Search Results (65)

Wave deformation and sediment transport nearest the shoreside are among the main reasons for sand erosion and beach profile changes. In particular, identifying the areas of incident-wave breaking and longshore current generation parallel to the shoreline is important for understanding the morphological changes of coastal beaches. In this study, a two-phase incompressible flow model along with a sandy sloping topography was employed to investigate the wave deformation and longshore current generation areas in a circular wave basin model. The finite volume method (FVM) was implemented to discretize the governing equations in cylindrical coordinates, the volume-of-fluid method (VOF) was adopted to differentiate the air–water interfaces in the control cells, and the zonal embedded grid technique was employed for grid generation in the cylindrical computational domain. The water surface elevations and velocity profiles were measured in different wave conditions, and the measurements showed that the maximum water levels per wave were high and varied between cases, as well as between cross-sections in a single case. Additionally, the mean water levels were lower in the adjacent positions of the approximated wave-breaking zones. The wave-breaking positions varied between cross-sections in a single case, with the incident-wave height, mean water level, and wave-breaking position measurements indicating the influence of downstream flow variation in each cross-section on the sloping topography. The cross-shore velocity profiles became relatively stable over time, while the longshore velocity profiles predominantly moved in the alongshore direction, with smaller fluctuations, particularly during the same time period and in measurement positions near the wave-breaking zone. The computed velocity profiles also varied between cross-sections, and for the velocity profiles along the cross-shore and longshore directions nearest the wave-breaking areas where the downstream flow had minimal influence, it was presumed that there was longshore-current generation in the sloping topography nearest the shoreside. The computed results were compared with the experimental results and we observed similar characteristics for wave profiles in the same wave period case in both models. In the future, further investigations can be conducted using the presented circular wave basin model to investigate the oblique wave deformation and longshore current generation in different sloping and wave conditions. Full article

Typhoons can significantly alter ocean hydrodynamic processes through their powerful external forces, greatly affecting marine biogeochemistry and ocean productivity. However, the specific impacts of typhoons with different tracks on coastal dynamics, including frontal activities and phytoplankton lateral transport, are not well understood. This study captured two distinct types of typhoons, namely Merbok (2017) and Nuri (2020), which landed from the right and left sides of the Pearl River Estuary (PRE), respectively, utilizing satellite remote sensing data to study their impacts on frontal dynamics and marine productivity. We found that after both typhoons, the southwest monsoon amplified geostrophic currents significantly (increased ~14% after Nuri (2020) and 48% after Merbok (2020)). These stronger currents transported warmer offshore seawater from the South China Sea to the PRE and intensified the frontal activities in nearshore PRE (increased ~47% after Nuri (2020) and ~2.5 times after Merbok (2020)). The ocean fronts limited the transport of high-chlorophyll and eutrophic water from the PRE to the offshore waters due to the barrier effect of the front. This resulted in a sharp drop in chlorophyll concentrations in the offshore-adjacent waters of PER after Typhoon Nuri (2020) (~37%). By contrast, despite the intensified geostrophic current induced by the summer monsoon following Typhoon Merbok (2020), its stronger offshore force, driven by the intense offshore wind stress (characteristic of the left-side typhoon), caused the nearshore front to move offshore. The displacement of fronts lifted the restriction of the front barrier and led more high-chlorophyll (increased ~4 times) and eutrophic water to be transported offshore, thereby stimulating offshore algal blooms. Our findings elucidate the mechanisms by which different track typhoons influence chlorophyll distribution through changes in frontal dynamics, offering new perspectives on the coastal ecological impacts of typhoons and further studies for typhoon impact modeling or longshore management. Full article

Rip currents at featureless beaches (i.e., beaches lacking sandbars or channels) are often hydrodynamically controlled, exhibiting intermittent and unpredictable behaviors that pose significant risks to recreational beach users. This study assessed occurrences of rip currents under a range of idealized morphology configurations and hydrodynamic wave forcing parameters using a wave-resolving Boussinesq-type model. Numerical experiments revealed that rip currents with durations on the time scale of 10 min are generated in the forms of vortex pairs, intensified eddies, mega-rips, and eddies shedding from longshore currents. In general, the key conditions that promote rip current formation at featureless beaches include shoreline curvature, headlands, moderately mild beach slopes (e.g., 0.02–0.03), normal or near-normal wave incidence, and large wave heights. Most importantly, this study highlights inherent uncertainties in rip current occurrences, particularly under conditions usually perceived as low risk: low wave heights, short wave periods, oblique wave incidence, and straight shorelines. These conditions can lead to transient rip currents and pose an unexpected hazard that coastal communities should be aware of. Full article

