"Breakwaters reduce the wave height at the shore in two ways," underlines Fredric Raichlen, author of "Waves." In other words, diffraction provides natural protection from extreme storm-generated waves and should be taken into consideration by engineers when building breakwaters. In a refractive process, the part of a wavefront that propagates over shallow water will slow down, and the part in deep water will keep going at the same original speed. The difference between diffraction and refraction is that refraction is the bending of a wave as it travels and propagates over different depths - diffraction needs an obstacle to force the bending of the wave. However, a good knowledge of the break can help improve the prediction. Several variables - like shoaling and refraction, tides, winds, and other bathymetric factors - can reduce the accuracy of surf forecasts for highly diffraction-influenced surf spots. The behavior of diffraction and the impact it has on surf breaks cannot be calculated with high precision. "For instance, a big northwest swell hitting the California coast would pound the west-facing areas, but south-facing breaks, like the Santa Cruz region, would be cleaner yet smaller from diffracted energy that wrapped in," explains Nathan Todd Cool, author of "The WetSand WaveCast Guide to Surf Forecasting." The waves resulting from diffraction are always weaker and smaller than before hitting the obstacle and bending.īut, oftentimes and during winter, filtering energy could be a good thing, especially with powerful long-period groundswells. Diffraction can actually transform a wave-protected shoreline into a world-class point break. In other words, it's not always bad to surf at a beach that is not directly facing the prevailing swell angle. There are several surf breaks around the world where diffraction results in spectacular, perfect-peeling waves breaking down the line for 100, 200, 300 yards, or more. The obstacle will block a portion of the wave's energy, forcing it to spread into the sheltered area behind the obstruction.įor example, if a west or southwest swell reaches a south-facing surf spot with a curved shoreline, the energy of the waves will diffract - or bend - toward the protected or hidden area of the coastline. A light ray speeds up as it passes from glass into air, and bends away from the normal by the same angle.Diffraction is a sudden change in the direction and intensity of waves after passing by a coastal feature or offshore obstruction. If the ray meets the boundary at an angle to the normal, it bends towards the normal. Glass is denser than air, so a light ray passing from air into glass slows down. In general, the denser the transparent material, the more slowly light travels through it. The density of a material affects the speed that a wave will be transmitted through it. The waves slow down as they enter the shallow water which causes the wavelengths to shorten. Water waves will change direction at a boundary between deep and shallow water. Refraction can cause optical illusions as the light waves appear to come from a different position to A ray diagram showing refraction of light at the boundary between air and glass It is important to be able to draw ray diagrams to show the refraction of a wave at a boundary. Refraction is the change in direction of a wave at such a boundary. Light waves may change direction at the boundary between two transparent materials. Different materials have different densities.
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