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CHAPTER 11. FLOOD <br />11-9 <br /> <br />Figure 11-3. Kittitas County Special Flood Hazard Areas <br />11.2.6 Frequency <br />Kittitas County experiences episodes of river flooding almost every winter. Large floods that can cause <br />property damage typically occur every 3 to 7 years. Urban portions of the county annually experience <br />nuisance flooding related to drainage issues. <br />11.2.7 Severity <br />The principal factors affecting flood damage are flood depth and velocity. The deeper and faster flood flows <br />become, the more damage they can cause. Shallow flooding with high velocities can cause as much damage <br />as deep flooding with slow velocity. This is especially true when a channel migrates over a broad floodplain, <br />redirecting high velocity flows and transporting debris and sediment. Flood severity is often evaluated by <br />examining peak discharges; Table 11-2 lists peak flows used by FEMA to map the floodplains of Kittitas <br />County. <br />Table 11-2. Summary of Peak Discharges within Kittitas County <br />Source/Location <br />Discharge (cubic feet/second) <br />10-Year 50-Year 100-Year 500-Year <br />Yakima River