Search Results (21)

Beach cusp geometry arises from coupled hydrodynamic and morphodynamic feedback in the swash zone. This study used the numerical model XBeach in nonhydrostatic mode to examine cusp development on an idealized sandy beach forced by monochromatic, bichromatic, and band-limited irregular waves. Simulations systematically varied foreshore slope (tan β = 0.05–0.15), wave period (8–12 s), and wave height (0.4–0.8 m), while grouped and irregular cases isolated the effects of infragravity modulation and spectral bandwidth. Under monochromatic forcing, cusp spacing increased primarily with wave period and foreshore slope, whereas wave height played a secondary role. Cusp spacing scaled strongly with horizontal swash excursion, supporting self-organization. Grouped and band-limited forcing increased shoreline excursion but weakened the direct proportionality between cusp spacing and swash excursion, indicating the temporal organization of forcing modulated pattern evolution. Across monochromatic, bichromatic, and irregular cases, spectral diagnostics did not show dispersion-aligned energy consistent with edge-wave forcing. The results support the interpretation of beach cusps as predominantly swash-driven, self-organized features whose geometry is controlled by slope and incident-wave timescale and modulated by spectral structure. Full article

This study proposes an integrated framework combining aerial photography of unmanned aerial vehicle (UAV), AI-based waterline detection, and a rigorous quality control (QC) scheme for estimating wave periods in the swash zone. The proposed approach automatically extracts instantaneous waterlines from high-resolution UAV videos and converts them into wave series using timestack analysis. The DeepUNet model achieved a pixel-level recognition score of 75.0% for both F1-score and Dice, demonstrating reliable performance in detecting thin waterline features. The integration of spatial and temporal QC further improves the robustness of waterline tracking and reduces false detections. Wave periods derived from wave series across different cross-sections in the swash zone exhibit spatial consistent and qualitative consistency when contextually compared with offshore data buoy observations, while the quantitative differences reflect variation in nearshore wave dynamics. These results confirm the feasibility and effectiveness of the proposed framework for high-resolution nearshore wave monitoring. Full article

In this study, a swash-zone model, using Larson and Wamsley formula (LW07), was combined into the Telemac-2D model system to examine the performance of modeling swash-zone processes through comparisons with field observation data. The experimental site was the Haeundae Beach in South Korea where Typhoon Phanfone occurred in October 2014, and bathymetric surveys were performed before and after the typhoon. Hydrodynamic data were also measured to validate the modeled data. The performance of LW07 was tested by running the model in two modes, with and without LW07. First, the model was run to simulate the shoreline response to an imaginary coastal breakwater. The result showed a clear discrepancy between the two modes as the sediments were considerably cumulated behind the breakwater in the case with the swash-zone formula (LW07) in the wide range along the shoreline behind the breakwater, indicating that the sediments more actively and rapidly responded to the shadowing by the breakwater with LW07. The model was also run for a realistic case from August to October 2014, which included the typhoon’s period during 2–6 October. The results showed that the morphological changes at both ends of the beach in the swash zone were simulated with higher accuracy with LW07, supporting the effectiveness of LW07 in simulating the short-term morphological changes induced by the typhoon attack. In particular, the successful simulation of the sand accumulation at the end sides of the beach’s swash zone indicates that LW07 was effective in estimating not only the cross-shore transport but also longshore transport, which was likely due to the characteristics of LW07 that calculated sand transport in both directions. The enhanced modeling performance with LW07 was likely due to the adjustment of the sediment transport rate to the instantaneous changes in the local beach slope, which could successfully control the erosion/accretion process in the swash zone more realistically. Full article

This work presents a new model for surf and swash zone morphology evolution induced by nonlinear waves. Wave transformation in the surf and swash zones is computed by a nonlinear wave model based on the higher order Boussinesq equations for breaking and non-breaking waves. Regarding sediment transport, the model builds on previous research by the authors and incorporates the latest update of a well-founded sediment transport formula. The wave and morphology evolution model is validated against two sets of experiments on beach profile change and is afterwards used to test the performance of a widely-adopted erosion/accretion criterion. The innovation of this work is the validation of a new Boussinesq-type morphology model under both erosive and accretive conditions at the foreshore (accretion is rarely examined in similar studies), which the model reproduces very well without modification of the empirical coefficients of the sediment transport formula used; furthermore, the model confirms the empirical erosion/accretion criterion even for conditions beyond the ones it was developed for and without imposing any model constraints. The presented set of applications highlights model capabilities in simulating swash morphodynamics, as well as its suitability for coastal erosion mitigation and beach restoration design Full article

