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.
Highlights
Severe wave overtopping at vertical caisson breakwaters and sea walls may cause a threat to people, accessibility, infrastructure and equipment at the crest and landside of the breakwater
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
To provide further insight into the spreading in the results using the proposed method, the value of γβ that would lead to a perfect match between the measured and the calculated discharge is calculated for each test. This means that all potential inaccuracies of the applied overtopping formula (Eq (11)), the applied method to account for a recurved parapet, and the applied method to account for oblique waves (Eq (10)), all affect the obtained values of γβ
Summary
Severe wave overtopping at vertical caisson breakwaters and sea walls may cause a threat to people, accessibility, infrastructure and equipment at the crest and landside of the breakwater. The crest level of vertical caisson breakwaters and seawalls is often based on estimates of the wave overtopping during storms. Wave overtopping is affected by the water levels, the wave loading, and the geometry of the structure. In order to assess the required crest level for vertical breakwaters and seawalls under oblique wave attack, information is required on the reduction of wave overtopping due to the angle between the waves and the structure. For vertical caisson breakwaters (examples are shown in Fig. 1) limited data are available to estimate the reducing effects of oblique waves. To reduce wave overtopping at vertical caisson breakwaters or at the crest wall at the top of a rubble mound breakwater, often use is made of a recurved parapet at the top of the seaward side of the front wall.
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