How Physicists Can Create Better Surfing Waves

Some surf spots are so legendary that surfers dream of riding their waves, like Peʻahi in Maui, known as "Jaws" for its massive Pacific waves, and Praia do Norte in Nazaré, Portugal, which hosts the largest waves ever surfed, reaching up to 30 meters high. Scientists are studying the physics behind these waves to understand their formation, especially as many prime surf spots are threatened by environmental changes. This knowledge could help preserve these locations or even allow for the creation of artificial waves. A typical surfable wave features a curling crest that forms a "barrel," and when it crashes, it creates whitewater. Surfers ride on the shoulder of the wave or within the barrel, a feat known as "getting tubed." While a wave's anatomy is easy to describe, defining what makes a wave "good" for surfing is more complex, as it depends on the surfer's skill level and personal preferences. To address this, scientists use mathematics to define a range of waves that surfers consider good, rather than a single ideal. Their approach involves four key parameters: wave height (from crest to trough), length (horizontal distance of a breaking wave), peel angle (the angle between the crest and whitewater), and breaking intensity. By analyzing the types of maneuvers possible with different parameter ranges, scientists can determine a wave's "surf-worthiness." They then reverse-engineer the physics that produce these desirable waves. Although no two waves break identically, waves in the same location with similar formation conditions tend to be alike, allowing scientists to trace back the factors influencing their creation. Waves originate in the deep, open ocean, far from shore. Wind blowing across the water creates small underwater circulation pockets, a process called trochoidal motion, which can grow into larger waves when the wind is stronger, such as during a storm. As waves gain energy, they evolve into swells with wavelengths of about 300 meters, capable of outrunning smaller, choppier waves and traveling long distances to the coast. The crucial stage for wave formation occurs when swells reach shallower water, approximately half their wavelength deep. Here, the bottom of the wave drags on the seafloor, slowing it down, while the top maintains its momentum. This disparity causes the wave to tumble over itself, forming a breaking crest. The surfability of a wave is heavily influenced by the seafloor's shape, known as bathymetry. For a wave to be surfable, it requires a non-zero peel angle, meaning it breaks unevenly, with one side breaking before the other. This typically happens on beaches with irregular shapes, which is why many famous surf spots are located near coral reefs. Scientists have studied the bathymetry of 34 renowned surf locations, identifying seafloor configurations that create good waves. Through computer simulations, they've learned how these configurations affect wave direction, speed, and shape. For instance, seafloor dips can increase wave speed and intensity, and the seafloor's slope relative to the coast impacts the wave's direction for optimal surfing. While bathymetry is a significant factor, other elements like wind speed and direction, swell period and height, and tide conditions are also critical for a great wave. Experienced surfers develop an intuition for these conditions, but they are rapidly changing due to environmental factors like rising seas, coastal erosion, and development, which alter bathymetry and coastline shape. Some coastal protection strategies, such as sediment replenishment, can inadvertently destroy surf breaks by changing the seafloor contours. Mathematical models of surf breaks are therefore vital. They enable scientists to design interventions that protect both coastlines and surf breaks. For example, underwater structures made of sandbags, rocks, or concrete can be arranged to direct sand flow, reducing erosion and shaping the bathymetry to create surf-worthy waves. Narrowneck Reef in Australia successfully implemented this strategy in 1999. In the future, these models could even transform unsurfable beaches into premier surfing destinations. Middleton Beach in Albany, Australia, for instance, now features an artificial reef designed using beach measurements and simulations to funnel waves for optimal breaking. These advancements are significantly impacting the physics community and providing surfers with a more scientific basis for understanding and appreciating their favorite waves.