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Surfzone wave characteristics, measured using a wave and tide gauge (WTG) during a flood tide, were studied at three different beaches having different nearshore slopes. The spectral wave characteristics viz., wave-height and mean wave period were estimated considering different sample sizes. Inter-comparisons of wave climate between each of three beaches for a similar tide level are presented. The wave-height and mean wave period values obtained from the wave analysis for each of the record using waves by wave method show that surfzone wave-height increased with time during a flood tide and the mean wave period decreased with time up to mid tide and then increased during the rest of the measurement period at Keri and Miramar beaches. At Candolim, the reversing trend of mean wave period increase is observed to occur much before reaching the mid tide level. The surfzone waves during a flood tide indicated that the wave-heights increased with time while the mean wave period showed a decreasing trend in general. The variation of breaker index showed a decreasing trend from low tide to high tide ranging between 0.45 and 0.23. The surf similarity parameter estimated corroborates with the visual observations.

Wave observations were carried out at the mouth of Danang Bay and off the Key Ha Cape in central Vietnam from April 1997 to February 1998 in a port development study by the Japan International Cooperation Agency. It is the first long-term measurement of waves in the west South China Sea by reliable wave measurement devices.

Wind waves due to typhoons as high as 9m in maximum height were successfully recorded, including those generated by Typhoons 9721 and 9726. Long period waves up to 16 seconds in significant period were revealed to exist. It is proved that the long period waves are swells from a large-scale typhoon remotely located in the west Pacific and propagated through the Luzon Strait to the central coast of Vietnam.

Wave hindcast calculations were made by a spectral method for the past 30 typhoons which affected the area from 1961 to 1997. Through statistical treatment of the hindcast waves, it is assessed that an offshore significant wave with a height of 9.7 m could be generated off Danang in a 50-year return period.

Seasonal wave climate is that the sea is rather calm, except the typhoon and northeast monsoon season specifically from September to November.

This paper investigates the spectral characteristics of low frequency fluctuations of natural wind velocity and atmospheric pressure, and the resonant evolution of long period waves by low frequency fluctuations of winds in a laboratory experiment. Laboratory experiments on the responses of wind waves under periodically fluctuating winds have been conducted to find an alternative generation mechanism for long period waves. The experiments show that the long period waves developed at the peak frequency of the low frequency fluctuations of wind speed and air pressure. Through the spectral analysis of fluctuating components of wind speed, air pressure and water surface elevation, the long period waves are found to be generated and resonantly developed by the fluctuating components of surface shear stress due to periodically fluctuating wind speed.