GASTON, Ore. (KOIN) — The federal government will begin work next week to determine the best way to improve the earthquake resistance of Scoggins Dam in Washington County.
The dam, which creates Henry Hagg Lake – a major county water source – was built in the 1970s, and so not designed to withstand intense earthquakes. This has become especially concerning as fear over The Big One grows.
“Scoggins Dam is at threat of failure in a major earthquake just like much of the infrastructure in the Northwest,” said Mark Jockers, a spokesman for local water utility Clean Water Services. “[With] the science that has emerged on the Cascadia Subduction Zone… there’s a recognition we need to shore up on this infrastructure.”
Should the dam collapse in the event of such a quake, it would not only cause massive flooding in the Forest Grove area, but severely damage water access, and “water is a lifeline resource after an earthquake,” Jockers said.
While CWS uses water from the lake, the dam itself is run by the federal Bureau of Reclamation. Of all the dams controlled by that bureau, Scoggins is the farthest west, and the closest to the Cascadia Subduction Zone. That’s made it a top concern for the feds, too.
Funding for an upgrade was included in the omnibus spending package signed by President Obama in 2015. In late July, the bureau and CWS will take the next step, studying their options. Crews will drill, collect samples, and take tests all around the site for several months.
The studying and planning phase will be extensive. It will likely be another 6 years before any construction begins, and an additional 3 years before upgrades are completed.
That’s because of the uniquely powerful and complex threat posed by The Big One, according to bureau engineer Chris Regilski.
“It’s not like the most standard kind of work that we’ve done before,” said Regilski. “It’s very difficult to model, to analyze, and to make sure that we do the most cost-effective method.”
At the moment, engineers are considering two specific methods of improving the dam’s seismic stability. One is to raise and reinforce the existing dam. The other is to add a second dam downstream, taking pressure off of Scoggins and adding a second layer of protection against massive flooding.
“Initially we were working with the federal government to get permission to pile our dirt on their dirt… simply to raise the existing dam,” said Jockers. “As this new science emerged… we started looking at other options.”
“What we find attractive about the downstream dam option… there’s a narrow spot a mile and a half down from the existing dam… it could allow for us to build a smaller, shorter, stable concrete facility,” he said. “That’s attractive because it could be the most cost-effective measure, [plus it provides] the stability of a concrete facility.”
Jockers said they should determine which option they’re going with sometime within the next 3 years.
He also said the dam is currently structurally sound, and that the upgrades are needed only because of the relatively newly-discovered threat of The Big One.
“The dam is safe as it’s designed,” he said. “The challenge is a major Cascadia Subduction Zone earthquake, which this dam was never designed for.”