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 * __How and why do River Valleys change downstream?__**

The river valley is subjected to three main landscape-shaping processes:
 * Erosion – wearing away/breaking up of rock/material
 * Transportation – movement of the broken up material from erosion
 * Deposition – the dumping of eroded material after transportation
 * __Processes of erosion__**

A river near to its source concentrates on erosion, and especially downwards erosion. There are four main ways in which a river erodes:
 * Hydraulic action
 * Abrasion
 * Attrition
 * Solution

Three videos on erosion by rivers - [] [] []
 * Hydraulic action**: this is the sheer force of the water hitting the bed and the banks. This is most effective when the water is moving fast and there is a lot of it.


 * Abrasion:** this occurs when the load the river is carrying repeatedly hits the river bed and the banks, causing some of the material to break off.


 * Attrition:** this is when the stones and boulders carried by the river knock against each other and over time weakened, causing bits to fall off and reduce in size.


 * Solution:** this occurs only when the river flows on certain types of rock, such as chalk and limestone. These are soluble in rainwater and become part of the water as they are dissolved by it.

Rivers tend to erode in one of two directions: downwards and sideways. The terms for this are vertical and lateral erosion. As a river gets further down its course vertical erosion becomes less important and lateral erosion takes over.

Below are some useful and interesting weblinks: [] []


 * __Processes of transportation__**

Bits of broken rock from erosion form the rivers load and it moves this by transportation. There are four methods by which a river transports its load:


 * Traction
 * Saltation
 * Suspension
 * Solution


 * Traction**: this is the method used for moving the largest material. This is too heavy to lose contact with the bed, so material such as boulders is rolled along.


 * Saltation**: this moves the small stones and grains of sand by bouncing them along the bed. This lighter load leaves the river bed in a hopping motion.


 * Suspension**: this is a means of carrying very fine material within the water, so that it floats in the river as it flows.

Below are some useful and interesting weblinks: [] []
 * Solution**: this is the dissolved load and occurs only with certain rock types that are soluble in rainwater. This is true of chalk and limestone and the load is not visible.


 * __Deposition__**

This is where the river dumps of leaves behind material that it has been carrying. It deposits the largest material first as this the heaviest to carry. The smaller the load, the further it can be transported, so this is deposited much further downstream than the larger load. Generally speaking the larger boulders are found at the top of the river nearer its source. The river drops some of it load where there is a fall in speed of the water or the amount of water is less. This often occurs when the gradient changes at the foot of a mountain or when a river enters a lake or the sea.

Below are some useful and interesting weblinks: []

__**Key terms**__


 * Channel:** the part of the river valley occupied by the water itself


 * Hydraulic action**: the power of the volume of the water moving in the river


 * Abrasion**: occurs when larger load carried by the river hits the bed and banks, causing bits to break off.


 * Attrition:** load carried by the river knocks, into other parts of the load, so bits break off an make the material smaller.


 * Solution:** the dissolving of certain types of rock such as chalk and limestone be rainwater. This is a means of transportation as well as an erosion process.


 * Load:** Material of any size carried by the river.


 * Traction:** The rolling along of the largest rocks and boulders


 * Saltation:** the bouncing movement of small stones and grains of sand along the river bed.


 * Suspension:** Small material carried within the river