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Geography > River Landscapes and Processes > Flashcards

River Landscapes and Processes Flashcards

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1
Q

Drainage basin

A

The area of land drained by a river and its tributaries

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2
Q

Watershed

A

The boundary of a drainage basin that separates one drainage basin from another
Usually in high land such as hills and ridges

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3
Q

Tributary

A

A stream or small river that joins a larger stream or river

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4
Q

Source

A

Starting point of a stream or river

Often a spring or lake

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5
Q

Confluence

A

A point where two streams or rivers meet

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6
Q

Mouth

A

The point where a river leaves its drainage basin and flows into the sea

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7
Q

What act together to change the river landscape?

A

Different processes in the drainage basin

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8
Q

Weathering

A

The breakdown and decay of rock by natural processes, usually acting on the river valley sides
Stays in situ

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9
Q

Mechanical (freeze thaw) weathering

A

When rainwater enters cracks or gaps and then freezes if temperatures drop below 0
Water expands by 10% and turns into ice and then exerts pressure on the rock, causing it to break into smaller pieces

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10
Q

Chemical weathering (acid rain)

A

All rain is slightly acidic
If the air is polluted by factories and vehicles, it can become more acidic
When rain falls on rocks, the acid in it can react with weak minerals, causing them to dissolve and the rock to decay

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11
Q

Biological weathering

A

The roots of plants, especially trees, can grow into cracks in a rock and split the rock apart

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12
Q

Mass movement

A

The movement of rocks and soil downslope due to gravity helped by weaker rocks, steep slopes and heavy rainfall

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13
Q

What speed can mass movement be?

A

Very slow- only a few mm a year- or sudden and rapid

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14
Q

Types of mass movement that affect river valleys

A

Soil creep
Sliding
Flows

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15
Q

Soil creep

A

Where individual particles of soil move slowly down a slope

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16
Q

Sliding

A

Where material moves rapidly downslope in one go, for example in a landslide
In a slump, material often rotates as it moves

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17
Q

Flows

A

Where masses of soil or rock, usually mixed with water, food like liquid downhill

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18
Q

What does river erosion involve?

A

The action of water wearing away the rocks and souls on the valley bottom and sides

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19
Q

Where do rivers have the most energy for eroding and transporting sediment?

A

When there is a large amount of water and a steep gradient

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20
Q

Four key erosion processes that affect river valleys

A

Corrosion/ abrasion
Attrition
Solution
Hydraulic action

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21
Q

Corrosion/ abrasion

A

Caused by material carried in the river rubbing against the river bed of the channel wearing them away
Causes most erosion

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22
Q

Attrition

A

Sediment particles carried in the river collide with each other, causing the edges to be knocked off
Continued collision of particles in the river caused them to become rounder and smaller downstream

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23
Q

Solution

A

River water is slightly acid so it can dissolve some rocks and minerals in contact with the water
Limestone and chalk are most affected

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24
Q

Hydraulic action

A

Results from the sheer force of the water hitting the river bed and banks and wearing them away
This action is particularly important during high velocity flows

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25
Q

Transportation

A

A river picks up and carries material as it flows downstream

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26
Q

The four types of transportation

A

Traction
Saltation
Suspension
Solution

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27
Q

Traction

A

Rolling stones along the bed

Needs the most energy

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28
Q

Saltation

A

Sand sized particles bounce along the bed in a leap frog movement

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29
Q

Suspension

A

Silt and clay sized particles are carried within the water flow

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30
Q

Solution

A

Some minerals dissolve in the water and are carried along

Needs the least energy

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31
Q

When does deposition occur?

A

When a river no longer has enough energy to carry its load

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32
Q

When is the heaviest material deposited first?

A

As the river’s discharge and velocity reduce

Eg after flooding

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33
Q

Where are rivers small and do not have a lot of power?

A

Near their source

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34
Q

What are spurs?

A

Valley side slopes that the river flows around in its upper course

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35
Q

What causes interlocking spurs?

