Search

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

Wave nonlinearity significantly influences wave attenuation and can cause sediment transport imbalances in vegetated zones, impacting shoreline stability and ecosystem-based coastal defences. Despite its importance, the parameterisation and mechanisms of wave nonlinearity evolution over flexible vegetation remain unclear. This study examines the mechanisms behind non-breaking wave nonlinearity evolution over flexible vegetation and provides parameterisation of wave nonlinearity, based on experimental data collected by Anderson and Smith (2014). The study derives a new set of empirical formulae for predicting wave nonlinearity in Spartina alterniflora, which considers Ursell number, relative vegetation width, vegetation submergence, and vegetation density. The predictions made using these formulae are in good agreement with the measurements. The results indicate a decrease in wave skewness across the span of vegetation, whereas wave asymmetry increases until it reaches a maximum before decreasing. The findings suggest a preferential dissipation of high harmonics compared to low harmonics in the vegetation zone. Additionally, bispectrum analysis reveals that vegetation enhances the difference interaction while suppressing the sum interaction between wave components. The findings enable improvements in our understanding of wave nonlinearity in vegetation, providing better predictive capabilities for wave attenuation and sediment transport, which are crucial for the design and optimization of coastal defence systems. • Non-breaking wave skewness keeps decreasing over the vegetation, while wave asymmetry initially rises to a maximum and then decreases. • Vegetation enhances the difference interaction while suppressing the sum interaction between wave components. • A new empirical formula for predicting non-breaking wave nonlinearity takes into account both vegetation properties and wave characteristics. [ABSTRACT FROM AUTHOR]

Waves running up and down the beach ('swash') at the landward edge of the ocean can cause changes to the beach topology, can erode dunes, and can result in inland flooding. Despite the importance of swash, field observations are difficult to obtain in the thin, bubbly, and potentially sediment laden fluid layers. Here, swash excursions along an Atlantic Ocean beach are estimated with a new framework, V-BeachNet, that uses a fully convolutional network to distinguish between sand and the moving edge of the wave in rapid sequences of images. V-BeachNet is trained with 16 randomly selected and manually segmented images of the swash zone, and is used to estimate swash excursions along 200 m of the shoreline by automatically segmenting four 1-h sequences of images that span a range of incident wave conditions. Data from a scanning lidar system are used to validate the swash estimates along a cross-shore transect within the camera field of view. V-BeachNet estimates of swash spectra, significant wave heights, and wave-driven setup (increases in the mean water level) agree with those estimated from the lidar data. • A new framework, V-BeachNet, provides estimates of alongshore variable swash motions using fully convolutional networks. • The study identifies sources of error in the calculation of swash using video images and computer vision algorithms. • V-BeachNet enables efficient extraction of swash data from archived or real-time video footage of the shoreline. [ABSTRACT FROM AUTHOR]

A proper prediction of the cross-shore profile evolution in the swash zone at time scales of days to years is important for evaluating beach management scenarios. However, this practical prediction is challenging due to a limited understanding of the complex physical processes in the swash zone. A quantitative evaluation of three existing practical swash-zone sand transport models, i.e. the Larson formula, the Van Rijn distribution model and the Karambas formula, has been conducted in this study. Measured net sand transport rates and beach profiles in seven large-scale flume tests, both low-energy accretive and high-energy erosive wave conditions, are used to assess these three models. Model performance is quantitatively evaluated with the Brier Skill Score (B S S), Root Mean Square Error (R M S E) and erosive/accretive volume. Overall, the Larson model shows the best performance. Nevertheless, the Larson model cannot capture the shoreline change, as it is assumed only valid for the higher part of the swash zone above the still water level (SWL). Additionally, it fails to predict the accretion in the upper swash zone during high-energy erosive conditions. Thus, two improvements are made for the Larson model by (1) extending the application of the Larson model from the still water level towards the run-down limit and by (2) developing shape functions for the equilibrium bed slope in the swash zone. The improved model is validated using six other large-scale wave flume tests. Results demonstrate that the improved Larson model works better than the original Larson model in predicting the profile evolution, shoreline change and total accretion/erosion volume in the swash zone. The improved model shows the potential to be coupled with wave-averaged morphological models for the nearshore zone to predict long-term evolutions of the entire beach profile. • A quantitative evaluation of existing practical swash zone models is conducted. • Current models cannot capture upper swash zone accretion in erosive wave conditions. • An improved model is proposed by incorporating local equilibrium slope shape functions. • The improved model can predict shoreline changes and profile evolutions accurately. [ABSTRACT FROM AUTHOR]

