Definition of river drift in US English:

river drift

noun

historical
  • Alluvial material deposited by a river in its valley (as opposed to that deposited by a glacier or ice sheet).

Origin

Mid 19th century; earliest use found in Henry Thomas De la Beche (1796–1855), geologist. From river + drift.

Pronunciation

river drift

/ˌrɪvə ˈdrɪft/