Rivers- river profiles
A river changes shape as it flows from its source (where a river starts) to its mouth (where a river flows into a sea or lake). The shape of both the long profile (a slice through the river from source to mouth) and the cross profile (a slice across the river) changes.
The source of a river is often - but not always - in an upland area. Near the source, a river flows over steep slopes with an uneven surface. It often flows over a series of waterfalls and rapids. Highland areas are usually composed of hard igneous rocks, which are ideal for forming such features.
As it flows down the steep slopes the water performs vertical erosion. This form of erosion cuts down towards the river bed and carves out steep sided V-shaped valleys.
As the river flows towards the mouth, the slopes become less steep. Eventually the river will flow over flat land as it approaches the sea.
The discharge (amount of water flowing) will increase as the river approaches the sea.
Rivers- river processes
River processes shape the land in different ways as the river moves from its source to its mouth.
Erosion involves the wearing away of rock and soil found along the river bed and banks. Erosion also involves the breaking down of the rock particles being carried downstream by the river.
There are four main forms of river erosion:
- Hydraulic action – the force of the river against the banks can cause air to be trapped in cracks and crevices. The pressure weakens the banks and gradually wears it away.
- Abrasion - rocks carried along by the river wear down the river bed and banks.
- Attrition - rocks being carried by the river smash together and break into smaller, smoother and rounder particles.
- Solution - soluble particles are dissolved into the river.