Spirit Lake: From an Emergency Tunnel to a Long-Term Vision

The Close Calls That Changed the Conversation

The existing outflow tunnel passes through several zones of fractured and weakened volcanic rock. Over time, pressure from the surrounding rock has deformed portions of the tunnel, causing its floor to rise and damaging its supports.

Major repairs were necessary in 1995–1996 and again in 2016–2017. Both repairs required closing the tunnel for extended periods. Both closures coincided with unusually wet conditions, and Spirit Lake rose to near its designated maximum safe operating elevation of 3,460 feet.

These experiences exposed a fundamental vulnerability: management of Spirit Lake currently depends on a single aging outlet, with no permanent backup system to manage rising water levels while the tunnel is closed.

The consequences of failure could be enormous. Approximately 50,000 people live downstream in areas potentially affected by catastrophic flooding and mudflows. Yet the problem could not be solved by engineering alone. Spirit Lake sits within the Mount St. Helens National Volcanic Monument, where Congress directed the Forest Service to protect geological, ecological, and cultural resources while allowing natural processes and ecological recovery to continue substantially unimpeded.

How could the Forest Service protect downstream communities while honoring the very natural processes, scientific opportunities, and landscape values for which the Monument was created?

In September 2015, members of Washington's congressional delegation asked the leaders of the Forest Service, U.S. Army Corps of Engineers, and U.S. Geological Survey to work together on a long-term solution. That request launched an ambitious scientific, engineering, and public engagement effort.

Science First, Then a New Way of Making Decisions

The Forest Service brought together leading scientific and engineering expertise. Researchers from the U.S. Geological Survey and Forest Service examined the volcano's geological history, the stability of the debris blockage, sediment transport, and potential future hazards. The U.S. Army Corps of Engineers evaluated engineering options and their associated risks.

The National Academies of Sciences, Engineering, and Medicine (NASEM) was also commissioned to examine how decisions about Spirit Lake and the broader Toutle River system should be made. Its 2018 report recognized something fundamental: there is no risk-free solution for managing Spirit Lake. All options involve uncertainties and tradeoffs among public safety, natural processes, environmental protection, research, recreation, and community interests.

Rather than recommending a single engineering solution, NASEM recommended a collaborative decision-making framework, including a technique known as Multi-Criteria Decision Analysis (MCDA).

The basic idea is straightforward: 1) develop a common scientific and technical understanding of the available options; 2) identify the different things people value; and 3) use a transparent method to examine how different priorities affect which management solutions are preferred.

Different people might reasonably arrive at different choices, even when working from the same scientific evidence. The challenge was to create a process in which those differences could be understood and discussed constructively.

Bringing the Community Into the Process

Following NASEM’s recommendations, the Forest Service implemented an extensive outreach effort that went well beyond the usual requirements for environmental review.

A particularly important part of this work was the Spirit Lake/Toutle-Cowlitz River Collaborative, which brought together Tribal representatives, federal and state agencies, local governments, conservation organizations, scientists, and community members. The Collaborative met approximately monthly during two years of focused discussions, examining scientific findings, engineering possibilities, environmental concerns, and the values that different participants brought to the decision. Additional meetings engaged researchers, conservation organizations, and local communities.

These conversations made a difference. One of the most important ideas to emerge was that the project could do more than improve the existing tunnel. It might also create a pathway toward reconnecting Spirit Lake with the North Fork Toutle River, restoring some of the natural hydrological and ecological processes interrupted by the 1980 eruption.

This concept combined a new, highly controllable pressure tunnel with the potential for future development of a natural habitat channel. The channel would not replace the engineered public safety system. Instead, the tunnel would maintain safe lake levels while scientists and engineers carefully evaluated how a surface channel could be established, potentially allowing fish to move between Spirit Lake and downstream waters.

This was a significant conceptual advance: engineering designed not simply to control nature, but also to create opportunities for natural processes to function safely. This approach is known as Engineering With Nature® (EWN) or, more broadly, Nature-Based Solutions.

Comparing the Alternatives

With support from engineering consultants Delve Underground and environmental consultants Catalyst Environmental Solutions, the Forest Service conducted an environmental review of the project in accordance with the National Environmental Policy Act (NEPA), evaluating nine alternatives for an outflow solution, including taking no new action. These alternatives ranged from repairing or replacing the existing tunnel to creating new outlets through the volcanic debris blockage.

The engineering feasibility analysis examined how well the options could function, what risks they would present during construction and operation, and their potential costs. The NEPA Environmental Impact Statement (EIS) evaluated effects on fish and wildlife, wetlands, sediment transport, cultural resources, research, recreation, scenery, and other resources.

The project team also developed an MCDA tool consistent with NASEM’s recommendations. It brought together three major dimensions:

1. Comparative risk: How reliably could each alternative protect downstream communities?
2. Community values: How well did the alternatives address priorities such as public safety, healthy ecosystems, research, education, and recreation?
3. Environmental consequences: What effects would each alternative have on the Monument and surrounding watershed?