With the recent development from grey infrastructures to green infrastructures, artificial reefs become more popular in coastal protection projects. To investigate the responses of beach profile evolution to the presence of an artificial reef, a non-hydrostatic model is established. Both hydrodynamic and morphodynamic evolution for the beach with and without an artificial reef are compared under regular wave conditions. In addition, the protected beach profile evolution by an artificial reef is discussed under irregular wave conditions. Three key parameters in non-hydrostatic simulation are considered for sensitivity analysis, including maximum wave steepness criterium (maxbrsteep), water depth factor (depthscale), and equilibrium sediment concentration factor (sedcal). The numerical results under regular wave conditions indicate that the artificial reef enhances wave attenuation by inducing wave breaking. In addition, the artificial reef reduces local flow velocity and offshore sediment transport by 51%, therefore decrease the total erosion by 53%. Over the artificial reef, wave skewness and asymmetry go through a drastic change. Under irregular wave conditions, short waves contribute to the wave energy mainly and reflection-induced standing wave effects decline considerably. It demonstrates that the artificial reef can protect the beach from regular and irregular waves by reducing erosion and offshore transport of suspended sediments. Moreover, in the wave breaking area, the increase of maximum wave steepness criterium may give arise to the wave height. The morphological evolution is more sensitive to water depth factor than equilibrium sediment concentration factor, because the former is a controlling factor for beach profile characteristics while the latter forms the sandbar varying irregularly in shape.

Submerged Reefs (SRs) are a kind of artificial fish habitat that can protect coasts and maintain ecological biodiversity. In this study, the flow field of the SR is simulated by solving a Reynolds-averaged Navier–Stokes equation closed with the Realizable k-ε model based on the finite volume method. The turbulent characteristics of SRs under different inflow velocities and submergences in the vicinity of the SR are analyzed. The wake vorticities are the primary turbulent pattern within and around the SR. The back wake and vorticity are chosen as critical indicators to quantitatively assess the hydrodynamic characteristics induced by the SR. The results show: (1) as the main flow passes through the SR, the upwelling is produced in front of the SR and a large-scale wake region is formed behind the SR which contains a clockwise vortex; (2) the length of the wake region formed behind the SR is positively and linearly correlated with both the inflow velocity and submergence; (3) the dipole-type vorticity patterns are induced within the compartment of the SR, where the area and average value of high vorticity have a positive correlation with the flow velocity and a negative correlation with the submergence, respectively.

Water depth substantially affects wave transformation over hybrid submerged breakwaters, yet the incremental effects of geotextile armoring and crest vegetation remain insufficiently understood. Experiments were conducted in the 50.0 m long, 0.8 m wide, and 1.2 m high wave flume at the Hydraulic and Harbor Engineering Laboratory of Tongji University. A hard submerged breakwater (HSB), a geotextile-armored submerged breakwater (GSB), and a vegetation-integrated ecological submerged breakwater (ESB) with identical core geometry were compared. Six irregular-wave conditions with H₀ = 0.06–0.16 m and T_p = 1.4–2.2 s were tested at h = 0.50 m, corresponding to an incident Ursell number range of U_ri = 2.97–27.26. Three still-water depths, h = 0.44, 0.50, and 0.56 m, were examined under H₀ = 0.12 m and T_p = 1.8 s, corresponding to a relative crest-submergence range of δ_c = $d_{\mathrm{c}}/\overline{H_{\mathrm{s},1}}$ = 0.33–1.38, where d_c is the still-water depth above the breakwater crest and $\overline{H_{\mathrm{s},1}}$ is the measured incident significant wave height at W1. Wave transformation, relative mean water-level adjustment, bulk wave coefficients, coefficient-based energy partition, wave spectra, and harmonic bicoherence were examined. With increasing U_ri, the energy partition shifts from transmission toward residual energy loss, while reflection remains secondary. Adding crest vegetation to the GSB reduces the transmitted energy fraction, T = K_t², where K_t is the wave-transmission coefficient defined as the ratio of transmitted to incident significant wave height, by an average of 5.2 percentage points over the tested U_ri range, whereas the tested partially exposed GSC armor alone produces no systematic attenuation improvement relative to the HSB. Increasing δ_c increases transmission while reducing reflection, residual energy loss, and relative mean water-level contrast. The incremental vegetation effect is non-monotonic and is greatest at d_c/l_v = 0.67, where d_c is the still-water depth above the breakwater crest and l_v is the upright vegetation blade length. Mean squared harmonic bicoherence, defined as the average squared bicoherence over the selected harmonic-coupling frequency-pair region, is consistently higher at the immediate lee-side gauge than at the seaward gauge, indicating enhanced coherent quadratic phase coupling among harmonic frequency components during wave transformation across the breakwater; this lee-side coupling generally weakens with increasing δ_c. Overall, relative crest submergence governs not only bulk attenuation but also the associated mean water-level and nonlinear phase-coupling responses, while crest vegetation provides a more consistent attenuation benefit than the tested GSC armor alone.