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Geography AS > Rivers > Flashcards

Rivers Flashcards

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1
Q

What is the chain of stores in the hydrological cycle?

A

Interception storage - surface - soil storage - groundwater storage

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2
Q

What is the transfer from soil to groundwater?

A

Percolation

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3
Q

What is the flow from surface to the river channel?

A

Overland flow

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4
Q

What is the flow from interception to surface?

A

Throughfall stem flow

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5
Q

What is the flow from groundwater to the river?

A

Base flow

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6
Q

What is the transfer from surface to soil?

A

Infiltration

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7
Q

Define precipitation

A

Water in any form that falls from atmosphere to surface

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8
Q

Define evapotranspiration

A

Total amount of moisture removed by evaporation and transpiration from a vegetated land surface

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9
Q

Define run-off

A

All the water that enters a river and eventually flows out of the drainage basin

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10
Q

What are the inputs and outputs of the drainage basin?

A

Inputs: precipitation

Outputs: run-off and evapotranspiration

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11
Q

Define river discharge? And what unit does it take?

A

The volume of water passing a measuring point in a given time. Unit is ‘cumecs’

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12
Q

Define lag time

A

Delay between maximum rainfall and peak discharge

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13
Q

Define receding limb

A

Fall in discharge from the peak back to base level

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14
Q

Define peak discharge

A

Highest level of flow in the channel

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15
Q

Define rising limb

A

Rise in discharge from base level to peak discharge

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16
Q

Define base level

A

Level of flow in the channel without rainstorm effects

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17
Q

What urbanisation processes increase effects of storm

A

Building roads : more run-off as roads are permeable. Therefore, water cannot regulate or transfer through the normal systems

Straightening river channels: leads to faster delivery of water downstream

Building drains and sewers

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18
Q

Define erosion

A

The break-up of rocks by the action of rock particles being moved over the earth’s surface by water

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19
Q

Define transport

A

Movement of particles from where they were eroded to where they are deposited

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20
Q

Define deposition

A

The laying down of solid material, in the form of sediment, on the bed of a river

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21
Q

What factors determine a river’s total energy?

A

1) weight of the water
2) height of river above base level
3) steepness of channel
4) smoothness of wetted perimeter

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22
Q

What are the dominant processes in a high-energy river?

A

Erosion and transportation

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23
Q

What are the dominant processes in low-energy rivers?

A

Deposition

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24
Q

What are the four main erosional processes?

A

1) abrasion
2) hydraulic action
3) corrosion
4) attrition

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25
Q

What direction of erosion dominates in the upper course?

A

Vertical

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26
Q

What type of erosion dominated in the lower course?

A

Lateral

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27
Q

What is abrasion?

A

The scraping action of the river load acts to wear away the river banks and bed

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28
Q

What is hydraulic action?

A

The movement of unconsolidated material due to frictional drag of moving water

(Particularly good at removing the banks from meanders)

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29
Q

What is Corrosion?

A

Where rocks are dissolved by weak acids in river water.

This is most effective on rocks that contain carbonates

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30
Q

What is attrition?

A

The reduction in the size of fragments and particles in a river as a result of sediment bumping into one another

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31
Q

It takes energy for a river to transport its load. What other processes expend a river’s energy at the same time as transportation?

A

Erosion and friction

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32
Q

What are the two main sources of the sediment that makes up a river’s load?

A

Material washed and fallen into river from valley sides

Material eroded itself from banks and the bed

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33
Q

Identify four main types of river transport. Provide a very short definition of each.

A

Traction

Saltation

Suspension

Solution

34
Q

Define capacity

A

The measure of the amount of material it can carry

35
Q

Define competence

A

The diameter of the largest particle it can carry for a given velocity

36
Q

If the velocity of a river triples, by how many times will its competence increase?

A

A river’s competence increases according to the sixth power of its velocity

37
Q

From small to big: what is the offer of sediment?

A

Clay - silt - sand - gravel - coarser material

38
Q

Why are small silt/clay particles more difficult to transport than sand?

A

They are hard to pick up (entrain) because they tend to stick together

39
Q

Why are large particles deposited soon after being swept up in a flow?

A

There is a small difference between critical erosion velocity and settling velocity for the larger particles

40
Q

What do particles get smaller the further downstream the river travels?

