Rivers p100-107

How and why do river valleys change downstream?

River valleys are subjected to erosion, transportation and deposition.

Erosion is prominent near the source, especially vertical erosion. Lateral erosion takes over as a river gets further down its course.

Hydraulic action is the force of water hitting the bed and banks. This is most effective when water is moving fast and there is a lot of it.

Abrasion is when the load of the river repeatedly hits the reiver bed and baks, causing material to break off.

Attrition is when the stones and boulders carried in the river knock against each other and are weakened over time, causing parts to break off.

Solution occurs only when the river is flowing on certain rock types such as chalk and limestone, which are soluble in rainwater and are dissolved to become part of the river.

Transportation is the process of the river moving its load. 

Traction is the method for moving very large material. The load is too heavy to leave the bed so the material is rolled along the bed of the river.

Saltation moves the small stones and grains by bouncing them along the bed. The lighter load moves in a hopping fashion.

Suspension is the means of carrying very fine material so that it floats in the water.

Solution is the dissolved load and this form of transportation only occurs over certain rock types that are soluble in rainwater such as chalk and limestone. The load is not visible.

Deposition is where the river leaves behind material it was carrying. Largest material is deposited first because it is heaviest to carry. The smaller the load, the further it is transported…