Modelling and predicting the future of sandy shorelines is a key challenge in coastal research and is critical for sustainable coastal management. However, currently the most skillful shoreline models strongly rely on data to calibrate the free parameters, and are thus restricted to a few well monitored sites in the world. Here we address the challenges and opportunities offered by optical satellite imagery to provide useful information for equilibrium shoreline model calibration on cross-shore transport dominated sites. We focus on Truc Vert beach, southwest France, where previous work showed good equilibrium model skill to reproduce shoreline change from the time scales of hours (storms) to decades. Satellite derived waterlines are extracted over 11 years (2009–2020) and further transformed into satellite derived shorelines (SDS) with different water level corrections (e.g. tide and/or run up) and varying alongshore averaging lengths, and thus different uncertainties, in order to test model performance. Successively the timeseries duration and sampling frequency required for model calibration were also investigated. The model calibrated using the SDS data showed similar skill as the model calibrated using in-situ alongshore averaged shoreline positions, even for the uncorrected SDS dataset which Root Mean Square Error (RMSE) are approximately 30 m. Alongshore averaging was found to be the only necessary processing of the SDS data while any other site-specific corrections did not significantly improve model skill. Finally to further investigate the effect of sampling frequency and noise in the dataset we performed an analysis using a synthetic shoreline. Our results suggest that the effect of noise is negligible as long as the sampling frequency remains high (dt ≤ 30 days). Pending further validation, results show the strong potential of using uncorrected SDS dataset for shoreline model calibration at cross-shore transport dominated sandy coasts. • Model calibration using uncorrected satellite-derived shoreline data. • Simulated annealing extracts information from raw satellite derived shoreline data. • New perspective in modelling sandy shoreline change even when lacking field data. • Sampling frequency more critical than data quality in model calibration. [ABSTRACT FROM AUTHOR]

Recent developments in satellite processing tools allow low-cost, fast and automatic processing of a large amount of information from Earth observation, enhancing the capability of detecting coastal changes from space at different temporal scales. Some works have assessed the quality of these data and applied it to detect coastal evolution locally, most of them focusing on mid-term and long-term changes in the coastline. In this work, we evaluate the capability to monitor changes in coastal morphology at various temporal and spatial scales using 1D (coastlines) and 3D (bathymetry) satellite-derived data obtained from site-specific processing methods. Local characteristics were included in several phases of the development of the satellite products used here: i) geolocated very high resolution images from each pilot site were used in the coregistration process to enhance geolocation accuracy in images from different missions, ii) different spectral indices were tested at each pilot site to obtain more reliable detection of the coastline at all sites and iii) measured topobathymetry data were used to obtain datum-based satellite shorelines and bathymetry. The accuracy and skill of those satellite products were assessed at several pilot sites in Spain. The results indicated high horizontal accuracy (RMSE < pixel size), with errors on the order of half of the pixel size (RMSE = 5.0 m and for Sentinel-2 and 18.8 m for Landsat5). Furthermore, the coastlines used here presented errors comparable to those obtained from the widely used open-source tool CoastSat. Time-series analysis using satellite-derived shorelines showed that coastal change processes can be detected at several temporal and spatial scales, such as short-term erosion and accretion events on a small beach, seasonal beach rotation, and long-term trends at local and regional scales. However, the results from satellite-derived bathymetry indicated that the quantitative assessment of the coastal morphology with 3D products is still limited. Some in situ measurements are necessary to obtain satellite data that represent site-specific conditions. However, the quantity of this auxiliary in situ measurements required to obtain reliable time series of satellite derived shorelines and bathymetry is significantly lower than the quantity required by traditional monitoring methods. The results are discussed, highlighting the gaps that need to be filled in the future so that satellite-derived products can be used in usual coastal change monitoring practices. • We assess the capability to monitor coastal changes with 1D and 3D satellite data. • Local characteristics are included in the development of the satellite data. • Coastal changes are detected at several temporal and spatial scales. • Long-term shoreline change in local and regional scales, and seasonal beach rotation are successfully detected. • Storm-induced erosion is monitored although cloud cover affects data availability. [ABSTRACT FROM AUTHOR]

Shoreline models have usually been recognized by professionals as the most appropriate tool for reproducing the long-term morphodynamic evolution of the shoreline of sandy beaches. Despite their underlying simplifications, the simulation of shoreline evolution at large temporal and spatial scales may imply significant computational efforts. Hence, to reduce computational costs, many approaches aimed to optimize the size of the input wave datasets have been proposed so far. A simplified novel method to reduce long-term offshore wave series is proposed herein. The rationale of the approach is to build reduced series that induce the same morphodynamic effects in the long-term as the ones induced by the whole, and more computationally expensive, original series. The method is conceived to define offshore reduced time series with the same chronological order of the complete series and is able to represent the bi-modal features of the wave climate. In-depth hydrodynamic and morphodynamic parametric analyses have been performed and it has been demonstrated that the method is capable to get reliable reduced offshore wave time series for reproducing the long-term evolution of sandy beaches with decreased computational costs. • Representative wave time series are crucial for long-term morphodynamic simulations. • Reduced time series allow saving computational time. • An effective method to reduce offshore wave series is proposed. • Reduced series can be effectively used for long-term morphodynamic simulations. [ABSTRACT FROM AUTHOR]

