Meteorologically generated long-period waves and their impact on the Dutch primary national flooding protection system

During storms, long-period water level oscillations can occur on the North Sea. The meteorological phenomena that cause these oscillations are known to a large extent and include atmospheric single pulse perturbations or oscillations of longer duration and larger spatial scale (De Jong in Origin and prediction of seiches in Rotterdam harbour basins, Delft University of Technology, ISBN 90-9017925-9, 2004). During such events, standing waves, or ‘seiches’, can occur in the ports along the Dutch North Sea coast. These seiches need to be considered in the height criteria for the dikes and other flood protection works around the port basins. Over the last decades, several projects on the climatology of seiching have been performed by Deltares under assignment by the Dutch Ministry of Public Works. Results of these projects served to update the height criteria for the storm surge barriers in the Port of Rotterdam, and as input to the design of two large new sea locks for other coastal ports, in IJmuiden and Terneuzen. This paper describes the three project locations: the statistical and hydrodynamical analyses of seiche events at these locations and the translation of the results into a buffer, or ‘seiche allowance’, to the height criteria.