A

Attrition

Average velocity is highest here and therefore able to transport more material

41
Q

Define the long profile

A

Illustrates the changes in the altitude of the course of the river from its source, along the entire length of its channel, to the river mouth.

42
Q

Define the cross profile

A

View of the valley from one side to another

43
Q

Describe the valley shale in the upper course

A

V shaped , steep sides narrow bottom. With interlocking spurs.

44
Q

Describe the valley shape in the middle course

A

Wide flood plain where valley sides are steadily lowered

45
Q

Describe the valley shape in the lower course

A

A wide flood plain with:

  • levées
  • oxbow lakes
  • bluffs
46
Q

What does a graded profile represent?

A

It shows the long profile after the irregularities are worn away by erosion. It’s ‘smooth’

47
Q

What determines the potential energy of a river at a given point?

A

Fixed by the altitude of the source of the stream in relation to base level

48
Q

What determines the kinetic energy of a river at a given point?

A

Generated by the flow of the river which converts potential energy into moving energy. It is determined by volume of flowing water.

49
Q

Explain formation of river terraces

A

Rejuvenation -base level change (isostatic)

River erodes vertically into former flood plain to produce features called river terraces

Remnant of a former flood plain left at a higher level after rejuvenation

When a river renews its downcutting power, it sinks its channel leaving former floodplain above

50
Q

If vertical erosion is rapid, what kind of terrace does it leave?

A

Paired terraces

51
Q

If vertical erosion is slower, what kind of terraces does it leave?

A

Unpaired terraces as river meanders

52
Q

Describe and explain an incised meander

A

They are particularly well developed

River’s base level falls, vertical erosion (due to rate it occurs)

Results in becoming incised or deepened

53
Q

describe entrenched meanders

A

They are symmetrical

They form when a river down cuts quickly

Therefore, little opportunity for lateral erosion

The vertical erosion leaves steep sides and a “gorge-like” appearance

54
Q

Ingrown meanders

A

These are asymmetrical

Form when a river downcuts less rapidly

River can then downcut laterally and vertically

Steeper cliffs in our bends and gentle cliffs on inner bends

55
Q

Formation of potholes

A

Where depressions exist in the channel floor, turbulent flow can cause pebbles to spin around and erode hollows through abrasion

Above river level (circular, round, oval)

Upper course - high GPE so sediment erodes downwards

Created during hugh stages of discharge

Original potholes join together through further erosion= bigger potholes

As holes get bigger, even bigger debris can become trapped in the pothole

56
Q

Formation of braided channels

A

Occurs in river’s where discharge rapidly fluctuates

Where the river is split into several channels

Features of river’s that have large loads of sand and gravel

Banks formed are generally unstable and easily eroded

As a result river comes very wide and not so deep

River can become choked - sandbars

57
Q

Formation of levées

A

Middle and lower courses

River is at risk from flooding during times of high discharge

If it floods the velocity of water falls as it goes over bank

Results in deposition (decrease in competence)

Coarse material deposited first

Subsequent floods increase the size of the banks

58
Q

Formation of deltas

A

Form when rate of deposition exceeds rate of sediment removal

They are a feature of deposition

Located at mouth of river

Occurs where velocity decreases and sediment increases

Bedload and suspended material dumped

Flocculation - Clay - Settles

59
Q

What is a meandering river?

A

Large, sweeping curves in a river’s middle and lower stages

60
Q

How do meanders form?

A

Form where alternating POOLS (deep) and RIFFLES (shallow) develop at equally spaced intervals

The spacing and distance between riffles and pools causes the river’s flow to become uneven and maximum flow to be concentrated one one side of the river

Turbulence increases in and around pools and the water speeds up, so the flow begins to twist and coil. Thalweg

This causes corkscrew-like currents in the river called helicoidal flow, which spiral from bank to bank between pools

This causes more erosion and feeling of the pools. Also, it causes eroded material to be deposited on the inside of the next bend, where river loses energy

61
Q

What are the human causes of floods?

A

Urbanisation
• often built on flood plains, susceptible to flooding
• tarmac = permeable

Deforestation
• increased soil erosion
• loss of interception

(REDUCED LAG TIME)

62
Q

Physical causes of floods

A

High levels of precipitation over a short period of time

Melting of snow

Lack of vegetation cover

Climatic hazards

63
Q

When do flood’s occur ?

