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

Riverside County's floodplain management is carried out by the Flood Control and Water Conservation District and Building and Safety under Ord. 458. The County reviews FEMA Flood Insurance Rate Maps (FIRMs) for each permit application. In Special Flood Hazard Areas (SFHAs - FEMA Zones A, AE, AH, AO, V, VE), new residential construction must have the lowest floor (including basement) elevated at least 1 foot above the Base Flood Elevation (free-board requirement stricter than the FEMA minimum of 0 feet). Non-residential structures may be flood-proofed instead of elevated. In floodways, no new construction is allowed unless a No-Rise Certification demonstrates no increase in BFE. Substantial improvement or substantial damage (50% of market value) triggers full compliance. A FEMA Elevation Certificate is required at final inspection. Manufactured homes in SFHAs must be anchored and elevated on properly designed foundations. Many unincorporated communities (Thermal, Mecca, North Shore of Salton Sea, Coachella Valley washes, Temecula creeks, San Jacinto Valley) sit in mapped SFHAs. Property owners in SFHAs are required to carry flood insurance if they have a federally backed mortgage; premiums under the new Risk Rating 2.0 can exceed $2,000/year. Letters of Map Amendment (LOMA) or Revision (LOMR) can remove individual properties from SFHAs when elevation or flood control improvements warrant.