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Waves

Fig. 1a. Irregular directional storm waves (including white capping)

Fig. 1b. Regular unidirectional swell.

There is typically a distinction between short waves, which are waves with periods less than approximately 20 s, and long waves or long period oscillations, which are oscillations with periods between 20-30 s and 40 min. Water-level oscillations with periods or recurrence intervals larger than around 1 hour, such as astronomical tide and storm surge, are referred to as water-level variations. The short waves are wind waves and swell, whereas long waves are divided into surf beats, harbour resonance, seiche and tsunamis. Natural waves can be viewed as a wave field consisting of a large number of single wave components each characterised by a wave height, a wave period and a propagation direction. Wave fields with many different wave periods and heights are called irregular.