City of Irvine
2020 Local Hazard Mitigation Plan
Figure 3-4: FEMA Flood Zones
Past Events
Southern California is a semiarid region with inconsistent storm seasons and naturally shallow river channels. It was historically prone to floods that affected the entire region after long periods of rain. The largest flood in the Southern California region was in 1938, when several inches of rain fell over three days, causing rivers across the region to overflow. The Santa Ana River overflowed, flooding areas in Fullerton and Anaheim. The Fullerton and Brea dams were constructed in the aftermath of this flood, with money from the Works Progress Administration. Widespread flood-caused destruction across Southern California led numerous local governments to pursue a campaign of concretizing riverbeds, including rivers and creeks in Orange County, to prevent erosion. The following is a list of recorded flood events in Orange County: 63,64,65 • Between December 1861 to January 1862, a 30-day-long period of rain called the “Noachian Deluge of California” poured across all of California. The Santa Ana River overflowed and spread across all the low-lying areas of Orange County between Anaheim and the Coyote Hills (present- day Fullerton) in a four-foot-deep sea. Twenty deaths were recorded in Orange County alone.
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