A

Rivers flowing around spurs, rather than eroding them

Spurs left interlocking with those from one side of the valley overlapping with the spurs from the other side

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36
Q

How is a waterfall formed?

A

Along a river when a band of hard, more resistant rock lies over a band of soft, less resistant rock
The river erodes the less resistant rock at a faster rate, gradually undercutting the more resistant rock
The continued erosion of the soft rock by abrasion and hydraulic action causes an overhand of the hard rock
Eventually the hard rock cannot support its own weight and collapses under the force of gravity

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37
Q

Formation of a plunge pool

A

After a waterfall is formed, the force of the falling water and abrasion by large, angular boulders leads to erosion of the river bed and the formation of a plunge pool

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38
Q

Formation of a gorge

A

Once a plunge pool is formed the soft rock continues to be eroded
As the hard rock collapses, a steep sided gorge is formed as the waterfall retreats upstream
Gorges form in hard rocks, where vertical erosion by rivers is dominant

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39
Q

Meanders

A

Bends in a river’s course

40
Q

Where are meanders commonly found?

A

A river’s flood plain

41
Q

What causes lateral erosion?

A

The flow of the water swings from side to side directing the line of maximum velocity and the force of the water towards the outside of the bend
An outer, steep bank is formed by undercutting

42
Q

What is the outer, steeper bank formed by lateral erosion called?

A

A river cliff

43
Q

What forms a slip-off slope?

A

The velocity and force of the water is less on the inside bend
This leads to deposition and the formation of a gently sloping bank

44
Q

What is a slip off slope?

A

A gently sloping bank

45
Q

What is a point bar?

A

The material deposited when a slip off slope is formed

46
Q

What shape is a point bar?

A

Curved

47
Q

Why is the cross section of a meander asymmetrical?

A

Erosion and deposition makes it steep on the outside of the bend, gentle on the inside

48
Q

Formation of an oxbow lake

A

Meander neck becomes narrower as it bends and develops
Eventually the river may erode right through the neck, especially during a flood
Water flows through the new, straight channel and the old bend is abandoned by the river
Deposition at the neck seals off the bend, which begins to dry up
This leaves behind a horse shoe shaped lake

49
Q

Flood plain

A

The flat area of land either side of a river in its lower course

50
Q

What forms a flood plain?

A

Lateral erosion on the outside bends of meanders means they migrate across the valley floor and can erode the valley sides
The valley floor becomes wide and flat

51
Q

What happens to flood waters during floods?

A

The flood waters spread out across the valley floor

52
Q

What happens when flood waters slow down?

A

They have less energy for transport so the river deposits fine sediments called alluvium

53
Q

What are the fine river deposits during flooding?

A

Alluvium

54
Q

What are levees?

A

Natural embankments of sediment formed along the banks of rivers that carry a large load and eventually flood

55
Q

What causes levees?

A

Repeated flooding causes river banks to get higher, forming levees because water and sediment come out of the channel as the river overflows its banks and are deposited as the river loses velocity

56
Q

What do geographers divide a river and its valley into?

A

Upper, middle and lower course

57
Q

What does a river’s long profile show?

A

Height and distance downstream from the river’s source to its mouth

58
Q

How does the shape of a river change from the source to the mouth?

A 
Source= curved shape, steeper
Mouth= flatter
59
Q

Upper course characteristics

A

High annual rainfall
Runoff is high from steep upland slopes
Geology mainly hard, igneous rocks which are resistant to erosion
Narrow, shallow channel full of angular stones

60
Q

What slows the river down in the upper course?

A

Friction with the bed and banks slows the river down because of the narrow, shallow channel with angular stones

61
Q

How does the upper course erode? What forms?

A

Vertically, cutting down into the landscape and forming a V-shaped valley

62
Q

Characteristics of V-shaped valleys in upper course

A

Steep slopes

Processes such as sliding and slumping take place

63
Q

Middle course of a river characteristics

A

Leaves upland area
Flows downstream
Valley becomes wider and flatter, gradient decreases

64
Q

What creates areas of floodplains in the middle course?

