Long water courses including main streams and tributaries.
Regions or areas bounded by drainage divides and occupied by drainage systems; specifically the tract of country that gathers water originating as precipitation and contributes it to a particular stream channel or system of channels, or to a lake, reservoir, or other body of water. [Glossary of Geology, 4th ed.]
Natural freshwater surface streams of considerable volume and a permanent or seasonal flow, moving in a definite channel toward a sea, lake, or another river; any large streams, or ones larger than brooks or creeks, such as the trunk stream and larger branches of a drainage system. [Glossary of Geology, 4th ed.]
Artificial embankments built along the bank of a watercourse or an arm of the sea, to protect land from inundation or to confine streamflow to its channel. [Glossary of Geology, 4th ed.]