Local Scour Around the Offshore Perforated Cubic Artificial Reef Under Combined Wave and Current Conditions

Abstract Artificial reefs (ARs), which are artificial underwater structures that function similarly to natural reefs, play a vital role in restoring fishery resources and marine ecosystems. However, local scour around ARs poses risks of burial or overturning, considerably impairing their functionality. In nearshore shallow water environments, it is indispensable to consider the combined effects of waves and currents. This study examines local scour around a perforated cubic artificial reef (AR) under combined wave-current conditions using tank experiments. In the experiments, a comprehensive investigation is conducted on various water depths, wave heights, wave periods, and current velocities aligned with the wave direction. The scale ratio is set to 1:13.3, while the Keulegan-Carpenter numbers (KC) vary within the range of 0.627 to 3.000 and the relative current strength parameter Ucw ranges from 0.471 to 0.683. The experimental results demonstrate that the influence of waves on scour diminishes with increasing water depth. The position of the maximum scour hole depth remains largely unaffected by variations in KC and Ucw, consistently appearing at the upstream corner of the artificial reef (AR). Nevertheless, arc-shaped sand ripples and fan-shaped scour area were identified at the upstream of the AR within specific ranges of Ucw and H/L (the non-dimensional ratio of water depth to AR side length). Furthermore, the relationships between maximum scour hole depth, scour hole volume, and various parameters, including water depth, wave height, wave period, KC, and Ucw, were also explored.