MOUNT ST. HELENS, Wash. (KOIN) — A shrinking drainage tunnel at Spirit Lake in the foothills of Mount St. Helens could result in catastrophic flooding if it’s not fixed.
Repairs are underway but engineers have their work cut out for them in the days ahead.
About a mile into the tunnel at Spirit Lake the ground has risen about 2 feet. The US Army Corps of Engineers said that’s threatening to constrict safe water flow.
“If we don’t have a tunnel there is no outlet. You risk the lake rising up til you get to the erodible material,” said project manager Chris Budai. “It starts piping, beaching, eroding the blockage and you have a catastrophic failure.”
Budai has been monitoring this tunnel since its completion in 1985. But it wasn’t until last year she found something wrong with it.
“When I saw the gross movement of a foot-and-a-half I notified the Forest Service immediately that we have a situation that had to be corrected right away,” she told KOIN 6 News.
The construction company hoped to begin work in December, but the record rainfall and the need to keep the drainage tunnel open changed that.
Also, a crucial piece of equipment — a remote-controlled excavator with a grinding head attachment — was held up by shipping issues and arrived late. Construction manager Brad Neu said they will use that to dig out approximately 40 feet of rising ground inside the tunnel and will reinforce the same area with steel ribs.
“It’s always a mystery when you start opening it up underground,” Neu said. “You think it may act one way when you open it up. It may do something totally different. That’s our biggest concern.”
The hope is to maintain regular water release into the north fork of the Toutle and other rivers.
The tunnel is critical, Budai said. Without a functioning tunnel, “you could cause a huge mudflow, very similar to what they experienced during the eruption of Mount St. Helens.”
If all goes well, the project will be completed by the end of February.
