Drainage Basin

A Drainage Basin is the area of land that drains water, sediment, and dissolved materials to a common outlet at some point along a stream channel.

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Other /More definition:
A drainage basin is a land area where precipitation runs off into streams, rivers, lakes, and reservoirs. It is a land feature that can be identified by tracing a line along the highest elevations between two areas on a map, often a ridge. Large drainage basins, like the area that drains into the Mississippi River contain thousands of smaller drainage basins. A drainage basin is also called a "watershed."