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Most existing sediment transport formulae to estimate transport rate in the coastal environment have a restricted range of applicability and are often used beyond this range. The aim of this paper is to investigate the limits of five of these formulae: the Bijker, Bailard, Van Rijn, Dibajnia and Watanabe, and Ribberink formulae. The sensitivity of these formulae to wave orbital velocity, wave period, wave asymmetry, sediment grain size, and steady current has been studied and tested against data for large velocities where significant errors can appear. The formulae behave in very different ways if one of the main parameters is slightly modified, particularly when fine sediments are present and phase-lag effect appears. But important discrepancies between formulae can also be observed for medium sand. At last, the wave-related sediment transport (due to wave asymmetry) has great importance for the morphodynamic and is only accounted for in the Bailard, Dibajnia and Watanabe, and Ribberink formulae. [Copyright &y& Elsevier]

Measurements of the longshore sediment transport rate (LSTR) along the surf zone at a 4-km-long beach on the central west coast of India were made over a 4-month period. During the study, both the lateral and vertical distributions of the sediment transport rate were measured with traps deployed on a line spanning the surf zone. Sediment transport in the swash zone was not considered in the present study. The longshore current was measured at each trap location. The breaking wave parameters were calculated from a directional wave buoy at 16-m water depth. The measured values were compared with those calculated from three selected empirical formulas. The standard coefficient values in the empirical formulas were used without calibration to the data sets. The measured average gross transport was 726 m3/day and that calculated were 1108, 1017, and 781 m3/day based on CERC, Walton and Bruno, and Van Rijn formula. During the data collection 69% of the time, the transport was direct towards north, and in the remaining period, it was direct towards south. The correlation coefficient between the longshore sediment transport rates measured and those calculated by CERC, Walton and Bruno, and Van Rijn formula were 0.38, 0.71, and 0.74, respectively. The average RMS error between the measured and the calculated longshore sediment transport rate based on CERC, Walton and Bruno, and Van Rijn formula were 0.91, 0.57, and 0.47. [Copyright &y& Elsevier]

Morphodynamic modeling is employed in the present work to predict the long-term evolution (over the next 100 years) of typical sedimentary coasts in the western Russian Arctic. The studied objects are the coasts of Varandey (the Barents Sea), Baydaratskaya Bay and Harasavey (the Kara Sea). The model developed takes into account both the short-term processes (storm events) and long-term factors (for example, changes in sea level, inter-annual variations in gross sediment flux, lack or excess of sediment supply). Predicted and observed morphological changes in coastal profiles are shown to agree well for time scales ranging from weeks to decades. It is revealed that under given environmental conditions, the morphological evolution is strongly influenced by storm surges and associated wind-driven circulation. The water level gradient created by a surge generates a seaward flow at the bed. This outflow is shown to be an important destructive mechanism contributing to the erosion and recession of Arctic coasts. The rate of change is found to depend on both the exposure of the coast (relative to the direction of dominant winds) and its height above the sea. The open coast of Varandey is expected to retreat as much as 300–500 m over 100 years, while recession of the less exposed coasts of Baydaratskaya Bay would not exceed about 100 m/century. If long-term sediment losses are insignificant, the rate of erosion decays with time and the morphodynamic system may tend toward equilibrium. It is concluded that the expected relative sea-level rise (up to 1 m over the nearest 100 years) is non-crucial to the future coastal evolution if an erosion activity is already high enough. [Copyright &y& Elsevier]

A previously published wave-averaged version of Bailard''s sediment transport formulation, intended for use in a numerical model of shelf sand transport, is compared against available field observations from literature. The objective was to test the performance of the transport relation over the wide range of hydrodynamical conditions that can occur at sea. A modified data analysis method was used to assess the reliability of the field observations. The modification consists of a method to cluster the data into classes to enable statistical analysis. The sediment transport formulation is part of the classification method. The method is in principle also suitable to reduce the size of data sets of non-cohesive sediment transport obtained with modern electronic equipment. The results show that the quality of the published field observations is fair, and that the wave-averaged Bailard formulation performs well for low and medium transport regimes in both currents and waves. For those conditions, it yields a slight overprediction of the transports, and a nearly uniform behaviour as a function of the conditions. The formulation underestimates transport rates for very high flow velocities in absence of waves, which is in agreement with earlier findings. The present version of Bailard''s wave averaged sediment transport formulation is suitable for computing the local transport rates of fine to coarse sand on continental shelves in conditions ranging from small currents to moderate currents combined with non-breaking waves. [Copyright &y& Elsevier]

A simple method is provided for calculating transport rates of not too fine (d50≥0.20 mm) sand under sheet flow conditions. The method consists of a Meyer-Peter-type transport formula operating on a time-varying Shields parameter, which accounts for both acceleration-asymmetry and boundary layer streaming. While velocity moment formulae, e.g.., Qs=Constant×u∞3, calibrated against U-tube measurements, fail spectacularly under some real waves (Ribberink, J.S., Dohmen-Janssen, C.M., Hanes, D.M., McLean, S.R., Vincent, C., 2000. Near-bed sand transport mechanisms under waves. Proc. 27th Int. Conf. Coastal Engineering, Sydney, ASCE, New York, pp. 3263–3276, Fig. 12), the new method predicts the real wave observations equally well. The reason that the velocity moment formulae fail under these waves is partly the presence of boundary layer streaming and partly the saw-tooth asymmetry, i.e., the front of the waves being steeper than the back. Waves with saw-tooth asymmetry may generate a net landward sediment transport even if u∞3=0, because of the more abrupt acceleration under the steep front. More abrupt accelerations are associated with thinner boundary layers and greater pressure gradients for a given velocity magnitude. The two “real wave effects” are incorporated in a model of the form Qs(t)=Qs[θ(t)] rather than Qs(t)=Qs[u∞(t)], i.e., by expressing the transport rate in terms of an instantaneous Shields parameter rather than in terms of the free stream velocity, and accounting for both streaming and accelerations in the θ(t) calculations. The instantaneous friction velocities u*(t) and subsequently θ(t) are calculated as follows. Firstly, a linear filter incorporating the grain roughness friction factor f2.5 and a phase angle ϕτ is applied to u∞(t). This delivers u*(t) which is used to calculate an instantaneous grain roughness Shields parameter θ2.5(t). Secondly, a constant bed shear stress is added which corresponds to the “streaming related bed shear stress” −ρ(u˜w˜)∞. The method can be applied to any u∞(t) time series, but further experimental validation is recommended before application to conditions that differ strongly from the ones considered below. The method is not recommended for rippled beds or for sheet flow with typical prototype wave periods and d50<0.20 mm. In such scenarios, time lags related to vertical sediment movement become important, and these are not considered by the present model. [Copyright &y& Elsevier]

To determine the effects of grain size and density gradation in oscillatory sheet-flow, experiments are conducted in an oscillating water tunnel. A formal derivation of a schematised transport model shows that the transport rates per sediment fraction can be determined with and without the assumption of an active layer. A technique that measures sediment composition from natural occurring radionuclides is used to determine the transport rates without that assumption of an active layer. The measurements on total sediment transport rates and suspended sediment concentrations show that effects of gradation are present. The effects of size gradation are mainly in the increased transport rates of the coarse fraction with respect to the uniform coarse material and the availability at the bed under similar conditions. The experiments on density graded sediments indicate that total mass-transport rates are larger than the mass-transport rates of quartz material, whilst the transport rates of the quartz fraction show that this fraction is not hindered by the availability at the bed. [Copyright &y& Elsevier]

Temporal and spatial variations of surf-zone currents and suspended sediment concentrations were investigated at the U.S. Army Engineer Research and Development Center''s Large-scale Sediment Transport Facility (LSTF). A longshore-uniform fine-sand beach, 35 m alongshore, 20 m cross-shore, and 25 cm thick was placed in the facility for these experiments. Two unidirectional, long-crested irregular wave conditions were examined, one resulted in predominantly spilling breakers and one in plunging breakers. Waves and currents, and sediment concentrations were measured at 20 and 16 Hz, respectively, at various longshore and cross-shore locations and throughout the water column. Both currents and sediment concentrations exhibit great temporal and spatial variations in the surf zone. The variation patterns, however, of the longshore current, cross-shore current, and sediment concentration are substantially different. Caution should be exercised when averaging these parameters over time and space.For the two wave cases examined, the temporal variations of longshore current, including those at principal incident-wave frequencies, were relatively small across most of the surf zone. Over 70% of the variations are within approximately ±60% of the mean value. The wave motion, with a strong peak at principal incident-wave frequencies, dominated the temporal variations of cross-shore current. Temporal variations of suspended sediment concentration under the irregular waves were episodic, characterized by occasional large values induced by suspension events or due to horizontal advection. The variance of the concentration at the peak incident-wave frequency was not significant except very near the bed.Time-averaged longshore-current profiles over the predominantly rippled sand bed were logarithmic in shape below the wave trough. Depth-averaged longshore current (excluding the portion of water column above wave trough) matched well with the current measured at an elevation of 1/3 of the water depth from the bed. Time-averaged cross-shore current profiles were characterized by an onshore mass flux near the surface, and a balancing offshore flow below the wave-trough level (undertow). Sediment concentration decreased very rapidly upward through the water column across most of the surf zone except at the plunging breaker line where relatively homogeneous concentration was measured throughout much of the water column above 4 cm from the bed. Depth-averaged sediment concentration over the range from 1 cm above the bed to the bottom of wave trough roughly equaled the concentration measured at an elevation from the bed equal to 20% of the still-water depth.A reasonable estimate of the time-averaged longshore sediment flux was obtained from the product of time-averaged profiles of longshore current and sediment concentration. Accurate estimates of time-averaged cross-shore sediment flux, however, could not be obtained from the product of time-averaged current and concentration. [Copyright &y& Elsevier]

