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Breach of Scoggins Dam could send damage downstream to Lake Oswego, West Linn

Open houses will provide new details and maps otherwise unavailable to public eye


by: SUBMITTED MAP - Scoggins Dam, visible on this map, releases water from Henry Hagg Lake that flows into the Tualatin River and eventually through Lake Oswego and West Linn.In 1971, Sherry Patterson felt not only the shock of the San Fernando earthquake but also a subsequent blow. A few minutes after the shaking stopped, she learned her apartment was in the path of a potential flood if a dam overflowed — and that dam was perilously close to failure. She began packing in case she had to evacuate.

Patterson and her husband have lived in the Lake Oswego area for four decades now, but she has long carried with her lessons learned from the Southern California catastrophe, which sparked her long-running interest in emergency preparation for natural disasters. Her experience also put her on the alert for similar problems, including the implications of a looming earthquake on Scoggins Dam.

Although Scoggins Dam is far west of the metropolitan area in Gaston, it controls releases from Henry Hagg Lake, sending water down Scoggins Creek toward the Tualatin River, which runs through Tualatin, Durham, Rivergrove and Lake Oswego on its path to the Willamette River in West Linn.

“If people survive the earthquake and then they think, ‘Oh, good, the worst is over,’ they have no idea they could be at risk of being affected by a debris flow” or floods, Patterson said.

The Bureau of Reclamation, which owns the dam, will host two open houses next week to talk about emergency preparation with downstream landowners.

On Jan. 9, in Hillsboro and in Forest Grove, experts will be on hand from the Tualatin Valley Irrigation District, Oregon Department of Geology and Washington County Sheriff’s Office to discuss risks identified for properties near the Tualatin River.

The meetings stem from a study completed in 2012 that identified earthquake-related risks for the 151-foot-tall structure. Organizations that store water at the dam, including the Lake Oswego Corporation, are now crafting a plan to mitigate those risks, although it’s unclear how Hagg Lake’s future expansion might alter the mitigation plan or updated maps that show hazardous locations.

Patterson pointed to other unanswered questions, such as availability of funding to compensate property owners for damages in the event of the dam’s failure, notification procedures for people in the inundation zones, evacuation plans for local schools and hospice or assisted-living facilities and data used to create models and craft the maps showing at-risk locations. Depending on the duration of the earthquake officials used for various scenarios, different properties might be considered at risk.

Adding to the uncertainty is the fact that the maps aren’t publically available in an easy-to-access location.

Chris Regilski, who heads up dam safety for the Bureau of Reclamation’s Pacific Northwest region, said the upcoming meetings are among the only times these maps will be available for public viewing, because they contain “sensitive material” that national security rules prohibit publishing.

He said the bureau sent meeting notices to about 2,000 property owners who live in areas that would be the hardest hit the quickest following a breach of the dam. But he couldn’t easily identify how many people might be affected in other areas or in specific locations such as Lake Oswego.

The inundation zones cross Clackamas, Multnomah and Washington counties, running through numerous cities, water districts and unincorporated communities. If an earthquake happened and the dam failed, residents would see some flooding along the Tualatin River, including in areas like West Linn and Durham, Regilski said.

Floodwaters wouldn’t arrive immediately, he said. For example, “the time to peak flows in the area around Durham is around 47 hours from the time of failure. By the time it gets to West Linn it’s 54 hours.”

Exactly how far up the riverbank those floods might reach is hard to explain without using maps.

“It’s hard to describe,” said Regilski. “That’s what we’ll have at the open house. ... Anyone in low-lying areas (near) the Tualatin River would be someone who should go to one of these meetings.”

Officials at some fire departments and emergency management organizations have copies of the latest maps already, although officials in Lake Oswego haven’t seen them.

Lake Oswego Fire Chief Ed Wilson said he plans to get copies on Wednesday, when some public officials will hold a tabletop drill to practice for a potential dam failure and its aftermath.

“After that I’ll have a better understanding of what the potential is downstream all the way into Lake Oswego,” Wilson said.

Larry Goff, the fire department’s operations chief, said previous materials mapping Scoggins Dam flood zones didn’t give him cause for concern.

“We haven’t had information that would show us that’s an issue,” Goff said.

If officials discover that the dam’s failure could cause a rapid rise on the Tualatin River near Lake Oswego, possibly spilling over at the Oswego Lake headgate and canal or leading to floods in the Rivergrove area, he said they’d take steps to address the risks.

Patterson has closely followed the potential impacts on Rivergrove, between Lake Oswego and Tualatin. And while her home is outside of the inundation zone, much of Rivergrove is within it, she said.

Patterson has been a commissioner on the Rivergrove Water District for almost 30 years. She’s also on the Lake Grove Fire District board, has attended numerous Oregon dam safety conferences, was among the Lake Oswego area’s first Community Emergency Response Team volunteers and contributed to work on the Oregon Resilience Plan for reducing risks and improving recovery from a likely major earthquake.

She stressed that her opinions on dam safety issues are her own and aren’t related to any of those organizations.

When she and her husband were living in an apartment and the San Fernando earthquake hit, they were unaware they lived in a dam’s potential flood zone.

“We had no idea,” Patterson said.

She worries the same could happen now with the Scoggins Dam in Oregon.

“The good news is we’re going to have some time to evacuate,” Patterson said. “But people need to know, because we really have to plan for evacuation.”

Two meetings on tap to talk dam flooding

What: Bureau of Reclamation, state and other officials will inform people about flood zones from a possible breach of the Scoggins Dam, which feeds into the Tualatin River.

When and where:

  • 1 to 3:30 p.m. Jan. 9 at Hillsboro Civic Center Auditorium, 150 E. Main St., Hillsboro

  • 6 to 8 p.m. Jan. 9 at city of Forest Grove Community Auditorium, 1915 Main St., Forest Grove

    Kara Hansen can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it. and 503-636-1281, ext. 107. Follow her on Twitter, @LOreporter.