Polk County, IA Environmental Rules: Flood Zones (2026)

Article 7, Section 1 of the Polk County Zoning Ordinance regulates development in flood hazard areas of the unincorporated county under authority the Iowa Legislature delegated to counties in Iowa Code Chapter 335. The Flood Insurance Rate Maps for Polk County and Incorporated Areas, dated February 1, 2019 and later revisions, and the Polk County Flood Insurance Study, are adopted by reference to identify the boundaries of the 1% Annual Chance (100-year) floodplain; both are on file at the Public Works Department. The ordinance splits the floodplain into two tiers: the floodway, which must remain permanent open space carrying 100 percent flood protection, and the floodway fringe, which carries 75 percent protection and allows more uses subject to additional standards.

Permitted floodway fringe uses with added standards include agriculture, nursery and outdoor recreation uses involving a structure or fill, and sand and gravel mining. Before any development starts in the floodplain, the owner must obtain a Floodplain Development Permit from the Zoning Administrator; the application must show the elevation of the 1% Annual Chance flood, the elevation of the lowest floor relative to the 1988 North American Vertical Datum, and, for improvements, the estimated cost against the building's prior market value. Subdivision proposals larger than five acres or fifty lots, whichever is less, must include 1% Annual Chance flood elevation data for any floodway fringe area.

A property owner who cannot meet the standards can seek a variance from the Board of Adjustment, but variances are barred in the floodway itself if they would raise flood levels.