Johnson County, KS Environmental Rules: Flood Zones (2026)

Authority: K.S.A. 12-734 (state floodplain management) and the Johnson County Zoning Regulations (floodplain provisions for unincorporated areas). FEMA NFIP rules are incorporated by reference. SMAC partners — the County and 20 cities — used watershed studies between 1998 and 2002 to generate updated 1% annual chance (100-year) floodplain maps for both current and ultimate (fully developed) conditions; FEMA adopted the resulting D-FIRMs on August 3, 2009. Building permit applications are checked against the FEMA flood maps. In the regulatory floodway, new construction is prohibited except for limited uses that do not raise base flood elevations. In the floodplain fringe (Special Flood Hazard Area outside the floodway), new residential structures must have the lowest floor elevated to or above the Base Flood Elevation (BFE), and non-residential structures may be elevated or dry-flood-proofed to the BFE. Substantial improvements (per NFIP, repairs/improvements equal to or exceeding 50% of market value) trigger full compliance. The Stormwater Management Program is funded by a dedicated 1/10th-of-one-percent county sales tax that has financed roughly $200 million in projects, plus the Stormwatch flood warning system and home buyouts for repetitive-loss properties. Floodplain administration inside incorporated cities (Overland Park, Olathe, Lenexa, Shawnee, etc.) is handled by each city's floodplain administrator.