the wave height H to the wavelength ?--exceeds about 0.17, so for H > 0.17 ?. In shallow water, with the water depth small compared to the wavelength, the individual waves break when their wave height H is larger than 0.8 times the water depth h, that is H > 0.8 h. Waves can also break if the wind grows strong enough to blow the crest off the base of the wave.

In shallow water, the base of the wave is decelerated by drag on the seabed.