May 26, 2020

How are the giant waves of Nazaré measured? We explain it to you



In the Costa da Prata Portuguese is Nazaré, a town known throughout the world for the huge size of the waves that form in front of its coast, often exceeding ten meters high. In fact, many of the highest waves ever surfed have ridden here. For example, in 2011, the surfer Garret McNamara conquered a record wave of 23.8 meters in Nazaré, a brand that was beaten in 2018 by Rodrigo Koxa, who surfed another 24.4 meters in the same place.

Now, why do such big waves form in front of this particular town? And how exactly is the height of these monstrous waves measured to determine if who has surfed them has broken the previous record?

Giant wave formation

The giant waves that form off the coast of Nazaré reach their great size thanks to the confluence of several factors. The most significant of all is the so-called «Nazaré Canyon», an underwater gorge of about 230 kilometers in length and up to 5 kilometers of maximum depth that flows into the coast of this town. This canyon acts as a kind of funnel (saving a lot of distances) that tends to redirect the energy of the waves and focus them in the direction of Nazaré.

To the presence of the canyon, it should be added that its depth decreases at a relatively high rate near the coast. As a result, as the waves approach Nazaré and enter deeper and deeper waters, the distance that separates them decreases and their height increases even more.

On the other hand, the waves that travel along the continental shelf that surrounds the canyon tend to interfere constructively with those that run along its surface in the direction of Nazaré, transferring part of its energy and contributing to its growth. And, to finish off the matter, the marine conditions of the place produce a current that propagates from the coast towards the sea and that increases the size of the waves more when it interacts with them.

Given all these factors, it is not surprising that in Nazaré some of the largest and most impressive waves in the world are formed. What is not so impressive is the method used to measure them.

Predictions of coastal waves

A few weeks ago we explained what that measuring the waves in the open sea is a more complicated task than it seems because the variations of height that the buoys register do not allow to distinguish each individual wave that passes under them, since they are all overlapping and arrive from different directions. As a result, open sea waves are measured using statistical patterns.

On the other hand, predicting the height of the waves in the coastal areas is a more direct process because the waves tend to adopt a preferred direction as they approach the mainland and the separation between each of them is better defined than in the open sea. In this case, it is possible to predict the height of the waves that will reach a specific point on the coast using mathematical models that take into account parameters such as the force of the wind and the direction in which it blows, the state of the tides, the waves in the background and the underwater topography of the area in question.

But, again, these models are not able to predict how high each individual wave will reach the coast, but only provide a figure that reflects the overall height of the waves at a specific place and time. If what you need is to know the size of a particular wave that has been ridden during a surfing competition, the method used is a little less … Sophisticated.

How to measure a record wave

The WSL Big Wave Award It is an annual surfing competition that rewards the different feats in different categories, such as the “wave of the year”, the “rowing of the year” or the biggest surfing wave. The latter is what interests us, because, as he explains the judge of big waves and editor of the SURFER portal, Grant Ellis, the height of the waves that each participant surfed is measured based on photographs and videos of the moment he was riding it. Knowing the height of each surfer and approximating how much they shrink when they are crouched on the board, the judges calculate the height of the wave approximately.

As you can imagine, this method is not accurate and estimates made by different people can lead to confusion. For example, on December 14, 2018, it was announced that surfer Tom Butler could have crowned a wave of 100 feet (33.3 meters), surpassing Rodrigo Koxa’s 24.4 meter record. But, although this news toured the networks like gunpowder at the time, the surf news portals did not mention anything of this brand again in 2019 and the Guinness book continues to show the Koxa record, so it is most likely that a more precise measurement of the wave would yield a figure lower than the 33.3 meters that were estimated at the beginning.

Another similar case occurred to Garrett McNamara. In 2013, many media outlets announced that they had surfed a wave that exceeded the 100-foot barrier, but McNamara himself was surprised at this figure and even claimed in an interview that this measurement is based on a single image that does not even They know if it could have been digitally altered.

In any case, the moral of this matter is that you can predict the average height of the waves that will hit the coast, but, again, once we look at an individual wave, things get complicated. And it is not surprising because, after all, we are talking about large bodies of water that are not only moving and constantly changing, but also exist for a short time and do not have well-defined borders.

DON’T KEEP IT UP:

  • There are several scales with which surfers measure the waves and not taking them into account can lead to confusion. For example, the height of a wave in the so-called “Hawaiian scale” corresponds to half of its actual height.

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