Butte County, CA Environmental Rules: Flood Zones (2026)

Article IV of Chapter 26, "Flood Hazard Prevention," starts at Section 26-20, which designates the Director of Public Works or a designee as the "flood plain administrator." Section 26-22 requires a development permit for new construction, substantial improvements, and other development, including manufactured homes and prefabricated buildings, within mapped Zones A, AE, AH, and AO, and imposes separate additional-review requirements within the county's official two-hundred-year floodplain maps for development agreements, discretionary permits, ministerial permits for a new residence, and tentative subdivision or parcel maps. Applications must include site plans, elevation data referenced to the National Geodetic Vertical Datum, and, in the two-hundred-year floodplain, a study of whether a two-hundred-year flood event would reach a depth of three feet or more.

Section 26-23(a)(3) sets the county's core rise limit: "The county will not allow development to increase the water surface elevation of the base flood more than one (1) foot at any point, nor will it allow any increase in the base flood elevation which adversely affects any neighboring property." Section 26-24(b)(1)(a) sets the elevation standard for Zones AE and AH: "The lowest floor elevation of new residential structures and substantial improvements to residential structures shall be elevated a minimum of one (1) foot or more above the BFE." Nonresidential structures in those zones may instead be floodproofed and certified watertight by a registered engineer or architect. Section 26-25 further requires that subdivision maps in the mapped flood zones record the regulatory flood elevation before recordation, and Section 26-26 bars new conventional septic systems within the ten-year floodplain.