Flood · Glossary
Floodplain
Updated 2026-07-18
Floodplain is land adjacent to or influenced by a watercourse or other flood source that can be inundated. In California, FEMA maps are important but local flood-control agencies, DWR data, and site drainage studies may identify additional hazards.
What it means
A floodplain can include channels, overbank areas, alluvial fans, coastal areas, and shallow-flow paths. Its extent depends on the flood probability being evaluated.
Why it matters for land decisions
Floodplain conditions can reduce buildable area and affect grading, access, utilities, and habitat review.
- Check federal and local mapping.
- Review actual site topography.
People also ask
Is every floodplain mapped by FEMA?
No. Small drainage features, changing conditions, and areas without detailed studies may be unmapped.
Who regulates floodplain development?
Cities and counties commonly administer adopted floodplain ordinances, with state and federal agencies involved in specific settings.
Official sources
Related terms
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