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The paper by Wang et al. (2024) targets an interesting topic in the context of particle methods, namely, volume conservation. This important feature is studied by focusing on the time variation of mean water level under three different scenarios corresponding to hydrostatics, standing wave and dam break, and through consideration of a few variants of the Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) fluid model. In this discussion, the discussers briefly discuss some issues that could have been further considered in the paper by Wang et al. (2024) to ensure rigorousness and comprehensiveness of the conducted comparative analysis. • Assessment of volume conservation in SPH must be from local, then to global domain. • Volume conservation is achieved only if the continuity equation in kernel domain is numerically resolved. • Analysis of volume conservation in SPH must include long-term and violent flow simulations. • Volume conservation studies in SPH should also be linked with energy conservation assessment. • Convergence analysis on SPH volume conservation should include error functions linked to both local and global domains. [ABSTRACT FROM AUTHOR]

This paper presents a physical model study of wave induced forces on a composite vertical breakwater, where the crown wave wall is retreated with respect to the front face of the caisson. Four different configurations (one flushed wall and three retreated wall configurations) have been tested under regular wave conditions, aiming at providing a first experimental insight on the increase/reduction of the wave loads acting on the structure. The analysis of the experimental results allows to describe the basic phenomena involved and to identify the physical/geometrical drivers, which are expected to play a role on the force increase/reduction factor. Thus, detailed processing of both forces/moments (synchronous analysis) and pressures (asynchronous analysis) on the whole structure, the wall and the caisson trunk, together with the analysis of reflection coefficients as a function of the wall position, are presented and discussed in the paper. The experimental evidences suggest that, at least for the four configurations tested, the global forces acting on the caisson vary significantly depending on the wall position, resulting in a reduction between 5% and 31% for high energy sea states. A similar behavior is found considering the global moments. Furthermore, the synchronous analysis of the forces highlighted that the physical/geometrical drivers, identified in the present study, can have both a concordant and antithetical action among them, then resulting in increasing or decreasing, respectively, forces acting on the structure, if compared with the flushed wall configuration. • New experiments on wave loads on a vertical breakwater with retreated crown wall. • Four wall configurations (one flushed and three retreated) tested under regular waves. • Basic physical phenomena involved and physical/geometrical drivers are investigated. • Physical/geometrical drivers can have concordant or antithetical action among them. • Global forces acting on the caisson vary significantly depending on the wall position. [ABSTRACT FROM AUTHOR]

National weather forecasting agencies routinely issue a range of hazard warnings. But to our knowledge, along sandy coastlines where storm waves and storm surge can result in widespread but location-specific beach erosion and beachfront flooding, no national-scale early warning service for these hazards is presently operational. This paper outlines the scientific basis and implementation of a new framework for large area coastal storm hazards forecasting, currently being tested along the southwest (Indian Ocean) and southeast (Pacific Ocean) coasts of Australia. The system provides 7-day rolling predictions of localized beach erosion and/or coastal flooding linked to forecasted extreme weather events. Coastal setting influences the nature and occurrence of these hazards, with sandy beaches along wave-dominated coasts more prone to erosion and at surge-dominated coasts to flooding. An existing nearshore water-level forecasting system and a new inshore wave modeling capability are used to forecast beach erosion and coastal flooding at every 100 m along the shore. At the regional scale O(100–1 000 km of coastline), a threshold-based decision tree model categorises the predicted extent, location, and severity of erosion and flooding. At a more local scale O(100–1 000 m), physics-based modeling using XBeach focuses on vulnerable or high-value locations, providing specific storm hazard indicators tailored to local needs. This two-tier approach is feasible for national implementation due to the reduced computational effort, limiting intensive modeling to pre-identified critical locations. Delft-FEWS manages the data and modeling workflow, ensuring scalability and compatibility with existing forecast infrastructure. Initial evaluations of the system are promising, with a detailed 2-year evaluation in progress. Future enhancements could include the use of satellite imagery for real-time beach width and dune topography assimilation and exploring alternative modeling approaches to further improve forecast accuracy. • A framework for coastal storm hazards early warning over very large areas is developed. • The severity of hazards is predicted every 100 m alongshore by parametric modeling. • Site-specific storm hazard indicators at vulnerable sites are predicted by XBeach. • 7-day rolling forecasts of storm hazards are communicated via a web portal. [ABSTRACT FROM AUTHOR]

In this paper, the hydrodynamic performance of a bottom-seated type oscillating water column (OWC) device is investigated by numerical and experimental methods. A coupled SPH (Smoothed Particle Hydrodynamics) - FDM (Finite Difference Method) is proposed to simulate the interaction between waves and the OWC device. The current SPH-FDM model improves grid encryption method, and expand the single-phase SPH-FDM to multiphase SPH-FDM. The results from SPH-FDM align closely with those from the published experimental measurements. Following the successful validations, SPH-FDM and experiment are employed for a series of simulations to investigate the performance of the OWC device. Compared to experimental method, SPH-FDM can obtain global flow field information and avoid the influence of free surface identification and capillarity on vortex determination. In addition, SPH-FDM can naturally captures free surfaces, so it supports further studies on the non-uniformity of water surface in the chamber of OWC which cannot be studied by PIV or pneumatic model. • An improved SPH - FDM is proposed to simulate the interaction between waves and an OWC device. • Simulations and experiments indicate that water levels near side walls of chamber differ from those in the middle of chamber. • Compared to experiments, SPH-FDM can get global information and avoid interference of free surface and capillarity. [ABSTRACT FROM AUTHOR]

This paper examines the impact of wave interactions in the inner-surf zone, including the swash, on shoreline excursion dynamics. Specifically, the study focuses on how the time lag between consecutive waves and the slope of the beachface affect shoreline dynamics. To investigate this, a laboratory experimental setup is developed to study the behaviour of two consecutive bore-type waves travelling over a fluid layer with constant depth, representing an idealized inner-surf zone, before impacting an inclined solid plane with slope β , representing the beachface. Bore waves are generated using two dam-break flow devices, with a controlled time lag Δ t between them. This simplified physical model allows for the assessment of semi-theoretical predictive models based on shallow water approximation, resulting in ballistic-type models for shoreline motion. By combining these approaches, the study characterizes different flow regimes in the (Δ t , β) parameter space. It is observed that varying Δ t at a fixed β distinguishes four interaction regimes, either wave–wave interaction in the inner-surf zone or wave-swash interaction in the swash, with possibilities of merging or collision depending on wave orientation. In particular, increasing Δ t leads to either bore–bore merging in the inner-surf, bore-runup merging in the swash, bore-backwash collision in the swash or bore–bore collision in the inner-surf. Bore–bore merging and bore-runup merging enhance runup, peaking when Δ t is such that merging occurs near the transition from the inner-surf to the swash. On the contrary, bore-backwash collision results in additional dissipation of the second bore's dynamics, leading to a reduced shoreline extension compared to that induced by the first bore. All processes within the swash, including the transition between bore-runup and bore-backwash regimes, as well as the enhancement and extra dissipation of the second bore's swash excursion, exhibit some level of dependence on β. Overall, the results from this physical model help characterize and explain local mechanisms triggered by wave interaction near the shoreline. Validating this model's relevance warrants specific attention through comparisons with field data. As an initial validation attempt, field data extracted from the literature are compared to the physical model, showing promising agreement. [Display omitted] • A laboratory experiment modelling the dynamics of two consecutive bores in the inner surf and swash. • Influence and role of bores interaction on the shoreline extension. • Full description of the flow regimes depending on both the beach face slope and the bore period. • Simple semi-theoretical models to characterize the bores interaction and the related shoreline motion. [ABSTRACT FROM AUTHOR]

