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2024 Coastal ocean processes > Section 2: Coastal systems, waves, storms > Flashcards

Section 2: Coastal systems, waves, storms Flashcards

1
Q

Define coasts

A

Where the land meets the sea

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2
Q

Define estuary

A

partly enclosed coastal body of brackish water with on or more rivers flowing into it, and a free connection to the open ocean

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3
Q

Length of UK coastline (not including islands)

A

~11,000 miles

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4
Q

Human activities at coasts

A

Habitat and source of food
Means of transport
Accessible, fertile land
natural resources
Water extraction and discharge of waste
Recreational activities

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5
Q

Bruntland report 1987

A

Must meet the needs of the present generations with comprising the ability of the future generation to meet their own needs

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6
Q

Number of people currently living in Low Elevation Coastal Zone (LECZ)

A

680 million (1 Billion by 2050)

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7
Q

Number of people living within 60 miles of the coast

A

2.4 billion (40% of global population)

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8
Q

Define Mangroves

A

Various types of salt-tolerant plant species (trees or shrubs) that occur in intertidal zone of tropical and subtropical coastlines

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9
Q

Define Seagrass

A

A group of flowering plants found in marine or estuarine waters, that tend to develop extensive underwater meadows

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10
Q

Define saltmarshes and mudflats

A

Ecosystems of brackish, shallow water with salt-tolerant plants such as herbs, grasses or shrubs. Usually found in the intertidal zone of sheltered marine and estuarine coastlines, in temperature and high latitudes

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11
Q

Define coral reefs

A

Carbonate structures which gradually built by stony corals, calcareous algae and other reef building organisms/ Warm-water corals reefs occur in coastal areas of tropical and subtropical regions

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12
Q

Define kelp forests

A

Kelp- a large algae seaweed which tends to occur in high density forests worldwide through temperature and polar coastal regions and some tropical waters

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13
Q

Ecosystem services

A

Provisioning (food, biomass, fuel and water)
Regulating (climate control, natural hazards, disease)
Supporting (nutrient cycles, soil formation, photosynthesis, PP, carbon sequestration)
Cultural (spiritual, aesthetic, recreational, ethical values)

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14
Q

Hazards to coastal areas

A

Flooding, erosion, big storms, tsunamis, sea level rise, harmful algal blooms, hypoxia, warming sea temperature, habitat degradation and loss

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15
Q

Indian Ocean Tsunami facts

A

Year: 2004 (boxing day)
Deaths: 228,000

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16
Q

UK flooding 2019/20 damages

A

£333 million

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17
Q

Drivers of flooding

A

Terrestrial: rivers, run-off, ground water
Atmosphere: wind, rain
Marine: waves, tides, tsunamis, storm surges, mean sea level
Morphology: geology (hard/soft), sediment characteristics supply

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18
Q

Space and time scale variation:
Turbulence

A

1mm, 1sec

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19
Q

Space and time scale variation:
Seiches waves

A

1m/1km, 1min

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20
Q

Space and time scale variation:
Tsunamis

A

100kms, mins to hours

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21
Q

Space and time scale variation:
Tropical surges

A

10/100kms, 12 hours

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22
Q

Space and time scale variation:
Extra-tropical surges

A

1000/10000kms, 10 days +

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23
Q

Up ? sea level rise in 2100

A

1.15m

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24
Q

What is a wicked problem

A

Complex, challenging, have multiple feedbacks, high uncertain and have ambiguous solutions

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25
Q

Coastal Risk management options

A

Do nothing
Protect (hold-the-line): seawalls, offshore breakwaters, beaches
Adapt (accommodate): flood proofing, hazard mapping, awareness, land use zoning
Retreat (re-align): land use zoning, coastal set back, managed retreat

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26
Q

What is resilience

A

The ability and time taken to build back better
Minimise loss, minimise recovery time, minimise cost

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27
Q

Causes of sea level change

A

Add/subtract: glacial melt, (rainfall- non existent)
Move: wind, currents, tides (biggest mover)
Change properties: thermal expansion

