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2025 Hazard Mitigation Plan Kittitas Gounty, Washington ,&/L*-rru=-*d\r !.rrr{!(oNr J change, the frequency of landslides in areas at risk is precipitation and wildfires (post-wildfire debris flows), expected to increase due to the impacts of extreme 172 The landslide annualized frequency value represents the average number of recorded landslide hazard occurrences in event days, per year over the period of record (11.8 years). Table 4-88 outlines the annualized frequency for landslides, based on FEMA NRI data, for Kittitas County. Table 4-88. Landslide Annualized Frequency (FEMA National Risk lndex) 4.6.6.5, Past Events There is little recorded information regarding landslides in Kittitas County. Between 1960 and 2023,there have been nine (9) significant landslide events in Kittitas County most of which have coincided with presidential disaster declarations for severe storms and flooding. The recorded events occurred on January 26,1965; December 18,1972; January 17,1997; January 9, 2009; October 11,2Q09; January 11,2011; November 12,2015; June 1,2018; and February 2020.173 Although there are no recorded fatalities in the County attributed to landslides, deaths have occurred across the west coast. The Oso Landslide of 2014 in Snohomish County, Washington provides context for the worst case scenario. This event caused 43 fatalities, destroyed 40 homes, and buried approximately one (1) mile of State Route 530. The landslide moved about 18 million tons of sand, till, and clay at an average speed of 40 miles per hour. 4.6.6.6. Vulnerability and lmpacts Life Safety and Health: ln the United States, landslides result in 25 to 50 deaths each year. Landslides can cause injuries and fatalities to anyone that gets trapped in a vehicle or structure during a landslide, either in transit or if they happen to be standing in the area when the landslide occurs. Buildings, roads, and other structures built on landslide prone slopes can collapse trapping people causing injury or death during a landslide incident. Additionally, landslides can block roads and pathways impacting access to emergency services potentially hindering evacuation efforts. 174 ln general, all of the population exposed to the higher risk landslide areas are considered to be vulnerable. As the population increases and many homes are built on property above or below bluffs and on steep slopes subject to mass movement, increases the number of lives endangered by this hazard. Property Damage and Critical Facilities: Landslides can severely damage or destroy homes, rendering them uninhabitable. Additionally, property value may decrease in landslide prone areas and the cost of repairs can be significant. Roads, bridges, and utility lines (e.9., power, communication, water, irrigation, and gas) are vulnerable and can be impacted by a landslide incident. Access to major roads is crucialto life safety and response operations after a disaster event and recovery operations. Landslides can block egress and ingress on roads, causing neighborhoods to become isolated, traffic problems, and delays tzz Washington State Emergency Management Division. (2023ll Washington State Enhanced Hazard Mitigation Plan. Retrieved from https://mil.wa.qov/asseV651ec296d76a9/2023_WA SEHMP finaL20231004.pdf. 173 Events prior to 2018 were obtained from the Spatial Hazard Events and Losses Database for the United States (SHELDUS) for the 2019 update of the Hazard Mitigation Plan. However, SHELDUS was not utilized the 2024 update and events that on or after 2018 were provided by the Kittitas County Public Works Department. 17a Centers for Disease Control and Prevenlion. (2024). Landslides and Mudslides and Your Safety. Retrieved from httos ://www.cdc.qov/land -mudslides/about/index.htm I 0.1 events per yearKittitas County 4 Annualized frequency is defined as the expected frequency or probability of a hazard occurrence per year Annualized FrequencyLocationEvents on Record 10-2021 Chapter 4: Hazard ldentification and Risk Assessment 146