Offshore artificial islands represent a novel way to develop and utilize marine space resources. Previous research has focused on predicting erosion and deposition distributions following the islands construction, utilizing laboratory experiments and numerical simulations. However, the absence of long-term continuous monitoring has hindered systematic studies on the geomorphological processes of these islands. A 20-years of underwater terrain monitoring scheme was conducted before and after construction of the Rudong Artificial Island in Jiangsu Province, China. The results were combined with on-site observations of tidal currents, suspended sediment concentrations, and surficial sediment to investigate the evolution of the water channel–sand ridge system and the development process of local scour around the artificial island. The results indicated that after the construction of the artificial island, its surrounding water channels showed an overall evolution trend of the north channel shifting towards the north, the middle channel widening and moving south, and the south channel extending westward and southward. Scour has been observed at the four corners of the artificial island, with the peak depths of 7.3 m, 5.6 m, 13.7 m, and 12.2 m at the southwest, northwest, northeast, and southeast corners respectively. The scour in the southwest and northwest corners reached an equilibrium within five years. However, in the southeast corner, continuous erosion of the shoal on the southeast side of the artificial island enhanced the local hydrodynamic force, leading to further scour development. The large-scale scour in the northeast corner was mainly caused by changes in the local flow field following the construction of water intake pipelines and their protection projects. These geomorphological changes are the joint results of the natural evolution of the radial sand ridges and local erosion and deposition from engineering construction. Currently, the sandbanks surrounding the island are still undergoing dynamic evolution following engineering construction, and local scour around the island has not yet reached equilibrium. • This paper focused on the geomorphological processes around an artificial island. • The island was built on a silty coast where tidal currents dominated its evolution. • Field terrain, hydrology, and sediment data spanning twenty years were collected. • The evolution of the radial sand ridges after the island construction was studied. • The development process and causes of local scour around the island were analyzed. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive investigation of the storm damage at a commercial port located in the Southwestern Black Sea Region that occurred on January 18–19, 2018. One week after the event, a field survey was conducted at the port focusing on significantly damaged mound breakwaters and protection structures that failed at several sections. A numerical wave modeling study is carried out to estimate the wave characteristics at deep sea, nearshore, and inside the port to assess the observed damage during the field survey. Widely used numerical models WAVEWATCH III, SWAN, and SWASH are utilized using nested computational domains and calibrated based on satellite measurements. As a result, the significant wave height of the storm is estimated as 7.8 m with a peak period of 12.4 s near the port area, approaching mainly from the northwest direction. The damage mechanisms of the mound structures are discussed based on the field observations and the wave modeling studies. The insufficient seaside armor unit sizes and the orientation of the breakwaters are found to be the main reasons for the damage. • Major damage, including failure of mound breakwaters at a port, is investigated. • The characteristics of the waves that caused the damage were estimated using calibrated models. • Damage mechanisms of the protection structures are discussed in detail. [ABSTRACT FROM AUTHOR]

Simply supported bridges along the United States Gulf Coast are highly vulnerable to extreme wave conditions and water elevations. A better understanding of the loading demands on the bridges under these extreme events will lead to improved designs and enhanced resiliency. Nonetheless, analyses through numerical models pose difficulties in terms of reliability and computational burden. On the other hand, experimental models for large-scale bridge superstructures are subject to limited space allocation and related scaling challenges. Hence, optimized Finite Element (FE) models that can simulate Wave-Superstructure Interaction (WSI) are a preferred viable solution to estimate loads experienced by these bridge superstructures. Nonetheless, the results of the FE simulations are highly dependent on the numerical parameters and configurations implemented in the model; thus, the implications of parameter selection must be assessed to help scholars and engineers develop reliable FE models. In this paper, an experimental scaled model was used to calibrate numerical models following the Coupled Eulerian-Lagrangian (CEL) technique in ABAQUS. This explicit approach solves the Navier-Stokes (NS) equations to simulate fluid flow, and the dynamics response of the structure depends on analysis parameters (mass scaling factor, damping hourglass control, displacement hourglass scaling factor, and bulk viscosity scaling factors) and configurations (mesh size). The results provide a platform to compare numerical outputs and find the best parameters that suit WSI models. Moreover, the force signals applied to the superstructure experience high oscillations due to WSI. Different digital filter designs have been used to remove unwanted oscillations and provide researchers with recommendations on generating models that deliver optimal results. • Optimizing explicit solver parameters is essential for estimating bridge load demands. • The combined hourglass control is crucial for mitigating numerical artifacts. • Modeling bridge part interactions with springs helps control interface rigidity. • Tuning spring stiffness avoids numerical spikes and prevent direct part contact. • Digital filtering should be used cautiously to avoid errors in force signals. [ABSTRACT FROM AUTHOR]

Adaptation of port infrastructures to climate change and sea level rise effects is highlighted as a key field among transportation systems' lines of action for adaptation, given their highly exposed location in coastal areas and position as critical nodes in logistic chains and local, regional and national economies. The present work proposes an adaptation assessment framework that, based on a high-resolution compound climate risk assessment, identifies the main threats that climate change may pose to port performance, defines a set of optimized adaptation measures and characterizes constraints for implementation, and finally evaluates the applicability and effectiveness of these measures under diverse climate scenarios and different time frames. The framework is applied in a study case located in the northern coast of Spain. It is shown that the proposed methodology enables port managers and planners to develop tailor-fitted adaptation plans, providing tools to make them coherent with actual and future uncertain climate conditions. • The paper develops a novel framework to prepare climate change adaptation plans for port and coastal infrastructures. • It identifies the main needs and limitations for adaptation of port infrastructures based on a compound CC risk assessment. • It identifies and optimizes a set of adaptation measures, considering measure combinations, based on risk-reduction criteria. • It assesses the adaptation options' effectiveness in reducing climate risk for different scenarios and time horizons. • The framework has been applied and validated for a case study located on the Atlantic coast in Spain. [ABSTRACT FROM AUTHOR]

This paper describes a 2D physical model study on the hydraulic performances of composite vertical breakwaters with retreated wave walls. The research is an expansion of a previous experimental study by the same Authors: a very large number of experiments, in the order of 2,000, have been carried out by exploring and varying a wide range of wave and geometrical parameters of the structure, to investigate their effect and importance. In order to make feasible the execution of this large number of tests, a small-scale wave flume was used and regular wave conditions were reproduced. The influence of the wave wall retreat has been investigated in terms of wave-induced forces, reflection coefficients and wave overtopping discharges, comparing the hydraulic performances of structures with retreated walls with those of a flushed wall configuration under the same wave conditions. The large number of experiments allowed to formulate a detailed description of the complex phenomena at hand, providing statistical indicators that can be used as guidelines for preliminary design purposes of such structures, quantifying the relevant sources of uncertainty. The analysis confirmed and extended the previous findings and indicates that, on average, the hydraulic performances of structures with retreated crown wall vary significantly from those of flushed wall configurations. Specifically: (I) the forces acting on the wave wall increase of a factor up to 1.5, due to the occurrence of impulsive loads; (II) the forces acting on the caisson trunk decrease of a factor up to 0.91; (III) the global forces can decrease reaching a minimum reduction factor of 0.87, although some dangerous exceptions, in which equal or larger loads, than those occurring for standard flushed wall configuration, have been registered; (IV) the reflection coefficients decrease of a factor up to 0.83; (V) the wave overtopping discharges increase up to 2.55 times those with flushed walls. • New small-scale 2D experiments on vertical breakwaters with retreated walls. • A wide range of wave and geometrical parameters is systematically investigated. • Almost 2,000 regular wave tests carried out to measure hydraulic performances. • Hydraulic performances of retreated wall structures are compared, in terms of ratios, with flushed wall ones. • Statistical indicators to be used as guidelines for preliminary design are provided. [ABSTRACT FROM AUTHOR]

Historic rock lighthouses are unusual structures that are situated in hostile marine environments to provide warning to mariners. Even in an era of satellite navigation their role continues to be an important one, but their survivability into the future is not assured. Out of concern for their ongoing service, the multidisciplinary STORMLAMP project is assessing their survivability under wave loading. This paper presents the various stages of investigations into the structural integrity and stability assessment of the Fastnet lighthouse, situated just off the coast of Ireland. The paper describes: Extreme Bayesian analysis to quantify waves of particular return periods resulting in a 1 in 250 year return period wave with H 0.1% of 17.6 m and an associated maximum force of 20,765 kN; logistically challenging field modal tests revealing the key modal parameters, like the modal masses of 1822 t and 1 675 t for 4.8 Hz and 5.0 Hz modes respectively, the cantilevered nature of the overall lighthouse and the directional effects due to the asymmetric contact with the granite rock; and details of a discontinuous finite element model that is used to determine the stability of the tower under the 1 in 250 year return period breaking wave condition, which is well within stability and material strength limits, causing maximum horizontal displacements in the order of 1 mm at the top of the tower. The overall assessment is that the sheer mass of the lighthouse and its interconnected joints are able to withstand the worst of the Atlantic storms. • Bayesian extreme values analysis is applied to 27 years of wave hindcast data. • Prior informative distributions for the shape and scale parameters are defined from the surrounding numerical nodes. • Field modal analysis is performed in order to identify dynamic parameters of the lighthouse. • For the first time, a discontinuous finite element model is applied to the analysis of the coastal structures. • The survivability of the historic Fastnet lighthouse is performed on the basis of the validated numerical structural model. [ABSTRACT FROM AUTHOR]

