Consensus Report

A Decision Framework for Managing the Spirit Lake and Toutle River System at Mount St. Helens (2017)

Each report is produced by a committee of experts selected by the Academy to address a particular statement of task and is subject to a rigorous, independent peer review; while the reports represent views of the committee, they also are endorsed by the Academy. Learn more on our expert consensus reports.

Public Briefing: January 25 at 2:00 p.m.

The public is invited to a presentation to learn about the findings of this study beginning at 2 p.m. on Thursday, January 25 at the Red Lion Hotel in Kelso.

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The massive volumes of volcanic debris deposited in the Spirit Lake and the Toutle River system during the 1980 eruption of Mount St. Helens in southwest Washington State drastically changed the region and left its 50,000 inhabitants at risk of chronic flooding as well as potentially catastrophic flooding. Engineering measures put in place in the 1980s to reduce flood risks and control sediments are in need of costly repairs or modification, presenting an opportunity to re-evaluate risk management strategies. Produced at the request of the U.S. Forest Service (USFS), this report proposes a decision framework to support long-term management of risks in light of the different economic, cultural, and social priorities of regional stakeholders and the respective roles of federal, tribal, state, and local authorities, and other groups in the region.

The recommended framework is a deliberative process that is reliant on the results of scientific and engineering investigations and decision analysis techniques that can account for the multiple objectives and values of interested and affected parties. The framework guides the decision-making process through five steps, from clarifying the decision problem to identifying the tradeoffs to be made when choosing among the various management options.

The report also finds that some information available to inform long-term management of the system is outdated and incomplete. Many data collection activities, such as groundwater monitoring within the debris blockage stopped in the 1980s or 1990s. Current characterization of the hydrogeology and geomechanics, and site-specific seismic hazard analyses at the locations of key elements in the system are needed, as is an integrated probabilistic risk assessment of the region. Agencies engaged in risk management should develop a coordinated monitoring system to track changes in factors that affect risk, and the data and analysis should be available to all.