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AS Geography Physical > Rivers > Flashcards

Rivers Flashcards

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1
Q

Inputs

Outputs

Stores

Transfers

A

1) ways in which water enters system
2) ways in which water leaves system
3) ways in which water is held in system
4) ways in which water is moved through and within system

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2
Q

Infiltration

Percolation

A

1) water soaking into the soil from the surface - vertically
2) water moving from the surface layers of soil into deeper layers of soil and rock - vertically

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3
Q

Evapotranspiration

A

Combined process of evaporation and transpiration that result in the loss of water from the leaf.
Transpiration is the loss of water through ting holes called stamata in the leafs surface.

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4
Q

Interception

A

Plants trap some of the precipitation so it may not immediately pass to the ground. Some water may drip to the ground as through-fall. Some may flow down the stem as stem flow. The precipitation may also evaporate directly off the leaf surface and never reach the ground.

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5
Q

Evaporation

Condensation

A

1) water changing from its liquid form to a gas (water vapour) and returning to the atmosphere
2) the process by which water vapour is converted into water

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6
Q

Ground water store

Ground water flow

A

1) water held below the water table in aquifers

2) water moving within rocks below the ground

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7
Q

Through flow

A

Water moving downhill through soil layers, generally slowly, but flow may concentrate along the line of roots/soil weaknesses which form natural pipes in which the flow will be faster

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8
Q

Overland/surface flow

A

Water moving across the surface of the ground. Occurs when rain cannot soak quickly enough into the ground due to tarmac surfaces or hard-baked soil.

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9
Q

Channel flow

A

Water moving downhill within rivers

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10
Q

Depression storage

A

Storage of water in hollows and holes in the ground surface to form puddles

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11
Q

What is the water balance/budget

A

The difference between inputs and outputs in a drainage basin.

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12
Q

What is the water balance model?

A

A theoretical graph that shows the balance between precipitation and evapotranspiration in any month.

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13
Q

Definition of drainage basin

A

An area of land drained by a river and its tributaries

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14
Q

Water table in winter

A

Precipitation is high and evapotranspiration/temp are low so there is soil moisture surplus.

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15
Q

Water table in summer

A

Evapotranspiration exceeds precipitation so soil moisture is utilised. This lowers soil moisture content and water tables

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16
Q

Water table in autumn

A

Precipitation again exceeds evapotranspiration so that soil moisture levels can be recharged so that field capacity is then reached again by beginning of winter

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17
Q

Soil moisture surplus

A

Soil water store is full which gives a surplus of soil moisture for plant use and runoff into streams

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18
Q

Soil moisture use

A

Plants must rely on stored water which is gradually used up

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19
Q

Soil moisture deficiency

A

Plants must have adaptions to survive for long periods or land must be irrigated

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20
Q

Soil moisture recharge

A

The soil water store starts to be recharged

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21
Q

Field capacity has been reached

A

The soil water store is now full

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22
Q

What is river discharge

A

The volume of water passing a given point at at given time. Measured in cubic metres per second (m3/s)

Calculated - velocity(m/s) X cross-sectional area (m2)

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23
Q

What is a storm hydrograph?

A

They show how a river responds to a period of rainfall.

Shows precipitation as bars and river discharge as a line

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24
Q 
Peak rainfall
Peak discharge 
Lag time 
Rising limb
Falling limb
A

1) when rainfall is at its highest
2) when river flow has reached its max
3) time between peak rainfall and discharge
4) when rivers flow is rising
5) when rivers flow being to fall after its peaked

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25
Q

How to work out lag time

A

Peak discharge - peak rainfall

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26
Q

Physical factors that affect discharge

A

Rain
Temp
Gradient/relief of the land
Rock/soil type

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27
Q

Human factors that affect discharge

A

Urbanisation

Deforestation/afforestation

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28
Q

Flash flood case study

A 
Boscastle, Cornwall Aug 2004
8 inches of rain 
River burst its banks
100 people airlifted 
Cars swept away
8 hours after rain, water began to recede 
Confluence of 3 rivers 
Geology is granite
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29
Q

What is erosion, transportation and deposition dependent on?

A

Energy

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30
Q

Erosion in a river

A

Vertically - steep sided valley - hard rock
Laterally - meanders - widens channel
Headward direction - water falls

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31
Q

Different types of erosion

A

Abrasion - rocks hitting the river bed and bank
Hydraulic action - the power of moving water erodes the river
Corrosion - rocks dissolved by acids and erode the river
Attrition - rocks hitting each other which make them smaller and rounder

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32
Q

What is transportation?