Abstract In this paired study, we apply a recently developed high-resolution bathymetry estimation algorithm ("cBathy") to X-band marine radar observations at two nearshore field sites. The algorithm exploits observations of the spatial structure of wave phase to attain wavenumber estimates, inverts the linear water wave dispersion relation for depth, and then applies a Kalman filter to objectively update the bathymetry estimates. Previously, performance has only been tested using optical video observations. In this first of two papers, performance of the algorithm using X-band radar image time series is tested at two disparate barred beach environments: Duck, NC, USA, and Benson Beach, WA, USA. Each of the test beaches is either co-located with (Duck, NC) or geographically close to (Benson Beach, WA) those utilized in the original algorithm verification. Concurrent echosounder surveys are used as ground truth. The bulk performance of the radar-derived bathymetry estimate at Duck, NC, achieves 0.49 m root-mean-square error (RMSE) with 0.26 m bias deep. This compares well with the bulk performance of the concurrent estimate derived using optical video (0.44 m RMSE and 0.23 m bias deep). The radar-derived bathymetry estimate performance at Benson Beach, is similar (0.35 m RMSE and 0.11 m bias shallow), and is comparable to that of an optical video derived estimate at a similar Pacific Northwest beach (0.56 m RMSE and 0.41 m bias shallow). At both beaches, significantly higher performance is achieved at locations deeper than 2 m (offshore of the surfzone) than at locations shallower than 2 m (surfzone), where errors are often a large fraction of the total depth. Lastly, several weeks of observations are utilized to assess the sensitivity of algorithm quality control to environmental conditions. Thresholds based on the shoreward component of wind stress and offshore wave steepness are identified and shown to impact the areal coverage of radar-derived bathymetric estimates. Overall, these results demonstrate the viability of marine radar observations as input to the cBathy algorithm and delineate some environmental constraints on algorithm performance. In the companion paper, the algorithm is extended to areas where tidal currents are important, including an ebb tidal shoal and an estuary mouth. Highlights • Depth estimation algorithm, cBathy, is applied to X-band radar image time series. • Performance is assessed at two beaches (North Carolina and Washington, USA). • Accuracy via radar is comparable to video-based performance (reported previously). • Frequency of updates increases with wave height and when wind blows toward shore. [ABSTRACT FROM AUTHOR]

Abstract A coupled finite particle method (FPM) is proposed to model wave-structure interaction. The coupled FPM combines the advantages of FPM, smoothed particle hydrodynamics (SPH), δ -SPH model and particle shifting technology (PST). The coupled FPM is more accurate than SPH for evaluating the interior fluid particles and more flexible than FPM for evaluating the free surface. The density diffusive term of δ -SPH model can allow for a relatively large CFL condition number and maintain a high computational efficiency. With the help of PST, the particle clustering and fracturing are eliminated effectively, and the well-conditioned corrective matrix is acquired. The coupled FPM method is tested by simulations of regular waves and the interaction between waves and the rigid plate. Then, the coupled FPM method is applied to model Oscillating Wave Surge Converter (OWSC) including two-dimensional (2-D) and three dimensional (3-D) simulations. All numerical results show that the coupled FPM is robust, and is capable to simulate wave-structure interaction accurately. The linked data are be associated to this paper, and the readers are able to download the source code that can be used to test regular waves contained in the paper. The web site of the code is https://data.mendeley.com/datasets/xjk3ccgr8t/draft?a=622fb107-3cb9-4c68-af8e-7b3ac1b3fc48. Highlights • The coupled FPM is proposed to model wave and structure interaction. • A 3-D geometry model is improved to detect the particles in the vicinity of free surface. • The coupled FPM method is developed to model Oscillating Wave Surge Converter (OWSC) including 2-D and 3-D results. [ABSTRACT FROM AUTHOR]

Abstract A common form of coastal protection in New South Wales, Australia, is the rubble mound breakwater. This consists of quarried rock or unreinforced concrete armour units. However, increased impact forces on these structures due to greater storm surge levels that are predicted by global warming models, suggest that they will require strengthening. Traditionally steel bar reinforcement is used to strengthen concrete; however, as steel is particularly susceptible to corrosion in aggressive coastal environments, it is not a robust solution. This paper reports on the potential of using macro-synthetic fibre reinforcement in reinforcing of breakwater armour units, in lieu of traditional steel reinforcing bars. To this end, a programme to ascertain the tensile capacity of 0.6 percent and 1.0 percent by volume of concrete reinforced with macro-synthetic fibres was implemented. The behaviour of this synthetic fibre reinforced concrete in Dolos type breakwater armour units was then examined using the finite element analysis software ATENA. The results of the numerical analysis indicate that the addition of synthetic fibres at these volume percentages into concrete armour units improves the post peak response under impact loading by a factor of two to three, compared with unreinforced units. Furthermore, the addition of fibres significantly reduced the maximum crack width for the same number of impact loadings and allows the units to withstand larger crack widths before failure. Highlights • This paper assesses the effectiveness of Dolosse concrete armour units reinforced with 0.6 percent and 1.0 percent of macro-synthetic fibres. • An experimental programme was developed to investigate the post crack capacity of the synthetic FRC. • The experimental results were used to simulate the properties of synthetic FRC in Dolosse breakwater armour units. • The addition of fibres significantly improves the breakwater armour unit's capacity to withstand higher and more numerous impact loads. [ABSTRACT FROM AUTHOR]

The risks posed by local scour around offshore monopile foundations are substantial and threaten the structural safety of these installations. It is therefore essential to study the mechanisms of local scour to mitigate these risks. Numerical simulation is an effective tool to help us understand the mechanisms of local scour. However, the accurate modeling of the local scour process remains to be challenging due to the complexity of sediment transportation, in which the continuity threatment of sediment phase is typically used, the discrete behavior of the sediment is hard to be described. Therefore, in this paper, in order to conduct the deepin investigation into the mechanism of the local scour around monopile, a three-dimensional CFD-DEM model was established by coupling the computational fluid dynamic method (CFD) and discrete element method (DEM). To increase the efficiency and accuracy of the CFD-DEM model, the coarse grain method (CGM) was used to decrease the number of required DEM particles in the simulation, and the angle of repose was used to calibrate the contact parameters between DEM particles. During the validation process of the numerical model, it was found that the development of the scour depth and the morphology of scour pit obtained by the CFD-DEM model showed good agreement with the previously published results. The CFD-DEM simulation revealed that seepage-induced vertical drag force plays a crucial role in the initial stage of local scour. Two sediment transportation processes, "Pile toe erosion-Slope avalanche" and "Push-Accumulation-Wash", were observed and the relationship between bedload sediment flux and the Shields number was quantified. In the end of this paper, the critical evaluation of the CFD-DEM method was conducted. • The first time that the CFD-DEM method is used to research the sediment motion during the local scour around monopile. • The coarse grain method is used to improve the efficiency of CFD-DEM coupling method. • The seepage-induced vertical drag force was proved to be crucial in the early stage of local scour around monopile. • The "Pile toe erosion-Slope avalanche" and "Push-Accumulation-Wash" process of sediment transportation were observed. • A method is proposed to convert the parameters of discrete phase into the continuous phase parameters. [ABSTRACT FROM AUTHOR]

