Subwatershed

Part of speech: noun

Definitions

1. A smaller drainage area that forms part of a larger river basin, where all the water flows into one particular tributary or stream
2. The local catchment region nested inside a bigger watershed, collecting rainfall and runoff that drains toward a single smaller channel
3. A secondary drainage zone contained within a larger basin, defined by the land that sheds water into one specific stream or lake

Etymology: "Subwatershed" is built from "sub-", a prefix meaning "under" or "below" in a subordinate sense, attached to "watershed." The base word has its own surprising history: "watershed" originally meant the ridge or line of high ground that divides one drainage basin from another, the literal "water-divide" of a landscape. Only later did it take on the figurative sense of a turning point, the dividing line between one phase and the next. "Subwatershed" follows the same logic on a smaller scale. It names a smaller drainage area nested within a larger watershed, the streams and land that feed into one tributary of a river system. Hydrologists and land managers use the term when they need to study or manage a portion of a larger catchment, so the prefix simply marks the smaller unit's place within the bigger one.

Synonyms: sub-basin, subcatchment