UK Evolving physical landscape - 4B - River processes Flashcards
Freeze-thaw weathering -
The action of water physical freezing and expanding in cracks causing them to break apart
Chemical weathering
The reaction of acidic rainfall with alkali rocks (limestone) causing the rock to break down
Biological weathering
The action of plant roots growing into cracks in rock causing the rock to break down
Hydraulic action
Fast flowing water is forced into cracks in the bank breaking it apart
Abrasion
Sand and pebbles are dragged along a river bed wearing it away
Solution
Alkaline rocks are dissolved by the acidic water
Attrition
Rocks and stones knock into each other wearing them away
4 types of river transportation
Traction
Saltation
Suspension
solution
As a type of river transportation, what is Traction
Large stones are dragged and rolled along the river bed
As a type of river transportation, what is Saltation
the picking up and dropping of material continuously creating a bouncing motion (causes abrasion)
As a type of river transportation, what is Suspension
Tiny particles are carried in the river current
As a type of river transportation, what is solution
Dissolved chemical are carried within the water
what are 2 different types of mass movement?
Soil creep
Slumping
What is a soil creep?
the slow movement of saturated material down a slope over at 2cm per year
What is slumping?
the rotational movement of material down a slope due to weathering and water
What is Deposition?
The dropping of material due to a loss of energy.
How is a v-shaped valley with interlocking spurs formed?
- River downhill eroding the landscape vertically -> cuts a deep notch down into the landscape using hydraulic action/Abrasion
- River erodes downwards = sides of the valley are exposed to freeze-thaw weathering -> loosens the rocks ->steepens valley sides
- Fallen rocks into river = more abrasion
River transports rocks downstream -> channel = wider and deeper = V-shaped valley between interlocking spurs
Waterfall formation
Rivers flows over bands of softer and harder rocks -> softer rock more quickly eroded
River undercuts harder rock through hydraulic action leaving an overhang = plunge pool below waterfall
Overhanging rock unsupported -> falls into the plunge pool
The waterfall is moved upstream – process continues = gorge is cut back into the hillside
Meander formation
Water turns round obstructions = areas of slower and faster water movement
Rivers flows from side to side in winding course but still straight channel = helicoidal flow.
Outside bend = water moves faster -> more energy to erode = river cliff
Inside bend = water moves slowly -> deposits material load = river beach/slip-off slope Continuous erosion/erosion = meander
Meander will migrate downstream -> change shape over time
How do Floodplains and Levees form?
River on floodplain with a very low gradient -> mainly depositing (silt and sand)
Silt deposited on the river banks and much less on the floodplain -> frequent flooding continues this build up.
When the river is flowing normally it deposits in the river bed
Usually the built-up levees protect the plain from flooding
How do Oxbow lakes form?
Meander formation then:
During flood the river will cut through the neck
River continues on its straighter path and the meander is abandoned ->New deposition seals off the ends and the cut-off
storm hydrographs
watch video and questiosn
Describe the upper course
The upper course as many tributaries which are narrow and. V-shaped
Each tributary doesn’t carry a lot of water but combined the tributaries all fill up the river channel further down
The sides of the tributaries tend to be like a valley With a large gradient either side so water run into the tributary
Describe the middle course
The tributaries merge together to form a channel, which is rounder in shape and deeper, to adjust to the increase in water
The more water that passes by, the larger the energy of the water of the water which leads to more erosion to take place to widen the channel The area around the river channel isflat and low-lying,which is the floodplain if the river needs to flood.
Describe the lower course
The lower course Carries the largest volume of water it is in a very wide and very deep channel
There are ridges either side of the river banks called levees
this size of the valley has increased so it is even wider and flatter than the middle course
Give 2 examples of hard engineering River defenses
River flood wall
Earth embankment
Advantages and disadvantages of River flood wall
Flood walls
Pros:
Can be used to raise the height of the river bank to a level where the river might not burst its banks.
Can be permanent features or incorporated into the design of an area and become invisible.
Can also be temporary structures
Cons:
Can prevent access to the river for leisure or economic purposes.
Advantages and disadvantages of Earth embankments
Advantages
Cheap with a one-off cost
Allows for flood water to be contained within the river
.
Disadvantages
Looks unnatural.
Water speeds up and can increase flood risk downstream.
