City of Irvine
2020 Local Hazard Mitigation Plan
Table 3-10: FEMA Flood Plain Categories 62
Category
Description
A
Within a 100-year flood plain, but the water height of the 100-year flood is not known Within a 100-year flood plain and the water height of the 100-year flood is known Within a 100-year flood plain, and the water height of the 100-year flood is between one and three feet but not specifically known Within a 100-year flood plain, protected by flood protection infrastructure such as dams or levees Within a 100-year flood plain, and the water height of the 100-year flood is between one and three feet and is specifically known Within a 100-year flood plain, protected by flood protection infrastructure that is not currently effective, but is being rebuilt to provide protection Within a 100-year flood plain for coastal floods, but the water height of the flood is not known Within a 100-year flood plain for coastal floods and the water height of the flood is known Within a 100-year flood plain for shallow coastal floods with a height between one and three feet. Within a 500-year flood plain, or within a 100-year flood plain with a water height less than one foot (found on older maps)
A1-30 or AE
AO
A99
AH
AR
V
V1-30 or VE
VO
B
C X
Outside of the 500-year flood plain (found on older maps) Outside of the 500-year flood plain (found on newer maps)
Within a 500-year flood plain, or within a 100-year flood plain with a water height less than one foot (found on newer maps)
X500
D
Within an area with a potential and undetermined flood hazard Within an area at risk of mudslides from a 100-year flood event Within an area at risk of mudslides from a 500-year flood event
M
N
P E
Within an area at risk of mudslides from a potential and undetermined flood event
Within an area at risk of erosion from a 100-year flood event
In Irvine, the 100-year and 500-year floodplains are not contiguous areas but consist instead of various pockets across the city. Most of these areas fall within the major drainages within the City, which include:
San Diego Creek Serrano Creek
•
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Borrego Canyon Wash Agua Chinon Wash Bee Canyon Wash Peters Canyon Wash Sand Canyon Wash
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•
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Figure 3-4 shows the mapped flood hazard zones for 100-year and 500-year flood events in Irvine. This map also depicts the 1-meter sea level rise data, which suggests that sea-level rise may affect drainage along San Diego Creek. To prevent potential flooding, Irvine has more than a dozen detention or retarding basins, generally located on, or adjacent to drainages within the City. The use of these facilities is intended to reduce downstream erosion by storing water for a limited period. These strategies can also assist with dam inundation impacts. Floodplain mapping studies are provided by the National Flood Insurance Program. Irvine participates in the program by adopting FEMA-approved floodplain studies, maps, and regulations. These studies may be funded through federal grants; state, city, and regional agencies; and private parties. The program is designed for flood insurance and floodplain management applications.
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