Which statement about watersheds is true?

• A. Watersheds never contain smaller streams
• B. Large rivers have small watersheds
• C. Watersheds always exceed their capacity
• D. Large rivers have large watersheds, and larger watersheds contain smaller ones

Answer: (D)

Watersheds are drainage basins—areas of land where all precipitation drains to a common outlet like a river. These basins are hierarchical, so larger watersheds include many smaller ones. A large river’s watershed collects runoff from a big area, and within that area there are sub-watersheds for its tributaries. This nesting is visible on maps as ridgelines that separate flow toward different rivers. So the statement that large rivers have large watersheds, and larger watersheds contain smaller ones, accurately describes how watersheds are organized. The other options clash with this idea: watersheds do contain many smaller streams, a large river generally has a large (not small) watershed, and “exceed their capacity” isn’t a defining rule for watersheds since capacity depends on rainfall and storage.