Swash Zone

The paper is devoted to the analysis of the shape of the swash edge line. Formation of the swash boundary is treated as an interfacial phenomenon. The simplest quantitative characteristic of the roughness of interface is its width w, defined as the root-mean-square fluctuation around the average position. For rough interfaces, the scaling with size of the system L is observed in the form w(L) / L f . The concept of scaling supplies a simple framework for classifying interfaces. It is suggested that the fine structure of the swash boundary results from the combined action of the pinning force applied by random defects of the beach and elasticity of distorted swash boundary. The roughness of the swash front was studied at the Mediterranean Sea coast for uprush and backwash flows. Value of exponent f for receding swash front line was 0.64 6 0.02, when in the case of advancing swash the value 0.73 6 0.03 was calculated. The scaling exponent established for the receding phase of the swash is very close to the values of the exponent established for the roughness of the triple line for water droplets deposited on rough surfaces, crack propagation front in Plexiglas, and for the motion of a magnetic domain walls. T he physics of swash, i.e. a layer of water that washes up on the beach after an incoming wave has broken, is complicated and intriguing. It includes perplexing hydrodynamic and sediment transport events 1-4 . The coastal strip is a highly dynamic zone and may include features with the dimensions ranging from microns to kilometers. Beach cusps are often arising in the swash zone presenting obstacles to the propagation of a wave front and promoting its breakdown 1-4 . In our paper, we address the roughness of the moving swash boundary at which a beach, water and air meet. The roughness of the swash edge is characterized by a scaling law that relates the statistical width w of the boundary (i.e. the root-mean-square fluctuation of the edge line around its average position) to its length L via w(L) / L f law 5-10 . We treat the behavior of this boundary as an interfacial phenomenon, without going into details of the formation of edge waves and beach cusps, covered broadly in literature 1-4 . This ''crude'' approach turns out to be productive and reveals the resemblance of the swash line to a broad diversity of effects arising from the random pinning of moving boundaries . Swash consists of two phases: uprush (onshore flow) and backwash (offshore flow). We concentrate mainly on backwash (offshore flow), when water recedes along the beach face. The receding water front is pinned by randomly distributed obstacles, produced by the beach and constituting the roughness of the swash edge line. It is plausible to suggest that the fine structure of the swash edge line results from the combined action of the pinning force applied by defects of the beach and the elasticity of the distorted swash boundary. The problem is common for a number of physical systems comprising interfaces moving in a disordered medium; for example, self-affine crack propagation 5-6 , wet front propagation and movement of interfaces between immiscible liquids in porous media , height distribution of growing surfaces , and growth of magnetic domain walls in disordered media 12 . However, the most investigated situation of interfaces moving over a disordered system of obstacles is the displacement of the triple (three-phase) line at which water, vapor and a rough (or chemically heterogeneous) surface meet . The shape of a triple line disturbed by the presence of random heterogeneities on the solid surface may be derived by a solution of the Laplace equation with the boundary conditions of the Young equation. With some simplifications, this is given by Shanahan 18 and de Gennes 19 . The simplest quantitative characteristic of an interface is its width w, defined as the root-mean-square fluctuation around an average position. For rough interfaces, scaling with size of a system L is observed, which is expressed in the form meaning that the average width w grows as the size L is increased. The concept of scaling introduced in the field of interfaces by Family and Vicsek 20,21 gave a simple framework for classifying interfaces in various processes. Scaling

This paper presents a new approach for estimating run-up on embayed beaches based on a study of the microtidal coast of Itapocorói Bay, Southern Brazil using the surf similarity parameter and wave height at break location. The four step methodology involved: 1) direct wave measurement (34 days), wave run-up measurement (19 days at 7 points within the bay), measurement of bathymetry and beach topography in the entire bay; 2) tests on available formulae to calculate wave run-up; 3) use of the SWAN spectral wave model to simulate wave parameters at breaking at each wave run-up measurement point and; 4) development of a new formula/approach to assess wave run-up on embayed beaches (in both exposed and protected areas). During the experiments the significant wave height varied from 0.5 m to 3.01 m, the mean wave period from 2.79 s to 7.76 s (the peak period varied between 2.95 s and 17.18 s), the mean wave direction from 72.5° to 141.9° (the peak direction varied from 39.2° to 169.8°) an...

Observational discoveries of coastal current structure in Ogata Coast, Japan, were summarized with respect to characteristics of wind and waves in the wave-shoaling region. The observations of flow structure under the storm condition (strong wind & high wave) showed that (1) the coastal longshore current that has a vertically uniform flow profile, was developed in the wide area of coastal zone including the surf zone, and (2) strong shear flow with undertow (offshore-going near-bottom current) was developed in the surf zone. As a generation mechanism of such flow structures, it was designated that sea surface stress was emphasized under storm condition with the energy transfer from wind to waves through whitecap dissipation of shoalkg waves. A mathematical model of whitecaps dissipation stress,z,, ,was proposed as an energy transfer interface between atmosphere and coastal ocean. Using this interface model, numerical Wind-Wave-Current System (WWC System) was established, in which the relation between wind stresses (wind field), whitecap breaker stresses (wave field) and bottom stresses (current field) were integrated. Enhancing effects of whitecap dissipation stress due to wave shoaling was also taken into consideration in the system.

