Benton County, OR Environmental Rules: Flood Elevation Requirements (2026)

Benton County defines Base Flood Elevation at BCC 51.020(5) as the height of the flood waters during a base flood at points along the water course, expressed in feet above mean sea level, the datum used throughout Chapter 83, the Floodplain Management Overlay Zone (/FP), which the Board of Commissioners adopted under the statutory authority of ORS 203.035. BCC 83.620(1) sets the county's freeboard standard for residential construction: new construction, conversion, and substantial improvement of any residential structure, defined at BCC 83.020 to include dwellings, accessory dwelling units, manufactured dwellings, and accessory living areas, must have the lowest floor, including any basement, elevated a minimum of 18 inches above the BFE.

That freeboard exceeds the bare federal NFIP minimum of at-BFE construction. Non-residential structures carry the same 18-inch floor at BCC 83.610, with a floodproofing alternative certified by a registered engineer or architect in place of elevation. Critical facilities, schools, nursing homes, hospitals, and police, fire, or emergency response installations, draw a stricter standard under BCC 83.500(3): they must be sited outside the special flood hazard area whenever a feasible alternative exists, and if built within it, the lowest floor must clear the BFE by 3 feet or reach the 500-year flood elevation, whichever is higher, with access routes elevated to the same standard.

Compliance is documented through Pre-, Mid-, and Post-Construction Elevation Certificates prepared by an Oregon-registered surveyor or engineer under BCC 83.260, reviewed and maintained by the county's Floodplain Administrator, a role assigned to the Planning Official.