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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
Coastal Risk management options
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
26
What is resilience
The ability and time taken to build back better Minimise loss, minimise recovery time, minimise cost
27
Causes of sea level change
Add/subtract: glacial melt, (rainfall- non existent) Move: wind, currents, tides (biggest mover) Change properties: thermal expansion
28
Define non-tidal residual
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
29
Why are waves and storm surges important (6)
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
Global circulation patterns
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
Highest angle of insolation
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
Northern hemisphere summer, angle of earth
North pole tilted towards the sun, sun's rays strike N.Hem more directly
33
Northern Hemisphere winter, angle of Earth
North pole tilted away, light from the sun is more spread out over a larger area
34
How is the global heat balanced
Excess heat from the equatorial zone is transferred towards the poles, in global circulation patterns (convection cells)
35
**Global convection cells from equator to poles
Hadley cell, Ferrel cell, Polar cell
36
Why do differences occur in circulation patterns over land and sea
Mountains, large solid mass, absorb heat better, land masses change heat more rapidly
37
What direction do these current flows in the Northern hemisphere: Doldrums Trade winds Westerlies Polar easterlies
Doldrums: no circulation Trade winds equator: east to west Westerlies 30o: west to east Polar easterlies 60o: north/east to west
38
Idealised pressure belts and resulting wind systems are significantly modified by:
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
Extratropical: N.Hem Cyclone
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
Direction of rotation in the N Hemisphere
Low pressure system: anti-clockwise depression, cyclone High pressure system: clockwise, anticyclone
41
Direction of rotation in the S Hemisphere
Low pressure system: clockwise High pressure system: anti-clockwise
42
Characteristics of a wave
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
Regular waves
Monochromatic Sinusoidal One single frequency
44
Irregular waves
Random Confused Changes in elevation, angle, direction, size frequency
45
Features of a sinusoidal wave
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
How to calculate wave steepness
Hight divided by length
47
How to calculate wave number
Number of wavelgnths per unit distance (1/L)
48
How to calculate wave frequency
Number of peaks (or troughs) which pass a fixed point per second (1?T)
49
What is the wave period
Time interval between two successive peaks (or troughs) passing a fixed point - in seconds
50
Irregular wave quantitative description
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
How does the wind generate capillary waves
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
How do capillary waves become gravitation waves
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
How does a wave system become a storm
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
How does a wave system become a storm
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
What is the critical value for wave steepness when whitecaps form
1/7
55
What is a fully developed sea
For a given wind speed, a maximum fetch and duration beyond which waves cannot grow
56
What waves are fastest within a region of blowing wind
Longest waves are the fastest, so can escape from the region of generation
57
What are the characteristics of waves that escape a region of generation
Have propagated into a region without wind generation, become swell waves, regularly spaces, long period/length, can indicate an oncoming storm
58
Deep water waves
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
Shallow water waves
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
What is shoaling
Wave experiences fraction, deforms wave and eventually breaks Water entering shallow water change in wave height
61
Refraction as transformative in shallow waves
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
Headland vs bay (refraction)
Headland: wave convergence, high energy zone Bay: waves spread, deposition, low energy zone
63
Diffraction as transformative in shallow water
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
Reflection as transformative in shallow water
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
When will a wave break
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
What is a spilling wave
Large wave height relative to the wave length- shallow beach slope White line as propagates
67
What is a plunging wave
(most desirable for surfers) shallow to intermediate beach slope Crest curls as it deforms, injects into the trough, classic barrel shape
68
What is a collapsing wave
Front face collapses- intermediate to steep slope Undefined shape
69
What is a surging wave
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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