This study examines the surf and swash zone dynamics of a microtidal, lowenergy, dissipative beach in Kos Island, Greece, using high-frequency optical monitoring with a Beach Optical Monitoring System (BOMS) and in situ wave measurements during the winter period. Increased wave heights induced the offshore migration of the wave-breaking zone with significant alongshore variability; however, no triggering of NOM (Net Offshore Movement) behavior was verified, while occasional rhythmic patterns were observed in the breaking location under moderate wave conditions. Shoreline dynamics showed transient erosional episodes coupled with elevated run-up excursions, yet the shoreline showed signs of recovery, suggesting a quasi-equilibrium state. Run-up energy spectra were consistently dominated by lower frequencies than those of incoming waves under both low-and high-energy conditions. This behavior is attributed to the nearshore sandbars acting as low-pass filters, dissipating high-frequency wave energy and allowing for lowerfrequency motions to dominate run-up processes. A widely used empirical wave run-up predictor corresponded well with the video observations, confirming its applicability to low-energy dissipative beaches. These results underscore the role of submerged sandbars in regulating wave energy dissipation and stabilizing beach morphology under low-tomoderate wave conditions.

The wave-dominated beach barrier of Villeneuve-Lès-Maguelone extends between Palavas and Frontignan (Gulf of Lions, northernmost Mediterranean Sea), along a slightly natural sandy protected area characterized by typical and well-expressed morphologies. In the nearshore, the sea bottom shows one or two approximately rectilinear sand bars. In 2010-2011, we performed a 6 month-long monitoring (autumn 2010/late spring 2011) of a 500 meter-long segment along this sand barrier. We used RTK D-GPS offering centimeter resolution to acquire sets of elevation data on the beach and the upper shoreface. The study is innovative because a full morphologic monitoring was performed each time the wave/ wind conditions changed significantly. These changes were tracked in real-time thanks to a set of hydrodynamic equipments deployed at sea, including well-known DREAL buoys. We identify from welldocumented data: (1) a beach reconstruction cycle at the shoreline after a moderate storm event (wave height at 3-4 m) and (2) how a sand bar in the nearshore migrates to the shoreline and drives the shoreline shift.

NUMERICAL MODELING OF SWASH ZONE MORPHOLOGICAL PROCESSES IN COARSE-GRAINED BEACHES WITH XBEACH OPEN-SOURCE MODEL
Document Type : Article

Authors

S. Maleki Taghiabad 1  M. Adjami  2  A. Ahmadi 3
1 Ph.D. candidate of Hydraulic Structures Engineering, Shahrood University of Technology, Iran

2 Assistant Professor in Coasts, Ports and Marine Structures Engineering, Faculty of Civil Engineering, Shahrood University of Technology, Iran

3 Associated Professor in Hydraulic Structures Engineering, Faculty of Civil Engineering, Shahrood University of Technology, Iran

10.24200/j30.2024.63280.3266
Abstract

The swash zone and its processes are significant in a beach system due to their considerable effects on beach hydrodynamics, morphodynamics, and ecosystems, including beach flows, aquifers, and sediment transport. Developing efficient numerical models to evaluate hydrodynamic-morphodynamic processes is essential, particularly in the swash zone. XBeach is a numerical model for beach simulations. In this regard, research gaps in this field have been considered in assessing the performance of the XBeach model based on the SB and NH modules, comparing the results of morphological process simulations, and sensitivity analysis of the results under different coastal conditions. Based on this, this research is dedicated to modeling three different laboratory models with varying hydrodynamic-morphodynamic conditions to evaluate the XBeach model's performance in simulating coarse-grained beaches' morphological processes. After calibrating and sensitivity testing the models, the results are extracted and compared with laboratory models in the numerical modeling process. The results of this research indicate that the XBeach model has an acceptable performance in modeling hydrodynamic and morphodynamic processes in the Swash region, and simulation with the NH module performs better compared to the SB module (with a reduction in modeling error of over in various models). Additionally, the results show that phase errors during water infiltration/percolation into the aquifer in XBeach lead to the expansion of numerical modeling errors in calculating changes in the seabed profile and aquifer water level.
Keywords

Swash zone  numerical modeling  beach hydrodynamics  XBeach model  gravel beaches

The aim of the present investigation is to clarify the role and evaluate the importance of air entrainment in the swash zone by carrying out a set of detailed laboratory experiments. Experiments involved generating a single, highly repeatable, large-scale, bore-driven swash event on a sand-rough impermeable beach with slope 1:10. Measurements that yield the characteristics of the entrained air, including the void fractions, bubble size and bed-parallel bubble velocity, and the hydrodynamics are obtained at five crossshore locations in the swash zone using an optical probe and a combined PIV/LIF system. The results show that two distinct bubble clouds enter the swash zone, the first is the result of local entrainment at the wave tip and the second are the remaining bubbles of the air that is entrained at the second plunge point of wave breaking before the wave starts climbing the beach. The void fractions are up to 0.20 and bubble size up to 20mm which are similar to air entrainment after wave breaking in the surf zone and deep water. Local entrainment of air continues in the swash zone, but void fractions decrease rapidly with distance up the slope and no air is present after flow reversal. Energy dissipation in the swash zone attributable to entrained air is at least of order 1% of the total energy dissipation. This is smaller than in the surf zone or deep water because of the smaller volume of entrained air and the greater total energy dissipation in the swash zone.