The coupled effects of waves and a subsurface current on the hydrodynamic loads on offshore slender structures in coastal water regions have been examined in this paper, especially the coupling of the weak nonlinearity of surface waves and the depth variation of a current profile. Based on a narrowband assumption, this paper firstly derives a novel semi-analytical framework which extends potential flow theory and the Direct Integration Method (DIM) proposed by Li and Ellingsen (2019), permitting the interaction between weakly nonlinear surface waves and an arbitrary depth-dependent subsurface current. This framework is numerically implemented, validated, and used to lead to the current-modified Morison equations which are used to analyze the loading on a bottom-fixed, vertically installed cylinder. We demonstrate the clear differences between the features of surface elevation and hydrodynamics loading exerted by the coupled interaction of irregular waves and a subsurface current in both operational and extreme sea states. Especially, we find that the occurrence probability of extremely large events represented by the statistical features of surface waves can be insignificant whereas the coupled effects of waves and current on the hydrodynamic loads are considerable, compared with the decoupled cases. This suggests that the conventional approach, which uses the statistical features of surface elevation to represent the extremely large wave events, and therefore risks posing to the safety of offshore structures, may not be sufficient when both the waves and a subsurface current are present and play a role in the hydrodynamic performances of offshore structures. Both the depth variation of a current profile and the direction between the wave propagation and current velocity are found to play an important role in the loads on offshore slender structures. A following and an opposing uniform current lead to overestimated and underestimated loads, respectively, compared to either a decoupled model or a coupled model with a more realistic representation of the current profile. • The coupling between the nonlinearity of water waves and a current is examined. • Hydrodynamic loads on offshore slender structures are analyzed. • An approximate theory more general than potential flow theory is used. • Differences between the proxies to extreme wave events and wave kinematics are shown. • A following current leads to increased loads, compared with the decoupled models. • An opposing current leads to decreased loads compared with the decoupled models. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental investigation of wave-induced liquefaction in the case of multiple wave exposures. The experiments include also standard progressive wave cases as well, for comparison. One kind of sediment was used in the experiments: silt (d 50 = 0.070 mm). Four scenarios were tested with multiple wave-climate exposures, including (1) multiple wave climates separated with "quiet", no-wave periods, and (2) those with no interruptions between the consecutive wave-climate exposures, resembling a storm situation. It was found that the first strongest wave climate (i.e., the first wave climate, which is strong enough to cause liquefaction) of a multiple wave-climate sequence "secures" the onset of liquefaction, independent of prior wave exposures. It was also found that the wave exposures following the "liquefying" wave (even with stronger wave properties) do not liquefy the soil. The experiments further showed that, after the completion of the liquefaction-compaction cycle, the pore pressure may still build up when the soil is exposed to a new wave climate in the sequence with an even stronger set of wave characteristics (wave height and wave period). However, the accumulated pore pressure will not be large enough to liquefy the soil. Likewise, after the completion of the liquefaction-compaction cycle, or after exposures to not one but a number of waves, again, even with stronger wave characteristics, the pore pressure may not even build up at all. The experiments shed further light on the circumstances in the field under which (1) the seabed soil would eventually become liquefaction resistant (with a very large relative density), and those under which (2) it would remain loose, both of which have been revealed by field surveys. Furthermore, it was found that, in the case when the wave-climate exposures are uninterrupted, the dissipation of the accumulated pore pressure is quite slow when compared with the situation where the wave-climate exposures are interrupted with "quiet", no-wave periods. The results have been explained in terms of physical processes involved. Also, implications of the results for practice have been discussed in detail. • Effect of history of wave exposure on seabed liquefaction is experimentally investigated in a standard wave flume. • The effect is found very significant, as detailed in the paper. • The first strongest wave climate of a multiple wave sequence "secures" the onset of liquefaction. • The exposures following the "liquefying" wave (even with stronger wave properties) do not liquefy the soil. • Circumstances in the field under which the seabed soil eventually become liquefaction resistant are unveiled. [ABSTRACT FROM AUTHOR]

Vegetated foreshores adjacent to engineered structures (so-called hybrid flood defenses), are considered to have high potential in reducing flood risk, even in the face of sea level rise and increasing storminess. However, foreshores such as salt marshes and mangrove forests are generally characterized by relatively strong temporal and spatial variations in geometry and vegetation characteristics (e.g., stem height and density), which causes uncertainties with regards to their protective value under extreme storm conditions. Currently, no method is available to assess the failure probability of a hybrid flood defense, taking into account the aforementioned uncertainties. This paper presents a method to determine the failure probability of a hybrid flood defense, integrating models and stochastic parameters that describe dike failure and wave propagation over a vegetated foreshore. Two dike failure mechanisms are considered: failure due to (i) wave overtopping and (ii) wave impact on revetments. Results show that vegetated foreshores cause a reduction in failure probability for both mechanisms. This effect is more pronounced for wave impact on revetments than for wave overtopping, since revetment failure occurs at relatively low water levels. The relevance of different uncertainties depends on the protection level and associated dike height and strength. For relatively low dikes (i.e., low protection levels), vegetation remains stable in design conditions, and plays an important role in reducing wave loads. In case of higher protection levels, hence for more robust dikes, vegetation is less important than foreshore geometry, because of expected stem breakage of the vegetation under these more extreme conditions. The integrated analysis of uncertainties in hydraulic loads, dike geometry and foreshore characteristics in this paper enables the comparison between nature-based flood defenses and traditionally engineered solutions, and allows coastal engineers to design hybrid flood defenses worldwide. [ABSTRACT FROM AUTHOR]

Coastal erosion is a major problem for shorelines everywhere in the world. In order to mitigate beach stability problems it is necessary to determine the equilibrium shape of the beach planform. Current equilibrium planform shape equations are only valid under certain simplifications; for instance, they are unable to predict the effect of nearshore islands and/or rocky bottoms, as well as the effect of several diffraction points. The aim of this paper is to present a new process-based shape equation that is able to overcome those limitations and estimate the static equilibrium shoreline of complex bathymetry beaches. The equation is based on the hypothesis that a pocket beach gets its static equilibrium planform when the mean surf-zone longshore velocity averaged over a period of time is null ( V ¯ = 0 ) in every point along the beach. Based on this hypothesis, the direction of the shoreline that nulls the mean surf zone longshore velocity along the beach is evaluated. Therefore, the shape equation is based on the longshore current velocity formula. The new equilibrium shape equation is applied to two Spanish beaches, namely Milagro beach and Cala Millor beach. Milagro beach has a very smooth bathymetry and the parabolic shape equation developed by Hsu and Evans (1989) is able to predict the equilibrium shoreline. Cala Millor is more complex: it has some rock outcrops along the beach and the parabolic shape equation does not work. The equilibrium shape equation presented in this paper simulates the equilibrium shoreline of both beaches successfully with a high R 2 (around 0.96) between the modelled shoreline and the real shoreline in both case studies. [ABSTRACT FROM AUTHOR]

Hurricanes have long been recognized as a strong forcing in shaping the coastal morphology, especially by redistributing sediments among coastal wetlands, bays and inner continental shelves. However, the contribution of hurricane-induced sediment transport to the sediment budget of a shelf – bay – wetland system has not been evaluated using a physics-based numerical model. There is a particular confusion on how sediment transport to coastal wetlands contributes to sediment accretion in wetlands and thus wetland adaptation to sea level rise. In this paper, we present a coupled modeling system for hurricane winds, storm surge, waves and sediment transport on the Louisiana coast, and use it to investigate two fundamental questions: (1) How much sediment is transported and deposited on coastal wetlands during a major hurricane event like Hurricane Gustav (2008), and (2) where is the source of the deposited sediment on the wetland soil surface. Our model successfully reproduced the measured basin-averaged sediment accretion in the Terrebonne and Barataria Basins after Gustav, and estimated that Hurricane Gustav imported approximately 27 million metric tons of sediment on wetlands in that area. The estimated deposition was mainly made up of mud suspended from the coastal bays, and the contribution of this sediment to wetland deposition was 88.7% in Terrebonne Bay and 98.2% in Barataria Bay within the tested range of sediment properties. This paper demonstrates a useful tool to help understand how sediment dynamics in the coastal zone during hurricane events play a significant role in the sediment budget of a deltaic coast. [ABSTRACT FROM AUTHOR]

This paper introduces a participatory Multi-Criteria Assessment (MCA) methodology developed through the Resilience Increasing Strategies for Coasts – Toolkit (RISC-KIT) project and implemented in nine case studies in Europe. The purpose of the MCA was to bridge the disciplinary divide between engineering sciences and social sciences, facilitate the communication and dissemination of local coastal risk assessments and Disaster Risk Reduction (DRR) measures' evaluation to a broad range of actors. The process addressed the importance of integrating scientific knowledge with stakeholders’ knowledge to understand and assess the possible social, political and economic implications of different DRR measures, which could foster or hinder successful implementation. The paper discusses the methodological aspects and implementation of the approach which included visualizing risk reduction of DRR measures using paper-based cards to support interaction and negotiation among participants to select preferred strategic alternatives (SA), and a participatory MCA where stakeholders evaluated the SA against three (self-weighted) criteria: feasibility, acceptability and sustainability. [ABSTRACT FROM AUTHOR]

This paper presents a new approach to guiding coastal stakeholders about making informed decisions about Disaster Risk Reduction (DRR) measures and alternatives. As part of the RISC-KIT project and tool box, the paper presents a holistic DRR measure approach including the biophysical environment, governance aspects and practical examples from coastal areas in Europe and elsewhere. The guide (see: www.coastal-management.eu ) is addressed to a wide variety of coastal stakeholders with a different level of knowledge about DRR measures with the aim to provide guidance and information. The paper gives an overview of the overall structure of the guide. [ABSTRACT FROM AUTHOR]

Recent and historic low-frequency, high-impact events have demonstrated the flood risks faced by exposed coastal areas in Europe and beyond. These coastal zone risks are likely to increase in the future which requires a re-evaluation of coastal disaster risk reduction (DRR) strategies and a new mix of PMP (prevention, e.g., dike protection; mitigation, e.g., limiting construction in flood-prone areas and eco-system based solutions; and preparedness, e.g., Early Warning Systems, EWS) measures. In response to these challenges, the RISC-KIT project has delivered a set of open-source and open-access methods, tools and management approaches to reduce risk and increase resilience to low-frequency, high-impact hydro-meteorological events in the coastal zone (the “RISC-toolKIT”). These products enhance forecasting, prediction and early warning capabilities, improve the assessment of long-term coastal risk and optimise the mix of PMP-measures. In this paper an introduction is provided to the objectives, products, applications and lessons-learned of the RISC-KIT project, which are the subjects of this Special Issue. Subsequent papers provide details on the tools and their application on 10 case study sites in Europe. [ABSTRACT FROM AUTHOR]