A

Energy that remains after frictional drag is overcome is available for transportation

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33
Q

Different types of transportation

A

Solution - dissolved rock carried along in the river
Suspension - fine, light material carried along in the river
Saltation - small pebbles and stones bouncing along river bed
Traction - large rocks rolling along river bed

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34
Q

What is deposition?

A

When river no longer has competence (power) to carry its load, often the result of drop in velocity

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35
Q

What is competence?

A

Measured in mm.
The size of sediment a river can transport
Size is measured by long axis
With more discharge and energy - competence is carried easily

36
Q

When does deposition occur?

A

When discharge is low
Water is shallower on inside of meander
When sediment capacity increases
River overflows its banks so velocity on outside channel is reduced - floodplain

37
Q

What is the Hjultsrom curve?

A

Shows the relationship between river velocity and size of particles that can be eroded, transported and deposited.

38
Q

Keys points of Hjulstrom curve

A

1) silt/sand are picked up at lowest velocities
2) clays are difficult to erode as pebbles, although small, they are cohesive and clay bed is smooth.
3) large boulders are dropped easily
4) clay particles can be transported in suspension at low velocities

39
Q

What is the Bradshaw model?

A

It illustrates the main changes expected down the long profile of a river

Can make hypotheses on expected changes in the channel characteristics down the long profile

40
Q

What leads to high velocity?

A

High discharge
High hydraulic radius
Increase of gradient
Low wetted perimeter

41
Q

What is velocity determined by?

A

Channel shape in cross section
Roughness of channel beds and banks
Channel gradient

42
Q

What is hydraulic radius

A

Shows channel efficiency

Cross sectional area - channel width X depth
___________________
Wetted perimeter

43
Q

How are rapids formed?

A

Rapids are created where there is a sudden increase in gradient or where there is an area of large angular bed load which increases local turbulence and erosion.

44
Q

How are waterfalls and gorges formed?

A

They occur where hard rock overlays soft rock. Sock rock is undercut by hydraulic action and abrasion. Over hanging hard rock collapses and creates plunge pool.
Waterfall retreats upstream where steep sided cutting is left - this is called a gorge.

45
Q

Give an example of a waterfall

A

High force on River Tees, Northern England.
Hard rock - whin sill
Soft rock - limestone and sandstone
22m high

46
Q

How are V- shaped valleys formed?

A 
Vertical erosion (abrasion, hydraulic action and solution) in the river channel results in the formation of a steep sided valley. 
Over time the sides are weakened by weathering and continued vertical erosion at the base.
Mass movement occurs down the valley sides which creates a distinctive V shape.
47
Q

How are potholes formed?

A

Potholes are formed where there are depressions, fine particles and large boulders may become trapped and swirled around by the current.
In resistant rock, potholes require hundreds of thousands of years to form.

48
Q

How are braided streams formed?

A

Braiding occurs when the river is forced to split into several channels separated by islands. It is most likely to occur when a river has variable discharge. The banks formed from sand and gravel are generally unstable and easily eroded. As a consequence the channel becomes very wide in relation to its depth.

49
Q

How are meanders formed?

A

Rivers in the middle course with too much kinetic energy starts to bend to use up the extra energy it has. Deposition occurs on the inside bend where the current is slower and erosion takes place on the outside bend where the current is faster.
Deposition creates a slip off slope and erosion causes a river cliff.

50
Q

How are ox bow lakes formed?

A

Oxbow lakes are features of both erosion and deposition.
An oxbow lake is formed by the increasing sinuosity of a river meander. The neck of the meander becomes narrower. During times of high discharge, the river cuts through this neck and the new cut becomes the main channel. The former channel is sealed off by deposition.

51
Q

How are levees formed?

A

In the middle and lower course, a river is at risk of flooding during times of high discharge. If it floods, the velocity of the water falls as it overflows the banks. This results in deposition, because the competence of the river is suddenly reduced. It is usual for the coarsest material to be deposited first, forming small raised banks (levees) along the sides of the channel.

52
Q

How are floodplains formed?

A

They are relatively flat areas of land either side of a river, which form the valley floor in the middle and lower courses of the river. They are composed of alluvium - river deposited silts and clays. Over time the floodplain becomes wider and the depth of the sediment increases.