Boundary layer dynamics are investigated using a 2‐D numerical model that solves the Volume‐Averaged Reynolds‐Averaged Navier‐Stokes equations, with a VOF‐tracking scheme and a k ‐ ϵ turbulence closure. The model is validated with highly resolved data of dam break driven swash flows over gravel impermeable and permeable beds. The spatial gradients of the velocity, bed shear stress, and turbulence intensity terms are investigated with reference to bottom boundary layer (BL) dynamics. Numerical results show that the mean vorticity responds to flow divergence/convergence at the surface that result from accelerating/decelerating portions of the flow, bed shear stress, and sinking/injection of turbulence due to infiltration/exfiltration. Hence, the zero up‐crossing of the vorticity is employed as a proxy of the BL thickness inside the shallow swash zone flows. During the uprush phase, the BL develops almost instantaneously with bore arrival and fluctuates below the surface due to flow in...

Changes in beach morphology are frequent, varying from small to larger spatio-temporal scales, being subjected to the ever-changing hydrodynamic action. Swash zone motions have direct impact on beach morphology and are necessary parameters for appropriate coastal management and hazard mitigation. This study investigates spatiotemporal variability in swash motion and shoreline dynamics, which additionally are essential from regulatory boundaries for appropriate spatial planning of the beach zone. The traditional mapping techniques commonly lack the temporal resolution needed for accurate mapping of the swash zone dynamics. An autonomous coastal optical system was deployed at a dissipative, microtidal sandy beach (Marmari, Kos Island) and provided high-frequency hourly records of the shoreline and the wave run-up/run-down positions, simultaneously to a wave logger deployed offshore the beach. Results reveal significant variability in shoreline and wave run-up maximum, even under moderate incoming wave action. The system's automatization process is robust, capable in providing accurate morphological data, which are crucial for coastal planning.

the exception of RCP8.5 under which a moderate increase is projected towards the end of the century. The present findings indicate that the anticipated increase in extreme total water levels due to relative sea level rise (RSLR), can be further enforced by an increase of the extreme SSL, which can exceed 30 % of the RSLR, especially for the high return periods and pathway RCP8.5. This implies that the combined effect could increase even further anticipated impacts of climate change for certain European areas and highlights the necessity for timely coastal adaptation and protection measures. The dataset is publicly available under this link: . Climate change • Coastal hazard • Storm surge • Coastal inundation • Marine storms • CMIP5 * Michalis I. Vousdoukas

At plunging breakers, air bubbles are entrained at the impingement of the water jet, formed at the top of the wave, with the water free surface in front. During the present study, air bubble entrainment at a pseudo-plunging breaker was investigated at near full-scale and further experimental work studied the bubble detrainment process. Experimental observations included the generation and propagation of waves downstream of the plunge point. Experimental results highlighted a number of unsteady air-water flow patterns and emphasise high levels of aeration: i.e., depth-averaged void fraction of more than 10% next to jet impact in shallow waters. Unsteady bubble injection experiments showed a strong vortical motion induced by the rising bubbles. Altogether, the results suggest that a dominant time scale is the bubble rise time d 1 /u r , which cannot be scaled properly with an undistorted Froude model. The study contributes to a better understanding of unsteady bubble entrainment at a pseudoplunging breaker and the associated vortical circulation.

In the scope of GLOBEX HYDRALAB IV project, laboratory experiments were performed in a 110-m-long beach, with a 1/80 rigid-bottom slope. With the free-surface elevation and cross-shore velocity data, the evolution of velocity nonlinearities along the profile (shoaling, surf and swash zones) is analyzed, both for short and long waves. To better investigate the different hydrodynamic processes at work, the third-order velocity moment terms are computed, and their relative importance along the profile is evaluated, relative to breakpoint position. Short-wave skewness, short-wave variance correlation to long-wave velocity and stirring by short waves and transport by mean flow were found to be the dominant terms outside the surf zone. Inside the surf zone, stirring by both short and long waves and subsequent transport offshore by the mean flow, and skewness of short waves were found to be the main driving mechanisms. In the swash zone, where long waves dominate, the third-order velocity moment terms tend to assume positive values. A thorough analysis of swash zone data processing and hydrodynamics is carried out and some of the current limitations of such processing are unraveled.

In the scope of GLOBEX HYDRALAB IV project, laboratory experiments were performed in a 110-m-long beach, with a 1/80 rigid-bottom slope. With the free-surface elevation and cross-shore velocity data, the evolution of velocity nonlinearities along the profile (shoaling, surf and swash zones) is analyzed, both for short and long waves. To better investigate the different hydrodynamic processes at work, the third-order velocity moment terms are computed, and their relative importance along the profile is evaluated, relative to breakpoint position. Short-wave skewness, short-wave variance correlation to long-wave velocity and stirring by short waves and transport by mean flow were found to be the dominant terms outside the surf zone. Inside the surf zone, stirring by both short and long waves and subsequent transport offshore by the mean flow, and skewness of short waves were found to be the main driving mechanisms. In the swash zone, where long waves dominate, the third-order velocity moment terms tend to assume positive values. A thorough analysis of swash zone data processing and hydrodynamics is carried out and some of the current limitations of such processing are unraveled.