Storms and extremely energetic events may significantly impact the form and structure of beaches, and so cause erosive processes and coastal damages. Efficient management actions require an up-to-date and accurate knowledge of beach morphological changes, with the shoreline position being a good indicator of such changes. This work proposes the use of the open-source Shoreline Analysis and Extraction Tool (SAET) software for the definition of satellite-derived shorelines (SDSs) from L8 and Sentinel-2 imagery to reveal the shoreline position changes at the beaches of the Ebro Delta, NE Spain. Spatial-temporal models (STMs) of shoreline changes enable a characterisation of how the beaches responded to the storms of 2020. In conjunction with wave data, STMs enable an analysis of the erosive response to storm events, as well as a monitoring of subsequent beach recovery in the short and medium term (<1 year). Results show how Storm Gloria (January 2020, Hs max = 7.62 m) acted as a disruptive event and shifting point in the shoreline trend. As a response to that storm, major erosive processes occurred along the delta that caused an average shoreline retreat of 47 m. A progressive recovery during the spring and summer was mainly associated with periods of low wave energy. Nevertheless, by the end of the year a complete recovery had been achieved for about half of the coast, while the other half showed an average erosion of more than 10 m when compared to the pre-storm situation. Both the erosive and the recovery processes took place unevenly on different sections of the coast, probably dependent on factors such as the orientation of the beach and the pattern of longitudinal sediment transport along the coast. • Automatic shoreline extraction from Sentinel 2 and Landsat 8 imagery using SAET. • Pre and post-storm characterisation of SDS position in time and space using STMs. • Storm Gloria (January 2020) caused an unprecedented and heterogeneous impact on the Ebro Delta. • Slow recovery occurred in the months following the event conditioned by orientation and wave patterns. • About half of the delta showed a significant shoreline retreat by the end of 2020. [ABSTRACT FROM AUTHOR]

The definition of the shoreline position from satellite imagery is of great interest among coastal monitoring techniques. Understanding the reality mapped by the resulting shorelines and defining their accuracy is of paramount importance. The assessment described in this paper constitutes a validation of the shorelines obtained by using the novel tool SAET (Shoreline Analysis and Extraction Tool) for automatic shoreline extraction. The resulting shorelines applying the different parameters available in SAET are assessed in 9 test sites with diverse morphology and oceanographic conditions along the Atlantic European and Western Mediterranean coasts. The reference data is obtained along large coastal segments (covering up to about 240 km) from nearly coincident very high-resolution satellite images. Different image processing levels and extraction methods have been tested, showing their key role in the accuracy of shoreline position. When defining the approximate shoreline position the Automated Water Extraction Index for images without shadows (AWEInsh) with a 0 threshold generally constitutes the best segmentation method. In turn, the employment of the mathematical morphological operations of dilation or erosion considerably improves the results in certain coastal typologies. On the contrary, the employment of atmospherically-corrected images has a smaller influence on the accuracy of the SDSs. Results support the idea that the magnitude of the errors is strongly related to the specific coastal conditions- In general, the lowest errors appear in low-energetic microtidal sites, contrary to the energetic and mesotidal coasts with gentle slopes. The shoreline errors range between 3.7 m and 13.5 m RMSE (root-mean-square error) among the different coastal types when selecting the most appropriate extraction parameters. The shoreline position identified with SAET shows a similar or better accuracy to that obtained by other tools. • Automatically S2 extracted shorelines compared against simultaneous from VHR images. • Shoreline errors vary in the different coastal typologies ranging 3.7–13.5 m RMSE. • AWEInsh = 0 threshold is the best-performing segmentation method overall. • Morphological operations enable to improve the accuracy in certain coastal typologies. • S2 atmospherically corrected images do not improve shoreline accuracy substantially. [ABSTRACT FROM AUTHOR]

The ability to repeatedly observe and quantify the changing position of the shoreline is key to present-day coastal management and future coastal planning. This study evaluates the capability of satellite remote sensing to resolve at differing temporal scales the variability and trends in shoreline position along sandy coastlines. Shorelines are extracted from 30 + years of publicly available satellite imagery and compared to long-term in-situ measurements at 5 diverse test sites in Europe, Australia, the USA and New Zealand. These sites span a range of different beach characteristics including wave energy and tide range as well as timescales of observed shoreline variability, from strongly seasonal (e.g., Truc Vert, France), to storm-dominated (e.g., Narrabeen-Collaroy, Australia), to only minor annual to multi-annual signals (e.g., Duck, USA). For the 5 sites, the observed typical horizontal errors varied between a root-mean-squared error (RMSE) of 7.3 m and 12.7 m. An analysis of the typical magnitudes of shoreline variability at temporal scales ranging from a single month up to 10 years indicates that, by the implementation of targeted image pre-processing then the application of a robust sub-pixel shoreline extraction technique, the resulting satellite-derived shorelines are generally able to resolve (signal-to-noise ratio > 1) the observed shoreline variance at timescales of 6 months and longer. The only exception to this is along coastlines where minimal annual to multi-annual shoreline variability occurs (e.g. Duck, USA); at these sites decadal-scale variations are successfully captured. The results of this analysis demonstrate that satellite-derived shorelines spanning the past 30 years as well as into the future can be used to explore and quantify intra- and inter-annual shoreline behaviour at a wide range of beaches around the world. Moreover, it is demonstrated that present-day satellite observations are also capable of capturing event-scale shoreline changes (e.g. individual storms) that occur at timescales shorter than 6 months, where this rapid response exceeds the typical magnitude of shoreline variability. Finally, several practical coastal engineering applications are presented, demonstrating the use of freely-available satellite imagery to monitor inter-annual embayed beach rotation, rapid storm-induced shoreline retreat and a major sand nourishment. • A refined sub-pixel resolution shoreline detection technique capable of mapping the sand/water interface is presented. • Satellite-derived shoreline accuracy is assessed at diverse sandy beach sites in Europe, Australia, the USA and New Zealand. • The observed RMSE in shoreline positions for the sites tested ranged between 7.3 m and 12.7 m. • Rapid (e.g., storm erosion, beach nourishment), seasonal and inter-annual shoreline changes are able to be captured. [ABSTRACT FROM AUTHOR]

As a result of climate change and the ensuing accelerating sea level rise, the Ninigret Trustom Pond beach barrier system, located along the southern shore of Rhode Island, USA, has become increasingly vulnerable to tropical storms, hurricanes, and Nor'easters affecting the region. In this work, we explore the ability of a segmented artificial reef (AR) to protect the Ninigret Trustom Pond beach barrier system, by reducing the incident wave energy and ultimately the beach erosion. A set of nine AR concepts are selected, which are predicted to be accretive based on Ranasinghe et al. 's (2010) design criterion (RVB), extended by van der Baan (2013) to apply to segmented submerged breakwaters. The effectiveness of each concept is then assessed through numerical simulations, for both average wave climate conditions and storm events, with and without sea level rise, using the 2D morphodynamic model XBeach. The AR concepts are evaluated based on their ability to reduce coastal erosion during the storm events, including with a near future sea level rise of 0.31 m (scenario based on local prediction by 2050 relative to 2020 following the intermediate NOAA scenario) , while ensuring a slightly accretive behavior in average wave conditions. The reduction of the coastal erosion during the storm events is quantified by comparing the subaerial eroded volume at the site, with or without sea level rise, when implementing each of the nine pre-selected AR concepts. While all concepts are found to protect the shoreline during storm events, including with the 0.31 m sea level rise scenario, four of the nine AR concepts, pre-selected to be accretive based on the RVB criterion, are found to be erosive in average conditions. Assuming a given submergence level, the distance to the shoreline and the AR lateral confinement ratio, L C , (gap width to length ratio of the segments) are the main controlling parameter. [ABSTRACT FROM AUTHOR]

Abstract This study investigates the possibility of combining two shore-based remote sensing techniques, 2D LiDAR and video imagery, to measure 3D intertidal beach topography. The shoreline elevation, measured on a single cross-shore section of the beach by a 2D LiDAR, was combined with the video-derived shoreline contour to finally obtain intertidal beach topography. Vertical root-mean-square error between differential GPS and remotely-derived intertidal beach profiles had an average value of 0.12 m, with maximum disparities of 0.14 m. Two 3D Digital Elevation Models (DEMs) of the beach produced over two tidal cycles demonstrated the feasibility of shore-based LiDAR-video system of describing in detail the short-term morphological evolution of the intertidal area. Results suggest that the LiDAR-video system can improve the capability of remotely surveying intertidal beach topography providing high quality measurements. Highlights • New shore-based remote sensing method that combines LiDAR and video observations to obtain 3D intertidal beach topography. • The RMS error between differential GPS and the LiDAR-video system topographic observations was in average 0.12 m. • The LiDAR-video system can perform 3D topography in beaches with complex morphological features (e.g., beach cusps). [ABSTRACT FROM AUTHOR]

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

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]

Bayesian networks (BNs) are increasingly being used to model complex coastal processes due to their ability to integrate non-linear systems, their transparent probabilistic framework, and low computational cost. A BN may be suited to descriptive or predictive application. Descriptive BNs are highly calibrated models that are useful for better understanding the physics and causal relationships driving a system. Predictive BNs are generalisations of a system that have skill at predicting outside of the training domain. The predictive and descriptive usefulness of a BN depends on its complexity and the amount of data available to train it, but there is often a trade-off; higher descriptive skill comes at the cost of reduced predictive skill. To demonstrate the differences between predictive and descriptive BNs in a coastal engineering context, a BN to predict shoreline recession caused by coastal storm events is developed and tested using an extensive 10-year dataset incorporating 137 individual storms events monitored at Narrabeen-Collaroy Beach, Australia. A parsimonious approach to BN development is used to separately determine the optimum predictive and descriptive BNs for this dataset. Results show that for this dataset two quite different BNs can be developed: one that is optimized to achieve the highest predictive skill, and a second network that is optimized to maximize descriptive skill. The optimum predictive BN is found to comprise 3 nodes (variables) and can predict the shoreline recession caused by unseen storm events with a skill of 65%. The optimum descriptive BN is composed of 5 nodes and can reproduce 88% of the training dataset, but with more limited predictive capabilities. The uses and limitations of these two different approaches to BN formulation are illustrated with example applications to coastal process modelling. It is anticipated that the insights provided in this paper will help to clarify the further development of Bayesian Networks applied to coastal modelling. [ABSTRACT FROM AUTHOR]

The Catalan coast, as most of the developed Mediterranean coastal zone, can be characterized as a high-risk area to the impact of storms due to the large concentration of values together with the dominance of eroding shorelines. In consequence, any long-term coastal management scheme must include a risk analysis to permit decision makers to better allocate resources. This can be done in a nested approach in which hotspots are first identified along the coast at a regional scale and secondly, they are further analysed to produce dedicated risk reduction strategies. In this work, we apply the methodology developed within the RISC-KIT project for identifying and analysing coastal hotspots in the Catalan coast as a test for applying it to Mediterranean conditions. Obtained results show that this methodology is very efficient in identifying hotspots of storm-induced flooding and erosion at a regional scale. The adoption of the response approach resulted in the direct assessment of the hazards' probability distributions, which allowed for the selection of the severity of the hotspots to be identified. When a given coastal stretch behaves as a hotspot for both hazards, it is identified as a very highly-sensitive area to storm impacts. In the study area, the Tordera Delta possesses this condition of very high “hotspotness.” This has been demonstrated by the large and frequent damages suffered by the site during the past decades. The paper analyses different aspects related to the risk management of this area, including stakeholder actions. [ABSTRACT FROM AUTHOR]

Managing coastal risk at the regional scale requires a prioritization of resources along the shoreline. A transparent and rigorous risk assessment should inform managers and stakeholders in their choices. This requires advances in modelling assessment (e.g., consideration of source and pathway conditions to define the probability of occurrence, nonlinear dynamics of the physical processes, better recognition of systemic impacts and non-economic losses) and open-source tools facilitating stakeholders' engagement in the process. This paper discusses how the Coastal Risk Assessment Framework (CRAF) has been developed as part of the Resilience Increasing Strategies for Coasts Toolkit (RISC-KIT). The framework provides two levels of analysis. A coastal index approach is first recommended to narrow down the risk analysis to a reduced number of sectors which are subsequently geographically grouped into potential hotspots. For the second level of analysis an integrated modelling approach improves the regional risk assessment of the identified hotspots by increasing the spatial resolution of the hazard modelling by using innovative process-based multi-hazard models, by including generic vulnerability indicators in the impact assessment, and by calculating regional systemic impact indicators. A multi-criteria analysis of these indicators is performed to rank the hotspots and support the stakeholders in their selection. The CRAF has been applied and validated on ten European case studies with only small deviation to areas already recognised as high risk. The flexibility of the framework is essential to adapt the assessment to the specific region characteristics. The involvement of stakeholders is crucial not only to select the hotpots and validate the results, but also to support the collection of information and the valuation of assets at risk. As such, the CRAF permits a comprehensive and systemic risk analysis of the regional coast in order to identify and to select higher risk areas. Yet efforts still need to be amplified in the data collection process, in particular for socio-economic and environmental impacts. [ABSTRACT FROM AUTHOR]

Training walls to improve navigability at river mouths alter natural sediment transport regimes, occasioning morphological changes in the nearby littoral zone. In addition, harbor channels and shorelines are susceptible to on-going changes in global circulation conditions and large-scale engineering interventions. Here we present a process-based modeling approach to determine the relationship between spatial patterns of erosion and deposition, seasonal river discharge, and the geometry of coastal defenses. The study uses the Magdalena River delta as an example, where the redistribution of freshwater and sediments after the construction of the "Tajamar" training wall heralded significant morphological changes in the area. The numerical experiments are used to describe how the erosion and deposition patterns within the estuary and delta of the Magdalena River are linked to the seasonal cycle of the Magdalena River and to the geometry of the hard structures. We demonstrate that the construction of the Tajamar and complementary hard structures would have decreased depositional fluxes in the littoral zone, leading to the observed shoreline retreat and disappearance of an extensive coastal lagoon system. It is shown that an aperture in the training walls may help restore the wetlands without compromising navigability. In addition, projected increases in mean sea level are shown to decrease velocities within the lower estuary, potentially causing increased sedimentation within the channel and more complex conditions for the management of safe navigation over the Magdalena River estuary. • Seawall construction on the Magdalena River, Colombia, resulted in the redistribution of freshwater and sediments. • Numerical experiments provide evidence that shoreline retreat was caused by the altered sedimentation regime. • A diversion system in the training walls may help restore sediment supply to the shorelines without risking navigability. • Sea level rise may increase rates of sedimentation within the estuary. [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]

