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Coastal Landscapes

Constructive and destructive waves, and how waves break

  • 3 things to know
  • Component 01

Overview

Recall questions on how waves change in shallow water and when they break, wave steepness and orbital motion, swash and backwash, spilling, plunging and surging breakers, the features and effects of constructive and destructive waves, berms, and wave refraction around a headland.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Key term

Describe the circular orbital motion of water in a deep water wave.

Key term

Why does the orbit of the water particles become elliptical close to the shore?

Key term

Define swash and backwash.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Explain what happens to a wave as it moves into shallow water.

    Model answer

    Friction with the sea bed slows the base of the wave, so its wavelength shortens, it steepens and its height increases until it becomes unstable.

  2. 2

    At what water depth does a wave usually break?

    Model answer

    When the depth falls to roughly 1.3 times the height of the wave.

  3. 3

    What is wave steepness, and at what value does a wave break?

    Model answer

    It is the ratio of wave height to wavelength, and a wave becomes unstable and breaks once that ratio exceeds about 1:7.

  4. 4

    Describe the circular orbital motion of water in a deep water wave.

    Model answer

    Each water particle travels in a closed circle as the wave passes, so the energy moves forward while the water itself stays largely in the same place.

  5. 5

    Why does the orbit of the water particles become elliptical close to the shore?

    Model answer

    The sea bed obstructs the bottom of the orbit, flattening the circle into an ellipse and finally into a to-and-fro movement.

  6. 6

    Define swash and backwash.

    Model answer

    Swash is the water rushing up the beach after a wave has broken, and backwash is the water draining back down the beach under gravity.

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AThe lower quartile is the 2nd value, 11 cm.
BThe upper quartile is the 6th value, 16 cm.
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