English: Shoaling coefficient K _S as a function of relative water depth h / L ₀ , describing the effect of wave shoaling on the wave height – based on conservation of energy and results from Airy wave theory . The local wave height H at a certain mean water depth h is equal to H = K _S H ₀ , with H ₀ the wave height in deep water (i.e. when the water depth is greater than about half the wavelength ). The shoaling coefficient K _S depends on h / L ₀ , where L ₀ is the wavelength in deep water: L ₀ = g /(2π) T ² , with T the wave period and g the gravity of Earth . The blue line is the shoaling coefficient according to Green's law for waves in shallow water, i.e. when the water depth is less than 1/20 times the local wavelength L = T √( gh ).