A combination of remote sensing, field surveys and sedimentological analysis of beach sands is used to assess changes of the shorelines consequent to the construction of a harbour at Damietta on the Nile Delta. The results indicate that harbour construction, and, in particular, the construction of two jetties that extend out from the harbour entrance, have created a discontinuity in the eastward-moving littoral drift. Imagery from Landsat Thematic Mapper provides crude assessments of the rate of up-drift accretion and down-drift erosion of the shorelines, despite the relatively coarse pixel size (30 m) and short time-scale of the monitoring period (1984–1987–1991). Conventional bathymetric surveys highlight changes in the nearshore environment associated with the growth of the updrift accretionary wedge and siltation of the harbour access channel. Beach sediments also provide a record of the changes in erosion and accretion-dominated process domains on both sides of the harbour entrance. The accretionary beaches west of the western jetty having a finer mean grain size with a tendency to poorer sorting skewed to the finer fraction and preferential increase in the assemblage of low-density non-opaque heavy minerals. The beach sands of the erosional shoreline east of the eastern jetty are characterised by coarser mean grain size with a tendency to better sorting skewed to the coarser fraction and heavy mineral assemblages dominated by opaques and high-density non-opaques. The synergistic use of remote sensing, bathymetric surveying and sedimentology provides evidence that changes have affected a much larger area than predicted at the time of harbour construction. [Copyright &y& Elsevier]

Sheet flow corresponds to the high velocity regime when small bed ripples are washed out and sand is transported in a thin layer close to the bed. Therefore, it is often assumed that sand transport in oscillatory sheet flow behaves quasi-steady: time-dependent transport rates are assumed to be instantaneously related to the near-bed orbital velocity. However, new experimental results show that even in sheet flow, phase lags between sediment concentration and near-bed velocity can become so large that they lead to a reduction of the net (wave-averaged) transport rate. A phase lag parameter is defined, which shows that phase lags become important for fine sand, high velocities and short wave periods. A semi-unsteady model is developed that includes the effects of phase lags on the net transport rate.New experiments were carried out in a large oscillating water tunnel with three different sands (D50=0.13, 0.21 and 0.32 mm) for a range of prototype, combined wave–current flow conditions. Measured net transport rates were compared with predictions of a quasi-steady model and the new semi-unsteady model. This comparison indicates that net transport rates are reduced if phase lags become important: the quasi-steady model overestimates the net transport rates and the semi-unsteady model gives better agreement with the data. Time-dependent measurements of velocities and concentrations show that the reduced net transport rates can indeed be explained by phase lag effects, because for tests with smaller net transport rates than predicted by the quasi-steady model, considerable phase lags between velocities and concentrations were observed, even inside the sheet flow layer. Verification of the semi-unsteady model against a larger data set confirms the occurrence of phase lag effects in oscillatory sheet flow. Also for the larger data set the semi-unsteady model yields better agreement with the data than the quasi-steady model. [Copyright &y& Elsevier]

A series of model intercomparisons, and model comparisons with field data, was carried out as part of the EU MASTIII SEDMOC Project (1998–2001). Initially, seven ‘research’ models were intercompared over a wide range of wave and current conditions, corresponding to both plane and rippled sand beds. These models included both one-dimensional vertical (1DV) formulations, varying in complexity from eddy viscosity and mixing length models to a full two-phase flow formulation, and also 2DV formulations capable of representing vortex shedding above sand ripples. The model results showed greatest convergence for cases involving plane beds, with predicted sand transport rates agreeing to well within an order of magnitude, and greatest divergence for cases involving rippled beds. A similar intercomparison involving (mainly) practical sand transport models, carried out over wide wave and current parameter ranges, also showed greatest variability in cases involving rippled beds. Finally, (mainly) practical models were compared with field data obtained at five contrasting field sites. The results showed that suspended sand concentrations in the bottom metre of the flow were predicted within a factor of 2 of the measured values in 13% to 48% of the cases considered, and within a factor of 10 in 70% to 83% of the cases, depending upon the model used. Estimates of the measured longshore component of suspended sand transport yielded agreement to within a factor of 2 in 22% to 66% of cases, and within a factor of 10 in 77% to 100% of cases. The results suggest that, at the present stage of research, considerable uncertainty should be expected if untuned models are used to make absolute predictions for field conditions. The availability of some measurements on site still appears to be a necessary requirement for high-accuracy sand transport predictions. However, for morphological modellers, the results may be viewed as more encouraging, since many of the present models exhibit agreement in their relative behaviour over wide ranges of wave and current conditions, which is a prerequisite to obtaining correct morphodynamic predictions. [Copyright &y& Elsevier]

A coastal area morphological modelling system is used to investigate the planform development (tombolo or salient) behind a single surface-piercing detached breakwater. A quasi three-dimensional (Q3D) description of the flow and the sediment transport, together with a revised bed level update scheme, were incorporated recently in the morphological modelling suite applied in the present investigation. The Q3D sediment transport formulation used allows simulating beach profile evolution and planform development simultaneously. Several breakwater layouts were investigated in a series of tests, in which the incident wave condition was taken as constant in time. The investigation was done for surface-piercing, shore-parallel breakwaters in a non-tidal environment. The morphological simulation results for the planform shape agree qualitatively with field observations and predictions from empirical rules. Using the simulation results, simple design curves for surface-piercing breakwaters are derived.The importance of properly accounting for the influence of wave diffraction when modelling sediment transport and morphology in the vicinity of shore-parallel structures is also investigated.The present paper summarises much of the work performed at DHI Water & Environment over the past 10 years within the field of coastal area morphological modelling. [Copyright &y& Elsevier]

The dominant hydrodynamic forcing and resulting sediment transport mechanisms in the swash zone are reviewed, combined with a discussion of future measurement and modelling requirements. The importance of swash zone processes in the overall behaviour of the nearshore littoral zone are identified, with the paper subsequently focusing on aspects that directly relate to sediment transport on beaches. The review considers analytical and numerical modelling work, and both field and laboratory data. The hydrodynamics of the swash zone are first discussed with reference to the surf zone boundary, swash characteristics, forcing mechanisms and shoreline oscillations. Subsequent sections consider more micro-scale processes such as the internal flow kinematics, turbulence, the bed boundary layer and infiltration/exfiltration through permeable beds. The second part of the paper outlines the fundamental mechanics of sediment transport in the swash zone, followed by a more detailed discussion of sediment transport modes induced by the dominant hydrodynamic conditions. Modelling concepts are reviewed, and the strengths and weaknesses of different approaches identified. A final summary and future modelling perspectives conclude the paper. [Copyright &y& Elsevier]

Experimental and numerical analyses have been used to assess the validity and potentialities of the integral swash zone model by Brocchini and Peregrine (Proc. Coastal Dynamics ''95, ASCE 1 (1996) 221) which is extended to include seabed friction effects previously neglected. Applications of the model to experimental data show it represents a simple and useful tool for modelling swash zone flows. The model allows for computation of integral swash zone properties and shoreline motion from local variables defined at the seaward limit of the swash. For most properties, correlation between local and integral properties is very good (correlation coefficient about 0.80).A suitable parametric form of frictional forces in the swash zone is defined on the basis of both experimental data and analytical investigation. Numerical tests showed that the proposed parameterization models well integral frictional forces within the swash zone. The parametric friction force improves capabilities of the integral swash zone model of representing real swash motions. This is particularly evident when considering the momentum equation: the correlation coefficient between the rate of change of the onshore momentum in the swash zone and its forcings increases from about 0.85 to about 0.95 due to the inclusion of the seabed friction. [Copyright &y& Elsevier]

In the past few years, two-phase models have been developed to describe the detail behaviour of fluid/sediment interactions and transport under the sheet flow conditions. Due to the complexity of the governing equations and uncertainties in the formulations of various stress terms, few complete solutions of these equations are known and the validations are thus far limited to only a few experimental data. In this paper, the numerical predictions of the behaviour of sheet flows using an improved version of an earlier two-phase flow model [Coastal Eng. 36(2) (1999) 87] are described. Although the general structure of the model was retained, a number of improvements had been made to give better account the underlying physics of the flow in areas very close to the stationary bed. All key flow parameters have been predicted and analysed in order to gain insight into the processes. Calculated time-dependent as well as time-averaged concentrations are compared with experimental data from purely oscillatory flows and oscillatory flow plus a current. Good qualitative agreements between predictions and measurements were achieved for the time-dependent concentrations while the time-averaged concentrations are quantitatively accurate as well. [Copyright &y& Elsevier]

Time series of vertical sediment fluxes are derived from concentration time series in sheet flow under waves. While the concentrations C(z,t) vary very little with time for &z.sfnc;z&z.sfnc;<10d50, the measured vertical sediment fluxes Qzs(z,t) vary strongly with time in this vertical band and their time variation follows, to some extent, the variation of the grain roughness Shields parameter θ2.5(t). Thus, sediment distribution models based on the pickup function boundary condition are in some qualitative agreement with the measurements. However, the pickup function models are only able to model the upward bursts of sediment during the accelerating phases of the flow. They are, so far, unable to model the following strong downward sediment fluxes, which are observed during the periods of flow deceleration. Classical pickup functions, which essentially depend on the Shields parameter, are also incapable of modelling the secondary entrainment fluxes, which sometimes occur at free stream velocity reversal. The measured vertical fluxes indicate that the effective sediment settling velocity in the high [(0.3

It is shown that the observed difference in sediment transporting efficiency by the swash uprush, compared with the downrush, could be mainly due to greater bed shear stress for a given velocity in the more abruptly accelerated uprush. The bed shear stress generated by an arbitrary free stream velocity time series is modelled in terms of usual wave boundary layer models plus a phase lead ϕτ of the bed shear stress compared with the free stream velocity at the peak frequency. With this approach, the total transport amounts in uprush and downrush can be modelled satisfactorily with the same sediment transport formula, without the need for different uprush and downrush coefficients. While the adaptation of sediment transport formulae from steady flow can thus lead to the right total amounts of sediment moved by this method, the timing of the instantaneous sediment transport rates are probably not accurately modelled due to the highly unsteady nature of the swash and the presence of pre-suspended sediment in the uprush. Nevertheless, the proposed method is a useful intermediate step before we have a complete understanding of sediment transport under very rapid accelerations and of the relative contribution of pre-suspended sediment to the onshore sediment transport in swash zones. [Copyright &y& Elsevier]

