Information centre /On the crest of a wave

Surfing is one of the fastest growing, and coolest, sports in the UK.  But by understanding the science of waves, surfers can not only impress the opposite sex, they will have a better chance ride the breakers to championship success - and they can help combat coastal erosion at the same time.

Exploring the Science of Surf

The University of Plymouth runs the world’s first degree in ‘Surf Science’.  It has been devised to introduce students to the science of waves and the science behind the manufacture and performance of extreme sports clothing and equipment. It’s not just the power of waves for surfing that’s being studied – but the complex physics of the effects of swash on the shoreline and its role in coastal erosion. The swash zone (the so-called “biting edge”) is the very shallowest part of the sea, where the waves meet the shore and it is here that many of the important processes that are responsible for coastal erosion take place.

Waves gather their energy from the wind.  It’s the frictional force of the wind blowing over the surface that creates waves. Then the wind speed, wind duration and the fetch (distance over which the wind blows) determine how big the waves get. A strong wind, blowing for a long time over a long distance will create the biggest waves – but they cannot grow bigger forever and will gradually become unstable and break.  The wave’s energy is then dissipated and the height is reduced.

The crest of a wave...
There are two main types of waves – wind-driven waves and swell waves. Wind-driven waves are directly forced by the wind, like waves close to a storm centre. As waves spread away from a storm centre, they become “free” (i.e. no longer forced by the wind) and can travel for large distances with little loss of energy. These are called “swell waves” and are easily recognised as long, regular trains of waves.

As waves reach the coast, they can break in two ways – spilling or plunging. Spilling breakers typically occur when wind-driven waves meet a gently sloping beach. These waves break in relatively deep water, creating a wide surf zone where lots of lines of turbulent bores can be seen, diminishing gradually shorewards.  In the UK, this is very common on west-facing beaches.

Plunging breakers occur when swell waves meet steeper sloping coasts. The energy is dissipated rapidly over a short distance.  These waves are typically found on reefs around oceanic islands, such as Hawaii and the Canaries. Winds blowing offshore can delay wave breaking and increase the plunging tendency.

Does size matter?
Small spilling breakers are ideal for learner surfers, while large plunging breakers are ideal for experts who can ride along inside the “tube” of the breaking wave. Good surfers are looking for swell waves that arrive from distant storms and are held up by offshore winds. So, in the autumn, deep low pressure areas often occur in the mid North Atlantic sending out swells that arrive on the west coast of the UK around three days later. If the weather conditions over the UK are calm and sunny, maybe with light offshore (east) winds, the surf will be excellent.  But strong local winds can spoil conditions - making it better for windsurfing than wave surfing.

But it’s about more than just surfing.  By studying the effects of waves, scientists can learn about the causes coastal erosion. Large spilling waves break far out to sea, so are not a problem, but the raised water levels at the shoreline can cause flooding, and the strong undertow erodes the beach sediment. Plunging breakers can directly cause erosion, breaking with violence on steep shores as can be seen at high tide on shingle beaches. In general, small swell waves (usually found in summer) build up beaches, and large storm waves (in winter) erode beaches.

Surf study
Two University of Plymouth staff who run the “Surf Science” degree course, Tony Butt and Paul Russell, are currently involved in a quarter of a million pound research project, investigating the role of swash in shoreline change.

“As a result of global warming, sea levels are rising and storms are increasing.  It’s vitally important that the processes that control shoreline change and coastal erosion are better understood,” said Paul. “As part of the research, large amounts of high-tech instruments have been placed on various Cornish beaches under a wide variety of wave conditions, providing information on what waves build up the beaches and what waves cause coastal erosion”.

Paul, a former European surfing champion and Noise role model, and Tony, one of Europe’s foremost big wave riders, have also teamed up to write a book about surfing and the science of waves. It’s the first book to include in-depth coverage of the science of waves from a surfer’s point of view.