Nearshore Wave Model Research Articles

A machine learning approach to nearshore wave modeling in large lakes using land-based wind observations

This study presents a novel machine learning-based (ML) framework that utilizes the ConvLSTM-1D model to simulate wave heights at a nearshore location in Lake Michigan using a nonuniform land-based array of wind observations from a broad geographic region as an input. This approach was applied to Lake Michigan to perform a 70-year ice-free hindcast of waves near Chicago, IL (USA). Because of annual winter gaps in Great Lakes buoy observations, output from the Wave Information System model (WIS) was used for the training, validation, and testing of the ML model. Models with different numbers of wind stations were tested, showing that a single wind station as an input feature produced a reasonably accurate wave height. However, the wave height model accuracy increased as more wind input data was included from around the lake, largely plateauing beyond the inclusion of four stations that spanned Lake Michigan’s southern basin. The optimized model lookback period was found to be 10 h for all models, suggestive of a fetch-limited temporal coupling between the wind observations and nearshore waves. The extended time series showed a statistically significant increase in the interannual standard deviation of the storm wave height and the storm height over the mean wave height while no correlation was found with the annual water level time series. The ML framework offers a promising avenue for utilizing historical wind records to extend wave height time series for nearshore locations, particularly in enclosed and semi-enclosed basins where waves are strongly linked to local winds.

An assessment of the impact of boundary conditions in dynamical downscaling techniques for fetch-limited waves

ABSTRACT The handling of boundary conditions (BCs) is a key issue for the development of dynamical downscaling techniques in which nearshore wave models require the definition of the sea conditions at the offshore boundaries. This study addresses the implications of using simplified BCs represented by bulk or partitioned wave parameters with respect to using the complete information from directional wave spectra. As a large-scale model, we used WAVEWATCH III (WW3) running over the Mediterranean Sea providing the wave BCs for the small-scale SWAN model. One year of measured directional wave spectra from three deepwater buoys allowed the assessment of the WW3 model accuracy. The nested SWAN model simulations propagated the wave field over three nearshore areas. The accuracy of SWAN simulations was assessed through the comparison of computed results with wave measurements from nearshore buoys. Being the wave conditions dominated by unimodal seas, modest differences of error metrics are found between the datasets forced by different types of BCs. Conversely, focusing the attention on multimodal seas, an accurate definition of wave BCs achieved by the use of the directional wave spectra or, in alternative, by the reconstruction of wave spectra from partitioned wave parameters becomes crucial for nearshore wave predictions.

Effects of Storm Waves Caused by Typhoon Bolaven (1215) on Korean Coast: A Comparative Analysis with Deepwater Design Waves

This paper employs the third-generation simulating waves nearshore (SWAN) ocean wave model to estimate and analyze storm waves induced by Typhoon Bolaven, focusing on its impact along the west coast and Jeju Island of Korea. Utilizing reanalyzed meteorological data from the Japan Meteorological Agency meso scale model (JMA-MSM), the study simulated storm waves from Typhoon Bolaven, which maintained its intensity up to high latitudes as it approached the Korean Peninsula in 2012. Validation of the SWAN model against observed wave data demonstrated a strong correlation, particularly in regions where wind speeds exceeded 20 m/s and wave heights surpassed 5 m. Results indicate significant storm wave heights across Jeju Island and Korea's west and southwest seas, with coastal grid points near islands recording storm wave heights exceeding 90% of the 50-year return period design wave heights. Notably, specific grid points near islands in the northern West Sea and southwest Jeju Island estimated storm wave heights at 90.22% and 91.48% of the design values, respectively. The paper highlights the increased uncertainty and vulnerability in coastal disaster predictions due to event-driven typhoons and emphasizes the need for enhanced accuracy and speed in typhoon wave predictions amid the escalating climate crisis.

