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Infragravity (IG) waves are important drivers of extreme run‐up, morphological changes, and seiches. While locally forced IG waves have been extensively investigated, recent studies have revealed the significance of free IG waves generated on distant beaches. This study focuses on free IG waves generated at a coast facing southeast in Japan during the passage of a typhoon. The relationship between incident short waves and free IG waves as well as their contributions to nearshore IG waves, in particular to seiches in a small port, are analyzed using unique measurement data and numerical experiments. During the typhoon passage, more than 75% of the observed IG wave energy originates from free IG waves at an observatory located at a depth of 23 m, and their peak direction is alongshore. Six‐year measurement data demonstrate that peak directions of free IG waves strongly depend on the incident wave angles of short waves and that swells from the south generate alongshore propagating free IG waves. A numerical model can reproduce the alongshore propagating free IG waves accurately when using a large computational domain. Moreover, numerical experiments performed using the model demonstrate that the alongshore propagating free IG waves are IG waves reflected from distant beaches. The free IG waves from distant beaches are small outside the port, but seiches in the port are amplified by more than 10%. The relationship between seiches and incoming free IG waves is further discussed based on the numerical experiments. Infragravity (IG) waves are ocean waves with long wavelengths which are generated by short waves. They play an important role in coastal hazards during storm conditions. Previous studies have focused on IG waves which are generated close to shore in the wave shoaling and breaking process. However, the importance of IG waves, which are generated at distant beaches and propagate freely across the sea, is not yet well understood. This study analyzes unique observation data recorded at a coast facing southeast in Japan during the passage of a typhoon and investigates the characteristics of these free IG waves using a numerical model covering a large computational domain. The observation data suggest that the directions of free IG waves strongly depend on the wave angles of incident short waves and that short waves from the south generate free IG waves propagating in the alongshore direction at the coast. The numerical experiments demonstrate that the alongshore propagating free IG waves originate from distant beaches and that they amplify the water level changes in a small port by more than 10%. This suggests that accurate risk assessment in ports during storms requires the consideration of free IG waves originating from distant beaches. Alongshore propagating free infragravity waves were observed during the passage of Typhoon LionrockThe alongshore propagating free infragravity waves originated from distant beaches more than 10 km awayThe alongshore propagating free infragravity waves amplified seiches in a small port by more than 10% Alongshore propagating free infragravity waves were observed during the passage of Typhoon Lionrock The alongshore propagating free infragravity waves originated from distant beaches more than 10 km away The alongshore propagating free infragravity waves amplified seiches in a small port by more than 10%

This review focuses on recent advances in process-based numerical models of the impact of extreme storms on sandy coasts. Driven by larger-scale models of meteorology and hydrodynamics, these models simulate morphodynamics across the Sallenger storm-impact scale, including swash,collision, overwash, and inundation. Models are becoming both wider (as more processes are added) and deeper (as detailed physics replaces earlier parameterizations). Algorithms for wave-induced flows and sediment transport under shoaling waves are among the recent developments. Community and open-source models have become the norm. Observations of initial conditions (topography, land cover, and sediment characteristics) have become more detailed, and improvements in tropical cyclone and wave models provide forcing (winds, waves, surge, and upland flow) that is better resolved and more accurate, yielding commensurate improvements in model skill. We foresee that future storm-impact models will increasingly resolve individual waves, apply data assimilation, and be used in ensemble modeling modes to predict uncertainties.

