Ch 2.2 What are the major fluvial processes? Flashcards
What is drainage density?
(Total length of the channels in a drainage basin)/ (Total area of the drainage basin)
How would the drainage density be higher?
- High annual rainfall -> Longer length.
- Steep basin slope -> Smaller in area.
- Impermeable rock layer at the surface -> Longer length.
- Bare land surface -> Longer length.
What are the characteristics of the three sections of the river?
The upper course is the steepest while the lower course is the gentlest.
How is the energy of a river affected?
- Amount of channel water.
- Speed of water flow.
Affecting the discharge. Thus the larger the discharge, the more energy a river has.
How to calculate the discharge?
Stream width x Average depth x River velocity,
What leads to increasing amount of channel water?
- Higher amounts of rainfall.
- Larger size of drainage basin. -> Collect more water.
- Steeper slope gradient. -> Less infiltration, more overland flow.
- Lower permeability of soils and rock -> Less infiltration, more overland flow.
- Sparse vegetation cover -> Less interception&infiltration, more overland flow.
What leads to increasing speed of water flow?
- Steeper channel gradient.
- Smooth channel -> Shorter wetted perimeter -> Smaller friction.
- Semi circular channel has a shorter wetted perimeter than rectangular or V-shaped channel -> Smaller friction.
- Fewer sediments amount carried in the channel -> Less energy is used to overcome the friction.
What is fluvial erosion?
Running water carrying load to remove fine particles from the river banks or river bed.
What are the directions of the fluvial erosion?
Headward erosion (Lengthens the river channel).
Vertical erosion (Deepens the river channel).
Lateral erosion (Widens the river channel).
What are the four types of fluvial erosion.
- Solution - Soluble minerals dissolved away.
- Abrasion - Load rubs against the bed/banks.
- Attrition - Rocks in the load collide and break.
- Hydraulic action - Water is pushed into cracks at the bank, where the air is compressed. The pressure created breaks up the rock.
What are factors that affect the rate of fluvial erosion?
- Erosive power of a river.
- Types of rock.
- Human Activities.
What are kinds of erosive power of a river?
- Characteristics of load.
- Energy of a river.
- Water quality.
Explain on the characteristics of of load.
- More load -> More tools for erosion.
- Heavier and angular load -> Greater potential for erosion.
What affects the energy of a river?
- Speed of river flow: Faster water flow -> Greater energy.
- Amount of channel water: More water -> more energy.
- Slope gradient: Steeper gradient -> Faster flow -> greater energy.
What water quality affects the rate of fluvial erosion?
Acidic water favour solution.
What are the type of rock that affects the rate of fluvial erosion?
Rocks with more cracks and more soluble minerals -> Erode more easily.
What are the human activities that affect the rate of fluvial erosion?
- Deforestation.
- Urbanisation.
- Industrial, farming and other activities.
How does deforestation affect the rate of fluvial erosion?
Less vegetation cover -> More overland flow -> More rocks and stones washed into the river -> More tools for erosion.
How does urbanisation affect the rate of fluvial erosion?
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.
How does the industrial, farming and other activities affect the rate of fluvial erosion?
Industrial, agricultural and domestic sewage pollute the river water -> Increasing the acidity of river water -> favours solution.
What is transportation?
Downstream movement of river load.
What are the four types of transportation?
- Suspension - Fine light materials are carried along without touching the river bed.
- Traction - Large and heavy boulders and rocks are rolled and dragged along the river bed.
- Saltation - Small tones and pebbles bounce along the river bed.
- Solution - Soluble minerals are dissolved and carried downstream.
What is fluvial deposition?
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.
What are the factors affecting fluvial deposition?
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.
What is sorting process?
The way a river deposits its load according to the size of it is called sorting process.
How does the deposition time changes from the near the river mouth to further away from the river mouth?
Earlier to later.
How does the size of load changes from the near the river mouth to further away from the river mouth?
Larger to smaller.
What is the explanation of the sorting process from near the river mouth?
Small drop of river energy, great drop of energy.
