A draining; a gradual flowing off of any liquid; also, that which flows out of a drain.

The mode in which the waters of a country pass off by its streams and rivers.

The system of drains and their operation, by which superfluous water is removed from towns, railway beds, mines, and other works.

Area or district drained; as, the drainage of the Po, the Thames, etc.

the entire area drained by a river and all its tributaries; a small valley.

There are two types of drainage. The first deals with sewerage and is a specific licensed trade area in itself. The second refers to the drainage of site stormwater etc from gardens to the street.

area of land drained by a stream or river.