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Earth Surface Science > Coastal Systems > Flashcards

Coastal Systems Flashcards

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1
Q

Why are coastal systems important?

A
  • The most important and intensely used of all areas settled by humans
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2
Q

Define coastal zone

A
  • A coastal zone is the interface between the land and water.
  • Coastal zones are continually changing because of the dynamic interaction between the oceans and the land
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3
Q

Outline coastal morpho dynamics

A
  • Coastal landforms and processes can be considered over a variety of temporal and spatial scales
  • Vital element to coastal response is the presence of strong feedback between form and process
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4
Q

What are the 3 linked elements in a coastal dynamic system?

A

1) Processes
2) Sediment transport
3) Morphology

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5
Q

Why are waves important in coastal processes?

A
  • Ocean waves are dominant agents in shaping the coast

- They drive nearshore sediment transport processes

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6
Q

How can the behaviour of ocean waves be measured/estimated?

A
  • Using a linear wave theory

- This gives a linearised description of the propagation of gravity waves on the surface of a homogeneous fluid layer.

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7
Q

What does linear wave theory say about deep water wave behaviour?

A

(h/L0 > 0.5) – wave typically sinusoidal and symmetrical in shape – wave not in contact with sea bed

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8
Q

What does linear wave theory say about intermediate water wave behaviour?

A

(0.5 < h/L0 < 0.05) – wave base begins to interact with sea floor (shoaling) changing wave motion and generating asymmetric waves, which undergo refraction (divergence and convergence)

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9
Q

What does linear wave theory say about shallow water wave behaviour?

A

(h/L0 < 0.05) - wave become increasingly asymmetric and ultimately will form breakers

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10
Q

What controls what waves can do?

A

The development of wave symmetry and breaking are critical controls over the work that a wave can do

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11
Q

Outline wave processes in shallow water

A
  • Wave breaking
  • Occurs when a wave becomes too steep and the horizontal velocities of the water particles in the crest exceed the velocity of the wave
  • Causes wave to disintegrate into bubbles and foam
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12
Q

Where do waves break?

A

Waves break in depth slightly larger than their height and the region of the beach where waves break is known as the surf zone

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13
Q

What are spilling breakers?

A

Spilling breakers are associated with gentle beach gradients and steep incident waves

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14
Q

What are plunging breakers?

A

Plunging breakers occur on steeper beaches than spilling breakers, with waves of intermediate steepness

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15
Q

What are surging breakers?

A

Surging breakers are found on steep beaches with low steepness waves

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16
Q

What are the two driving forces for ocean tides?

A
  • Gravitational attraction of:
  • Earth – moon system
  • Earth – sun system
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17
Q

What do tides cause?

A

Tides cause a twice daily rise and fall in water level

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18
Q

Why do tidal ranges vary?

A

Tidal range varies over time, due to the interaction between the tidal forces of the earth – moon system and the earth – sun system

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19
Q

What are spring tides?

A

When earth, moon and sun are all aligned, during either a full or new moon, the tidal forces of the moon and the sun combine causing extra-large tides, known as spring tides

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20
Q

What are neap tides?

A

When moon is at a right angle to earth with respect to the sun, tidal forces of the moon and sun compete, resulting in extra-small tides known as neap tides

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21
Q

What is a storm surge?

A
  • Elevated water level compared to tidal predictions

- Strom surge levels can be in excess of 5m under extreme conditions

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22
Q

What are the 3 factors which the amount of storm surges depend on?

A
  • 1 – low pressure
  • 2 – onshore wind
  • 3 – coastal topography
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23
Q

How are tsunami causes?

A
  • Tsunami waves are generated by displacement of a large mass of water
  • A displacement of the sea bed by a submarine earthquake
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24
Q

What is the wavelength of a tsunami wave?

A
  • In the open ocean, a tsunami typically has a wavelength of a few hundred km and a height less than a metre
  • However, they become significantly greater in height as they near shore
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25
Q

What is coastal classification?

A
  • Coasts are classified to help assess different forcing factors - sea level history, geology, climate, waves and tides
26
Q

What were the early approaches to classifying coasts?

A
  • Early approaches distinguish between submerged and emerged coasts
  • Typical submerged coasts are drowned river (rias) and glacial valleys (fjords)
  • Another type of classification distinguishes between primary and secondary coasts
27
Q

What are primary coasts?

A

Primary coasts result mainly from non-marine processes and include drowned river valleys and delta coasts

28
Q

What are secondary coasts?

A

Secondary coasts result mainly from marine processes or organisms

29
Q

What are the limitations of the early classification approaches?

A

They emphasise on the geological inheritance and sea level history. This leaves only limited concern for the hydrodynamic processes

30
Q

What are modern classification approaches like?

A

Most modern classifications are process-based and consider process-form models rather than inheritance

31
Q

How are beaches formed?

A
  • Wave deposited sand or gravel landform along marine, lacustrine and estuarine shorelines
  • Classic open system process-form relationship: transfer of energy and mass
32
Q

What do beaches respond to?

