Auburn, WA Environmental Rules: Flood Zones (2026)

Auburn participates in the National Flood Insurance Program (NFIP) and enforces FEMA Flood Insurance Rate Maps (FIRM) for King County and Pierce County and Incorporated Areas. Auburn has substantial mapped floodplain exposure: the Green River runs through the city center and carries a Zone AE designation along much of its corridor, with the Howard Hanson Dam upstream providing partial flood control but not eliminating Auburn's flood risk. The White River and tributaries such as Mill Creek and Bowman Creek also carry mapped floodplains. 68 flood hazard areas and related critical areas sections of ACC Title 16 regulate development in Special Flood Hazard Areas (Zones A and AE).

New construction and substantial improvements in the floodplain must have the lowest floor elevated at least one foot above the Base Flood Elevation (BFE); enclosures below BFE must be flood-vented with engineered openings to allow equalization. Fill, dumping, and placement of obstructions in the floodway are prohibited. Stream buffers under the Critical Areas Ordinance often extend 50 to 200 feet from the ordinary high water mark of the Green River and typically exceed the regulatory floodplain boundary. Flood insurance is federally required for structures in Zones A and AE with a federally backed mortgage, and homeowners should request an elevation certificate before permit submittal. gov.