County Ordinance 458 regulates three types of floodplains within Unincorporated Riverside County
Current Zone Designations (as of August 28, 2018)
||Approximate 1%-annual chance floodplain. No base flood elevations [BFE]
|AE, without floodway -
||1%-annual chance floodplain based on a detailed study. Base flood elevations are provided and can be found on the Flood Insurance Rate Map [FIRM] and the Flood Insurance Study [FIS] profiles.
|AE, with floodway -
||Same as AE but the floodplain is separated into two regions: floodplain fringe and floodway. Development is allowed within a 1%-annual chance floodplain but new development creates obstruction to flood flows that raise the water surface elevation. To limit this surcharge to 1.0-foot, a “floodway” is designated which restricts development to only the areas outside of the floodway [i.e. floodplain fringe, see Figure 1].
||Areas of shallow 1%-annual chance flooding [1 to 3 feet depth]. This is a detailed floodplain depicting sheet flow on sloping terrain. Instead of a base flood elevation, average depths within the floodplain as shown on the Flood Insurance Rate Map. For areas of alluvial fan flooding, velocities are also provided.
||Areas of shallow 1%-annual chance flooding [1 to 3 feet depth]. This is a detailed floodplain depicting areas of ponding. Base flood elevations are provided on the Flood Insurance Rate Map.
|Shaded X -
||Represents 1 of 3 things:
- 0.2%-annual chance floodplain
- 1%-annual chance floodplain with average depth < 1 foot or having a drainage area less than 1 square mile
- Areas protected by levees from the 1%-annual chance flood
|Unshaded X -
||Areas outside of 0.2%-annual chance floodplain
||Areas that have not been studied by FEMA. Flood hazards are undetermined but possible.