53
Q

How are deltas formed?

A

Deposition occurs as the velocity and sediment-carrying capacity of the river decrease on entering the lake or sea, and bed load and suspended material are dumped. Deltas form only when the rate of deposition exceeds the rate of sediment removal.

54
Q

What physical factors which cause floods?

A
  • size and shape of river channel
  • amount of precipitation
  • geology/ rock and soil type
  • climate
  • gradient of area
  • vegetation cover
55
Q

What human factors cause floods?

A
  • deforestation
  • afforestation
  • urbanisation
56
Q

What is return period?

A

Return period also known as a recurrence interval is an estimate of the likelihood of an event - floods and earthquakes.
It is a statistical measurement based on historic data which predicts the average return period over time.

57
Q

MEDC flood case study?

A 
Cumbria Floods - Cockermouth, Cumbria, UK
The Cocker and The Derwent rivers 
2009 
72 hours of rainfall 
314mm in 24 hours
58
Q

Human and physical causes of Cumbria floods

A

Human

  • urbanisation reduces infiltration and increases run off
  • The EA refused to continue dredging the Cocker - residents argued aggraded bed caused the flood

Physical

  • The Cocker has high rates of sedimentation which reduces bank full capacity and increases flood risk
  • Confluence of Cocker and Derwent - increase in discharge
  • Antecedent rain
  • Steep gradient in the area
  • located on pronounced meander - risk increases due to high velocity
59
Q

Primary and secondary effects of Cumbria

A

Primary

  • 1 police officer was killed - swept away by water after bridge collapsed.
  • infrastructure destroyed (220 bridges)
  • damage to homes, businesses and infrastructure resulted in £276m bill
  • businesses cut off and trade stopped

Secondary

  • 18 schools closed
  • a year on, 150 flooded households had still not returned to their properties
  • tourism suffered - £15m hit with £2.5m lost on cancelled bookings alone
  • 198 people sought psychological help
  • 110 farms affected - deposition of silt and gravel on fields
60
Q

Socio-economic impacts of Cumbria floods

A

Social

  • 1 death
  • schools closed
  • 500 people spent night in emergency shelters
  • businesses ruined
  • people traumatised
  • 1 year one, people haven’t returned to homes

Economic

  • Gordon brown gave £1m for clean up process and £5.4m to repair
  • insurance costs and claims
  • tourism suffered
  • businesses and trade cut off
61
Q

Immediate and long term responses of Cumbria floods

A

Immediate
- Cumbria fire and rescue service helped rescue and evacuate the community
Long term
- 50 different organisations got involved during and after the flood including the EA who issued flood warnings and provided boats and staff to rescue people

62
Q

LEDC flood case study?

A

Pakistan floods - Pakistan Indus river

2010

63
Q

Physical and human causes of Pakistan floods

A

Physical

  • monsoon rainfall in 3 weeks when it’s usually 3 months
  • jet stream brought heavy rain - 274mm in 24 hours
  • River Indus has high sediment capacity from Himalayas

Human

  • deforestation on Himalayas caused surface run-off
  • densely populated, constrained floodplain
  • levees built increased bank full capacity but exacerbate the flooding
64
Q

Primary and secondary effects of Pakistan floods

A

Primary

  • Infrastructure destroyed - Sukkur barrage was breached
  • villages washed away
  • Swat Valley was isolated due to lack of communication
  • 2000 dead, 20m homeless and 11,000 schools damaged

Secondary

  • 10m people exposed to unsafe water - caused cholera and typhoid
  • Taliban took advantage of vulnerability and gained support in exchange for aid
  • Poverty increased
  • Total economic damage = £billion (10% of GDP)
65
Q

Social and economic impacts of Pakistan floods

A

Social

  • poverty, poorly built infrastructure and over population increased exposure and risk to people
  • Swat Valley was isolated, helicopters could not reach area, donkeys were the only way
  • poor communication increased deaths

Economic

  • two-thirds of people depend on farming - fields were ruined (80% of fields waterlogged)
  • £10 billion worth in damage
66
Q

Immediate and long term responses to Pakistan floods

A

Immediate

  • American helicopters attempted to rescue from swat valley but heavy rainfall meant they could not reach area
  • International help was slow - donor fatigue
  • President Zardari was criticised for slow response

Long term

  • Families returning to home were give $230 and food packages for one month
  • Angelina Jolie visited to increase exposure to global audiences.
67
Q

What are the two types of sea level change?