The present study is focused on sand transport in combined wave–current flow (at any angle between them) in the intensive flow regime. The present model is based on the 1DV approximation. The mathematical method for the continuous description of processes from the immobile bed to the formation of sheet flow and suspended load is presented. The way of modelling of sediment–flow interaction is proposed, in which the near-bed flow is divided into three layers, as done previously by Kaczmarek and Ostrowski [Kaczmarek, L.M., Ostrowski, R., 1998. Modelling of a three-layer sediment transport system in oscillatory flow. Proc. 26th ICCE, ASCE, 2559–2572] for pure oscillatory flow. Measured by Katopodi et al. [Katopodi, I., Ribberink, J.S., Ruol, P., Lodahl, C., 1994. Sediment transport measurements in combined wave–current flows. Proc. Coastal Dynamics ''94, ASCE, 837–851] and Dohmen-Janssen [Dohmen-Janssen, M., 1999. Grain size influence on sediment transport in oscillatory flow. FEBODRUK BV, ISBN 90-9012929-4, Enschede, The Netherlands], the time-averaged velocity profiles are compared with results provided by the present model for the respective conditions. The laboratory data of combined wave–current flow were further used to compare the model results for instantaneous and time-averaged concentration in the bedload (pick-up) layer and the contact load (upper sheet flow) layer, as well as for net sediment transport rate in the case of unidirectional (γ=0) wave–current interaction. The model cases for non-zero wave–current angle were tested in the context of longshore sediment transport rate against field radio-isotopic tracer data of Lubiatowo (Poland) by Pruszak and Zeidler [Pruszak, Z., Zeidler, R.B., 1994. Sediment transport in various time scales. Proc. 24th ICCE, ASCE, 2513–2526] and field luminescent tracer data of Ancao Peninsula (Portugal), by Balouin and Howa [Balouin, Y., Howa, H., 2000. Correspondence contact with University of Bordeaux].Generally, the agreement between the model results and the experimental data was found satisfactory in the context of the apparent roughness and time-averaged velocity profiles above the bed boundary layer. Further, the anti-phase behaviour of measured bedload concentration with respect to sediment concentration in the contact load layer and the asymmetric effects resulting from wave–current interaction are well represented by the model. Consequently, the present theoretical approach provides a useful tool for predictions of sand transport under wave–current flow within an accuracy factor of 1.5 either way. [Copyright &y& Elsevier]

The Haringvliet estuary is part of the Dutch Delta coast. Since 1950, several large coastal engineering projects have been carried out in the Haringvliet area. The most important of these is the closure of the estuary by the construction of a dam with sluices (finished in 1970). Land reclamation projects of the Maasvlakte (1964–1976) and the so-called Slufter (1986–1987) have also been carried out. These projects have profoundly affected the hydrodynamics and therefore the morphology of the area. New interventions are under discussion and to be able to predict their impact on the morphology, it is necessary to understand the morphological developments caused by the past interventions. In this study, the development with time of the sand volume in the Haringvliet estuary after closure has been studied using bathymetric measurements of the years 1970, 1972, 1979, 1980, 1986 and 1990 until 1999. The changes in sand volume above NAP (Dutch Ordnance Level) −10 m relative to 1970 have been determined. The area in which these volumes have been calculated had to be chosen very carefully to diminish the effects of all other human interventions. As was expected, the estuary shows sedimentation. It could be concluded that the adaptation time scale is about 11 years and that the equilibrium volume has almost been reached in the year 2000. [Copyright &y& Elsevier]

Although seagrass canopies are known to enhance particle sedimentation, there is still limited knowledge about how seagrasses modify the vertical distribution of sediment particles; especially when particles come from allochthonous sources. This study determined the volume of particles trapped by the seagrass leaves, the amount that remains in suspension both within and above the canopy, and the amount deposited onto the seabed. A set of laboratory experiments were conducted in which hydrodynamic conditions and canopy densities were varied to mimic real field conditions. This study demonstrated and quantified previously recorded observations concerning the fate of sediment in seagrass meadows. Seagrass meadows decreased the amount of suspended sediment by capturing the sediment on the blades of the seagrass and by enhancing particle sedimentation on the seabed. However, particles trapped by the blades of seagrass in the whole canopy increased with canopy density and reduced the number of particles in suspension within the canopy. The ecological implications were significant, since a seabed covered by vegetation, when compared to a bare seabed, produced a reduction in the suspended sediment particles within the canopy, improving water clarity. Furthermore, canopies (compared to bare substrates) enhanced seabed sedimentation and the denser the canopy was, the greater the amount of sediment deposited on the seabed. • Seagrasses modify the amount of sediment deposited on the seabed. • Canopy density controls the amount of both suspended and leaves deposited sediment. • Trapping of sediment by leaves depends on the particle size for covers above 50%. [ABSTRACT FROM AUTHOR]

Increasing pressures on coastal environments induced by sea level rise and coastal squeeze has meant that tracking the morphological evolution of sedimentary coasts from the last known survey, pre-empting storm impacts and forecasting potential beach recovery following extreme events is of substantial and increasing societal importance. Equilibrium models for forecasting coastal evolution have figured prominently in the literature in the past two decades and show a strong potential for fulfilling this societal need. In particular some very skilful shoreline evolution models have been proposed based on equilibrium concepts. These models are stable, simple and permit long-term (O(10) years) predictions of coastal change. However, equilibrium models are typically highly empirical and in many cases do not consider explicitly the impact of dynamic sea level, which is modulated by tides, surge and global sea level rise. Equilibrium-based models of shoreline evolution have shown particular promise, but these models generally do not consider the role of the sub- and supra-tidal morphology on coastal evolution (e.g. the importance of coastal dune systems). This contribution presents a new model for For ecasting C oastal E volution (ForCE), which addresses these issues. The model algorithm adopts a reduced complexity but fundamentally physics-based approach, whilst maintaining equilibrium principles. Unlike, most prior models, the sub- and supra-tidal areas are represented explicitly in the model, as are sea level variations. Sediment transport is equated directly with the disequilibrium in wave energy dissipation flux, leading to a sediment transport formulation that negates the normal intermediate step of computing surfzone currents, generally required in process models. Two components of sediment transport are considered: The first is forced by the turbulent kinetic energy associated with wave breaking and the second diffusive term, is related to a sea bed-slope disequilibrium. The first component perturbs the equilibrium profile and dominates in the surfzone, whilst that latter component plays an important role in beach recovery. Equations are developed for a depth-averaged, beach profile model, assuming longshore uniformity. These computational efficient and stable equations facilitate long forecasts (>decade) and easy comparisons with a field data at cross-shore transport dominated field sites. At the test field site, the model is capable of reproducing qualitative observations of nearshore sand-bar dynamics and quantitative comparisons with measured coastal state indicators including both the shoreline displacement (r = 0.90, N.M.S.E. = 0.145) and intertidal beach volume (r = 0.87). • Days to decades prediction of coastal evolution • Accurate predictions of storm erosion & post-storm beach recovery • Skilful long-term prediction of beach volume and shoreline change & bar-dynamics • Explicit consideration sub- and supra-tidal topography & water level • Stable, efficient, equilibrium model suitable for longterm probabilistic forecasts [ABSTRACT FROM AUTHOR]

This study aims at improving the XBeach model in predicting dune erosion in the presence of belowground (land-based) biomass under varying hydrodynamic conditions. In this regard, the XBeach model was extended by a literature-derived root model, which increases the critical velocity for erosion in user-defined areas due to additional root cohesion. The model was validated by using the results of a small-scale wave flume experiment as a basis, where the presence of belowground biomass reduced the measured dune erosion. Control runs considering an exclusively sand-based dune, which served as a comparison in the physical experiment, were used to setup and calibrate a one-dimensional (1D) XBeach model. Due to the application to small-scale, default parameters related to sediment transport were scaled within the scope of calibration. Results showed that the XBeach model is not capable to reproduce the observed control dune profiles satisfactorily for all hydrodynamic conditions. Subsequently, the calibrated model was applied to the physical model runs with belowground biomass. Regardless of the hydrodynamic conditions, applying the root model led to a decrease in the mean sediment concentrations and, in turn, the model-predicted erosion in the vegetated area was mainly driven by avalanching. As a result, erosion volumes were reduced in the vegetated area and a higher agreement with the measurements was achieved. At this stage, the root model is highly simplified and only validated for collision at small-scale. In this regard, the translation of the model setup to field scale would eliminate the need for parameter scaling and could result in an overall better performance of the default model. Further research should address the influence of belowground biomass on the time evolution of dune failure and avalanching. • Novel approach to consider effect of belowground biomass on dune erosion volumes. • XBeach model extension and 1D-modelling of small-scale wave flume experiment. • Novel root model increases critical velocity for erosion in user-defined areas. • Accounting for belowground biomass improves erosion volume estimates considerably. • Large underprediction of overwash volumes due to general model-data mismatch. [ABSTRACT FROM AUTHOR]

In sandy environments, like the beach-dune system, buildings not only affect the airflow, but also the aeolian sediment transport in their surroundings. In this study, we determine how the horizontal size of sediment deposition patterns around buildings depends on the building's dimensions. Four one-day experiments were conducted at the beach using box-shaped scale models. We tested 32 building geometries, where scale model height, width and length ranged between 0.3 and 2.0 m. The deposition patterns were substantial in size: the total length and width of the deposition area were up to an order of magnitude larger than the horizontal building dimensions. It was found that the size of upwind and downwind deposition patterns depended more on the building width perpendicular to the wind direction (w), than on the building height (h). Building length had little influence. Especially the combined effect of w and h correlated well with horizontal deposition size. This is expressed in a new scaling length B for deposition around buildings, with B = w 2 / 3 · h 1 / 3. As a first validation, the spatial dimensions of the initial deposition patterns observed around a scale model of 2.5 × 12 × 2.5 m, placed at the beach for five weeks, showed good agreement with those predicted based on B. • Outdoor scale experiments successfully captured aeolian sand dynamics. • Horizontal deposition dimensions can be ten times larger than the building dimensions. • Building width and height determine the horizontal size of deposition patterns. • A characteristic building length scale links building size to aeolian deposition size. [ABSTRACT FROM AUTHOR]

