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GCSE Geography AQA 8035 SRCC > Rivers > Flashcards

Rivers Flashcards

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1
Q

Define long profile

A

The change in the gradient of the river course from the upper course to the lower course.

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2
Q

Define cross profile

A

A cross section of the river - this shows a ‘slice’ of the river valley and channel

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3
Q

What is a v-shaped valley?

A

A valley with steep sides and a narrow bottom that has been formed by erosion

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4
Q

What is a tributary

A

A smaller river or stream flowing into a larger river

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5
Q

What is a confluence

A

The point where two rivers meet

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6
Q

Define load

A

The amount carried by a river

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7
Q

What are the characteristics of the upper course of a river

A
  • steep gradient
  • narrow v-shaped valley
  • narrow & shallow river
  • large angular sediment load
  • mostly erosion taking place
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8
Q

What are the characteristics of the middle course of a river

A
  • shallower gradient
  • asymmetrical valley cross section
  • deeper and wider river channel
  • smaller / rounder load
  • balance between erosion and transportation taking place
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9
Q

what are the characteristics of the lower course of the river

A
  • very low gradient
  • very wide, very deep river channel
  • small suspended load
  • mostly deposition taking place
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10
Q

define erosion

A

the wearing away of rock by the natural processes e.g. river / sea

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11
Q

name 4 processes of erosion

A

hydraulic action
abrasion
attrition
solution

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12
Q

define hydraulic action

A

fast flowing water pushes air into cracks and the force of this causes the channel to break up over time

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13
Q

define abrasion

A

sand and pebbles are dragged along the river bed, wearing it away

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14
Q

define attrition

A

rocks and stones wear each other away as they knock against each other

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15
Q

define solution (erosion)

A

rocks e.g. limestone are dissolved in acid rainwater

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16
Q

define transportation

A

the movement of eroded material by natural processes e.g. river / sea

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17
Q

name the 4 processes of transportation

A
  1. traction
  2. saltation
  3. suspension
  4. solution
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18
Q

define traction

A

largest material rolled and dragged along the river bed, often only moving in times of flood

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19
Q

define saltation

A

smaller stones and pebbles are bounced along the river bed

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20
Q

define suspension

A

smaller particles (e.g. sand and silt) are carried within the river channel

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21
Q

define solution (transportation)

A

some material is dissolved into the river water and transported this way

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22
Q

define deposition

A

when a river drops the sediment it is carrying

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23
Q

when does a river deposit its load?

A
  • drier weather (less water, so less energy)
  • velocity decreases (less speed, so less energy e.g. inside a bend)
  • river floods (water flows onto the flood plain, increase in friction, so energy decreases depositing fine silt and clay)
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24
Q

name the landforms formed by erosion

A

waterfall
gorge
interlocking spurs

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25
Q

name the landforms formed by erosion and transportation

A

meanders

ox-bow lakes

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26
Q

name the landforms formed by deposition

A

floodplains

levees

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27
Q

name the landforms found in the upper course of a river

A

waterfalls
gorges
interlocking spurs
rapids

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28
Q

what is a waterfall

A

vertical fall of water over a steep drop

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29
Q

how does a waterfall form?

A
  1. water flows over harder rock with softer rock beneath
  2. the softer rock is eroded by hydraulic action and abrasion, much faster (differential erosion) creating a step in the river
  3. the hard rock is undercut by erosion creating an overhang
  4. the hard rock is also eroded, but much slower. eventually it collapses into the plunge pool
  5. this process repeats over time causing the waterfall to retreat and a gorge to form downstream
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30
Q

what is a gorge

A

a steep-sided cut through landscape formed by a waterfall retreating

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31
Q

what is a plunge pool

A

the area of deep water at the bottom of the waterfall formed by hydraulic action and abrasion

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32
Q

what are interlocking spurs

A

hillsides that look like a zip formation - the river winds around the sections of land that stick out (spurs)

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33
Q

how are interlocking spurs formed?

