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Definition of Refraction:
The propensity of waves to align the wave front in shallow water with the depth contour, according to Snell's law. Also: Change of wave propagation direction due to the interaction with currents.
This is the common definition for Refraction, other definitions can be discussed in the article

Refraction of obliquely incident waves when entering shallow coastal. Bending of the wave crests to become parallel to the shore. Image Google Earth.


When incident waves are approaching the coast from different directions (directional spread), refraction in shallow water will bend the wave fronts such that they tend to align with the depth contours. The wave directional spread will thus become narrower.

Wave refraction is described by Snell's law. Along each wave ray

[math]\Large\frac{\sin \theta}{c}\normalsize = constant , \qquad (1)[/math]

where [math]\theta[/math] is the wave ray direction and [math]c[/math] the wave propagation speed.

Refraction and diffraction have to be considered together[1]. See Komar 1998[2] for the construction of wave rays from Eq. (1).

Related articles

Wave transformation
Shallow-water wave theory


  1. Huntley, D.A. and Bryan, K.R. 2022. Waves. Chapter 8.03, Treatise on Geomorphology 2nd edition. Elsevier
  2. Komar, P.D. 1998. Beach Processes and Sedimentation. Prentice-Hall