A

Beaches respond to changing wave conditions especially the exchange of sediment between the upper beach and the surf zone, and development of berm and bar profiles

33
Q

What are the different beach types?

A

1) Reflective beaches
2) Intermediate beaches
3) Dissipative beaches

34
Q

Describe reflective beaches

A
  • Narrow and steep
  • Calm conditions result in sediment transport in the nearshore zone in onshore direction, resulting in a steepening of the beach profile and berm generation
  • Energetic wave conditions induce offshore sediment transport, causing destruction of berm and a flat beach with bars
35
Q

Describe intermediate beaches

A
  • Complex and dynamic
  • Typically has nearshore bar morphology which dissipates significant amount of wave energy through wave breaking
  • The upper part of intermediate beaches is rather steep and reflective
36
Q

Describe dissipative beaches

A
  • Wide and flat
  • Wide surface zone with multiple spilling breakers
  • The majority of the incoming wave energy is dissipated during the wave breaking process
37
Q

How are wave dominated coasts a closed system?

A

They are closed systems in terms of longshore sediment transport and are characterised by a curve platform

38
Q

What is a spit?

A

A spit is a classic example of a drift aligned barrier and is a narrow accumulation of sand or gravel with one end attached to the mainland and the other projecting out into the sea or across the mouth of an estuary or bay

39
Q

What are barrier systems?

A

Most barrier systems are made up of sand, but gravel barriers are also frequently found, especially at higher latitudes where glacial processes over the last few hundred thousand years have produced vast quantities of gravel size material

40
Q

What are the different types of coastal barrier?

A
  • Transgressive barriers

- Regressive barriers/sand plains

41
Q

What are transgressive barriers?

A

Those that migrate landward under the influence of rising sea level and or a negative sediment budget

42
Q

What are regressive barriers/sand plains?

A

Those that develop under the influence of a falling sea level and or a positive sediment budget

43
Q

What are estuaries?

A
  • They are the main tide dominated costal landform

- They represent zones of mixing between fluvial and marine processes

44
Q

What are the 3 different zones of an estuary?

A

1) Inner zone
2) Central zone
3) Outer zone
- Zones are unique with respect to their energy regime, sediment type and morphology

45
Q

What part of an estuary do river processes dominate?

A

River processes dominate at the head of an estuary and their influence decreases towards the mouth

46
Q

What part of an estuary do marine processes dominate?

A

Marine processes are the most important at the mouth and their role decreases towards the head

47
Q

What is the energy regime in in the inner zone?

A

The energy regime on the inner zone is river dominated

48
Q

What is the energy regime in the outer zone?

A

The outer zone is marine dominated - waves and tides

49
Q

What is the energy regime in the central zone?

A

Mixed

50
Q

What are wave dominated estuaries?

A
  • Typically, in coasts with high energy
  • Outer zone often has barrier system and tidal inlet, dominated by wave processes
  • Often has bay head and ebb tidal delta within the inner zone
  • Infills through seaward aggradation of bay head delta
51
Q

What are tide dominated estuaries?

A
  • Can be found in any coastal setting
  • Scouring action of tidal currents keeps the estuary relatively open and gives them a typical funnel shape
  • A single meandering channel is commonly found and is mostly tide dominated
  • Also significantly influenced by river processes during times of high discharge
52
Q

What are the key processes operating within estuaries?

A
  • Mixing fresh and saline water – less dense fresh water tends to remain at the surface, forming a halocline
  • Degree of water mixing varies – wave dominated estuaries generally les mixed, preserving stratification
  • Tidal prism = volume of water entering estuary on flood tide
53
Q

Describe the lower inter-tidal zone of an estuary

A

Lower inter-tidal zone typically devoid of vegetation, due to excess shear strength during flow preventing seedling establishment

54
Q

Describe the upper inter tidal zone of an estuary

A

Upper intertidal zone less energetic, this gets colonised by slat tolerant grasses/reeds known as salt marsh – mangrove in sub tropics

55
Q

What are coastal cliffs?

A
  • Coastal cliffs can be defined as ‘steep slopes that border ocean coasts’
  • Occur along approximately 80% of worlds coastline
56
Q

What is the main factor that controls cliff erosion?

A
  • The main factor that controls cliff erosion is the hardness of rock, related to lithology
  • Other factors include wave energy and cliff height
57
Q

What are rocky coasts?

A

Rocky coasts are continually being cut back by the sea and are characterised by erosional features

58
Q

What are Sunamura’s (1992) three main types of rocky coasts?

A

1) Sloping shore platform
2) Sub-horizontal shore platform
3) Plunging cliff

59
Q

What is erosion accomplished by?

A
  • Mass movement
  • Rock breakdown processes
  • Marine rock removal
60
Q

Why is mass movement common along rocky coasts?

A
  • Mass movements are common along rocky coasts due to prevailing steep, unstable, slopes
  • Many physical, chemical and biological processes weaken and loosen rock material, enhancing mass movement

Earth Surface Science (17 decks)

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