A

in the upper course, rivers aren’t powerful enough to erode laterally so they wind around the hillsides creating a zig-zag shaped flow

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34
Q

Name the landforms found in the middle course

A

meanders

ox-bow lakes

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35
Q

what is the thalweg

A

line of fastest flow

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36
Q

what is a meander

A

bend in the river

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37
Q

what is an ox-bow lake

A

horse-shoe shaped lake that is formed when a meander is cut off and becomes isolated

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38
Q

explain how an ox-bow lake forms

A
  1. the fastest flow is on the outside of the meander resulting in erosion (hydraulic action and abrasion) on the outside bend
  2. the neck of the meander is eroded and it becomes narrower
  3. when there is high discharge (often in flood) the river cuts through the meander and takes a straight course
  4. as the flood waters go down, deposition occurs at the edge of the straight channel cutting off the ox-bow lake
39
Q

name the landforms found in the lower course

A

floodplains

levees

40
Q

what is a floodplain

A

the flat area where a river floods

41
Q

what are mudflats

A

large flat areas of mud which is fine silt and clay deposited by a river, often when in flood

42
Q

what is a levee

A

a raised river bank

43
Q

how is a levee formed?

A
  • Levées form in lower course - raised river bed found alongside the river
  • When flooding occurs water flows over the sides of the channel
  • The velocity of the river decreases rapidly as the proportion of friction has increased significantly so the river starts to deposit material
  • It would have been carrying larger sediments in the bank full stage as the river had more velocity, and these are deposited first at the edges of the river channel
  • Finer sediments e.g. silt and mud are carried much further across the floodplain (as they are lighter) and deposited later as flood waters recede
  • Over time, and after many floods, the height of the banks can be raised by as much as 2m
44
Q

define river discharge

A

the amount of water flowing through the channel at a given point and time
measured in cumecs (cubic metres per second)

45
Q

list the factors affecting river discharge

A

precipitation
relief
geology
landuse

46
Q

when does flooding happen

A

when the level of a river gets so high it spills over the banks

47
Q

how does prolonged precipitation affect discharge

A
  • after a long period of rain, the soil becomes saturated which means that no other rainfall can infiltrate, so this increases surface runoff, which increases discharge quickly
48
Q

how does heavy rainfall affect discharge?

A

water arrives too quickly for infiltration
so there’s more surface runoff
discharge increases, increasing the risk of flooding

49
Q

how does geology affect discharge?

A

clay soils are impermeable so there is less infiltration and more surface runoff
sandy soils allow infiltration, reducing surface runoff

50
Q

how does relief affect discharge

A

steep-sided valleys cause water to flow faster to the river, so it flows too quickly for infiltration, increasing surface runoff, increasing discharge

51
Q

how does urbanisation affect discharge

A

buildings made from impermeable materials e.g. concrete and tarmac
impermeable surfaces increases surface runoff and drain quickly into rivers, so discharge quickly increases

52
Q

how does deforestation affect discharge

A

cutting down trees means there are less trees to intercept and store water, also less trees to take water up from the soil moisture storage, so there is more water as surface runoff and it gets to the river quicker, increasing discharge

53
Q

what is a hydrograph

A

graph that shows the relationship between precipitation and discharge

54
Q

what is a flashy hydrograph

A

more likely to flood
lower lag time
steep rising and falling limb
high peak discharge

55
Q

what is a gentle hydrograph

A

less likely to flood
longer lag time
more gentle rising and falling limbs
lower peak discharge

56
Q

what is lag time

A

the time between the peak rainfall and peak discharge

57
Q

what is antecedent rainfall

A

previous or prior rainfall

58
Q

define interception

A

when trees catch rainwater and store it, using it to grow / photosynthesise

59
Q

define infiltration

A

when water soaks from the ground into the soil

60
Q

what is impermeable rock

A

rock that is impossible for water to soak into e.g. granite

61
Q

what is permeable rock

A

rock that allows water to pass through e.g. limestone

62
Q

define surface runoff

A

water flowing over the land

63
Q

what is hard engineering

A

man-made structures built to control flow of rivers and reduce flooding

64
Q

what is soft engineering

A

schemes set up using knowledge of a river and its processes to reduce the effects of flooding