Coastal permeable groins have been used to protect beaches from erosion for centuries. However, the hydraulic functioning of permeable groins has not been fully understood and their design heavily depends on engineering experiences. In this study, numerical experiments were executed to investigate the effects of layout configurations of a permeable groin system on longshore currents. The non-hydrostatic SWASH (Simulating WAve till SHore) model was employed to carry out the numerical simulations. Two data sets obtained from physical laboratory experiments with different permeable groin layouts on different slopes are used to validate the accuracy of the model. Then, the longshore current reduction by the permeable groin system with varying configuration parameters (e.g., groin spacing, groin length) was numerically investigated under different environmental conditions (e.g., a slight or a moderate wave climate). From the calculation results of numerical experiments, it is indicated that permeable groins function efficiently to reduce the maximal longshore current velocity under the condition that the groin length ranges from 84% and 109% of the wave breaker zone width. The longshore current reduction rate monotonously decreases with the increase in groin spacing; permeable pile groin functions best to reduce longshore current with the minimal groin spacing-groin length ratio 1:1 among the range between 1:1 and 2:1. When the groin spacing–groin length ratios are 1:1 and 1.5:1, the longshore current reduction is not sensitive to the investigated wave conditions in this study. When the spatial ratio is 2:1, the permeable pile groin system functions worse under a moderate wave climate than under a slight wave climate, from the view of longshore current reduction. Full article

Beach width is an important factor for tourists’ comfort, and the backshore is a swash zone where sediment moves quickly. Artificial sandy beaches focus on beach width stability and evolution. This paper is based on an artificial beach project in Haikou Bay, where, in view of the existing conditions, a new type of beach profile that can protect beach berm and width without being eroded by large wave action. Numerical simulation based on XBeach model were conducted to predict the morphodynamical responses of the beach, including a diagnosis of the erosion spots under storm and normal wave events, respectively. Sediment fluxes along and across the shoreline under varied scenarios, dependent on profile width and backshore slope, were discussed. It was found that normal waves with lower heights and longer periods can induce stronger erosion than storm waves due to the landform of the inner-bay in Haikou Bay. Engineering and biological methods to reduce beach erosion during wave action were discussed. Biological methods such as green-plants-root-system can retain berm surface sediment without allowing it to be transported offshore by wave action. The design concept of this artificial beach project may inspire more beach design and protection projects in coastal zones. Full article

We present a fully coupled 2DV morphodynamic model, implemented in OpenFOAM^® that is capable of simulating swash-zone morphodynamics of sandy beaches. The hydrodynamics are described by the Reynolds-averaged Navier–Stokes (RANS) equations with a $k-\omega$ turbulence model and the Volume of Fluid (VoF) approach for discriminating between air and water. Sediment transport is described in terms of bedload and suspended load transport. We show that the default divergence scheme in OpenFOAM can become numerically unstable and lead to negative sediment concentrations, and propose a solution to avoid this problem. The model performance is assessed in terms of surface elevation, flow velocities, runup, suspended sediment concentrations, bed profile evolution and sediment transport volumes by comparing with measurements of field-scale (wave height of 0.6 m) solitary waves. The model shows reasonable agreement in terms of hydrodynamics and predicts the correct sediment transport volumes, although the deposition is predicted more onshore compared to the measurements. This is partially attributed to an overprediction of the runup. The model shows that the suspended sediment concentration displays a strong vertical dependence. These results show the potential of depth-resolving models in providing more insight into morphodynamic processes in the swash zone, particularly with respect to vertical structures in the flow and suspended sediment transport. Full article

Low tide terrace (LLT) beaches are characterised by a moderately steep beach face and a flat shallow terrace influencing the local hydro-morphodynamics during low tide. The upper beachface slope ($\beta$) and the terrace width ($L_t$) are the main morphological parameters that define the shape of LTT cross-shore beach profiles. This work aims at better understanding the behaviour of $\beta$ and $L_t$ and their link with the incoming wave forcing. For this purpose, our results are based on 3.5 years times series of daily beach profiles and wave conditions surveys at two different microtidal LTT beaches with similar sediments size but different wave climate, one at Nha Trang (Vietnam) and the other one at Grand Popo (Benin). While they look similar, two contrasting behaviour were linked to two sub-types of LTT regimes: the first one is surf regulated beaches (SRB) where the swash zone is highly regulated by the surf zone wave energy dissipation on the terrace, and the second is swash regulated beaches (SwRB) acting in more reflective regime where the terrace is not active and the energy dissipation is mainly produced in the swash zone, the terrace becomes a consequences of the high dynamics in the swash zone. Finally, extending the common view of an equilibrium beach profile as a power law of the cross-shore distance, the ability of a simple parametrized cubic function model with the Dean number as unique control parameters is proposed and discussed. This simple model can be used for the understanding of LLT environments but it can not be extended to the whole beach spectrum. Full article

