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

Chapter 8:4 of the UDO, the Floodplain Management Regulations, applies only to the unincorporated areas of Johnson County. 6(B)(1) requires a Floodplain Development Permit before any floodplain development begins, defining 'development' broadly to include buildings and other structures, mining, dredging, filling, grading, paving, excavation, drilling operations, or storage of materials or equipment, plus the placement of factory-built homes. 6(B)(2) must state the elevation of the base flood and the elevation of the lowest floor (including basement) relative to the North American Vertical Datum of 1929, along with a description of the work and property, use or occupancy intended, and cost estimates for improvements to existing buildings.

6(B)(3): up to 500 cubic yards can go into the Floodway Fringe, General Floodplain, or Shallow Flooding overlay districts under the same permit, while anything over 500 cubic yards additionally needs a Fill Plan approved by the Floodplain Administrator showing one-foot contours, floodway boundaries, and fill depth and location. In every case, fill depth cannot exceed 5 feet measured from natural grade, and no fill may be placed within 25 feet of the floodway or anywhere it could accelerate a channel meander; fill must be soil or rock only, since sanitary landfill material is barred anywhere in the floodplain.

7. The Administrator must act on a completed application within a reasonable time and give written reasons for any denial, and completed developments must submit FEMA map-revision data within six months.