The present work is dedicated to the study of the swash zone bed evolution at a high temporal and spatial resolution to investigate single-wave to wave-group time scales. The measurements are obtained in a large scale wave flume with a 1/15 sloping beach of well-sorted sand (d50 = 250 m). The wave regime considered is a random Jonswap spectrum (peak enhancement factor = 3.3, significant wave height HS = 0.53 m and peak period Tp = 4.14 s). A stereoscopic technique (Astruc et al., 2012) has been used to measure the sand bed evolution in the swash zone over a 3×2 m area. This experiment allows us to capture the swash dynamics and the bottom evolution at the different temporal scales. The results prove the strong correlation between wave forcing and swash zone response over the entire experiment, even if the bottom evolves. At shorter time scales, we can observe the signature of gravity and infragravity waves. We showed that at both time scales, the erosion process exhibits a strong va...

The present work is dedicated to the study of the swash zone bed evolution at a high temporal and spatial resolution to investigate single-wave to wave-group time scales. The measurements are obtained in a large scale wave flume with a 1/15 sloping beach of well-sorted sand (d50 = 250 m). The wave regime considered is a random Jonswap spectrum (peak enhancement factor  = 3.3, significant wave height HS = 0.53 m and peak period Tp = 4.14 s). A stereoscopic technique (Astruc et al., 2012) has been used to measure the sand bed evolution in the swash zone over a 3×2 m² area. This experiment allows us to capture the swash dynamics and the bottom evolution at the different temporal scales. The results prove the strong correlation between wave forcing and swash zone response over the entire experiment, even if the bottom evolves. At shorter time scales, we can observe the signature of gravity and infragravity waves. We showed that at both time scales, the erosion process exhibits a stron...

Large-scale laboratory experiments presented in this paper involved bore-driven swash on permeable immobile coarse-grained beaches. Two different sediments were used (d 50 = 1.5 and 8.5 mm) resulting in different beach permeability and surface roughness. The experiments yielded detailed measurements of swash depth and velocities, wetting front, pressure, and groundwater levels across the swash zone. This paper is focused on the processes occurring within the beach. The measurements provide the shape of the wetting front and the groundwater table and reveal the behavior of air in the unsaturated region of the beach. Air is initially at atmospheric pressure, but the pressure builds up when air becomes encapsulated between the saturated region formed below the swash and the groundwater table. For the 1.5 mm beach, entrapped air significantly affected the water exchange between the swash and the subsurface. The considerable buildup of interstitial air pressure reduced vertical hydraulic gradients and thus infiltration rates. At the lower end of the beach the hydraulic gradients even became negative, indicating flow reversal and exfiltration. In contrast, for the 8.5 mm beach the rate of infiltration was only slightly affected by the buildup of pore-air pressure. The vertical hydraulic gradients were more than twice the magnitude of those within the 1.5 mm beach. The results presented in the paper clarify the mechanisms that drive and impede the water exchange between the surface and subsurface flow. In particular, infiltration into the initially unsaturated part of the beach and the resulting air entrapment play a significant role in swash and similar flows.

A high accuracy boundary element method is used to compute the propagation of solitary waves from a constant depth region onto a plane slope. Initial wave heights range from H/h = 0.06 to 0.775, slopes between 1:35 and 1:1.73 (30°) have been investigated. The prebreaking shoaling shows very different characteristics on gentle slopes (1:20 and less) and on steeper slopes. A diagram constructed on the basis of a large number of numerical experiments gives a simple limit between which waves break on which slopes and which not. Typical examples of the range of wave behavior are shown. Waves that do not break at run up often break during run down. The velocity fields for the two types of breaking are compared and found to be very different. A simple explanation for this is offered.

The focus of the present study was the behaviour of a bubble plume created by a circular free falling jet. The objective was to find a relation between the disturbances on the jet surface and the air entrainment process. To achieve this, the instabilities of the free falling jet were characterized and compared with the size distribution and generation rate of the bubbles created in the plume.The bubble trajectories were obtained and used to determine the jet-pool interaction after the impact.

Climate scenarios produce climate change-related information and data at a geographical scale generally not useful for coastal planners to study impacts locally. To provide a suitable characterization of climate-related hazards in the North Adriatic Sea coast, a model chain, with progressively higher resolution was developed and implemented. It includes Global and Regional Circulation Models representing atmospheric and oceanic dynamics for the global and sub-continental domains, and hydrodynamic/wave models useful to analyze physical impacts of sea-level rise and coastal erosion at a sub-national/local scale. The model chain, integrating multiple types of numerical models running at different spatial scales, provides information about spatial and temporal patterns of relevant hazard metrics (e.g., sea temperature, atmospheric pressure, wave height), usable to represent climate-induced events causing potential environmental or socio-economic damages. Furthermore, it allows the discu...

This paper reviews mainly conceptual models and experimental work, in the field and in the laboratory, dedicated during the last decades to studying turbulence of breaking waves and bores moving in very shallow water and in the swash zone. The phenomena associated with vorticity and turbulence structures measured are summarised, including the measurement techniques and the laboratory generation of breaking waves or of flow fields sharing several characteristics with breaking waves. The effect of air entrapment during breaking is discussed. The limits of the present knowledge, especially in modelling a two-or three-phase system, with air and sediment entrapped at high turbulence level, and perspectives of future research are discussed.

