South Coldwater Creek cascades down to join the flow of water exiting the downstream end of the Spirit Lake drainage tunnel the Army Corps of Engineers completed in 1985. (U.S. Army Corps of Engineers)
The U.S. Forest Service is reviewing ways to prevent Spirit Lake from overflowing, including updating or replacing an aging tunnel built to drain the lake after the 1980 Mount St. Helens eruption.
The plan aims to protect downstream communities from catastrophic floods, and may or may not use the tunnel intake gate the agency is replacing at the site today.
A virtual presentation earlier this month broke down a handful of “long-term resilient solutions,” said project consultant Dan Tormey, including revamping the existing tunnel, building a new one that would have a greater flow rate, building a new pressurized tunnel and constructing a couple open channel options.
Tormey, president of Catalyst Environmental Solutions, said the project would release its draft environmental impact statement early this summer, but he could not provide a construction timeline. When an option is selected, the project would take between three and 10 years to complete, he added.
Work on that project started in 2024 and is expected to be completed in 2027, said Charles Lassiter, a spokesman for the Gifford Pinchot National Forest. The gate replacement fixes the structure nearing the end of its design life but might not be used in the long-term solution the Forest Service is reviewing for the entire tunnel, he added.
Over time, its function has reduced, threatening to overwhelm the natural dam that holds back billions of gallons of water and risking sending that water down the Toutle River Valley into cities where more than 50,000 people live.
The problem was created by Mount St. Helens’ 1980 eruption, which sent more than 1 million Olympic swimming pools’ worth of debris into the Upper Toutle Valley.
One consequence of that was debris blocked the giant lake’s natural outflow. The U.S. Army Corps of Engineers built the tunnel in 1985 to drain the lake after various stop-gap measures. Over the years, the tunnel has needed substantial repairs in 1995, 1996 and 2015-16, Tormey said.
Possible solutions
Tormey said the most important factor of the project is to reduce risk to public safety. He said the project also is weighing concerns including the integrity of ongoing research in the area, environment and anadromous fish passage, the economy and local native nations’ interests.
The eventual project would likely combine multiple options to make sure there is both a primary and backup way for the lake to drain.
Tormey explained the potential pros and cons of each approach. The entirely machine-excavated channel option didn’t score high marks because it would require about a million dump truck loads to clear out the material and had high risks if the natural dam failed during the project.
A related option, however, seemed to score well. That approach would use a pressurized tunnel to lower levels of the lake and some excavation to start a channel for water to flow out. But that approach would then let the water fully erode its own channel, leading to potential fish passage benefits.
Federal funding would cover the project, he said. But he did not provide potential costs of the project options.
Lassiter also said the project’s environmental review will take until 2026. Then, the project must select a plan before seeking funding. The funding component alone could take “several years or more,” he said.
About the project: The Murrow News Fellowship is a state-funded journalism project managed by Washington State University. Local partners are The Columbian and The Daily News. For more information, visit news-fellowship.murrow.wsu.edu.
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