2020 Local Hazard Mitigation Plan

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

Borrego Canyon Wash Agua Chinon Wash Bee Canyon Wash Peters Canyon Wash Sand Canyon Wash

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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