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

Yolo County sits squarely in the Sacramento River floodplain, and substantial portions of the county are inside FEMA-mapped Special Flood Hazard Areas (the 1% annual-chance / 100-year floodplain). The major flood corridors are: the Sacramento River and the Yolo Bypass on the eastern edge (with Clarksburg, the Pocket, and the West Sacramento corridor most affected); Cache Creek through the central county; Putah Creek along the southern boundary (affecting Winters); and the Colusa Basin Drain in the northern county (Knights Landing, Dunnigan). The county adopted a Floodplain Management Ordinance to qualify for NFIP participation, with development standards including a floodplain development permit, an elevation certificate, and a requirement that the lowest floor of new and substantially improved structures be at or above the Base Flood Elevation. Yolo County Building Inspection Services administers the program. When FEMA remapped Yolo County floodplains in the late 2000s, none of the county's levees met the new certification standards, which placed tens of thousands of residents (including in Clarksburg, much of West Sacramento, and adjacent areas) into the SFHA and triggered the federal flood insurance purchase requirement for federally backed mortgages. The Yolo County Flood Governance Study and the West Sacramento Area Flood Control Agency have been working since to recertify and upgrade levees. Tribal, state (DWR), and federal (USACE, FEMA) coordination is the rule rather than the exception in Yolo County floodplain projects.