Laserfiche WebLink
CHAPTER 12. LANDSLIDE <br />12-2 <br />• The presence of impermeable soils, such as silt or clay, which are mixed with granular soils <br />such as sand and gravel <br />Flows and slides are commonly categorized by the form of initial ground failure. Figure 12-1 through Figure <br />12-4 show common types of slides. The most common is the shallow colluvial slide, occurring particularly <br />in response to intense, short-duration storms. The largest and most destructive are deep-seated slides, <br />although they are less common than other types. <br /> <br />Figure 12-1. Deep Seated Slide Figure 12-2. Shallow Colluvial Slide <br /> <br />Figure 12-3. Bench Slide Figure 12-4. Large Slide <br />Slides and earth flows can pose serious hazard to property in hillside terrain. They tend to move slowly and <br />thus rarely threaten life directly. When they move—in response to such changes as increased water content, <br />earthquake shaking, addition of load, or removal of downslope support—they deform and tilt the ground <br />surface. The result can be destruction of foundations, offset of roads, breaking of underground pipes, or <br />overriding of downslope property and structures. <br />12.2.1 Past Events <br />There is little recorded information regarding landslides in Kittitas County. According to the Spatial Hazard <br />Events and Losses Database for the United States (SHELDUS), there have been four recorded landslide <br />events in Kittitas County since 1960. These events occurred on January 26, 1965, December 18, 1972, and <br />October 11, 2009. All of these events coincided with presidential disaster declarations for severe storms <br />and flooding. The combined estimated damage for these events amounts to $15 million. In addition, while <br />not recorded in the SHELDUS database, there were disaster declarations for Kittitas County that included <br />landslide events on January 17, 1997, January 6, 2009, January 11, 2011, and November 12, 2015. There