Enhanced Typhoon-Induced Design Wave Height Estimation for Ocean Engineering Applications Using High Performance Computing

Coastal construction heavily depends on accurately estimating design wave parameters. This paper presents a technique for calculating ocean engineering design wave heights that addresses the challenges of inadequate wind speed and measured wave data in the field using High Performance Computing (HPC). The proposed method combines the Simulating WAves Nearshore (SWAN) wave model driven by wind with two different wind field models: the NCEP/NCAR reanalysis wind field and the Jelesnianski typhoon model wind field. By combining these models, the study reduces the underestimation of wind speed and inaccurate depiction of typhoon-related details. The method's effectiveness is demonstrated by applying it to calculate the design wave elements of the deep-sea breeding platform in Dongluo Island, Fujian. The study results show that the platform can experience a maximum wave height of 9.42 m during a 50-year recurrence period. The research shows that the platform's southwest corner is the most vulnerable location. This new calculation method is a significant improvement in ocean engineering design since it overcomes the limitations that come with the lack of wind speed and measured waves. By utilizing multiple wind field models, the calculated wave heights' accuracy and reliability is considerably enhanced. The application of this method to the breeding platform in Dongluo Island has yielded valuable insights for designing resilient structures in similar oceanic environments. This study demonstrates the important application of computational numerical simulations in the field of ocean engineering, providing high-precision predictive capabilities for structural design and risk assessment.

A general method to determine the optimal whitecapping dissipation coefficient in the SWAN model

Whitecapping dissipation is a critical term in affecting the accuracy of wave height modeling. However, the whitecapping dissipation coefficient (Cds), as a primary factor influencing whitecapping, is commonly determined through trial and error in various studies. In this study, we present a general method for calibrating the Simulating Waves Nearshore (SWAN) wave model using the whitecapping dissipation term, demonstrated through a detailed study in the South China Sea (SCS). Theoretical analysis reveals that the optimal Cds value shows a one-to-one correspondence with the applied wind field. Expectedly, under high-quality wind field conditions, the optimal Cds values tend to fall within a narrow range, regardless of the model domain or time span. Numerical experiments executed in the SCS further consolidated this inference, encompassing two common wind input schemes (ST6 and YAN) and three distinct whitecapping dissipation schemes (KOMEN, JANSSEN, and WST). Based on the experimental results, we have identified an optimal Cds range for each whitecapping dissipation scheme. Cds values within the optimal range consistently outperformed the default Cds in the SWAN model. Subsequent experiments verified the method’s applicability to the Gulf of Mexico and the Mediterranean Sea. The findings suggest that this research holds substantial promise for practical applications on a global scale.

Regional wave climate projections forced by EURO‐CORDEX winds for the Black Sea and Sea of Azov towards the end of the 21st century

AbstractWave phenomena impact high commercial value coastal and offshore activities, infrastructures and transportation. The knowledge of future wave conditions allows for consistent long‐term planning and decision‐making. The present study aims to provide robust, reliable projections of the potential future wave conditions of the Black Sea under the influence of climate change. For this purpose, an eight‐member dynamic wave climate ensemble that accurately represents the Black Sea's present wave climate has been produced, and future projections are assessed and analysed here. The wave climate ensemble was obtained by forcing the Simulating Waves Nearshore spectral wave model with eight regional wind fields from the EURO‐CORDEX. The future simulations of the regional wind fields are based on the RCP8.5 high‐emission scenario. The historical wave climate of the ensemble was evaluated against ERA5 reanalysis data. Projected changes in the mean wind and wave characteristics are examined by comparing historical and future simulations. In addition, the projected trends in the annual means during the future period of the wave simulations for significant wave height (Hs) and wave energy flux are also analysed. The projections for Hs and wind speeds are pronounced with significant decreases down to −10% across the basin, especially in the eastern region of the Black Sea. Changes in the Hs 99% percentiles of up to 16% are projected to occur. The projected changes in the annual mean of the wave energy flux are close to the projected changes in Hs means, while the seasonal changes (between −15% and 12%) are expected to be higher.

Coastal erosion and climate change: A review on coastal-change process and modeling.

