Moving water particles in a wave of oscillation cannot move up and down when they run into the bottom. This interference of the bottom with the moving water particles forces the wave to slow down . Slowing of the wave causes shortening of the wavelength and a corresponding increase in the wave height . Finally, as the water continues to shallow, the upper part of the wave runs away from the lower part. The wave breaks , turns into a wave of translation and washes up onto the shore.
Waves reach shallow water sooner in front of headlands.
These waves slow down and the wavelength shortens in front of the headlands, but waves in the bays continue at the same speed and wavelength because they have not yet come into the shallow water. Longshore currents and beach drift Oscillation waves that are breaking at an angle to the shoreline produce translation waves that move diagonally up and down the beach. This diagonal swash and backwash on the beach creates a longshore current just offshore that moves parallel to the beach and also produces beach drift, which is transport of sand along the beach . When two longshore currents converge, a rip current is formed. Swim parallel to the shore to escape a rip current.