Drainage basins refer to the area of land drained by a major river and its tributaries. All rivers flow from the source (often in the mountains) to the mouth (the sea). The drainage basin is regarded as a closed system because water never leaves. Instead, it is recycled from one state to another.
The hydrological cycle within a drainage basin is different in that it is a closed system. Input will vary. Water transfer and storage will also vary from one drainage basin to another.
A major component of the water cycle is the drainage basin system.
There are many inter-relationships within this system:
The dividing lines of mountain ranges are known as watersheds, and the areas between them are called drainage basins.