Coastal erosion is a normal process of nature. However, the rate of coastal erosion, and the frequency and intensity of coastal flooding events, are now on the rise around the world due to the changing climate. Current responses to coastal erosion are primarily determined by site-specific factors, such as coastal elevation, coastal slope, coastal features, and historical coastline change rate, without a systematic understanding of the coastal-change processes in the context of climate change, including spatiotemporal changes in sea level, regional changes in wave climate, and sea ice coverage. In the absence of a clear understanding of the coastal-change processes, most of the current coastal responses have been built upon a risky assumption (i.e., the present-day coastal change will persist) and are not resilient to future climate change. Here, we conduct a literature review to summarize the latest scientific understanding of the coastal-change processes under climate change and the potential research gaps towards the prediction of future coastal erosion. Our review suggests that a coupled coastal simulation system with a nearshore wave model (e.g., SWAN, MIKE21, etc.) can play a critical role in both the short-term and long-term coastal risk assessment and protective measure development.

Advancements in nearshore wave modeling: A unified one-layer nonhydrostatic approach

This work presents a novel one-layer nonhydrostatic formulation and model for nearshore waves. The proposed governing equations define velocities and pressures at arbitrary distances from the still water and only contain spatial derivatives of maximum second order. The formulation can be unified into the existing nonhydrostatic models by defining the variables at the middle depth and neglecting certain additional terms. A Stokes-type Fourier analysis was performed to analyze the formulations' properties and determine the location of variables. The proposed formulation exhibited a clear superiority in describing both the linear and nonlinear properties of the coastal waves. The equations were numerically solved using a hybrid-finite, volume-finite difference scheme. The resulting model accurately described the wave-breaking and runup processes that occurred due to the adoption of a shock-capturing scheme and seabed elevation reconstruction. The suggested novel numerical model was validated against two theoretical benchmark tests and three wave transformation experiments.

Deriving spatial wave data from a network of buoys and ships

The real-time provision of high-quality estimates of the ocean wave parameters at appropriate spatial resolutions are essential for the sustainable operations of marine structures. Machine learning affords considerable opportunity for providing additional value from sensor networks, fusing metocean data collected by various platforms. Exploiting the ship-as-a-wave-buoy concept, this article proposes the integration of vessel-based observations into a wave-nowcasting framework. Surrogate models are trained using a high-fidelity physics-based nearshore wave model to learn the spatial correlations between grid points within a computational domain. The performance of these different models are evaluated in a case study to assess how well wave parameters estimated through the spectral analysis of ship motions can perform as inputs to the surrogate system, to replace or complement traditional wave buoy measurements. The benchmark study identifies the advantages and limitations inherent in the methodology incorporating ship-based wave estimates to improve the reliability and availability of regional sea state information.

Hybrid modelling to improve operational wave forecasts by combining process-based and machine learning models

Operational wave forecasting plays an important role in ensuring safe navigation and in the prediction of tidal windows for harbour approach channels. The underlying nearshore process-based wave models need to be accurate for a wide range of different conditions, from more common mild wave conditions to the occasional high energy (storm) conditions. In this work, an innovative hybrid modelling approach is proposed to improve the accuracy of operational wave forecasts. An operational wave model is combined with a machine learning model which is trained using wave measurements within the wave model domain. This hybrid modelling approach is applied to the Dutch North Sea, covering four major harbour approach channels.The final hybrid operational wave model results in a significant average error decrease compared to just the process-based model, amounting to 21.7% for the wave energy density and 25.3% for the wave direction. The error reduction for the spectral wave parameters is even larger, with a 33.3% smaller error in spectral wave height and a 38.8% smaller error in spectral wave period. As this approach is generically applicable to spectral wave models, it contains the potential for significant improvements in operational modelling.

Field observations and numerical modeling of swash motions at an engineered embayed beach under moderate to energetic conditions

Wave run-up is a key factor for the assessment of coastal flood risk during large swell events. The behavior of swash motions along embayed beaches is strongly influenced by particular features such as rocky headlands, irregular morphology, or tides, that have not received much attention in the past. In the present paper, swash motions along an engineered embayed beach were investigated under moderate to energetic wave conditions through field observations and numerical computations. Using pressure sensors and video-derived run-up data a Boussinesq-type nearshore wave model was found to capture the relevant wave transformation and swash zone processes reasonably well. The tidal water level variations were found to have a significant impact on the overall swash amplitudes and to condition the respective role of short- and long-wave components to the swash motions. In the studied configuration, the tidal level rise was shown to cause a transition from a very dissipative to a reflective or intermediate beach configuration depending on incident wave energy. Moreover, swash amplitudes were observed to vary significantly alongshore with differences of up to a factor of 2.2. Numerical results suggest that both the foreshore slope and the sub-tidal morphology play a key-role in the alongshore swash distribution.

