Ch 2.2 What are the major fluvial processes?

Question 1

What is drainage density?

Answer 1

(Total length of the channels in a drainage basin)/ (Total area of the drainage basin)

Question 1

How would the drainage density be higher?

Answer 1

1. High annual rainfall -> Longer length.
2. Steep basin slope -> Smaller in area.
3. Impermeable rock layer at the surface -> Longer length.
4. Bare land surface -> Longer length.

Question 2

What are the characteristics of the three sections of the river?

Answer 2

The upper course is the steepest while the lower course is the gentlest.

Question 3

How is the energy of a river affected?

Answer 3

1. Amount of channel water.
2. Speed of water flow.
   Affecting the discharge. Thus the larger the discharge, the more energy a river has.

Question 4

How to calculate the discharge?

Answer 4

Stream width x Average depth x River velocity,

Question 5

What leads to increasing amount of channel water?

Answer 5

1. Higher amounts of rainfall.
2. Larger size of drainage basin. -> Collect more water.
3. Steeper slope gradient. -> Less infiltration, more overland flow.
4. Lower permeability of soils and rock -> Less infiltration, more overland flow.
5. Sparse vegetation cover -> Less interception&infiltration, more overland flow.

Question 6

What leads to increasing speed of water flow?

Answer 6

1. Steeper channel gradient.
2. Smooth channel -> Shorter wetted perimeter -> Smaller friction.
3. Semi circular channel has a shorter wetted perimeter than rectangular or V-shaped channel -> Smaller friction.
4. Fewer sediments amount carried in the channel -> Less energy is used to overcome the friction.

Question 7

What is fluvial erosion?

Answer 7

Running water carrying load to remove fine particles from the river banks or river bed.

Question 8

What are the directions of the fluvial erosion?

Answer 8

Headward erosion (Lengthens the river channel).
Vertical erosion (Deepens the river channel).
Lateral erosion (Widens the river channel).

Question 9

What are the four types of fluvial erosion.

Answer 9

1. Solution - Soluble minerals dissolved away.
2. Abrasion - Load rubs against the bed/banks.
3. Attrition - Rocks in the load collide and break.
4. Hydraulic action - Water is pushed into cracks at the bank, where the air is compressed. The pressure created breaks up the rock.

Question 10

What are factors that affect the rate of fluvial erosion?

Answer 10

1. Erosive power of a river.
2. Types of rock.
3. Human Activities.

Question 11

What are kinds of erosive power of a river?

Answer 11

1. Characteristics of load.
2. Energy of a river.
3. Water quality.

Question 12

Explain on the characteristics of of load.

Answer 12

1. More load -> More tools for erosion.
2. Heavier and angular load -> Greater potential for erosion.

Question 13

What affects the energy of a river?

Answer 13

1. Speed of river flow: Faster water flow -> Greater energy.
2. Amount of channel water: More water -> more energy.
3. Slope gradient: Steeper gradient -> Faster flow -> greater energy.

Question 14

What water quality affects the rate of fluvial erosion?

Answer 14

Acidic water favour solution.

Question 15

What are the type of rock that affects the rate of fluvial erosion?

Answer 15

Rocks with more cracks and more soluble minerals -> Erode more easily.

Question 16

What are the human activities that affect the rate of fluvial erosion?

Answer 16

1. Deforestation.
2. Urbanisation.
3. Industrial, farming and other activities.

Question 17

How does deforestation affect the rate of fluvial erosion?

Answer 17

Less vegetation cover -> More overland flow -> More rocks and stones washed into the river -> More tools for erosion.

Question 18

How does urbanisation affect the rate of fluvial erosion?

Answer 18

More surfaces covered with cement -> Less infiltration -> More overland flow -> Increases river discharge -> Greater river energy.
Slope cutting -> increases slope gradient -> More overland flow -> More channel water -> More energy.

Question 19

How does the industrial, farming and other activities affect the rate of fluvial erosion?

Answer 19

Industrial, agricultural and domestic sewage pollute the river water -> Increasing the acidity of river water -> favours solution.

Question 20

What is transportation?

Answer 20

Downstream movement of river load.

Question 21

What are the four types of transportation?

Answer 21

1. Suspension - Fine light materials are carried along without touching the river bed.
2. Traction - Large and heavy boulders and rocks are rolled and dragged along the river bed.
3. Saltation - Small tones and pebbles bounce along the river bed.
4. Solution - Soluble minerals are dissolved and carried downstream.

Question 22

What is fluvial deposition?

Answer 22

When a river loses energy, it drops its load. The load will be deposited on the river bed as sediment. The process is known as fluvial deposition.

Question 23

What are the factors affecting fluvial deposition?

Answer 23

Decrease in the amount of channel water. - Water supply decrease, High evaporation.
Decrease in speed of water flow. - River joining a large body of water, Increase of channel friction, Increase in amount of load, Decrease in channel gradient.

Question 24

What is sorting process?

Answer 24

The way a river deposits its load according to the size of it is called sorting process.

Question 25

How does the deposition time changes from the near the river mouth to further away from the river mouth?

Answer 25

Earlier to later.

Question 25

How does the size of load changes from the near the river mouth to further away from the river mouth?

Answer 25

Larger to smaller.

Question 26

What is the explanation of the sorting process from near the river mouth?

Answer 26

Small drop of river energy, great drop of energy.