Hydrological characteristics and processes which operate in rivers and drainage basins. 

Drainage basin and water divide  is the area drained by a main river and its tributaries, bounded by a watershed. Components of a drainage basin are main stream, tributaries and distributaries, wetland and estuary (mouth of a river which is tidal), the exit of the basin (where the waters join another water body such as a river, lake, sea, or ocean). Watershed or water divide is an imaginary line that separates adjacent drainage basins. It is generally a highland or ridge or plateau.