Oblique Wave Transmission Over Low-Crested Structures

Wave transmission over low-crested structures have often been the subject for research, as the wave field behind these structures determines what will happen in this area. Detached low-crested structures are often parallel to the coastline and in most cases wave attack will be perpendicular to this coastline and therefore, perpendicular to the structure. This situation can be simulated by small scale physical modeling in a wave flume. Recent research, including all data of the above given references and new extensive data sets, has enlarged the insight on the topic. The results from 2D tests are: (1) prediction formulae for the wave transmission coefficient K; and (2) a description of change of spectral shape because of wave transmission. In some situations low-crested structures are not parallel to the coast. T-shaped groynes are an example, but also breakwaters for a harbor where under very extreme storm surge, the structure can be considered as low-crested. In these situations wave attack is very often not perpendicular to the alignment of the structure and in many situations even quite oblique wave attack and transmission occurs. But what will be the difference with perpendicular attack? More in detail: (1) are the prediction formulae for k still valid; (2) is the spectral change (more energy to high frequencies) similar to perpendicular wave attack; (3) is there any influence of short-crestedness of waves; and (4) are wave directions similar in front of the structure and after transmission? Only a three-dimensional investigation in a short-crested wave basin can give answers to these questions. Within the EU-project DELOS these tests have been performed and are the subject of the paper.