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<br />002863 <br /> <br />8.0 THREE CASE HISTORIES OF LANDSLIDING IN COLORADO <br /> <br />Introduction <br /> <br />Basis for selection of case studies: The three case studies presented in the <br />Colorado Landslide Mitigation Plan were selected to depict a wide range of <br />potential consequences, probability of occurrence, and amenability to <br />mitigation planning and follow-up measures. <br /> <br />Case study number one is the Dowds Junction Slide Complex of Eagle County: <br />This is a very large old slide area with an ongoing modern history of small <br />but costly and inconvenient slide activity at its toe in the Eagle River <br />Valley. Special interest in this as a case study derives from: 1) It <br />exemplifies the worldwide problem of evaluating the probability and potential <br />consequences of major reactivation of extremely large old slide masses. The <br />real need for this type of analysis and contingency planning was heightened by <br />the Thistle, Utah landslide disaster in 1983, and subsequently by the East <br />Muddy Creek landslides of 1986, in Colorado. 2) Even preliminary analyses of <br />the potential consequences of valley-blocking slides at this location <br />indicated immense potential damage and disruption to both infrastructure and <br />private property. 3) The fact that the State of Colorado declared a Landslide <br />Alert at this location in 1985, and as a result, state and local agencies <br />conducted extensive geologic investigations, monitoring and emergency <br />exercises. <br /> <br />Case study number two is the Glenwood Springs area of Garfield County: This <br />is one of Colorado's older communities that has been affected by debris flows <br />throughout its history. Both significant parts of existing development and <br />otherwise attractive potential growth areas are subject to the debris-flow <br />hazard. It was considered a good case study because: 1) It typifies the <br />debris-flow hazard in Colorado that affects dozens of our mountain <br />communities. 2) The area has been subject to successively more detailed <br />hazard studies by the Colorado Geological Survey in cooperation with the town <br />and Garfield County over the past fourteen years. 3) The excellent <br />information base and relative predictability of hazard zones makes a variety <br />of mitigation efforts an attractive possibility. <br /> <br />- 78 - <br />