At a Glance
- The Detroit Dam's spillway could be breached.
- The report cites the dam's proximity to the Cascadia Subduction Zone.
- The fault is capable of producing a large earthquake.
A major earthquake could unleash "potentially catastrophic" flooding from a dam in Oregon that would threaten the state capital and other communities downstream, according to the U.S. Army Corps of Engineers.
Officials said the dam, near the town of Detroit about 45 miles southeast of Salem, is not otherwise in danger of failure.
“People downstream of Detroit Dam should feel really confident in the condition of this infrastructure,” Dustin Bengtson, Willamette Valley Project deputy operations project manager for the Corps, told the Statesman Journal. “We’re just being extremely conservative in our risk assessment given the critical values and the thousands of people that live downstream.”
The Corps released a draft environmental assessment this month that calls for reducing maximum water levels in the dam's reservoir by 5 feet to reduce pressure on the spillway's gates.
"There is a low probability of a large earthquake that could result in a breach of the spillway," the report states. "However, a breach would result in a potentially catastrophic flood if it occurred and risk is high enough to warrant immediate actions."
(MORE: Oregon Launches Earthquake Alert System)
The report notes that the dam is about 150 miles east of the Cascadia Subduction Zone, a 600-mile fault that runs from northern California up to British Columbia and is capable of producing very large earthquakes.
Information on the state of Oregon's website says the fault has the potential to produce an earthquake of more than 9.0 magnitude. Scientists predict a 37% chance that an earthquake greater than 7.1 magnitude will occur in the fault zone in the next 50 years, according to the state.
The Corps report says shaking from a major earthquake could cause supports for the dam's spillway gates to buckle. The plan to reduce the water level is a temporary solution while experts further study the dam.
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“The chances of a breach right now is very, very low. Around 0.01 percent,” Ross Hiner, dam safety program manager for the Corps, told the Statesman Journal. “But we want to move it even lower.”
But the move isn't without controversy. Reducing the reservoir's water levels could impact boat ramps and docks, which Detroit Mayor Jim Trett fears would affect tourism in his community.
“Unfortunately, 5 feet is huge for us,” Trett said.
The town was devastated by a wildfire last year that destroyed dozens of homes and other buildings. Rebuilding efforts are still underway.
“It’s just another poke in the eye for us and for the community," Trett told KOIN-TV.
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