As low-lying coastal areas can be impacted by flooding caused by dynamic components that are dependent on each other (wind, waves, water levels—tide, atmospheric surge, currents), the analysis of the return period of a single component is not representative of the return period of the total water level at the coast. It is important to assess a joint return period of all the components. Based on a semiparametric multivariate extreme value analysis, we determined the joint probabilities that significant wave heights (Hs), wind intensity at 10 m above the ground (U), and still water level (SWL) exceeded jointly imposed thresholds all along the Corsica Island coasts (Mediterranean Sea). We also considered the covariate peak direction (Dp), the peak period (Tp), and the wind direction (Du). Here, we focus on providing extreme scenarios to populate coastal hydrodynamic models, SWAN and SWASH-2DH, in order to compute the 100-year total water level (100y-TWL) all along the coasts. We show how the proposed multivariate extreme value analysis can help to more accurately define low-lying zones potentially exposed to coastal flooding, especially in Corsica where a unique value of 2 m was taken into account in previous studies. The computed 100y-TWL values are between 1 m along the eastern coasts and a maximum of 1.8 m on the western coast. The calculated values are also below the 2.4 m threshold recommended when considering the sea level rise (SLR). This highlights the added value of performing a full integration of extreme offshore conditions, together with their dependence on hydrodynamic simulations for screening out the coastal areas potentially exposed to flooding. Full article

Understanding swash zone dynamics is of crucial importance for coastal management as the swash motion, consisting of the uprush of the wave on the beach face and the subsequent downrush, is responsible for driving changes in the beach morphology through sediment exchanges between the sub-aerial and sub-aqueous beach. Improved understanding of the probabilistic characteristics of these motions has the potential to allow coastal engineers to develop improved sediment transport models which, in turn, can be further developed into coastal management tools. In this paper, novel descriptors of swash motions are obtained by combining field data and statistical modelling. Our results indicate that the probability distribution function (PDF) of shoreline height timeseries ($p\left(\zeta \right)$) and trough-to-peak swash heights ($p\left(\rho \right)$) measured at a high energy, sandy beach were both inherently multimodal. Based on the observed multimodality of these PDFs, Gaussian mixtures are shown to be the best method to statistically model them. Further, our results show that both offshore and surf zone dynamics are responsible for driving swash zone dynamics, which indicates unsaturated swash. The novel methods and results developed in this paper, both data collection and analysis, could aid coastal managers to develop improved swash zone models in the future. Full article

Accurate wave runup estimations are of great interest for coastal risk assessment and engineering design. Phase-resolving depth-integrated numerical models offer a promising alternative to commonly used empirical formulae at relatively low computational cost. Several operational models are currently freely available and have been extensively used in recent years for the computation of nearshore wave transformations and runup. However, recommendations for best practices on how to correctly utilize these models in computations of runup processes are still sparse. In this work, the Boussinesq-type model BOSZ is applied to calculate runup from irregular waves on intermediate and reflective beaches. The results are compared to an extensive laboratory data set of LiDAR measurements from wave transformation and shoreline elevation oscillations. The physical processes within the surf and swash zones such as the transfer from gravity to infragravity energy and dissipation are accurately accounted for. In addition, time series of the shoreline oscillations are well captured by the model. Comparisons of statistical values such as $R_{2\%}$ show relative errors of less than $6\%$. The sensitivity of the results to various model parameters is investigated to allow for recommendations of best practices for modeling runup with phase-resolving depth-integrated models. While the breaking index is not found to be a key parameter for the examined cases, the grid size and the threshold depth, at which the runup is computed, are found to have significant influence on the results. The use of a time series, which includes both amplitude and phase information, is required for an accurate modeling of swash processes, as shown by computations with different sets of random waves, displaying a high variability and decreasing the agreement between the experiment and the model results substantially. The infragravity swash $S_{IG}$ is found to be sensitive to the initial phase distribution, likely because it is related to the short wave envelope. Full article

