Plans to build a water cooling tower and fish passage system at Detroit Dam in Oregon’s Santiam Canyon might not require draining the reservoir after all.
The U.S. Army Corps of Engineers released its draft environmental impact study for the project on May 24, capping more than a year of reviewing public feedback and analyzing construction alternatives.
Jeff Ament, project manager for the Corps in Portland, said the agency is recommending both structures be built entirely “in the wet,” meaning it would not empty Detroit Lake during construction. The work is expected to take up to two years.
Detroit Dam is one of 13 multi-purpose dams operated by the Corps in the Willamette Basin. Located on the North Santiam River about 45 miles east of Salem, the dam provides both flood control in winter and water storage for farms and cities in the summer.
The 450-foot-tall dam is also a barrier for endangered native spring chinook salmon and summer steelhead, blocking both adult and juvenile fish from traveling to the Pacific Ocean and back to spawn.
To protect the species, the National Marine Fisheries Service wrote a biological opinion, or BiOp, in 2008 requiring changes in dam operations. One of those changes included the project at Detroit Dam, adding facilities to aid fish passage and survival.
First, the Corps would build a water temperature control tower at Detroit Dam. The tower works by mixing warm surface water at the reservoir with cooler water at deeper levels, meeting temperature targets for fish downstream.
The design then calls for a floating screen about the size of a football field to capture juvenile fish at Detroit Lake, so they can be safely moved around the dam via truck or bypass pipe. Each structure is expected to cost between $100 million and $250 million to construct, or up to $500 million combined.
“We are trying to recover the species per the 2008 BiOp,” Ament said.
However, the project generated significant controversy last year over the prospect of drawing down Detroit Lake so workers could build it on dry ground. Without a full reservoir during the summer, members of the public worried it would impact everything from recreation at Detroit to water supplies for farms and cities.
Both the cities of Salem and Stayton — with a combined population of nearly 178,000 people — get their drinking water from the North Santiam River. The Santiam Water Control District also draws water from the river to irrigate 17,000 acres of farmland and provides cooling water to NORPAC Foods, a food processing cooperative.
“A lot of people were very upset,” Ament said. “It’s a rather large impact.”
Ament said the Corps received about 200 comments during a public scoping period in early 2018. Based on those comments, he said the agency has recommended building underwater, adding to the total cost but avoiding an estimated $200 million in economic damage.
For agriculture alone, draining the reservoir would cost the industry $50 million for one year, and $139 million for two years.
Brent Stevenson, manager of the Santiam Water Control District, said the Corps’ recommendation is a huge development for farmers.
“I’m glad (the agency) heard our community speak,” Stevenson said.
While building in the water is a particularly challenging feat, Ament said the risks can be minimized with proper planning, design and oversight.
As for staging the project, Ament said the Corps recommends using an Oregon Parks and Recreation maintenance yard off Highway 22. Other possibilities included the Mongold day-use area or Detroit Lake State Recreation Area campground, though those were met with concern from members of the public.
A series of community meetings will be held to discuss the draft environmental impact study, part of a 60-day public comment period that began May 24.
Meetings are scheduled for May 29 at the Gates Fire Hall, June 4 at the Oregon Department of Fish and Wildlife headquarters in Salem and June 6 at the Stayton Community Center. All meetings will be from 5:30 to 7:30 p.m.