Logs, boulders, gravel and other materials are being strategically placed downstream from the Pelton-Round Butte dam complex, the latest effort by Portland General Electric to restore salmon and trout habitats on the Deschutes River that have been altered by dams.
The 131-year old public utility is placing 1,500 tons of river rock at two locations in the Lower Deschutes this week. About 30 boulders and 30 logs are being lowered by a helicopter. Also being dropped are six rootwads — root systems of upended trees that are useful in protecting streambanks from erosion.
Salmon and steelhead populations were cut off along the Upper Deschutes River, above the hydroelectric dam project, when it was constructed in the 1950s and 1960s. This project is in the Lower Deschutes below the dams, where fish populations have fared better.
“A lot of people are talking about the reintroduction effort above the dam, which is separate from the status of fish populations below the dam,” said Jason Seals, assistant district fish biologist for the mid-Columbia fish district.
“The highest density of fall chinook spawning in the entire Lower Deschutes can be found below the dam, so it’s a critical area for spawning. I am sure that those fish will be there and use those areas,” Seals said.
The project is part of a six-year effort to locate and enhance key places where fish are likely to spawn, said Rebekah Burchell, senior biologist for the Pelton-Round Butte dam complex.
“The project objectives are to enhance populations of fall chinook, summer steelhead and redband trout spawning areas and rearing habitats,” Burchell said.
Steelhead trout and other fish use boulders, fallen logs and vegetation for protection in rivers.
During spawning, these fish lay their eggs on the gravel bottom of the river. Females scoop out a hole called a redd and lay their eggs inside, after which the male trout will fertilize the eggs — the eggs are then covered with gravel until they hatch.
“The Deschutes is known as a world-class location for redband trout fishing,” said Steve Corson, spokesman for Portland General Electric, which co-manages the project with the Confederated Tribes of Warm Springs.
“We’re augmenting natural islands in the lower Deschutes River that will provide improved shelter and spawning habitat for salmon and steelhead in the river.”
The population of fall chinook in the Deschutes was at record levels three to four years ago, Seals said. The number of returning fish has been lower during the last two years due to ocean conditions but have been generally robust during the past decade.
Conditions in the river have been better for fish over the past decade thanks to the installation of a so-called selective water withdrawal tower just above Round Butte Dam, in Lake Billy Chinook. The 273-foot-high tower helps to stabilize water temperatures in the river.
Fish will also benefit by this week’s deposit of gravel, as the natural flow of gravel downriver has been stopped by the upstream dams.
“The dam has been in place for 50 to 60 years, and there have been no gravel recruitment through the dam. Without the dams, you’d get sediment transport, but with the dam, that has not happened,” said Seals.
Spawning gravel is being laid at the upper of the two sites, about a quarter mile from the Reregulating Dam, the lowest of the three dams in the complex. This portion of the river is controlled by the Confederated Tribes of Warm Springs, which offered consent for the project.
At the second augmentation site, about a mile downstream, workers are placing gravel, wood and boulders around an island, trying to protect it from further decay. That site is held by a private landowner.
Augmentation of the spawning sites is needed in this area because there are no other inputs.
Further downstream, the Shitike Creek flows into the Deschutes bringing with it gravel and wood.
“Conditions for fish in this portion of the river are good with lots of spawning activity already. We are enhancing it because our license requires us to conduct gravel augmentation studies and remediation efforts due to the lack of natural flow of gravel and wood between the dams and Shitike Creek,” Burchell said.
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