A Decision Framework for Managing the Spirit Lake and Toutle River System at Mount St. Helens (2018) / Chapter Skim
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1 Introduction
1 Introduction
Pages 19-42
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From page 19... ...
Debris avalanche material and large volumes of pyroclastic flow deposits were directed north of Mount St. Helens into the North Fork Toutle River valley (see Figures 1.1 and 1.2)
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From page 20... ...
. Much of the material from the eruption debris avalanche was deposited in the North Fork Toutle River valley, blocking the flow of water from Spirit Lake to the North Fork Toutle River.
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on the North Fork Toutle River. SOURCES: Map by authors; base map: @OpenStreetMap and contributors, including the USGS's The National Map: National Boundaries Dataset, 3DEP Elevation Program, Geographic Names Information System, National Hydrography Dataset, National Land Cover Database, National Structures Dataset, and National Transportation Dataset; U.S.
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gravity-fed tunnel to drain water west into South Coldwater Creek and eventually into the North Fork Toutle River (see Figure 1.3)
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Water exiting the tunnel enters the North Fork Toutle River circa 6 miles (10 km) downstream of the tunnel outflow.
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This National Academies of Sciences, Engineering, and Medicine (National Academies) report is a response to a request from the USFS to develop a framework for technical decision making regarding management not just of water levels in Spirit Lake but also of coordinated management of water and sediment transport in the entire Spirit Lake and Toutle River system.
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The committee was also asked to identify alternatives for future management and to describe gaps in information needed to inform those decisions. The committee explored the state of the technical knowledge, the concerns of interested and affected parties, and the roles and interests of the USFS, the USACE, the USGS, and other entities with responsibilities for managing water and related land resources in the Spirit Lake and Toutle River region.
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The history of characterization, monitoring, and management associated with the Spirit Lake debris blockage and tunnel, other efforts to control outflow of water and deposits from the 1980 debris avalanche, and the risk of failure of the debris blockage will inform committee findings and recommendations. The committee will: • consider the adequacy of existing information and risk analyses for the area; • suggest additional information needed to support implementation of the decision framework; and • identify possible alternatives for long-term management of water levels and sediment transport in the Spirit Lake/Toutle River system.
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Brief biographies of the committee members can be found in Appendix A INSTITUTIONAL SETTING The USFS has responsibility for management of lands and water within the footprint of the Gifford Pinchot National Forest and the Mount St.
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Deci ions s made about control of water levels at Spirit Lake, for example, can have consequences for sediment management downstream, while decisions made regarding management of the SRS can have implications on the ecology of the region up- and downstream. Any decision made in the region may impact the responsibilities and concerns of federal, state, and local agencies; Native American Tribes; private-sector organizations; and individual citizens and citizen groups.
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From page 29... ...
Helens depending on where the earthquake originates. The specific consequences of a mega earthquake on the Spirit Lake and Toutle River region have not been quantified by investigators.
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For instance, interested and affected parties in the region have called for river restoration measures that would enhance recreational benefits and restore natural fish runs and wildlife habitat and populations. Concerns have also been raised about social and economic disruption resulting from increases in routine flooding along the Toutle and Cowlitz Rivers; the environmental and cultural effects of the sediments captured behind the SRS; flooding caused by continued channel infilling; and potential volcanic or seismic activity that may destabilize large quantities of water and sediment behind the SRS.
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DEFINING TERMS IN THE STATEMENT OF TASK Several terms in the committee's statement of task (see Box 1.1) may be d efined differently by interested and affected parties given their various perspectives.
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Their respective missions can be relatively limited in scope, resulting in the ad hoc management of infrastructural elements at Spirit Lake, the North Fork Toutle and Toutle Rivers, and downstream into the Cowlitz River. As already stated, however, few if any elements of the system are truly independent of other elements.
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With respect to sediment control, the planning area might be limited mostly to the North Fork Toutle River, or it may need to include the South Fork Toutle River and other tributaries. The extent of the system and region for any set of management decisions depends on the consequences of concern and varies depending on the decisions to be made.
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The committee attempted to hear from a wide array of interested and affected parties to determine the range of concerns and how they might affect the choice of a decision framework. The groups with whom the committee attempted to communicate during the conduct of this study are listed in Table 1.1.
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Forest Service; U.S. Geological Survey Tribal Agencies Cowlitz Indian Tribe; Yakama Nation State Agencies Washington Department of Archeology and Historical Preservation; Washington Department of Ecology; Washington Department of Fish and Wildlife; Washington Department of Natural Resources; Washington Department of Transportation; Washington State Governor's Office for Regulatory Innovation and Assistance; Washington State Parks and Recreation Commission Local Agencies Cowlitz County (Board of Commissioners, Emergency Management, Tourism)
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occurring within the planning period and the understanding that longer time frames are necessary for ecosystem regeneration. Many of the interested and affected parties who provided input to the committee expressed concern over what they perceived to be the overly short management time frames for structures like the SRS (discussed further in Chapters 5 and 6)
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The framework for decision making recommended by the committee assumes active collaboration and engagement among interested and affected parties so that both physical and sociopolitical considerations can be addressed fairly. During the conduct of its study, the committee found either that few new data have been collected and analyzed since initial hazard characterization efforts immediately following the 1980 eruption, or that such data and analyses could not be provided to the committee.
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Information Gathering The conclusions and recommendations in this report are based on the assess ent of publicly available information and data. The USFS, in col m laboration with the USACE and the USGS, provided a compendium of characterization and management data related to the Spirit Lake and Toutle River system.
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One day of the meeting included visits to points of interest in the Toutle River valley and the Monument, including the Johnston Ridge Observatory, the Spirit Lake tunnel outlet, the SRS, and one of the levees that was improved following the eruption. Scientific and technical experts from the USFS, the USACE, the USGS, and Centralia College in Chehalis, Washington, guided the visits.
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REPORT ORGANIZATION This report provides a technical foundation and organization process for decision making that draws on lessons from risk management decision processes established elsewhere. It is assumed that decisions made using the framework will be grounded in reliable data; that those data will be used in analytically rigorous models of the larger system and system interconnections; that the concerns of the multiple interested and affected parties will be recognized; and that preferred actions will be selected in consideration of the sources and levels of available funding.
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. Whereas Chapters 6-8 satisfy the requirement in the statement of task to recommend a decision framework, the committee identifies good practices throughout the report.
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