How to Measure Wave Height
Surfers sometimes want to know the height of the wave they just rode in certain scientific measurements. See why that’s kind of impossible.
Ocean waves can sometimes be quite complicated and even life-threatening, so measuring them isn’t exactly like measuring your children’s height. You cannot tell them: “Come on, son, stand up straight near this door frame and let me mark your height, so, if anybody moves into this place after us, they can scoff at our folly and repeat the same ritual once they have their own kids.”
For one thing, measuring wave height requires more science than just a tape measure. Furthermore, it requires a whole new level of precision, which renders it an impossible task, especially when it comes to measuring big waves. You need to measure those at their highest point right before they break, so it’s only a momentary number.
Being there, recording that, and measuring it to perfection is not easy. That’s why there are so many claims about records broken in big wave surfing and so little confirmation provided by either Guinness World Records or World Surf League.
Yet, there are still certain methods for measuring wave heights. Although none of them offer an exact measurement (in the end, it’s mostly up to your friends and foes standing and watching from the shore), they’re still valid ways for determining wave height. Now, let’s tell you a bit about waves, talk a bit about the history of wave measurement, and learn how it’s done.
How Waves Work and Why Measuring Wave Height Poses a Problem
An ocean wave is not like the little trickles you witness on your local sea surface on windy days. It’s formed a long way away from the shore, whether due to strong storms or earthquakes that happen under the ocean. It travels long distances, and when it arrives at a certain shore, it’s at the peak of its power.
During their travel, these waves draw water from the bottom of the ocean and release it at their top. So, not only does the distance they travel affect how big they get, but also the depth of the ocean along their route. A wave that travels in an underwater canyon will have more water to feed itself with. Therefore, it'll be much bigger than one that travels on underwater plateaus.
In addition, the wave period, meaning the interval between subsequent waves, also has an effect on the wave size. Waves passing through a certain spot in a more frequent manner means that there’s little energy left for the next wave in line, no matter how deep the ocean is. When the wave period is longer, on the other hand, there’ll be more water for the wave to draw power from, and such waves can reach up to a significant wave height.
Once the wave nears the shore, the water gets shallower, and shallow water means that there’s little energy to draw momentum from, so waves start breaking. Normally, the wave height measured aims to ascertain the vertical distance between the highest and lowest point of a breaking wave. However, throughout surfing history, exactly which point should be considered the lowest point of a wave has proved controversial.
Some claim it should be the trough of the breaking wave, but the trough happens only when the wave is curled down on the ocean surface to draw water from the bottom. Some say it should be the ocean surface behind the wave, but the water level behind a huge wave rises above average due to the sheer power of the wave. And sometimes, you can fit another wave to the discrepancy between these two numbers.
So, how can a fairly accurate wave height be estimated?
A Brief History on How to Measure Wave Height
Small waves are easy to measure if you’re an average-sized surfer. You go into the water, start surfing, and after a while, you’re instinctively aware of what to call that wave: knee-high, waist-high, shoulder-high, head-high, overhead, double overhead, etc.
But when the wave height is above double overhead, you might find yourself a little bit in trouble. Honestly, saying, “Well, mate, it was a double overhead, then a waist on top of it, and then a knee over that waist,” can’t really cut it. Although surfers came up with different labels for those huge waves like “bomb,” “gnarly,” and “bitchin,” none of these actually gave an idea about the height of the wave except for: “Yeah, that really sounds quite big.”
The Hawaiian Scale
Not being able to accurately describe the huge wave you just rode is certainly a problem, and that was especially the case for Hawaii’s notoriously big waves in the 1940s and 1950s. Not that the locals really cared about the exact measurement of the waves they were riding, but the Californians who started frequenting Hawaiian shores back then needed a tangible number to brag about and spite each other once they returned home.
Thankfully, there were two Californians who wanted to resolve the issue once and for all: Walter and Phillip “Flippy” Hoffman. They were brothers, so you can imagine the sort of rivalry they had between themselves. One wouldn’t let the other brag too much about the height of the wave he just rode.
After a session, Walter would suggest a measurement of the wave he just conquered, and Phillip would just cut the estimate in half, claiming that waves should be measured from their back and not from the open wave face. In more certain terms, it meant that the waves consisted of only a crest, and the trough was simply insignificant.
Yes, that’s how the measurement method known as the Hawaiian Scale was conceived. Nowadays, it’s not taken seriously anymore because, first, it’s not really a sensible method for measuring waves, and second, it may downgrade the scale of lots of big waves, including those gargantuan ones you see in big wave spots like Nazaré, by half.
Although it wasn't a sound way to measure waves, the Hawaiian scale is at least able to provide a scientific number regardless: that of the wave amplitude.
The Bascom Method
Willard Newell Bascom was a legendary Californian oceanographer, engineer, and adventurer (also an imaginative person since he was a renowned treasure hunter).
Although he had controversial thoughts like “Human waste is good for fish in the long term because it might feed them,” his contributions to treasure-hunting and surfing are undeniable. After all, he’s the guy who first thought of using neoprene in the making of wetsuits.
However, that wasn’t the main reason behind his popularity. In the 1960s, he came up with a wave measurement method that’s now known as the Bascom Method. Unlike the Hawaiian Scale that downgraded the wave height, the Bascom Method provided a boost for the number. If a wave measured 5 feet on the Hawaiian Scale, Willard Newell Bascom would have probably told you that it was actually 10 feet and made you happy.
Bascom suggested that you should stand on the beach and align your eyes with the wave crest and horizon. Then, you should simply stare down the wave to the sea level that happened to be the wave’s trough. It was pretty popular in California because it resulted in an overestimation of the wave height. As we said above, the trough of larger waves is significantly lower than the ocean level.
The Surfable Wave Face Method
Come to think of it, neither of the methods above is actually satisfactory. The first one humbles you when there’s no need, and in the second, numbers are boosted like oil prices in times of war. So, there should be a way in the middle, right? Well, no one should worry about it because humanity will always find a safe way in the middle… Right?
Well, at least when measuring waves, yes. The surfable wave face method is that middle way, and the rationale behind it is quite sensible as well. The trough is not where a surfer should be, and the back of the wave is quite inconsequential. So, let’s just stick to the surfable areas within the vertical distance of a wave: from the shoulder to the peak.
The result? Well, if a wave measures 10 feet with the Bascom Method and 5 feet on the Hawaiian Scale, The Surfable Wave Face Method will tell you that it was actually 7,5 feet. In other words, it’s not as degrading as the Hawaiian Scale, so the wave height will still make you happy, and it’s not as magnified as the Bascom Method, so the outcome is much more realistic.
You can obviously argue against the science of these methods, but if you’re riding big waves and thinking that describing waves with the parts of your body (knees, waist, chest, head) is imprecise and impractical, they’ll at least give you a number to hang on.