Question

How do gravity waves change in terms of wave length, height, shape, phase speed, and particle motion when approaching shallower water? Why does refraction typically occur under such condition? (20%

Answer 1

Gravity waves are waves generated in a fluid medium or at the interface between two media when the force of gravity or buoyancy tries to restore equilibrium.

As the energy of a wave passes through water, the energy sets water particles into orbital motion. The water particles near the surface move in circular orbits with diameters approximately equal to the wave height. Notice also that the orbital diameter, and the wave energy, decrease deeper in the water. Below a depth of half the wavelength (D = 1/2 L), water is unaffected by the wave energy.

When deep-water waves move into shallow water, they change into breaking waves. When the energy of the waves touches the ocean floor, the water particles drag along the bottom and flatten their orbit.

Because of the friction of the deeper part of the wave with particles on the bottom, the top of the wave begins to move faster than the deeper parts of the wave. When this happens, the front surface of the wave gradually becomes steeper than the back surface. Wavelength in this region decreases and the wave-height increases.

This condition can be treated as if the medium is changed, hence the refraction of the medium occurs.