Partnerships for Reducing Landslide Risk Assessment of the National Landslide Hazards Mitigation Strategy (2004) / Chapter Skim
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1 Introduction
1 Introduction
Pages 6-25
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From page 6... ...
In this report, the term "landslide" will include all types of gravitycaused mass movements, ranging from rock falls, through a variety of slumps and slides, to debris flows. Both subaerial and submarine mass movements are included.
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However, impetus for an increased emphasis on this program was provided by the House Report accompanying the Department of the Interior Appropriations Bill for FY 2000, which directed the USGS to develop a comprehensive strategy to address the hazards posed by landslides. During 1999-2000 the USGS convened a series of workshops and meetings to plan and develop a national strategy, resulting in the compilation of USGS Open-File Report 00-450, National Landslide Hazards Mitigation Strategy A Framework for Loss Reduction (Spiker and Gori, 2000~.~ This report proposed a national strategy based on partnerships between the USGS as the responsible federal agency and an array of federal, state, local, community, and industry partners.
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The committee has reviewed the National Landslide Hazards Mitigation Strategy (Spiker and Gori, 2000) and agrees that the nine major components identified in the proposed national strategy, ranging from basic research activities to improved public policy measures and enhanced mitigation, are the essential elements required to address the hazards arising from landslides at a national level.
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However, the wide variation in the nature and extent of existing state and local agency activities means that these are treated in a more generic sense when compared with federal agencies, where the committee was able to evaluate current activities on a nationwide basis and suggest specific roles in a future national partnership strategy. One issue that the committee grappled with was the extent to which other non-landslide ground failure hazard mitigation should or could be addressed in this assessment.
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Direct costs can be defined as the costs of replacement, rebuilding, repair, or maintenance resulting from direct landslide-caused damage and destruction of property or installations (Schuster and Fleming, 1986; Schuster, 1996; Schuster and Highland, 2001~. All other costs of landslides are indirect, for example: · reduced real estate values in areas threatened by landslides; · loss of tax revenues on properties devalued as a result of landslides; · loss of industrial, agricultural, and forest productivity, and of tourist revenues, as a result of damage to land or facilities or interruption of transportation systems;
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From page 11... ...
Nevertheless, the survey may have underestimated these costs because many state transportation departments do not maintain detailed records of their landsliderelated highway maintenance costs. Indirect public costs are diverse and include such disparate elements as loss of tax revenues, reduced capacity or capability of lifelines, reduced productivity of government forests, and impacts on the quality of sport fisheries.
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From page 12... ...
, which, in combination with a local debris flow, destroyed or badly damaged 11-12 homes in the small town of La Conchita (O'Tousa, 1995~. In the late winter and early spring of 1998, heavy rainfall again caused major landslide activity and damage totaling approximately $156 million in the 10-county San Francisco Bay region (Godt and Savage, 1999~.
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INTRODUCTION 13 Although landslides are common throughout the Appalachian region and New England, the greatest landslide hazard in the eastern United States, at least in terms of financial losses within a fairly restricted area, is from landslides affecting clay-rich soils in Pittsburgh, Pennsylvania, and Cincinnati, Ohio (see Box 1.3~. Landslides also occur across the Great Plains and into the mountain areas of the western United States, where weathered shales and other clay-rich rocks occur near the surface, and they are particularly common where there are steep slopes, periodic heavy rains, and vegetation loss following wildfires.
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4 PARTNERSHIPS FOR REDUCING LANDSLIDE RISK FIGURE 1.1 The 1995 La Conchita landslide, southern California. SOURCE: Schuster and Highland (2001)
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Hurricane Camille in 1969 caused extensive debris flows in central Virginia although the exact number cannot be ascertained; most of the 150 who died as a result of Hurricane Camille are thought to have been victims of debris flows triggered by heavy rains associated with the hurricane (Williams and Guy, 1973~. In October 1985, heavy rain in Puerto Rico from Tropical Storm Isabel caused a major rock slide that obliterated much of the Mameyes district of the city of Ponce.
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found that 81% of sediment transported within the Mameyes River basin was contributed by mass wasting. An equally important aspect is that sediment levels may remain high for decades following major landslide events, increasing flood risks for downstream communities and threatening efforts to restore fisheries and aquatic ecosystems (e.g., Madej,1995~.
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No standards have been established in the United States, and maps vary widely in their detail and accuracy and, consequently, their usefulness. It is important that not only should landslide occurrence or relative slope stability be established for an area, but also the sediment and wood production associated with landslides should be estimated, because sediment and woody debris strongly influence aquatic habitats.
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Although mitigation options could include this type of financial arrangement to pool the exposure of individuals to landslide hazards and to compensate for losses, such mechanisms have not been widely applied in the United States and there seem to be considerable obstacles to providing a broadly based national landslide insurance program (see section 5.2~. As a consequence, the mitigation of landslide hazards for many existing developments and transportation networks is accomplished by using a variety of monitoring and warning systems which protect lives and property but do not prevent landslides or by resorting to expensive engineering stabilization solutions.
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1.6 OVERVIEW OF NATIONAL STRATEGY PRIORITIES Landslides are widely distributed geographically and pose differing types of hazards depending on geologic setting and terrain type. The diversity of landslide problems, and the breadth of the needed elements of a national landslide hazard reduction program, can be illustrated by examples: · Debris flows triggered by extreme rainfall events have had devastating effects in mountainous regions of the United States, and there are indications that differences in climate, materials, vegetation, and topography may cause a variety of debris flow phenomena in different regions.
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From page 22... ...
The matrix presented in Figure 1.3 evaluates the six broad landslide types2 against five activities that should be included in an effective national strategy to address the diversity of landslide hazard problems: 1. Improvement of the science base to provide an adequate understanding of landslide triggering and landslide movement mechanisms is an essential first step to fill gaps in current understanding and is a fundamental requirement for other activities.
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Once initial movement has occurred, bedrock slides can be identified with current technology and there is high payoff potential associated with mapping them in areas of high risk in order to assist regulation. Improved mitigation methods and the establishment of appropriate risk assessment techniques are needed.
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The elements of a national landslides hazards mitigation strategy are dealt with in more detail in the following chapters; Chapter 2 describes requirements and priorities for research into landslide processes; Chapter 3 describes the status of mapping and monitoring techniques and their application; Chapter 4 describes the importance of loss and risk assessment; Chapters 5 and 6 describe the technology transfer and integration components of a national mitigation strategy; and Chapters 7 and 8 describe the partnerships and funding that will be required for implementation of an effective national strategy. Chapter 9 contains the committee's conclusions and recommendations.
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Key Terms
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