Wave:
1. How are wave generated?
-Waves are created by the frictional drag of air as it moves over the water.
-This explains why high waves are usually associated with windy, stormy conditions, and still seas are associated with calm weather conditions.
- In open water, the bobbing of the waves results from an orbital motion.
- However, close to the land this orbital close to land this orbital motion is interrupted by friction with sea bed, forcing it to become more elliptical in shape. This causes the wave to extend upwards and break.
- Water rushes up the beach as swash & then draws back towards the sea as backwash.
• It is controlled by:
(a) Wind strength (velocity)
(b) Fetch (distance of open sea that waves can travel over)
(c) The depth of the sea
(d) Period of time
* The longer the fetch the greater the wave energy e.g. Brunei Bay short fetch, South Pacific long fetch.
Wind velocity- the stronger the wind the greater the energy transferred e.g. Storm waves
Period of time- the longer the time the wind blows the greater the energy
Characteristics of a wave:
- Wave length-the distance between two successive crests or trough
- Wave frequency-the number of waves per minute.
- Wave height/amplitude-the distance between the trough and the crest
- Fetch-the amount of open water over which a wave has passed
- Velocity- the speed a wave travels at, influenced by wind, fetch and depth of water.
- Swash- the movement of water up the beach
- Trough-depression between two waves
- Backwash-the movement of water down the beach.
- Wave orbit-The shape of the wave, It varies between circular and elliptical. The orbit diameter decreases with depth, to a depth roughly equal to wavelength (which is the distance between neighbouring crests or troughs) when no further movement occurs as related to wind energy (this point is called the wave base)
- Longshore drift-the irregular movement of particles along a beach as they travel obliquely up the slope of a beach with the swash and directly down this slope with backwash
- Wave period-the time taken to travel through one wave length.
- Wave steepness-the ratio of wave height to wave length. This cannot exceed a ratio of 1:7. At this point the wave becomes to steep and overbalances.
