This paper experimentally explored the influence of the wave spectrum shape variation on breakwater design. The energy spectrum function generally considered for the design of coastal structures is the JONSWAP spectrum. The laboratory results were therefore used to assess the impact of changing the spectrum shape parameter (PEF). We analysed armour stability and wave overtopping in a wave flume with a geometric similarity ratio of 1:30. The experimental results showed that the PEF has maximum influence on overtopping and wave pressures on the crown wall. For a PEF value of 3.3, overtopping was much higher (30% to 100% higher) than with a PEF of 1. Pressure on the crown wall was 20% higher with a PEF of 3.3 in comparison with that for a PEF equal to 1. The stability of the breakwater’s block armour is less sensitive to the PEF variation.

In this article, we present a study that focuses on forecasting the one hundred-years return period waves height using two methods; i) Peak Over Threshold (POT) and ii) Annual Maxima (MA). The analysis is carried out at three points at the Atlantic coast of northern Morocco. The results obtained by these two methods indicate a difference of less than 10 % and have shown that to ensure safe dimensioning of maritime structures, the application of the two statistical methods is necessary. This is explained by the drawbacks encountered in both methods. In the MA method, the inconvenience is linked to the choice of non-extreme events when no significant storm is recorded during one year, furthermore, the non-consideration of important events recorded in other year. In the second method (POT), the difficulty consists in the uncertainty of the calculations by the POT method due to the mistrust associated with the choice of the censoring threshold.

In a study of extreme waves by the Peak Over Threshold (POT) method, the determination of the threshold of data censoring is an essential step. A wrong choice of the threshold can lead to erroneous results of the wave height design and consequently a bad design of maritime structures such as breakwaters for deep sea ports. In this study, we analyzed the influence of the threshold variation on the results of the hundred-year return period waves, generally considered for the design of maritime structures. The sensitivity study allowed us to confirm that the exponential model is the best probability distribution to describe wave data in two points on the Moroccan Atlantic coast for the wave data period from 1958 to 2019. This study also confirmed that a wrong choice of the statistical distribution and a wrong choice of the threshold lead to significant errors in the estimation of design wave height.