Field Observations of Wave Group Transformation during High Waves

The characteristics of wave groups propagating over the continental shelf toward the coastal region are investigated using the envelopes computed by the Hilbert transform from field observations and related to the evolution of the amplitude and phase modulations. The measurements are performed by 3 wave gauges located over a few lengths of typical wind wave groups, in water of relatively shallow water depths. During the observation period, the significant wave height exceeds 3m for four days due to the passing of typhoon. It has been observed that the distribution of waves in a group approaching a shore becomes more uniform at the wave growth and wave decay stages of these high waves. During these periods the significant wave height tends to decrease with approaching the coastal zone.