LONGVIEW — A report released Friday suggests that a wider array of choices should be considered for the long-term stability of Spirit Lake to ensure that it does not breach its volcanic debris dam and unleash catastrophic flooding along the Toutle, Cowlitz and Columbia rivers. Among the possibilities: constructing a second drainage tunnel into the lake as a backup to the existing conduit.
In addition, according to the report, assessments of flooding and geologic hazards caused by the 1980 eruption of Mount St. Helens are based on old information that needs updating, and a broader array of interest groups should be involved in deciding how to handle the risks posed by Spirit Lake, the erosion of volcanic debris and the volcano itself. Distrust, competing missions and perspectives among all the players now interferes with good, long-term decision making, the report says.
The report’s technical-sounding title — “A Decision Framework for Managing the Spirit Lake and Toutle River System at Mount St. Helens” — hints at its character. The 250-page document is academically dense, repetitive and intimidating even for someone intimately familiar with the volcano.
Produced by the National Academies of Sciences, Engineering, and Medicine, the $570,000 effort reviewed hundreds of studies and papers about the flooding and geological hazards at the volcano but did not involve any new research of its own. It suggests but does not recommend specific actions. Its chief value, perhaps, is that it was written largely by scientists from outside the region, and in that sense it offers some fresh perspective and raises some interesting questions and reminders.
For one, despite the complacency that has developed with living with the volcano and its troubles for nearly 40 years, the region must be prepared to deal with those challenges for many more years, the report says.
“The legacy of the 1980 eruption and the prospect of future volcanic, seismic, and flood events mean that risk management in the Spirit Lake Toutle River system will be challenging for decades to come,” the report said. “Engineering measures now in place … do not represent long-term solutions to the region’s risk management challenges. Because the Spirit Lake outflow tunnel serves as the only drainage for Spirit Lake, disruption of tunnel operations leaves the debris blockage vulnerable to breaching. The tunnel has required major repairs and is not operating optimally. Additional expensive repairs are necessary, and, as for any constructed facility, continued costly maintenance will be needed. Downstream, the (sediment retaining dam) is close to reaching its sediment trapping capacity and plans to increase that capacity by raising the SRS spillway provide only short-term solutions to the sediment transport problem.”
Despite a yearning for restoration of fisheries, game abundance and return to pre-eruption “natural” conditions, “interested and affected parties (do not) understand that the 1980 volcanic eruption (a natural and recurring process) changed the system to create a different natural setting and a ‘new normal’ for the foreseeable future. No measures taken could revert the system back to pre-1980 conditions,” according to the report.
In addition, when people speak of long-range solutions to problems, what time frame do they mean, the study asks. Is it 2035, when a federally authorized flood management program for the volcano expires, or hundreds of years, as the Cowlitz Tribe would prefer?
The planning time frame affects what measures should be taken: For example, if the outlook is hundreds of years, the area almost certainly will be subject to a massive earthquake and further eruptions. And whereas fisheries’ restoration in the North Toutle Valley faces short-term difficulty, flood-control decisions made today could affect long-term fishery recovery efforts.
As the major land manager of the area, the U.S. Forest Service commissioned the study at the request of Congress after the agency found that the tunnel draining Spirit Lake will need major repairs, some of which were undertaken in 2015-16. In the course of that work, the U.S. Forest Service asked the National Academies how best to handle the flood risks related to the Spirit Lake and Toutle River system.
Because it was instigated by the Spirit Lake danger, much of the report revolves around the lake and the tunnel the U.S. Army Corps of Engineers cut through Harry’s Ridge in 1983-85 to provide an outlet for the lake. Debris from Mount St. Helens’ eruption of May 18, 1980 raised the lake more than 200 feet and blocked its old outlet into the Toutle River. Scientists determined that if the lake rose too much, it would breach the blockage and cause catastrophic flooding that would wipe out communities along the Toutle and Cowlitz rivers and wreak havoc on the Columbia River from Portland to Astoria, Ore.
The drainage tunnel, the Academies notes, cuts across five fault lines, including one that caused the upheaval of the tunnel floor, prompting emergency repairs in 2015-16. In addition, information about the debris blockage itself is inadequate and out of date, particularly about groundwater flow, a major factor affecting its stability. The blockage is a hodgepodge of different types of deposits, too, some of which are more stable than others.
Given these uncertainties — and the scale of damage should the blockage fail — the study suggests the region consider a backup plan should the existing drainage tunnel fail. Options could be cutting a backup drainage tunnel into the lake or constructing a “dry spillway” into the Toutle that would prevent dangerous rises in the lake. Other options could involve lowering or even draining the lake.
Such steps “would provide redundancy and flexibility” to keeping the lake safe, the report says.
The study repeatedly calls for expanded cooperation and decision-making. A lack of trust among agencies and the public — as well as lack of up-to-date science, competing values and overlapping authorities — make it difficult to develop alternatives to the risks posed by Spirit Lake and Toutle River sediment problem, the report says.
A public presentation about the report will be made in the local area early next year, according to Forest Service spokeswoman Sue Ripp.
“The Forest Service just received the report,” Ripp said Friday, “and will be reviewing the information to identify how to best move forward with the committee recommendations.”
