Update of hydraulic boundary conditions for the Flemish coast

In 2020 HKV carried out the updating of the hydraulic boundary conditions (the HR) for the Flemish Coast, on behalf of the Belgian Hydraulic Laboratory (WL) and the Coastal Department (AK). The HR consisted of calculated water levels and waves that can occur during extreme storms. They are used in design projects, coastal safety assessments and studies into the failure behavior of structures.

The assessment of the Flemish coast (dunes, dikes and structures) has so far been carried out in a semi-probabilistic manner, using water levels and waves at one return time (of the design storm surge) to assess whether the coast is safe enough. One of the possible future-oriented ambitions is to gradually switch to a fully probabilistic method, with which the probability of failure of the flood defenses can be calculated. The first step is to make the HR suitable. HKV supported the WL and AK in this step by calculating probability distributions, correlations between parameters and statistical uncertainties.

In collaboration with Deltares, thousands of wave calculations are also carried out to determine which waves can be expected in shallow water at various combinations of water levels, wind and waves in deep water. In the project the strengths of the methods from Flanders, the Netherlands and the international literature were brought together to arrive at a state-of-the-art method for deriving HR.