Distribution functions of extreme sea waves and river discharges

Some of the important elements to be considered by the designer in the field of water defenses and hydraulic structures include the determination of the maximum environmental loads such as maximum wave height, maximum water level and maximum river discharge at locations of interest. These maxima can be estimated by various statistical methods based on observations. The main point of interest is the behaviour of each method for predicting these extrema and its deviation from the true value. An overview of statistical methods is given to determine the extreme values of river and sea related variables. The method of Regional Frequency Analysis (RFA) is proposed to predict the occurrence probabilities of these extrema. The RFA intends to extend the dataset by pooling the data of neighboring locations and establishes the regional growth curve of a so-called “homogenous region”. An important aspect is the formation of the homogeneous regions because only for those regions data can be pooled. Statistical methods will also be presented to derive homogeneous clusters. Applications include the prediction of extreme river discharges in Northwest and Central Europe and extreme waves along the Dutch North Sea coasts.