Fluvial Processes

Question 1

What is abrasion (corrasion)?

Answer 1

The scraping, scouting and rubbing action of materials carried along by a river. Most effective in short turbulent periods of high discharge.

Question 2

What is hydraulic action?

Answer 2

Caused by the sheer power of moving water; it is the movement of loosed unconsolidated material due to the frictional drag of the moving water on sediment lying on the channel bed.

Question 3

What is corrosion?

Answer 3

The minerals in the rock are dissolved by weak acids in the river water and carried away in solution. Most active on rocks that contain carbonates such as limestone and chalk.

Question 4

What is attrition?

Answer 4

The reduction in the size of fragments and particles within a river due to the processes of erosion. The fragments strike one another as well as the river bed.

Question 5

What are the four main processes of river erosion?

Answer 5

Abrasion
Hydraulic action
Corrosion
Attrition

Question 6

What are the four main processes of river transportation?

Answer 6

Traction
Saltation
Suspension
Solution

Question 7

What is traction?

Answer 7

Large stones and boulders are rolled along the river bed by water moving downstream. This only happens at times of high discharge.

Question 8

What is saltation?

Answer 8

Small stones bounce or leap-frog along the channel bed- occurs in high energy conditions.

Question 9

What is suspension?

Answer 9

Very small particles of sand and silt are carried along by the flow of the river.

Question 10

What is solution?

Answer 10

Dissolved minerals are transported within the mass of the moving water.

Question 11

When does deposition usually occur?

Answer 11

• reduced gradient e.g. lake
• reduced discharge e.g. dry weather
• shallow water
• increase in the calibre (load) e.g. tributary bringing in larger particles
• the river floods and overtops its banks = reduced velocity on the floodplain