Prediction of extreme significant wave height from daily maxima

For prediction of the extreme significant wave height in the ocean areas wh ere long term wave data are not available, the empirical method of extrapol ating short term data (1 similar to3 years) is used in design practice. In this paper two methods are proposed to predict extreme significant wave hei ght based on short-term daily maxima. According to the daa recorded by the Oceanographic Station of Liaodong Bay at the Bohai Sea, it is supposed that daily maximum wave heights are statistically independent. The data show th at daily maximum wave heights obey log-normal distribution, and that the nu mbers of daily maxima vary from year to year, obeying binomial distribution . Based on these statistical characteristics, the binomial-log-normal compo und extremum distribution is derived for prediction of extreme significant wave heights (50 similar to 100 years). For examination of its accuracy and validity, the prediction of extreme wave heights is based on 12 years' dat a at this station, and based on each 3 years' data respectively. The result s show that with consideration of confidence intervals, the predicted wave heights based on 3 years' data are very close to those based on 12 years' d ata. The observed data in some ocean areas in the Atlantic Ocean and the No rth Sea show it is not correct to assume that daily maximum wave heights ar e statistically independent; they are subject to Markov chain condition, ob eying log-normal distribution. In this paper an analytical method is derive d to predict extreme wave heights in these cases. A comparison of the compu tations shows that the difference between the extreme wave heights based on the assumption that daily maxima are statistically independent and that th ey are subject to Markov Chain condition is smaller than 10%.