LONGVIEW — The Spirit Lake drainage tunnel needs millions of dollars in repairs to head off a potentially catastrophic failure, a reality that U.S. Forest Service officials say gives further impetus to constructing a controversial road across a crucial Mount St. Helens research area.
The U.S. Army Corps of Engineers, which built the tunnel in 1982-85 to prevent catastrophic flooding along the Toutle, Cowlitz and Columbia rivers, told the Forest Service in 2016 that the tunnel’s inlet gate should be replaced by 2021.
There is no emergency, but Forest Service officials hope to start the work by June 2021 and have already requested funding, said Rebecca Hoffman, manager of the Forest Service-managed Mount St. Helens National Volcanic Monument.
“We have to make sure we provide for public safety. We can’t wait until it becomes an emergency,” Hoffman told said in a pre-Thanksgiving interview.
Forest Service officials will publish a formal proposal for the project in mid-December, said Hoffman and Chris Striebig, Spirit Lake project leader for the Forest Service.
The 8,500-foot-long tunnel drains Spirit Lake under Harry’s Ridge and into South Coldwater Creek, where the waters eventually merge with the North Fork of the Toutle River. The tunnel controls the lake at about elevation 3,440 feet above sea level and prevents it from rising and breaching the debris blockage that dammed its natural outlet into the North Fork during the eruption of Mount St. Helens on May 18, 1980. Federal studies say a breach of the blockage would cause catastrophic flooding downstream.
The tunnel, cut through rock that includes an active fault, is the lake’s only outlet. A National Academy of Sciences panel two years ago expressed concern about the lack of a backup system to control the lake level.
The tunnel inlet consists of a vertical shaft topped by a concrete wall. A cast-iron gate embedded in the wall controls the flow of lake water into the shaft, where it then cascades into the tunnel itself. The gate is corroding, and the mechanism used to raise and lower it failed this past summer, requiring about $75,000 in repairs and helicopter time, Striebig said.
If the inlet gate suddenly broke off or got jammed shut, no flooding would immediately occur downstream. But officials would lose control of lake levels, Striebig said. Any large, uncontrolled rush of water could damage the tunnel walls and cause them to collapse and block the outlet, Striebig said. Then there would be no way to keep the lake from rising to levels that could threaten the debris blockage.
The gate “is functioning right now. … But that was a warning sign. It’s going to break down. … I don’t want to wait around and find out,” when that will be, said Chris Budai, Spirit Lake project manager for the Corps’ Portland District.
The Corps wants to cut out the old gate and replace it with two steel gates, Budai said.
It all sounds simple, but due to the remote, roadless location on the west shore of Spirit Lake and the short summer work window, the project will take two or maybe even three years, Budai said. A coffer dam would need to be built to keep the work area dry, and a staging area also would need to be constructed, she said.
Cost estimates for the project range from $5 million to $15 million and will take at least two, possibly three years, she said.
“It is a very difficult area to work in, to try to figure out how to get equipment and personnel in there. And we have a short (seasonal) work window and you have to be efficient. … There are a lot of unknowns,” Budai said.
A major one is access. The Forest Service wants to re-establish a primitive road to the south shore of Spirit Lake basin from Windy Ridge, which rises above the east shore of the lake. Equipment still would have to be barged from the lake shore to the tunnel inlet, but that would be far easier, faster and less costly than other alternatives, such as helicoptering in crews and equipment, Budai said.
The road also would allow the Forest Service to conduct test drilling of the debris blockage holding back Spirit Lake, an effort prompted by the National Academy report.
In April, the Forest Service backed off an earlier proposal to re-establish the road. Conservationists and researchers fear road construction and drilling would disturb some of the 33 research projects covering hundreds of acres on the south shore of Spirit Lake and which are tracking the return of life.
It is one of the most intensely studied plots of ground in the world. The researchers contended that the Forest Service had not done enough analysis or study of alternatives to protect research opportunities, which is one of the primary reasons Congress created the 110,00-acre National Volcanic Monument in the first place. Soil disturbance, pollution from equipment and possible introduction of invasive species were among scientists’ concerns.
Hoffman, the monument manager, said her office is working with the scientific community to “minimize the impact on research” and is assembling a report on the status and nature of all the research taking place in the area. Officials have met with researchers, Hoffman said, still acknowledging that “they are not on board” yet with the plans.
John Bishop, a Washington State University Vancouver biologist who has studied the Spirit Lake area for 30 years, said Hoffman and the Forest Service seem to be more sensitive to researchers’ concerns this time. However, the research community is still “wary.”
“It’s clear that the (inlet gate) needs to be replaced,” he said Tuesday. “I still think that the Forest Service needs to ensure that the impacts scientific study can be kept to a minimum. … These are very important things for public safety, but they are not an emergency as far as we can tell. We have to figure out how to deal with them but to do it properly and carefully.”