Impact of bed level changes during an extreme storm on the wave characteristics at the Frisian dikes : SBW Waddenzee

Morphological changes are not taken into account in the evaluations of the HBC. However, the measured bed levels consist of inherent inaccuracies and are subject to changes. Three different time scales can be distinguished for changes in the bed levels: period of several years, period between measurement and storm event and the period during a single storm. At least the changes during the latter period should be included in the determination of the boundary conditions at the primary coastal structures. In 2007 a study was carried out by WL | Delft Hydraulics to investigate the effects of neglecting morphological changes during a yearly-averaged storm. One of the main conclusions of that study read that no significant impact of the short-term bed level changes during a yearly-averaged storm was found in the computed wave characteristics at the toe of the Frisian dikes. The present study complies with the recommendation to perform a similar investigation to the impact of bed level changes during an extreme 1:4000 years storm, since the HBC are based on such an extreme condition.