How a river works
A river is water flowing in a channel from a higher source to a lower base level, usually the sea. It does three kinds of work: erosion (wearing away the bed and banks), transportation (carrying the load) and deposition (dropping the load). The path a river follows from source to mouth is its course.
Key idea
Erosion dominates in the fast, steep upper course; transportation and deposition become more important in the gentler middle and lower courses where the river slows and widens.
Landforms along the course
- Upper course — steep gradient, fast flow; forms V-shaped valleys, waterfalls and rapids.
- Middle course — the river winds, forming meanders.
- Lower course — gentle gradient; forms flood plains, oxbow lakes and, at the mouth, a delta.
Example
The Rajang River in Sarawak, Malaysia's longest river, is used for water supply, transport, fishing and hydroelectric power, and it deposits a large delta at its mouth.
Sustainability of rivers
Rivers give water for domestic, farming and industrial use, transport routes, fisheries, and hydroelectric power. They are threatened by pollution, sedimentation from land clearing, over-extraction and rubbish dumping. To keep rivers healthy for the future we should treat waste water, control riverbank development, replant riverside vegetation, gazette river reserves and educate the public.
Remember
- Three river actions: erosion, transportation, deposition.
- Upper course = erosion; lower course = deposition.
- Sustainable use balances present needs with protecting rivers for the future.