This paper describes studies of the bed friction factor in nonstationary free surface flow, for the specific case of bores moving in shallow water and breaking waves on beaches. Data from a set of experiments carried out in a laboratory flume, including measurements of water level displacement and fluid velocity through LDV, are used to evaluate the bottom stress and the mean flow velocity. The results of other measurement techniques in similar conditions are used to critically assess our results. It is found that the friction factor is higher and the transition from laminar to turbulent boundary layer takes place at higher Re numbers than values obtained in separate studies of turbulent bottom boundary layer including an additional source of turbulence.

Turbulence and water surface elevation measurements were carried out in the swash zone which was induced by plunging and collapsing breakers in a wave flume. Three different period regular waves were generated on a 1r10 smooth impermeable concrete beach and the water surface elevations were collected by a number of wave gauges and a run-up meter lying on the bottom. Velocity measurements were carried out by a Laser Doppler velocimeter system, at spatial steps of 1 mm from the bottom, along three vertical sections in the swash zone. The data have been used to describe the wave front dynamics, to derive the length and velocity macro and micro scales and the Eulerian frequency spectrum. In some points, it shows a double structure. The results add to and expand on similar results obtained by other researchers in the surf zone.

The paper is devoted to the analysis of the shape of the swash edge line. Formation of the swash boundary is treated as an interfacial phenomenon. The simplest quantitative characteristic of the roughness of interface is its width w, defined as the root-mean-square fluctuation around the average position. For rough interfaces, the scaling with size of the system L is observed in the form w(L) / L f. The concept of scaling supplies a simple framework for classifying interfaces. It is suggested that the fine structure of the swash boundary results from the combined action of the pinning force applied by random defects of the beach and elasticity of distorted swash boundary. The roughness of the swash front was studied at the Mediterranean Sea coast for uprush and backwash flows. Value of exponent f for receding swash front line was 0.64, when in the case of advancing swash the value 0.73 was calculated. The scaling exponent established for the receding phase of the swash is very close to the values of the exponent established for the roughness of the triple line for water droplets deposited on rough surfaces, crack propagation front in Plexiglas, and for the motion of a magnetic domain walls. w(L)!L z , ð1Þ meaning that the average width w grows as the size L is increased. The concept of scaling introduced in the field of interfaces by Family and Vicsek  gave a simple framework for classifying interfaces in various processes.

The present work analyzes the hydro-morphodynamics characterizing the swash region during the uprush stage. A comparison is illustrated between the sediment transport measured in a series of dam-break experiments and that predicted by the numerical hydro-morphodynamic model of Postacchini et al. (2012). The primary aim is to investigate the differences arising between the weakly coupled or uncoupled model and the measurements, in terms of hydrodynamics, tip celerity and sediment transport. The hydrodynamics are well described by the model and results have been used to calibrate both friction factor and subgrid turbulent viscosity. Comparison of numerically-computed tip celerity with experimental data reveals a fairly good agreement, i.e. a mean error of about 10%, while modeled sediment transport differs by about 40% from the available data. No evident differences are found between results obtained from the coupled and uncoupled model runs (2% for the celerity and 11% for the sediment transport rate at the tip), suggesting that for the specific flow under investigation, at the leading edge of the swash front, hydro-morphological coupling is not an issue of fundamental importance. However, for the special case here of a swash forced by a dam-break, scour occurs at the dam location, and in this case the erosion of the bed is significantly larger in the uncoupled model.

The objective of the proposed work is to assess the possible wind power dynamics along the European coastal environment in the context of the very predictable future development of the offshore wind energy extraction. From this perspective, 15 reference points have been selected in the Baltic, Mediterranean and Black seas, representing 5 representative locations for each sea, respectively. The proposed analysis is based on the wind fields provided by a Regional Climate Model (RCM) for the future time period 2021-2050. These data are processed and analysed considering the Representative Concentration Pathway (RCP) scenarios 4.5 and 8.5. In the first RCP scenario (4.5), an enhancement of the greenhouse gas emissions until 2040 is considered followed afterwards by a decline. On the other hand, the second scenario assumes that the greenhouse gas emissions enhancement will continue during the entire 21st century and after. The first scenario is considered as the most realistic approach, ...

Coastal imagery obtained from a coastal video monitoring station installed at Faro Beach, S. Portugal, was combined with topographic data from 40 surveys to generate a total of 456 timestack images. The timestack images were processed in an open-access, freely available graphical user interface (GUI) software, developed to extract and process time series of the cross-shore position of the swash extrema. The generated dataset of 2% wave run-up exceedence values R 2 was used to form empirical formulas, using as input typical hydrodynamic and coastal morphological parameters, generating a best-fit case RMS error of 0.39 m. The R 2 prediction capacity was improved when the shore-normal wind speed component and/or the tidal elevation η tide were included in the parameterizations, further reducing the RMS errors to 0.364 m. Introducing the tidal level appeared to allow a more accurate representation of the increased wave energy dissipation during low tides, while the negative trend between R 2 and the shore-normal wind speed component is probably related to the wind effect on wave breaking. The ratio of the infragravityto-incident frequency energy contributions to the total swash spectra was in general lower than the ones reported in the literature E infra /E inci >0.8, since low-frequency contributions at the steep, reflective Faro Beach become more significant mainly during storm conditions. An additional parameterization for the total run-up elevation was derived considering only 222 measurements for which η total,2 exceeded 2 m above MSL and the best-fit case resulted in RMS error of 0.41 m. The equation was applied to predict overwash along Faro Beach for four extreme storm scenarios and the predicted overwash beach sections, corresponded to a percentage of the total length ranging from 36% to 75%. Keywords Wave run-up. Beach dynamics. Swash zone. Nearshore waves. Video imaging of waves. Image processing Responsible Editor: Michel Rixen This article is part of the Topical Collection on Maritime Rapid Environmental Assessment

Four examples of air-entraining flows at the free surface of a liquid are briefly considered: (a) the transient impact of a jet, (b) the application of an excess pressure, (c) two counter-rotating vortices below the surface, and (d) a disturbance on a vortex sheet.

