The hydrological cycle
The hydrological cycle is also known as the water cycle. Seas and oceans contain 97 per cent of the world's water, and ice holds 2 per cent. That leaves just 1 per cent of the world's water as fresh water on land or in the air. This water is recycled again and again through the process of evaporation, condensation and water transfers such as surface run-off.
The key stages in the hydrological cycle
Terminology for the study of rivers
- Drainage basin - the area of land drained by a river.
- Catchment area - the area within the drainage basin.
- Watershed - the edge of highland surrounding a drainage basin. It marks the boundary between two drainage basins.
- Source - The beginning or start of a river.
- Confluence - the point at which two rivers or streams join.
- Tributary - a stream or smaller river which joins a larger stream or river.
- Mouth - the point where the river comes to the end, usually when entering a sea.
Key features of a river