Abstract: Based on the incompressible Reynolds-Averaged Navier-Stokes (RANS) equations coupled with thek-ω SSTturbulence closure and the Volume of Fluid (VOF) method, a numerical model is established in this study to simulate wave-induced circulation in an idealized reef-lagoon-channel system under monochromatic wave conditions. The model is validated by comparing numerical results with measured flow velocity data from physical basin experiments reported in the literature. Subsequently, a systematic investigation is conducted to examine the effects of reef platform elevation, lagoon width and water depth, as well as channel width and water depth on wave transformation and horizontal wave-induced circulation. The results indicate that wave setup on the reef flat drives shoreward and alongshore currents, forming a two-dimensional horizontal circulation. Wave setup decreases with reductions in reef flat elevation and lagoon width, but shows little sensitivity to variations in channel width and lagoon water depth. Specifically, as reef flat elevation decreases, the shoreward current initially intensifies then weakens, whereas the alongshore current strengthens consistently. Increasing lagoon width or decreasing channel water depth enhances the alongshore current but weakens the shoreward current. An increase in channel width causes both the shoreward and alongshore currents to first increase and then decrease. Although minor variations in flow rates at individual control sections occur with changes in topographic parameters, the total flow rate within the system remains dynamically balanced. This study elucidates the regulatory mechanisms of key morphological parameters on wave-induced circulation in coral reef-lagoon-channel systems, providing scientific insights for ecological conservation and coastal engineering in coral reef environments.

Key words: Monochromatic waves, wave-induced current, Navier-Stokes equations, Coral reefs