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2025 Hazard Mitigation Plan <br />Kittitas County, Washington <br /> <br /> <br />Chapter 4: Hazard Identification and Risk Assessment 126 <br />FIRM maps.152F <br />152 The 500-year floodplains show areas with a 0.2% chance of flooding each year. The <br />Kittitas County FIRMs initially became effective on May 5, 1981, and the current FIRMs became effective <br />on September 24, 2021. Figure 4-15 illustrates the Kittitas County SFHA, including each Flood Zone, <br />and the 500-year floodplain <br />Figure 4-15. Kittitas County Special Flood Hazard Area <br /> <br />4.6.5.3. Hazard Extent/Intensity <br />Flood depth and velocity are the primary factors affecting flood extent/intensity. The deeper and faster <br />floods flow the more damage they can cause. However, shallow flooding with high velocities can cause <br />as much damage as deep flooding with slow velocity. This is especially true when a channel migrates <br />over a broad floodplain, redirecting high velocity flows and transporting debris and sediment. Flood <br />extent/intensity is often evaluated by examining peak discharges. Table 4-64 lists the peak flows utilized <br />by FEMA to map Kittitas County’s floodplains.153F <br />153 <br /> <br /> <br />152 Ibid. <br />153 Kittitas County. (1996). Comprehensive Flood Hazard Management Plan. Retrieved from <br />https://www.co.kittitas.wa.us/uploads/documents/public- <br />works/flood/documents/1996%20Kittitas%20County%20Comprehensive%20Flood%20Hazard%20Management% <br />20Plan.pdf.