Analysis of Extreme Events in the Coastal Engineering Environment

[摘要] ENGLISH ABSTRACT : Coastal zones are subject to storm events and extreme waves with certain returnperiods. The return period of such events is defined as the average time intercedingtwo independent, consecutive events, similar in nature, i.e., with the same return level.Coastal structures have to be designed to provide sufficient protection against flooding orerosion to a desired return level associated with a particular return period, for example100 years. Statistical analyses of measured wave data over a time series are used forthese estimations.In this study, wave data, measured by a Datawell Waverider buoy, is analysed bymeans of extreme value analyses. This dataset covers only approximately 18 years. Extremevalue theory provides a framework that enables extrapolation in order to estimatethe probability of events that are more extreme than any that have already been observed.It can, for example, be used to estimate wave return levels over the next 100years given only an 18 year history. Different methods for making these estimations areimplemented and evaluated.Datasets containing periods where data values are absent (i.e., gaps in a dataset), aswell as the effects these missing values have on the estimation of extreme values, are alsoinvestigated. Methods for the treatment of gaps are evaluated by using NCEP (NationalCentre for Environmental Prediction) hindcast data, containing no missing values, andcreating incomplete datasets from this data. Estimations are then made based on theseincomplete sets. The resulting estimations are compared to the estimations made basedon the complete NCEP dataset.Finally, recommendations are made for conducting optimal extreme value analyses,based on this study.

[发布机构] Stellenbosch University