1. 2.2 What are the major fluvial processes?
Part B

2. Direction of fluvial erosion Vertical erosion / Downcutting
How can a river erode the land?
Three directions of fluvial erosion
The higher the energy of the river, the more the erosive power.
Direction of fluvial erosion
Vertical erosion / Downcutting
Lateral erosion
Headward erosion

3. Three directions of fluvial erosion
Vertical erosion / Downcutting
A river removes rocks from its bed.
The valley will be deepened.

4. Three directions of fluvial erosion
Lateral erosion
Original valley
A river removes rock along the banks.
The valley is widened.

5. Three directions of fluvial erosion
Headward erosion
Loose rock debris is brought down by the overland flow behind the river source.
The river source extends backward.
The valley is increased in length.

6. Ways of fluvial erosion
How can a river erode the land?
Four ways of fluvial erosion
Ways of fluvial erosion
Abrasion
Attrition
Hydraulic action
Corrosion / Solution

7. Four ways of fluvial erosion
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8. How can a river erode the land?
What factors control the rate of erosion of a river?
Angularity, amount and weight of load
Speed of water flow
Erosive power of river
Resistance of rock
Amount of channel water
Channel gradient
Rate of fluvial erosion
Water quality (acidity, temperature)
Rock structure
Mineral composition

9. How can a river erode the land?
How do human activities cause more fluvial erosion?
Industrial activities:
discharge of pollutants
water acidity
fluvial erosive power
Deforestation:
interception overland flow
amount of channel water
fluvial erosive power
Cutting a slope:
slope gradient and infiltration overland flow
amount of channel water
fluvial erosive power

10. In what ways does a river carry its load?
Apart from erosion, river energy can carry the eroded materials as ‘load’.
The downstream movement of eroded material is called ‘transportation’.
The higher the energy of a river, the ( less / more ) efficient its transportation.
The Huang He

11. In what ways does a river carry its load?
Four ways of transportation
Large particles hop and bounce along the river bed
Small particles are carried in the water without touching the river bed
Dissolved minerals carried by water
Suspended load
Suspension
Bed load
Solution
Dissolved load
Very large particles roll or slide on the river bed
Bed load
Traction
Saltation

12. In what ways does a river carry its load?
What factors control the amount of load in a river?
(Credit: Tsui Chung Pong David)
The Huang He carries a large amount of load.
The load of the river is mainly silt from the Huangtu Gaoyuan (Loess Plateau). It gives the yellowish colour to the river.

13. In what ways does a river carry its load?
What factors control the amount of load in a river?
1 Energy of a river
Larger amount of channel water
A river can carry (more / less) load
More energy for transportation OR
A river can carry (heavier / lighter) load
Higher speed of water flow

14. In what ways does a river carry its load?
What factors control the amount of load in a river?
2 Rate of erosion
The erosion rate of the river basin controls the supply of load.
( Dense / Sparse ) vegetation helps hold the soil and prevents it from being eroded.

15. In what ways does a river carry its load?
What factors control the amount of load in a river?
3 Presence of lakes
Lakes along a river channel help trap the load.
This ( increases / decreases ) the amount of load that will reach the river.
(Credit: Tsui Chung Pong David)

16. What makes a river lose its energy?
Deposition occurs when a river loses its energy.
The deposited materials are called ‘sediment’.
Amount of channel water decreases
(More / Less) energy for transportation
The load deposits OR
Speed of water flow decreases
(Credit: Tsui Chung Pong David)

17. What makes a river lose its energy?
How does a river drop its load?
Please click below for footage
The smallest and lightest sediment deposits last.
What is the sequence of deposition?
The largest and heaviest sediment deposits first.

18. What is the sequence of deposition of these four types of load?
What makes a river lose its energy?
How does a river drop its load?
What is the sequence of deposition of these four types of load?
The heaviest load (i.e. __________) will deposit first and form the bottommost layer.
pebble
silt
The finest one (i.e. _______) forming the top layer.

19. What makes a river lose its energy?
How does a river drop its load?
The load forms layers at different distances from the mouth of the river.
River
Pebbles and sand
Silt
Clay
Sea

20. Skill box How can we show the variation of river discharge over time?
Let us see how we can interpret a hydrograph.
By a hydrograph.

21. How can we show the variation of river discharge over time by a hydrograph?
Rainfall
Discharge
Base flow
This is a hydrograph.

22. How can we show the variation of river discharge over time?
River discharge varies after rain.
Discharge is low before rain starts.
When rain starts, discharge begins to rise.
After reaching the peak, the discharge starts to drop.

23. It is the maximum amount of water a river can hold.
How can we show the capacity of the channel?
It is the maximum amount of water a river can hold.
Bankfull discharge
If the discharge is below the bankfull discharge, it means that the river is able to hold the rainwater.

24. How can we show the capacity of the channel?
The channel cannot hold the flood water
Bankfull discharge
If the discharge is above the bankfull discharge, _________ occurs.
flooding

25. What is the cut-off of a river?
Rainfall decreases or stops
Base flow runs out
Period of cut-off
It rains again
River discharge falls