2. temporal variations

Question 1

Diurnal tides

Answer 1

The energy represented by tidal currents is significant in eroding, transporting and depositing material.
In estuaries, the rising tide can pick up (entrain) sediment and transport it inland.
Once high tide is reached, the current reverses, transporting material in the opposite direction.
Current velocities are relatively low at the start and end of each cycle and at their maximum in the middle of the rising or falling tide.
Different sized particles are, therefore, entrained and deposited at different times and in different locations.

Question 2

Onshore breeze

Answer 2

A sea breeze or onshore breeze is a gentle wind blowing from sea toward land, that develops over bodies of water near land due to differences in air pressure created by their different heat capacity. It is a common occurrence along coasts during the morning as solar radiation heats the land more quickly than the water.

Question 3

Constructive waves

Answer 3

Constructive waves tend to occur during the summer. Constructive waves are low, flat and gentle, with wavelengths up to 100 m and a low frequency of 6–8 waves per minute. They are characterised by a relatively more powerful swash, which carries sand and shingle up the beach, and a relatively weaker backwash. Constructive waves contribute to the formation of beach ridges and berms.

Question 4

Destructive waves

Answer 4

Destructive waves tend to occur during storms and in winter. Destructive waves are steep in form and break at a high frequency, at 13–15 waves per minute. They have a plunging motion that generates little swash and a relatively more powerful backwash; this transports sediment down the beach face, resulting in a net loss of material.

Question 5

How do waves form

Answer 5

On the run-up to a coastline, the depth of the water becomes shallower and a wave is forced to slow down. As it slows, its wavelength decreases and its height increases. This entire process is called shoaling. The wave’s height can only increase so far however. Above a height of around one seventh the wavelength of the wave, the wave becomes unstable and it breaks.

Question 6

Eclipse

Answer 6

In water that is much deeper than the wavelength of the wave, particles follow an almost closed circular path. The radius of the path depends on the wavelength of the wave and the depth of the particle, decreasing with increasing depth. At a depth of around one wavelength, the radius is so small the particles effectively don’t move. In water that isn’t much deeper than the wavelength of the wave, the particles follow an almost closed elliptical path. This increase in eccentricity happens because the sea bed starts to interfere with the motion of the particles.