The performances of phase-averaged parametric nearshore wave transformation models depend significantly on a reliable estimate of the wave breaker index γ (the breaker height-to-depth ratio), a free model parameter that essentially controls the amount of breaking energy dissipation. While the previous studies have suggested separate relationships between γ and the offshore wave steepness (s 0) or the normalized local water depth (kh), the parameterization of γ still requires further investigation considering a wider variety of conditions and a sounder physical basis. In this study, we use the field datasets of wave height and the inverse modelling approach to reveal a composite dependence of γ on both s 0 and kh. Specifically, the results show a positive dependence of γ on kh for larger s 0 , and a negative dependence of γ on kh for smaller s 0. Based on such composite relationships, a new γ formula is proposed, and its performance is verified against the available datasets of wave height in three coasts and 14 laboratory tests. Implementation of this new formula in a parametric wave model leads to the error reduction of wave height prediction by 10–24% (mean = 19%) relative to seven widely used models in literatures. In particular, a remarkably higher model accuracy is obtained under wave conditions with small offshore wave steepness, which is important for studying onshore sediment transport and beach recovery. Two counteractive physical mechanisms for wave nonlinearity effects, namely the breaking intensification mechanism and the breaking resistance mechanism, are suggested to explain the opposite γ - kh relationships within different ranges of s 0. • The composite dependence of wave breaker index on both the offshore wave steepness and the normalized local water depth. • A new formula for wave breaker index used for parametric wave transformation modelling leads to improved wave height prediction especially under wave conditions with small offshore wave steepness. • Two counteractive physical mechanisms to explain the composite relationships. [ABSTRACT FROM AUTHOR]

A non-hydrostatic phase-resolving numerical model (SWASH) is used to investigate the wave-driven nearshore hydrodynamics corresponding to new observations from a three-dimensional physical model in a wave basin. In the physical model, waves from a passing storm are simulated by varying the energy and duration of waves generated by a paddle over time and the beach morphology is surveyed in high spatial-resolution using a 3D laser scanner after each segment of the storm. An oblique incident wave angle introduces spatially variability in wave energy along the beach and results in morphologic differences during the storm, with active transport of beach sand by the wave-driven circulation. SWASH is validated using wave and current observations at each stage of the storm, indicating low root-mean-squared errors between model results and wave measurements, where the high-resolution model is able to predict wave shoaling, breaking and generation of the alongshore current. Model-data agreement is not as high for the velocity, suggesting spatial variability in bottom friction and horizontal mixing, and evolution of the bed in the physical model, could explain the differences. The detailed numerical model results indicate that the alongshore current is generated by wave breaking in the nearshore zone, and it increases in speed across a wider surf zone for increasing wave energy during the storm. This is associated with a bottom shear stress that exceeds the critical bed shear stress, with the potential to initiate motion and transport sediment in agreement with the experimental observations. • A physical model is implemented in a wave basin with a long and steep sandy beach. • Wave energy is varied over time to simulate a passing storm. • Wave breaking generates an alongshore current that induces morphologic change. • Phase-resolving simulations of nearshore hydrodynamics are run for storm phases. • Results improve understanding of nearshore circulation and bed shear stress. [ABSTRACT FROM AUTHOR]

In the present study, we addressed the potential impact of climate change on coastal erosion along the 28 beaches of the Basque Coast (150 km). A shoreline evolution model including cross-shore and alongshore sediment transport formulations, short- and long-term processes and hard structure treatment is developed. The historical analysis of the shoreline evolution is performed by forcing the model with waves and storm surges from reanalysis data, and with tides from in situ water level measurements. The model is calibrated and validated by using morphological information derived from the KostaSystem coastal video monitoring system. The analysis of the future impact of climate change on the sandy beaches is carried out using two sea level projections (RCP 4.5 and RCP 8.5 scenarios) and their confidence intervals, combined with synthetic wave series that allowed a probabilistic fashion outcome. The results show that the shoreline mean erosion due to both short- and long-term processes is in the range of 10–45 m under the RCP 4.5 scenario and 14–66 m under RCP 8.5 by the year 2100, which indicate the great vulnerability of the beaches of the Basque Coast. Still, the response of the studied systems is highly variable, owing to the intrinsic characteristic of each site. This result points to the difficulty of taking general management measures and highlights the need for management strategies at the local level. • A shoreline evolution model suitable for urban beaches is set up along the sandy systems of the Basque Coast. • The model outcome is validated against the data obtained from a video monitoring system and handled in a probabilistic way. • A new climate change beach impact indicator (beach recovery potential loss) is analysed. • Shoreline mean erosion is in the range of 10–45 m under the RCP 4.5 scenario and 14–66 m under RCP 8.5 by the year 2100. • Results point to the need of local management strategies. [ABSTRACT FROM AUTHOR]

In many places, sandy coastlines and their associated assets are at high risk of erosion and flooding, with this risk increasing under climate change and sea level rise. In this context, dynamic cobble berm revetments represent a potentially sustainable protection technique to armour sandy beaches, reduce wave runup and protect the hinterland against wave attack. However, the behaviour and performance of such structures is not well understood. The dynamic cobble berm revetment located in North Cove, WA, USA, was monitored over a spring tidal cycle in January 2019. A representative 60 m alongshore section was monitored over 10 days using 2D laser scanner (lidar) measurements, GPS ground elevation surveys, Radio Frequency Identification of individual cobbles and revetment thickness measurements. These data were used together to assess the dynamic behaviour and functionality of the revetment throughout the experiment. Over the course of the experiment, the surface elevation changed by up to ±0.5 m, and the revetment volume reduced by an average 0.67 m3/m. These changes were found to be caused by relatively large significant wave height and high water levels. The revetment demonstrated a dynamic stability and the capacity to quickly reshape under changing hydrodynamic conditions. The instrumented cobbles were transported along and cross-shore and accumulated at the toe of the revetment, but were never transported seaward of the toe. The revetment also managed to recover some of the lost volume under moderate wave conditions. The revetment behaviour was found to be influenced by variation in the cobble-sand matrix. The underlying sand dynamics – i.e. , accumulation or removal of sand within the cobbles – were found to govern the overall volume changes and were important to the overall stability of the revetment. Seven possible transport regimes were identified, and a model of the internal sand dynamics was developed. During the spring tidal cycle measured here, the revetment protected the sand scarp immediately landward and prevented flooding of the hinterland, while armouring the underlying sand. Over time, renourishment will likely be required due to longshore sediment transport, and preliminary guidelines for this and other aspects of design are suggested. • A field experiment was undertaken on a dynamic cobble berm revetment in North Cove, US. • The revetment showed a dynamic stability and a rapid adaptability to external forcing. • The water level at the toe of the structure appeared to be the primary driver of change. • A novel model highlighting the importance of internal sand dynamic was created. • Guidelines are proposed for design and nourishment of the structure. [ABSTRACT FROM AUTHOR]

Along much of the world's coastline, coastal barriers serve as the first line of defense against oceanic and meteorological forces. Extreme storms cause large morphological changes on coastal barriers through high sediment transport rates, which may degrade their defensive capabilities. The understanding of morphological impacts is therefore important for coastal resiliency, but is often challenged by site-specific characteristics, such as land cover and sediment availability, and their poorly understood impacts on the governing physical processes. The Caminada Headlands, Louisiana, USA presents unique considerations for morphodynamic modeling with regard to its low-lying topography, variable land cover, nearshore muddy substrate and sand deficiency. This study investigates the effects of land cover and limited sediment supply on low-lying barrier island morphology under storm conditions by using physics-based numerical models. A high-resolution, local-scale sediment transport/morphodynamic model (XBeach) of the Caminada Headlands is verified for Hurricane Gustav's (2008) impact using pre- and post-storm LIDAR surveys. When accurate input data are used to create physics-based numerical models these tools are robust in hindcasting storm impacts and provide a wealth of information as to the governing processes, which is otherwise difficult to obtain observationally. The simulation results show that a short-duration overwash regime dominates the morphological change in this low-lying barrier and is influenced by backbarrier wetland deterioration. The morphological response to overwash is modulated by backbarrier land cover and topography, as reduced accommodation space limits landward transport during the subsequent inundation regime. An intact backbarrier marsh reduces landward washover sediment transport distances and promotes deposition at supratidal elevations. In light of these findings, simultaneous restoration/creation of backbarrier wetlands in conjunction with subaerial beach renourishment may be an effective form of increasing the resiliency of low-lying barriers subject to frequent overwashing. • A basin-scale hydrodynamic-wave and local-scale sediment transport model constructed for barrier washover simulations. • A hindcast of Hurricane Gustav's (2008) hydrodynamics and morphological impact to Louisiana verified with multiple data. • A relationship between storm-driven washover sediment transport and backbarrier wetland land cover/topography investigated. • Limited nearshore sand sediment supply influences the accuracy of storm-driven washover sediment transport modeling. [ABSTRACT FROM AUTHOR]

