The Wonder of Waves

Watching waves is a really relaxing thing to do. Where do they come from? Where will they end? When will they break? But it is also these same waves that can prevent us from swimming in the sea.......

The surface of the sea is never really flat. The smallest sea breeze can create ripples. Where I swim on the south coast we are in the middle of a shallow south facing bay that stretches from Selsey Bill in West Sussex to Beachy Head in East Sussex. Our beaches are made up of sea defense shingle and we have very little shelter from the prevailing south westerly winds. So when there are certain types of waves of significant size, we cannot swim in the sea safely. The key to choosing a time to swim is understanding your local beach topography, tide times and states and of course waves.

What are waves?

Here's the physics bit. Waves are energy. Specifically transport energy. The medium that transports this energy is water. Yep I'll leave that one with you for a while for you to ponder. From a sea swimmers perspective this is only relevant in the context of how waves are created so you can better understand forecasts and make safe swim choices.

How are waves created?

Waves are created by wind/air moving across the surface of the sea. The energy is created by friction between the water and air molecules. This energy is then stored in the wave it creates. What this friction creates, depends on the conditions. A gentle local breeze will create RIPPLES sometimes referred to as capillary waves. You can see the gusts on the waters surface as it breaks the surface tension. If these conditions continue for any length of time the ripples will mature into WAVES sometimes referred to as gravity waves or wind swell. The vertical disturbance of the water is no longer due to surface tension and they can travel further and last after the the wind has dropped. However, if the wind continues to blow at speed for a significant amount of time over a large area of the sea SWELL or ground swell will be created. Swell contains more stored energy and can travel huge distances across vast oceans. A storm in the Caribbean creating capillary waves, gravity waves and then swell can arrive on UK south coast shores a few days later .

Parts of a Wave

• Crest - the highest point of a wave

• Trough - the lowest part of the wave

• Wave height -The vertical distance between the wave trough and the wave crest

• Wavelength - The distance between two consecutive wave crests

• Period - the time taken for two consecutive wave crests to pass a stationary point.

• Wave face - the front of the wave facing the shore