Corps of Engineers may trim Detroit Reservoir maximum level, to ease quake threat

Informational presentation set for next Monday; public comments sought

PORTLAND, Ore. (KTVZ) -- The U.S. Army Corps of Engineers is considering a plan to reduce Detroit Reservoir’s maximum pool elevation by five feet, beginning this summer, to reduce the likelihood of overstressing the dam's spillway gates during a large earthquake, a move that could impact boat ramp access in some years.

The Corps' Portland District on Monday invited members of the public to join a virtual informational briefing via WebEx on Monday, March 22 from 5-7 p.m. on the plan to restrict Detroit Dam’s maximum pool elevation to 1558.5 feet (from 1563.5 feet),"in order to reduce the life-safety risk associated with large seismic events."

In 2020, the district completed a seismic hazard analysis for Detroit Dam. The hazard study found the risk to be higher than Corps officials previously thought.

A structural analysis has shown a possibility of the spillway gates buckling under the force of a full reservoir during a large earthquake, the agency said.

Even though the probability of breach is low, the Corps sad it wants to take immediate action to reduce risk to acceptable levels because the potential impacts of a breach of the spillway gates are high, with Detroit Dam located upstream of many communities, including the state capital of Salem.

The reservoir spans the Linn County–Marion County border in the Cascades on the North Santiam River, near the city of Detroit.

The Corps said it has a public safety responsibility, when a project has known safety issues, to take appropriate interim risk reduction measures, including reservoir releases. Corps responsibilities require operation of dams in a manner that reduces the project’s probabilities of failure when there are known issues with the integrity of the project.

The pool restriction may affect a few boat ramps in some years, at the end of the recreation season. However, the Corps said the proposed plan should have little to no impact on recreation such as fishing, non-motorized boating, swimming, camping, hiking, nature viewing, and picnicking.

The public and media are invited to find out more during a live presentation, which is for informational purposes only.

Public comments on the proposed action will not be taken for the record during the meeting and anyone interested in submitting a comment on the proposed action or the Environmental Assessment must submit them via email or by mail.

All comments, whether by conventional mail or email, must be received no later than the expiration date of this public notice to ensure consideration.

When: Monday, March 22: 5-7 p.m.

Where: https://usace1.webex.com/meet/PDXCorps.publicmeetings

Call in number: 1-844-800-2712

Access Code: 199-430-8599

The U.S. Army Corps of Engineers released for public comment a draft Environmental Assessment evaluating alternatives for the Corps’ proposed seismic risk reduction. The EA is currently available for a 15-day public review here.

Submit Public Comments Here: DetroitPoolRestrictions@usace.army.mil. The Corps will review all comments received and all comments, whether by conventional mail or email, must be received no later than the expiration date of this public notice to ensure consideration. The report will be available for download.  

Willamette Valley Project: The U.S. Army Corps of Engineers operates 13 dam and reservoir projects in the Willamette River drainage system. Each dam contributes to a water resource management system that provides flood damage reduction, power generation, irrigation, water quality improvement, fish and wildlife habitat and recreation on the Willamette River and many of its tributaries. Since their completion, the dams have cumulatively prevented over $25 billion in flood damages to the Willamette Valley. For more information, visit: www.nwp.usace.army.mil/.