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Floodplain Information

Are you in a Floodplain?

View our GIS Floodplain Viewer map to see current designated floodplains within Riverside County.

Regulated Floodplains

Within unincorporated Riverside County, County Ordinance No. 458 regulates three types of Special Flood Hazard Areas (SFHA): FEMA, DWR Awareness Maps and Special Studies. Floodplain Delineation studies identify land areas (floodplains) subject to inundation by a flood that has a one-percent probability of being equaled or exceeded in any given year, also known as a 100-year flood. Any development in a regulated flood hazard area (floodplain) must meet the requirements of local, state and federal regulations.

Unidentified Floodplains

It is important to understand that floodplains and flood hazards exist in areas that have not yet been documented by a Floodplain Delineation Study. Although your property may not have been in a floodplain when you moved in, that could change in the future. Your area may not have been studied yet, or the floodplain limits might be modified because of changes that occurred during flooding events, or development in the area caused some change. Updated topographic mapping may result in a revision of the floodplain limits.

Revise a Floodplain

As part of the development process, a project may be conditioned to revise a floodplain. For FEMA floodplains, a Conditional Letter of Map Revision (CLOMR) and Letter of Map Revision (LOMR) is required to revise the Flood Insurance Rate Map (FIRM). MT-2 Application Forms, fees and supporting engineering data are required for a CLOMR/LOMR package. For other Ordinance No. 458 SFHA (non-FEMA) revisions, supporting engineering data for the pre-development and post-development SFHA limits will be processed through the District to update the limits reflected on the GIS Floodplain Viewer Map.