Coastal zones are under increasing risk as coastal hazards increase due to climate change and the consequences of these also increase due to on-going economic development. To effectively deal with this increased risk requires the development of validated tools to identify coastal areas of higher risk and to evaluate the effectiveness of disaster risk reduction (DRR) measures. This paper analyses the performance in the application of two tools which have been developed in the RISC-KIT project: the regional Coastal Risk Assessment Framework (CRAF) and a hotspot early warning system coupled with a decision support system (EWS/DSS). The paper discusses the main achievements of the tools as well as improvements needed to support their further use by the coastal community. The CRAF, a tool to identify and rank hotspots of coastal risk at the regional scale, provides useful results for coastal managers and stakeholders. A change over time of the hotspots location and ranking can be analysed as a function of changes on coastal occupation or climate change. This tool is highly dependent on the quality of available information and a major constraint to its application is the relatively poor availability and accessibility of high-quality data, particularly in respect to social-economic indicators, and to lesser extent the physical environment. The EWS/DSS can be used as a warning system to predict potential impacts or to test the effectiveness of risk reduction measures at a given hotspot. This tool provides high resolution results, but needs validation against impact data, which are still scarce. The EWS/DSS tool can be improved by enhancing the vulnerability relationships and detailing the receptors in each area (increasing the detail, but also model simulations). The developed EWS/DSS can be adapted and extended to include a greater range of conditions (including climate change), receptors, hazards and impacts, enhancing disaster preparedness for effective risk reduction for further events or morphological conditions. Despite these concerns, the tools assessed in this paper proved to be valuable instruments for coastal management and risk reduction that can be adopted in a wide range of coastal areas. [ABSTRACT FROM AUTHOR]

In predicting storm impacts on sandy coasts, possibly with structures, accurate runup and overtopping simulation is an important aspect. Recent investigations (Stockdon et al., 2014; Palmsten and Splinter, 2016) show that despite accurate predictions of the morphodynamics of dissipative sandy beaches, the XBeach model (Roelvink et al., 2009) does not correctly simulate the individual contributions of set-up, and infragravity and incident-band swash to the wave run-up. In this paper we describe an improved numerical scheme and a different way of simulating the propagation of directionally-spread short wave groups in XBeach to better predict the groupiness of the short waves and the resulting infragravity waves. The new approach is tested against field measurements from the DELILAH campaign at Duck, NC, and against video-derived runup measurements at Praia de Faro, a relatively steep sandy beach. Compared to the empirical fit by Vousdoukas et al. (2012) the XBeach model performs much better for more extreme wave conditions, which are severely underestimated by existing empirical formulations. For relatively steep beaches incident-band swash cannot be neglected and a wave-resolving simulation mode is required. Therefore in this paper we also test the non-hydrostatic, wave-resolving model within XBeach for runup and overtopping against three datasets. Results for a high-quality flume test show non-hydrostatic XBeach predicts the run-up height with good accuracy (maximum deviation 15%). A case with a very shallow foreshore typical for the Belgian coast at Wenduine was compared against detailed measurements. Overall the model shows correct behavior for this case. Finally, the model is tested against a large number (551) of physical model tests of overtopping from the CLASH database. For relatively high overtopping discharges the non-hydrostatic XBeach performs quite well, with increasing accuracy for increasing overtopping rates. However, for relatively low overtopping rates of less than 10–20 l/m/s, the model systematically underestimates measured overtopping rates. [ABSTRACT FROM AUTHOR]

With the increasing impact of climate change and relative sea level rise, low-lying coastal communities face growing risks from recurrent nuisance flooding and storm tides. Thus, timely and reliable predictions of coastal water levels are critical to resilience in vulnerable coastal areas. Over the past decade, there has been increasing interest in utilizing machine learning (ML) based models for emulation and prediction of coastal water levels. However, flood advisory systems still rely on running computationally demanding hydrodynamic models. To alleviate the computational burden, these physics-based models are either run at small scales with high resolution or at large scales with low resolution. While ML-based models are very fast, they face challenges in terms of ensuring reliability and ability to capture any surge levels. In this paper, we develop a deep neural network for spatiotemporal prediction of water levels in coastal areas of the Chesapeake Bay in the U.S. Our model relies on data from numerical weather prediction models as the atmospheric input and astronomical tide levels, while its outputs are time series of predicted water levels at several tide gauge locations across the Chesapeake Bay. We utilized a CNN-LSTM setting as the architecture of the model. The CNN part extracts the features from a sequence of gridded wind fields and fuses its output to several independent LSTM units. The LSTM units concatenate the atmospheric features with respective astronomical tide levels and produce water level time series. The novel contribution of the present work is in spatiotemporality and in prioritization of the physical relationships in the model to maintain a high analogy to hydrodynamic modeling, either in the network architecture or in the selection of predictors and predictands. The results show that this setting yields a strong performance in predicting coastal water levels that cause flooding from minor to major levels. We also show that the model stands up successfully to the rigorous comparison with a high-fidelity ADCIRC model, yielding mean RMSE and correlation coefficient of 14.3 cm and 0.94, respectively, in two extreme cases, versus 12.30 cm and 0.96 for the ADCIRC model. The results highlight the practical feasibility of employing fast yet inexpensive data-driven models for resilient coastal management. • A deep learning model is developed to predict a wide range of coastal water levels using wind and tides as input. • CNN layers extract features from the wind field and fuse them to independent LSTM units, creating spatiotemporality. • The model compares well with the data for different storm scenarios. • The model is comparable to or surpasses a high-fidelity hydrodynamic model while taking a fraction of a second to run. [ABSTRACT FROM AUTHOR]

Improving ocean wave energy capture in a cost-effective manner is a challenging task. Multi-chamber oscillating water column (OWC) devices are gaining favor due to their potentially efficient characteristics. This research experimentally investigated the hydrodynamic performance of a land-based OWC wave energy capture system with multiple chambers (ranging from 1 to 5). The free surface elevation, air pressure fluctuations, hydrodynamic efficiency, and reflection coefficient are considered. The hydrodynamic efficiencies of the overall, and sub-chambers in the OWC system with varying numbers of chambers are graphically presented. The influence of geometrical design parameters and wave conditions are also considered in evaluating the performance of the multi-chamber OWC system. It is found that the multi-chamber arrangement improves the hydrodynamic energy extraction characteristics compared to the traditional single-chamber setup. The sloshing mode of the chamber water column is utilized to effectively capture wave energy. As the number of chambers increases, the wave attenuation capability of the system improves for long waves. Yet, the overall efficiency declines when the number of OWC chambers exceeds 3. The chamber draft has the most substantial impact on the wave energy capturing capability, while the effects of opening ratio and wave height are attenuated due to multiple water-column interactions inside the chambers. The isometric sub-chamber structure demonstrates overall efficiency and wave attenuation advantages for short waves. The paper aims to guide the design and optimization of a multi-chamber OWC system. • Hydrodynamic performance of a land-based multi-chamber OWC system is investigated experimentally. • The multi-chamber OWC system demonstrates the advantages of overall efficiency and reflective property. • The dependence on geometrical parameters and wave conditions is comprehensively examined. • The chamber draft exerts the most significant impact on hydrodynamics compared to other parameters. [ABSTRACT FROM AUTHOR]

The beach slope β is a key component characterizing the coastal response to wave forcing. Here we investigate the rapid adaptation of the upper beach slope to a given wave forcing, for the case of a lower flat platform. Such types of morphology are found on coral and rocky reef beaches and low tide terrace environments. The influence of the lower platform on this rapid equilibrium beach state is shown to be significant depending on the breaking wave regime. In particular, the width of the platform and its water level can affect the wave dissipation along the inner surf and thus the wave structure entering the swash. This paper provides a classification of the beach slope equilibrium values as a function of the Dean number on a short time scale (individual wave action), based on both offshore and swash wave conditions. A decreasing trend of the beach slope with increasing offshore Dean number (Ω 0) is found for Ω 0 ≲ 2. 7. For Ω 0 ≳ 2. 7 it is observed that the beach slope gradient is strongly controlled by the surf zone dissipation and it becomes necessary to define the swash Dean number (Ω s w) to classify the slope. Finally, a semi-empirical formula for the beach slope evolution in the case of a low tide platform is introduced and tested on two natural low-tide terrace beaches. • Definition of rapid equilibrium beach face slope associated to individual wave action. • Distinction between swash and surf dominated beaches on LTT beaches using Dean number based on offshore or local swash flow characteristics (Ω 0 or Ω s w). • Swash-dominated beaches respond directly to offshore wave forcing. • In surf-dominated beaches the inner-surf zone cannot be disregarded. • A simplified model is proposed to predict the rapid evolution of the beach slope as a function of the swash Dean number Ω s w. [ABSTRACT FROM AUTHOR]

