Alex Trahan

The Dutch Water Defenses are designed and maintained according to hydraulic load 
estimates determined from extreme value analysis of wind and wave data from the 
North Sea. Commonly, this analysis involves selection of extremes via peaks-over-threshold which are then fit to a generalized Pareto distribution. This process 
assumes the data are independent and identically distributed (iid). The first can be 
achieved through declustering, but the second is more difficult to confirm and may 
be violated by seasonal variation and other temporal trends.
In this study, the importance of this violation will be investigated by applying a time-stratified (seasonal) model and a time-varying model (here a non-homogeneous 
Poisson process) for full-year return value estimates which can be compared to the 
results of current, non-seasonal methods. In addition, an effort will be made to 
estimate seasonal return values (eg. Separate summer and winter estimates), since 
the critical failure modes may be different in different seasons.
The Dutch Water Defenses are designed and maintained according to hydraulic load estimates determined from extreme value analysis of wind and wave data from the 

North Sea. Commonly, this analysis involves selection of extremes via peaks-over-threshold which are then fit to a generalized Pareto distribution. This process 

assumes the data are independent and identically distributed (iid). The first can be achieved through declustering, but the second is more difficult to confirm and may 

be violated by seasonal variation and other temporal trends.

In this study, the importance of this violation will be investigated by applying a time-stratified (seasonal) model and a time-varying model (here a non-homogeneous 

Poisson process) for full-year return value estimates which can be compared to the results of current, non-seasonal methods. In addition, an effort will be made to 

estimate seasonal return values (eg. Separate summer and winter estimates), since the critical failure modes may be different in different seasons.