This paper showcases the results of three-dimensional numerical modeling of coastal zone hydrodynamics, based on a recently developed three-dimensional analytical model incorporating a three-dimensional formulation of radiation stress. The study examines the influence of cross-shore and alongshore bathymetric variability on hydrodynamic model results, focusing on internal volumetric current transport, bottom friction, free surface elevation, and velocity distributions. Using coastal zone cases with increasing complexity and wave datasets, we analyze differences between 2D and 3D model solutions, as well as theoretical calculations based on analytical solutions. Results indicate that in idealized, homogeneous bathymetric conditions, 2D and 3D models yield similar outputs. However, increased bathymetric complexity introduces significant variations, particularly in velocity fields and transport dynamics. Alongshore variability further modifies these distributions, emphasizing the role of lateral gradients often neglected in simplified models. The study demonstrates that neglecting alongshore bathymetric heterogeneity can lead to underestimation of key hydrodynamic variables, affecting model accuracy in coastal applications. Two-dimensional current transport fields reveal circulation patterns and possible rip current formations, suggesting that the proposed model framework provides improved insights into real-world coastal hydrodynamics. These findings highlight the necessity of incorporating three-dimensional bathymetric variability in predictive models to enhance accuracy in coastal engineering and environmental management applications. Full article

Lateral cavities along coastlines strongly influence sedimentary morphology and ecological processes by modifying local flow dynamics. This study employed high-resolution large-eddy simulation to investigate flow structures and momentum exchange mechanisms in a semi-circular lateral cavity driven by longshore currents. Model validation against experimental data confirmed the LES’s capability to capture both recirculating flow and turbulent structures accurately. The impact of Reynolds number was examined across three cases ($Re$ = 12,000, 17,000, and 22,000). From $Re$ = 12,000 to 17,000, a significant upstream shift of the primary vortex core occurred, accompanied by stronger shear layer turbulence and intensified secondary vortices. Between $Re$ = 17,000 and 22,000, the flow features stabilized, indicating a transition toward quasi-equilibrium. These changes enhanced vertical momentum transfer and turbulence production within the cavity. Spectral analysis revealed dominant KH frequencies governing periodic momentum exchange and indicating a transition from viscosity-damped upstream turbulence to fully developed shedding downstream. Full article

Sediment transport and shoreline changes causing shoreline morphodynamic evolution are key indicators of a coastal structure’s operational continuity. To reduce the computational costs associated with sediment transport modelling tools, a novel procedure based on the combination of a support vector machine for image classification and a trained neural network to extrapolate the shore evolution is presented here. The current study focuses on the coastal area over the Amir-Abad port, using high-resolution satellite images. The real conditions of the study domain between 2004 and 2023 are analysed, with the aim of investigating changes in the shore area, shoreline position, and sediment appearance in the harbour basin. The measurements show that sediment accumulation increases by approximately 49,000 m²/y. A portion of the longshore sediment load is also trapped and deposited in the harbour basin, disrupting the normal operation of the port. Afterwards, satellite images were used to quantitatively analyse shoreline changes. A neural network is trained to predict the remaining time until the reservoir is filled (less than a decade), which is behind the west arm of the rubble-mound breakwaters. Harbour utility services will no longer be offered if actions are not taken to prevent sediment accumulation. Full article