The bay of Port-Bouët is threatened by extreme sea level (ESL) events, which result from the combination of storm tide, wave runup and sea level rise (SLR). This study provides comprehensive present-day and future ESL elevation scenarios at local scale along the bay, to understand the evolution of the phenomenon and promote adaptation at neighbourhood level. The methodological steps involve firstly, a reconstruction of historical storm tide and wave runup data using respectively a hydrodynamic model (D-flow FM) and the empirical model of Stockdon et al. Secondly, the generalised pareto distribution (GPD) model fitted to the peaks-over-thresholds (POT) method is applied on the data to calculate their extreme return values. Thirdly, we combine extreme storm tide and wave runup through the joint probability method to obtain present-day ESLs. Lastly, the present-day ESLs are integrated with the recent SLR projection to provide ESL estimates for the years 2030, 2050 and 2100. Results sho...

Global warming is expected to drive increasing extreme sea levels (ESLs) and flood risk along the world's coastlines. In this work we present probabilistic projections of ESLs for the present century taking into consideration changes in mean sea level, tides, wind-waves, and storm surges. Between the year 2000 and 2100 we project a very likely increase of the global average 100-year ESL of 34-76 cm under a moderate-emission-mitigation-policy scenario and of 58-172 cm under a business as usual scenario. Rising ESLs are mostly driven by thermal expansion, followed by contributions from ice mass-loss from glaciers, and ice-sheets in Greenland and Antarctica. Under these scenarios ESL rise would render a large part of the tropics exposed annually to the present-day 100-year event from 2050. By the end of this century this applies to most coastlines around the world, implying unprecedented flood risk levels unless timely adaptation measures are taken.

This paper proposes a method to infer the future change in the wind-wave climate using reanalysis wind corrected to statistically match data from a regional climate model (RCM). The method is applied to the sea surface wind speed of the reanalysis ERA5 from the European Centre for Medium-Range Weather Forecasts. The correction is determined from a quantile mapping between ERA5 and the RCM at any given point in the geographical space. The issues that need to be addressed to better understand and apply the method are discussed. Corrected ERA5 wind fields are eventually used to force a spectral wave numerical model to simulate the climate of significant wave height. The correction strategy is implemented over the Adriatic Sea (a semi-enclosed basin of the Mediterranean Sea) and includes the present-day period (1981–2010) and the near-future period (2021–2050) under the two IPCC RCP4.5 and RCP8.5 concentration scenarios. Evaluation against observations of wind and waves gives confidence...

Climate change is likely to increase the pressure on the environment and on human systems that are requiring new assessment tools aimed at supporting decision-makers and stakeholders towards a more sustainable and effective management of the coastal environment and its resources. This research appraises an ensemble of models that integrates complex interactions of climate and anthropogenic impacts on vulnerable Mediterranean coastal areas with application to the Gulf of Gabes, Tunisia. Starting from Global and Regional Circulation Models, the models' ensemble includes simulations of marine and atmospheric dynamics and biogeochemical processes in coastal waters under expected anthropogenic forcings, with a spatial domain ranging from subnational to local. In the case study area, the simulations showed that atmospheric temperature increase is likely to be around 4°C in the summer months of 2100, relative to 1961-1990. In order to obtain the most reliable estimate of sea-level rate variations, satellite altimetry data have been processed over a period of 15 years (1993-2007) showing that sea-level changes on the Tunisian shelf were of the order of 2 mm/ year. This value was considered as a reference for the sealevel change scenarios. As far as the water quality is concerned, the areas most impacted by pollution are located near major towns and human infrastructures, such as harbours. The set of results obtained by the proposed models' ensemble may be suitable for supporting a scientific dialogue with stakeholders and for the implementation of exposure scenarios supporting a regional risk assessment approach to the entire Gulf of Gabes area. Keywords Models' ensemble Á Model simulations Á Gulf of Gabes Á A1B climate change scenario Á Present climate scenario Electronic supplementary material The online version of this article (

This theoretical study extends Fuhrboter's work and includes the effects of air bubble entrainment. Result shows that there is a correlation between the sudden reductions of wave height and entrained of air bubbles into the water. Moreover, the study reveals that air entrainment occurs very short way in plunging breakers comparatively to spilling breakers.