A man-made dune-beach-spit system at the south-east side of the island of Texel (Prins Hendrik site) has been built in 2018–2019 to strengthen the traditional dike. The core of the dune-beach-spit system consists of medium fine sand with a d 50 of 0.25–0.3 mm. The beach is covered with an armour (protection) layer of coarse materials with relatively large gravel and shell fractions to reduce wind erosion and thus maintenance costs. In the design phase of the project the aeolian sand transport model of Bagnold was used to estimate the long-term erosion losses of sand at the new dune-beach system. This transport model was validated in the design phase by using detailed sand transport and bed roughness measurements at a nearby site called The Hors. This site is a wide natural beach plain of sand (d 50 = 0.23 mm), where 147 high-quality datasets have been collected using a wind mast equipped with 5 cup anemometers and various sand traps. It is shown that the measured sand transport rates at the Hors can be reasonably well represented by the modified Bagnold-equation for dry sand. After completion of the new dune-beach system, a field experiment was performed at the Prins Hendrik site to verify the sediment transport predictions and erosion loss of sand. Data from two permanent wind masts and one short, mobile wind mast were used to derive the effective roughness of (stationary) bed forms. Sand transport rates were measured at various locations using a new trap sampler. The measured sediment transport in the armoured beach zone can be reasonably well represented by the Bagnold-equation using a multi-fraction approach with hiding-exposure coefficient. The predicted transport rates have been used to estimate the annual loss of sand from the Prins-Hendrik site. • Aeolian transport in conditions with sand, gravel, shells and bed forms is studied on Texel, the Netherlands. • Using the measured overall shear velocity leads to overprediction of transport rates. • Using a multi-fraction approach, transport rates in armoured conditions can be reasonably well predicted. • Transport rates on a sandy beach can be significantly reduced (factor 3 to 4) by the placement of an armour layer. [ABSTRACT FROM AUTHOR]

A number of models are available for science and engineering purposes that numerically simulate nearshore hydrodynamics and the corresponding morphological evolution. However, the models include adjustable coefficients in parameterizations for physical processes that need to be calibrated, and thus there remains room for improvement by including additional physics. One such model is XBeach, which can simulate erosion during storms with proper calibration based on observations. The modeled sediment transport, especially in the cross-shore direction, is sensitive to the adjustable coefficients, with preferred values that are site and event specific. Here, the skill of XBeach is investigated by comparing 1-dimensional (cross-shore) depth-averaged simulations with observations of waves, currents, and sandbar migration across an Atlantic Ocean beach. Calibration of coefficients improved the agreement of the computed results with observed wave heights, offshore-directed mean currents (undertow), the wave-orbital-velocity third moments (skewness and asymmetry), and onshore/offshore sandbar migration although the proposed coefficient values depend on the parameterizations used. For example, including a variable breaking-wave roller energy model resulted in more skillful predictions of undertow than using the default constant coefficient value. Using the calibrated roller coefficients and corresponding undertow, XBeach simulated the observed offshore migration of the sandbar. Onshore transport in XBeach is driven by non-sinusoidal wave-orbital velocities, and proposed values for coefficients depend on the parameterization used to estimate skewness and asymmetry and the associated transport, as well as on incident wave conditions. XBeach calculations of cross-shore sediment transport rates were compared with those estimated by a commonly used sediment transport formula based on laboratory experiments. The inter-comparison suggests that using a wave-induced onshore transport parameter 3 or 4 times larger than the default value may at least in part compensate for the lack of bottom-boundary-layer-streaming-driven-onshore transport in XBeach. • XBeach is successfully applied to simulate onshore and offshore sandbar migration. • Revised roller dissipation model improved undertow prediction in the bar region. • The calibrated onshore transport depends on the modeled wave skewness/asymmetry. [ABSTRACT FROM AUTHOR]

Accurate knowledge of the sediment budget of a coastal cell is necessary for coastal management and predicting long-term coastal change. An important component in the sediment budget of many wave-dominated embayed coastlines is the amount of sediment that bypasses rocky headlands, which present partial barriers to alongshore transport. As yet, there is no universal method for estimating bypass rates. Here we show that wave-forced bypassing of an isolated headland can be estimated using a parameterisation of wave conditions, shoreface slope, sediment size, headland toe-depth and cross-shore extent. XBeach was used to simulate instantaneous rates of alongshore flux off the apex of an idealised and isolated headland, with >1100 simulations, testing various wave and morphological factors. Key variables were headland cross-shore extent as the ratio of toe-depth to bed slope (X H = h toe /tanβ) and surfzone extent as a function breaking depth and slope (X s = h b /tanβ). The critical ratio controlling bypassing was found to be X H /X S (equivalent to h toe /h b , for an idealised headland). Bypass is predicted as: Q bypass = Q 0 f(X H /X S) ; where Q 0 , the alongshore transport rate immediately updrift of the headland, is based on an existing expression (Van Rijn, 2014) and f(X H /X S) is a negative exponential function. This formulation accurately replicated bypass rates modelled by XBeach, generally to within a factor of two. Headland shape was found to be a lower-order control on bypass and was excluded from the parameterisation. Preliminary analysis suggests the expression may also be applied to groynes, though more specific testing is required. Once adapted to time-varying wave and water levels, the expression succesfully predicted bypass rates for three observed headlands over a single event. Best results were obtained using measured toe-depth to parameterise headland morphometry. Further field data are required for robust calibration, in particular for large and complex headlands that vary substantially from the idealised model used for development. The bypass expression can be used to provide a first-pass estimate of wave-forced bypassing for a wide-range of headland types; this will be of use to coastal managers, scientists and engineers working on rocky and embayed coastlines. • First parametric formula to predict rates of sediment bypassing isolated headlands. • Developed using XBeach across a wide-range of wave and morphologic scenarios. • Critical ratio is headland extent/surfzone width (equal to toe-depth/breaking depth). • Successfully predicts observed bypassing for three headlands over a single event. [ABSTRACT FROM AUTHOR]

In natural beaches, sea-beds consist of graded sediments. In swash and surf zones, wave actions lead to selective transportation and segregation of sediments. Thus, size segregation needs to be considered while determining the sediment transport rate and morphological dynamics on beaches. However, because of the strong non-linearity and the large deformed free surface, previous experimental or observational investigations failed to obtain enough knowledge about the sorting process in the swash zone. In this study, as the first investigation step of the size sorting process in the swash zone, an experiment was conducted with an oscillatory water tank, while the vertical sorting process was observed. Moreover, to further investigate the structure of the flow and movable bed, a 3D numerical simulation was performed. A coupling scheme of the discrete element method (DEM) and the moving particles semi-implicit (MPS) method was applied to reproduce the vertical sorting progress. The result revealed that the development of the vertical sorting brought about bed surface armoring and a horizontal velocity transition. Additionally, an acting force investigation disclosed that the inertia of the water surface gradient induced oscillations of the sediments, which consisted of elements, in the water tank while leading to frequent element collisions and contacts, which caused the elements to be pushed upward. • An experiment for the vertical sorting in an oscillating water tank is conducted. • DEM-MPS coupling model is applied to a numerical simulation of the sorting process. • A contribution of the contacting force to the thrusting of particles is revealed. [ABSTRACT FROM AUTHOR]

Tidal inlets are crucial landforms that control the exchange of water and sediment between the open sea and back-barrier basins. Despite the well-established relationship between tidal prism and inlet cross section area, some aspects of tidal inlet geometry remain unconstrained. What processes set their width to depth ratio (or aspect ratio)? What controls the presence of a single-thread versus a compound channel within the same inlet? Do these relationships change with engineering activities? These questions were investigated by compiling and analyzing a database with 226 inlets worldwide. We found that the aspect ratio has a weak dependency on tidal range and wave height. The aspect ratio varies by at least an order of magnitude, and this variability is likely associated with the variability in the widening process, e.g., the bank erodibility. Engineered inlets tend to have smaller widths and aspect ratios than natural inlets. Within natural inlets, multiple channels tend to form when the inlet width exceeds approximately 1 km. We developed an idealized barrier-inlet system using the detailed 2D hydro-morphodynamic model Delft3D to investigate the long-term morphological evolution of inlets. Two parameters greatly affect the aspect ratio: the transverse bed gradient factor for sediment transport (α bn) and the dry cell erosion factor (θ sd) , which allows for erosion of dry cells adjacent to a wet cell. Removing the dry cell erosion effectively "armors" the side of the inlets and thus produces inlets with a small aspect ratio, which resembles the geometry of engineered inlets. From model sensitivity analysis, we found that α bn = 5–10 and θ sd = 0.3–1.0 provides inlet configurations that best agree with observations. Despite the dry cell erosion and the transverse transport parameters being a simplified representation of bank erosion processes, their calibration allows to reproduce realistic inlet aspect ratio. • Existing knowledge of tidal inlet geometry was expanded using a comprehensive dataset and morphodynamic model. • We compared natural and engineered inlets, highlighting their differences in aspect ratios and channel configurations. • Appropriate values for 2 key model parameters (dry cell erosion factor and transverse bed gradient factor) were identified. [ABSTRACT FROM AUTHOR]

New experiments involving the three-dimensional current-induced live-bed scour beneath submerged horizontal pipelines are presented, spanning larger Shields parameter and cylinder-to-sediment diameter ratio than previous studies. Specific emphasis is on gaining a better understanding of, and ability to predict, the span migration velocity during the initial and subsequent development of such a scour hole. Consistent with previous experimental observations, both a primary (faster) and secondary (slower) span migration are observed. Process visualization of suspended sediment patterns are in line with prior speculation that this transition coincides with reduced local bed shear stress amplifications as the scour hole both deepens and widens. Dimensional analysis and physical insight are combined, leading to a new rational model for predicting the span migration velocity in both live-bed and clear-water regimes, with predictions naturally coinciding at the limit of far field incipient motion conditions. In both regimes the data cluster as predicted, and fitted closed-form expressions are provided for predicting the span migration velocity. The rational approach likewise includes a new and simple criterion for the transition from primary to secondary migration in the live-bed regime. In the clear-water regime the model incorporates primary dependence on the ratio of the Shields parameter to its critical value, resolving apparent contradictions with a previous study which suggests that the depth-based Froude number is the most important governing parameter. The developed rational model can be used to quantitatively predict all known major features of the span migration velocity in the early stages of the three-dimensional (live-bed and clear-water) scour beneath submerged horizontal cylinders induced by perpendicular flow, and can hence be regarded as the first complete model for this evolution. • New experiments are conducted involving 3D scour beneath submerged circular cylinders exposed to steady currents. • Both a primary (faster) and secondary (slower) span migration velocity are observed, consistent with prior studies. • A new rational model is proposed for predicting the primary span migration velocity in both live-bed and clear-water scour regimes. • Predictions for live-bed and clear-water regimes coincide naturally at the limit of far field incipient motion conditions. • A new and simple criterion is proposed for the transition from primary to secondary span migration in the live-bed regime. [ABSTRACT FROM AUTHOR]