Process‐based morphodynamic models can be useful in understanding coastal dune responses to disturbances, as well as possible evolutionary patterns. To this aim, we employ Duna, a simplified 1D morphodynamic model, to assess the influence of dune morphology (height and slope) on sand transfer and deposition across the dune profile for different beach widths and wind incidence angles through idealized experiments. Simulations of real conditions show good model performance, both in wind flow reproduction and in topographic change along the dune profiles tested. The idealized experiments show that wind speed increases and sand accumulation decreases logarithmically with dune height and linearly with stoss slope along the dune profile. Fetch and cosine transport limiting parameters are reflected in the sand accumulated windwards from the toe, while sand transfer to the dune appears controlled by multiple factors; the higher the dune and/or the narrower the beach, the likelier that maximum accumulation occurs under oblique winds. Results point to two different types of evolution for high dunes. Either the vegetation is dense enough to maintain the stoss position, in which case vertical growth near‐ceases and seaward progradation is promoted, or the stoss is eroded and landward retreat dominates, in which case sand transfer to the crest and lee continues as a mixture of low input from the beach and recycled sand from the stoss. Coastal dunes are sensitive ecosystems whose survival depends on their adaption to changing conditions. Thus, it is important to understand how dune characteristics (i.e., shape, vegetation type, and cover) and prevailing conditions (i.e., wind speed and direction, beach width) determine where and when sand is deposited onto the dune, promoting growth. This is the result of a complex balance between winds that bring sand to the dune from the adjacent beach (main sand provider), the dune topography (decelerating winds near the dune toe and accelerating them along the slope, up to the dune crest) and dune plants (slowing winds down in their vicinity and trapping wind‐blown sand). The main controls on these complex interactions have been incorporated into the Duna model for aeolian sand transport. After tuning parameters and verifying that simulated results are accurate, Duna is used to assess the impacts of dune shape (height and slope), beach width, vegetation coverage and wind angles to wind flow and topographic changes on the dune. Results show that both wind speed and sand accumulation vary logarithmically with dune height and linearly with slope. The simulated sand distribution along the dune is used as a basis to draw generalized dune growth patterns. Duna morphodynamic model is calibrated and validated against Computational Fluid Dynamics model results and field dataThe influence of dune shape (height and slope), wind incidence, vegetation density and beach width on dune growth is investigatedDune height and plant cover are the main factors controlling accumulation patterns, sand recycling and vertical growth Duna morphodynamic model is calibrated and validated against Computational Fluid Dynamics model results and field data The influence of dune shape (height and slope), wind incidence, vegetation density and beach width on dune growth is investigated Dune height and plant cover are the main factors controlling accumulation patterns, sand recycling and vertical growth

The presence of large bottom roughness, such as that formed by benthic organisms on coral reef flats, has important implications for the size, concentration, and transport of suspended sediment in coastal environments. A 3 week field study was conducted in approximately 1.5 m water depth on the reef flat at Ningaloo Reef, Western Australia, to quantify the cross‐reef hydrodynamics and suspended sediment dynamics over the large bottom roughness (∼20–40 cm) at the site. A logarithmic mean current profile consistently developed above the height of the roughness; however, the flow was substantially reduced below the height of the roughness (canopy region). Shear velocities inferred from the logarithmic profile and Reynolds stresses measured at the top of the roughness, which are traditionally used in predictive sediment transport formulations, were similar but much larger than that required to suspend the relatively coarse sediment present at the bed. Importantly, these stresses did not represent the stresses imparted on the sediment measured in suspension and are therefore not relevant to the description of suspended sediment transport in systems with large bottom roughness. Estimates of the bed shear stresses that accounted for the reduced near‐bed flow in the presence of large roughness vastly improved the relationship between the predicted and observed grain sizes that were in suspension. Thus, the impact of roughness, not only on the overlying flow but also on bed stresses, must be accounted for to accurately estimate suspended sediment transport in regions with large bottom roughness, a common feature of many shallow coastal ecosystems. Shear stresses imposed by roughness on the flow are much larger than those acting on bed sedimentSuspended sediment concentrations and fluxes are suppressed by the large reef roughnessAccounting for reduced shear stresses within the roughness improves sediment transport predictions

Complicated channel geometry and currents may aggravate the interactions between passing ships and berthed ships, which should be evaluated and taken into account in a port design. A method for predicting the ship-ship interactions, based on a non-hydrostatic shallow water flow model, is presented in this paper and is validated by comparing the numerical results with experimental data. The method is subsequently applied to predict the interaction forces acting on a berthed ship due to a passing ship in ports. The influences of the difference of the water depths between the dock and the main channel, the dock geometry, the current and another berthed ship in the dock on the ship-ship interactions are studied. Analysis based on the numerical results is carried out, which is useful for the port design.

