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Waves are great fun, but they can be dangerous. Understanding how they work will keep you safer.

A large wave breaking at Porthtowan Beach

Photo: RNLI / Nathan Williams

Understand waves

Powerful breaking waves have the potential to bring out the big kid in all of us. They are one of the most exciting and impressive features of our UK and Irish coastlines and they are the primary force shaping coastal change. 

One of the crucial elements of sea safety and for anyone who visits the coast, is to know the basics about waves so that they can keep themselves and others safe.

Waves are formed by friction when the wind blows across the surface of the sea, causing a swell as water particles rotate and move forwards. They can also be caused by seismic activity.

The movement of a wave up the beach is known as the swash, its movement down the beach is known as the backwash. Depending on which is stronger, waves can be either constructive or destructive.

Size and power

Aerial view of a busy beach on a sunny day

The size and power of a wave is influenced by three main factors:

  • how strong the wind is
  • how long it has been blowing
  • how far the wave has travelled (known as the fetch).

How steeply a beach slopes or shelves and the topography of the sea bed near the beach will also affect the size and type of wave.

On the south coast of England, south-east winds (ones originating from the south-east and heading north-west), have less open sea across the English Channel than south-west winds blowing in from the Atlantic Ocean.

So as a basic rule of thumb:

  • south-east winds have a shorter fetch and cause smaller waves
  • south-west winds have a longer fetch and cause larger and more powerful waves.

Waves move in sets and the ‘seventh wave’ – the bigger wave in the middle of a set – often comes further up the beach. That it always happens on the seventh wave is a myth, but sometimes it does!

Spilling waves

Spilling waves are softer and more consistent waves that break gradually as they approach the shore. They are ideal for beginner board riders. Start off in the shallow white water before you progress to deeper water and unbroken waves.

Dumping waves

Dumping waves break powerfully in shallow water and should be avoided. They most commonly occur at low tide and break quickly with a lot of force making them dangerous for beginners.

Surging waves

When a wave breaks it loses some of its power and momentum. Watch out for surging waves - they don’t break, so they can knock you off of your feet more easily and drag you into deeper water.

Our four top tips

Huge wave crashing high over the harbour wall and lighthouse in Wick Bay

1. Wave dodging

Wave dodging is for sunny, calm days and gentle waves!

It may seem fun to wait for a wave to sweep up the beach or along a harbour wall, but only 15cm of water can knock you off your feet. Bear this in mind when the weather is stormy or conditions are rough.

And don’t be caught out by the ‘seventh wave’. Remember that the wave in the middle of a set is often bigger and can reach further up the beach or along the promenade.

Enjoy the power of the water from a safe and respectful distance - preferably from a window seat in a cafe with a warm cup of tea!

2. Get to know rips

Rips are strong currents running out to sea between waves, which can quickly drag people and debris away out to deeper water.

They are especially powerful in larger surf, but never underestimate the power of any water.

Find out how to identify rip currents and what to do if you ever find yourself caught in one.

3. Know your limits

The right kinds of waves offer a lot of fun, but always stay mindful of your own limits - not just physically but in experience.

Rough and choppy water, strong currents (such as those that can occur during bad weather and spring tides) and dumping waves inspire thoughts of adventure, but they can quickly sap even the most experienced sea users of energy.

If the water is rough, don’t go in. If you feel conditions change while in the water, err on the side of caution and get out until they are calm enough to go in again.

4. Always plan ahead

  • Plan your trips to the beach beyond packed lunches and paddle boards.
  • Consult tide times and local knowledge to make sure it’s safe to be out.
  • In lifeguarding season, always choose a lifeguarded beach and swim between the red and yellow flags.
  • When the sea conditions are rough, enjoy the waves from a respectful distance