Comparison of the predicted and the observed wave spectral parameters during the storms at Filyos coasts, The Southwestern Black Sea

In-situ wave measurement data are mainly used to validate the bulk wave parameters predicted by numerical models. Although the frequently used third-generation wave models are spectral models, determination of various spectral parameters and validation with the observed data are not common. This study covers the spectral analysis of selected storm records of a nearshore wave measurement campaign carried out at Filyos coasts with the complex bottom topography in Turkey, Southwestern Black Sea. The bulk wave and the spectral parameters are also calculated by a third-generation nearshore wave model, SWAN (Simulating Waves Nearshore), forced by the ERA5 offshore wave data, which is the newest re-analysis of the European Centre for Medium-Range Weather Forecasts (ECMWF) for the selected storms. Before using ERA5 offshore wave data, they are calibrated by the wave data of the satellite radar altimeter. In-situ measured bathymetry data are used in the SWAN model. Observed and predicted bulk wave and spectral parameters are compared, and the statistical error measures are calculated not only for the significant wave height, the peak period, and the peak wave direction but also for the three different spectral periods, three different frequency width parameters, a directional width and, a spectral peakedness parameter for the first time. Low values of statistical error measures show that the current wave predictions have a good agreement with the observed ones in terms of the significant wave height, Hs, and the peak period, Tp. However, the SWAN model predicts a slightly narrower frequency and directional spectrum with higher peaks, although the error measures are low. Moreover, SWAN can not predict the wide range of spectral shape occurrences that the observed spectra have. The development of the various spectral parameters during the storms is also investigated for the first time. It is found that the frequency and directional spreading of the observed spectra become wider and unsharpened in the late stages of the storm compared to the early stages. However, the same tendency is not observed clearly in the predicted directional spreading.

Wave Climate and the Effect of Induced Currents over the Barrier Reef of the Cays of Alburquerque Island, Colombia

The Alburquerque Cay Islands belong to a group of western Caribbean atolls, with a barrier reef of coral that is more than 8 km in diameter. An understanding of the reef ocean dynamics and its direct relationship to the functioning of the ecosystem is important since the significant energies that are involved should play a fundamental role in the coral and fish distributions in the coral reef, which are fundamental for its sustainability. The microtidal regime and the predominance of the trade winds produces coastal circulation, which is induced by waves breaking against the barrier. The study of the water dynamics that are described in this paper was carried out by using a stationary model that is based on the shallow-water equations theory, with consideration to the radiation stress gradients in the waves, whose patterns were evaluated with the pseudo-data of a reanalysis of a virtual buoy in front of the atoll and were propagated in the domain of interest by using the simulating waves nearshore (SWAN) spectral model. The results demonstrate the bi-modal behavior of the currents of water jets, with the occurrence of extreme waves with velocities greater than 1 m/s along the barrier. For the mean wave regime, circulation occurred around the coral mounds. This circulation suggests that the reef, the orientation of which coincides with the direction of the predominant waves, was formed under these average conditions. The wave climate is primordial to the reef environment, and climate change may affect the coral health.

Coastal erosion risk assessment and applied mitigation measures at Ezbet Elborg village, Egyptian delta

Coastal areas globally suffer from serious erosion and sedimentation problems. The assessment of coastal erosion risk is fundamental for better coastal management. The main goal of the current study was to enhance coastal management by identifying the coastal erosion risk and suggest possible mitigation measures. The study was developed for the Egyptian Northern Coast. MIKE 21 was used to evaluate the erosion and test the proposed measures. First, a bathymetric survey of the study area was conducted. Then the tidal data, storm surge, and global sea rise data were collected. The offshore wave data, shoreline data were compiled. And then, the different nearshore wave modeling and wave propagation were modeled. The model was calibrated using measured data in 2014 and validated using measured data in 2016. Future shoreline changes for the years 2029, 2039, and 2049 were depicted. A suitable mitigation measure was used and tested for the same years. The groins with a specific size and arrangement were tested. The main goal of the study is to find a suitable solution to protect the coast and investigate its impact on the shoreline in the next 30 years. The proposed mitigation measure minimized the coastal erosion of the study area rigorously.

