The Science of Surf: Understanding Wave Refraction and Its Role
Surfing involves understanding various ocean dynamics, from swells to bathymetry. Wave refraction, the bending of waves due to changes in depth, plays a crucial role in how waves break. This phenomenon, distinct from wave reflection, shapes surf conditions worldwide.
Wave refraction occurs when a wave transitions from deep to shallow water, altering its speed and direction. The portion of the wave in shallower water slows, while the rest continues at its original speed. This creates unique conditions at each surf spot.
Ground swells are more prone to refraction than wind swells. Wind swells,generated by surface winds,lack the deepwater impact of ground swells. This difference substantially affects wave behavior.
Concave vs. Convex Refraction
Refraction manifests in two primary forms: concave and convex. Concave refraction occurs when waves approach a shallow reef surrounded by deep water. The wave slows upon hitting the reef, bending and focusing energy toward the center, creating powerful waves like those at Teahupo’o and Pipeline.
Convex refraction happens when a swell encounters a headland. The energy focuses on the shallower water near the headland, slowing that part of the wave while the rest continues at speed. This defocuses energy, typical of point breaks such as J-Bay and Skeleton Bay, which often have less power but longer rides.
Beach breaks, however, are more complex. They depend on how waves interact with sandbars, which can produce either hollow waves or closeouts. High swell periods at beach breaks often result in closeouts because the sandbars cannot effectively break up the swell.
Refraction vs. Reflection
While refraction involves waves bending due to depth changes, reflection occurs when waves bounce off a barrier, such as a seawall. The angle of impact and the
