La Conchita Landslide Risk Assessment
Abstract
Following the disastrous landslide in La Conchita in 2005 that resulted in ten deaths, the State of California selected our team to prepare a risk assessment for a committee of key stakeholders. The stakeholders represented the State of California, Ventura County, members of the La Conchita community, the railroad, and the upslope ranch owner (where the slide originated); a group with widely varying views and interests. Our team was charged with characterizing the major hazards, developing a series of mitigation concepts, evaluating the benefits and costs of mitigation, and gathering stakeholder input throughout the process. Two unique elements of the study were the methodologies utilized for the consequence assessment and for the decision-making framework. La Conchita is exposed to multiple slope hazards, each with differing geographical distributions, as well as depth and velocity characteristics. Three consequence matrices were developed so that the potential financial losses, structural vulnerabilities, and human safety exposure could be evaluated. The matrices utilized semi-quantitative loss evaluations (both financial and life safety) based on a generalized understanding of likely vulnerability and hazard characteristics. The model provided a quantitative estimate of cumulative losses over a 50-year period, including losses of life based on FEMA evaluation criteria. Conceptual mitigation options and loss estimates were developed to provide a range of risk management solutions that were feasible from a cost-benefit standpoint. A decision tree approach was adopted to focus on fundamental risk management questions rather than on specific outcomes since the committee did not have a consensus view on the preferred solution. These questions included: 1. Over what time period can risks be tolerated before implementation of decisions? 2. Whose responsibility is it to identify a workable risk management solution? 3. Who will own the project? The decision tree developed for assessment can also be used in the reverse direction to evaluate a project impasse or to evaluate owners and time-frames associated with a particular risk management outcome. Although the processes developed were specific to the La Conchita study, we believe that they are applicable elsewhere for localized multi-hazard assessments and/or committee-led risk management efforts.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMNH41C1246K
- Keywords:
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- 9800 GENERAL OR MISCELLANEOUS