The floating log mat of Spirit Lake, left behind after the May 18, 1980, eruption of Mount St. Helens can be clearly seen from the Windy Ridge viewpoint.
The National Academies of Science, Engineering and Medicine have released a new report that will offer a framework for decision makers as they try to find a solution to ongoing watershed and public safety issues in the Toutle River system and Spirit Lake near Mount St. Helens.
The volcanic eruption of the mountain in May 1980 deposited sediment in the Toutle River Valley and blocked the outflow of Spirit Lake that created long term changes to the hydrology of area watersheds. Following the eruption, a 1.5-mile tunnel was dug at the outflow end of Spirit Lake in order to allow for drainage that would protect the nearly 50,000 downstream residents from a collapse of the earthen dam put in place by the eruption. However, recent inspections have shown that the tunnel is at risk of failure, and emergency repairs have already been started.
The study also noted that a sediment trap was put in place on the Toutle River in the aftermath of the eruption, but that structure is nearing its capacity. Local flooding on the Toutle and Cowlitz river systems is compounded by those sediment flows, according to the report.
The report says that in order to assure the best outcome of future management projects, updated information is needed since much of the data currently being utilized was collected in the 1980s and 1990s and is considered outdated or incomplete. Additionally, the report cited recent revelations about the likelihood of a Cascadia Seismic Zone earthquake that would affect Mount St. Helens and the surrounding area as a matter of concern that warrants additional examination.
“Our report stresses the importance of thinking of Spirit Lake and the Toutle River as a system,” said committee chairman Gregory Baecher, Glenn L. Martin Institute professor of engineering at the University of Maryland, College Park, in a press release. “Using an analytic process that is also deliberative will help decision-makers identify the many objectives, alternatives, and impacts of those alternatives for managing that system.”
In order to help guide the impending decision making process, the Academies provided a five-step formula. Part of their recommendation is to foster as much useful input from assorted interest groups as possible from the outset of the process. The Academies suggested including agencies with authority or interest in the system, those who experience safety, economic, cultural or life-quality impacts from the management decisions, and anyone with specialized knowledge related to potential impacts. The report also suggests that a “neutral support team” should be created in order to provide technical and scientific expertise, decision analysis, stakeholder engagement and group facilitation. Additionally, the report suggests that a lead position should be created so that one person is in charge of keeping the process moving forward based on continuous analytic decision making.
The report noted that a logical first step in the process would be to create a framework for decisions regarding managing water levels at Spirit Lake. Options listed in the report include constructing a dry spillway as a backup outlet or installing a second modern drainage tunnel that would provide redundancy and flexibility.
The consideration of operational risks should also be paramount to the decision-making process, according to the report. Examples of those risks include rapid lake level rise when the tunnel is closed for repair and the possibility for failure in engineered structures such as the sediment traps and levees. A report noted that, “such risks do not appear to have been systematically considered so far.”
Members of the study committee are expected to convene in Southwest Washington in early 2018 in order to provide a public briefing on their findings and recommendations.
A press release noted that the study was funded by the U.S. Department of Agriculture’s Forest Service. The National Academies of Sciences, Engineering and Medicine are private, nonprofit institutions that provide independent, objective analysis and advice.
