Gilroy, CA Environmental Rules: Flood Elevation Requirements (2026)

Chapter 27E, the Floodplain Management Ordinance, adopts by reference the Flood Insurance Study for Santa Clara County and its accompanying Flood Insurance Rate Maps (FIRMs) dated May 18, 2009, plus the Uvas Creek Overflows Floodplain Management Study, as the basis for its special flood hazard areas under Section 27E.7. Section 27E.5 defines the base flood elevation (BFE) as the water surface elevation on the FIRM for a flood with a one percent or greater annual chance of occurring, i.e. the 100-year flood. Section 27E.17(c)(1) then sets the freeboard standard: in AE, AH, and A1-30 zones, the lowest floor of a new or substantially improved residential structure, including any basement, must be elevated at least one foot above that base flood elevation.

In an AO zone without a specified depth number, the required elevation rises to three feet above the highest adjacent grade. Nonresidential and mixed-use buildings may meet the same elevation standard or be dry floodproofed instead, per Section 27E.17(c)(2), with a registered civil engineer or architect certifying the floodproofing design. Once a residential structure is complete, a registered civil engineer or licensed land surveyor must certify the lowest-floor elevation, and the floodplain administrator, the director of public works or a designee under Section 27E.13, must verify it before the certification is accepted.

Where no BFE is shown on the FIRM for a given site, Section 27E.14(c) requires the floodplain administrator to obtain and reasonably use other available federal, state, or engineering data, at the applicant's expense for any required hydrologic and hydraulic analysis.