coastal landscapes as a system

Waves - energy

A wave possesses potential energy as a result of its position above the wave trough, and kinetic energy caused by the motion of water within the wave.

Waves - motion

Waves do not move the water forward, but rather impart a circular motion into the individual water molecules.

Moving ball phenomenon

As a moving wave passes beneath the ball, it rises and falls but does not move horizontally across the water surface

Formula for calculating the amount of energy in a wave in deep water

P = H(2)T

P= power(energy) kw

H= height of wave in metres

T= time interval between wave crests in seconds, also known as the wave period

The relationship between wave height and wave energy is non-linear

Atlantic vs English Channel waves

Atlantic waves are eight times higher than English Channel waves but have 70 times more energy

Wave anatomy

Swell waves

Storm waves

shallow water

Typically at a depth of half the wavelength.

Here, the deepest circling water molecules come in contact with the sea floor

What happens when friction between waves and sea floor is increased?

• Waves slow down as they drag across the bottom.

• Wavelength decreases and successive waves start to bunch up

• The deepest part of the wave slows down more than the top of the wave

• The wave begins to steepen as the crest advances ahead of the base

• Eventually, when water depth is less than 1.3 x wave height, the wave topples over and breaks against the shore.

• ONLY AT THIS POINT - significant forward movement of water as well as energy

What happens after a wave breaks?

• water moves up a beach as the swash, driven by the transfer of energy that occurs after the wave breaks

• Speed of this water will decrease the further it travels due to the uphill gradient of the beach

• When there is no available energy to go forwards, the water is drawn back down the beach, this is the backwash

• The energy comes from gravity and always occurs on a perpendicular coastline, down the steepest slope angle

Constructive waves

• low in height

• Long wavelength and a low frequency

• Typically around 6 to 8 waves per minute

How do constructive waves break

By spilling forwards, the strong swash travels a long way up the gently sloping beach due to the long wavelength, backwash returns to the sea before the next wave breaks

Destructive waves

• Create a height, shorter wavelength and a higher frequency

• Often about 12 to 14 per minute

How do destructive waves break

• They break by plunging downwards and so there is little forward transfer of energy to move water up the deeply sloping beach as squash

• Friction from the steep beach slows swash and so it does not travel far before returning down the beach as backwash

Relationship between beach gradient and wave type (high energy)

High energy waves often occurring during winter months tend to remove material from the top of the beach and transport it to the offshore zone reducing beach gradient.

Relationship between each gradient and wave type (low energy)

Low energy waves, typically during the summer months, build up the beach faces deepening the profile

What are tides

The periodic rise and full of the sea surface and are produced by gravitational pool of the moon

What effect does the moon have on the tides

The moon pulls the water towards it creating a high tide and there is a compensatory bulge on the opposite side of the Earth. at locations between the two bulges, there will be a low tide. As the moon orbits the Earth the high tides follow it.

When do the highest tides occur

• When the moon Sun and Earth are all aligned into the gravitational port is at its strongest

• This happens twice each lunar month and results in spring tides with a higher tidal range

How are neap tides with a low range produced?

Twice a month, the moon and sun are at right angles to each other and the gravitational pool is therefore the weakest

how can tidal range be a significant factor in the development of coastal landscapes?

Tidal range influences where wave action occurs, the weathering processes that happen on land exposed between tides, and the potential scouring effect of waves along coast with a high tide range