In this study, a physics-based morphology model is developed and to test the feasibility of the morphology model proposed in this study as the platform for the optimal design of the beach nourishment project, the beach restoration process by the infra-gravity waves underlying the swells in a mild sea is numerically simulated. As a hydrodynamic module, the IHFOAM wave toolbox having its roots in the OpenFoam is used. Speaking of the morphology model, a transport equation for suspended load and the Exner type equation constitute the morphology model. In doing so, the probability theory first introduced by Einstein and the physical model test by Bagnold are used as the constituent sub-model of the morphology model. Numerical results show that among many flow features that are indispensable in forming sand bars over the flat bottom and swash zone, the partially skewed and asymmetric bottom shearing stresses, a shoreward Stokes drift near the free surface, boundary layer streaming near the seabed, and undertow toward the offshore were successfully simulated using the morphology model proposed in this study. It was also shown that plunging type breaker occurring at the final stage of the shoaling process, and its accompanying second breaker, sediment entrainment at the seabed, and the redistribution of suspended load by the down rush of preceding waves were successfully reproduced in the numerical simulation, and agreements with our experience in the field were very encouraging. In particular, the sand bar formation process over the flat bottom and backshore were successfully reproduced in the numerical simulation, which has been regarded as a challenging task. Full article

Artificial reefs are being implemented around the world for their multi-functions including coastal protection and environmental improvement. To better understand the hydrodynamic and morphodynamic roles of an artificial reef (AR) in beach protection, a series of experiments were conducted in a 50 m-long wave flume configured with a 1:10 sloping beach and a model AR (1.8 m long × 0.3 m high) with 0.2 m submergence depth. Five regular and five irregular wave conditions were generated on two types of beach profiles (with/without model AR) to study the cross-shore hydrodynamic and morphological evolution process. The influences of AR on the processes are concluded as follows: (1) AR significantly decreases the incident wave energy, and its dissipation effect differs for higher and lower harmonics under irregular wave climates; (2) AR changes the cross-shore patterns of hydrodynamic factors (significant wave height, wave skewness and asymmetry, and undertow), leading to the movement of shoaling and breaking zones; (3) the beach evolution is characterized by a sandbar and a scarp which respectively sit at a higher and lower location on the profile with AR than natural beach without AR; (4) the cross-shore morphological features indicate that AR can lead to beach state transformation toward reflective state; (5) the scarp retreat process can be described by a model where the scarp location depends linearly on the natural exponential of time with the fitting parameters determined by wave run-up reduced by AR. This study demonstrates cross-shore effects of AR as a beach protection structure that changes wave dynamics in surf and swash zone, reduces offshore sediment transport, and induces different morphological features. Full article

The evolution of wind waves in coastal zones leads to changes in the shape of the wave spectrum. Along the coast of Kerala, due to the presence of mudbanks during the southwest monsoon, we could observe downshifting of the peak frequency in the wave spectral data. The present study aims at proving the mechanism of frequency downshifting and possible influence of the downshifting process on mudbank formation. The results of SWASH (Simulating WAves till SHore) modeling and bispectral analysis shows that frequency downshifting occurs due to the difference nonlinear triad interactions of the main frequency peak of the wave spectrum with frequencies of the infragravity range independent of the viscosity of the medium. The increase in wave dissipation accelerates frequency downshifting additionally, decreasing the wave energy in the main peak frequency. It is shown that frequency downshifting can be one of the possible wave mechanisms of mudbank formation due to essentially different wave attenuation coefficients at the beginning and end of this process. For muddy cohesive sediments, it will lead to formation with an erosive profile at first and then an accumulative profile, i.e., mudbank formation. Full article

The southwestern coast of Spain is in a tidal zone (mesotidal) which causes the equilibrium profile to be developed in two different sections: the breakage section and the swash section. These two sections give rise to the typical bi-parabolic profile existing in tidal seas. The existence of areas with reefs/rocks which interrupt the normal development of the typical bi-parabolic profile causes different types of beach profiles. The objective of this article is designing an easy methodology for determining new formulations for the design parameters of the equilibrium profile of beaches with reefs in tidal seas. These formulations are applied on 16 profiles to quantify the error between the real profile data and the modelling results. A comparative analysis is extended to the formulations proposed by other authors, from which it is found that better results are obtained with the new formulations. Full article