LO1: River Processes

Source

Where a river starts

Mouth

Where the river reaches a large body of water + ends

Tributary

A smaller river that joins the main channel

Watershed

The boundary of / between a drainage basin - normally with high relief

Confluence

Where two or more rivers meet

Main channe;

The biggest and most significant river in the drainage basin

Drainage basin

An area of land where all precipitation is collected and drained into the river

Erosion

The action of the water wearing away the bed and banks of a river, including rocks within the water
In water

Weathering

Rocks are broken down at or near to the surface of the ground (occurs on the land)
On land

Mass movement

The downslope movement of rocks and soil due to gravity
On land

Transportation

Eroded material is moved along by difference processes depending on its size + energy of the water
In water

Deposition

When there isn’t enough energy to carry the eroded material, it is dropped / deposited
In water

Four types of erosion

• Hydraulic action

• Abrasion

• Attrition

• Solution

Hydraulic action

The sheer force of the river water compressing air into creaks which wears out the rocks via pressure

Abrasion

The scraping away of the bed + the banks by the bed load in the river

Attrition

The bed land smashes into itself becoming smaller + more rounded over time

Solution (erosion)

The bed and banks dissolve by the river (chalk + limestone)

Three types of weathering

• Mechanical

• Biological

• Chemical

Mechanical

When rainwater enters cracks in rocks, freezing at temperatures below 0, the water expands, forming ice and exerting pressure

Biological

The roots of the plants (trees) can grow into cracks in the rock + split it apart

Chemical

All rain is slightly acidic. If air is polluted then it’s more acidic. Rain falling on rocks causes acid to react with weak minerals and dissolve - decaying rocks

Four types of weathering going in reducing amounts of energy

• Traction

• Saltation

• Suspension

• Solution

Traction

Stones roll along the river bed

Saltation

Particles the size of sand grains bouncing over each other along the river bed

Suspension

Water flow carries silt + clay sized particles

Solution (transportation)

The river water dissolves some minerals

Two types of mass movement

• Soil creep

• Slumping

Soil Creep

Individual particles of soil move slowly down slope (gravity) and collect at the bottom of the valley
River may then erode the material

Slumping

Bottom of valley is eroded by river. Slope steepens + material above slides down, rotating
Movement is often triggered by periods of heavy rain, saturates overlying rock, heavy + liable to slide

Why does deposition occur

River no longer has enough energy to carry its load. As river discharge reduces, heaviest material is deposited first