When waves propagate into shallow water their
characteristics change as they begin to feel the bottom,
as we have already noted in Section 1.2.5. The wave
period remains constant, but the speed decreases as does
the wavelength. When the water depth becomes less than
half the wavelength, there is an initial slight decrease in
wave height*. The original height is regained when the
ratio h/λ is about 0.06 and thereafter the height increases
rapidly, as does the wave steepness, until breaking point
is reached: