Search

The main purpose of the research was to develop appropriate tools for forecasting the effects of storms. The use of the high-resolution SWAN wave model powered by AROME wind fields to couple it with the SWANOneSed sediment transport model and a model using the Ruggiero formula, predicting the extent of the flooded shore, allowed the development of reliable tools for forecasting the effects of storms. Validation using qualitative analysis showed that the results obtained from the coupled SWANOneSed model are characterized by high consistency in intensification and direction of changes. The model using the Ruggiero formula obtained a high value of the correlation coefficient, i.e. 0.970 and 0.992 for the Satbałtyk-Xbeach model data, based on the Hunt&Mase formula, and the high-resolution Pleiades Neo satellite data, respectively. By combining models from the SWAN family, i.e. the SWAN and SWANOneSed wave model and a model using the Ruggiero formula, it was possible to obtain reliable and compatible tools enabling an uninterrupted and synchronized operational process of generating forecasts of storm effects. [Display omitted] • The coupling of the SWAN & SWANOneSed enables reliable and operational forecasting. • Measured & terrain surveyed data-fed model are consistent with other observed data. • Formula van Rijn reliably reproduces sediment transport in various types of coasts. • The Ruggiero formula is applicable in various parts of the Polish coast. [ABSTRACT FROM AUTHOR]

Beaches are important coastal features that provide vital ecosystem services; however, these systems are threatened by coastal erosion, sea-level rise, and coastal squeeze. Beach nourishments are a commonly applied coastal protection measure to mitigate erosion and flood risks while maintaining or enhancing recreational values. Nourishments vary in scale from mega-nourishments to small-scale nourishments, where the latter has typically been less studied due to the limited resources for monitoring. Meanwhile, with rising sea levels, the implementation of small-scale nourishments is expected to increase, and there is a need for more knowledge about the morphological evolution and technical lifetime of these interventions. In this study, the morphological responses of small-scale beach nourishment (total volume 20,000 m3 which amounts to 30 m3 added per m alongshore) are observed and quantified over various timescales, considering the initial adjustment, long-term development, and event-driven response. The investigated nourishment is implemented in a partly sheltered coastal embayment in the semi-enclosed Baltic Sea, which has a complex interaction between waves and water levels. Furthermore, the beach is surrounded by hard structures, a rock revetment at the back, and a harbor mole and a groin, influencing the longshore and cross-shore sediment transport. The results show that substantial reduction in subaerial volume can be attributed to specific events. In addition, we observed considerable spatial variation in the sediment re-distribution induced by hard structures and variability in the nearshore bathymetry. The lifetime of the beach nourishment is just over two years. The nourished material remains in the system at the end of the lifetime but is not available for beach recovery. Still, the added subaerial volume has eroded at the midsection, and the protective beach width has been reduced, leaving the rock revetment exposed with reduced protection for the hinterland. The energy conditions at the site are highly episodic, which impacts morphological evolution, and observations indicate that the development is event-driven. • Beach morphodynamics in a low-energy coastal embayment • Episodic wave activity and water level variations are influenced by basin effects. • Morphological response of a small-scale beach nourishment at different timescales • Beach nourishment performance during an extreme storm surge [ABSTRACT FROM AUTHOR]

While the impact of the spatio/temporal variability of grain size on morphological beach state is reasonably well understood, relatively little is known on its impact at a scale of days/months on aeolian sediment transport. This study focuses on five short intensive wind events during which aeolian sediment transport measurements, beach surface sampling and elevation change surveys were carried out for 1 to 3 days, over a 16-month period on a microtidal beach dominated by offshore winds. Monthly observations show a high temporal variability in beach grain size in relation to the decoupling between hydrodynamic and aeolian processes, from medium sand after a marine storm and inundation of the beach, to very coarse sand after several weeks of storm-force winds. During each wind event, topographic change on the beach ranged from zero, to 0.55 m. The time scale of coarsening depended on the initial beach grain size and could be very fast when the beach was composed of medium sand (e.g. 388 μm sand changed to coarse sand of 547 μm in 40 h). In contrast, it took one month to transition from a coarse median beach grain size of 883 μm to a very coarse one of 1323 μm. This variability in grain size results in dramatically different rates of sediment flux. For example, during average wind speeds of 10 to 14 m/s the sediment flux when the beach was composed of medium sized sand ranged between 21 and 154 kg/m/h compared to 0.4 to 50 kg/m/h when the beach was composed of coarse and very coarse sized grains. Overall, this study highlights the importance of beach grain size variability on aeolian sediment transport and shows that for similar incident wind and climatic conditions aeolian sediment transport rates vary dramatically. The study demonstrates the importance of taking care when using a constant median grain size in the calculation of long-term aeolian sand transport on beaches with heterogeneous spatial and temporal beach grain size variability. • Transport rates can be ten times greater on medium-sized beach than coarse one. • Offshore wind generate a grain size sorting, the finest sands are exported seaward. • Topographic variations of the beach depends on its grain size and sand supply. • The return of fine sediments depends on marine storms occurrence and intensities. [ABSTRACT FROM AUTHOR]

Beach loss is a growing global challenge that threatens the safety of coastal communities, the health of coastal ecosystems, recreational amenities, and regional economies dependent on tourism. Spatial gradients in longshore sediment transport, or divergence of drift (DoD), is a primary driver of beach width change over multi-annual time scales, but the response of any particular beach can be challenging to characterize and predict. Here we present a new method to characterize DoD using a non-uniform segmentation of the coastline informed by the spatial distribution of longshore transport potential, including the location of physical barriers identified using satellite imagery, and both maxima and reversals in longshore transport potential derived from nearshore wave data. The method demonstrates improved capacity to predict beach width trends at sandy beaches compared to methods that rely on a uniform segmentation of the coastline. In an application to southern California where satellite data documents two decades of beach width change, the non-uniform segmentation method correctly predicts the sign of beach trends at 93% of transects within a littoral cell and achieves a linear correlation between DoD and beach width trends exceeding 0.8. Moreover, we find that a minimum of five years of data are required to establish consistently strong correlations between DoD and beach width changes. Conversely, use of a uniform segmentation is shown to be unreliable for estimating beach width trends due to strong sensitivities to shoreline segment size. This work shows the potential to leverage nearshore wave data and satellite-based beach width data for improved characterization of shoreline dynamics relevant to beach erosion management. • A new shoreline modeling method is presented for estimating divergence of drift. • Segment boundaries are identified using longshore transport characteristics. • Strong correlations were shown between divergence of drift and beach width trends. • A littoral Peclet number characterizes the dominant longshore transport mechanism. [ABSTRACT FROM AUTHOR]

This paper presents the use of an Eulerian–Eulerian multi-phase model to examine sediment transport over a gravel beach under regular waves. A previously published full-scale experiment is reproduced numerically; the simulated wave deformation, flow velocity, pore pressure, and morphological evolution are consistent with measurements. The multi-phase model can produce berm formation for smaller waves and beach erosion for larger waves as observation in previous field studies. The sensitivity analysis suggests that the nonlinear component of drag has significant effect on the berm formation through infiltration and exfiltration. The two simulated forces applied on the sediment (drag and buoyancy) are examined. The drag is the main force directly for sediment transport; therefore the sediment transport rate has high correlation with depth-averaged flow velocity. The buoyancy that is caused by plunging flow impacting beach face can push the sediment landward in the bore front, where the flow acceleration has its peak. The flow acceleration is considered in some previous sediment transport models empirically for simulating morphological evolution of gravel beach under waves. The buoyancy links the flow acceleration and sediment transport rate in the bore front. • Sediment transport in a gravel beach is simulated using a multiphase model. • The drag is the main force directly for sediment transport. • The buoyancy links the flow acceleration and sediment transport rate in the bore front. • The nonlinear drag has the effect on berm formation. [ABSTRACT FROM AUTHOR]

Storm surge, a major disaster in coastal areas, is generated by tropical cyclones. Strong currents and waves during storm surges often cause sediment transport and beach erosion, significantly damaging the coastal ecosystem. This paper presents a flow-wave-sediment-morphodynamic coupled model to predict morphodynamic changes caused by overwash during storm surges. In the model, the flow field is calculated using the generalized shallow water equations coupled with the Simulating Waves Nearshore (SWAN) model, while sediment transport and bed changes are computed using a non-equilibrium total-load sediment transport model. The model solves the governing equations by employing the explicit finite-volume approach based on a rectangular mesh. The Godunov-type central upwind scheme is adopted to calculate the interface fluxes, thereby solving the complex Riemann problem. A series of numerical experiments considering wave-induced longshore current and short-term bed erosion are conducted to validate the established model and demonstrate its ability to simulate waves, flow fields, and bed changes during storm surge. Specifically, we used the model to simulate the morphological evolution of the Santa Rosa barrier island caused by Hurricane Ivan's storm surge, and the results indicate that the model accurately predicts the real-case erosion process caused by storm surge and overwash during the hurricane. The simulated results clearly explain overwash development, including washover fans, foredune erosion, and back-barrier deposition. It demonstrates that the front dune significantly eroded with the Santa Rosa barrier island coastline retreating by a maximum of about 80 m during the storm surge. More than three breaches with a width of up to 135 m were formed on the sandy barrier due to wave overwash, while the topography at the breach changed significantly. • A new flow-wave-sediment-morphodynamic coupled model is developed to predict morphodynamic changes caused by overwash during storm surges. • A series of numerical experiments conducted using the new model demonstrates its ability and it successfully predicts the overwash erosion of the Santa Rosa barrier island during Hurricane Ivan's storm surge. [ABSTRACT FROM AUTHOR]

During August 2018 – November 2019, the transport pathways of dredge material from a specially constructed nearshore feeder berm were investigated as part of a collaborative study by the City of South Padre Island, U.S. Army Corps of Engineers–Galveston District, U.S. Geological Survey, Partrac GeoMarine Inc., and Texas A&M University, into the efficacy of beneficial use dredge material (BUDM) as a method of replenishing the beach profile and shoreface at South Padre Island, Texas with sediment. Dual-signature (fluorescent and ferrimagnetic) tracer particles, designed to be hydraulically equivalent to the dredge material, were placed on the berm, and a sampling program was initiated to monitor the spatiotemporal movement of tracer particles under the influence of the prevailing hydrodynamic regime. Wave and current data were collected and were used together with available metocean data to identify the forcing mechanisms of sediment transport; improved understanding garnered from the consideration of multiple datasets can be used to inform future coastal management decisions. Tracer analysis results indicated low magnitude, shoreward transport of dredge material from the berm and along shore transport in both northerly and southerly directions. Small amounts of tracer detected in beach face samples demonstrated connectivity between the constructed feeder berm and the shoreface. However, the generally low tracer concentration within beach face samples indicated low rates of sediment transport for berm sediments, and a low magnitude sediment transport pathway from the berm directly to the beach face, with possible storage of sediment in the nearshore bar system. Given that the berm was at or beyond the closure depth and considering the relatively weak prevailing near bottom hydrodynamic conditions, the potential for sediment to be mobilized and transported during the study period was generally low. Periods of higher energy waves, driven by north-northwest winds, were identified as a key driver of sediment transport but due to the infrequent nature of these events the sediment transport regime across the area of interest was temporally limited. Longshore movement of sediment was both north and south, mainly dependent on prevailing wind directions and resulting longshore currents. We discuss implications for coastal zone management and the use of feeder berms as an artificial beach nourishment mechanism to replenish sediments lost by coastal erosional processes. The insight into nearshore emplacement of material can be used by local governments and coastal managers to optimize the efficacy of berm emplacement and implement such schemes as a cost-effective nourishment option, or when onshore placement of material is not feasible. • Hydrodynamic and tracer measurements were effective monitors of sediment transport. • Hydrodynamic monitoring indicated relatively weak sediment transport conditions. • Tracer sampling confirmed that transport to replenish the beach was low magnitude. • Consider sediment transport regime before selection of BUDM placement area. • Licensed BUDM placement areas may not be optimal for beach nourishment. [ABSTRACT FROM AUTHOR]

Predicting the future behavior of beach and nearshore systems requires an accurate delineation and understanding of coastal cell boundaries, sediment transport pathways, and sediment sources and sinks. Unfortunately, there is a paucity of field datasets on beach and nearshore morphological change that extend fully from the top of the dunes to beyond the depth of closure to enable quantification of the sediment budget. Here, for the first time, we employ a total sediment budget approach, examining a sandy and embayed beach located in the north coast of SW England, to investigate inter- and multi-annual embayment scale sediment dynamics over a 10-year period that includes extreme storm erosion and post-storm recovery. We demonstrate that, despite the deeply embayed nature of the beach, the shoreline orientation roughly parallel to the dominant wave direction and the overwhelmingly cross-shore forcing of the inter-tidal beach volume, the system is neither closed, nor balanced. The very significant net changes in the recorded sediment volume from dune top to depth of closure (−14.5 m ODN), representing a loss of c. 100 m3 m−1 during the extreme storm period and a gain of c. 200 m3 m−1 during the recovery period, indicate that significant sediment transport occurs seaward of the base of the terminating headlands and beyond the morphological depth of closure. The results further indicate that the inter-tidal region is partly uncoupled from the sub-tidal region, with the former region dominated by cross-shore sediment fluxes, whereas the subtidal region is also significantly affected by longshore sediment fluxes. A conceptual model is presented that balances the observed volume changes with inferred fluxes, forced by variations in total and alongshore wave power. This study contradicts the general assumption that when sediment exits the inter-tidal, it rests undisturbed in the sub-tidal, waiting for a period of low-moderate energy to bring it onshore. The large sediment volumetric variations across the lower shoreface (depth of 5–20 m), which are of the same order of magnitude as, but uncorrelated with, those occurring in the inter-tidal region, are suggestive of an energetic longshore transport system across this deeper region. It is possible that this transport system extends along the whole north coast of SW England and this finding may lead to a shift in understanding of sediment budgets along exposed and macrotidal embayments globally. Unlabelled Image • Full sediment budget was produced along an exposed macrotidal embayment and linked to wave forcing. • Inter- and sub-tidal volumes are not inversely correlated, indicating decoupling. • Sediment budget suggests significant exchange around headlands and/or across depth of closure. • Beaches on this coast type can be considered part of an extended coastal cell. [ABSTRACT FROM AUTHOR]

The twin ambits of climate change and coastal development have raised public awareness of shoreline management. Simultaneously, they have highlighted a gap in our understanding of sediment transport and morphodynamic processes at time and space scales appropriate for shoreline management purposes. Here, we analyse an exceptional set of beach surveys gathered over a period of twenty-two years along the Suffolk coast, eastern UK, that extends over approximately 80 km to investigate the meso-scale shoreline variations. The surveys have been made biannually along fixed transects spaced at approximately 1 km intervals as part of a strategic monitoring exercise undertaken by the coastal authorities to assist in shoreline management planning. Changes in beach volume, foreshore slope and shoreline position have been computed to investigate both spatial and temporal changes. The analysis reveals some distinct responses to the physical processes of tides and waves, anthropogenic interventions and geological controls. Neither a clear relationship between the presence of sea defences and beach response nor an ordered regional-scale shoreline movement are evident. Temporal variations in beach volumes and position provide a similarly complex picture with recessionary, accretionary and stable behaviour all apparent within the study site. There is evidence of quasi-cyclic behaviour at some locations as well as a reduction in variability over time-scales beyond approximately five years. • Historic beach surveys over a period of 22 years along a frontage of 80km have been analysed for their meso-scale dynamics. • Meso-scale morphological changes of protected and unprotected beaches have been classified. • The majority of beaches fronting hard defences don't exhibit erosive trends; the majority of those without hard defences do. • Beach morphodynamics are constrained to the synoptic scale, with little coherent variation at the meso-scale. [ABSTRACT FROM AUTHOR]

Depth of Closure (DoC) calculation has been analysed for engineers and researchers during decades due to its relevant importance on marine works, such as beach nourishments or littoral defense projects. Several methods can be found in the literature related to the evaluation of DoC. However, they just focus on the bottom elevation change, leaving aside the cross-shore sediment transport issue. This work deals with all requests of the DoC definition and presents a new method based on the comparison of repetitive beach profiles. The main contribution of this research is the methodology presented to quantify the cross-shore sediment transport by the calculation of the Net Cross-shore Sediment Transport Parameter (NCSTP C). Its application to a complex area of the East Spanish coast concludes that NCSTP C values less than or equal to 10% can be considered as no significant. The differences between several criteria based on the change of the bottom elevation are also studied in order to evaluate if they are relevant for engineering works. The new methodology developed is a great advance in the knowledge of this imaginary boundary (DoC), since it allows to discriminate between different possible DoC values when applying any method based on profile surveys comparison. • New method to obtain the Depth of closure from profile surveys. • Quantification of the net cross-shore sediment transport. • 762 periods of time analysed over 22 years (1992–2014). • Five profile survey criteria have been compared. • The new method permits the selection of the DoC among several possible values. [ABSTRACT FROM AUTHOR]

In this study the numerical model Delft3D is implemented on high-resolution grids to evaluate beach morphological response to groins and submerged breakwaters under sea-breeze conditions. The numerical model is compared with field measurements from three sites on the northern Yucatan coast of Mexico. At these sites, relatively low energy waves with significant wave heights arrive at a steep oblique angle to the coast that drives high sediment transport rates. After calibration of the model, by adjustment of model free parameters, the model results show accurate representations of the diurnal variation of hydrodynamic conditions (wave height and current velocity) driven by the daily sea-breezes. Moreover, the morphodynamic model shows a good representation of the rapid morphological changes, particularly of the accretion pattern caused by a temporary groin and the subsequent recovery following the structure removal. However, erosion patterns at the downdrift areas of structures were not reproduced, owing to the numerical model limitations of simulating swash morphodynamics. Model validation with field observations of the beach response behind submerged breakwaters enabled the model to be used for a parametric study. Following previous work, new equations are developed in the present study that show an improvement for predicting shoreline changes near submerged breakwaters under sea-breeze conditions. Despite the limitations in reproducing downdrift erosion, overall the high-resolution modelling approach satisfactorily simulates the hydrodynamic and the updrift accretion responses to coastal structures on sandy beaches with oblique waves. • Simulations of beach change near groins and submerged breakwaters are performed. • Results are compared to measurements at three sites with high sediment transport rates. • New equations show improved prediction of shoreline change near submerged structures. [ABSTRACT FROM AUTHOR]

Rising sea levels are expected to cause widespread coastal recession over the course of the next century. In this work, new insight into the response of sandy beaches to sea level rise is obtained through a series of comprehensive experiments using monochromatic and random waves in medium scale laboratory wave flumes. Beach profile development from initially planar profiles, and a 2/3 power law profile, exposed to wave conditions that formed barred or bermed profiles and subsequent profile evolution following rises in water level and the same wave conditions are presented. Experiments assess profile response to a step-change in water level as well as the influence of sediment deposition above the still water level (e.g. overwash). A continuity based profile translation model (PTM) is applied to both idealised and measured shoreface profiles, and is used to predict overwash and deposition volumes above the shoreline. Quantitative agreement with the Bruun Rule (and variants of it) is found for measured shoreline recession for both barred and bermed beach profiles. There is some variability between the profiles at equilibrium at the two different water levels. Under these idealised conditions, deviations between the original Bruun Rule, the modification by Rosati et al. (2013) and the PTM model predictions are of the order of 15% and all these model predictions are within ±30% of the observed shoreline recession. Measurements of the recession of individual contour responses, such as the shoreline, may be subject to local profile variability; therefore, a measure of the mean recession of the profile is also obtained by averaging the recession of discrete contours throughout the active profile. The mean recession only requires conservation of volume, not conservation of profile shape, to be consistent with the Bruun Rule concept, and is found to be in better agreement with all three model predictions than the recession measured at the shoreline. [ABSTRACT FROM AUTHOR]

Underneath rock slopes of rubble mound structures often one or more granular filter layers are present. These filter layers prevent base material washout. In contrast to traditional filters, geometrically open filters allow for some movement of base material. In order to design such open filters the amount of erosion and accretion of base material needs to be predicted. Based on 2D physical model tests Van Gent and Wolters (2015) presented a method to estimate the erosion and accretion of sand underneath rock slopes. Since the developed method was only valid for perpendicular wave attack, a new study has been performed to assess effects of oblique wave attack on the amount of erosion and accretion of sand underneath a rock slope. For that purpose 3D physical model tests were performed in a wave basin with 5 different wave angle between 0° (perpendicular wave attack) and 75°. Based on the test results it was shown how the effects of wave obliquity can be taken into account in the design of open filters. In addition, the effect of the storm duration on open filters has been studied. This led to an extended design method to predict the amount of erosion and accretion of sand underneath rock slopes under wave loading. [ABSTRACT FROM AUTHOR]

Disequilibrium-type models for two beach profile parameters, P , the shoreline position and net bulk sediment transport, are developed for laboratory experiments that demonstrate morphological hysteresis in the evolution to equilibrium of beach profiles under sequences of different wave climates. The model principle follows the classical disequilibrium approach but with non-monotonic relationships between the forcing and the chosen beach profile parameter at equilibrium, P eq , previously verified and presented in part 1 of this work (Baldock et al., 2017). Two such relationships are required to model beach profile evolution that exhibits morphological hysteresis. The model coefficients are derived for monochromatic and random wave experiments and subsequently used to model data obtained from cyclic erosive and accretive wave conditions of shorter durations, alternating through multiple cycles. In these conditions equilibrium conditions were not reached and hysteresis does not occur. The model is used to investigate the morphological feedback between the outer and inner bars and the resulting behaviour of the bulk transport, and the relative depth over the bar crest is shown to be an attractor in this case. The model coefficients and morphological time-scales derived from the cyclic experiments are very similar to those derived from the equilibrium experiments for the bulk transport. Normalised mean square model errors range from 1% to 20% when applied to independent data. The data from the cyclic wave conditions can be inverted to derive the conditions expected at equilibrium, which match those observed, indicating a robust model relationship between the forcing and P eq . The relationship between the forcing and P eq can also be determined directly from the cyclic experiments. This approach may be more robust than determining the relationship from periods where P is stationary since, in a time-series of P versus the forcing, stationary points can occur due to changes in wave conditions, in addition to the instances when P = P eq . [ABSTRACT FROM AUTHOR]

Novel series of experiments are presented that demonstrate morphological hysteresis in the evolution to equilibrium of beach profiles under sequences of different wave climates. The experiments were conducted in a wave flume at medium scale using both monochromatic and random waves, representing 2D conditions. Beach profiles were obtained with high spatial resolution at frequent intervals with a laser profiler, from which shoreline location, bar position and sediment transport rates were derived. Experiments were conducted for sequences of wave climates, where a sequence comprised of 6–13 sequential tests, each commencing with the beach profile from the preceding test. Each test was run until equilibrium conditions were obtained and had a constant wave height, increased or decreased relative to the preceding test. Cyclical conditions were also included, with erosive and accretive wave conditions of short durations alternating through multiple cycles, so that equilibrium conditions were not reached during a test. With a sequence of increasing wave heights, the relationship between the shoreline position and the bulk cross-shore sediment transport, at equilibrium, was non-monotonic, indicating a maximum in the landward sediment transport rate. For test series comprised of a sequence of increasing wave heights followed by a sequence of decreasing wave heights, morphological hysteresis was observed in the equilibrium shoreline position and bulk cross-shore sediment transport, such that shoreline recession, or offshore transport, continued in some instances after reductions in wave height. This is inconsistent with classical equilibrium type shoreline evolution models. However, when equilibrium conditions were not reached, in the cyclic sequences, no such morphological hysteresis was observed and a dynamic equilibrium is reached. The morphological hysteresis occurs because of the decay, stranding, or increased relative depth, of the breaker bar following a reduction in wave height, often in conjunction with a new breaker bar generated by further offshore transport in the inner surf zone. Similar sequences of morphological response are evident in field data and larger scale tests in the literature. Finally, it is shown that the morphological hysteresis can be explained using the classical equilibrium beach state model of Wright et al. (1985) by introducing the concept of a subsequent alternate active beach state, which may occur following a change in wave conditions. [ABSTRACT FROM AUTHOR]

Coastal dunes provide many ecosystem services including protection of infrastructure from wave overtopping and habitat for native species. Foredunes grow at different rates and assume different forms (i.e., short and wide to tall and narrow) depending on a range of factors including pre-existing beach and dune morphology, wind, wave, and water levels, sediment grain size, and vegetation characteristics, yet the relative importance of these factors on foredune growth is understudied. Here, we quantify foredune evolution (2016–2019) and explore the relative influence of a suite of metocean, sedimentary, and ecological factors for dune growth on three barrier islands in the U.S. North Carolina Outer Banks (Cape Lookout National Seashore). We incorporate observed and hindcast wind, wave, and water level data into the process-based, coupled beach-dune evolution model, Windsurf, to explore the relative contribution of factors likely to influence foredune growth at the annual timescale (2016–2017). Our cross-shore topographic profile observations show varied interannual foredune change rates and characteristics, including horizontal retreat and progradation at the dune toe and vertical erosion and accretion at the dune crest. Model results indicate that, of the factors explored, pre-existing morphology had the greatest influence on the type of foredune growth that occurred (i.e., incipient dune development, widening of the dune, and/or vertical accretion), which dramatically altered the final shape of the dune. Variations in wind and wave climates were associated with the relative contribution of marine- and aeolian-driven bed elevation changes and were particularly influential during storms. In addition, increases in the minimum elevation of vegetation on the dune profile (analogous to the cross-shore distance between the shoreline and established vegetation line, i.e., the vegetation limit, as coined by Duran and Moore, 2013) increased dune crest height and dune volume. Moreover, variations in the minimum vegetation elevation resulted in a larger range of dune crest elevations and dune volumes than differences in the median sand grain size. We suggest that insights into the relative influence of metocean, sedimentary, and ecological factors to dune growth can assist in the development of practical coastal management strategies. • Pre-existing beach-dune morphology had the largest influence on dune growth type. • Exposure to the dominant wave direction led to increased dune volume. • Higher minimum vegetation elevation and finer sand resulted in taller dunes. • Minimum vegetation elevation influenced dune growth more than sand grain size. [ABSTRACT FROM AUTHOR]

Experimental results involving shoreface nourishment scenarios are presented. The experiments are performed at small scale and the effects of nourishment placement and timing in relation to long-term cross-shore profile development are investigated. Four different nourishment scenarios are tested experimentally, with nourishment positioned both in the trough of a pre-developed profile as well as along the bar of the profile. The results demonstrate that under all scenarios the erosion of the shoreline slows relative to the case without nourishment. The two cases where the nourishment was placed along the bar reduced erosion of the shoreline more compared to the two cases with nourishment in the trough onshore of the bar. Compared to past experiments on nourishment presented in the literature, the present experiments were run for a longer duration, and the concepts of equilibrium profile and the development towards such an equilibrium were investigated. Curiously, the experiments showed a reversal of the sediment transport rate from being primarily offshore directed across the entire profile to onshore directed in the inner surf zone region closest to the shoreline. This reversal of transport rate occurred without changing the incoming wave conditions and resulted in deposition at the shoreline. This either questions the existence of equilibrium beach profiles or at the very least shows that the development towards such an equilibrium will not always be monotonic in time. • Shoreface nourishments are performed at model scale investigating the influence of timing and placement on long term profile development. • Placement of nourishment can disturb the cross-shore profile shape over long time. • After long time running with the same wave climate the transport rate changed from offshore directed to onshore directed in the inner surf zone. • The change in sign was related to cessation of wave-breaking and resulted in sand returning to an otherwise eroding beach. [ABSTRACT FROM AUTHOR]

Beach accretion is the natural mechanism that allows dry beaches to recover. Human response to climate change produces hardening of the coasts and the incident marine climate, which increases beach erosion produced during winter and prevents a full recovery during summer. Beach nourishments are performed all around the world to fight coastal erosion with a nature-friendly philosophy. Softer techniques as beach scraping are also widely applied. A kind of beach scraping is proposed here as an innovative nature-assisted beach enhancement technique, that aims to accelerate naturally produced sand accretion on the beach profile. It consists of mechanically ploughing the intertidal area of a beach to create ridges and furrows. Prototype-scale laboratory experiments were performed to analyse its effectiveness under controlled conditions. Seven 1 h tests having different water levels and the same initial bottom geometry and sea state conditions (H s = 0.3 m, T p = 7 s) were performed. Sea state, sand, and initial slope characteristics assured accretive conditions. Ploughed and flatbed initial slope geometries were simultaneously tested into two sub-channels of the wave flume. The results indicate that the bottom roughness is 3.57 times larger for the ploughed geometry. Consequently, wave energy dissipation is larger for the ploughed geometry, and therefore, the significant wave height at the shoreward end of the study area is 11% smaller for the ploughed geometry. This smaller wave height under the ploughed morphology leads to more accretive conditions, as observed from the measured onshore sediment transport, which is 2.9 times larger than the natural transport, and the larger accreted sediment volume in all seven test cases. These results demonstrate the effectiveness of ploughing to enhance natural beach accretion under highly probable accretion conditions. Further research is required to define the thresholds of marine conditions in which the potential of beach ploughing can be exploded. • Working with nature. • Ploughing the intertidal area of a beach enhances natural accretion. • Real scale laboratory experiments measuring sediment transport. • Mechanically ploughing increases bed roughness. • Extra wave energy dissipation is produced by ploughing. [ABSTRACT FROM AUTHOR]

A moderate-size (344,000 m3) subaerial beach nourishment was placed in 2012 in front of flood-prone homes at Imperial Beach, California. The subaerially persistent coarser-than-native nourishment sand spread alongshore over a ∼ 4 km span. By winter 2018/19 subaerial sand volumes in front of the flood-prone homes were eroded to near pre-nourishment levels, while sand accumulated near a river mouth ∼ 1.5 km to the south. The observed alongshore patterns of post-nourishment erosion/accretion are consistent with the modeled convergence/divergence of alongshore currents driven by wave radiation stress S x y gradients associated with refraction over a relic cobble ebb shoal. The same alongshore patterns of subaerial erosion/accretion were observed in the 6 years preceding the nourishment, indicating a wave-driven erosion hotspot in front of the flood-prone homes, and an accretion hotspot near the region of river mouth migration. Over the 13-yr observation period, the river mouth migrated 600 m southward and closed in 2016, possibly owing to nourishment sand and El Niño intensified local drift convergence. The computationally efficient drift (radiation stress) gradient model uses simplified wave and surfzone dynamics, assumes proportionality between alongshore sediment transport and the radiation stress component S x y , but nevertheless captures the overall patterns of alongshore nourishment evolution and provides a framework to inform sand management. • The subaerial influence of relatively coarse beach nourishment sand spans 4 km of coast 6 years after placement. • Accretion and erosion hotspots are persistent, 6 years before and after nourishment. • A simple drift divergence model that captures refraction over an ebb shoal describes the alongshore variable sand volume trends. [ABSTRACT FROM AUTHOR]

Estimating sediment budget is a challenge that requires understanding the morphological relationship between the subaerial beach and the upper and lower shoreface. Based on a unique dataset of monthly measured topographic and bathymetric measurements, this study describes the morphodynamics of the subaerial and subtidal sections of a highly-dynamic beach over a 5-year period (2015–2020). Typically, the beach presents a longshore bar trough (LBT) state at the end of the winter, driven by net offshore sediment transport. The nearshore morphology evolves into more reflective states (rhythmic bar beach, RBB; transverse bar rip, TBR; and low tide terrace, LTT) driven by onshore sediment transport when the incident wave-energy decreases over the spring and summer. Seasonal variations of the incident wave-energy resulted in large subaerial-subtidal exchanges of sediment (200–300 m3 m−1), but these exchanges were an order of magnitude smaller in yearly scales. Subaerial and upper-shoreface morphological changes varied alongshore. Larger variations existed in the south, influenced by persistent rip channels. Instead, alongshore processes resulting from changes in wave direction may control the morphodynamics in the center and north. The subtidal section in north and center gained significant amount of sand (300 m3 m−1) during high-energy conditions, which contributed to a net annual gain of 60 m3 m−1. The origin of that sediment is currently unknown, it could have bypassed from an adjacent beach, shifted alongshore or inputted from the lower shoreface deeper than the depth of closure. This research shows the presence of very large monthly-to-seasonal total volume fluctuations relative to net annual or multi-annual changes, and highlights that comparatively small additions to the annual sediment budget could potentially contribute to the long-term stability of the beach. • Largest morphological variations in the south influenced by persistent rip channels. • Very large monthly-to-seasonal volume fluctuations relative to net annual changes. • Small additions to the annual budget could contribute to long-term beach stability. [ABSTRACT FROM AUTHOR]

The typically curved and stable planform shape of embayed beaches is often observed in the presence of rigid headlands. The long-term alongshore equilibrium shape is variable and is controlled by headland geometry, cellular circulation patterns and wave obliquity at the shoreline. We use a process-based morphological model to simulate the development of embayed beaches depending on different environmental conditions and geological settings (i.e., topography and geometry). The embayment is allowed to develop from an initially straight beach to one which is curved under idealized wave forcing conditions and without external sediment input. Bay development can be approximated with an exponential function with coefficients representing rate of growth and bay size. Long-term shoreline cutback is both uniform (shoreline translation) and non-uniform (shoreline rotation) and is parameterized. Alongshore gradients in flow and transport patterns are related to long-term non-uniform shoreline cutback. Rotation of the beach ceases as the bay matures, leading to a curved shoreline planform, which is a remnant of decaying erosion processes. [ABSTRACT FROM AUTHOR]

The sand dredging activities may cause various physical and environmental changes such as beach erosion, evolution of beach profile, change in current and wave field. To evaluate the relationship among the volume of sand dredging, method of sand dredging, time of sand dredging, shoreline retreat and evolution of beach profile, some experiments were conducted and a two-dimensional numerical model was used. The effect of sand dredging volume on shoreline retreat was investigated by dredging various amounts of sand at one time under the same regular wave condition. The results showed that the relationship between shoreline retreat and dredging volume is nonlinear. In the other considerations, sand bar was dredged as different methods i.e. periodic sand dredging method under the same regular wave condition as well as one time dredging under different regular wave conditions. The final shoreline retreat in the last two methods was nearly equal to the first method, however, the progress of shoreline retreat was slower. After sand dredging in all cases, the beach profiles were not translated to the same original form. Infill rate of the bar after sand dredging is also discussed in term of average absolute sediment transport rate. [ABSTRACT FROM AUTHOR]

A field-based experimental study of beach scarp morphodynamic evolution was conducted on the shoreface of a macrotidal sandy beach subject to storms combined with spring tide events (Luc-sur-Mer, France). Both video and in-situ measurements on an artificial berm are used to understand beach scarp evolution over one tide during stormy conditions. Image time stacks are used to analyze the swash action on the beach scarp and topographical data of the scarp are recorded with a terrestrial scanner laser to quantify the morphodynamic response of the beach scarp to wave action. This work provides a new and unique dataset about beach scarp changes and berm morphology in particular under rising tide and oblique wind-wave conditions. During one stormy event, the berm was completely destroyed. However, contrasting alongshore changes were measured during the erosive phase with different crest and foot scarp retreats and eroded volumes between the west and the east side of the berm. The beach in front of the scarp also shows a contrasting residual evolution, indicating an evident longshore sediment transport on the study area as a consequence of incident oblique wave conditions. A strong connection between beach evolution and beach scarp changes is clearly identified. The scarp erosion increases on the west side of the berm when the beach level is lowered and reduces when the beach surface rises on the east side. The beach slope and foreshore elevation as a result of a longshore sediment transport between east and west profiles, influence swash activity. Overall, water depth and swash activity became progressively different along the scarp during the experiment. Swash measurements indicate that the presence of the beach scarp strongly influences the swash motion. At high tide, the reflection of the uprush on the scarp front induces a collision between the reflected backwash and the following uprush dynamic. These collisions reduce and sometimes stop the motion of the following uprush, reducing the incoming swash excursion. Consequently, the scarp presence modifies the swash interaction that normally appears on a planar beach surface. With a beach scarp, the swash energy level is substantially attenuated and its spectrum is characterized by a large band. The number of uprush impacts on the scarp front calculated from video images reaches about 25 per 5 min. In spite of the swash energy attenuation due to swash/swash interactions, these impacts provoke the berm destruction in about two hours. However, the onshore migration of the swash zone induced by the rising tide appears to be important to explain scarp destruction, compensating the attenuated swash activity due to backwash-uprush interactions. [ABSTRACT FROM AUTHOR]

Understanding time scales of beach response (erosion and recovery) to extreme storms is particularly relevant for management of coastal land and risk. Observations show that rock-bounded platform beaches are generally remarkably stable and only occasionally respond to extreme storm wave forcing with abrupt morphological changes. The present work aims to understand the conditions leading to the disruption of beach stability (storm thresholds for morphological changes) and to comprehend the conditions of the subsequent recovery. Results obtained at two rock-bounded beaches of the western Portuguese coast over five years provided the foundations of a new conceptual morphodynamic model. This model explains abrupt beach disruption as a consequence of full inundation of the beach profile during extreme storms, together with strong wave reflection at the rigid landward boundary, causing major erosion of the subaerial beach. We argue that the timescale of post-storm recovery depends essentially on the fate of the sediment transported offshore during the storm event. If sediments remain within the beach sediment cell (underwater beach section) beach recovery to pre-storm conditions is very fast, while recovery is much slower if sediments exit the beach sediment cell. In the latter case, beach recovery depends on external sand sources, which can lead to recovery time scales of several years. • We investigate conditions leading to abrupt morphological changes in rock-bounded platform beaches. • Total water level adequately describes thresholds for significant erosion during major storms. • A conceptual model explaining patterns of erosion and recovery is proposed. • Abrupt erosion is triggered by wave reflection at the landward hard boundary of the beach. • Beach recovery depends on the geological framework, which controls sediment exchanges with adjacent sediment cells. [ABSTRACT FROM AUTHOR]

Abstract: Numerical cross-shore profile evolution models have been good at predicting beach erosion during storm conditions, but have difficulty in predicting the accretion of the beach during calm periods. This paper describes the progress made in modifying and applying the public domain XBeach code to the prediction and explanation of the observed behaviour of coarse-grained beaches in the laboratory and the field under accretive conditions. The paper outlines in details the changes made to the original code (version 12), including the introduction of a new morphological module based upon Soulsby's sediment transport equation for waves and currents, and the incorporation of Packwood's infiltration approach in the unsaturated area of the swash region. The competence of this modified model during calm conditions for describing the steepening of the profile, and the growth of the beach berm is demonstrated. Preliminary results on the behaviour of the beach subject to both waves and tides are presented. Good agreement is found between the model simulations and large-scale laboratory measurements, as well as field observations from a composite beach in the UK. The reasons for the model's capabilities are discussed. [Copyright &y& Elsevier]

Beaches are dynamic systems characterized by frequent morphological changes due to storm events, gradients in longshore sediment transport, seasonal variations in wave climate and more. The complexity of variations in beach morphology can increase significantly after a beach nourishment, particularly when coastal structures are involved. This study investigates the impacts of a groin field, consisting of both notched and traditional groins, on the morphological evolution of a beach in Deal, New Jersey, USA. More specifically, an evaluation of the performance and specifications of the notched groins is undertaken. In 2016, the beach in Deal was nourished and three of the eight groins comprising the groin field were concurrently notched in order to promote increased movement of longshore sediment transport while maintaining a stable shoreline. The study site was monitored nine times over a period of two years (2018–2019) using Unmanned Aerial Systems Structure from Motion (UAS-SfM) photogrammetry. The near-term morphological response of the study site was evaluated by analyzing high-resolution digital elevation models (DEMs) and longshore sediment transport estimates based on measured wave data. The elevation change maps established that in general, the groin notching was partially successful in reducing shoreline asymmetry in consequence of sediment transport bypassing through the notches. Differences in behavior and patterns of elevation change adjacent to each individual notched groin was observed even though they were all notched according to the same specifications. While all three notched groins were effective in stabilizing the adjacent shoreline, they varied in their effectiveness at promoting longshore sediment transport through the notch. This is likely attributable to the relative location of the notched groins within the groin field and the characteristics of the post-nourishment morphological evolution; the direction of net annual longshore sediment transport at Deal beach is northward, which caused the southern areas of the study site to narrow and the northern areas of the study site to widen. Consequently, the notched groins in the wider sections of beach did not function as intended, as the notches filled in with sediment causing them to mimic the behavior of a traditional groin, including restricted longshore sediment transport and significant erosion/accretion offsets. In the narrower section of beach, the notched groin functioned as designed, such that the notch was located in the swash zone and therefore allowed bi-directional sediment transport and maintained a stable and relatively symmetrical shoreline. Thus, the notched groins performed most effectively when the notch was consistently located toward the seaward end of the swash zone. • Groin notches function optimally when the notch is located in the swash zone. • Improperly constructed notches can fill-in with sediment and behave like traditional groins. • Notch specifications can vary to account for position and uncertainty in the equilibrated beach. • Notch designs should reflect the direction and magnitude of net longshore sediment transport. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes field measurements that document the formation of barchan dunes in the Moroccan Atlantic Sahara desert. The first mechanism described is the transformation of patches and proto-dunes at Cap Juby beach to barchan dunes of elementary size. This transformation is discussed in relation to the wind speed and saturation length. The second mechanism is the ejection of small barchans of elementary size by other small barchans in response to the perturbation of the target barchan by two other impacting small barchans. This remote initiation is discussed in relation to the bulk flux transported by the barchan dunes involved in this interaction and to their morphology. Other modes of barchan initiation observed in the field are also presented. [Copyright &y& Elsevier]

Abstract: New large-scale laboratory data are presented on the influence of long waves, bichromatic wave groups and random waves on sediment transport in the surf and swash zones. Physical model testing was performed in the large-scale CIEM wave flume at UPC, Barcelona, as part of the SUSCO (swash zone response under grouping storm conditions) experiment in the Hydralab III program (Vicinanza et al., 2010). Fourteen different wave conditions were used, encompassing monochromatic waves, bichromatic wave groups and random waves. The experiments were designed specifically to compare variations in beach profile evolution between monochromatic waves and unsteady waves with the same mean energy flux. Each test commenced with approximately the same initial profile. The monochromatic conditions were perturbed with free long waves, and then subsequently substituted with bichromatic wave groups with different bandwidth and with random waves with varying groupiness. Beach profile measurements were made at half-hourly and hourly intervals, from which net cross-shore transport rates were calculated for the different wave conditions. Pairs of experiments with slightly different bandwidth or wave grouping show very similar net cross-shore sediment transport patterns, giving high confidence to the data set. Consistent with recent small-scale experiments, the data clearly show that in comparison to monochromatic conditions the bichromatic wave groups reduce onshore transport during accretive conditions and increase offshore transport during erosive conditions. The random waves have a similar influence to the bichromatic wave groups, promoting offshore transport, in comparison to the monochromatic conditions. The data also indicate that the free long waves promote onshore transport, but the conclusions are more tentative as a result of a few errors in the test schedule and modifications to the setup which reduced testing time. The experiments suggest that the inclusion of long wave and wave group sediment transport is important for improved near-shore morphological modeling of cross-shore beach profile evolution, and they provide a very comprehensive and controlled series of tests for evaluating numerical models. It is suggested that the large change in the beach response between monochromatic conditions and wave group conditions is a result of the increased significant and maximum wave heights in the wave groups, as much as the presence of the forced and free long waves induced by the groupiness. The equilibrium state model concept can provide a heuristic explanation of the influence of the wave groups on the bulk beach profile response if their effective relative fall velocity is larger than that of monochromatic waves with the same incident energy flux. [Copyright &y& Elsevier]

Abstract: This study focuses on barred beach shoreface nourishments physically simulated in a wave flume. The attack of a schematic storm on three different nourishments is analysed. The apex and waning storm phases lead respectively to offshore and onshore sediment transports. Nourishments in the trough and on the outer bar feed the bar and increase wave dissipation offshore. The bar acts as a wave filter and reduces shore erosion (lee effect). In contrast, nourishment on the beach face leads mostly to shore feeding and reconstruction (feeder effect). With successive nourishments, the beach face clearly becomes steeper and onshore sediment transport is reduced during moderate wave climates. The surface grain size analysis reveals marked variations. Coarser sediments are sorted on the bar and the upper beach face. These locations correspond to large wave dissipation zones during the storm apex. [ABSTRACT FROM AUTHOR]

Abstract: Sediment supply provides a fundamental control on the morphology of river deltas, and humans have significantly modified these supplies for centuries. Here we examine the effects of almost a century of sediment supply reduction from the damming of the Elwha River in Washington on shoreline position and beach morphology of its wave-dominated delta. The mean rate of shoreline erosion during 1939–2006 is ~0.6 m/yr, which is equivalent to ~24,000 m3/yr of sediment divergence in the littoral cell, a rate approximately equal to 25–50% of the littoral-grade sediment trapped by the dams. Semi-annual surveys between 2004 and 2007 show that most erosion occurs during the winter with lower rates of change in the summer. Shoreline change and morphology also differ spatially. Negligible shoreline change has occurred updrift (west) of the river mouth, where the beach is mixed sand to cobble, cuspate, and reflective. The beach downdrift (east) of the river mouth has had significant and persistent erosion, but this beach differs in that it has a reflective foreshore with a dissipative low-tide terrace. Downdrift beach erosion results from foreshore retreat, which broadens the low-tide terrace with time, and the rate of this kind of erosion has increased significantly from ~0.8 m/yr during 1939–1990 to ~1.4 m/yr during 1990–2006. Erosion rates for the downdrift beach derived from the 2004–2007 topographic surveys vary between 0 and 13 m/yr, with an average of 3.8 m/yr. We note that the low-tide terrace is significantly coarser (mean grain size ~100 mm) than the foreshore (mean grain size ~30 mm), a pattern contrary to the typical observation of fining low-tide terraces in the region and worldwide. Because this cobble low-tide terrace is created by foreshore erosion, has been steady over intervals of at least years, is predicted to have negligible longshore transport compared to the foreshore portion of the beach, and is inconsistent with oral history of abundant shellfish collections from the low-tide beach, we suggest that it is an armored layer of cobble clasts that are not generally competent in the physical setting of the delta. Thus, the cobble low-tide terrace is very likely a geomorphological feature caused by coastal erosion of a coastal plain and delta, which in turn is related to the impacts of the dams on the Elwha River to sediment fluxes to the coast. [Copyright &y& Elsevier]

Abstract: Landsat Enhanced Thematic Mapper imagery (ETM) of 2002 and aerial photography of 1955, combined with published charts and field observations were used to interpret geomorphological changes in the coastal zone between Kitchener drain and Damietta spit in the northeastern Nile delta previously recognized as a vulnerable zone to the effects of any sea-level rise resulting from global warming. The interpretation resulted in recognition of several changes in nine identified geomorphological land types: beach and coastal flat, coastal dunes, agricultural deltaic land, sabkhas, fish farms, Manzala lagoon, saltpans, marshes and urban centers. Reclamation of vast areas of the coastal dunes and of Manzala lagoon added about 420 km2 to the agricultural deltaic land. About 48 km2 of sand dunes, marshes, sabkhas and salt pans have been converted to productive fish farms. The main urban centers have expanded, and new urban centers (Damietta harbor and the New Damietta city) have been constructed at the expense of vast areas of Manzala lagoon, coastal dunes, and backshore flats. As the consequence of human activities the size of Manzala lagoon has been reduced to less than 50%. Short-term shoreline changes along the coast of the study area established from beach profile survey, spanning the years of 1990 to 2000, reveal longshore patterns of erosion versus accretion. The rate of shoreline retreat has increased in the downdrift side of Damietta harbor (−14 m/year), whereas areas of accretion exist within the embayment of Gamasa and in the shadow of Ras El Bar detached breakwater system, with a maximum shoreline advance of ~15 m/year. A sandy spit, 12 km long, has developed southeast of Damietta promontory. These erosion/accretion patterns denote the natural processes of wave-induced longshore currents and sediment transport, in addition, the impact of man-made coastal protection structures. [Copyright &y& Elsevier]

Abstract: Beach profile equilibrium is the principal concept assumed by most numerical modelling. The response of beach profile configuration to natural and anthropogenic changes could be predicted to help in selecting the most appropriate engineering design required to mitigate coastal erosion and accretion alongshore. Thus, in order to apply coastal engineering projects, the predicted profile of equilibrium should be close enough to the measured profile. Therefore, before application of numerical modelling techniques, equilibrium expressions have to be validated at the study site. This research aims to assess the validity of the equilibrium profile concept on the Nile Delta coast based on beach profiles surveyed in 1990 from the main promontories; Abu-Quir Bay, the Rosetta promontory and the El-Burullus promontory. The results indicate that the equilibrium beach profile is consistent with the measured profiles at the study sites beyond 200 m distance offshore at −4 m depth. In contrast, the equilibrium status is not valid along the beach face at −1 m depth. Accreted beaches at Abu-Quir bay and Burullus promontory are characterized by wide berms and gentle beach face whereas eroded stretches at Rosetta promontory have a narrow berm and steep beach faces. The measured profiles are also compared with the exponential beach profile concept. An exponential hypothesis is not valid along the Nile Delta coast. Profiles measured at Abu-Quir, Rosetta and El-Burullus depart significantly from the exponential equation. Despite the fact that equilibrium expression can describe beach profiles along the Nile Delta, one equilibrium profile equation is not sufficient to assess all beach profiles. This can be explained as the morphology of beach profiles is subjected to some factors including; sediment characteristics, wave parameters and closure depth, which vary alongshore. Analysis of the validity of the equilibrium beach profile is recommended to get accurate results in modelling simulations and design the most appropriate engineering projects required for shore protection. [Copyright &y& Elsevier]

Abstract: The 2004 Indian Ocean tsunami devastated the coastal areas along the Andaman western coast of Thailand and left unique physical evidence of its impact, including the erosional landforms of the pre-tsunami topography. Here we show the results from monitoring the natural recovery of beach areas at Khuk Khak and Bang Niang tidal channels of Khao Lak area, Phang-nga, Thailand. A series of satellite images before and after the tsunami event was employed for calculating the beach area and locating the position of the changed shoreline. Field surveys to follow-up the development of the post-tsunami beach area were conducted from 2005 to 2007 and the yearly beach profile was measured in 2006. As a result, the scoured beach areas where the tidal channel inlets were located underwent continuous recovery. The return of post-tsunami sediments within the beach zone was either achieved by normal wind and wave processes or during the storm surges in the rainy season. Post-2004 beach sediments were derived mainly from near offshore sources. The present situation of the beach zone has almost completed reversion back to the equilibrium stage and this has occurred within 2 years after the tsunami event. We suggest these results provide a better understanding of the geomorphological process involved in beach recovery after severe erosion such as by tsunami events. [Copyright &y& Elsevier]

Abstract: Large tsunamis are major geomorphic crises, since they imply extensive erosion, sediment transport and deposition in a few minutes and over hundreds of kilometres of coast. Nevertheless, little is known about their geomorphologic imprints. The December 26, 2004 tsunami in Sumatra (Indonesia) was one of the largest and deadliest tsunamis in recorded human history. We present a description of the coastal erosion and boulder deposition induced by the 2004 tsunami in the Lhok Nga Bay, located to the West of Banda Aceh (northwest Sumatra). The geomorphological impact of the tsunami is evidenced by: beach erosion (some beaches have almost disappeared); destruction of sand barriers protecting the lagoons or at river mouths; numerous erosion escarpments typically in the order of 0.5–1.5 m when capped by soil and more than 2 m in dunes; bank erosion in the river beds (the retreat along the main river is in the order of 5–15 m, with local retreats exceeding 30 m); large scars typically 20–50 cm deep on slopes; dislodgement of blocks along fractures and structural ramps on cliffs. The upper limit of erosion appears as a continuous trimline at 20–30 m a.s.l., locally reaching 50 m. The erosional imprints of the tsunami extend to 500 m from the shoreline and exceed 2 km along riverbeds. The overall coastal retreat from Lampuuk to Leupung was 60 m (550,000 m2) and locally exceeded 150 m. Over 276,000 m3 of coastal sediments were eroded by the tsunami along the 9.2 km of sandy coast. The mean erosion rate of the beaches was ~30 m3/m of coast and locally exceeded 80 m3/m. The most eroded coasts were tangent to the tsunami wave train, which was coming from the southwest. The fringing reefs were not efficient in reducing the erosional impact of the tsunami. The 220 boulders measured range from 0.3 to 7.2 m large (typically 0.7–1.5 m), with weights from over 50 kg up to 85 t. We found one boulder, less than 1 m large, at 1 km from the coastline, but all the others were transported less than 450 m (<7 m a.s.l.). No fining landward boulder size distribution could be detected. The coincidence of different size modes, from boulders to fine sands, with independent spatial distributions, suggests that all the material was not transported in suspension, but rather by a combination of suspension and bed load transport. Finally, the spatial and size distributions of tsunami boulder deposits mostly depend on the location and characteristics of their source (coral reef, beach rock, platform, dams), together with clast and surface interference during transport. One year after, the coastal environment in northwest Sumatra is still in a post-tsunami dynamic. Thus, the difference between the largest tsunamis (height>30 m) and the moderate tsunamis (height<10 m) could be their long-term impact on coastal environments. [Copyright &y& Elsevier]

Abstract: A technique is described to observe and quantify wave-by-wave bed-level changes in the swash zone. The ultrasonic instrument system is non-contact with the beach face surface being measured and the sensors remain outside of the fluid flows causing sediment movement. Sensor resolution combined with the electronic noise inherent within a digital network data-logging system results in a (conservative) measurement accuracy of ±1 mm, equating to a couple of sand grain diameters in height. Illustrative field results demonstrate the practical use of the instrumentation, and a simple data pre-processing method to separate swashes and intervening bed-level ‘events’ is discussed. These example data reveal rather complex fluctuations of the bed observed over time periods of minutes to hours. Rather strikingly, gross bed-level changes per wave are revealed to be up to many orders of magnitude larger than the observed net rate of beach face evolution. It is outlined how observations of successive bed-level changes at multiple locations within a dense grid, combined with a consideration of sediment continuity, will now enable the total net sediment transported per uprush–backwash to be quantified. [Copyright &y& Elsevier]

Abstract: Numerical modeling of a beach nourishment project is conducted to enable a detailed evaluation of the processes associated with the effects of nearshore dredge pits on nourishment evolution and formation of erosion hot spots. A process-based numerical model, Delft3D, is used for this purpose. The analysis is based on the modification of existing bathymetry to simulate “what if” scenarios with/without the bathymetric features of interest. Borrow pits dredged about 30 years ago to provide sand for the nourishment project have a significant influence on project performance and formation of erosional hot spots. It was found that the main processes controlling beach response to these offshore bathymetric features were feedbacks between wave forces (roller force or alongshore component of the radiation stress), pressure gradients due to differentials in wave set-up/set-down and bed shear stress. Modeling results also indicated that backfilling of selected borrow sites showed a net positive effect within the beach fill limits and caused a reduction in the magnitude of hot spot erosion. [Copyright &y& Elsevier]

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 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]

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]

Dunes are key elements of coastal landscapes in almost every latitude. They host high levels of biodiversity and provide important benefits to society; e.g. protection against floods and erosion, or recreation. Coastal dune growth is constrained by intrinsic factors, which are critical when managing dune systems or choosing coastal dune restoration as an alternative green solution for coastal protection. Here, the evolution of a beach-dune system, characterized by a reflective coarse sandy beach and low dunes, is explored to identify the favourable and optimal conditions for dune growth in these settings. Dune growth capacity is evaluated by analysing the topographical changes observed along a coastal dune over two different temporal scales (interannual and event scale) and comparing the observations with theoretical approximations of sediment transport potentials. Observations and predictions over interannual scale document that (1) temporal variability in external conditions (wind regime) and spatial variability of estimated wind fetch length, alone, fail to explain alongshore dune growth patterns and (2) optimal conditions for dune growth occur when storms (strong winds) impact the study area, jointly with low runup levels, at zones of shoreline progradation and absence of direct human influence. Conversely, lowest values of dune accumulation are associated with areas where shoreline retreat was documented. Observations from event timescales suggest that sediment transport potential can be reached over zones with no significant signs of beach erosion, if runup levels remain low and the event duration is shorter than the time scale of sand surface depletion within the upper beach. Unlabelled Image • The growth capacity of a dune adjacent to a reflective coarse sandy beach is evaluated. • Accumulation at interannual and event scales is compared to potential transport. • Longshore variability partially associated with backshore width. • Wind intensity and shoreline trend imprint a first order signal at interannual scale. • Optimal conditions for dune growth occur if strong winds blow over a stable beach. [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]

Morphological variations in a sandy-muddy transitional beach (SMT-beach) are expected to coincide with sand-mud transition (SMT) boundary migrations. SMT migrations of SMT-beaches should also differ in river estuaries and semi-enclosed bays due to their contrasting dynamic sedimentary environments. However, the anticipated diversity of SMT migrations of estuarine and bay beaches and their potential morphodynamic responses are still poorly understood. Thus, four measurements of SMT spatial distributions and typical profiles of 6 estuarine beaches and 6 bay beaches located along the macrotidal coasts of the Taiwan Strait, East Asia are presented, and these sites were studied in April and August of 2018 and 2019, respectively. The results show that the SMT boundary of the estuarine beaches continuously migrates landward with increased elevations. Simultaneously, the SMT boundary of bay beaches synchronously remains relatively stable with minor fluctuations and relatively stable elevations. The SMT migration amplitudes present a significantly positive linear correlation with SMT elevation changes, which are strongly controlled by the sediment supply. Following the SMT migration processes, both estuarine and bay beaches display clear erosion during the summer monsoon period that is mainly associated with strong river discharge and monsoon rainfall, respectively. In contrast, all beaches present distinct accretion and recovery during the winter monsoon period that are mainly due to the decreased monsoon rainfall and river discharge and/or the strengthened onshore sediment transport. Despite limitations, the results of this study have clarified the diverse SMT migrations of estuarine and bay beaches and aid in a better understanding of their possible morphodynamic responses. Unlabelled Image • SMT migration of estuarine beach has a significant difference from that of bay beach. • A landward SMT migration is linearly correlated with an increased SMT elevation. • Sediment supply drives the contrasting SMT migrations of estuarine and bay beaches. • All SMT-beaches present dominate erosion in summer and clear accretion in winter. [ABSTRACT FROM AUTHOR]

This study provides laboratory observations of the nearshore hydrodynamics and detailed topographic surveys associated with the morphological response of a beach-dune system to oblique waves during a storm event. A physical model consisting of a 20 m long sandy steep beach constructed in a wave basin, and a wave paddle oriented obliquely to the beach shoreline is used to generate irregular waves at the offshore boundary. In the experiment, the wave height is varied over time in five segments to simulate the change in the energy from a passing storm and is varied alongshore to initiate an alongshore gradient in waves and wave-driven currents. To simulate a constant storm surge, a high mean water level relative to the dune is used, enabling waves to reach the dune toe. The results indicate the formation and evolution of a beach scarp. The retreat of the scarp initially corresponds to time-varying wave energy, but becomes controlled by the changing nearshore beach slope over time. The alongshore current magnitude is governed by the spatio-temporal variability in wave energy and is the main driver of sediment flux. The sand that is eroded from the dune initially deposits at the dune toe when nearshore circulation is weak. However, as the wave energy increases sediment is transported along the beach and is deposited, increasing the surf zone width. The experimental results indicate that small waves at high water levels relative to the dune can drive the formation of a beach scarp. In addition, different levels of incident wave energy drive different rates of sediment transport and morphological evolution with high alongshore variability throughout a storm event. [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]

Sandbanks can occur downdrift of headlands across embayments as a result of tidal currents and wave forcing, and may present a potentially valuable resource of marine aggregate material. Large sandbanks can alter tidal flows and, through refraction and dissipation, increase or decrease wave exposure along the shoreline of an embayment. The impact of offshore sandbanks on shoreline morphodynamics at varying timescales has not been rigorously investigated. Here we show, for the first time, that removing, lowering or raising a headland-associated sandbank can have a significant impact on longshore sediment transport. A Delft3D model of Start Bay and Skerries Bank, UK, validated on hydrodynamic observations, was used to conduct the numerical experiments. Results indicate that removing or lowering the bank generally reduces dissipation and increases wave heights, increasing longshore flux in the lee of the bank. Raising the bank generally has the opposite effect, increasing dissipation and lowering flux. Under oblique waves, the bank may protect the adjacent shoreline by refracting waves away from the coast. Shoreline flux for the region directly onshore of the bank acts as a continuous function of bank height (R 2 = 0.7), but correlations for distal regions are increasingly non-linear or absent. A raised bank would reduce transport rates to near-zero across extensive sections of the bay, reversing the long-term net flux at points distal (>5 km from bank) from the bank location, causing currently eroding regions to accrete. Our results demonstrate that moderate (≤5 m) elevation changes to a sandbank will likely produce significant variations in wave power at the shoreline, which will: (i) modify the shoreline response for individual storms; and (ii) substantially change shoreline morphology at decadal timescales. From a broader perspective, this study can be used to inform planning decisions involving naturally varying banks and/or potential mining of sandbanks, aiding shoreline protection strategies for locations with similar embayment-sandbank configurations. Unlabelled Image • First robust study of bank control on inshore waves and longshore transport • 20% change to bank elevation (≤5 m) significantly impacts longshore flux. • Directly in lee of bank, shoreline flux is a continuous function of bank depth. • Bank protects shore, dissipating direct waves and refracting away oblique waves. • Raised bank would substantially accrete distal (>5 km) currently eroding shoreline. [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]

Numerical coastal erosion models are used by engineers to predict the magnitude of storm erosion at the coastline. In particular, the 'dry' region of the beach, extending landwards from the waterline to include the beach face, berm and dunes, is a particular focus of interest to managers, planners and other coastal practitioners. However, the choice of the most appropriate numerical model to predict subaerial beach erosion requires careful consideration of the strengths and limitations of each model, and the quality and quantity of field data available for both model calibration and prediction. While no model can perfectly replicate observed upper beach erosion, this study specifically assesses the quantity of field calibration data required to achieve optimum model performance for coastal storm erosion modelling applications. Two of the most commonly used, but differently formulated, coastal erosion profile models are compared: the process-based and more complex model XBeach, and the semi-empirical and significantly simpler model SBEACH. A rigorous calibration technique (the Generalised Likelihood Uncertainty Estimation) is applied to both models, using a comprehensive dataset of pre- and post-storm topographic measurements collected over four differing storm events at Narrabeen-Collaroy Beach in southeast Australia, as well as at two adjacent embayed beaches. When applying the two numerical models using their default parameters (i.e., with no model calibration), SBEACH was found to be the more skilful model and XBeach default parameters were found to have no predictive skill along this stretch of coastline. Once calibrated with detailed field observations obtained before and after a single storm event, XBeach validation skill rose considerably and provided predictions of subaerial beach profile change with greater skill (87% better Brier Skill Score on average for the same calibration data) than SBEACH. Overall XBeach model performance was found to marginally improve when field observations obtained from additional storm events were included in the calibration process, whereas SBEACH showed negligible improvement. A comparison was made of the options available for transferring previously-calibrated parameters to adjacent locations, finding spatial proximity to be the most sensitive indicator of model performance for a transferred parameter set. Due to the alongshore variability in pre-storm topography as well as wave exposure at the sites tested, the spatial coverage of data was more important for the calibration process than the magnitude of the individual storm(s) used for a specific calibration. The results of this study underscore the need for careful consideration of the available calibration field data when choosing and optimising coastal erosion models. • Default XBeach parameters were found to be non-skilful at coastal sites in southeast Australia. • The XBeach model outperformed the SBEACH model when one or more calibration storm event field datasets were available. • Collection of calibration pre- and post-storm field data at specific locations of interest was important. • Spatial proximity was found to be a good performance indicator of calibrated parameter values transferred to new locations. [ABSTRACT FROM AUTHOR]