Field-tested numerical model simulations are used to estimate the effects of an inlet, ebb shoal, wave height, wave direction, and shoreline geometry on the variability of bathymetric change on a curved coast with a migrating inlet and strong nearshore currents. The model uses bathymetry measured along the southern shoreline of Martha's Vineyard, MA, and was validated with waves and currents observed from the shoreline to ~10-m water depth. Between 2007 and 2014, the inlet was open and the shoreline along the southeast corner of the island eroded ~200 m and became sharper. Between 2014 and 2015, the corner accreted and became smoother as the inlet closed. Numerical simulations indicate that variability of sediment transport near the corner shoreline depends more strongly on its radius of curvature (a proxy for the separation of tidal flows from the coast) than on the presence of the inlet, the ebb shoal, or wave height and direction. As the radius of curvature decreases (as the corner sharpens), tidal asymmetry of nearshore currents is enhanced, leading to more sediment transport near the shoreline over several tidal cycles. The results suggest that feedbacks between shoreline geometry and inner-shelf flows can be important to coastal erosion and accretion in the vicinity of an inlet. [ABSTRACT FROM AUTHOR]

Rapid deterministic modelling of shoreline evolution at regional and coastal-scheme scale enables Monte-Carlo simulations by which long-term shoreline statistics can be estimated. This paper describes UnaLinea, a fast, accurate finite difference solver of the one-line sediment continuity equation. The model is verified for the evolution of an initially straight shoreline of a plane beach subject to regular breaking waves at constant angle of incidence in the presence of either a groyne or a continuous single-point feed of sediment. Grid convergence and stability tests are used to obtain accurate, stable results, with satisfactory computational efficiency. Influences of wave input filtering and event-based sediment loading are considered. The rapid deterministic model is applied to Monte-Carlo simulations of the evolution of the west coast of Calabria, Italy for different scenarios including increased sediment load from a river and selected beach nourishment. The potential role of probabilistic shoreline evolution in regional coastal flood-risk assessment is explored through application to an idealised stretch of the Holderness coastline, U.K., where flood depths and expected damage are estimated for a 1000 year return period event. [ABSTRACT FROM AUTHOR]

A morphodynamic model based on the wave-driven alongshore sediment transport, including cross-shore transport in a simplified way and neglecting tides, is presented and applied to the Zandmotor mega-nourishment on the Dutch Delfland coast. The model is calibrated with the bathymetric data surveyed from January 2012 to March 2013 using measured offshore wave forcing. The calibrated model reproduces accurately the surveyed evolution of the shoreline and depth contours until March 2015. According to the long-term modeling using different wave climate scenarios based on historical data, for the next 30-yr period, the Zandmotor will display diffusive behavior, asymmetric feeding to the adjacent beaches, and slow migration to the NE. Specifically, the Zandmotor amplitude will have decayed from 960 m to about 350 m with a scatter of only about 40 m associated to climate variability. The modeled coastline diffusivity during the 3-yr period is 0.0021 m 2 /s, close to the observed value of 0.0022 m 2 /s. In contrast, the coefficient of the classical one-line diffusion equation is 0.0052 m 2 /s. Thus, the lifetime prediction, here defined as the time needed to reduce the initial amplitude by a factor 5, would be 90 yr instead of the classical diffusivity prediction of 35 yr. The resulting asymmetric feeding to adjacent beaches produces 100 m seaward shift at the NE section and 80 m seaward shift at the SW section. Looking at the variability associated to the different wave climates, the migration rate and the slight shape asymmetry correlate with the wave power asymmetry (W vs N waves) while the coastline diffusivity correlates with the proportion of high-angle waves, suggesting that the Dutch coast is near the high-angle wave instability threshold. [ABSTRACT FROM AUTHOR]

The morphologic evolution of a beach nourishment project constructed in Long Branch, New Jersey, USA is investigated using the method of empirical orthogonal functions (EOF). Most applications of EOFs on beach fill projects have focused on traditional linear fills on relatively long, straight, uninterrupted coastlines. The Long Branch project was unique in that it was designed as a feeder beach and was constructed within a groin field. The method of EOF analysis is applied to help identify patterns representing distinct physical processes in data sets of shoreline position and shoreline slope at the site. The first three modes, determined from the shoreline position data set, explain more than 90% of the variation from the mean shoreline. The first and third modes represent variations of the fill's spreading as material moved to the north in the direction of the net littoral drift. Several shore-perpendicular structures interrupt the longshore transport and regulate the spreading. One of these structures is a large outfall pipe that was identified during the beach profile surveys to have a dominant influence over the shoreline evolution. The second mode identified in the shoreline data set is related to seasonal or storm impacts, and represents the transition between a reflective summer condition and a dissipative winter state. Several of the modes derived from the beach slope data set, represent processes similar to those identified in the shoreline data set. The first mode explains 43.1% of the variation in the beach slope data, and represents the seasonal transition between reflective and dissipative beach states. The second mode represents the equilibration of slopes within the beach fill and the initial spreading of the fill. Derivatives of the temporal coefficients of both the shoreline and beach slope data sets are consistent with a reduction in the rate of changes as equilibrium is approached, and an acceleration of changes during storms. [ABSTRACT FROM AUTHOR]

Long-term decadal-scale shoreline change is an important parameter for quantifying the stability of coastal systems. The decadal-scale coastal change is controlled by processes that occur on short time scales (such as storms) and long-term processes (such as prevailing waves). The ability to predict decadal-scale shoreline change is not well established and the fundamental physical processes controlling this change are not well understood. Here we investigate the processes that create large-scale long-term shoreline change along the Outer Banks of North Carolina, an uninterrupted 60 km stretch of coastline, using both observations and a numerical modeling approach. Shoreline positions for a 24-yr period were derived from aerial photographs of the Outer Banks. Analysis of the shoreline position data showed that, although variable, the shoreline eroded an average of 1.5 m/yr throughout this period. The modeling approach uses a three-dimensional hydrodynamics-based numerical model coupled to a spectral wave model and simulates the full 24-yr time period on a spatial grid running on a short (second scale) time-step to compute the sediment transport patterns. The observations and the model results show similar magnitudes (O(10 5 m 3 /yr)) and patterns of alongshore sediment fluxes. Both the observed and the modeled alongshore sediment transport rates have more rapid changes at the north of our section due to continuously curving coastline, and possible effects of alongshore variations in shelf bathymetry. The southern section with a relatively uniform orientation, on the other hand, has less rapid transport rate changes. Alongshore gradients of the modeled sediment fluxes are translated into shoreline change rates that have agreement in some locations but vary in others. Differences between observations and model results are potentially influenced by geologic framework processes not included in the model. Both the observations and the model results show higher rates of erosion (∼−1 m/yr) averaged over the northern half of the section as compared to the southern half where the observed and modeled averaged net shoreline changes are smaller (<0.1 m/yr). The model indicates accretion in some shallow embayments, whereas observations indicate erosion in these locations. Further analysis identifies that the magnitude of net alongshore sediment transport is strongly dominated by events associated with high wave energy. However, both big- and small- wave events cause shoreline change of the same order of magnitude because it is the gradients in transport, not the magnitude, that are controlling shoreline change. Results also indicate that alongshore momentum is not a simple balance between wave breaking and bottom stress, but also includes processes of horizontal vortex force, horizontal advection and pressure gradient that contribute to long-term alongshore sediment transport. As a comparison to a more simple approach, an empirical formulation for alongshore sediment transport is used. The empirical estimates capture the effect of the breaking term in the hydrodynamics-based model, however, other processes that are accounted for in the hydrodynamics-based model improve the agreement with the observed alongshore sediment transport. [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]

A new reduced-complexity, 1-D shoreline model has been developed, calibrated, and tested with a set of shoreline positions detected from high-resolution satellite images. Motivated by recent large interannual water level fluctuations and associated shoreline changes in the Great Lakes, the model is built on previous models that are based on the disequilibrium concept, with extensions for water level effects. Unlike other shoreline models, the model includes two different sources of disequilibrium, wave disequilibrium and water level disequilibrium. The model also includes a passive flooding term to account for the instantaneous effect of the water level changes on the shoreline position. Case studies forced by seasonally-varying waves and water levels varying on seasonal and interannual timescales highlight the model's ability to enhance wave-driven shoreline change when water level variations are additionally present. The model was applied to two sites along the Lake Michigan shoreline, Jeorse Park and West Beaches, with shoreline time series extracted from multispectral satellite imagery. When calibrated and applied to an eleven year period of decreasing water levels, the new model shows significant skill in simulating and forecasting the shoreline position in the two study areas, with modest improvement over existing models. The simulation results additionally highlight the dominance of water level disequilibrium over wave disequilibrium for the study sites. When applied to a nearly forty year simulation of West Beach, the new model shows excellent ability to model the shoreline response to water level and wave fluctuations over a range of timescales. Comparison models are seen to be incapable of capturing the water level effects, particularly when water level trends differ from the calibration period. Overall, the model results and parameters show the importance of the newly introduced water level disequilibrium in modulating wave-driven shoreline change. Finally, while the shoreline model was motivated by Great Lakes coastal processes, it may provide new predication abilities for coastlines where water level fluctuations and trends play a role in shoreline changes. • A new shoreline model is developed, tested, and compared to existing models. • The model is based on the concept of combined wave and water level disequilibrium. • The model is applied to two case studies along the Lake Michigan shoreline. • The model successfully simulates shoreline changes enhanced by water level changes. [ABSTRACT FROM AUTHOR]