Coastal upwelling that cools sea temperatures and nutrifies the euphotic layer is the focus of this research, motivated by how these processes benefit the marine ecosystem. Here, atmosphere–ocean reanalysis fields and satellite radiance data are employed to link South African coastal upwelling with nearshore winds and currents in the 2000–2021 period. Temporal behavior is quantified in three regimes—Benguela, transition, and Agulhas—to distinguish the influence of offshore transport, vertical pumping, and dynamic uplift. These three mechanisms of coastal upwelling are compared to reveal a leading role for cyclonic wind vorticity. Daily time series at west, south, and east coast sites exhibit pulsing of upwelling-favorable winds during summer. Over the western shelf, horizontal transport and vertical motion are in phase. The south and east shelf experience greater cyclonic wind vorticity in late winter, due to land breezes under the Mascarene high. Ekman transport and pumping are out of phase there, but dynamic uplift is sustained by cyclonic shear from the shelf-edge Agulhas current. Temporal analysis of longshore wind stress and cyclonic vorticity determined that vertical motion of ~5 m/day is pulsed at 4- to 11-day intervals due to passing marine high/coastal low-pressure cells. Height sections reveal that 15 m/s low-level wind jets diminish rapidly inshore due to topographic shearing by South Africa’s convex mountainous coastline. Mean maps of potential wind vorticity show a concentration around capes and at nighttime, due to land breezes. Air–land–sea coupling and frequent coastal lows leave a cyclonic footprint on the coast of South Africa that benefits marine productivity, especially during dry spells with a strengthened subtropical atmospheric ridge. This work has, for the first time, revealed that South Africa is uniquely endowed with three overlapping mechanisms that sustain upwelling along the entire coastline. Amongst those, cyclonic potential vorticity prevails due to the frequent passage of coastal lows that initiate downslope airflows. No other coastal upwelling zone exhibits such a persistent feature. Full article

Multiple submerged breakwaters (MSBWs) are commonly used coastal protection structures due to their specific advantages over the emerged ones. Rip currents, as the inevitable natural hazard in the gaps of these constructions, are investigated numerically in the present study. A fully nonlinear mild-slope equation (NMSE) model possessing both fully nonlinear and fully dispersive properties is validated and adopted in the simulations. With four monochromatic wave conditions of different wave heights, periods and incidences representing low-energy, typical, storm and oblique waves tested, the flow patterns and the low-frequency oscillations of the rip currents are studied. For the convenience of risk assessment, the rip risk level is divided into three degrees according to the maximum rip flow speed. The effects of the configurations of the MSBWs on the rip current system as well as the rip risk level are examined, considering different breakwater widths, heights, forms, gap widths and gap numbers. Simulation results suggest that the cross-shore configurations of MSBWs influence the rip risk level by inducing different wave energy dissipations but the longshore configurations of MSBWs by changing flow field patterns. Full article

This study analyses climate variability on the north coast of Peru to understand how the local weather is coupled with anomalous ocean conditions. Using high-resolution satellite reanalysis, statistical outcomes are generated via composite analysis and point-to-field regression. Daily time series data for 1979–2023 for Moche area (8S, 79W) river discharge, rainfall, wind, sea surface temperature (SST) and potential evaporation are evaluated for departures from the average. During dry weather in early summer, the southeast Pacific anticyclone expands, an equatorward longshore wind jet ~10 m/s accelerates off northern Peru, and the equatorial trough retreats to 10N. However, most late summers exhibit increased river discharge as local sea temperatures climb above 27 °C, accompanied by 0.5 m/s poleward currents and low salinity. The wet spell composite featured an atmospheric zonal overturning circulation comprised of lower easterly and upper westerly winds > 3 m/s that bring humid air from the Amazon. Convection is aided by diurnal heating and sea breezes that increase the likelihood of rainfall ~ 1 mm/h near sunset. Wet spells in March 2023 were analyzed for synoptic weather forcing and the advection of warm seawater from Ecuador. Although statistical correlations with Moche River discharge indicate a broad zone of equatorial Pacific ENSO forcing (Nino3 R~0.5), the long-range forecast skill is rather modest for February–March rainfall (R² < 0.2). Full article

This study involves an integrated and innovative approach employing high-frequency monitoring, which is rare in studies focusing on solid waste on beaches. Eight drone flights were performed over a tourist beach in the Colombian Caribbean to achieve two main objectives: (i) to quantify the changes in marine macro-litter (>2.5 cm) density, focusing on the differences between the period when the beach was closed due to the COVID-19 pandemic and the subsequent reopening period; and (ii) to map changes in the abundance of marine macro-litter on the coast, with an emphasis on single-use waste. The number of items of litter on the beach increased 9-fold between the closed and reopening periods, and the main items found were crisp/sweet packets (n = 304, 13% of the total waste), plastic cups (n = 248, 11%), and expanded polystyrene (food containers) (n = 227, 10%). The factors contributing to the presence and distribution of the marine macro-litter were tourists, the use of the beach, and offshore wind direction. The results revealed that Salgar Beach can be considered a marine macro-litter exporter since waste is incorporated into the longshore current and redistributed either to nearby beaches or the ocean. This study emphasizes the potential for using drone images in an integrated approach to monitoring the presence of marine macro-litter as well as the efficiency of programs for combatting litter at sea. Full article

