Floodway (road)

A floodway is a flood plain crossing for a road, built at or close to the natural ground level. It is similar to a causeway, but crosses a shallow depression that is subject to flooding, rather than a waterway or tidal water.
They are designed to be submerged under water, but withstand such conditions. Typically floodways are used when the flood frequency or time span is minimal, traffic volumes are low, and the cost of a bridge is uneconomic – in most cases, in rural areas.