Waves in coastal areas and fjords can present inhomogeneities that affect the responses of very large floating structures. However, spatial inhomogeneities of waves are usually not included in model testing. In this paper, the feasibility of generating inhomogeneous wave conditions in an Ocean basin is investigated. For that purpose, a fast linear numerical model of a basin of constant depth is applied, and an optimization method is presented, that allows to find the control signal for the multiflap wavemaker. Comparisons with experiments in SINTEF's Ocean basin demonstrate the validity of the method for generating simple monochromatic synthetic waves, as well as short-crested irregular waves representing realistic conditions in Sulafjorden. • A new method to generate inhomogeneous waves for model tests is proposed. • The method was tested with short-crested inhomogeneous fjord waves in an Ocean basin. • The wavemaker control signal is found by optimization using a linear numerical model. [ABSTRACT FROM AUTHOR]

In this paper, an innovative framework is introduced for assessing the impact of climate change on coastal structures, with a primary emphasis on modeling future climate conditions. The framework encompasses several key components: the development of a new climate emulator to facilitate multivariate extreme value analysis; a hybrid statistical–numerical wave propagation strategy; and the integration of a novel compound modeling approach specific to coastal structure sites. These advancements are designed to effectively manage multiple climate scenarios and models within the context of high uncertainty. The methodology is applied and validated for a coastal structure located on the Mediterranean coast in Spain. Focusing on compound wave and sea-level events, the projections indicate an increase in the frequency and severity of extreme conditions, exacerbating coastal impacts such as wave overtopping. For instance, the present-day 500-year coastal flooding level would be associated with a return period of 50 years by mid-century under a stabilization scenario and would be further reduced to 25 years under a high-emission global warming scenario, resulting in important consequences for structure performance if no adaptation is implemented. • Develops a framework for assessing the impact of climate change on coastal structures. • It develops a new climate emulator to facilitate multivariate extreme value analysis. • It encompasses a hybrid statistical–numerical wave propagation strategy. • It integrates a novel compound modeling approach specific to coastal structures sites. • It has been applied and validated for a coastal structure in Spain. [ABSTRACT FROM AUTHOR]

The paper presents three dimensional simulations of scour around a pair of piles arranged side-by-side configurations under combined wave–current flow conditions using a computational fluid dynamics model. The Reynolds-averaged Navier–Stokes (RANS) equation is solved using the k- ω turbulence model in the present work. The Exner equation is used to measure the variations in bed elevation. The level-Set approach is used to capture the free surface realistically. The numerical model couples the hydrodynamic module with the morphological module to simulate the scour process. For accurate erosion and deposition calculations in the sediment bed, the morphological model employs a modified bed shear stress formula on a sloping bed in combination with a sand slide algorithm. In the present study, the simulations have been done in a truncated numerical wave tank with the Dirichlet boundary condition and active wave absorption method. The numerical model is validated with the experimental results of combined wave–current hydrodynamics and scour around a pair of piles. The validated numerical model is utilized to study the effect of the gap ratio and the effect of K C number in the various combined wave–current environment. In low KC conditions, normalized scour depth increments owing to waves alone, weak currents, and moderate currents are less, whereas the scour depth increases dramatically for waves with high currents. It is also found that the gap flow between the piles increases the depth of scour in a significant manner. For a given pile gap ratio, the scour depth is dependent on the K C number, which implies the larger the K C number, the larger scour depth. For a given KC number, the scour hole stretch in the flow direction reduces as the gap ratio increases, whereas the perpendicular stretch increases. It is also observed that the normalized scour depth decreases as the gap ratio increases for a fixed K C number and fixed U c w. It is evident from the present research that the normalized scour depth increases with increase in K C number for a fixed wave–current parameter (U c w). • CFD simulation of 3D scour around side-by-side piles in combined wave-current flow. • Open-source CFD tool REEF3D is used. • The level-set method (LSM) depicts realistic free surface motion precisely. • Numerical scour and hydrodynamics validate the experimental results. • The Exner equation is used to measure the variations in bed elevation. [ABSTRACT FROM AUTHOR]

Bottom friction dissipation is a key factor for wave attenuation in nearshore environments presenting complex geomorphological structures, such as rocky or coral shores. The present paper reports on a series of laboratory experiments performed in a wave flume with controlled wave conditions and seabed structures. Using the frequency-integrated short-wave analysis and classical models for bottom friction and breaking dissipation, the wave friction factor and the hydraulic roughness parameter were estimated from the experimental data. The former varies from 0.17 to 98 while the latter varies from 0 to 0.291 m. The observations reveal the combined influence of several topographical metrics, including the standard deviation, the skewness, the directionality and the effective slope of the seabed elevation. A metric-based multi-varied model for the hydraulic roughness parameter is proposed and confronted with other field data recovered on coral and rocky shores. • A novel laboratory database for wave frictional dissipation over rough bottom. • Classical bottom friction models globally remain robust even for very large roughness. • Hydraulic roughness parameter is not solely controlled by standard deviation. • Metric-based hydraulic roughness model improves bottom friction modelling. [ABSTRACT FROM AUTHOR]

There is a pressing need for a fast and efficient satellite remote sensing tool to estimate coastal bathymetry for any coastline in the world. To date, satellite methods for deriving bathymetry have mainly focused on linking the radiometric response to a known water depth, as with SPOT, Landsat and Sentinel. Here, wave properties (static and dynamic) are approximated using the small time delay between the different color bands of Sentinel-2 to then calculate a depth using wave linear dispersion theory. In this paper, we present a spatial correlation method within the S2Shores (Satellites to Shores) Python toolbox: a processing chain/toolbox of coastal observations using methods applied to optical satellites. The resulting individual bathymetries are finally qualified according to the standards of the International Hydrographic Organization, anticipating their operational use. • S2Shores spatial-correlation method for optical satellite coastal observations. • Bathymetry qualified with the International Hydrographic Organization standards. • Wave characteristics from the time delay between spectral bands of Sentinel-2. [ABSTRACT FROM AUTHOR]

In this paper the Empirical Orthogonal Function (EOF) method is applied to extract from the experimental data, related to landslide-tsunamis around the coast of a conical island, the spatial modes that contribute to the wave field. For each mode the wavenumber and the frequency are calculated by analyzing the shape along the coast and the time function. The relevant modes are then compared with those obtained through numerical eigenanalysis of the long wave equation around the considered island. It was possible to associate each EOF mode with some eigenvectors and the corresponding eigenfrequencies, both on the basis of the spatial shape, the wavenumber calculated along the coast and the frequency. Results confirm that landslide-generated waves propagate along the coast as trapped edge waves and the zero-th order mode is the most important. Further of exploring the physics, it is believed that this paper can be of use as some of the most relevant and straightforward techniques for modal identification are applied to the same problem and dataset. [ABSTRACT FROM AUTHOR]

This paper presents an experimentally validated, closed-form set of equations for predicting forces on rectangular buildings impinged by nominally unsteady tsunami inundation flows. The shallow water waves that drive the tsunami inundation flows described in this paper are generated using a novel tsunami simulator, uniquely capable of generating very long period waves featuring the characteristic draw-down of real-world tsunami. We describe an experimental study of the forces acting on a rectangular building occupying 10–80% of a channel, fixed in a free-surface-channel flow driven by shallow water waves with periods of 20–240 s. An idealised topography and a 1:50 Froude scale are adopted. A one dimensional model based upon open-channel flow principles is proposed for unsteady flows driven by prototype tsunami waves, providing empirical estimates for drag and hydrostatic coefficients. It is observed that the pressure field around the buildings is hydrostatic irrespective of the flow being steady or unsteady. An empirically derived force prediction equation, dependent upon the Froude number of the incoming flow and blocking fraction is presented, which provides good agreement with the experimental results. The equations presented in this paper will provide engineers, tsunami modellers, and risk evaluation experts with a convenient method of tsunami inundation force determination without recourse to computationally expensive multi-scale numerical models. [ABSTRACT FROM AUTHOR]

