$5 million solution for Cougar Dam “cul-de-sac?”
BLUE RIVER: A $5 million floating fish collector is on its shakedown cruise behind Cougar Dam. But don’t expect the experimental craft to travel too far. The hull is being moored vertically to the reservoir bottom in four places, and anchored horizontally by cables extending to the dam face and adjacent hills.
Ten semi trailers were used to transport the Portable Floating Fish Collector to the site. At the end of March it will be used to carry out research in support of the Cougar Downstream Fish Passage Project.
Research by the U.S. Geological Survey last winter showed that out-migrating juvenile salmon are able to move fairly quickly through Cougar Reservoir, and they tend to pass the dam quickly and relatively successfully - if they can be convinced to enter the dam’s temperature control tower.
“The problem is the ‘cul-de-sac’ at the corner of the reservoir where the dam’s temperature control tower is located. Flow conditions there make it hard for fish to find and enter the tower,” said David Griffith, a fish biologist from Program, Planning and Project Management Division’s environmental group. “We need to know if we can provide better conditions that are conducive to getting the fish to enter the tower.”
Griffith added that the tentative solution the PDT identified to solve the ‘cul-de-sac’ issue would be very costly, and is based on many assumptions that need to be validated to justify the expense.
The solution was a small-scale experimental fish collector – the PFFC.
The problem, according to PDT civil engineer Jeff Sedey, was that something like that didn’t exist.
“A few utilities are using large-scale collectors as permanent fish passage solutions, but only at reservoirs that fluctuate up to about 50 feet,” he said. “There was no small-scale collector out there built to stand a 180-foot reservoir fluctuation like we see at Cougar.”
So the PDT had to design one pretty much from scratch. They contracted engineering firm HDR to develop the engineering report, and called upon the design expertise of the naval architects at Art Anderson Associates, who had helped design permanent collectors at Swift, Clackamas West Fork, and other sites.
“We were certainly emulating the full-scale collectors, but everything – particularly the mooring systems – was so much more complicated due to the reservoir fluctuation issue,” Sedey said.
The result is a large pump-driven intake and collection structure surrounded on three sides by a floating hull that is anchored in place.
The collector’s pumps were designed to generate an attraction flow of about 100 cubic feet per second.
“We’re going to park the collector right in the middle of the flow near the temperature control tower and see if the fish will find it,” said Kristy Fortuny, the project’s technical lead from Engineering and Construction Division.
The PFFC is equipped with a tag detector and other equipment to help determine how efficient it is at collecting fish.
In addition to serving as a research vessel for fish behavior, attraction, and passage success, Griffith said, the PFFC also will provide valuable information about the operations and maintenance requirements for whatever permanent solution is ultimately decided upon.
“Debris loading, maintaining moorage in a fluctuating reservoir, daily boarding and operations – what does it take, from and operations and maintenance standpoint, to run these things?” he asked.
According to Fortuny and Sedey, the Corps’ Portland District isn’t the only organization interested in finding out if the PFFC might be one path to juvenile passage at high-head dams like Cougar.
“Downstream passage at high-head dams has been elusive,” Sedey said. “This kind of technology is exciting to the region as a whole.”
“Lots of other Corps districts and other agencies have been expressing an interest in the PFFC’s design and performance,” Fortuny added. “NOAA Fisheries and U.S. Fish and Wildlife, for example, are both very interested and have provided a lot of input.”
The PPFC’s relative portability and flexibility will allow it to be redeployed to Detroit or – more likely – Lookout Point Reservoir after its initial two-year research project at Cougar.
“We have a lot of questions at Lookout Point about the ability of juvenile fish to transit the reservoir,” Griffith said. “They enter the reservoir at a very small size, and are hard to track. We don’t know very much about where they are dropping out – due to predation at Lookout Point or Dexter, or passage at Lookout Point Dam, or some other factors. We hope the PFFC will help us find some of those answers.”
If so, then Portland District’s big experiment will have proven itself more than portable, effective and valuable enough.
Image above: Courtesy USACE. The Portable Floating Fish Collector is being moored near Cougar Dam’s temperature control tower. Its pumps will generate an attraction flow of about 100 cubic feet per second to help juvenile fish find it and also aid in collecting out-migrating juvenile salmon and other fish.
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