Statistical methods to assess the hydrodynamic boundary conditions for risk based design approaches in coastal engineering : methods and application to the German North Sea coastline

Worldwide, coastal areas are considered important settlement and industrial areas and host some of the most valuable ecological systems of our planet. At the same time, they are particularly vulnerable to natural catastrophes; this includes the low lying areas along the German North Sea coastline. In the past, and partly even today, coastal structures were most often designed with simple deterministic approaches. Nowadays, risk based design methods become more and more important in modern coastal engineering applications. Thereby, one of the main challenges consists in estimating the input variables or relevant loading parameters for coastal defence structures, respectively. These parameters need to be determined for current and possible future climate conditions in order to guarantee high safety standards throughout the expected lifetime of a structure (e.g. 100 years). This thesis deals with the important loading parameters for coastal defence structures, i.e. mean sea level (MSL), storm surges and wind waves, as well as with their statistical assessment, representing an integral part of any risk analysis.
In order to analyse past changes in MSL along the German North Sea coastline, methods to generate long and high quality observational MSL time series are further developed and new analysis techniques are introduced. With these methods and based on tide gauge data dating back to the mid 19th century, observed changes in mean sea level are reconstructed and analysed in detail. To achieve meaningful results from risk assessments it is furthermore indispensable to consider a large sample of storm surge scenarios. Such scenarios can be derived with hydrodynamic model simulations or with empirical approaches, whereas both methods are very time consuming and therefore restrict the number of scenarios. Here, a stochastic approach to simulate storm surge scenarios is introduced. The results can be used as input data for risk analyses or other applications, but can also be considered as a basis for statistical assessments. In this thesis, multivariate statistical models based on Copula functions are developed and applied. With these statistical models it is for the first time possible to take all relevant loading parameters (i.e. selected storm surge and wave parameters) into account. Hence, the exceedance probabilities to be used within risk assessments can be calculated more reliably than before, as demonstrated in the German Bight study area.