The erosion of marine sediments, although difficult to predict, can lead to important implications in offshore engineering, sedimentology and coastal management. Continued research is, therefore, warranted to compile high-quality erosion data from which to develop models to better predict the erosion resistance of different types of marine sediments. In this paper, dimensional analysis is performed to express the threshold shear stress as a function of a selection of soil properties that are commonly linked to the erosion process of sediments. To identify the dominant dimensionless group, an experimental investigation on the erosion threshold was carried out using fine-grained sediments that were systematically prepared to ensure variations in (i) particle size distribution (i.e. fines content), (ii) bulk density, and (iii) hydraulic permeability. The samples included silica, carbonate and marine sediments, each of which are expected to have limited or no clay-mineral content. The measurements were analysed and compared with existing literature and predictive models. It was found that marine sediment samples with limited fines content showed good agreement with the empirical Shields curve, irrespective of particle size distribution, bulk density and permeability. In contrast, for finer marine sediment it was found that variations in these soil properties modify the threshold shear stress away from the Shields curve. Across each of these parameters only permeability appeared to independently correlate with the observed range of threshold measurements. Motivated by this finding, a model is introduced to predict the threshold shear stress as a function of permeability and the reference erosion rate that is used to define when the threshold is reached. The resulting expression is shown to quantitatively explain the experimental data and is found to also agree with existing data from the literature for quartz sediments with a wide range in fines content. An apparent advantage of the new model is that it is consistent with existing studies that identify variations in threshold shear stress due to changes in bulk soil parameters – including fines content and bulk density – since each of these parameters also affect permeability. • The effect of soil properties on the erosion behaviour of marine sediments. • Unique relationship between permeability and erosion threshold discovered. • Novel empirical relationship proposed to predict threshold shear stress for fine-grained sediments. • New model predicting threshold conditions agrees well with existing data from literature. [ABSTRACT FROM AUTHOR]

Laboratory wave flume experiments in coastal engineering and physical oceanography are widely used to provide an improved understanding of morphodynamic processes. Wave flume facilities around the world vary greatly in their physical dimensions and differences in the resulting distortion of the modelled processes are reconciled using scaling laws. However, it is known that perfect model-prototype scaling of all hydro and morphodynamic processes is rarely possible and there is a lack of understanding to what extent distorted models can be used for direct morphological comparison. To address this issue, distorted scale laboratory flume experiments were undertaken in three different facilities, with the aim to measure and compare beach profile evolution under erosive waves and increasing water levels. A novel approach was developed to transform and scale the different experimental geometries into dimensionless coordinates, which enabled a direct quantitative comparison of the beach profile evolution and sediment transport rates between the differing distorted experimental scales. Comparing results from the three experiments revealed that the dimensionless scaled morphological behaviour was similar after the same number of waves – despite very different degrees of model distortion. The distorted profiles appeared to be suitable for comparison as long as a modified version of the Dean number is maintained between them. The new method was then validated with two further published datasets, and showed good agreement for both dimensionless profile shape, dimensionless sediment transport and morphodynamics parameters. The new approach scales the sediment transport by the square of the runup, proportional to HL, rather than H 2, and yields good agreement between the datasets. It is further shown that the new scaling method is also applicable for comparing distorted profile evolution under water level increase, as long as the water level is raised in a similar way between the experiments and by the same total increment relative to the significant wave height (Δh/H s). • Three distorted laboratory wave flume experiments of different scales are compared. • Development of a new scaling methodology for comparing beach profiles of distorted experiments. • Analysis and validation of the method for a fixed and increasing water level. • Qualitative and quantitative comparison of distorted profiles possible by scaling with HL. • Two examples of application of the method, for a fixed and increasing water level. [ABSTRACT FROM AUTHOR]

Abstract: The method of Wang [Wang, Y.-H., 2007. Formula for predicting bedload transport rate in oscillatory sheet flow. Coastal Engineering 54, 594–601] to predict the wave friction factor is discussed. At the threshold of sediment entrainment the proposed equation produces a wide scatter of data points when plotted against an equation based on the Shields parameter. It is shown that a better correlation coefficient can be obtained by calculating the critical wave friction factor directly from the wave period, as well as the sediment and water properties. [Copyright &y& Elsevier]

Understanding the boundary layer flow structure at the tip of a swash flow is important for improving predictions of wave run-up, coastal flooding and sediment transport processes on beaches, but this is difficult to investigate experimentally. Recently, there has been debate regarding the mechanics of boundary layer growth during the uprush flow. Here, an extensively validated RANS model is used to investigate the swash tip dynamics during a dam-break driven swash event. The model enables the analysis of the spatial and temporal variation of important parameters, in particular the water surface gradients, the bed shear stress, and the non-uniformity of the velocity profile. The rate of flow convergence of surface particles toward the tip, and the ratio of the depth-averaged flow velocity and celerity of the swash tip are also obtained. The flow depth varies with distance behind the wave tip approximately as a power law, with a power of 1/2–3/4. The surface elevation dips offshore at distances greater than 0.2 m behind the front. The shear stress decreases quite slowly in the spatial region immediately behind the wave tip, and is in very good agreement with the flat-plate boundary layer model of Barnes and Baldock (2010). The model results indicate that the boundary layer structure is well-developed or depth-limited at the wave tip, and fits a power-law velocity profile with an exponent of order 1/3, consistent with a rough bed. The normalised vertical variation in the velocity profile is very uniform in the region 1 m behind the wave tip, and matches that for a 1/3 power law. Alternate logarithmic fits to the velocity profile yield consistent values of bed roughness at different locations, but corresponding to a grain size that is about twice that used in the experiment. The rate of flow convergence of surface particles toward the wave tip is also consistent with a fully developed boundary layer and a 1/3 power law. • RANS model used to investigate boundary layer structure at a swash tip. • The model provides high resolution spatial data. • The boundary layer is fully-developed at the wave tip, with a 1/3 power law velocity profile. • Bed shears stress predicted by a flat-plate boundary layer model agrees very well with the RANS model. • The rate of flow convergence of surface particles toward the front is consistent with the power-law profile. [ABSTRACT FROM AUTHOR]

Novel observations of bar features and migration patterns at three Italian sandy beaches in Senigallia (central Adriatic Sea) and Terracina (central Tyrrhenian Sea) are presented. While two of these beaches are unprotected, one is artificially embayed through the presence of a concrete jetty. Bar locations and motions are analysed with video imagery data sets from coastal monitoring stations. Wave climate from the Copernicus oceanographic model is used to correlate hydrodynamics and beach morphology. Clear net offshore migration (NOM) patterns are identified at all beaches, although exhibiting different response scales. At the low-slope beach of Senigallia (mean surf zone slope of 0.009) bars are more sensitive to seasonal changes in wave climate, with offshore shifts in winter and inactivity in summer. Mean annual migration rates of up to 0.26 m/day and 0.09 m/day are observed for outer and inner bars, respectively. No significant response to single storms is observed, except during a single NNE storm. No distinct erosive or accretive trend for the shoreline is evidenced. At the steep beach of Terracina (mean surf zone slope of 0.018), conversely, bars are strongly responsive to single storm events, with displacements of up to 25–50 m across a single storm. The mean inter-annual migration rate is 0.08 m/day for the single/outer bar, whereas a slight onshore trend (-0.02 m/day) for the newborn inner bar is established. The presence of an artificial jetty at the Misa river mouth in Senigallia, finally, leaves the bar system, typically oscillating around an equilibrium position, susceptible to larger seasonal oscillations and strong offshore migration due to two ESE storm events. Numerical simulations of nearshore circulation for two storms from different directions predict the birth of longshore currents, higher ratios of significant wave height to water depth, and stronger bottom orbital velocities over bars in case of the ESE storm, suggesting a greater tendency for offshore-directed sediment transport. • Video-based observations of sandbar dynamics at three microtidal beaches. • All bar systems show offshore-directed migration trends and occurrence of NOM. • Response to seasonal climate at mildly sloping beaches, to storms on steep beaches. • A river jetty increases seasonal response of OPE-behaving bars, giving episodic NOM. • Numerical simulations highlight the role of wave direction at bounded beaches. [ABSTRACT FROM AUTHOR]

The progressive expansion of offshore wind energy towards greater water depths demands for an optimization of foundation structure designs to a wider range of load conditions. In offshore waters, wind driven wave irregularity and directionality become important aspects of realistic sea states. To further improve the scour prediction in marine environment a novel experimental study was conducted to investigate the influence of directionally spread (3D) irregular waves on the scouring process. The tests were carried out in the 3D wave basin of the Ludwig-Franzius-Institute, Leibniz University Hannover, Germany. A monopile structure was simulated by a transparent pile made of acrylic glass. The study was set up to progress understanding and explore dissimilarities of scour development and patterns induced by directionally spread (3D) and unidirectional (2D) waves. The model tests were complemented by tests with superimposed oblique currents. Despite identical total wave energy in terms of m 0 between the directionally spread and unidirectional wave spectra, minor but distinct differences in scour depth and rate could be observed, which inevitably can only be attributed to the presence and role of the wave spread. For wave-only conditions final scour depths S / D induced by directionally spread waves were on average 33% smaller than those for unidirectional waves. Furthermore, final scour depths decreased with increasing wave spreading and displayed a growing dependency on KC numbers with increasing wave spreading. In combined wave and current conditions of up to U c w < 0.62 scour depths were found to be slightly larger and scour progression over time faster for directionally spread than for unidirectional waves. Differences regarding the scouring rates and depths have been found to decline with flow conditions further approaching current dominated regime. A prediction approach to estimate the maximum scour depth induced by either directionally spread or unidirectional random waves is proposed. Reasonable results and insights of the present study help advancing the understanding of scour development under more realistic, i.e. natural sea-state, conditions for a more reliable design of marine and offshore infrastructure. • Novel experimental study on the scouring process around a pile due to directionally spread waves is presented. • A comparison of scour depths and rate induced by directionally spread and unidirectional waves is carried out. • Distinct differences in scour depth and rate could be observed, that are linked to the presence of wave directionality. • A prediction approach to estimate the maximum scour depth induced by directionally spread random waves is proposed. • Results help understand the scour development under natural sea-states for a more reliable design of offshore structures. [ABSTRACT FROM AUTHOR]

