<P> In SI units, with c deep (\ displaystyle c_ (\ text (deep))) in m / s, c deep ≈ 1.25 λ (\ displaystyle c_ (\ text (deep)) \ approx 1.25 (\ sqrt (\ lambda))), when λ (\ displaystyle \ lambda) is measured in metres . This expression tells us that waves of different wavelengths travel at different speeds . The fastest waves in a storm are the ones with the longest wavelength . As a result, after a storm, the first waves to arrive on the coast are the long - wavelength swells . </P> <P> For intermediate and shallow water, the Boussinesq equations are applicable, combining frequency dispersion and nonlinear effects . And in very shallow water, the shallow water equations can be used . </P> <P> If the wavelength is very long compared to the water depth, the phase speed (by taking the limit of c when the wavelength approaches infinity) can be approximated by </P> <Dl> <Dd> c shallow = lim λ → ∞ c = g d . (\ displaystyle c_ (\ text (shallow)) = \ lim _ (\ lambda \ rightarrow \ infty) c = (\ sqrt (gd)).) </Dd> </Dl>

When are waves affected by the sea floor