Coastal Environments

WAVES

- Created by transfer of energy from the wind blowing over the sea surface.

- Energy aacquired by waves depends on strength of wind, length of time it is blowing and distance over which it blows (FETCH).

- When waves approach shallow water, friction with sea bed increases, base of the wave begins to slow down - increases height and steepness of the wave until upper part plunges forward and the wave 'breaks' onto the beach.

- Any rush of water up the beach is called SWASH, water running down the beach into the sea is BACKWASH.

- Waves are CONSTRUCTIVE or DESTRUCTIVE.

Constructive Waves

- Low waves, with a long wavelength (up to 100m).

- Have a low frequency of around 6 - 8 per minute.

- As they approach the beach the wave front steepens slowly - gentle spill onto beach surface.

- Swash loses volume/energy as water percolates through beach material - gives very weak backwash, insufficient force to pull sediment off the beach.

- Material is slowly moved up the beach leading to the formation of berms.

Destructive Waves

- High waves with a steep form and a high frequency of 10 - 14 per minute.

- On approach to the beach they rapidly steepen and plunge down when breaking.

- Creates powerful backwash - little forward movement of water, inhibits swash from the next wave.

- Little material is moved up the beach - leaving backwash to pull material away.

- Commonly associated with steeper beach profiles.

- Force of each way may project some shingle towards the rear of the beach - forms a large ridge (STORM BEACH).

Effects Of Waves

- Constructive waves build beach up, result in steeper beach profile - encourages waves to become more destructive (associated with steeper profiles).

- Destructive waves move material back towards the sea, reducing beach angle/encouraging more constructive waves.

Should encourage state of equilibrium but impossible with othe factors (wind strength/direction) not being constant.

- When waves approach a coastline of irregular shape they are refracted - become increasingly paralell to coastline.

Tides

- Def: The periodic rise and fall in the level of the sea.

- Caused by gravitational pull of the sun/moon (moon has greater influence due to proximity). Moon pulls water towards it, creating a high tide - compensatory bulge on the other side of the Earth. Areas of the world between the two bulges experience the tide at its lowest.

- As moon orbits the earth, high tides follow it. When moon, sun and Earth are in a straight line (twice a lunar month), the tide-raising force is strongest.

- Produces highest monthly tidal range (SPRING TIDE).

- Twice a month the moon/sun positioned 90 degrees to each other in relation to Earth - gives lowest monthly tidal range (NEAP TIDE).