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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. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the evolution of wave shape over a low-crested structure (LCS) using a 2-D RANS-VOF model. The model predictions of surface elevation and wave skewness and asymmetry are in good agreement with the recent measurements collected in a small scale wave channel at the University of Cantabria (UCA). The empirical formulae relating wave skewness and asymmetry to local Ursell number by Peng et al. (2009) have been extended to include the effect of wave reflection and the ramp in front of LCS and a wider range of Ursell number in the present study. In the presence of LCS, wave skewness decreases slightly above the seaward slope, then increases rapidly up to a maximum value above the structure crest, and decreases drastically above the leeward slope. Wave asymmetry decreases sharply above the seaward slope to a negative minimum value at the structure crest, and then increases rapidly to a positive value above the leeward slope. Our bispectral analysis indicates that sum interactions increase skewness and decrease asymmetry while difference interactions have opposite effects and that the former dominate above the seaward slope and on the structure crest but the latter dominate above the leeward slope of LCS. The observed wave shape evolution over a LCS can be attributed to the changes in the interplay of sum and difference interactions. We found that incident wave height and wave period, relative structure freeboard, structure crest width and structure porosity are the controlling factors for wave shape evolution over LCS. This study provides new insights on the role of wave skewness and asymmetry in the breakwaters stability and sediment transport around the structure and on the beaches behind it. [Copyright &y& Elsevier]

Sea level rise increases community risks from erosion, wave flooding, and tides. Current management typically protects existing development and infrastructure with coastal armoring. These practices ignore long-term impacts to public trust coastal recreation and natural ecosystems. This adaptation framework models physical responses to the public beach and private upland for each adaptation strategy over time, linking physical changes in widths to damages, economic costs, and benefits from beach recreation and nature using low-lying Imperial Beach, California, as a case study. Available coastal hazard models identified community vulnerabilities, and local risk communication engagement prioritized five adaptation approaches—armoring, nourishment, living shorelines, groins, and managed retreat. This framework innovates using replacement cost as a proxy for ecosystem services normally not valued and examines a managed retreat policy approach using a public buyout and rent-back option. Specific methods and economic values used in the analysis need more research and innovation, but the framework provides a scalable methodology to guide coastal adaptation planning everywhere. Case study results suggest that coastal armoring provides the least public benefits over time. Living shoreline approaches show greater public benefits, while managed retreat, implemented sooner, provides the best long-term adaptation strategy to protect community identity and public trust resources. [ABSTRACT FROM AUTHOR]

Beach nourishment, a common practice to replenish an eroded beach face with filling sand, has become increasingly popular as an environmentally friendly soft engineering measure to tackle coastal erosion. In this study, three 200 m long offshore submerged sandbars were placed about 200 m from the shore in August 2017 for both coastal protection and beach nourishment at Shanhai Pass, Bohai Sea, northeastern China. A series of 21 beach profiles were collected from August 2017 to July 2018 to monitor the morphological changes of the nourished beach. Field observations of wave and tide levels were conducted for one year and tidal current for 25 h, respectively. To investigate the spatial-temporal responses of hydrodynamics, sediment transport, and morphology to the presence of three artificial submerged sandbars, a two-dimensional depth-averaged (2DH) multi-fraction sediment transport and morphological model were coupled with wave and current model and implemented over a spatially varying nested grid. The model results compare well with the field observations of hydrodynamics and morphological changes. The tidal range was around 1.0 m and the waves predominately came from the south-south-east (SSE) direction in the study area. The observed and predicted beach profiles indicate that the sandbars moved onshore and the morphology experienced drastic changes immediately after the introduction of sandbars and reached an equilibrium state in about one year. The morphological change was mainly driven by waves. Under the influences of the prevailing waves and the longshore drift toward the northeast, the coastline on the leeside of the sandbars advanced seaward by 35 m maximally while the rest adjacent coastline retreated severely by 44 m maximally within August 2017–July 2018. The model results demonstrate that the three sandbars have little effect on the tidal current but attenuate the incoming wave significantly. As a result, the medium-coarse sand of sandbars is transported onshore and the background silt is mainly transported offshore and partly in the longshore direction toward the northeast. The 2- and 5-year model simulation results further indicate that shoreline salient may form behind the sandbars and protrude offshore enough to reach the sandbars, similar to the tombolo behind the breakwater. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an integrated investigation of physical processes generating impulsive pressures under the action of plunging breakers impinging on gravel beaches. This work is an extension of a recent investigation which suggested that wave impacts from plunging breakers acting on gravel beaches may be a key mechanism to enhance sediment mobilisation. In particular, comparisons of full scale laboratory measurements against model results from a well-validated phase/depth-resolving numerical model based on the Reynolds–Averaged Navier–Stokes (RANS) equations are presented. This represents the first attempt at comparison with such a tool against observed hydrodynamics on steep (slope~1/8) gravel beaches at prototype scale. In order to understand how impulsive pressures are generated under plunging waves, the numerical model is used to carry out a detailed investigation to examine the role of each of the acceleration terms in the momentum balance. Consistent with prior studies, numerical results show that under plunging breakers the local acceleration (∂u/∂t) alone cannot be used as a proxy for pressure gradients. However, the contribution of the third term (w∂u/∂z) of total acceleration is recognized for the first time and indicates that this term has an important role in both the induced pressure gradient and sediment mobilisation as induced by this particular type of breaking. Furthermore, results suggest that a parameterisation of the pressure gradient in terms of ∂u/∂t+u∂u/∂x, may not suffice when dealing with plunging breakers and hence there is a lack of a suitable parameterisation of this process in the present literature. Thus, for different types of breaking it may be necessary to consider a different characterisation of the pressure gradient toward the parameterisation of sediment transport inside the surf zone. [Copyright &y& Elsevier]

Fast and accurate estimation of wave runup is needed for coral-reef islands, but most of the existing formulae are not applicable in this context. Tree-based models were applied to the comprehensive numerical database of Pearson et al. (J. Geophys. Res. Oceans. 122, 10099–10117) to identify the essential predictor parameters for runup in coral-reef environments and classify different runup regimes on which a set of runup formulae was developed. It was found that, wave conditions, reef roughness, and reef-flat length are generally crucial for predicting runup, while the importance of forereef and beach slopes depends on the relative reef submergence (reef submergence normalized by off-reef wave height). The forereef slope is more important than the beach slope when waves mainly break over the forereef at low relative reef submergences but less important when waves mainly break over the reef flat and the beach at middle and high relative reef submergences. The proposed formula set was validated against data from laboratory and field coral reefs, which implies that the formula set has the potential for fast prediction of runup along coral-reef islands at broad scales for flooding assessment. • Four regimes of wave runup over reef-lined beaches are identified. • An explicit runup formula set corresponding to the four regimes is derived. • The formula set is validated against data of laboratory and field coral reefs. • Beach slope is more important than forereef slope at high water levels. [ABSTRACT FROM AUTHOR]