Numerical Simulation and Observational Data Analysis of Mesoscale Eddy Effects on Surface Waves in the South China Sea

Surface current velocities of mesoscale eddies have a unique annular structure, which can inevitably influence surface wave properties and energy distribution. Sensitivity experiments of ideal mesoscale eddies on waves were carried out by the Simulating WAves Nearshore (SWAN) wave model to investigate these influences. In addition, China–France Oceanography SATellite Surface Wave Investigation and Monitoring (CFOSAT-SWIM) observational data of a large warm-cored eddy in the South China Sea (SCS) during the period of October–November 2019 were used to validate the influence of mesoscale eddies on waves. The results illustrated that mesoscale eddies can alter wave properties (wave height, period, and steepness) by 20–30%. Moreover, wave direction could also be modified by 30°–40°. The current effect on waves (CEW) was more noticeable with strong currents and weak winds, and was governed by wave age and the ratio of wave group velocity to current velocity. Wave spectra clearly indicated that current-induced variability in wave energy distribution happens on a spatial scale of 5–90 km (i.e., the sub- and mesoscales). Through comparing the difference of wave energy on both sides of an eddy perpendicular to the wave propagation direction in an eddy, a simple way to trace the footprints of waves on eddies was devised.

Evaluation of Implicit and Explicit Wave Dissipation Models for Submerged and Emergent Aquatic Vegetation

Ascencio, J.A.; Jacobsen, N.G.; McFall, B.C.; Groeneweg, J.; Vuik, V., and Reniers, A.J.H.M., 2022. Evaluation of implicit and explicit wave dissipation models for submerged and emergent aquatic vegetation. Journal of Coastal Research, 38(4), 807–815. Coconut Creek (Florida), ISSN 0749-0208. To address the important research question of whether implicit (bottom friction) or explicit (stem drag) dissipation models are most appropriate for the prediction of wave attenuation due to aquatic vegetation, the Simulating Waves Nearshore (SWAN) spectral wave model has been extended with an explicit frequency-dependent dissipation model for submerged and emergent vegetation. The new explicit model is compared to existing explicit and implicit dissipation models in SWAN, and the distinguishing features of each of the dissipation models are quantified. The present work verifies the implementation of the new and existing dissipation models, outlines their distinguishing features, and compares model predictions against experimental data. The emphasis is on the transformation of the spectral wave periods Tm0,1 and Tm–1,0 over a canopy. Model evaluation based on academic and laboratory cases allows for recommendations regarding applicability of the three dissipation models, where the new method has the broadest applicability, since it bridges the gap in applicability between the other two dissipation models. The implementation of Jacobsen, McFall, and van der A (2019; A frequency distributed dissipation model for canopies; Coastal Engineering, 150, 135–146) is publicly available in SWAN version 41.31B.

Swell Conditions at Potential Sites for the Colombian Antarctic Research Station

The objective of this paper was to characterize swell conditions in the coastal zone of the South Shetland Islands, where our preliminary analyses evaluated potential locations for the Colombian scientific station. The Simulating Waves Nearshore (SWAN) spectral model was implemented for the Bransfield Strait. The boundary conditions were selected by a cluster analysis of the wave climate from global hindcasting obtained with the WAVEWATCH III model. Some comparisons between the model and wavemeter measurements were made. The results demonstrated that optimal sea state conditions for the scientific base are present in the South Bay, Livingston Island.