A 2D laser-scanner was deployed at the high tide runup limit of a pure gravel beach (Loe Bar, Cornwall, England) to measure high-frequency (2.5 Hz) swash hydrodynamics and topographic changes during an energetic wave event. Measurements performed with the laser-scanner were corrected to compensate for levelling and orientation errors, and a variance threshold was applied to separate the beach topography from the water motions. Laser measurements were used to characterise the swash hydrodynamics and morphological changes during one tidal cycle through the calculation of several parameters, such as the 2% exceedence of the runup maxima (R 2%), swash flow velocity skewness (< u 3 >), runup spectra and cumulative topographic changes. Results indicate that despite the small net morphological changes over the tide cycle, significant sediment mobilization occurs. A clear asymmetrical morphological response was found during the different tidal phases: the rising tide is dominated by accretion whilst the falling tide is dominated by erosion. The main factor controlling this asymmetrical morphological response is the step migration that, depending on the tide phase, controls the wave breaking point and consequently the dominant sediment transport direction. During the rising tide, step development decreases the shoreface slope and reduces the runup energy, whilst during the falling tide the step remobilization increases the shoreface slope and energy on the runup.

Topographic surveys are used to assess response characteristics of eight gravel beaches to storm conditions across the south of England. Using profile volumes, pre- and post-storm, from surveys undertaken within a short temporal interval a quantitative assessment of beach response to corresponding wave conditions has been undertaken. Wide disparity in site response is found with contrasting accretionary and erosive behaviour observed un-correlated with nearshore hydrodynamics. In addition predictive runup corresponds poorly with measured effective runup.

A 2D laser-scanner was deployed on four different coarse-grained beaches (Chesil, Loe Bar, Hayling Island and Seascaleall in UK) to measure the swash morphodynamics during energetic wave conditions (offshore Hs > 2m). Field observations performed with the laser-scanner showed that different types of coarse-grained beaches present contrasting morphological responses under energetic hydrodynamics. The surf scaling parameter, a proxy of the morphological condition and wave steepness on the swash, showed an inverse relationship with the extreme vertical runup illustrating that runup is enhanced by low steepness swell waves for a given coarse-grained beach\slope; nevertheless additional parameters are needed to explain the entire runup variability.

Beach cusps are a common feature of steep reflective and intermediate beaches. Although many observations of beach cusp spacing exist, there are few observations quantifying the incipient formation, evolution and eventual destruction of these features. Beach cusp morphodynamics were analyzed using a 3-year dataset of video images collected at Tairua Beach (New Zealand). Twenty-four beach cusp episodes were selected to monitor the cycle of beach face changes, from planar to the appearance of the cusp patterns and back to planar again. Observations show that beach cusp disappearance can be ascribed not only to the erosive influence of storms but also to the persistence of accretionary conditions leading to the infilling of beach cusp bays and the development of an alongshore continuous berm. We also report observations of changes in beach cusp spacing over time which can be attributed to the merging of adjacent cusps within the cusp field, with the overall cusp spacing readjusting to accommodate the disappearance of a horn. Although the selforganization theory provides a better fit to the data and theory, we were unable to conclusively refute any of the mechanisms causing beach cusp formation since both existing theories, subharmonic standing edge wave and self-organization, can predict the trend in the observed beach cusp spacing. These observations show that initial beach cusp formation primarily occurs (around 70% of the episodes analyzed) under mildly accretionary conditions and, when accretion persists, the pattern disappearance is likely to occur as a result of bay infilling to form a featureless berm.

The hydrodynamics in the swash zone significantly affected the sediment transport mechanisms that mostly control beach face morphology especially under different weather conditions. Rainfall distribution patterns during dry and wet seasons in Peninsular Malaysia will influence groundwater table elevation and the beach profile. This study is aimed at investigating the effects of seasonal variations to beach groundwater elevations and surface profile changes. This work was undertaken at the Desaru Beach, Johor. Rainfall depth, groundwater table, tides, beach profiles, swash depth and swash velocity data were monitored and investigated at the study area. The results showed that the groundwater table was affected by rainfall patterns; higher during the wet season and lower during the dry season. The beach profile also showed erosive condition due to increasing of offshore sediment transport during the wet season, whereas in the dry season the beach profile showed accretion condition due to the increasing of onshore sediment transport. Swash properties like swash water depth and velocity were also monitored and analysed during this study in order to get a clear view about the saturation level effect due to seasonal variations into a infiltration processes at the swash zone. Finally the data showed that there is a lag time between rising and falling of groundwater tables and tides due to the lower hydraulic conductivity effect.

Plunging breakers could induce one of the most devastating forces on an offshore structure. As compared to non-breaking wave, a plunging breaker would induce an additional slamming load on an offshore structure. Current industry guidelines for design breaking wave slamming coefficient do not take into account of the geometric cross section of the offshore structures and the breaking wave parameters. The slamming load is affected by a few factors; the capability of the structure to entrap air upon the onset of plunging breakers, breaking wave parameter-rise time, just to name a few. This research paper attempts to expand the correlation of the slamming load coefficient to the geometric cross section of the section and the rise time of the impact breaking wave. It was found out that the geometrical cross section of cylinders do have significant impact on the slamming coefficient. The rise time of the plunging breaker does have an impact on the slamming load itself, but the impact the rise time had on the slamming coefficient is indistinctive.

This paper describes studies of the bed friction factor in nonstationary free surface flow, for the specific case of bores moving in shallow water and breaking waves on beaches. Data from a set of experiments carried out in a laboratory flume, including measurements of water level displacement and fluid velocity through LDV, are used to evaluate the bottom stress and the mean flow velocity. The results of other measurement techniques in similar conditions are used to critically assess our results. It is found that the friction factor is higher and the transition from laminar to turbulent boundary layer takes place at higher Re numbers than values obtained in separate studies of turbulent bottom boundary layer including an additional source of turbulence.