A

Eustatic and Isostatic

68
Q

What does Eustatic mean?

A

Sea level change is caused by change in volume of sea water as ice caps and glaciers melt and freeze - internationally

69
Q

What isostatic mean?

A

Sea level change is caused by the uplift and subsidence of land - has more effect on small islands - nationally

70
Q

inter-glacial phases are …..

A

warmer

71
Q

glacial phases are ……

A

colder

72
Q

Why there is there sea level change?

A
  • global warming - thermal expansion
  • Ice sheets are melting faster than snow is replacing them
  • post glacial rebound
73
Q

Hard engineering:

A

Flood management seeks to reduce the frequency and magnitude of flooding and, therefore, to limit the damage that floods cause.

74
Q

Examples of hard engineering:

A

The banks and channel can be modified - Mississippi River, USA

Dams and weirs can be built to regulate the rate at which water passes down a river - China

75
Q

Explain how a river channel can be modified to reduce flooding:

A

The banks and channel can be modified - straightened and deepened to enable the river to carry a larger volume of water.
Artificially raised and strengthened banks from a significant part of this strategy. - Mississippi River, USA

76
Q

Explain how Dams reduce flooding:

A

Three Gorges Dam, China - Yangtze River

The Dam allows the amount of water in a river downstream to be controlled.
Water in the river is used to generate HEP
Water is normally stored as a reservoir and a base for sailing, leisure and water sports
Improves navigation along the river

77
Q

What are the consequences of building the Three Gorges Dam?

A

It is expensive (£25 billion)
Can destroy natural ecosystems
Causes sediment to get trapped in upper section
Supply of deposited sediment downstream is cut off and erosion can increase
Reduces alluvium levels on floodplains and fertility of the soil - affecting agriculture
People must be relocated (1.2 million people)

78
Q

Soft engineering:

A

Softer approaches to flood management are mainly concerned with flood abatement - changing land use upstream.

79
Q

Example of afforestation to reduce flooding:

A

Yellow River, China:
Afforestation increases interception slows down the rate at which water reaches a river and greater evapotranspiration by trees reduces the amount that reaches the channel.
Although this can be effective long term, it takes time for the trees to mature.

80
Q

Example of floodplain zoning to reduce flooding:

A

Rhine River, Germany:
Floodplain zoning allows certain areas of the floodplain to flood naturally - land uses are limited to grazing and recreation in such areas.

81
Q

Example of forecasting floods and warnings:

A

Met Office/ The EA:
Forecasting floods and warnings, in areas where flooding is regular and unavoidable. In Bangladesh the yearly floods cannot be prevented, but if people are given enough warning they can take refuge in flood shelters.

82
Q

When does river rejuvenation occur?

A

Rejuvenation occurs : when there is either a fall in sea level relative to the level of land or a rise in land relative to the sea.
This enables a river to renew its capacity to erode as its potential energy is increased.

83
Q

What landforms are created by river rejuvenation?

A

Knickpoints
Waterfalls
River terraces
Incised meanders

84
Q

Outline the formation of a knickpoint:

A

When a river is rejuvenated, adjustment to the new base level starts at the sea and gradually works its way up the river course.

The river gains renewed cutting power (vertical erosion) which encourages it to adjust its long profile.

The knickpoint is where the old long profile joins the new.

85
Q

Outline the formation of waterfalls:

A

Headward erosion upstream may mean that a waterfall cuts back through the valley towards its source until the long profile eventually adjusts to its new energy equilibrium.

86
Q

Outline the formation of a river terrace:

A

Where a river renews its downcutting, it sinks its new channel into the former floodplain, leaving the old floodplain above the level of the present river.

The terraces are cut back as the new valley is widened by lateral erosion.

An example of this is the River Thames - They provide useful shelter from floods in a lower course river valley.

87
Q

Outline the formation of a incised meander:

A

If a rejuvenated river occupies a valley with well-developed meanders, renewed energy results in them becoming incised or deeped.

When incision is slow and lateral erosion is occurring, an ingrown meander may be produced.

With rapid incision, where downcutting or vertical erosion dominates, the valley is more symmetrical, with steep sides and gorge like appearance. These are described as entrenched meanders.

AS Geography Physical (4 decks)

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