Influence of oblique wave attack on wave overtopping at caisson breakwaters with sea and swell conditions

Abstract

The amount of wave overtopping at coastal structures such as vertical caisson breakwaters is strongly dependent on the angle of wave attack. The reducing effects of oblique waves on wave overtopping compared to perpendicular wave attack has been studied by means of three-dimensional wave basin tests. In these physical model tests the caisson breakwater has been exposed to wave conditions with wave angles between perpendicular and very oblique waves (i.e. 0°–75° in steps of 15°). Short-crested and long-crested waves have been tested and analysed. Also, crossing bimodal conditions have been studied with directional wind waves approaching the breakwater under a different angle than the simultaneous unidirectional swell conditions. Vertical caisson breakwaters with and without a recurved parapet (also referred to as a bullnose or a recurved wave return wall) have been tested. The measurements showed the large influence of oblique waves on wave overtopping. Also, the influence of a recurved parapet can be large although the influence reduces for larger wave angles. Guidelines have been proposed to account for the influence of oblique waves on wave overtopping at vertical caisson breakwaters with and without a recurved parapet, as well as for crossing bimodal conditions with simultaneous sea and swell conditions from different directions.