Sioux City, IA Environmental Rules: Flood Zones (2026)

Chapter 20.07 is Sioux City's NFIP-conforming floodplain ordinance and is the local mechanism for participating in the National Flood Insurance Program (42 U.S.C. ch. 50). NFIP communities must adopt and enforce floodplain management regulations meeting 44 CFR section 60.3 minimums; an Iowa-specific layer of authority for floodplain management lies in Iowa Code chapter 455B (which gives the Iowa DNR oversight of flood-plain construction) and Iowa Administrative Code 567 chapter 70 et seq. (DNR floodplain rules). FEMA's effective Flood Insurance Study and FIRMs for Woodbury County / Sioux City identify the regulated Special Flood Hazard Areas (Zones AE, A, AO) along the Missouri River, Big Sioux River, Floyd River, and the Perry Creek diversion. Sioux City has significant levee infrastructure along the Missouri River, but levees are not absolute protection and FEMA's regulatory floodplain still applies. The city's flood history is severe: the 2011 Missouri River flood (driven by record snowpack and prolonged USACE reservoir releases), the 2019 Midwestern floods (Iowa's $1.6 billion damage total - a state record), and the June 2024 floods that forced mandatory evacuations in Riverside and other low-lying neighborhoods demonstrate that the published FIRMs are not theoretical. Chapter 20.07 typically requires a floodplain development permit from the city Building Official before any construction, fill, grading, manufactured-home placement, or substantial improvement (>= 50 percent of pre-damage market value) in an SFHA; residential lowest-floor elevation at or above the Base Flood Elevation (with freeboard set by the city, commonly +1 ft above BFE in Iowa NFIP communities); non-residential dry-floodproofing as an alternative; anchoring of manufactured homes; and prohibition of certain critical and hazardous-material facilities in the floodway. Floodplain development permits in unincorporated Woodbury County are handled by the county Community Economic Development office, separate from Sioux City's process.