Antioch, CA Environmental Rules: Flood Zones (2026)

FEMA's Flood Insurance Rate Maps (FIRMs) for Contra Costa County, effective for Antioch, identify several Special Flood Hazard Areas (SFHAs) along the San Joaquin River shoreline (northern Antioch, including portions of Wilbur Avenue and the waterfront), Marsh Creek, Sand Creek, and their tributaries. Zone AE (1% annual chance flood with base flood elevation determined) and Zone A (1% annual chance, BFE not determined) are the primary floodplain designations in Antioch. The City of Antioch participates in the National Flood Insurance Program (NFIP) and enforces Antioch Municipal Code Chapter 8-4 Floodplain Management to comply with 44 CFR Part 60. Key requirements for new construction or substantial improvements (defined as 50% of structure value) within an SFHA include: lowest finished floor elevated to at least 1 foot above the BFE (freeboard), wet or dry floodproofing for non-residential structures, venting of enclosed areas below the BFE, anchoring to resist flotation, use of flood-resistant materials per FEMA Technical Bulletin 2, and submission of an Elevation Certificate after construction. Mortgage lenders require flood insurance for federally backed loans on properties in SFHAs; premiums are tied to the FEMA map, elevation, and foundation type under FEMA Risk Rating 2.0. Homeowners can check their flood zone at the FEMA Flood Map Service Center or call Antioch Community Development. The 2019 Delta levee and California Central Valley Flood Protection Plan provide regional context; levee-protected areas are still at residual risk. Report flood-related concerns or ponding to Antioch Public Works at (925) 779-6950.