What Is a Floodway?

A regulatory floodway is the channel of a river or stream plus any adjacent floodplain areas that must remain open to carry floodwater. Under NFIP regulations (44 CFR 60.3), communities must designate and regulate floodways to ensure that the 1% annual chance flood (the base flood) can pass through without increasing the water surface elevation by more than a designated height. In most states, that limit is 1 foot.

The floodway is determined through hydraulic modeling. Engineers calculate the width of channel and floodplain needed to convey the base flood discharge. Any remaining area within the floodplain but outside the floodway is called the flood fringe.

Floodways are shown on FEMA Flood Insurance Rate Maps (FIRMs) as hatched or shaded areas along rivers and streams. On newer maps, the floodway is shown directly on the FIRM. On pre-1986 maps, floodways were shown on a separate document called the Flood Boundary and Floodway Map (FBFM).

The NFIP imposes strict development restrictions in the floodway (44 CFR 60.3(d)). The fundamental rule is that no encroachment (including fill, new construction, substantial improvements, and other development) is permitted within the floodway if it would cause any increase in the base flood elevation.

In practice, this means almost all new construction in the floodway is prohibited. Even small structures or additions must be accompanied by a "no-rise certification" from a licensed engineer demonstrating that the proposed development will not raise flood levels at all. This is a high bar that most projects cannot meet.

Floodways are only designated in riverine flood zones where detailed engineering studies have been conducted. Not every flood zone has a floodway.

• Zone AE: Floodways are typically designated along studied streams and rivers in Zone AE areas. This is the most common zone where you will see floodway boundaries on the FIRM.
• Zone A: Because Zone A is studied by approximate methods only, no floodway is designated. However, communities must still review proposed development for potential flood elevation impacts.
• Coastal zones (V, VE): Floodways do not apply to coastal areas. Coastal flooding is driven by storm surge and wave action, not channelized flow.
• Zone X: Floodways are not designated outside the SFHA.

Where BFEs have been established but no floodway has been designated, communities must review all proposed development to determine whether it would cause increases in the BFE. The absence of a designated floodway does not mean the area is free from floodway-like restrictions.