The characteristics of waves around an entrance of a lagoon in South China Sea

The characteristics of the waves around a lagoon entrance in South China Sea were observed during the past one and half years based on the wave measurements.The measured results show that the monsoon plays an important role.In summer,waves mostly come from the southeast,among which the wave components of non-dimensional periods larger than 0.2 are fetch-trapped waves.In winter the waves may be divided into two groups,the fetch-trapped waves and the waves from the open sea.The skewness of the directional distribution functions is within+8 around zero.The power relationship between the direction spread and kurtosis is also investigated.Besides,it is found that the waves with the significant wave heights greater than 1.5 m are caused by typhoons or cold air.The frequency components of wave energy driven by cold air appear in the high frequency range at first,and change to the lower frequency range afterwards.The waves driven by typhoon mostly come from the open sea.