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a level geography > 8.1. Coastal Processes > Flashcards

8.1. Coastal Processes Flashcards

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1
Q

Waves

A

Oscillation of the water surface which are generated by the frictional drag of wind as it blows across open water
- wave direction is a reflection of wind direction

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2
Q

What is the main agent that causes change in coastal environment

A

Waves

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3
Q

Factors influencing wave size

A

1) Wind speed
2) Length of time that the wind blows in a constant direction
3) Length of fetch
- coastlines facing a large ocean have a larger fetch than coastlines around an enclosed sea

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4
Q

What causes a big wave

A
  • High wind speed
  • long length of time that the wind blows in a constant direction
  • long length of fetch
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5
Q

Fetch

A

The distance of sea over which the wind can blow

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6
Q

Wave crest

A

As the water in a wave falls, it forms the wave trough.

- This is the lowest point between two wave crests

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7
Q

Wave height

A

The difference in height between a wave crest and wave trough

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8
Q

Wave length

A

The distance between two wave crests

- waves are not usually evenly spaced

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9
Q

Wave period

A

The time taken for a wave to travel through one wave length

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10
Q

Wave velocity

A

The speed of movement of the wave crest

- can be calculated by dividing the average wave length by the average wave period

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11
Q

Wave frequency

A

The number of waves that break on the beach in a given period of time

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12
Q

Wave steepness

A

Calculated using the formula:

  • wave height / wave length
  • rato cannot exceed 1:7 (0.14) because at that point the wave will break
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13
Q

Wave energy

A

In deep water the energy of a wave is proportional to the wave length multiplied by the wave height squared

  • this means that even a small increase in wave height can produce a large increase in wave energy
  • wave energy is directly related to height
  • energy of a wave is released when it breaks
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14
Q

Plunge line

A

The point at which the wave breaks

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15
Q

Swash

A

The body of foaming water that rushes up the beach when a wave breaks
- it obtains its energy from the energy released by the breaking wave

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16
Q

Backswash

A

The water which returns down the beach after a wave has broken

17
Q

How do waves break?

A
  • As waves move into shallow water (depth of water less than half the wave length) the movement of the water within the wave is slowed because of friction with the sea bed
  • This reduces wave velocity, reducing the wave length and increasing the height
  • The movement of water particles becomes elliptical rather than circular and the base of the wave slows down compared to the crest of the wave
  • The wave steepens and then breaks
  • Most of the breaking wave rushes up the beach as a swash
18
Q

Types of wave

A

1) destructive - high energy

2) constructive - low energy

19
Q

Destructive waves (DRAW diagram too)

A

high energy waves

  • waves that remove sediment from a beach
  • steep, high waves that have a short wave length and a high wave frequency (over 10 waves per minute)
  • often are storm waves
  • weak swash and strong backswash
  • sediment is removed from the beach by this strong backswash
  • tends to form longshore bars near the low tide mark
20
Q

Constructive waves (DRAW diagram too)

A

low energy waves

  • low, gentle waves that add sediment to a beach
  • long wave length and a low wave frequency (fewer than 8 waves break per minute)
  • as they break, they spill up the beach producing a strong wash, but weak backswash so sediment is pushed up the beach and the backswash is not strong enough to pull the sediment down
  • tend to form berms at the top of the beach
21
Q

Types of wave breakers

A

1) spilling breakers
2) plunging breakers
3) surging breakers

22
Q

spilling breakers

A
  • constructive waves break in this way along a flat or gentle beach gradient
  • steep waves (large height relative to wavelength) associated with gentle beach gradients.
  • they are characterised by a gradual peaking of the wave until the crest becomes unstable, resulting in a gentle spilling forward of the crest.
23
Q

plunging breakers

A
  • destructive waves break in this way along beaches with steeper gradients
  • waves of intermediate steepness that tend to occur
    on steeper beaches than spilling breakers.
  • they are distinguished by the shoreward face of the wave becoming vertical, curling over and plunging
    forward and downward as an intact mass of water.
24
Q

surging breakers

A
  • destructive waves also break in this way, rushing up a very steep beach
  • low steepness and are found on steep beaches.
  • In surging breakers the front face and crest of the wave remain relatively smooth and the wave slides directly up the beach without breaking.
  • In surging breakers a large proportion of the wave energy is reflected at the beach.
25
Q

factors that determine the nature of the breaking

wave:

A

1) Wave energy

2) Slope of sea bed

26
Q

swell waves

A
  • waves generated by winds far away and have travelled long distances over deep water
  • their direction is thus not necessarily the same as the local wind idrection
  • relatively long, of moderate height
  • tend to build up the coastal profile
27
Q

wind waves

A
  • also called storm waves or sea
  • these are waves generated by the local winds and have traveled only short distances
  • normally relatively steep (high and short)
  • tend to be destructive for the coastal profile because they generate an offshore (not onshore) movement of sediments
28
Q

wave refraction

A
  • bending of waves which causes waves to change direction
  • occurs when different parts of a wave travel at different speeds
  • occurs because waves initially approach a beach at an angle
  • waves refract when one part of a wave enters shallow water and slows, whereas the rest of the wave still is in deeper water and travelling faster
  • waves refract parallel to shore
29
Q

orthonogals

A

lines drawn at right angles to the wave crests and they show where wave energy is concentrated

30
Q

refraction along a straight shoreline

A
  • waves approaching the shore at an angle first “feel bottom” close to shore
  • this causes the segment of the wave in shallow water to slow, causing the crest of the wave to refract or bend so that the waves arrive at the shore nearby parallel to the shoreline
31
Q

refraction process at a discordant coastline

A
  • Waves approach a discordant (irregular) coastline (bays and headlands).
  • The waves meet the headlands first where there is shallow water; the waves here slow down and break.
  • This causes the wave front to bend (refract) around the headlands.
  • The waves are now parallel to the bay and
    low in energy.

a level geography (30 decks)

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