Minimisation of the uncertainty in estimation of extreme coastal wave heights

Accurate information on extreme wave conditions is often required for inshore and offshore structure designs, coastal inundation and erosion hazard studies, coastal construction planning, and coastal port operations. Estimates of extreme wave heights are commonly extrapolated from historical wave records based on extreme-value theory. Although a large number of studies have been undertaken to develop and improve methodologies in extreme wave analysis, there still exists much uncertainty in estimates of extreme waves. This study is to investigate main causes of this uncertainty based on historical wave buoy data collected off the NSW coast of Australia. It is found that the uncertainty is caused mainly by short wave record, missing storm wave data, different methods for generation of return wave height data, too low/high POT thresholds, subjective plotting positions, unsuitable distribution functions, different distribution parameter estimators, and ad-hoc criteria on selection of the best-fit function. The likelihood errors of the uncertainty are evaluated and the detail on how to minimise the uncertainty is also proposed