River Landscapes and Processes

Some important words and definitions:

Fluvial Landscape – a landscape created by rivers and their tributaries.
Tributary – a small river or stream which joins to a larger one.
River or drainage basin – an area drained by a single river together with all of its tributaries.
Confluence – where 2 or more streams, rivers or tributaries join together.
Watershed – The boundary line between different river/drainage basins. (Sometimes these are referred to as Catchment areas)
Source – The starting point of a river or stream. (watercourse) – This maybe a spring or just an area of boggy/marshy land.
Channel – the space between the banks of the watercourse in which the river flows, and may vary form a few meters to hundreds of kilometres.
Mouth – the point at which the river enters the sea or a lake.
Delta – the mouth of a river that splits into many channels (or distributaries) e.g. The River Mississippi or the River Nile.
Long Profile – the cross-section of a rivers course from its source to its mouth.
Cross Profile – a section across the valley of the river at any given point.

How Do Rivers Shape The Land?

There are 4 main processes by which a river can cause erosion (wearing away) and 4 processes by which a river can transport (move) material.

Processes of erosion

Attrition – breaking up of material into smaller and smaller particles.
Corrosion – fire material rubs (like sandpaper) and gradually wears away the channel sides.
Corrosion – dilute acids in water help break down and dissolve particles.
Hydraulic Action – the sheer force of flowing water “hitting” the banks causes them to be worn away and collapse.

Processes of transportation

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How Do Rivers Shape The Land?

There are 4 main processes by which a river can cause erosion (wearing away) and 4 processes by which a river can transport (move) material.

Processes of erosion

Attrition – breaking up of material into smaller and smaller particles.
Corrosion – fire material rubs (like sandpaper) and gradually wears away the channel sides.
Corrosion – dilute acids in water help break down and dissolve particles.
Hydraulic Action – the sheer force of flowing water “hitting” the banks causes them to be worn away and collapse.

Processes of transportation

Traction – the movement of large rocks and boulders along the channel – usually in times of flood.
Saltation – smaller stones and particles literally bounce along the river bed.
Suspension – fine material carried along in the water itself.
Solution – dissolved material transported by the river water.

Most erosion occurs when a river is in flood (or spate). It can then carry huge amounts of material in suspension as well as being able to move the largest of boulders lying on its bed (or channel). Erosion can both deepen and widen. This is more usual in mountainous areas nearer to the source of the river. Here the river forms a series of characteristic landforms which include “V” – shaped valley with interlocking spurs as well as waterfalls and rapids.

The Formation of a Cap Rock Waterfall

How do meanders and oxbow lakes form?

As rivers get nearer to their mouths they flow in increasingly wide gentle sided valleys (with a saucer shape cross-section.) The channel increases in width and depth and the natural physical process causes it to 2meander” (from the River Meander in N. America). As a river goes round a bend most of the water is pushed to the outside of the bend and erosion takes place. The opposite happens on the inside of the bend – where deposition takes place

Cross Section of a river bend

Diagrams showing the formation of meanders and ox-bow lakes