmental monitoring program, including the need to make sure the construction didn't harm bull trout, a federally protected species, added to the expense.
Ever since the reservoir was drained, water temperatures in the South Fork McKenzie have risen and fallen with the natural cycle of rivers - warmer in summer, cooler in winter. And spawning salmon returned.
According to district fish biologist Jeff Ziller of the Oregon Department of Fish and Wildlife, some of those spawners are probably "strays" from the mainstem McKenzie, and some are likely the progeny of surplus hatchery salmon released to spawn in tributary streams above the reservoir.
Spawning salmon will return to the base of the dam every year from now on, if the temperature control system works the way its designers say it will. In addition, biologists say, native redside trout and bull trout will benefit from a "normal" temperature regimen in the McKenzie system.
In the long run, fishermen should also benefit from having stronger populations of salmon and trout.
"It could be a very sizeable boon to the river," Ziller said, especially if salmon are able to fully utilize the spawning and rearing habitat upstream from the dam.
"It's not out of the question," Ziller said, that the wild salmon runs could come back so strongly that the harvest of some wild spring chinook would again be allowed. Currently, anglers may retain only hatchery fish marked with a clipped fin.
The first moment of truth for the temperature control project will arrive next spring.
"We're on track to complete construction in December," said George Miller, the Army Corps of Engineers project manager on the dam retrofit. "We'll be able to maintain flood control during the winter season and should be in a position to have the reservoir up to a level where we can manage for temperature control in the April time frame."
At that point, operators of the dam will be like a mother drawing a bath for a toddler, tinkering with the temperature of water flowing out of the dam until it is just right.
Right for spawning. Right for egg incubation. And right for insects that fish need to feed upon.
"We are going to be able to deliver temperature control," Miller said, adding that the Corps' computer modeling indicates the project will impact water temperatures as far downstream as Vida. "The task is going to be to determine how to use it to manage for fisheries' benefit."
Managing the temperature will be accomplished by raising or lowering outlet weir gates to be installed on three 9-foot-wide vertical channels cut into the face of the concrete tower. One channel feeds water to the penstock and turbines (which produce electricity for the Bonneville Power Administration grid). The other two are "regulating outlets," used to spill excess water during times of high runoff.
Most of the time, the gates will simply draw water from the surface of the reservoir, where the temperature will mimic that of a stream flowing out of a natural lake. If need be, however, the gates can be lowered to whatever depth has water closest to the ideal temperature. Temperature sensors installed on the face of the tower will provide that data to the dam's operators.
The weir gates can be maneuvered to any point between the top of the reservoir's "full pool" level and the bottom of the three outlet channels in the tower, a range of 150 feet. "They can be adjusted in an almost infinite range," Miller said.
Salmon will benefit most from the temperature control project, although bull trout and native redside trout will also benefit. For example, Corps biologists predict, the warmer water and more abundant insect life will produce bigger rainbow and cutthroat trout.
And while the 4.5 miles of South Fork between the dam and its confluence with the mainstem McKenzie is good for spawning, Ziller said, "the biggest advantage for spring chinook, I believe, is going to be" the improved conditions for out-migration.
Previously, he said, there was a narrow time frame during which salmon smolts could find their way out of the reservoir. Openings leading to the regulating outlets and the turbine intake were too far below the surface most of the year to be found by migrating fish.
"What the temperature control tower will do is allow fish to migrate at any time of the year, because a large portion of the water will be taken right off the surface," Ziller said.
Before the reservoir was drained, he said, research indicated that "survival through the turbines was around 85 percent and through the regulating outlets was around 70 percent."
Ziller hopes those survival rates can be improved upon, in part because the dam retrofit includes the latest "fish-friendly" turbine blades.
Reasonably effective downstream passage would make it effective to capture returning adults below the dam and truck them upstream so they could spawn in the South Fork or one of its tributaries.
That was the original fish passage plan when Cougar Dam was constructed. But, as noted earlier, the actual operation of the dam threw cold water on that scheme - literally, and in the form of a downstream fish passage tower that never worked.
The Corps of Engineers, Miller said, "is discussing building a permanent fish trap below the dam," and will likely seek congressional approval for doing that.
Prior to the construction of Cougar Dam, the South Fork of the McKenzie produced about 4,000 returning adult chinook per year, or about one-third of the entire McKenzie run.
With a workable upstream and downstream fish passage at the dam, Ziller said, production in the South Fork could, "in really good years, be several thousand fish." Due to the additional rearing habitat provided by the reservoir, production could be even greater than it was in the 1960s.
Meanwhile, the temperature control project could have an impact felt beyond the McKenzie watershed.
"This is a pilot project that could have huge ramifications, if it's successful for wild salmon recovery, throughout the Willamette Valley and possibly elsewhere," Ziller said.
CAPTION(S):
Once these intake towers at Cougar Dam are submerged, the Army Corps of Engineers will be able to control the temperature of the water flow to restore the natural movement of fish in the South Fork McKenzie River. The project is expected to be completed in December. Water that has passed through the towering dam (right) could affect river temperatures as far downstream as Vida. Kevin Clark / The Register-Guard The Cougar Dam project relies upon moveable gates that can take in water of various depths in an effort to control the river's temperature. The deeper the gates go, the cooler the temperature. If the control towers are effective in restoring wild salmon runs, Cougar Dam could become a template for future projects. When the dam was built in 1963, it altered the river's seasonal temperature changes and made the water unfit for salmon reproduction.
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| Title Annotation: | Recreation; Cougar Dam's temperature control tower expected to benefit salmon |
|---|---|
| Publication: | The Register-Guard (Eugene, OR) |
| Date: | Sep 23, 2004 |
| Words: | 1650 |
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