The Simple Rule of Rough Water Exits

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Copper Coast Impact Zone – Force Four Wind

Where do waves break and what is the Impact Zone?

The impact zone is a surfing term for the area where waves are breaking. It is the horizontal distance in which waves break from shallow to deep water. For open water swimming we must also consider vertical distance, the difference between the minimum and maximum heights of waves. We could think of the Impact Zone as a zone of increased unpredictability.

I wrote about waves and their impact on swimming many years ago, but I want to return to a couple of salient point about breaking waves:

1. Waves break in depths of 1.3 times their height.
2. A wave that breaks will often create a subsequent waves that will break again in shallower water.

What actually happens is that friction of the bottom causes the underwater part of the wave to slow so that the faster moving top of the waves falls over in front. The wave trips or spills.

The height of a wave is from the lowest point of the trough to the peak. This seems obvious but in practice, most people will underestimate the height because they think the trough is just the bottom of the wave face, whereas it’s often out in front of the wave.

A wave that encounters a sharp decrease in depth will break suddenly. This is why waves that break on reefs are usually more powerful, because the sudden depth allows bigger waves to break. The sudden depth change might result in an narrow impact zone.

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Beach exits

• Sandy Beaches
  

On beaches with a more gradual depth change, waves will break in decreasing depth. So a twelve-foot wave will break in fifteen feet of water, but this might result in a subsequent mushy six-foot waves, which will break in eight feet of water, resulting in a further three-foot wave which will break in chest deep water. This combination of gradually decreasing depth causing subsequent waves of lesser heights to break in shallower depths, means the impact zone in front of beaches is much wider, that is, it reaches further out to sea and is consequently more difficult to swim through.

The previous points are based on a shallow gradient beaches. (In Ireland this would include long shallow beaches like Tramore, Myrtleville or Lahinch).

Beaches with steep gradients are sometimes called destructive -formation or -action beaches. Steep beaches are subject to destructive wave breaking, and feature sudden depth changes and vertical crashing waves.

The steep gradient amplifies the breaking power of the waves in the sudden depth change, constraining the area of the impact zone, somewhat similar to reefs.  So exits to such beaches can result in impacts with swimmers being suddenly and unexpectedly being lifted and dropped in very shallow water. At which time the sand you think of as soft presents a compacted and hard surface onto which you can be thrown.  In fact destructive-action steep beaches can present such a hazard that surfers coined another phrase for them; kamikaze breaks.

Such as beach is Bunmahon on the Copper Coast, known for its steep waves which suits body-boarders and surfers.

The US NOAA site has a nice gif of how waves break dependent on beach gradient.

The gradient of the beach affects how the waves break

Another hazard of beaches relevant to exits, (whose broader features I’ve included in the Features and Hazards of the different types of open water swimming locations three-part series ), is that of “channels” or “rips”. Rips on beaches are the small areas in the water along a beach where the water from incoming waves flows back through the waves back out beyond the impact zone. As such they present an outward current that can be very powerful and gave rise to the myth of the “undertow” especially on steep destructive action beaches.

Rips are usually but often not easily recognised as an area where less waves are breaking and so present a deceptively attractive exit point.

An outward surface current may or may be visible through the flow of foam or bubbles. They are rarely wide, often not more than ten to twenty metres. Bunmahon beach, already mentioned above, actually combines destructive with a concentrated outward channel, which has resulted in a number of drownings. Other destructive action beaches include Australia’s famous Bondi beach and California’s Newport Beach and the infamous Wedge beach break wave.

Rips (unhelpfully often called rip tides, which have nothing to do with tides) run out from and parallel to or diagonal from the beach.These rips combined with destructive wave action on steep beaches, is a noted regular cause of ocean drownings. A swimmer trying to approach a beach through a channel or rip should not waste energy trying to overcome the current, but should swim along the shore until they pass out of the channel. Though not strictly speaking a rough exit, the hazards channels present means they should be accounted in the same category.

A safer method is to stop and duck under the water as the wave approaches and allow it to pass overhead, and continue to progress toward the beach in the gaps between waves. However in onshore conditions (wind blowing off the sea toward land) , the water will be rough and the interval between waves too short to do this, and the swimmer must continue onward. If you have not learned the difficult skill of body-surfing (which is outside the scope of this article), the best option is to drop your legs as the wave passes, and assume a more vertical position in the water. This reduces the chance of being thrown onto your head by the wave.
When approaching a beach from the ocean in pronounced waves, depending on the severity of the conditions, it may be best to stop swimming in the last twenty five metres or so, take the vertical position and merely allow the waves to move you onto the beach using only a small amount of swimming.
By being vertical you can with correct timing and often allow larger waves to catch you and deposit you virtually standing on the beach. The reason for stopping this far out is to allow for the variability of waves coming from behind, which can have an height (amplitude) difference of double the surrounding waves. This is not a beginner skill, but when mastered and in the right conditions can allow a person to seemingly walk directly out of crashing waves.

Onshore waves break onto Dover’s steep shingle Shapkespeare Beach, the traditional starting point of English Channel solos

• Shingle and stone beaches

Shingle or stone beaches are much more difficult than sand. The risks associated with crashing waves and rips are present, to which are added a hard yet unstable underfoot surface and the possibility of bruises, lacerations and impacts. Shingle beaches are also more likely to be steep. (Sand beaches can become shingle and vice versa, as the result of single storm). The best known example to many experienced swimmers of this type of beach is Shakespeare Beach or Dover Harbour’s shingle beach. Even in good conditions the harbour beach is difficult to climb without footwear. In rough conditions it requires skill and the confidence and/or skill common to experienced open water swimmers to navigate. But no-one travels a second time to Dover without bringing sandals, and one can will regularly see swimmers having sandals thrown out to them before they attempt exit the water.

Bunmahon at low tide belies it’s strong rips and steep beach on higher tide, the lifeguard flag making it look more benign that it is

Note: Many beaches, especially beaches in higher tide ranges, are a mix of both sand and shingle and as mentioned above, some change. Dover beach has sand below the shingle on a low spring tide, as does Kilfarrassey on the Copper Coast. Other beaches are the opposite, with submerged rocks and shingle below the sand slope, such as Clonea beach also on the Copper Coast. Annestown beach, also on the Copper Cost, has changed for sand to shingle and back a number of times over the past two decades.

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Beaches, often considered the most safe exit, therefore present their own challenges which like all things related to the sea, must be understood and appreciated.

In the next and final part we’ll look at the remaining important types of rough water exits.

Related articles:

How To: Swimming in rough water.

How waves can interfere with swimmers and cut down on their speeds

How To: Understanding Rough Water: Force Three.

How To: Understand Waves for Swimmers – Part 1.

How To: Understand Waves for Swimmers – Part 2.

How To: Understand the Beaufort Wind Scale – An essential observational skill for the OW Swimmer.

How To: Understand the Features and Hazards of the Different Types of Open Water Swimming Locations – I – The Ocean.