A

Where a river’s discharge exceeds the capacity of its channel to carry that discharge

64
Q

What were the conditions in York before the flood ?

A

Upper course very steep

Seams of permeable limestone

Arable farming in upland areas means there is no interception

New housing areas and out of town shopping areas

65
Q

What were the conditions in Bangladesh?

A

Confluence of 3 river’s (Meghna, Ganges, Brahmaputra)

Snow melt from the Himalayas

Low-lying country

Cyclones

Deforestation

Urbanisation

66
Q

What were the impacts of flooding in York?

A

500 homes inundated

250 evacuated from homes

300 year old bridge closed

Gas leak

Phone signal problems

Road closures

67
Q

What was the response in York?

A

10,000 sandbags used

600 military personnel

125 mountain rescue members

Countless volunteers

14,000 joined a Facebook group offering help

Facilities like sports centres offered accommodation

Nestlé donated £100,000

£1 million donated in one month

68
Q

What were the impacts in Bangladesh?

A

Death toll: more than 800
Homeless: 36 million out of a possible 125 million

Dhaka alone: 100,000 displaced

Dirty floodwater

15,000 km road destroyed
900 bridges destroyed

$7 billion damages

38% land area flooded

69
Q

What was the response in Bangladesh?

A

Infrastructure issues meant that help couldn’t get to rural areas quick enough

Foreign aid: rice, clothing, medicines (21 million from U.K.)

Water purification tablets provided

Dhaka integrated flood protection project 
•radio to issue warnings
•cluster villages 
•embankments created
•sluice gates 
•slope protection
70
Q

Factors that influence the storm hydrograph

A 
Human:
Urban land use 
Flood defences 
Deforestation
Agricultural land use
Physical:
Intensity of rainfall
Antecedent soil moisture
Steepness of slopes
Rock type
Permeability of soil 
Vegetation
71
Q

Drainage basin

A

DB/Catchment area is an area that is drained by a river and its tributaries.

Water shed splits drainage basins

72
Q

Flood management - Taunton

A

Flood alleviation scheme

River Tone constructed in 1960’s

The defences comprise of: 
•raised walls 
• green corridor by French weird
• technocentric bridge 
• channelisation 
• river wall - increase bank full capacity 
• embankment created
73
Q

Flood management in York (river Ouse)

A

Soft engineering vs. Hard engineering vs. Integrated management

There has been an attempt to manage this river holistically

  • afforestation (reduce flashy response)
  • flood warnings (latest technology)
  • Clifton kings washlands - takes up excess capacity water with sluice gates
  • The Foss Barrier - 8 pumps capable of 30 tonnes water/second
74
Q

Key words

A

Alleviation

Mitigation

75
Q

Oil patterns

A

•Production: Saudi Arabia 9.7 bbl/day
High producers and use own resources
Majority produced in Middle East, USA and Russia

•Consumption: USA close to 21 bbl/day (most by four-fold
China-Japan-Germany-Russia
High consumption usually occurs in developed or highly populated areas

•Trade: Brazil to USA and China more than 1 million b/day
Nigeria and Algeria export a lot
Saudi Arabia greatest distributor

76
Q

Gas patterns

A

•Production: North America has the largest production of gas (29 trillion cubic feet)
Russia+Middle East around 26 trillion cubic feet

•Consumption:
N.America, Europe and Asia high consumers
There has been an increase in consumption because: increase pop. , better technology, increase in demand and decrease in other energy resources

77
Q

What are TNC’s?

A

TNC is one that operates in at least two countries

Centres of production in one part of the world and HQ in another. Therefore, TNC’s tend to be hierarchical

In 2007, 6 out of ten largest TNC’s were oil companies

78
Q

8 different functions of a TNC (BP example)

A 
Exploration 
Drilling 
Extraction
Transport
Storage 
Refining (manufacturing)
Distribution and sales
Training and workforce
79
Q

Facts about BP

A

84,000 employees

Annual income of €360 billion

17,000 retail sites

80
Q

Exploration and extraction in BP

How many countries is BP active?
Which ones?

How many barrels a day?

A

2005: active in 26 countries

Incl. Angola/Azerbaijan and Gulf of Mexico

4 billion barrels a day

81
Q

What is production?

A

The process of drilling and extracting

Geography AS (4 decks)

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