The hydrodynamics in the swash zone significantly affected the sediment transport mechanisms that mostly control beach face morphology especially under different weather conditions. Rainfall distribution patterns during dry and wet seasons in Peninsular Malaysia will influence groundwater table elevation and the beach profile. This study is aimed at investigating the effects of seasonal variations to beach groundwater elevations and surface profile changes. This work was undertaken at the Desaru Beach, Johor. Rainfall depth, groundwater table, tides, beach profiles, swash depth and swash velocity data were monitored and investigated at the study area. The results showed that the groundwater table was affected by rainfall patterns; higher during the wet season and lower during the dry season. The beach profile also showed erosive condition due to increasing of offshore sediment transport during the wet season, whereas in the dry season the beach profile showed accretion condition due to the increasing of onshore sediment transport. Swash properties like swash water depth and velocity were also monitored and analysed during this study in order to get a clear view about the saturation level effect due to seasonal variations into a infiltration processes at the swash zone. Finally the data showed that there is a lag time between rising and falling of groundwater tables and tides due to the lower hydraulic conductivity effect.

The beach is a complex system area where many natural and anthropogenic factors may influence the coastal processes. These processes include erosion and accretion, which may pose a significant problem. Understanding their causes is, therefore, essential not only for researchers but also the community, especially in mitigating the effects of monsoons and executing coastal development plans. Hence, this study tried to understand the natural impact and changes at a coastal stretch in Terengganu, Malaysia, which was affected by the Northeast Monsoon. This study determined the profile of four beaches on the stretch through cross-shore transects in monthly intervals. Beach surface sediment samples were also collected at four sampling stations facing several islands off the coast for particle size analysis. Besides that, the significance of the wave height was illustrated. Most beaches where the sampling stations were located had been affected by erosion. However, some did experience accretion during the Northeast Monsoon. The sediment sizes ranged from very coarse to fine sand. The beach morphology changes were essential in executing coastal management plans. Therefore, this study could provide clearer information for future coastal developments, especially in beaches along Terengganu.

A continued increase in the popularity of surfing, coupled with the potential for adverse impacts by coastal construction projects on favored surfbreaks, has recently confronted engineers with the problem of defining and quantifying a &#39;good&#39; surfbreak. A rudimentary analysis of surfing mechanics demonstrates that conditions can be examined in terms of the joint statistical climate of 1) breaker peel rate, and 2) attainable board speed as characterized by the Irribarren Number. Assuming a planar beach and using linear wave theory, two theoretical models for the joint probability density of peel rate and Irribarren Number can be used to appraise short-term surfing conditions. Results indicate that the shortcrested character of real waves plays a primary role in enhancing surfbreak. For practical calculations of longterm surfing climate at specific sites, offshore wave gage data can be transformed across a measured beach profile to predict breaker conditions in the outer surf z...

Large-scale laboratory experiments presented in this paper involved bore-driven swash on permeable immobile coarse-grained beaches. Two different sediments were used (d 50 = 1.5 and 8.5 mm) resulting in different beach permeability and surface roughness. The experiments yielded detailed measurements of swash depth and velocities, wetting front, pressure, and groundwater levels across the swash zone. This paper is focused on the processes occurring within the beach. The measurements provide the shape of the wetting front and the groundwater table and reveal the behavior of air in the unsaturated region of the beach. Air is initially at atmospheric pressure, but the pressure builds up when air becomes encapsulated between the saturated region formed below the swash and the groundwater table. For the 1.5 mm beach, entrapped air significantly affected the water exchange between the swash and the subsurface. The considerable buildup of interstitial air pressure reduced vertical hydraulic gradients and thus infiltration rates. At the lower end of the beach the hydraulic gradients even became negative, indicating flow reversal and exfiltration. In contrast, for the 8.5 mm beach the rate of infiltration was only slightly affected by the buildup of pore-air pressure. The vertical hydraulic gradients were more than twice the magnitude of those within the 1.5 mm beach. The results presented in the paper clarify the mechanisms that drive and impede the water exchange between the surface and subsurface flow. In particular, infiltration into the initially unsaturated part of the beach and the resulting air entrapment play a significant role in swash and similar flows.

A 2D laser-scanner was deployed at the high tide runup limit of a pure gravel beach (Loe Bar, Cornwall, England) to measure high-frequency (2.5 Hz) swash hydrodynamics and topographic changes during an energetic wave event. Measurements performed with the laser-scanner were corrected to compensate for levelling and orientation errors, and a variance threshold was applied to separate the beach topography from the water motions. Laser measurements were used to characterise the swash hydrodynamics and morphological changes during one tidal cycle through the calculation of several parameters, such as the 2% exceedence of the runup maxima (R 2%), swash flow velocity skewness (< u 3 >), runup spectra and cumulative topographic changes. Results indicate that despite the small net morphological changes over the tide cycle, significant sediment mobilization occurs. A clear asymmetrical morphological response was found during the different tidal phases: the rising tide is dominated by accretion whilst the falling tide is dominated by erosion. The main factor controlling this asymmetrical morphological response is the step migration that, depending on the tide phase, controls the wave breaking point and consequently the dominant sediment transport direction. During the rising tide, step development decreases the shoreface slope and reduces the runup energy, whilst during the falling tide the step remobilization increases the shoreface slope and energy on the runup.