Flood Zones in Clinton County, Iowa

The 1965 flood and the levee it produced

The Mississippi River at Clinton crested at a record 24.85 feet on April 28, 1965 -- nearly nine feet above flood stage -- at a time when the city had no levee protecting it, and the flood caused an estimated $5,286,600 in damage. That event set in motion a major federal infrastructure response: the U.S. Army Corps of Engineers began a seven-year, $28.9 million levee construction project in August 1974, ultimately building an 8.1-mile levee, 4,330 feet of concrete floodwall, six pumping stations, seven closure structures, five major street crossings, 17,320 feet of new sewer, and 23 gatewells, dedicated in June 1981. The levee system runs along the Clinton riverfront from Mill Creek to 25th Avenue North and has protected the city from a repeat of 1965-scale flooding in the decades since.

A levee's existence and its FEMA accreditation are two different questions

A physical levee protecting a piece of land from flooding and that levee being formally accredited by FEMA on the current Flood Insurance Rate Map (FIRM) are not the same thing, and conflating them is a common mistake. For FEMA to map the area behind a levee as reduced-hazard rather than as part of the base floodplain, the levee must be certified by a qualified professional engineer (or the responsible federal agency) and continue to meet minimum standards under 44 CFR 65.10. When a levee is mapped as accredited, land behind it is shown as moderate-hazard on the FIRM, and the federal requirement for mortgage lenders to mandate flood insurance is lifted for property in that area. If a levee's accreditation lapses or was never granted for a specific segment, property behind it can still show as being within a mapped flood zone despite physical levee protection. Clinton County's Zoning Department can confirm a specific parcel's current FIRM zone designation and whether it sits behind an accredited levee segment -- don't assume protection status from the levee's visible presence alone.

Floodplain permits here can require three separate approvals

Clinton County requires a floodplain development permit before any development -- farm or non-farm -- proceeds within Zone A of the county's current Flood Insurance Rate Map. What's distinctive about Clinton County specifically is that permits for property within either the Mississippi River floodplain or the Wapsipinicon River floodplain can also require separate approval from Iowa DNR's Flood Plain Division and the U.S. Army Corps of Engineers, layered on top of the county's own floodplain-permit sign-off. That's a three-agency structure rather than the county-only process common in many inland counties, and it can meaningfully extend the timeline for any construction project within these two rivers' mapped floodplains.

Notably, Clinton County's newly-amended commercial wind-energy ordinance (adopted December 2025) separately imposes its own 10-mile setback from the Mississippi River and 5-mile setback from the Wapsipinicon River for turbine siting -- a distinct, much larger buffer aimed at wind development rather than floodplain construction, and not a substitute for the standard floodplain-permit process described here. Don't conflate the two: a parcel can clear (or fail) the wind-setback distance independent of its FEMA flood-zone status, and vice versa.

What to check before buying near the river

1. Confirm the parcel's current FIRM flood-zone designation with the Clinton County Zoning Department, and specifically ask whether it sits behind an accredited levee segment or an unaccredited one.
2. If the parcel is within the Mississippi or Wapsipinicon River floodplain, ask directly whether Iowa DNR's Flood Plain Division or the Army Corps of Engineers would need to separately approve a specific proposed project, in addition to the county floodplain permit.
3. Do not assume flood-insurance requirements are waived simply because a levee exists nearby -- confirm current FEMA accreditation status for the specific levee segment protecting the parcel.
4. If evaluating land near the river for a use that might also implicate the wind-energy ordinance's river setbacks, treat the two regulatory questions (floodplain permitting vs. wind-turbine siting) separately rather than assuming one answers the other.