Measure the frequency and wavelength of a water wave then compute its velocity. Observe the waves. Notice their crests and troughs. The amplitude of the wave, A, is the distance in meters between the center of the wave and its crest.
Surfers measure the wave height between the bottom of the trough and the top of the wave.
The scientists amplitude is thus half of the surfers wave height. This is the period, T, of the wave in seconds. Measure the periods between several waves, the period will vary. Find the average period. Bouys out in the ocean measure the period of waves the reports from these buoys can be found on the internet.