A study of wave-driven flow characteristics across a reef under the effect of tidal current

Abstract

Recent field observations have improved our understanding of the role of tidal currents in modulating the wave dynamics over coral reefs. In this study, detailed flow measurements are conducted across an idealized reef profile in a wave-current flume. A typical plunging breaker propagating over both the flooding (shoreward) and the ebbing (seaward) tides are tested, respectively, and compared to the scenario without tidal current (wave only). Laboratory results are reported for the cross-shore distributions of wave height and mean water level as well as the vertical variation of cross-shore mean current below wave trough across a reef. Subsequently, to reproduce the laboratory measurements, the Reynolds-Averaged Navier-Stokes (RANS) equations with a stabilized k-ω SST turbulence model are solved to establish a numerical wave tank. The Volume of Fluid (VOF) method is used to track the free surface and an existing wave generation module is modified to consider the tidal current effect on waves. The numerical model is first validated by the experimental measurements based on the aforementioned three wave-current scenarios. Subsequently, the mean flow field around the reef surf zone and the cross-shore distribution of turbulent kinetic energy (TKE) and Reynolds shear stress along the reef profile are examined via numerical simulations.