A

Wider and flatter valleys

65
Q

Direction of erosion in the middle course

A

Sideways, through lateral erosion, as well downwards

Some deposition eg on inside bends of meanders

66
Q

Why does sediment become smaller and more rounded in the middle course?

A

They will be eroded by the river and transported downstream

67
Q

What increases as more tributaries join a river?

A

Its discharge

68
Q

How does the climate change in the lower course?

A

Average annual rainfall decreases

69
Q

Geology of the lower course

A

Softer, sedimentary rocks eg sandstone

70
Q

What does lateral erosion create in the lower course?

A

A wide valley and river channel with a flat bottom

71
Q

Why is the river’s velocity greatest in the lower course?

A

Less friction with the river beds and banks because the channel is deep and smooth

72
Q

What does a muddy river show?

A

A high sediment load

73
Q

What does a high sediment load encourage?

A

Deposition eg at the mouth where the flow is checked by the sea

74
Q

What does the Bradshaw Model summarise?

A

How the river changes between the upper, middle and lower course

75
Q

Width

A

Distance from one bank to another

Increases from source to mouth

76
Q

Depth

A

Distance from surface of the water to the river bed

Increases from source to mouth

77
Q

Velocity

A

How fast the river is flowing

Increases from source to mouth

78
Q

Discharge

A

The volume and speed at which water flows through the river channel
Increases from source to mouth

79
Q

Gradient

A

Steepness of a river bed

Decreases from source to mouth

80
Q

Channel roughness

A

How rough the river’s bed and banks are

Decreases from source to mouth- becomes smoother, so less friction

81
Q

Sediment size and shape

A

The material carried by the river

Decreases and becomes smaller and rounder

82
Q

Contours

A

Lines joining places of equal height above sea level

Tell us how much the land slopes

83
Q

What do contours close together on a map show?

A

Where land slopes steeply

84
Q

What do contours further apart on a map show?

A

Gentle slopes

85
Q

What do areas with few contours, or none at all, have?

A

Little or no gradient

Flat

86
Q

What can worsen flooding?

A

Human activities

87
Q

Average annual cost of damage from flooding

A

Between £500 million and £1 billion

88
Q

When does a river flood?

A

When it overflows it’s bank (exceed river bank discharge) causing water to spread out onto nearby land

89
Q

Physical factors that can lead to flooding

A 
Intense rainfall 
Duration of rainfall 
Snow melt
Rocks 
Relief
90
Q

How does intense rainfall cause flooding?

A

During periods of heavy rainfall, soil and rocks can quickly become saturated
As infiltration reduced, water flows over the surface and into the river at a faster rate

91
Q

How does duration of rainfall cause flooding?

A

Long periods of rainfall cause the soil to become saturated and prevent further infiltration or rainwater, leading to increased surface runoff

92
Q

How does snow melt cause flooding?

A

In some places a lot of snow falls during the winter months

When temperatures rise above 0 in spring, all snow that has built up melts releasing large volumes of meltwater

93
Q

How do rocks cause flooding?

A

Different rock types in the catchment can affect flooding
Permeable rocks reduce surface runoff because they allow water to soak in
Impermeable rocks don’t allow water to pass through them so rainwater runs off the surface, straight into the channel

94
Q

How does relief cause flooding?

A

Water reaches the river channel much faster where slopes are steeper

95
Q

Human causes of flooding

A

Deforestation

Urbanisation

96
Q

How does deforestation cause flooding?

A

Vegetation collects, stores and uses water from rainfall, this is called interception
Plant roots encourage water to pass into soil and rock so vegetation reduces runoff
If it is removed, more water can reach the river channel more quickly

97
Q

How does urbanisation cause flooding?

A

In towns and cities, rainwater will not infiltrate the hard, impermeable surfaces of concrete and tarmac causing the water to runoff immediately into drains and river channels

Geography (6 decks)

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