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River Landscapes and Processes Flashcards

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
Transportation
A river picks up and carries material as it flows downstream
26
The four types of transportation
Traction Saltation Suspension Solution
27
Traction
Rolling stones along the bed | Needs the most energy
28
Saltation
Sand sized particles bounce along the bed in a leap frog movement
29
Suspension
Silt and clay sized particles are carried within the water flow
30
Solution
Some minerals dissolve in the water and are carried along | Needs the least energy
31
When does deposition occur?
When a river no longer has enough energy to carry its load
32
When is the heaviest material deposited first?
As the river’s discharge and velocity reduce | Eg after flooding
33
Where are rivers small and do not have a lot of power?
Near their source
34
What are spurs?
Valley side slopes that the river flows around in its upper course
35
What causes interlocking spurs?
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
36
How is a waterfall formed?
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
37
Formation of a plunge pool
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
38
Formation of a gorge
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
39
Meanders
Bends in a river’s course
40
Where are meanders commonly found?
A river’s flood plain
41
What causes lateral erosion?
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
What is the outer, steeper bank formed by lateral erosion called?
A river cliff
43
What forms a slip-off slope?
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
What is a slip off slope?
A gently sloping bank
45
What is a point bar?
The material deposited when a slip off slope is formed
46
What shape is a point bar?
Curved
47
Why is the cross section of a meander asymmetrical?
Erosion and deposition makes it steep on the outside of the bend, gentle on the inside
48
Formation of an oxbow lake
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
Flood plain
The flat area of land either side of a river in its lower course
50
What forms a flood plain?
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
What happens to flood waters during floods?
The flood waters spread out across the valley floor
52
What happens when flood waters slow down?
They have less energy for transport so the river deposits fine sediments called alluvium
53
What are the fine river deposits during flooding?
Alluvium
54
What are levees?
Natural embankments of sediment formed along the banks of rivers that carry a large load and eventually flood
55
What causes levees?
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
What do geographers divide a river and its valley into?
Upper, middle and lower course
57
What does a river’s long profile show?
Height and distance downstream from the river’s source to its mouth
58
How does the shape of a river change from the source to the mouth?
``` Source= curved shape, steeper Mouth= flatter ```
59
Upper course characteristics
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
What slows the river down in the upper course?
Friction with the bed and banks slows the river down because of the narrow, shallow channel with angular stones
61
How does the upper course erode? What forms?
Vertically, cutting down into the landscape and forming a V-shaped valley
62
Characteristics of V-shaped valleys in upper course
Steep slopes | Processes such as sliding and slumping take place
63
Middle course of a river characteristics
Leaves upland area Flows downstream Valley becomes wider and flatter, gradient decreases
64
What creates areas of floodplains in the middle course?
Wider and flatter valleys
65
Direction of erosion in the middle course
Sideways, through lateral erosion, as well downwards | Some deposition eg on inside bends of meanders
66
Why does sediment become smaller and more rounded in the middle course?
They will be eroded by the river and transported downstream
67
What increases as more tributaries join a river?
Its discharge
68
How does the climate change in the lower course?
Average annual rainfall decreases
69
Geology of the lower course
Softer, sedimentary rocks eg sandstone
70
What does lateral erosion create in the lower course?
A wide valley and river channel with a flat bottom
71
Why is the river’s velocity greatest in the lower course?
Less friction with the river beds and banks because the channel is deep and smooth
72
What does a muddy river show?
A high sediment load
73
What does a high sediment load encourage?
Deposition eg at the mouth where the flow is checked by the sea
74
What does the Bradshaw Model summarise?
How the river changes between the upper, middle and lower course
75
Width
Distance from one bank to another | Increases from source to mouth
76
Depth
Distance from surface of the water to the river bed | Increases from source to mouth
77
Velocity
How fast the river is flowing | Increases from source to mouth
78
Discharge
The volume and speed at which water flows through the river channel Increases from source to mouth
79
Gradient
Steepness of a river bed | Decreases from source to mouth
80
Channel roughness
How rough the river’s bed and banks are | Decreases from source to mouth- becomes smoother, so less friction
81
Sediment size and shape
The material carried by the river | Decreases and becomes smaller and rounder
82
Contours
Lines joining places of equal height above sea level | Tell us how much the land slopes
83
What do contours close together on a map show?
Where land slopes steeply
84
What do contours further apart on a map show?
Gentle slopes
85
What do areas with few contours, or none at all, have?
Little or no gradient | Flat
86
What can worsen flooding?
Human activities
87
Average annual cost of damage from flooding
Between £500 million and £1 billion
88
When does a river flood?
When it overflows it’s bank (exceed river bank discharge) causing water to spread out onto nearby land
89
Physical factors that can lead to flooding
``` Intense rainfall Duration of rainfall Snow melt Rocks Relief ```
90
How does intense rainfall cause flooding?
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
How does duration of rainfall cause flooding?
Long periods of rainfall cause the soil to become saturated and prevent further infiltration or rainwater, leading to increased surface runoff
92
How does snow melt cause flooding?
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
How do rocks cause flooding?
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
How does relief cause flooding?
Water reaches the river channel much faster where slopes are steeper
95
Human causes of flooding
Deforestation | Urbanisation
96
How does deforestation cause flooding?
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
How does urbanisation cause flooding?
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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