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Geography > Rivers,Floods and Management > Flashcards

Rivers,Floods and Management Flashcards

1
Q

What is a drainage basin?

A

The area surrounding the river where the rain falling on the land flow into the river.
This area is also called the river’s catchment.

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2
Q

What is an input into the drainage basin?

A

Precipitation

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3
Q

What are the storages in a drainage basin?

A 
Interception e.g. Buildings 
Vegetation storage e.g. Plants
Surface Storage e.g. Puddles
Groundwater storage e.g. Soil
Channel storage e.g. Rivers
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4
Q

What is surface runoff(overland flow)?

A

Water flowing over land

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5
Q

What is through flow?

A

Water moving slowly downhill through the soil

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6
Q

What is infiltration?

A

Water soaking into the soil

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7
Q

What is percolation?

A

Water seeping down through the soil into the water table

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8
Q

What is base flow?

A

Groundwater flow that feeds into rivers through river banks and river beds

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9
Q

What is groundwater flow?

A

Water slowly flowing below the water table through permeable rock

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10
Q

Name four outputs of the hydrological cycle

A

Evaporation
Transpiration-Evaporation through plant leaves
Evapotranspiration
River discharge

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11
Q

What is river discharge?

A

The volume of water(in cubic metres) that flows in a river per second.
It’s measured in cumecs.

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12
Q

What is the peak discharge?

A

The highest point on the graph, where the river discharge is at its greatest

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13
Q

What is the lag time?

A

The delay between peak rainfall and peak discharge

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14
Q

What is the rising limb?

A

The part of the graph up to peak discharge

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15
Q

What is the falling limb?

A

The part of the graph after peak discharge

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16
Q

Name seven physical factors that affect lag time and peak discharge

A 
Drainage basin characteristics
The amount of water present in the drainage basin
The rock type
The soil type
Vegetation
Precipitation
Temperature
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17
Q

How does human activity affect the hydrograph?

A

Man-made drainage basins

Man-made impermeable materials

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18
Q

What is headward erosion?

A

Headward erosion makes the river longer.
It happens near a river’s source as throughflow and surface runoff causes erosion at the point the water enters the river channel.

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19
Q

What is vertical erosion?

A

Vertical erosion deepens river channels.

It happens in the upper stages of a river.

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20
Q

What is lateral erosion?

A

Lateral erosion makes the river wider.

It happens in the middle and lower stages of a river.

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21
Q

What is hydraulic action?

A

The pressure of the water breaks rock particles away from the bed and banks.
Its strongest in Rapids and waterfalls, and during floods.

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22
Q

What is abrasion(corrasion)?

A

Eroded pieces of rock in the water scrape and rub against the bed and banks, removing material.
Most erosion of river beds and banks happens by abrasion.

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23
Q

What is attrition?

A

Eroded rocks smash into each other and break into smaller fragments.
Their edges also get rounded off as they rub together.
Attrition doesn’t erode the bed and banks- it just makes the particles of rock in the river smaller and more rounded.

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24
Q

What is cavitation?

A

Air bubbles in turbulent stretches of water implode causing shockwaves that break pieces of rock off the banks and bed.

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25
Q

What is corrosion(solution)?

A

The dissolving of rock by chemical processes.
Carbon dioxide dissolves in water to form a weak acid, which reacts with rocks like limestone and chalk, breaking them down.

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26
Q

What is transportation?

A

The process of eroded material being carried in a river

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27
Q

What is solution?

A

Substances that can dissolve are carried along in the water.

E.g. Limestone is dissolved into river water that’s slightly acidic.

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28
Q

What is suspension?

A

Very fine material,like silt and clay particles, is whipped up by turbulence and carried along in the water.
Most eroded material is transported this way.

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29
Q

What is saltation?

A

Larger particles, like pebbles or gravel, are too heavy to be carried in suspension.
Instead, the force of the water causes them to bounce along the river bed.

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30
Q

What is traction?

A

Very large particles, e.g. Boulders, are pushed along the river bed by the force of the quart.

