River Processes

Question 1

What can erosion affect?

Answer 1

The length, depth and width of a river.

Question 2

What can be eroded?

Answer 2

Bed and banks

Makes river longer, deeper and wider.

Question 3

What form of erosion makes a river longer? Where does it happen?

Answer 3

Headward erosion

Happens near a river’s source.

Question 4

What form of erosion makes a river channel deeper? Where does it happen?

Answer 4

Vertical erosion

Happens in the upper stages of a river.

Question 5

What form of erosion makes a river wider? Where does it happen?

Answer 5

Lateral erosion

Happens in middle and lower stages of a river.

Question 6

What are the 5 main ways in which river erosion happens?

Answer 6

Hydraulic action 
Abrasion (corrasion)
Attrition
Cavitation
Corrosion (solution)

Question 7

What is hydraulic action?

Answer 7

Pressure of the water breaking rock particles away from the bed and banks.

Question 8

What is abrasion (corrasion)?

Answer 8

Eroded pieces of rock in water scrape and rub against the bed and banks - removing material.

Question 9

What is attrition?

Answer 9

Eroded rocks smash into each other and break into smaller fragments. Edges get rounder as they rub together

Doesn’t erode, just makes particles smaller.

Question 10

What is cavitation?

Answer 10

Air bubbles in turbulent stretches of water implode causing shockwaves that break pieces of rock off river bank and bed.

Question 11

What is corrosion (solution)?

Answer 11

Dissolving of Rick by chemical processes.

CO2 dissolves in water to form weak acid which reacts with rocks like limestone and chalk - breaking them down.

Question 12

What is transportation?

Answer 12

The process of eroded material being carried in a river.

Question 13

How are particles transported?

Answer 13

The velocity of a river provides the energy needed for it to transport eroded material.

Question 14

What is the eroded material being carried by a river called?

Answer 14

Load

Question 15

What are the 4 ways that the load can be transported?

Answer 15

Solution
Suspension
Saltation
Traction

Question 16

What is solution?

Answer 16

Substances that can dissolve are carried along IN the water - limestone dissolves if water is acidic.

Question 17

What is suspension?

Answer 17

Very fine material (silt + clay) is taken up by turbulence and carried along in the water.

Most eroded material is transported in this way.

Question 18

What is saltation?

Answer 18

Larger particles (pebbles or gravel) are too heavy to be carried in suspension, instead, force of water bounces them along the river bed.

Question 19

What is traction?

Answer 19

Very large particles (boulders) are pushed along the river bed by force if water.

Question 20

Define bedload.

Answer 20

Material transported by traction or saltation.

Question 21

What is deposition?

Answer 21

The process of dropping eroded material.

Question 22

When does deposition occur?

Answer 22

When the river loses its energy

When it slows down, it loses energy and drops some of its load.

Question 23

What are the 5 ways that speed and energy can be reduced?

Answer 23

Reduced rainfall
Increased evaporation
Friction
Reduced velocity
The sea

Question 24

How does reduced rainfall reduce speed and energy of a river?

Answer 24

Causes lower discharge, means the river slows down, has less energy.

Question 25

How does increased evaporation reduce speed and energy?

Answer 25

Slows down river discharge.

Question 26

How does friction reduce speed and energy?

Answer 26

Shallow areas of the river and close to the bake, reduced speed of river, reducing its energy.

Question 27

How does reduced velocity reduce speed and energy?

Answer 27

E.g. narrow section of river, loses energy.

Question 28

How does the sea reduce speed and energy?

Answer 28

The sea absorbs the energy, energy is lost.

Question 29

What is the capacity of a river?

Answer 29

Total load a river can transport at a given point.

Question 30

What is the capacity of a river measured in?

Answer 30

Volume, weight or mass

Question 31

How is the load of the river divided?

Answer 31

Can divided into categories of partial size.

Sizes range from silt and clay (0.1mm) to big boulders.

Question 32

Define competence.

Answer 32

Maximum particle size that a river is capable of transporting at a given point.

Question 33

What does the Hjulström curve show?

Answer 33

The link between river velocity and competence.

Shows how processes of erosion, deposition and transportation vary with the river velocity.

Question 34

What affects competence?

Answer 34

The amount of energy it has (relates to velocity)

Question 35

What does the critical erosion velocity curve show?

Answer 35

The MINIMUM velocity needed for the river to pick up and transport particles of different sizes.

Question 36

What does the mean settling velocity curve show?

Answer 36

The velocities at which particles of different particle sizes are deposited.

Shows the competence of the river at different velocities.

Question 37

What does the graph show about different particle size and the speed they are eroded? Why does this happen?

Answer 37

Particles of sand can be eroded quicker at lower velocities than clay and silt.

Because silt and clay particles stick together more than sand - harder to dislodge - requires more energy to erode them.

Question 38

What causes erosion?

Answer 38

Energy of a river flowing downhill.