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28
Q

Define non-tidal residual

A

The meteorological component of sea level that remains once the tidal component has been removed and primarily contains the meteorological contribution to sea level
Most dramatic meteorological sea level change occur during storms, when low atmospheric pressure allows sea level to rise and strong winds force water towards the coastline and generate large waves

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29
Q

Why are waves and storm surges important (6)

A

1.Strong influence on sea level- coastal flooding, cause damage
2. Influence on currents and sediment transport -coastal erosion
3. Design of coastal and offshore structures eg light houses
4. Renewable energy generation eg tidal energy
5. Recreation eg surfing
6. Navigation, safety at sea

30
Q

Global circulation patterns

A

The air in the atmosphere and the water of the ocean are continually moving. Powerful air currents, jet stream, Gulf stream, small swirls and eddies
Driven by the energy from the sun and the rotation of the Earth

31
Q

Highest angle of insolation

A

At the equator 2% of radiation reflected if sun overhead
High/low latitudes solar radiation spread over a larger surface area (40% radiation reflected)

32
Q

Northern hemisphere summer, angle of earth

A

North pole tilted towards the sun, sun’s rays strike N.Hem more directly

33
Q

Northern Hemisphere winter, angle of Earth

A

North pole tilted away, light from the sun is more spread out over a larger area

34
Q

How is the global heat balanced

A

Excess heat from the equatorial zone is transferred towards the poles, in global circulation patterns (convection cells)

35
Q

**Global convection cells from equator to poles

A

Hadley cell, Ferrel cell, Polar cell

36
Q

Why do differences occur in circulation patterns over land and sea

A

Mountains, large solid mass, absorb heat better, land masses change heat more rapidly

37
Q

What direction do these current flows in the Northern hemisphere:
Doldrums
Trade winds
Westerlies
Polar easterlies

A

Doldrums: no circulation
Trade winds equator: east to west
Westerlies 30o: west to east
Polar easterlies 60o: north/east to west

38
Q

Idealised pressure belts and resulting wind systems are significantly modified by:

A
  1. Earth’s tilt- produces seasons
  2. The air of continents get colder in the winter and warmer in the summer than the air over the adjacent oceans (because of the heat capacity of water compared to rock)

In winter, continents usually develop high pressure cells, during summer develop low pressure cells

39
Q

Extratropical: N.Hem Cyclone

A

Easterly wind (cold front) passes westerly wind (warm front)
Easterlies deflect to the left, westerlies to the left, create an detached cyclone
High and low pressure front interact

40
Q

Direction of rotation in the N Hemisphere

A

Low pressure system: anti-clockwise depression, cyclone
High pressure system: clockwise, anticyclone

41
Q

Direction of rotation in the S Hemisphere

A

Low pressure system: clockwise
High pressure system: anti-clockwise

42
Q

Characteristics of a wave

A

Transfers a disturbance from one part of a material to another
The disturbance is propagated through he material without any substantial overall movement of the material itself
The disturbance appears to be propagated with constant speed

43
Q

Regular waves

A

Monochromatic
Sinusoidal
One single frequency

44
Q

Irregular waves

A

Random
Confused
Changes in elevation, angle, direction, size frequency

45
Q

Features of a sinusoidal wave

A

Crest: maximum vertical disturbance above mean sea level
Trough: Maximum disturbance above mean sea level
Wave length: distance between two points of the same height (eg crest)
Wave height: maximum vertical distance between the highest and low points of the wave
Wave period: time it takes to observe a whole wave
Amplitude (sinusoidal wave): maximum displacement under the crest or above the trough to the still sea level
Slope: steepness of the wave, the change in vertical elevation over horizontal distance

46
Q

How to calculate wave steepness

A

Hight divided by length

47
Q

How to calculate wave number

A

Number of wavelgnths per unit distance (1/L)

48
Q

How to calculate wave frequency

A

Number of peaks (or troughs) which pass a fixed point per second (1?T)

49
Q

What is the wave period

A

Time interval between two successive peaks (or troughs) passing a fixed point - in seconds

