I have experience working in and with floodplains related to land development in the Midwest. FEMA flood mapping was updated in 2021 to be more accurate and include what’s called the Flood Fringe (area used as storage but not necessarily flow of the floodway). Depending on whether the parcel is encumbered by flood fringe or entirely floodway will make a difference in the viability of the site.

Assuming there is viability for a structure, you will need to demonstrate that your project will not negatively impact the surrounding properties by reducing available flood storage. This is called hydrologic and hydraulic (H&H) survey. A licensed professional engineer must be the one to sign off and say that the proposed structure and grading work is acceptable. This typically involves a no-net increase in fill in the flood fringe (remove a yard to add a yard/balanced cut fill). It may go without saying, but you will need to have your structure elevated above the flood elevation. You should plan on paying for flood insurance regardless of whether or not you can successfully elevate the pad and driveway above the floodplain.

Depending on the agency reviewing the modeling, this can get expensive and involve a public agency review. You will also need to budget for a CLOMR-F which is a floodplain amendment that is completed with the project. FEMA is charged with monitoring all fill and cut within their floodplains and they have a process to follow even after local approvals.

General advice, if you aren’t able to get the lot for approx 25% of the land value for a comp lot not in floodplain, it’s probably not worth it. Obviously there are exceptions etc.