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Corps Considers Mixing Tower At Detroit Dam, Would Be One Of Three In Oregon
Posted on Friday, February 23, 2018 (PST)

As it looks for ways to help reintroduce anadromous fish upstream of Willamette Valley dams, the U.S. Army Corps of Engineers is considering adding a $100 to $200 million water temperature control tower in the Detroit Reservoir.


A tower would aid downstream juvenile passage with attractor flows in the reservoir and it would help control discharge water temperatures downstream of Detroit Dam and Big Cliff Dam, the Corps’ re-regulation dam downstream, and beyond into the Santiam River system.


The idea ran into stiff opposition at local Corps open houses, however, when the agency explained that to build the 300 foot tall tower it may have to drain the reservoir for up to two years, a prospect that local merchants and water users in Salem and Stayton, Oregon said would be economically devastating, according to news reports. The Corps recently said the project could impact thousands of Willamette Valley residents.


“In the long-term, this project has a lot of positives, from a healthier environment for fish to better operation of the dam,” Marion County commissioner Kevin Cameron was quoted saying in a Salem Statesman Journal article. “But there is a huge risk in the short-term.”


The Corps has not made the decision to build the water temperature control tower, but it is considering it as an option as part of a National Environmental Policy Act review. It just completed the initial public scoping process Jan. 23, the first step in the NEPA process. The construction project is addressing a reasonable and prudent alternative recommended by the 2008 Biological Opinions for the Willamette Valley, the Corps said.


The final product in the NEPA process will be an environmental impact statement for the project. The Corps expects to complete a draft EIS, along with alternatives, by the Fall of 2018.


If it decides to move ahead with building the tower, construction wouldn’t begin until 2021.


The project, like many of its fish-related projects in the Willamette Valley, is part of a broader effort to reduce the effects of Corps-operated dams on winter steelhead and spring chinook salmon, the Corps said. Both species are listed as threatened under the federal Endangered Species Act.


The Corps operates and maintains 13 multipurpose dams and reservoirs (including Detroit Dam and Lake) in the Willamette River Basin in Oregon, collectively referred to as the Willamette Valley Project (see


But the issues at Detroit Dam aren’t new, the Corps said. It’s just gained momentum due to the public comment process in November and December, and ending Jan. 6.


“We want to find a solution together,” said Kelly Janes, Portland District environmental resource specialist, who spearheaded outreach to stakeholders across the valley. “Input from the community is critical. For this process alone, we’ve received substantial information that will really guide our construction process and our environmental analysis of potential impacts.”


The tower at Detroit Dam would actually be the second such tower built by the Corps and the third in Oregon. One is at Cougar Dam in the Willamette River system and the other is at the Pelton Round Butte Complex of dams on the Deschutes River in Central Oregon and is the target of a two-year old court case.


The Corps began operating its first Willamette Valley water temperature control tower in 2010 at Cougar Dam on the South Fork of the McKenzie River, a dam that was built in the 1960s.


Biologists estimated that habitat upstream of the dam supported as many as 4,000 adult spring chinook prior to the dam being built. However, water released from the dam was cooler than pre-dam river temperatures in the spring and summer and warmer in the fall and winter, which is one reason fewer chinook returned to the river and juveniles emerged from gravel redds earlier, the Corps said.


“Wild adult spring Chinook salmon began returning to the South Fork McKenzie River almost as soon as the temperature control tower came on line,” the Corps said on its website ( “Returns to the new adult fish collection facility downriver of the dam since it opened in 2010 have ranged between 250 and 525. We expect similar returns in the future until a long-term solution is implemented to help improve survival of juvenile salmon attempting to pass the dam on their way downstream from their spawning grounds to the ocean.”


The third temperature control tower was built at the Pelton Round Butte Complex of Dams by its owners Portland General Electric and the Confederated Tribes of the Warm Springs Reservation in 2009, and it was built for similar reasons as the tower at the Corps’ Cougar Dam.


Like the Corps in its efforts to reintroduce salmon and steelhead upstream of its Willamette basin dams, PGE and the Tribes also began a reintroduction program in 2010. The mixing tower serves as a surface attractor to help juvenile salmon and steelhead that rear upstream find their way downstream to the dam where they are trapped, marked and transported below the dams. The tower is an integral part of the utility’s reintroduction efforts.


Called a selective water withdrawal facility, the tower reaches nearly 270 feet below Lake Billy Chinook’s surface.


“This structure needs to be connected to the original intake structure to supply water for power generation while attracting fish and withdrawing water from the upper 40 feet of the reservoir,” Steve Corson, spokesperson for PGE, said.


The components of the structure are a floating surface collection structure (SWT), which screens surface water to exclude fish from powerhouse flow while directing juveniles to the transfer facility, a vertical flow conduit (VFC), a bottom structure (SWB), an access bridge (ABR) and the fish transfer facility (FTF). The SWB directs water from the SWT/VFC to the original powerhouse intake and also provides for direct water withdrawal from the bottom of the reservoir into the original power tunnel, Corson explained.


During operation, powerhouse flows are drawn from the surface structure or mixed with water from the bottom of the reservoir, depending on fish passage or water quality requirements.


PGE did not drain the reservoir to install the SSW, but instead built the majority on the water on barges next to the dam. The SWB was floated into place and anchored to bedrock at the reservoir bottom, 270 feet deep.


Construction was not without its problems. A portion of the VGC failed when the structure was initially deployed, Corson said. However, the problem was corrected and the SWW was deployed with a delay of seven months.


The Deschutes River Alliance says that PGE’s tower is likely the cause of water quality violations in the Deschutes River downstream of the dams and has sued the utility in U.S. District Court of Oregon over those alleged violations of the Clean Water Act. DRA filed its original petition Aug. 12, 2016. The case is still working its way through court.


Also see:


--CBB, December 8, 2017, “Corps Seeking Public Input On Detroit Dam Fish Passage, Temperature Control Scoping Process,”


-- CBB, June 16, 2017, “Willamette BiOp For Fish: Four Subbasins Focus Of Corps’ Salmon Reintroduction Programs Above Dams”


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