River Channel Processes defintions

Question 1

Erosion

Answer 1

Erosion is the continually shaping and wearing away of the bed and banks of the river channel by the power of water.

Question 2

Hydraulic action

Answer 2

Is the force of the water pushing into cracks and hitting against the river’s banks.

The repeated action weakens the riverbank as air in the cracks is compressed and pressure builds up.

Collapsing air bubbles create small shock waves in a type of hydraulic action known as cavitation.

In rivers, hydraulics action is a low and ineffective process of erosion.

Question 3

Corrasion/abrasion

Answer 3

Corrasion/abrasion - occurs when sediment in the river is thrown into or scraped along the banks of the riverbed.

This process is extremely common and is the main form of erosion within the river.

During times of high discharge the river has a greater capacity to transport larger material, which results in the greatest amount of damage.

Potholes may form as stones become trapped in depressions and hollows and are continually swirled around by eddies in the turbulent water.

Question 4

Attrition

Answer 4

Is the process by which stones and sediment within the river become increasingly rounded. As material is transported it collides with other objects in the river. The collisions cause the stones to break into smaller pieces and the edges and points of the stones to break off.

Question 5

Corrosion/solution

Answer 5

Corrosions/solution - is a continuous chemical process that occurs independently from river flow. Water that has slightly acidic properties. E.g. result of decomposing organic material (humic acid) or acid rain (carbonic acid), will chemically dissolve and weaken certain types of rock. Limestone is composed of calcium carbonate and is particularly vulnerable to corrosion.

Question 6

Load transport

Answer 6

Is the movement of sediment by the river

Question 7

Capacity

Answer 7

Is the total load of material actually transported

Question 8

Competence

Answer 8

The maximum size of material that river is capable of transporting

Question 9

Traction

Answer 9

Is when the largest stones, boulders and cobbles are rolled along the riverbed by strong turbulent currents

Question 10

Saltation

Answer 10

Is where smaller bedload such as pebbles, stones and gravel are lifted and carried temporarily in the flow in a hopping or bouncing motion

Question 11

Suspended load

Answer 11

Is when very fine particles of sand and silt are carried in suspension in fast flowing water.

Question 12

Dissolved load/ solution

Answer 12

The process by which small dissolved sediments and minerals are transported within the river.

Question 13

Critical erosion velocity

Answer 13

The lowest velocity at which sediment of a given size can be transported.

Question 14

Deposition

Answer 14

Deposition is where the river drops its load when the river no longer has enough energy to carry the load. Deposition may occur when a river becomes shallower or when the volume of water decreases.