Fluvial Processes + Transportation Flashcards
What is Hydraulic Action?
Where the sheer force of the water erodes the river bed and the bank. This is most effective when the river is flowing fast and there is lots of water (flood conditions)
What is Abrasion?
Where stones in transport are thrown at the river bed and the river banks causing some of the material to break off (i.e. erosion)
What is Attrition?
It is where the stones and boulders carried by the river knock against each other, causing pieces to break off. The stones become smaller, smoother and more rounded.
What is a solution?
This process of river erosion occurs when water flows over certain type of rocks like chalk or limestone. These are soluble in slightly acidic river water and are dissolved by it.
Vertical Erosion
Vertical Erosion is the downward erosion which deepens the river channel
Lateral Erosion
Lateral Erosion is the sideward erosion which widens the river channel
What Occurs in the Upper Course section of a river?
- Vertical Erosion
- Narrow V-shaped Valley
- Pot-Holes
- Interlocking spurs
- Waterfalls
- Rapids
- Gorges
- Large Boulders
What Occurs in the Middle Course of a River?
- Lateral Erosion
- Transportation
What occurs in the lower course of a River?
- Transportation
- Deposition
- Friction is reduced, so greater velocity (speed of water flow)
How does Traction work?
This is the method that the river uses for moving the largest type of material. The boulders that are too heavy to lift off the river bed are rolled along in Traction
How does Saltation work?
This moves the small stones and grains of sand by BOUNCING them off the river bed.
How does Suspension work?
This is when the river carries along fine light material within the river downstream.
How does Solution work?
This is when the local rocks are dissolved chemically into the river. This can only occur with soluble rocks (like limestone) that dissolve in rainwater.
Capacity of a river?
The capacity of a river is the amount of material it can carry (i.e. the total volume of load). A river’s capacity increases according to its velocity.
What’s the COMPETENCE of a river?
The competence of a river is the largest particle it can carry for a given velocity
What is the definition of Deposition?
Deposition is the laying down of sediment carried by wind, flowing water, the sea or ice. Sediment can be transported as pebbles, sand and mud, or as salts dissolved in water.
Why do rivers deposit sediment??
Deposition occurs whenever a river loses energy and velocity falls. This can be when:
- a river enters a shallow area (when it floods and comes into contact with a flood plain)
- at the base of a waterfall
- on the inside bend of a meander-toward its mouth where it meets another body of water
What is the long profile of a river?
The long profile of a river shows the gradient of a river as it jounreys from source to mouth
The long profile of a river is a way of displaying the channel slope (gradient) of a river along its entire length. Therefore it shows how a river loses height with increasing distance towards the sea
What is a meander and how is it formed?
As a river erodes laterally to the right side then the left side, it forms large bends and loops called meanders. The force of the water erodes the river bank on the outside of the bend where due to reduced friction, the water flow has most energy. On the inside bend, where river flow is slower, material is deposited as there is more friction forming a slip-off slope or river beach.
What is the cross river profile?
The cross profile of a river shows how the width and depth of the river valley and channel change as you travel downstream.
Why does the cross profile of a river change along its course?
In the upper course, the river erodes its bed by hydraulic action and abrasion.
As the river flows downstream tributaries increase the volume of water, velocity and its erosive power. This enables it to cut a deeper channel becomes wider as the gradient becomes more gentle leading to less vertical erosion. By the middle course of the river lateral erosion becomes the dominant type of erosion causing the river to become wider.
Explain the formation of a waterfall
Waterfalls form where there are layers of horizontal rock.
Hard rock is on top of the soft
Where the soft rock is close to the surface under the hard, it is eroded faster by abrasion and hydraulic action and an overhang is created of the cap rock
Over time, this will get bigger and eventually it will collapse creating a waterfall,
Repeated erosion by material in the plunge pool deepens the waterfall
Difference between hard and soft engineering
Hard engineering river management involves building artificial structures ewhich try to control natural processes
Soft engineering involves taking a more sustainable and natural approach to managing rivers
Social, economic and environmental affects of flooding
Social: -Damage to property -Injury or loss of life Economic: -Cost of repairs -Reduced toursim -Closure of businesses Environmental: -Loss of habitat -Loss of wildlife
