Dam deluge always possible?

Cougar holds back 70 billion gallons

By Tom Conning

USACE Public Affairs Office

BLUE RIVER: Roughly 70 billion gallons of water flows over Niagara Falls every 24 hours and the same amount sits ominously behind Cougar Dam. If Cougar were to completely fail, that water would rush 60 miles down the McKenzie River, washing away everything in its path, until it reached the Eugene and Springfield area.

The deluge could make Eugene and Springfield look like Corvallis, Oregon City and Portland after the Flood of 1996; although no dams failed during that event. That image, and the desire to do everything possible to keep it from becoming reality, was the backdrop for a recent inspection at Cougar Dam, May 24th.

Graham Hilson, Willamette Valley Project general maintenance manager, lives downstream of Cougar and takes these inspections personally.

“My family and I live within a half mile of the Willamette River main stem and we’re well within the flood plain, so beyond my professional duties I have personal interest too,” said Hilson. “It’s good to be a little worried with so much at stake, recognizing the communities we could impact narrows our focus and attention where it matters most. I have a high level of confidence in the performance of our dams under any scenario.”

Hilson isn’t the only one expressing confidence in the dam. Erica Medley, Portland District geologist and Dam Safety Program team member, says being involved with the Corps’ robust dam safety program inspections shows her the structures are reliable.

Medley spends a good portion of her day reviewing data, conducting research and investigating the District’s dams.

“Public safety is the Corps’ first priority,” said Medley. “We inspect, evaluate, maintain and repair our structures to minimize risks to the public.” “We have good communication with local emergency management officials so that emergency response plans are in place in the event of an emergency,” she continued.

Additionally, reliable doesn’t equal fail-safe. Anyone living downstream of a dam should be aware of the risks and be prepared to take action to protect lives and property.

Medley recently led the May 24 assessment where an interdisciplinary team of geotechnical, geological, hydraulic, structural and mechanical engineers visited Cougar Dam to examine it during a Periodic Inspection, which happens every five years. This is just one of many types of analyses the Corps does at its dams. Others include field studies – also beginning at Cougar – Periodic Assessments at 10-year intervals, risk assessments and annual inspections. All of them are done to ensure the dams are reliable and operating as intended.

Photo Courtesy Corps of Engineers. An aerial view of flooding along the Willamette River during the Flood of 1996. The Eugene and Springfield area could look like this if Cougar Dam completely failed.