BACKGROUND – A massive debris flow during the 1980 eruption of Mount St. Helens created Castle and Coldwater lakes, and blocked the natural outflow from Spirit Lake. To maintain a safe water level in Spirit Lake, in 1985 the U.S. Army Corps of Engineers (USACE) constructed a tunnel, completed a 1.6 mile, 11-ft diameter shaft bored horizontally through rock on the Mount St. Helens National Volcanic Monument.
As the tunnel ages its components require repair and replacement, and total deferred maintenance is in the tens of millions of dollars. The 2017 National Academies of Science, Engineering, &Medine report provides recommendations for improved understanding of options for long-term management of the outflow from Spirit Lake.
Where is the Spirit Lake Outflow Area?
SPIRIT LAKE PROJECT WORK – Spirit Lake and the Toutle River drainage system affects many local and downstream partners and people. Some of the recent project work completed by the Forest Service, USACE, and U.S. Geological Survey includes:
critical repairs to a section of the tunnel
installed a log debris barrier to protect Spirit Lake outlet
added a new tunnel flow sensor in addition to other investments to reduce risk and improve safety
developed an emergency operations plan and held table top exercises to practice plan
The Geologic, geomorphic, & hydrologic context underlying options for long-term management of the Spirit Lake outlet near Mount St. Helens, WA. https://www.fs.fed.us/pnw/pubs/pnw_gtr954.pdf
