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City of Santa Ana Emergency Operations Plan <br />Part I Basic Plan <br />Identification of Flood -Prone Areas <br />Flood maps and Flood Insurance Studies (FIS) are often used to identify flood -prone areas. The National Flood <br />Insurance Program (NFIP) was established in 1968 to provide flood insurance to the nation's flood -prone <br />communities. A Flood Insurance Rate Map (FIRM) is the official map produced by FEMA delineating Special <br />Flood Hazard Areas (SFHA) in communities where NFIP regulations apply, and these provide assessments of the <br />probability of flooding in a specific location. FIRMS are developed by combining water surface elevations with <br />topographic data. Information derived through this process illustrates areas with the potential for inundation during <br />a 100-year or 500-year flood. <br />100-Year/500 Year Floods <br />A 100-year flooding event is a flood having a 1 % chance of being equaled or exceeded in magnitude in any given <br />year. Contrary to popular belief, it is not a flood occurring once every 100 years. Similarly, a 500-year flood is a <br />larger flood having a 0.2 % chance of occurring in any given year. The 100-year or 500-year floodplain is the area <br />adjoining a river, stream, or watercourse covered by water in the event of a 100-year or 500-year flood. The <br />Figures below illustrate these floodplains in Orange County and the City. <br />Figure 71: 100-Year and 500 Year Floodplains in Orange County <br />71 <br />