What Is (Ocean) Wave Diffraction?

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Wave diffraction describes a sudden shift in the direction and force of a wave after it meets an obstruction.

The obstruction blocks the wave and it bends around the blocked area.

If, for instance, a western swell hits a curved south-facing shoreline, the waves will bend (“diffract”) toward an obstructed area of the shoreline.

This diffraction pattern can result in peeling waves that break for several hundred yards. As a result, it’s not necessarily a bad idea to avoid beaches that don’t directly face the swell angle, although it all depends on the individual surf spot.

The Difference Between Refraction and Diffraction

Refraction occurs when waves move from one medium to another.

For example, if waves move from deep water to shallow water, they will slow down and change direction.

This is refraction.

Diffraction occurs as a result of an obstacle, such as an island. The waves hit, move, change shape, and then envelop.

Examples of Refraction and Diffraction

Refraction and diffraction are often used in reference to light waves, and this might be the easiest way to understand them.

When you look at something through a glass of water and notice a distortion, this is refraction. The light waves are moving through the air and into the glass, changing speed in the process.

As for diffraction, the best example is the famous single slit experiment, whereby a light wave passes through a circular aperture and then spreads as it propagates.

Diffraction patterns are also seen in sound waves.

How Diffraction Protects

Diffraction is a process often considered by engineers building breakwaters as it helps to provide protection against heavy storm waves.

By placing obstructions in the way of the storm, it will ensure that only a small part of the immense storm energy passes through the gap. Furthermore, the energy will then be spread laterally, essentially dispersing it.