This paper presents a computational model for coast wave motions with multiple wave breakings. In the Boussinesq model, the wave breaking judgment method is combined with the wave recovery judgment condition, which stops the wave breaking process when triggered. The energy dissipation of wave breaking is corrected, and the dissipation of wave energy is maintained at about 10% during the wave recovery stage, so that the dissipation caused by the residual turbulent motion of wave breaking and the increase in wave height caused by the shallowing of waves due to the water bottom slope are offset. By comparing the calculation results with the experimental results, it is proved that this model can be used to calculate multiple wave breakings. This model is applied to discuss the influence of wave incident angle and wave period on wave height and longshore current and gives the distribution characteristics of wave height and longshore current under multiple wave breakings. Full article

Wave-induced currents play a critical role in coastal dynamics, influencing sediment transport and shaping bottom topography. Traditionally, long- and cross-shore currents in coastal zones were analyzed independently, often with two-dimensional models for longshore currents and undertow being used. The introduction of quasi-three-dimensional models marked a significant advancement toward a more holistic understanding. Despite recent proposals for fully three-dimensional models, none have achieved widespread acceptance, primarily due to challenges in accurately capturing depth-dependent radiation stress. This paper presents an innovative analytical model advocating for comprehensive three-dimensional approaches in coastal hydrodynamics. The model, based on novel simplification rules, refines relationships governing turbulent stress tensors and provides valuable insights into wave-induced stresses. It offers analytical solutions for both homogeneous and general coastal zones, laying the foundation for future advancements in numerical modeling techniques. Full article

Numerical modeling of wave transformation, hydrodynamics, and morphodynamics in coastal regions holds paramount significance for combating coastal erosion by evaluating and optimizing various coastal protection structures. This study aims to present an integration of numerical models to accurately simulate the coastal processes with the presence of coastal and harbor structures. Specifically, integrated modeling employs an advanced mild slope model as the main driver, which is capable of describing all the wave transformation phenomena, including wave reflection. This model provides radiation stresses as inputs to a hydrodynamic model based on Reynolds-averaged Navier–Stokes equations to simulate nearshore currents. Ultimately, these models feed an additional model that can simulate longshore sediment transport and bed level changes. The models are validated against experimental measurements, including energy dissipation due to bottom friction and wave breaking; combined refraction, diffraction, and breaking over a submerged shoal; wave transformation and wave-generated currents over submerged breakwaters; and wave, currents, and sediment transport fields over a varying bathymetry. The models exhibit satisfactory performance in simulating all considered cases, establishing them as efficient and reliable integrated tools for engineering applications in real coastal areas. Moreover, leveraging the validated models, a numerical investigation is undertaken to assess the effects of wave reflection on a seawall on coastal processes for two ideal beach configurations—one with a steeper slope of 1:10 and another with a milder slope of 1:50. The numerical investigation reveals that the presence of reflected waves, particularly in milder bed slopes, significantly influences sediment transport, emphasizing the importance of employing a wave model that takes into account wave reflection as the primary driver for integrated modeling of coastal processes. Full article

Rip currents are fast offshore currents generated during the breaking process of waves propagating nearshore, posing a potential life safety threat to coastal bathers. This study utilizes a Boussinesq phase-resolving model to investigate the formation mechanism of rip currents at Dadonghai Beach, based on its actual topography, and explores the characteristics of rip current formation under various wave conditions, with an emphasis on analyzing vortices, the mean water level and the spatial distribution of average velocity. The results indicate that rip current formation is significantly influenced by wave height and period. The increase in wave height and period results in more intense rip currents and higher water level fluctuations on arc-shaped beaches and on both sides of the bay, leading to complex vortex distributions. An increase in the angle of wave incidence hinders rip current formation in arc-shaped beach areas but is favorable to the generation of deflection rips on both sides of the bay. Furthermore, an increase in bottom friction inhibits rip current formation. When the water depth decreases in the channels, rip currents transition into longshore currents. The findings of this research offer valuable scientific insights into the formation mechanisms of rip currents and contribute to their prediction and prevention. 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