In recent years, increasing attention has been paid to assess the dispersal of resuspended sediments and related water quality problems due to dredging operations. This paper presents an analytical model aimed to predict the temporal evolution and spatial distribution in the far field of the suspended sediments concentration increase related to dredging activities or open water sediments disposal. In particular, whatever the dredging source strength and geometry can be considered to define the suspended sediments concentration leaving the immediate vicinity of the resuspension source. Indeed, a feature of the model is the removing of the hypotheses of continuous source and steady state, peculiar to the majority of available theoretical models. Hence, the proposed model is able to describe different dredging resuspension sources and to provide the temporal and spatial picture of the resulting plume. Of course, some hypotheses have to be assumed in order to make possible to achieve the analytical solution of the governing equation: the model is two dimensional in the horizontal plane; the ambient currents are assumed to be homogeneous in space and slowly time varying; the turbulent diffusion coefficients and flocculent settling velocity are homogeneous in space; the water depth is constant; the domain is infinite. Even with its limitations, the model is still able to provide a worst case preliminary assessment of sediments plume migration very useful to guide more detailed numerical analysis and to select the more appropriate simulation scenarios. The analytical model is detailed in order to be used for numerical model testing purposes. A series of practical applications is described through the paper (i) to catch the general features of the involved far field phenomena, (ii) to compare the model results to those of previous researches and (iii) to provide a series of benchmark cases useful for the testing of numerical models. The proposed model may be also used as a first rough prediction of the area affected by plume dispersion by considering different dredging scenarios (i.e. different equipment and operational techniques and forced by site-specific environmental conditions), and thus to provide a basis for more sophisticated modeling aimed to support dredging projects planning and management. [ABSTRACT FROM AUTHOR]

This paper presents a newly developed Overlapping Domain Decomposition (ODD) method, which forms the basis of a near-far field coupling solver for a wide range of wave-structure interaction problems. In this method, the computational domain is decomposed into near and far fields which are then modeled separately by solving the viscous Navier-Stokes equations (NSE) and the Potential Laplacian equation (PLE) respectively. A Finite volume method (FVM) is adopted to discretize both the NS and PL equations. The free surface problem is solved in both domains but using totally different strategies. In the potential domain, a moving mesh free surface tracking method is adopted where arbitrary polyhedral mesh adapts to the time-varying shape of the interface using vertex-based automatic mesh motion solver. Meanwhile, at the free surface, the boundary conditions are formulated using an ordinary differential equation (ODE) derived from the Bernoulli's equation. In the viscous domain, however, the volume of fluid (VOF) method is used to predict the location of free surface. The novelty of the reported method lies in two-folds. First, the introduction of the so called overlapped buffer zone eliminates the need of performing time costing iterative schemes in the non-overlapping domain decomposition methods to ensure the matching of free surface elevation at the domain boundaries. The concept of a buffer zone is borrowed from the relaxation zone technique which is commonly used near the inlet to ensure a stable wave generation or near the outlet to absorb the reflected waves in numerical wave simulations. Second, an in-house developed OVERSET method is adopted for the viscous domain solver to handle large object displacement in the case of an extreme event. The proposed method has been implemented in the OpenFOAM platform (foam-extend-3.1). To validate the method, the propagation of a solitary wave is first simulated and the resulting wave parameters are compared with the corresponding analytical, as well as pure VOF solution. Meanwhile, a comparison of the CPU time between the single domain approach and the current method has been provided. Next, the measured wave impact loading for a single body which is partially submerged will be used to further test the method. Last but not least, the method is applied to simulate the spilling wave breaking near the beach. Various numerical examples presented in the paper demonstrate the accuracy and efficiency of the proposed method. Towards the end, computation of a sinking semi-submersible platform will be presented to demonstrate further the capability of the method. [ABSTRACT FROM AUTHOR]

Tsunamis are traveling waves characterized by large amplitudes and long wavelengths close to the coastline. Often, the first couple of leading waves are either leading-elevation N-waves (LEN waves) or leading-depression N-waves (LDN waves). These waves are usually devastating, causing serious damage to coastal infrastructures or even human casualties. Among various natural disasters related to tsunamis, harbor oscillations are one of the most frequent disasters around the world, which can cause excessive movements of moored ships and rupture mooring lines inside the harbor. In this article, transient harbor oscillations induced by various incident N-waves are first investigated. The transient oscillations are simulated by a fully nonlinear Boussinesq model, FUNWAVE-TVD. The incident N-waves include the TS-type and MS-type isosceles LEN and LDN waves. The TS- and MS-type N-waves correspond to the waveform expressions proposed by Tadepalli and Synolakis [1] and Madsen and Schäffer [2], respectively. This paper focuses on the effects of the incident wave amplitude and its type on the relative wave energy distribution inside the harbor. The maximum runup and rundown of various incident waves are also discussed. For comparison, the transient oscillations excited by solitary waves are also considered. The harbor used in this paper is assumed to be long and narrow and has constant depth; the free surface movement inside the harbor is essentially one-dimensional. This study reveals that, for the given harbor, for the range of the incident wave amplitude and the incident wave types studied in this paper, the larger tsunamis lead to a more uniform relative wave energy distribution inside the harbor. The relative wave energy distributions induced by the LDN waves are always more uniform than those induced by the LEN waves, while the relative wave energy distributions induced by the solitary waves are more concentrated than those induced by the various N-waves. When the incident wave amplitude is relatively large, the maximum runups of the LDN waves are considerably larger than those of the solitary waves, while those of the LEN waves are much less than those of the solitary waves. [ABSTRACT FROM AUTHOR]

Estimation of wave overtopping over the crest of coastal structures is crucial to design effective and cost efficient countermeasures against storms. Semi-empirical formulas are often used for wave overtopping assessment, but they are not always applicable for complex structures which exist in reality (e.g. a storm wall on a dike in a shallow or very shallow foreshore). Detailed numerical models such as Eulerian and Lagrangian RANS models have potential to simulate overtopping of complex coastal structures with good accuracy. However such models require significant computational resources. The use of such models is often not feasible for the design of coastal structures, which often requires multiple iterations and model runs over a reasonably long period of time (e.g. wave trains with 1000 individual waves). In this paper we investigated the applicability of the simplified depth integrated wave transformation model SWASH for wave overtopping estimation of impermeable coastal structures in shallow foreshores. The validation results demonstrate the capability of SWASH to predict mean wave overtopping discharge with good accuracy compared to results from four different overtopping experimental campaigns (comprising 124 individual cases). The overall performance of SWASH to estimate mean wave overtopping discharge is as accurate as those obtained by semi-empirical equations in literature. However, in order to obtain accurate mean wave overtopping discharge with the SWASH model, the incident wave properties at the toe of the dike need to be accurately reproduced. For cases where this is not possible, a correction method is proposed in this paper. Detailed validation of the instantaneous wave overtopping also shows a good agreement with physical model data. In one example, a single, intensive overtopping event was not well resolved by the SWASH model and the instantaneous wave overtopping was under-predicted. However, this did not contribute significantly to the mean wave overtopping discharge. An additional advantage of the SWASH model is that specific coastal structure geometries can be modelled in SWASH if they are not covered by semi-empirical equations. Even in a case with rapidly varied flow (e.g. vertical wall on a dike) the model shows sufficient robustness. In this paper the details on the SWASH model configuration and post processing methods are outlined to enable the reader to reproduce reliable wave overtopping estimation over impermeable coastal structures in shallow foreshores. [ABSTRACT FROM AUTHOR]

This paper demonstrates the capability of a new state-of-the-art flood modelling system consisting of multiple nested models to simulate urban coastal flood inundation. A flood event in Cork City, Ireland which occurred in November 2009 is analysed in detail. The new flood modelling system comprises of two dynamically linked models: an ocean model (POM) of the northeast Atlantic (ca. 5 km grid) and a coastal flood model, MSN_Flood, which resolves the hydrodynamics of Cork Harbour and its sub region at four spatial scales 90 m, 30 m, 6 m and 2 m through a cascade of four nested grids. Flood water propagation through Cork City floodplains is simulated by the 2 m grid model. The POM-MSN_Flood modelling system, presented for the first time in this paper, was used to investigate the dynamics of coastal flooding resulting from a complex set of tides, storm surges, rivers inflows and the interactions between them. Unlike many flood models, the modelling system used in this research provides a full description of water levels and flow regimes, both in coastal waters and urban floodplains. Validation results clearly demonstrate that the model is capable of resolving hydrodynamics at scales commensurate with flow features including the large scale processes of the NE Atlantic Ocean and the fine resolution circulation of coastal waters. With regards to urban flooding, the model was found to accurately determine flood wave propagation patterns, flood wave heights, speeds and inundation extents. Ultimately, the model was used to investigate mechanisms of flooding resulting from multiple process drivers and to assess flood risk to human safety. Such an analysis facilitates better understating of the mechanics and dynamics of complex coastal urban flooding and would therefore be of interest in the field of coastal management. [ABSTRACT FROM AUTHOR]

