Author(s): Sebastian Dan; Corrado Altomare; Tomohiro Suzuki; Tim Spiesschaert; Marc Willems; Toon Verwaest
Keywords: Very oblique waves; Overtopping reduction; WaveL ab; Vertical quay; Sloping dyke
Abstract: The overtopping discharge is one of the most important issues when the safety of a coast is considered. Usually the waves approach the structures at angles between 0°and 45°and for this directions there are well documented formulae to estimate the overtopping discharge (i. e. Eur Otop Manual, 2007). However, in some particular situations, such as inside of two Belgian harbors, the waves can approach the quay at a very oblique angle. This situation was not investigated comprehensively in the previous studies. The main objective of the present research is to study the overtopping reduction at very oblique wave angles, while additional objectives regard the influence of storm return walls and slopes for the overtopping discharge. To test the hypothesis that the overtopping largely decreases for very oblique waves a 3D physical experiment was designed in the wave tank of Flanders Hydraulics Research, Antwerp. The scale of the experiment was decided to be 1: 50 and the structure mimicking a harbor quay has 8 m length, 0. 2 m height and 1 m width, in model scale. On top of the structure a storm return wall (0. 02/0. 04 m) is placed at different positions with respect to the front edge of the quay. On the back of the structure 16 boxes were placed to collect the overtopping volumes. The water level is ranging between-0. 015 and+0. 020 m with respect to the quay level, while the waves have Hs=0. 03-0. 06 m and T p =1. 1-1. 7 s. The wave angle used for simulations is 80°with respect to the structure normal. The wave characteristics are measured using 17 wave gauges placed in arrays in such way to characterize the total wave height pattern at the toe of the structure. The mentioned analysis was performed using Wave Lab v3. 54 (Aalborg University). As the wave paddle has no active absorption system a generous amount of passive absorption mattresses was placed around the basin to minimize the wave reflection. After finalisation of 71 tests the results show a clear decrease in the measured overtopping volumes with respect to those calculated. Moreover there is high variability of the overtopping volumes along the structure. The experiment result in new overtopping reduction factors for very oblique waves at the vertical quays and advise for the height and position of the storm return wall.