Bridge over the Tyne at Bywell - geograph

A flood arch is a small supplemental arch bridge provided alongside a main bridge. It provides extra capacity for

floodwater A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrolog ...

. The space beneath a flood arch is normally dry and often carries a towpath or similar. In some cases it borders on the shallow edge of a river, but this does not carry substantial flow in normal conditions. A bridge with multiple arches across a flowing river would instead be termed a

viaduct A viaduct is a specific type of bridge that consists of a series of arches, piers or columns supporting a long elevated railway or road. Typically a viaduct connects two points of roughly equal elevation, allowing direct overpass across a wide v ...

. For some bridges, flood arches were added after the first bridge had been constructed, often after initial flooding. Pant-y-Geotre Bridge - geograph

References

Arches and vaults Bridge components {{bridge-type-stub