This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A new study led by surfing scientists at the Scripps Institution of Oceanography at UC San Diego revealed the physical relationships underlying a pattern familiar to generations of surfers. Scripps Ph.D. student Kanoa Pick and Scripps oceanographer Falk Feddersen led the research, which takes a closer look at what happens when waves approach the shore and begin to break.
The study was published July 27 in the Journal of Fluid Mechanics. "Surfers are incredibly observant," said Pick, the lead author of the study. "They learn to recognize how changes in the swell and seafloor affect a wave, even if they don't express those relationships through equations.
Science gives us a way to test that intuition and quantify the physics behind it." While waves are often broadly classified as either "spilling" or "plunging" breakers, the researchers wanted to understand more precisely how the shape of a breaking wave changes depending on the slope of the seafloor and the wave's offshore height, and what those changes mean for turbulence and sand transport. Using a two-dimensional, fully nonlinear potential-flow model, the researchers simulated solitary waves shoaling and overturning across a range of seafloor slopes and wave heights. Shoaling occurs when waves enter shallower water and grow taller.
They found that steeper slopes produce larger, more horizontally oriented overturning waves with thicker jets of water projecting from the crest, while gentler slopes produce smaller, more inclined overturns with thinner jets. The researchers discovered how to predict the size, shape and orientation of an overturning wave with knowledge of the seafloor slope and offshore wave height. These predictions included the size of the overturn (i.e., barrel) and its projecting jet, as well as the overturn aspect ratio and angle.
This goes beyond classifying waves as simply spilling or plunging by describing the precise geometry of how they break. The researchers also connected the shape of a breaking wave to how quickly it steepens as it moves into shallower water. More rapid wave steepening produced larger overturns and jets with greater potential energy.
This is important because when the overturning jet impacts the water's surface, its potential energy is rapidly converted into turbulence and bubbles. Pick and Feddersen found that jet potential energy is strongly related to jet size, linking the geometry of a breaking wave to the turbulence generated as it breaks. That turbulence is a key driver of processes such as sand suspension and transport in the surf zone.
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