Regulatory Floodplain

The regulatory floodplain is the one that governs what you may build, and it is set by the local floodplain administrator — not necessarily by FEMA. Jurisdictions may adopt more current rainfall data, model fully-developed watershed conditions rather than existing conditions, or add creek buffers and water-quality zones on top. Each of those makes the regulated area larger than the federal map. Because FEMA maps are updated on their own cycle, the two can diverge for years. The only reliable check is with the local floodplain administrator for the specific parcel.