Wave shadow zones as a primary control of storm erosion and recovery on embayed beaches

Waves interact with headlands on embayed beaches through refraction, diffraction and attenuation and can create alongshore gradients in wave energy and beach response. This energy gradient shifts alongshore with changes in wave direction, especially during storms when waves may come from a direction different to average conditions. To better predict embayed beach storm responses, improved identification of exposed and headland shadowed zones is needed. Here we present a generalised geometric approach to quantify the alongshore distance shadowed by headlands, called the shadow edge (Ysh), differentiating exposed and headland shadowed zones. Our approach uses headland geometry collected from readily available imagery, combined with measured or modelled storm wave direction, reducing the reliance on complex nearshore wave models derived from relatively scarce bathymetric data. We use monthly topographic beach surveys (2015–2019) at nine embayed beaches in SE Australia to investigate the impacts of headland and embayment geometry relative to storm wave direction (i.e., exposure). Further, beach responses were compared to erosion and recovery rates across different embayment geometries with varying levels of geological control on beach morphodynamics. We found that storm frequency, headland shadowing and embayment geometry control the alongshore magnitude of beach erosion and recovery rates. Mean subaerial beach volume losses to six high-energy storms were on average 3.5 times higher in exposed zones (42.7 ± 40.7 m3/m) than headland shadowed zones (12.1 ± 23.6 m3/m). Our geometric approach provides a simple alternative to predict headland influence on beach morphodynamics. The approach can be applied at a regional scale and could be integrated into early warning systems to predict coastal erosion.

Optimization of SWAN Wave Model to Improve the Accuracy of Winter Storm Wave Prediction in the East Sea

In recent years, as human casualties and property damage caused by hazardous waves have increased in the East Sea, precise wave prediction skills have become necessary. In this study, the Simulating WAves Nearshore (SWAN) third-generation numerical wave model was calibrated and optimized to enhance the accuracy of winter storm wave prediction in the East Sea. We used Source Term 6 (ST6) and physical observations from a large-scale experiment conducted in Australia and compared its results to Komen’s formula, a default in SWAN. As input wind data, we used Korean Meteorological Agency's (KMA’s) operational meteorological model called Regional Data Assimilation and Prediction System (RDAPS), the European Centre for Medium Range Weather Forecasts’ newest 5th generation re-analysis data (ERA5), and Japanese Meteorological Agency's (JMA’s) meso-scale forecasting data. We analyzed the accuracy of each model’s results by comparing them to observation data. For quantitative analysis and assessment, the observed wave data for 6 locations from KMA and Korea Hydrographic and Oceanographic Agency (KHOA) were used, and statistical analysis was conducted to assess model accuracy. As a result, ST6 models had a smaller root mean square error and higher correlation coefficient than the default model in significant wave height prediction. However, for peak wave period simulation, the results were incoherent among each model and location. In simulations with different wind data, the simulation using ERA5 for input wind datashowed the most accurate results overall but underestimated the wave height in predicting high wave events compared to the simulation using RDAPS and JMA meso-scale model. In addition, it showed that the spatial resolution of wind plays a more significant role in predicting high wave events. Nevertheless, the numerical model optimized in this study highlighted some limitations in predicting high waves that rise rapidly in time caused by meteorological events. This suggests that further research is necessary to enhance the accuracy of wave prediction in various climate conditions, such as extreme weather.

Wave power assessment in Faroese waters using an oceanic to nearshore scale spectral wave model

It is expected that wave power will first become an economically competitive energy source in isolated electrical grids located in exposed regions. One such candidate is the Faroe Islands. The goal of this paper is to map the local wave power potential around the Faroe Islands using the spectral wave model MIKE 21 SW. A model is set up for the entire North Atlantic Ocean. The model is forced by 10 years of ERA5 re-analysis wind data and is validated against several directional offshore wave buoys along with nearshore acoustic Doppler current profile measurements. The results show that the wave climate is dominated by waves from south-to-west and to a lesser extent from northerly directions, while waves from other directions are more moderate and infrequent. The average wave energy flux at nearshore locations to the west and north is 45–55 kW/m, while significantly lower flux of 10–25 kW/m is found at eastern locations. The results show that the maximum significant wave heights are 12–14 m to the west, 9–13 m to the north and 8–9 m to the east. This energy assessment will provide the basis for an evaluation of wave energy absorption concepts suitable for deployment in the Faroese waters.