The total area drained by a river & its tributaries.
Drainage Basin
The part of the river mouth which is tidal.
Estuary
Where a river begins
Source
A: The natural path or trench that a river flows through. It has the banks on the sides and the bed on the bottom. B: Water flowing in stream and river channels.
A. River Channel B. Channel Flow
Where the river flows into the sea.
Mouth
A small river meeting a larger river.
Tributary
The high ground that separates two drainage basins.
Watershed