Scientists say long-term solutions needed to prevent floods near Mount St. Helens
Scientists say local, state, and federal agencies need to work together and explore long-term solutions to deal with flood risks from Spirit Lake near Mount St. Helens.
The 1980 eruption unleashed a massive landslide that plugged the only outlet from Spirit Lake on the north side of the mountain, creating a natural dam. The lake rose more than 200 feet after the slide, causing concern the newly created dam would fail, putting as many as 50,000 people downstream at risk of catastrophic floods.
The Army Corps of Engineers dug a 1.6-mile tunnel underneath the dam after the eruption to prevent failure. It has worked since then.
In a new report from the National Academies of Sciences, Engineering, and Medicine, scientists warn that the tunnel needs constant repairs and is not operating optimally.
The U.S. Forest Service went in to repair a 30-foot section of tunnel in 2016 that was damaged by shifting rock underneath.
While it is an unlikely scenario, scientists say tunnel failure could result in dam failure. They suggest agencies look into other options like a second tunnel or a spillway to act like a redundancy should the first tunnel fail or become overwhelmed. They even suggested draining the lake.
“It hasn’t happened in 32 years. The tunnel's job is to keep the lake at an appropriate level so it doesn't get into high levels of that debris blockage,” said Chris Strebig, Spirit Lake project manager with the Forest Service.
The Forest Service manages the lake. In 2015, Congress directed it to review and analyze options for a long-term solution that removes the threat of catastrophic failure.
"Congress mandated the National Academies to undertake a study, not to figure out what to do, but how to create a decision framework that would allow for cooperation between everyone involved," said Greg Baecher, chair of the committee that produced the report.
Strebig says they have invested $12 million in recent years to monitor the lake and dam, including the installation of a barrier to prevent logs from clogging the tunnel.
“We are investing in that tunnel to keep that outflow going the way it should. We are working closely to more understand the risks out there,” Strebig said.
Ernie Schnabler, Cowlitz County’s emergency management director, says they deal with the worst of the worst scenarios. He says they have plans should the natural dam at Spirit Lake fail.
“If that would happen, there would be tons of debris that's in the bottom of the lake, together with the water, would be washing out, would take everything out in the Toutle Valley, would take Castle Rock out, and bring a flood wave [into Kelso]. I kid you not, with 25 to 30 feet height,” he said.
More broadly, the report says information that informs long-term management of the area near Spirit Lake is outdated or incomplete, and recent information about how the Cascadia Seismic Zone earthquake warrants more examination.
Strebig says they will examine how extreme rainfall, earthquakes, or volcanic activity will affect the area.
“What's the best way to provide outflow not for this generation, but generations down the road?” Strebig said.
“You need to really look downrange, what can we really do to mitigate against something like that and what can we do today to invest our money into better solutions?” said Schnabler.
There will be a public meeting in early 2018 to discuss findings from the report.