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31
Q

What is the river’s bed load?

A

Material transported by traction or saltation is called the river’s bed load

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32
Q

What is deposition?

A

The process of dropping eroded material

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33
Q

Name five ways the river loses energy and deposits its eroded material

A 
Reduced rainfall
Increased evaporation or abstraction 
Friction 
When the river is forced to slow down e.g. Before a narrow section in the river channel
When the river meets the sea
34
Q

What is the capacity of a river?

A

The total load(measured in volume, weight or mass) that a river can transport at a given point).
The load of a river can be divided into different categories according to particle size.

35
Q

What is the competence of a river?

A

The maximum particle size that the river is capable of transporting at a given point

36
Q

What does the Hjulström curve show?

A

The link between river velocity and competence

37
Q

What does the long profile show?

A

How the river’s gradient changes from its source to the sea(mouth) by showing the height of the river bed above the base level for the whole level of the river

38
Q

What is the base level?

A

The lowest point that the river can erode to-usually sea level

39
Q

Describe the upper stage of the long profile for a river

A

The gradient is steep and the river is high above sea level, which give its lots of potential energy

40
Q

Describe the middle stage of the long profile for a river

A

As the gradient decreases, more potential energy is converted to kinetic energy- the river gains velocity

41
Q

Describe the lower stage of the long profile for a river

A

The river has little potential energy, but lots of kinetic energy- it flows faster

42
Q

What happens to the velocity and discharge of a river as you go downstream?

A

Increases

43
Q

What is the hydraulic radius?

A

The channels cross-section area divided by the length of the wetted perimeter

44
Q

What does a larger hydraulic radius show?

A

A smaller proportion of water is in contact with the wetted perimeter.
So friction is lower, which reduces energy loss, increasing velocity and discharge.

45
Q

How does channel roughness affect the efficiency of the river?

A

Protruding banks and large, angular boulders on the river bed increase the wetted perimeter and cause more friction.
This reduces efficiency, velocity and discharge.

46
Q

What types of erosion occurs at each stage of the long profile for the river?

A

Upper stage-Mainly vertical erosion and by abrasion
Middle stage-Mainly lateral and by abrasion
Lower stage-some lateral erosion occurs during the formation of meanders

47
Q

What type of transportation occurs at each stage of the long profile for the river?

A

Upper stage-Mainly large particles such as boulders carried by traction or saltation during high energy conditions
Middle stage-More material carried in suspension as particle sizes decreases and some larger particles moved by saltation.
Lower stage-Mainly smaller particles such as clay and silt carried by suspension

48
Q

What type of deposition occurs at each stage of the long profile for the river?

A

Upper stage-Little deposition which are mainly the largest particles deposited in the river bed as energy drops
Middle stage-Sand and gravel are deposited across the flood plain as the river floods and friction reduces the river’s energy
Lower stage-smaller particles such as sand, silt and clay are deposited on the flood plain

49
Q

What does the cross profile of the river show?

A

What the cross-section of the river channel or the river valley looks like

50
Q

What does the upper stage of the cross profile for a river show?

A

Upper stage valleys are steep V shapes.

Vertical erosion creates valley floors and steeply sloped sides.

51
Q

What does the middle stage of the cross profile for a river show?

A

Middle stage valleys are wider, caused by lateral erosion.

Deposition creates a flood plain on the valley floor.

52
Q

What does the lower stage of the cross profile for the river show?

A

Lower stage valleys are wide with gently sloping sides.

There’s a much wider flood plain caused by deposition.

53
Q

Where do waterfalls form?

A

Where a band of hard rock meets softer rock

54
Q

How do waterfalls form?

A

Soft rock is eroded more than the harder rock, causing a “step” in the river bed.
The water flowing over the step speeds up due to the lack of friction as if drops over the step.
This increase in speed gives the water greater erosive power, causing further erosion of the soft rock and undercutting of the harder rock.

55
Q

How are plunge pools formed?

