Wave refraction
Besides wave height changes due to shoaling and from wave breaking, the direction in which the waves propagate is affected also as the waves approach the beach. If the propagating wave crests are oblique to the depth contours, the direction of propagation will change such that the wave crests become more parallel to the depth contours (see Fig. 45). This "wave refraction" can be understood since the wave celerity (the velocity of wave propagation) decreases with the water depth. Thus the distance between wave crests (the wave length) is less in shallow water than in deeper water. The theory is similar to the optical theory of light passing through different media which is described by Snel's Law.

Wave diffraction
If an incoming wave field passes an obstacle such as a groyne or a breakwater, a shadow zone exists on the lee side of the structure. However, the water surface in this shadow zone is not perfectly flat as could be expected from the direction of propagation of the waves. Waves propagate into this shadow zone with a smaller height than the incident waves and with a direction which has changed from the direction of the incident waves. Apparently, wave energy has been transmitted perpendicular to the incident wave direction into the shadow zone. This phenomenon is called diffraction (see Fig. 46).

Wave reflection
Wave reflection (see Fig. 47) from very steep shores leads to an increase in the wave height (100% for complete reflection).