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2 Research Priorities in Landslide Science A [though the Disaster Relief Act of 1974 (now the Robert T. Stafford Disaster Relief and Emergency Assistance Act the Stafford Act) delegates the responsibility to issue disaster warnings for land- slides to the Director of the U.S. Geological Survey (USGS), it is important to appreciate that this is neither an easy nor a routine task. Some landslide events are widespread, whereas others are local. Some occur suddenly, while others develop slowly over time. Many landslides are triggered by ground saturation caused by intense storms, spring snowmelt, or irriga- tion and other human disturbance of surface or subsurface drainage systems. Others are triggered by earthquakes and volcanoes, and still others appear to occur for no obvious reasons. Therefore, an understand- ing of landslide processes the science of landslides is an essential requirement both for issuing warnings and for undertaking the host of other mitigation activities ranging from land-use planning to the construc- tion of engineered solutions. The National Landslide Hazards Mitigation Strategy (Spiker and Gori, 2000) proposes that the USGS should lead a research program directed at developing a predictive understanding of landslide processes and trigger- ing mechanisms. The strategic objective of such a research program would be the following: Develop a research agenda and an implementation plan to improve understanding of landslide processes, thresholds, and triggers and to improve the ability to predict landslide hazard behavior. 26

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RESEARCH PRIORITIES IN LANDSLIDE SCIENCE 27 Develop improved scientific models of ground deformation and slope failure processes that could be implemented in predicting landslide hazards. Develop predictive systems capable of interactively displaying changing landslide hazards in both space and time in areas prone to dif- ferent types of hazard-triggering mechanisms, such as severe storms and earthquakes. The committee concurs that an expanded research effort that would contribute to an improved understanding of landslide processes and their triggering is an essential component of a national landslide hazards miti- gation program. However, such research activities should be prioritized to address those areas of landslide science with the highest payoff poten- tial namely, debris flow, bedrock slide, and submarine landslide mecha- nisms (as outlined in section 1.6~. This chapter focuses on the strategic research objectives presented in the proposal and an assessment of the role and efficacy of such research in landslide hazard mitigation. Reliable landslide warnings and effective mitigation must be under- pinned by an understanding of the mechanics of landslide processes. For any potential landslide situation, this implies finding answers to the following questions: How would the landslide be initiated? What are the warning signs? How large will it be? How far will it move? How fast will it move? Answers to the preceding questions will vary with landslide type and with the nature of the material composing the slide mass. A single rock landing on a highway may cause dire results, and a small, fast-moving landslide in a high-population-density area may pose a greater threat to public safety than a large, slow-moving slide. In Hong Kong, slides with volumes as low as 200m3 have caused fatalities (Works Bureau, 1998~. The diversity of landslide problems was emphasized in the matrix presented in Figure 1.3, showing those activities that have a high payoff potential within the next five years. In addition, although many aspects of landslide process mechanics are well understood for many landslide types, the understanding of slide mobility the mass and speed of earth movements is inadequate to support hazard warnings and other means of mitigation for all landslide types. The scientific research program for a national landslide hazards mitigation strategy should include investigat- ing models of ground deformation, slope failure processes, landslide

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28 PARTNERSHIPS FOR REDUCING LANDSLIDE RISK triggering, and prediction. Basic science activities should be directed toward answering a series of questions: 1. Debris Flows: Often triggered by extreme rainfall events, debris flows have had devastating effects in mountainous regions. How are they initiated? How can runout characteristics be established? What controls their magnitude-frequency relationships and return periods? 2. Bedrock Slides: A large part of the United States is underlain by weak bedrock in which ancient and current landslides are found. What factors control the distribution of bedrock slides? How do they respond to climatic events? What controls their velocity? How safe should a stable slide be to support development? 3. Submarine Slides: The national strategy for landslide hazard mitiga- tion should extend to the offshore, recognizing the special problems- particularly the difficulties involved with surface and subsurface sam- pling and in situ geotechnical measurement associated with submarine landslides. How can they be effectively mapped? What is the role of gas hydrates in slope instability? How can their geotechnical characteristics be assessed? How can geotechnical characteristics be translated into risk assess- ments? To answer these questions, a comprehensive research program should be designed to produce improvements in the following: in situ characterization, laboratory characterization, advances in formulating geomechanical and geohydrological models, advances in kinematic modeling, and field studies at sites to facilitate in situ characterization and model validation. Many important questions related to landslide processes can be addressed only by a scientific research program based at a number of