A

As the hard rock is undercut, it can collapse.
A deep plunge pool is carved out by abrasion at the foot of the waterfall as the bits of collapsed rock are swirled around by turbulence.

56
Q

How is a steep-sided gorge formed?

A

Over time more undercutting of the harder rock causes more collapse.
The waterfall will retreat leaving behind a steep-sided gorge.

57
Q

What is a pothole?

A

Potholes are small circular hollows in the river bed

58
Q

How are potholes formed?

A

They’re formed by abrasion as turbulence swirls a river’s bedload round in a circular motion, causing it to rub and scrape out holes

59
Q

What are Rapids?

A

Relatively steep sections of river with turbulent flow where there are several sections of hard rock

60
Q

What are meanders?

A

Large, sweeping curves in a river’s middle and lower stages formed by erosion and deposition

61
Q

Where do meanders form?

A

Where alternating pools(areas of deep water) and riffles(shallow water) develop at equally spaced intervals along a stretch of river.
The distance between pools is 5-6 times the width of the river bed.

62
Q

How do meanders start to form?

A

Because the river channel is deeper in pools it’s more efficient, so it has greater energy and more erosive power.
Energy is lost as the river flows over a riffle because of friction.

63
Q

How does meanders form?

A

The spacing and distance between riffles and and pools causes the river’s flow to become uneven and maximum flow to be concentrated on one side of the river.
Turbulence increases in and around pools as the water speeds up, so the flow of water begins to twist and coil.

64
Q

What is helicoidal flow?

A

Corkscrew like currents in the river, which spirals from bank to bank between pools

65
Q

What does helicoidal flow cause?

A

More erosion and deepening of the pools.

It also causes more eroded material to be deposited on the inside of the next bend, where the river loses energy.

66
Q

How are large meanders formed?

A

The combination of erosion and deposition exaggerates the bends.
This combined process also creates the meanders’ distinctive asymmetric cross-section.

67
Q

How are oxbow lakes formed?

A

When the neck of the loop of a meander is broken through, often during flooding.
Deposition dams off the loop, leaving an oxbow lake.

68
Q

When does braiding occur?

A

When rivers are carrying a vast amount of eroded sediment(e.g. in meltwater).

69
Q

How does braiding occur?

A

If the river’s velocity drops, or the sediment load becomes too much for the river to carry, sediment is deposited in the channel

70
Q

What is braiding?

A

Where the river is divided into many small, winding channels that eventually rejoin to form a single channel

71
Q

What are levees?

A

Natural, raised embankments former as a river overflows its banks

72
Q

How are levees formed?

A

During a flood, material is deposited across the whole flood plain as the river loses velocity and energy due to increased friction.
The heaviest material(e.g.sand and gravel) is dropped first, closest to the river channel.
Over time the material builds up on the river band, creating a levee.

73
Q

When are deltas formed?

A

When a river reaches the sea(or a lake), the energy of the river is absorbed by the slower moving water of the sea(or lake)

74
Q

How do deltas form?

A

The river deposits its load which builds up on the sea bed, until the alluvium(deposited sediment) rises above sea level, partially blocking the mouth of the river.
The river has to braid into several distributaries in order to reach the sea, forming a delta.

75
Q

When do flood plains form?

A

When a river overflows its banks and floods the flat land either side of the river(the flood plain), there’s an increase in the wetted perimeter and reduction in hydraulic radius

76
Q

How do flood plains form?

A

Increased friction reduces the velocity of the river and causes fine silt and sand to be deposited across the flood plain

77
Q

What is rejuvenation?

A

A river is said to be rejuvenated if its base level is lowered

78
Q

How can rejuvenation be caused?

A

By either the ground level rising(crustal uplift) or by a drop in sea level

79
Q

How does rejuvenation occur?

A

A drop in the base level gives the river greater potential energy, increasing its vertical erosion potential

80
Q

What are the results of rejuvenation?

A

The long profile of the river is extended and a knickpoint(a sharp change in gradient, often a waterfall) will form and mark the junction between the original long profile and the new one

Geography (2 decks)

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