Floodway vs floodplain: what is a regulatory floodway?
A regulatory floodway is the channel of a river or stream plus the nearby land that must be kept open to carry the 1% annual-chance flood without raising the water more than a set height, usually one foot.
In more detail
The floodplain is all the land that floods in the base flood. The floodway is its fast-moving core. The rest of the floodplain, outside the floodway, is the flood fringe.
New building, fill or other development in the floodway needs an engineering study showing it will not raise flood heights, often called a no-rise certification. In practice that rules out most construction.
Floodways are shown with crosshatching inside zone AE on FEMA maps.
What it means when you buy
Land in the floodway is close to unbuildable, and existing buildings there are hard to expand. Check where the floodway line runs before you pay for acreage near a creek.
How the free flood check shows it
The free flood check shows floodway lines where FEMA maps them, so you can see how much of the parcel is truly usable.
Check the flood zone for an address, free
Enter any US address to see its FEMA flood zone and a map of the flood areas around it. Add your email to see which buildings sit in the flood zone and the risk numbers.