That area, measured in a horizontal plane, enclosed by a topographic (drainage) divide from which direct surface runoff from precipitation normally drains by gravity into the stream above the specified point.
DRAINAGE AREA (OF A STREAM AT A SPECIFIED LOCATION)
Meaning of DRAINAGE AREA (OF A STREAM AT A SPECIFIED LOCATION) in English
Environmental engineering English vocabulary. Английский словарь экологического инжиниринга. 2012