Complicated channel geometry and currents may aggravate the interactions between passing ships and berthed ships, which should be evaluated and taken into account in a port design. A method for predicting the ship-ship interactions, based on a non-hydrostatic shallow water flow model, is presented in this paper and is validated by comparing the numerical results with experimental data. The method is subsequently applied to predict the interaction forces acting on a berthed ship due to a passing ship in ports. The influences of the difference of the water depths between the dock and the main channel, the dock geometry, the current and another berthed ship in the dock on the ship-ship interactions are studied. Analysis based on the numerical results is carried out, which is useful for the port design.

Understanding directional spectra of infragravity (IG) waves composed of free and bound components is required due to their impacts on various coastal processes (e.g., coastal inundation and morphological change). However, conventional reconstruction methods of directional spectra relying on linear wave theory are not applicable to IG waves in intermediate water depths (20–30 m) due to the presence of bound waves. Herein, a novel method is proposed to reconstruct directional spectra of IG waves in intermediate depth based on weakly nonlinear wave theory. This method corrects cross‐spectra among observed wave signals by taking account of the nonlinearity of bound waves in order to reconstruct directional spectra of free IG waves. Numerical experiments using synthetic data representing various directional distributions show that the proposed method reconstructs free IG wave directional spectra more accurately than the conventional method. The method is subsequently applied to observations of severe sea‐states at two field sites. At these sites, free IG waves are not isotropic and have clear peak directions. Numerical modeling of the wave fields shows that these peak directions correspond to the reflection of IG waves from the shore and/or coastal structures. Additionally, the validity of the underlying weakly nonlinear wave theory of the present method is assessed by a newly proposed method employing bispectral analysis. The bound wave response generally agrees with the theory at the field sites but deviates slightly for energetic sea states. The applicability of the present method on a sloping bottom is further discussed by an analytical solution. Infragravity (IG) waves, long waves whose wave period is much longer than sea and swells, are known to play important roles in coastal inundation and beach topographic change during high wave conditions. However, the magnitude of IG waves propagating to beaches is not well understood. This is because conventional methods to estimate directional distributions (wave energy propagating to each direction) of sea and swells are not applicable to IG waves that are composed of “free” and “bound” components. In this study, a novel method to estimate directional distributions of IG waves is proposed. The method estimates directional distributions of free IG waves by considering bound IG waves in observed wave data based on their theoretical solution. This method is tested in numerical experiments using synthetic wave data, and the results demonstrate its high applicability and superiority over the conventional method. Applying this method to field measurement data reveals that free IG waves are directionally focused owing to the reflection from the shore and coastal structures. These findings violate the assumption of uniform directional distributions of free IG waves implemented in recent numerical models. The new method will help future studies to elucidate the magnitude of IG waves propagating to beaches. A new method to reconstruct directional spectra of free infragravity waves based on weakly nonlinear wave theory is proposedThe method is verified to accurately reconstruct directional spectra of free infragravity waves from synthetic dataDirectional distributions of free infragravity waves vary diversely owing to wave reflection from nearby beaches and coastal structures A new method to reconstruct directional spectra of free infragravity waves based on weakly nonlinear wave theory is proposed The method is verified to accurately reconstruct directional spectra of free infragravity waves from synthetic data Directional distributions of free infragravity waves vary diversely owing to wave reflection from nearby beaches and coastal structures

Climate-change (CC)-driven sea-level rise (SLR) will result in coastline retreat due to landward movement of the coastal profile (that is, the Bruun effect). Coastline change adjacent to commonly found tidal inlets will be influenced not only by the Bruun effect, but also by SLR-driven basin infilling and CC-driven variations in rainfall/runoff. However, as a model that accounts for all of the above-mentioned processes has been lacking so far, most coastal CC impact studies until now have considered only the Bruun effect. Here, we present a scale-aggregated model capable of providing rapid assessments of coastline change adjacent to small inlet-estuary/lagoon systems due to the combined effect of CC-driven SLR and variations in rainfall/runoff. Model applications to four representative systems show that the Bruun effect represents only 25–50% of total potential coastline change, and underline the significance of coastline change due to SLR-driven basin infilling and CC-driven variations in rainfall/runoff.