50
Q

Irregular wave quantitative description

A

Significant wave height (Hs): average wave height of one third of the highest waves in the record. Approximately corresponds to visual estimates of wave periods. Used in prediction of flooding
Mean wave period (Tz): mean period of all waves in the wave record (zero-crossing wave period)

51
Q

How does the wind generate capillary waves

A

Frictional stress between air and ocean surface creates a transfer of energy. This deforms the surface into small rounded waves, short wavelengths (cm). Surface tension is dominant restoring force trying to move back to smooth ocean surface

52
Q

How do capillary waves become gravitation waves

A

An increase in capillary waves means the sea gets rougher in character. This catches more wind- transferring more energy. Gravity waves reacher greater heights, gravity replaces surface tension as the dominant restoring force

53
Q

How does a wave system become a storm

A

Storms characterised by choppy waves, short wavelengths moving in many directions
1. Wind speed increase
2. Increase of duration wind blows in one direction
3. Increase in fetch (distance)

53
Q

How does a wave system become a storm

A

Storms characterised by choppy waves, short wavelengths moving in many directions
1. Wind speed increase
2. Increase of duration wind blows in one direction
3. Increase in fetch (distance)

54
Q

What is the critical value for wave steepness when whitecaps form

A

1/7

55
Q

What is a fully developed sea

A

For a given wind speed, a maximum fetch and duration beyond which waves cannot grow

56
Q

What waves are fastest within a region of blowing wind

A

Longest waves are the fastest, so can escape from the region of generation

57
Q

What are the characteristics of waves that escape a region of generation

A

Have propagated into a region without wind generation, become swell waves, regularly spaces, long period/length, can indicate an oncoming storm

58
Q

Deep water waves

A

If the water depth (D) is greater than one half of the wavelength (L) the waves are not affected by the ocean floor
D > L/2
No bottom friction
No net movement, local movement is cancelled within the circular motion

59
Q

Shallow water waves

A

If the depth (D) is less than one-twentieth of the wavelength
D < L/20
Interaction with the seabed, wave slows down, wave height increases. Waves shoal and break

60
Q

What is shoaling

A

Wave experiences fraction, deforms wave and eventually breaks
Water entering shallow water change in wave height

61
Q

Refraction as transformative in shallow waves

A

Wave approaches coast at angle to bottom contours
Deeper part of the wave travels faster than the rest, friction
Results in a rotation of the wave crest with respect to the bottom contours
Nearshore currents, sediment transport and coastal morphology impact this

62
Q

Headland vs bay (refraction)

A

Headland: wave convergence, high energy zone
Bay: waves spread, deposition, low energy zone

63
Q

Diffraction as transformative in shallow water

A

Energy is transferred along the wave crest rather than the direction of wave propagation
Occurs when a wave encounters a feature: island breakwater or offshore reef
A wave shadow zone is created behind the obstacle, but diffraction causes the wave energy to spread into this zone

64
Q

Reflection as transformative in shallow water

A

In certain conditions (eg presence of wall/breakwater) waves do not break in shallow water - reflect on shore
Interaction reflected and incoming waves result in the formation of standing waves
Water particles move vertically and horizontally
Properties of the water do not change, only the direction

65
Q

When will a wave break

A

The wave reaches shallow water, experiences friction, slows down, potential energy rises (wave height increases) to balance total energy, deforms, crest becomes steeper and more angular, shape cannot be sustained, breaks

66
Q

What is a spilling wave

A

Large wave height relative to the wave length- shallow beach slope
White line as propagates

67
Q

What is a plunging wave

A

(most desirable for surfers) shallow to intermediate beach slope
Crest curls as it deforms, injects into the trough, classic barrel shape

68
Q

What is a collapsing wave

A

Front face collapses- intermediate to steep slope
Undefined shape

69
Q

What is a surging wave

A

Wave slides up the beach without breaking- steep beach slope
Significant sliding of the water up and down the beach face, dangerous, break over a long distance

2024 Coastal ocean processes (9 decks)

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