The effects of sea level rise (SLR) are relevant to the future evolution of coasts and estuaries. This study analyses the importance of different SLR trends on the morphological evolution of a mixed-energy fine-sediment coast (the Caofeidian Sea in Bohai Bay, China) using a validated numerical model. Results show that SLR produces spatially non-uniform relative morphodynamic responses, depending on the local coastline (uninterrupted or inlet-interrupted) and wave exposure. In the Caofeidian Sea, the uninterrupted coast is exposed to waves and tidal currents, and SLR reduces the accretion of tidal flats via heightening waves. On the inlet-interrupted coast, the morphological response to SLR is dominated by changes in tidal asymmetry and current velocity. In low SLR scenarios, the enhanced flood tidal asymmetry makes the system initially resilient to SLR. For high SLR scenarios, tidal sediment transport capacity is dampened by the reduction in current velocities, which accelerates the degradation of tidal flats along the inlet-interrupted coast. Differences among results with eight theoretical SLR trends show that the magnitude of SLR-induced morphological change is influenced by the target value (0.5 and 1.0 m) and rising mode (abrupt growth, linear growth, parabolic growth, and exponential growth) of the SLR. A newly-introduced parameter (equivalent SLR, E SLR), which reflects the time-weighted average value of an SLR trend for a period of time, shows a strong linear relationship with SLR-induced morphological change. Results suggest that the morphological response to other SLR scenarios for the Caofeidian Sea is expected to be interpolated from the E SLR ratios without performing extra time-consuming simulations. • SLR triggers erosion of tidal flats on the uninterrupted coast via heightening waves rather than enhancing currents. • Morphological response of inlet-interrupted coast is subject to net sediment flux controlled by tidal asymmetry and currents. • Morphodynamic modelling that neglects the SLR trends has a limited predictive capacity of SLR effects on the coasts. [ABSTRACT FROM AUTHOR]

The response of nourished beaches to sea level rise is investigated experimentally with random waves in a laboratory wave flume (20 m × 1 m × 1 m), following on from a previous investigation of the response of non-nourished beaches (Atkinson et al., 2018). The nourishments are placed on beach profiles previously exposed to sufficient durations of waves to have approached a near-equilibrium state, i.e., with stable shoreline, bars and berms. Nourishment was placed in three different locations: on the berm, within the bar trough, and as a shoreline placement. In the latter case, and following Bruun rule concepts (Bruun, 1962), the volume of sediment placed was estimated a priori to lead to zero recession under the chosen water level rise. The nourished beaches were then exposed again to sufficient durations of waves to reach a near-equilibrium state at the raised water level. The shoreline recession and the mean recession of the profile following a rise in water level are compared for both the nourished and non-nourished beaches, and to theoretical estimates based on Bruun rule concepts and a previously developed Profile Translation Model (PTM). Quantitative agreement is found with the variants of the Bruun Rule that account for nourishment and with the PTM, and the predicted recession is within an order of ±30% of the observed recession. Overall, the PTM provides the best estimate of the recession. The mean recession of the profile is found to be in better agreement with the model predictions than the recession measured at the shoreline, because the latter is affected by changes in profile shape around the still water line. The efficacy of the nourishment was investigated from the reduction in the observed recession. The efficacy depends on how the recession is measured. For the mean recession, highest efficacy was observed when all the nourishment is added into the active profile. Conversely, for the shoreline recession, highest efficacy was observed with the nourishment placed on the upper beach because it prevents additional recession through wave overtopping. • Direct comparison of nourishment and non-nourishment experiments. • Nourishment reduces recession associated with sea level rise. • Nourishment placed further landward reduces chance of loss of sediment offshore. • The effective nourishment volume is important to consider when predicting recession. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on scour at complex bridge piers exposed to combined waves and current. Regular waves were produced with various strength and superimposed on co-directional current with constant velocity. The key parameters tested and discussed include Keulegan–Carpenter (K C) number, relative current strength U c w , pile-cap elevation, and pier skewness. The scour hole patterns and scour mechanism were found to depend on the flow type combination, and, compared with steady current, the superposition of waves may restrain the development of scour hole due to migrating bed-forms. Three types of scour temporal evolution (i.e. ascend-descend, asymptotic, and transferred type) were identified, and the scouring processes (structure exposure, cyclic sediment motion, etc) at the scour initiation and development stages were also discussed. The dimensional time scale decreased for higher bed mobility with a power functional relationship, while the non-dimensional time scale peaked when the maximum near-bed velocity components contributed by current and waves are similar. The dependence of the equilibrium scour depths, both original and normalized, on the tested parameters was also analysed. It was found that the normalized scour depth at complex piers increases with greater K C and U c w and tends to be much larger than that for single piers. The increase of bed mobility did not lead to scour peaks at the clear-water threshold as what is usually observed for current-only scour. The influence of pile-cap elevation on the equilibrium scour depth was found to be much weaker than that under steady current. Furthermore, new scour prediction method is proposed to incorporate extra terms taking the influence of pile-cap elevation and pier skewness into account. The prediction accuracy is improved significantly. Finally, more suggestions regarding design considerations are also given. • Scour patterns under combined co-directional waves and current at complex piers with different skewness. • Three temporal scour evolution types are observed for different pier configurations. • The relationship between current strength, or Shields parameter, with time scales can be expressed by power functions. • The effects of KC, current strength, Shields parameter, pile-cap elevation, and pier skewness on scour depth are discussed. • A new scour prediction method for complex bridge piers is proposed with significantly improved accuracy. [ABSTRACT FROM AUTHOR]

Accurate suspended sediment concentration measurements are key to understand and quantify the sediment transport patterns in the surf and swash zones. One of the most widely used instruments to collect suspended sediment concentrations is the Optical Backscatter Sensor (OBS). However, the OBS is known to give erroneous readings when deployed in bubbly environments like the surf zone. The present study aims to quantify the influence of an aerated wave breaking environment on the OBS sediment concentration measurements. Experiments are performed in a large wave flume, which ensures full air entrapment under plunging breaking waves, and avoids scale effects that could affect the volume of entrapped air, the air bubble penetration depth and the residence time of air bubbles in the post-breaking turbulent eddies. OBS measurements are obtained at 66 locations along a fixed bed profile for 14 regular breaking wave conditions. In the absence of suspended sediment particles, OBS voltage measurements are used as a proxy for air bubble content. The presented OBS results show peaks up to 1.49 V (31% of the OBS measurement range, corresponding to 16 g/l for sediment with d 50 = 0.25 mm) produced by air bubbles in the most energetic tested wave breaking conditions, while the maximum time-averaged value obtained is 0.48 V (10% of the OBS measurement range, corresponding to 5 g/l). The results highlight the importance of considering the presence of air bubbles where OBS are deployed to measure suspended sediment concentrations. A good correlation is found between the breaker depth index and the air bubble distribution and two predictive formulas are derived to forecast the area of air bubble influence in the surf zone. • Plunging wave breaking over a barred profile. • Large scale laboratory experiments allow bigger residence times of air bubble in the water column. • Air bubbles importantly affect OBS measurements when deployed around the breaking area. • OBS voltages are consistent and repeatable for air bubble events across the breaking area. • Two formulations are presented to predict the distance and depth at which the air bubbles will interfere with OBS. [ABSTRACT FROM AUTHOR]

This paper presents a numerical model designed to simulate subaqueous cross-shore profile behavior, including response of feeder mounds and barred systems. The present model development builds on the semi-empirical model proposed by Larson et al. (2013), designed to simulate the evolution of longshore bars exposed to incident waves, as well as the exchange of material between the bar and the berm region. Here, efforts are made to expand the theory for the evolution of a single-bar to a 2-bar system, where the volumes of the individual bars (inner and outer) and their responses are modeled. In order to investigate the predictive capacity of the model, this exploratory numerical tool is first calibrated and validated against data from Duck, North Carolina, USA, where 2 bars typically appear (inner and outer). Field data derived from nearshore sand placement projects (Silver Strand State Park, California, and Cocoa Beach, Florida, USA), involving the construction of artificial longshore bars, are also employed to test the model in complex situations with diverse wave climates and typical beach profile shapes. The study presented in this paper shows that the equilibrium-based model is skilled at predicting the time-varying volume of the outer bar (ε = 0.39; NMSE = 0.24), suggesting that this morphological feature is strongly influenced by offshore wave forcing in a predictable, equilibrium-forced manner. Model skill was lower (ε = 0.51; NMSE = 0.29) when predicting the inner bar evolution at Duck, remaining questions about the predictability and the equilibrium-driven cross-shore behavior of more transient features. Model prediction of the evolution of feeder mounds (artificial bars) proved to be also successful through description of hypothetical bars characterized by zero equilibrium bar volume, leading to a good agreement with the field observations. Overall, the potential for using rather simple models to quantitatively reproduce the main trends of cross-shore volume changes in bars in a time perspective from years to decades has been demonstrated. • Simple model to predict long-term evolution (years to decades) of 2-bar systems as well as the response of feeder mounds. • Simulation of individual bar volumes exposed to incident waves following an equilibrium-forced approach. • Short calculation times while keeping the model stability. • Potential for merging with a shoreline evolution model. [ABSTRACT FROM AUTHOR]

