2019_KittitasCountyHMP_Volume 1_For Adoption

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CHAPTER 7. AVALANCHE 7-7 over highways, catchment basins to stop avalanche flow, and diversion dams and berms to keep snow off highways. Avalanche control is important along Snoqualmie Pass. I-90 is a heavily traveled corridors that connects major Puget Sound communities to Eastern Washington through the Cascade Mountains. Snoqualmie Pass is the state’s only Interstate highway link through the Cascades. It averages nearly 450 inches of snow each winter and has a daily traffic volume of 32,000 vehicles (including 8,000 trucks). A two-hour closure of the pass costs the state’s economy more than $1 million. WSDOT also identifies Blewett Pass on US 97 as being at risk to avalanche. 7.5.4 Environment Avalanches are a natural event, but they can negatively affect the environment. This includes trees located on steep slopes. A large avalanche can knock down many trees and kill the wildlife that lives in them. In spring, this loss of vegetation on the mountains may weaken the soil, causing landslides and mudflows. 7.6. VULNERABILITY In general, everything that is exposed to an avalanche event is vulnerable. More and more people are working and building in or using the high mountain areas of the Cascades in potential avalanche areas. These individuals often have little experience with, caution regarding, or preparation for, avalanche conditions. The increasing development of recreational sites in the mountains brings added exposure to the people using these sites and the access routes to them. The risk to human life is especially great at times of the year when rapid warming follows heavy, wet snowfall. 7.7. FUTURE TRENDS IN DEVELOPMENT Future trends in development cannot be determined until the avalanche hazard areas are accurately mapped. From review of the buildable lands analysis, which projects the location and density of development based on current land use regulations, there is no significant housing or employment capacity that has the potential to be developed in these areas. 7.8. SCENARIO In a worst-case scenario, an avalanche would occur in the Cascade Mountains after a series of storms. Storms starting with low temperatures and dry snow, followed by rising temperatures and wetter snow, are most likely to cause avalanches. Avalanches occurring in the Snoqualmie Pass vicinity, causing prolonged closure of Interstate 90, would have significant economic impact not only on Kittitas county, but also on all counties along the I-90 corridor. 7.9. ISSUES The only issue of concern in the event of an avalanche is the threat to recreational users and property. The U.S. Forest Service, National Park Service, National Weather Service and Washington Department of Transportation currently have programs to monitor avalanche zones and forecast avalanche danger. However, there is no effective way to keep the public out of avalanche -prone areas, even during times of highest risk. A coordinated effort is needed among state, county and local law enforcement, fire, emergency management, public works agencies and media to provide winter snow pack and avalanche risk information to the public. A national program to rate avalanche risk has been developed to standardize terminology and provide a common basis for recognizing and describing hazardous conditions. This United States Avalanche Danger