65
Q

name 4 hard engineering strategies

A

dams and reservoirs
channel straightening
embankments
flood relief channels

66
Q

name 5 soft engineering strategies

A 
flood warnings
preparation
flood plain zoning
planting trees
river restoration
67
Q

how do dams regulate flow

A

create a reservoir to store water and the flow of water is regulated through the flood gates being released

68
Q

what are the benefits of building a dam

A
  • reservoirs store water which reduces risk of flooding

- water in reservoir can be used for drinking, or for HEP

69
Q

what are the costs of building a dam

A
  • very expensive
  • reservoirs can flood existing settlements
  • eroded material caught in the reservoir, and not deposited downstream reducing soil fertility, affecting crop yields
70
Q

how does channel straightening reduce flooding

A

meanders cut out, channel straightened moving water away from settlements faster

71
Q

what are the benefits of channel straightening

A

-water moves away quickly reducing flooding

72
Q

what are the costs of channel straightening

A
  • flooding moved downstream

- more erosion downstream as water is flowing faster

73
Q

how do embankments reduce flooding

A

raised river banks increase capacity so the river can hold more water

74
Q

what are the benefits of embankments

A

-river can hold more water so less flooding

75
Q

what are the costs of embankments

A
  • fairly expensive

- risk of severe flooding when they are breached

76
Q

how do flood relief channels reduce flooding

A

channels divert water away from settlements

77
Q

what are the benefits of flood relief channels

A
  • river discharge is reduced so less flooding

- gates on flood relief channels enables water flow to be controlled

78
Q

what are the costs of flood relief channels

A
  • increased discharge at confluence of relief and main channel
  • if water level gets too high relief channels can flood
79
Q

how do flood warnings reduce flooding

A

-environment agency communicates warnings to give people time to prepare

80
Q

what are the benefits of flood warnings

A
  • impact of flooding is reduced

- farm land still receives fertile alluvial deposits

81
Q

what are the costs of flood warnings

A
  • don’t stop the flood

- some may not access warnings

82
Q

how does preparation reduce flooding

A

buildings modified to reduce damage

people make plans e.g. emergency kit with torch and blankets

83
Q

what are the benefits of preparation

A
  • impact of flooding is reduced

- people less anxious

84
Q

what are the costs of preparation

A
  • doesn’t guarentee safety in flooding
  • doesn’t stop the flood
  • expensive
85
Q

how does floodplain zoning reduce flooding

A
  • it doesn’t!

- restrictions on building can reduce impermeable surfaces and expensive landuse near the river

86
Q

what are the benefits of floodplain zoning

A
  • risk of flooding is reduced - less impermeable surfaces

- impact of flooding is reduced

87
Q

what are the costs of floodplain zoning

A
  • expansion of urban area is limited

- not useful if areas already built on

88
Q

how does afforestation (planting trees) reduce flooding

A

increases interception, and increases lag time as infiltration rates are higher

89
Q

what are the benefits of afforestation

A
  • discharge and flood risk are reduced

- vegetation reduces soil erosion and provides habitats for wildlife

90
Q

what are the costs of afforestation

A

-local flood risk can increase if no other action is taken

91
Q

how does river restoration reduce flooding

A

this makes the river more natural e.g. removing man-made levees, so the floodplain can flood naturally

92
Q

what are the benefits of river restoration

A
  • flooding reduced downstream as discharge is reduced
  • little maintenance is needed
  • better habitats for wildlife
93
Q

what are the costs of river restoration

A

-local flood risk increases

GCSE Geography AQA 8035 SRCC (2 decks)

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