River Revision

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Erosion, Transportation and Deposition

What is Erosion?

Erosion is the wearing away of the banks and the bed of the river.

How does a river erode?

Hydraulic action

The sheer force of the water breaks the rock particles away from the river channel.

Abrasion/Corrasion

Eroded rocks picked up by the river scrape and rub against the channel, wearing it away. Most erosion happens by abrasion.

Solution/Corrosion

River water dissolves some types of rock, e.g. chalk and limestone

Attrition

Eroded rocks picked up by the river smash into each other and break into smaller fragments. Their jagged edges also get rounded off as they rub together. The further material travels, the more eroded it gets - attrition causes particle size to decrease between a river's source and its mouth.

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What is Transportation?

Transportation is the movement of the rivers load down the river.

How does a river transport its load?

Traction

Large particles like boulders are pushed along the river bed by the force of the water.

Saltation

Pebble-sized particles are bounced along the river bed by the force of the water eroding the bed and lower banks of the river

Solution

Soluble materials dissolve in the water and are carried along.

Suspension

Small particles like minerals, silt and clay are held in the water, these help to cause corrasion.

What is Deposition?

Deposition is when the river slows and loses its energy, in the lower corse of the river, depositing the eroded material it's transporting.

The reasons for why this happens is as follows:

The volume of water in the river falls.

The amount of eroded material in the water increases.

The water is shallower, e.g. on the inside of a bend.

The river reaches its mouth.

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The River Valley

Long and Cross Profiles of Rivers:

The path of a river as it flows down hill is called its course.

Rivers have an upper (closest to the source), middle course and lower course (closest to the mouth of the river).

Rivers form channels and valleys as they flow downhill.

They erode landscapes, the transport the material to somewhere else where it is deposited.

The shape of the valley and the channel changes along the river depending on whether erosion or deposition is having the most impact.

The long profile of a river shows you how the gradient (steepness) changes over the different courses.

The cross profile shows you what a cross section of the river looks like.