Cross-shore profile response to energetic wave events is challenging to predict because the physics are poorly understood and wave and topographic data are often sparse or unknown. Six events with varying duration, wave intensity and beach slopes are used to calibrate and assess two process-based cross-shore models, CShore and XBeach, at two southern California beaches. Model performance is quantitatively evaluated using high resolution spatiotemporal survey observations along with Brier Skill Scores (BSS) and a Beach Elevation Change Error (BECE) metric that evaluates alongshore-averaged upper beach volume predictions. XBeach is tested with default and site-calibrated parameters. Calibration improved skill for all profiles and events, however XBeach skill scores often remained low and in no case correctly predicted the offshore bar formation. Notably, XBeach is sensitive to the beach profile's calibration depth extent. Upper beach calibration produced significantly different skill than when the full profile was considered. CShore was tested using both the 'Atlantic' and 'Pacific' parameters. Both models predict profile change with limited skill. In their present forms, CShore and XBeach are unable to accurately predict beach profile change on these typical southern California beaches, but when calibrated may provide qualitatively useful beach face erosion estimates. • XBeach and CShore are calibrated and evaluated at two southern California beaches. • Model performance is assessed using the Brier Skill Score and a 'Beach Elevation Change' fit measure. • CShore and XBeach did not accurately predict beach profile change in moderate events. • XBeach calibration is sensitive to beach profile depth extent. • Generally, CShore 'Pacific' parameters produced lower skill scores than 'Atlantic'. [ABSTRACT FROM AUTHOR]

Although commonly used for the validation of morphological predictions, point-wise accuracy metrics, such as the root-mean-squared error (RMSE), are not well suited to demonstrate the quality of a high-variability prediction; in the presence of (often inevitable) location errors, the comparison of depth values per grid point tends to favour predictions that underestimate variability. In order to overcome this limitation, this paper presents a novel diagnostic tool that defines the distance between predicted and observed morphological fields in terms of an optimal sediment transport field, which moves the misplaced sediment from the predicted to the observed morphology. This optimal corrective transport field has the "cheapest" quadratic transportation cost and is relatively easily found through a parameter-free and symmetric solution procedure solving an elliptic partial differential equation. Our method, which we named effective transport difference (ETD), is a variation to a partial differential equation approach to the Monge–Kantorovich L 2 optimal transport problem. As a new error metric, we propose the root-mean-squared transport error (RMSTE) as the root-mean-squared value of the optimal transport field. We illustrate the advantages of the RMSTE for simple 1D and 2D cases as well as for more realistic morphological fields, generated with Delft3D, for an idealized case of a tidal inlet developing from an initially highly schematized geometry. The results show that by accounting for the spatial structure of morphological fields, the RMSTE, as opposed to the RMSE, is able to discriminate between predictions that differ in the misplacement distance of predicted morphological features, and avoids the consistent favouring of the underprediction of morphological variability that the RMSE is prone to. • An optimal transport field moves misplaced sediment to the observed morphology. • The optimal, rotation-free transport field is found by solving a Poisson equation. • The new RMSTE error metric is the root-mean-square of the optimal transport field. • Unlike the RMSE, the RMSTE detects misplacement distances of predicted features. • The RMSTE avoids the tendency of the RMSE to reward underprediction of variability. [ABSTRACT FROM AUTHOR]

Sand nourishments are increasingly applied as adaptive coastal protection measures. Predictions of the evolution of these nourishments and their impact on the surrounding coastline contain many uncertainties. The sources that add to this uncertainty can be delineated between intrinsic and epistemic uncertainty, i.e. inevitably in the system or related to knowledge limitations. Effects of intrinsic uncertainty (e.g. due to wave climate variability) on coastal evolution can be significant. In studying these effects, it has often been assumed that intrinsic uncertainty is dominant over epistemic uncertainty (e.g. introduced by the model), yet the magnitude of both contributions have not been explicitly quantified to assess the validity of this assumption. This paper examines the relative importance of intrinsic and epistemic uncertainty in coastline modeling of a large-scale nourishment. It uses a probabilistic framework in which sediment transport is considered to be a function of random wave forcing (intrinsic) and model (epistemic) uncertainty, calculating transport using a one-line model. The test case for this analysis is the mega-nourishment, the Sand Engine, located in the Netherlands. The applied wave climate variability is obtained from long term wave observations, whereas model uncertainty is quantified using the Generalized Likelihood Uncertainty Estimation (GLUE) method relying on monthly observations. We find that the confidence intervals on predicted volume losses increase substantially when including both intrinsic and epistemic sources of uncertainty. A global sensitivity analysis shows that ignoring model uncertainty would underestimate the variance by at least 50% after a 2.5-year simulation period for the Sand Engine, hence producing significant overconfidence in the results. These findings imply that for coastal modeling purposes a dual approach should be considered, evaluating both epistemic and intrinsic uncertainties. • Wave climate variability and model uncertainty both influence prediction uncertainty. • Model uncertainty can be estimated from observations through the GLUE method. • Wave climate variability explains less than half of the predicted variance after 2.5 yr. • Assessing only wave climate variability can produce significant overconfident results. • Evaluating both intrinsic and epistemic uncertainty is essential in predicting shoreline evolution. [ABSTRACT FROM AUTHOR]

New large-scale experiments on the influence of storm sequencing on beach profile evolution are presented. The experiments comprised three sequences that commenced from the same initial beach profile. Each sequence consisted of two storms of different energy, with each storm followed by a recovery phase. A specific focus of the experiments was the influence of storm chronology as well as the influence of the recovery wave energy and duration on beach evolution. The breaker bar and the shoreline are studied as indicators for the beach response. Both evolve towards an equilibrium location for each wave condition where the breaker bar reaches its equilibrium much faster than the shoreline. Overall, no enhanced beach erosion due to storm sequencing is observed. Despite a similar cumulative wave power of the three sequences, the final beach configuration of each sequence seems to be determined by the last wave condition instead of previous storms. However, storm sequencing is important when the beach profile has not yet fully recovered before being disrupted by the subsequent storm. In this case, the second storm does not necessarily cause further erosion but can result in onshore sediment transport and hence, form part of the recovery. The bulk onshore sediment transport as well as the shoreline recovery rate vary depending on the wave condition and the profile disequilibrium and show a maximum value for a recovery condition with an intermediate wave energy. The very low energy condition that was performed for a long duration (24 hours) generated a near-stationary beach profile with typical features of a reflective beach. • New large-scale experiments on storm sequencing and beach response. • The beach evolves towards an equilibrium state under the performed storm sequences. • The rate of beach change varies depending on the antecedent beach morphology. • Largest bulk onshore sediment transport occurs for intermediate low energy conditions. • A very low energy condition of long duration (24 h) results in a reflective beach profile. [ABSTRACT FROM AUTHOR]

On October 29, 2012, storm surge and large waves produced by Hurricane Sandy resulted in the formation of a breach in eastern Fire Island, NY. The goals of this study are to gain a better understanding of the physical processes that govern breach behavior and to assess whether process-based models can be used to forecast the evolution of future breaches. The wilderness breach grew rapidly in size during the first winter following formation. Growth of the breach was accompanied by the formation of a complex of flood shoals inside Great South Bay, a primary channel that flowed through the eastern part of the flood shoals, and an ebb shoal on the ocean side of the breach. From the summer of 2013 through late 2015, the breach continued to change and evolve, albeit at a much slower pace than in the first year after formation. A hybrid combination of Delft3D and XBeach models is used to hindcast the morphodynamic evolution of the wilderness breach over the first three years after formation. The formation of the breach during Hurricane Sandy is not part of the simulations. Model simulations are initiated with a post-storm topography in which the breach is already present. The models are capable of hindcasting the main morphodynamic changes of the wilderness breach. The spatial patterns, as well as the bulk statistics, such as breach geometry and sediment volume changes, are reasonably well reproduced by the model. The model sheds light on previously unknown processes of breach evolution, especially regarding sediment transport and flow regimes within the breach complex. • A hybrid combination of Delft3D and XBeach models hindcasts the morphodynamic evolution of a barrier island breach. • Model results are validated against a wide range of field observations. • The models shed light on previously unknown processes of breach evolution regarding sediment transport and flow regimes. [ABSTRACT FROM AUTHOR]

Observations of the depth integrated and time averaged sediment transport on a mixed sand and gravel (MSG) beach are presented and analysed to examine the performance of a new portable streamer trap. Measurement of the longshore sediment transport rate in the surf zone remains one of the great challenges in coastal engineering and coastal sciences. Sediment traps for sand beaches have proven useful in the past, but are not suitable for MSG beaches. This paper describes a portable depth-integrated streamer trap designed to measure the depth-integrated combined bed load and suspended longshore sediment transport on MSG beaches. The device consists of a polyester sieve cloth mounted into a rectangular holding frame. The stability of the device is achieved by gravity: the combined weight of the device and the operator, who is standing on and down-current of the device. The device has been tested in the field under moderate wave conditions at Minsmere, UK. We show that the observed suspended and bed load sediment transport are proportional to the wave energy flux, as formulated in the standard theoretical model, CSHORE. The data suggest that the empirical efficiency of wave breaking and bed load parameter are several orders of magnitude larger than that previously observed for uniform fine sand values. • Measurement of the longshore sediment transport rate in the surf zone remains one of the great challenges in coastal engineering and coastal sciences. • Streamer traps for sand beaches have proven useful in the past, but are not suitable for Mixed Sand and Gravel (MSG) beaches. • This paper describes a portable depth integrated, streamer trap designed to measure the depth-integrated combined bed load and suspended longshore sediment transport on MSG beaches. • The device has been tested in the field under moderate wave conditions at Minsmere, UK. • Empirical efficiency of wave breaking and bed load are several orders of magnitude larger than for uniform fine sand values. [ABSTRACT FROM AUTHOR]