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RESEARCH PRIORITIES IN LANDSLIDE SCIENCE 29 long-term field sites around the nation, selected for their generic interest and their capacity to yield important results. These problems would range from material characterization, to pore pressure response studies, to geomechanical analyses, to large deformation evaluation, according to the specific priorities for landslide type and geological environment. The selection of field sites and the development of site-specific programs should be based on partnerships between the USGS and other federal or state agencies. Specific activities at a given site could be undertaken by the private sector as well as by public agencies, which will facilitate tech- nology transfer. Although priority should be given to debris flow and weak bedrock slide field sites, and to submarine slide sites where possible, other types of slides should not be excluded if a suitable opportunity is available. In the past, landslide activities within the USGS have focused primarily on field-based hazard mapping and assessment. Although mechanistic studies have not been a dominant part of the USGS program, the development of a debris flow flume and related studies into the funda- mentals of debris flow mechanics (Iverson, 1997) is an important exception. In developing a research program, it is important to realize that research into landslide mechanisms by or on behalf of federal agencies has not been the prerogative of the USGS alone. Different agencies bring different skills and experience to address the research agenda: In the past, the U.S. Army Corps of Engineers (USAGE) conducted extensive research into landslides in clay-shale slopes, particularly when the USACE was closely involved with operation of the Panama Canal (Lutton et al., 1979) and during the construction, operation, and mainte- nance of major dams on the Missouri River (e.g., USACE, 1983, 1998~. In addition, the USACE has both conducted and supported research into seismically induced liquefaction. Although landslide-related research within the USACE is currently at a low level, experimental facilities and experienced personnel exist within laboratories and district offices of that . . Orgamzatlon. Although current expenditures directed toward landslide issues are modest, research into landslide mechanisms has been conducted at universities for many decades, mainly in departments of civil engineering but also within geological engineering and engineering geology programs. Almost all theoretical methods of slope stability analysis have emerged from university-based research. Demonstration projects and technology synthesis related to land- slide hazard assessment and mitigation have also been supported by the Federal Highway Administration, often in partnership with state depart- ments of transportation. The focus on user needs has been both appropriate and effective. This effort has been directed to a large degree at problems

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30 PARTNERSHIPS FOR REDUCING LANDSLIDE RISK of rock fall and small slides, where the basic scientific understanding is generally adequate. However, there are also situations in which large slides threaten or impact transportation corridors, but because of restricted legislative mandates, the authorities are unable to assess the full range of regional considerations. The U.S. Forest Service supports research stations in the Pacific Northwest that have been important in documenting the relationships between timber management practices and slope instability and the influ- ences of landslides on rivers and river ecosystems. It has been the lead agency in establishing the role of root strength in controlling shallow soil stability. Although the USGS undoubtedly is a major stakeholder in influencing this agenda and in conducting some of the research, the diversity of skills and perspectives of other stakeholders (federal and state agencies, uni- versities, private sector) should be recognized as an asset and incorpo- rated into the national research program at the outset. In particular, the intrinsic value of merit-based competitive selection of research projects, as implemented by the National Science Foundation, should be emphasized as an effective means of conducting such research. Although research into the science of landslide processes, in accordance with the priorities based on payoff potential outlined here, should be undertaken as an important component of a comprehensive national landslide hazards mitigation strategy, the committee emphasizes that such research should be carried out in concert with other critically important research activities into new technologies for mapping and monitoring; new mitigation approaches; the intermixed physical science and social science issues related to public awareness, understanding, and professional education and capacity build- ing; and particularly, the application of risk analysis techniques to guide mitigation decisions described in the following chapters.