La formation des vagues

How waves are formed ?


Waves have a real impact on a wide range of water sports. This natural phenomenon must therefore be factored in and fully understood if you want to be able to surf, paddle, dive or sail as well as possible.

How waves are formed

Surftrip "test mission" in Galicia

What are waves? How are they created?
A wave is an oscillating movement of the surface of an ocean, sea or lake. The term "swell" is used when it is located offshore.

A swell is created by the wind, when it begins to blow on a stretch of calm water. Ripples then appear on the surface of the sea, gradually turning into waves (called "swell") and they then make their way to the coasts.

How waves are formed

Swell spread

The rate at which the swell grows is determined by three factors:

  • windspeed
  • how long the wind lasts
  • how far the swell moves

The longer the swell lasts, the longer the gap between successive waves and the greater its energy.
This swell will generate big, powerful waves with long gaps between each wave (between 15 and 20 seconds) and the waves will last for longer.
The shorter the period the swell is maintained over a long distance, the weaker the waves and the shorter the gap between them (between 8 and 12 seconds), and they will fade away more quickly.

When the swell turns into waves

As the swell gets closer to the coast, the distance between the water and the seabed is reduced. This impacts on the size of the swell that in turn increases in size more and more, ending up by breaking.

How waves are formed

The shape of the waves depends mainly on the form of the seabed and of the beach enabling the horizontal movement of the swell to be transformed into a vertical movement. So a slightly sloping beach will only produce weak and rather flat waves. On the other hand, a beach with a deep face followed by a shallow bed will create large, powerful waves.

To simplify things:

  • Flat shoreline= flat wave, ideal for beginners (Example of a spot: Hendaye)
  • Gentle, gradual slope = spiller (example of a spot: the Basque coast)
  • Steep shoreline = surging wave (example of a spot: Hossegor)

What impact do on-shore and off-shore winds have on waves?

On-shore and off-shore winds refer to the wind that blows on the coast, changing the nature of the waves (not the same wind as the one explained above that generates the swell).
On-shore winds come from the sea and tend to push the waves down and the sea becomes choppy. This makes the conditions less favourable for surfing or bodyboarding.
Conversely, off-shore winds come from the land and usually whips up bigger waves while smoothing out the water, thus improving surfing and bodyboarding conditions.
Depending on the time of day and the differences in temperatures observed, waves are either impacted by the on-shore breeze during the day or the off-shore breeze at night and early morning…The two patterns below explain this phenomenon.

How waves are formed

How waves are formed

Another important factor: tides

Depending on the spot, tides can have a considerable impact on waves. They can directly impact on the water depth thus altering the characteristics of the waves. Some spots will therefore be more favourable for surfing and bodyboarding at high-tide, while others will be better when the tide is low. The Tribord Club provides details about the characteristics of a host of spots.

Is it a myth to say "The 7th wave is always the biggest"?

Not necessarily! It's true that in a rather anarchic group we often see after every six waves that there's one that is generally the biggest of the group. In groups when the swell is more "perfect" this number increases to nine or ten. These scientific observations are the work of Leo Holthuijsen, an expert in the field of understanding and modelling waves.

Make sure you carefully check conditions before going into the sea

Before taking (or not) to the water, you should check thoroughly check conditions, in order to be ready to go surfing or bodyboarding:

  • pay close attention to the nature of the groups of waves for a few minutes and not just a few seconds (surfers- try to pick out the best "peaks" i.e. the place where the wave first breaks)
  • anticipate the places for getting into and out of the water (in certain spots such as the Basque coast, coming out of the water is sometimes complicated when there's a high tide whereas there's no problem when the tide is low)
  • carefully pick out the currents in order to use them as much as possible once you're in the water
  • adapt your time in the water to the tides based on the location and type of sport you're planning to do

How waves are formed

Surftrip "test mission" in Galicia

By way of a conclusion, we can therefore say that the waves we see on our beaches are mainly the result of two natural factors: the wind and water depth. However, by studying these two factors, forecasters are able to give us increasingly reliable indications and, above all, more precise information about the waves we can expect to see... You can find a weather forecast service on the Tribord Club site.
However, don't forget to observe and analyse the conditions of the spot you're going to in real time because nature is anything but predictable!

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