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2025 Hazard Mitigation Plan <br />Kittitas County, Washington <br />4.6.2.4. Probability and Frequency <br />Dam failure has a low probability of occurrence (a significant occurrence of this hazard is likely to occur <br />within 100 years) and usually coincides with events that cause them (e.9., eafthquakes, landslides, <br />excessive rain, and snowmelt). Between 1950 and 2023, there have been three (3) Federal disaster <br />declarations due to dam failure in the United States, none of which have occurred in the State of <br />Washington.e2 However, dam safety incidents, which are less severe than dam failures, have occurred. <br />Like dams, levee failures have a low probability of occurrence (a significant occurrence of this hazard is <br />likely to occur within 100 years) and usually coincide with events that cause them (e.9., earthquakes and <br />heavy rainfall). Between 1950 and 2023, there has been one (1) Federal disaster declarations due to a <br />levee failure in the United States.,e3 <br />4.6.2.5. Pasf Events <br />According to DSO records, 19 notable dam failure events occurred in the State of Washington between <br />1918 and 2023. None of these occurred within or impacted Kittitas County and to date, Kittitas County <br />has not had a Presidentially Declared Disaster caused by dam or levee failure..ea <br />4.6.2.6. Vulnerability and lmpacts <br />Life Safety and Health: Dam and levee failures can lead to loss of life or injury to individuals in the <br />immediate downstream area, property damage, and disruption of essential services (e.9., power, water <br />supply, transportation). The potential for loss of life is affected by the capacity and number of evacuation <br />routes available to those living in potential inundation areas. The vulnerable populations include everyone <br />who is downstream from dam and levee failures. <br />Property Damage and Critical lnfrastructure: Vulnerable properties are those closest to the dam and <br />levee inundation areas. These properties would experience the largest, most destructive surge of water. <br />Low-lying areas are also vulnerable since they are where the dam and levee waters would accumulate. <br />Transportation routes (e.9., roads, bridges, railroads) are vulnerable and have the potential to be <br />destroyed, creating isolation issues within the community. Transportation infrastructure most vulnerable <br />to dam and levee failure are those that are already in poor condition and would not be able to withstand <br />a large water surge. Additionally, overhead power lines, cable and phone lines could be vulnerable, and <br />loss of these utilities could create additional isolation issues for the inundation areas. <br />Economy: Kittitas County's economy can be affected by a dam failure due to loss of homes, businesses, <br />and infrastructure (e.9., transportation infrastructure, irrigation facilities). A dam or levee failure that is <br />significant enough to impact Kittitas County may cause high impact (greater than $10 Million) on the local <br />economy based on loss of business revenue, crops, worker wages, and local tax revenues or in the <br />impact on local GDP. <br />Changes in Development and lmpact of Future Development: Changes in development have <br />minim-ally increased (4% or less) the vulnerability of Kittitas County to dam and levee failures. Future <br />development may minimally increase (4% or less) the impact of dam and levee failures within Kittitas <br />County. <br />e2 Federal Emergency Management Agency. (n.d.). Declared Disasters. Retrieved from <br />https ://www.fema. qov/d isaste r/decla rations. <br />e3 lbid. <br />ea State of Washington Department of Ecology. (2019). Washington State Notable Dam Failures and lncidents <br />Retrieved from https://appswr.ecoloqv.wa.qov/docs/WaterRiqhts/wrwebpdf/damfailure-ws.pdf. <br />Chapter 4: Hazard ldentification and Risk Assessment 92