Will coastal towns survive the rising pressure, or better, the rising sea level in future decades? Waves overtop dikes, and the overtopping flow on the crest of the dike can cause damage. Wave impacts from these overtopping flows already became of interest in coastal engineering the past few years, but very little literature and almost no design formulae are available yet for irregular waves. This paper gives such design formulae for practical use. Experimental modeling at three different scales (small, middle and large scale) has been carried out to measure such impacts. The tested geometry was a smooth sloping dike (only non-breaking waves) with a promenade at crest level and a storm wall at the end of this promenade. The outcome of this paper are three methodologies to a) calculate wave impact forces on such a storm wall as a function of the hydraulic parameters; b) determine the (Weibull) distribution of all impacts in one test, with the shape and scale parameters also linked to the hydraulic parameters; and c) to provide an indirect approach to calculate the impact forces on the storm wall. In this last approach, the (distribution of the) individual overtopping waves are linked to the (distribution of the) overtopping flow parameters, which are then linked to the (distribution of the) impact forces. Finally, the empirical formulae from the aforementioned three methodologies are compared; analogies and differences are discussed, and guidance is provided to design storm walls against post overtopping impact forces. Results show that forces from waves overtopping the dikes are in the order of 20 to 40 kN/m prototype scale in the dimensionless freeboard (R c /H m0 ) range of 1 to 2. This is (much) lower compared to impact forces on vertical walls as calculated by the Shore Protection Manual. [ABSTRACT FROM AUTHOR]

Knowledge of the incident and reflected waves present in laboratory experiments is a key issue in order to correctly assess the behaviour of the tested structure. Usual applied reflection separation algorithms are based on linear wave theory. These linear methods might result in unreliable estimates of the incident and reflected waves in case the waves are nonlinear. In the present short paper a new nonlinear reflection separation algorithm optimized for regular waves is presented. The method separates the superharmonics into bound/free and incident/reflected components. The separation in bound and free components is possible because they travel with different celerity. The new method is an extension of the Lin and Huang (2004) method as they used linear dispersion so indirectly assumed the bound waves to be of 2nd order maximum. They did thus not take into account the amplitude dispersive effect of nonlinear waves (3rd and higher order). The present method uses nonlinear wave celerity in order to overcome this limitation. It is shown in the present paper that for highly nonlinear regular waves none of the existing state-of-the-art tools are reliable. The new method showed on the other hand a good match for all of the tested synthetically generated wave conditions including shallow and deep water and proved also to be robust to noise. Even though the new method is developed for horizontal sea bed it is demonstrated to provide reasonable results on numerical data for vertical asymmetric waves on mildly sloping foreshores. [ABSTRACT FROM AUTHOR]

Tsunami are very long gravity waves that may cause significant damage to coastal sea walls. The majority of relevant design codes and research papers that describe methods for predicting tsunami loads on coastal walls consider the scenario of transitory force from a bore-led wave. This does not relate to tsunami that do not form bore waves. Bore fronts generally cause short term spikes in force, which may have little effect on the vulnerability of massive structures. Post disaster accounts suggest that most coastal walls show damage that implies failure modes that occur over moderate to long durations. Therefore it is likely that the bore front assumption gives an overly conservative prediction of maximum force, and may not capture the full timescale of tsunami loading. This paper uses a pneumatic tsunami generation facility to determine the force loading on two vertical coastal sea walls during tsunami inundation. Two sea-wall models, 0.15 and 0.25 m high, with crown widths of 0.1 m (7.5 and 12.5 m at a nominal prototype scale of 1:50) are tested. It is shown that bore fronts only occur for short period waves over the bathymetry tested. Bore fronts cause a very short period spike in force, which is followed by a transitory force approximated by the hydrostatic pressure equation. The loading of tsunami length waves of periods ≥ 40 s (280 s prototype at 1:50 scale), which do not break is not greater than 1.2 times the hydrostatic force. Overtopping volume is positively correlated to the time duration of positive upstream head over the crest, rather than its maximum value. Overtopping causes a small increase in the horizontal load due to the addition of a drag and momentum load. The magnitude and time of these effects are small and short-lived in comparison to the hydrostatic load. The results compare well with available equations based on hydrostatic force and the engineer may apply a desired multiplying coefficient of a factor of at least 1.2 to account for any added pressure and momentum, and the factor of safety intended. • Tsunami loads on vertical walls are no greater than 1.2 times the theoretical hydrostatic load. • Only shorter wave periods break and form bores; longer tsunami-length waves do not break. • Tsunami overtopping volume is related to the duration of positive head over the crest. • Tsunami overtopping applies a relatively small (against the hydrostatic load) additional horizontal force. [ABSTRACT FROM AUTHOR]

A process based assessment of the probability of failure of a flood embankment, as well as an assessment of the consequences of failure of an embankment require insights into the stresses on the landside slope of an embankment. These assessments are hindered by the empirical nature of the wave overtopping parameters. Failure initiation is often linked to an allowable mean overtopping discharge which forms the input for the overtopping volumes distribution. The high level of uncertainty associated with predicting the mean overtopping discharge therefore leads to high levels of uncertainty in predicting wave overtopping volumes. The mean overtopping discharge is thereby not directly related to run-up parameters. This paper addresses these issues by presenting new distributions for the velocity, discharge, depth, volume, and shear stresses at the crest for those waves that overtop which have been derived from the wave run-up parameters. The proposed distributions are independent on the mean wave overtopping discharge and the large inaccuracies associated with predicting this. The proposed method has the added benefit of being able to express overtopping parameters in terms of each other. The paper also provides a method for determining the change in these random overtopping values along the landside slope, thereby facilitating a direct comparison between wave overtopping events and overflow events. [ABSTRACT FROM AUTHOR]

The objective of this paper is to compare two methodologies adopted in the context of long-terms statistics: Equivalent Triangular Storm (ETS) and Peak Over Threshold (POT), applied both with the Goda model and with the Generalized Pareto Distribution. Both methodologies are currently used for conducting long-term statistics oriented to the determination of relevant input parameters adopted in the design of coastal structures. The paper proposes a dissemination of the key characteristics of the methods and elucidates the fundamental steps necessary for mechanizing the methods starting from available wave data. Then, it discusses numerical results pertaining to both Mediterranean and Ocean data. In this context, the paper focuses on the stability of the methods with respect to the (subjectively) selected storm thresholds. It shows that the ETS method is more stable than the POT. Results pertain to both omnidirectional and directional return values. [ABSTRACT FROM AUTHOR]

An experimental study of periodic waves interacting with near-orthogonal turbulent currents is presented in this paper. Mean velocity profiles for current-alone, wave-alone and combined wave–current flows are measured with Acoustic Doppler Velocimeters to resolve the changes in mean flow kinematics due to wave–current interaction. In this study, the near-bottom wave orbital velocity is approximately 1.5 times greater than the depth-averaged current velocity, and the log-profile method is used to determine the bottom roughness from the measured velocity profiles. The primary focus is on 90° wave–current interaction, while selected findings for 60° and 120° wave–current orientations are also presented. In the smooth bed experiment, the interaction is shown to be linear due to the relatively low Reynolds-number flows generated in the facility — a relatively common scenario in small-scale laboratory setups that has not received much attention in previous studies. The smooth turbulent flow equation, with modification of the input shear velocity, is found to accurately predict the mean flow roughness for linear interaction. The bottom roughness is subsequently increased with the introduction of a layer of uniform 12.5 mm marbles to achieve a more realistic rough turbulent flow regime. The results agree qualitatively with previous experimental findings that showed a reduction in the near-bottom mean velocity due to a wave-enhanced (apparent) roughness. However, the Grant–Madsen (GM) model is found to over-estimate the apparent roughness when the angle of wave–current interaction is large, implying a lack of directional sensitivity of this model under “strong-wave, weak-current” conditions. A tentative explanation of this shortcoming is given in the paper. However, it is not possible to extend the GM model analysis to the present near-orthogonal wave–current flows, as results suggest that both 60° and 120° wave–current cases are sufficiently contaminated by the wave-induced mass transport component in the current direction to invalidate the use of the log-profile method to resolve the bottom roughness. In addition to the modification of current profiles by waves, the present study also shows a drastic transformation of wave-induced mass transport profiles by the external turbulent currents. The veering of mean flow over depth is consistent with the superposition of a wave-induced return flow on the external current, while additional veering in the near-bottom region may be attributed to turbulence asymmetry induced by the current component in the direction of the near-bottom wave orbital velocity which is shown to vary locally by ± 10° due to parasitic waves emanating from the current inlet and outlet. [ABSTRACT FROM AUTHOR]