Hybrid 2D/one-line shoreline models are becoming increasingly applied over the mesoscale (101–102 years; 101–102 km) to inform coastal management. These models typically apply the one-line theory to simulate changes in shoreline morphology based on littoral drift gradients calculated from a 2DH coupled wave, flow, and sediment transport model. However, the key boundary conditions needed to effectively apply hybrid 2D/one-line models and their applicability beyond simple planform morphologies are uncertain, which can potentially comprise coastal management decisions. To address these uncertainties, an extensive numerical modelling campaign is carried out to both assess the sensitivity and calibrate an advanced hybrid 2D/one-line model (MIKE21) against six variables in three different sandy coastal system morphologies: (a) a simple planform morphology with a gentle sloping profile, (b) a simple planform morphology with a steep sloping profile, and (c) a complex planform morphology. The six variables considered include nearshore discretisation, bathymetry, bed friction, sand grain diameter, sand porosity, sediment grading, and the weir coefficient of hard defence structures. Five key conclusions are derived from the sensitivity testing and calibration results. First , the optimal boundary conditions for modelling shoreline evolution vary according to coastal geomorphology and processes. Second , specifying boundary conditions within physically realistic ranges does not guarantee reliable shoreline evolution predictions. Third , nearshore discretisation should be treated as a typical calibration parameter as (a) the finest discretisation does not guarantee the most accurate predictions, and (b) defining a discretisation based on process length scales also does not guarantee reliable predictions. Fourth , hybrid 2D/one-line models are not valid for application in complex planform morphologies plausibly because of the one-line theory assumption of a spatially invariable closure depth. Fifth , hybrid 2D/one-line models have limited applicability in simple planform morphologies where the active beach profile is subject to direct human modification, plausibly due to the one-line theory assumption of a constant time-averaged coastal profile form. These findings provide key theoretical insights into the drivers of shoreline evolution in sandy coastal systems, which have practical implications for refining the continued application of shoreline evolution models. • The hybrid 2D/one-line shoreline modelling approach is tested in three coastal morphologies. • Optimal boundary conditions correspond to observed coastal morphology. • The nearshore discretisation in shoreline models should be treated as a calibration parameter. • The hybrid 2D/one-line shoreline modelling approach is limited to simple planform morphologies. [ABSTRACT FROM AUTHOR]

Longwave response in a reef-lagoon bathymetry adjacent to a shore is studied by performing a series of numerical experiments. We consider the problem such that the length scale of the lagoon is comparable to the reef. A series of offshore reefs is formed periodically in the alongshore direction, parallel to the shoreline; adjacent reefs are separated with aperture channels. We impose cnoidal waves for the incident longwave train with the length scale comparable to the reef and lagoon dimensions. Our results reveal that the incident waves amplify in the region behind the reef, and attenuate in the region directly exposed to the aperture; the resulting variation of wave amplification along the shore is found to be substantial. This somewhat counterintuitive outcome is caused by a combination of diffraction and refraction of the long waves interacting with the reef-lagoon bathymetry of comparable length scale. We also found that the pattern of the offshore wavefield may not identify the reef bathymetry characteristics; it is because the pattern of offshore wave formation is influenced by a complex combination of wave reflection from the reef-lagoon system. The induced residual currents are also examined. The results show that notable offshore-directed residual currents are formed in the aperture channel only when the reef height is high with respect to the ambient water depth and when the aperture width is narrow compared with the reef's alongshore breadth. Otherwise, the residual currents in the onshore direction are formed, although the magnitude is very small. It is demonstrated that the residual currents are induced by a combination of the gradients of the mean water surface and the time average of horizontal momentum flux. • Substantially amplified runup directly behind the reef and attenuated runup in the area exposed to the aperture channel. • Difficult to characterize the reef formation from the offshore wave field. • Notable residual currents through the aperture channel only when the reef height is higher than one-half the water depth. [ABSTRACT FROM AUTHOR]

The effects of bed friction are modelled for the flow near the moving shoreline during the uprush phase of a swash event by extending the Pohlhausen method used by Whitham (1955) to a sloping bed. The tip of the swash near the moving shoreline is treated in an integral sense as a region of uniform velocity, being acted on by the forces of friction, gravity, and the pressure force induced by the frictionless flow behind the swash tip. The bed shear stress is parameterized by using the quadratic dependence on velocity. The theory is compared to data of the shoreline velocity and position in the swash of breaking solitary waves, and the friction coefficient is determined from direct measurements of bed shear stress. The theoretical predictions are in good agreement with the laboratory results in terms of time history of the shoreline velocity and position, as well as the run-up. [ABSTRACT FROM AUTHOR]

The Bruun rule is the most widely used method for determining shoreline response to sea level rise. It assumes that the active portion of an offshore profile rises with rising sea level, and the sand required to raise the profile is transported from the shoreline. It is difficult to evaluate the efficacy of the Bruun rule because sea level rise often has a lesser effect on shoreline change than that produced by sand sources, sinks, and longshore transport gradients. In addition, some shorelines have advanced seaward with rising sea level. Dean (1987) showed that equilibrium profile theory predicts that rising sea levels produce landward sand movement forced by nonlinear waves. This paper presents an equation with terms representing all phenomena affecting shoreline change including Bruun-rule recession, onshore sand transport, sand sources and sinks, and longshore transport gradients. As an example of its use, rates of onshore transport are determined along the 275-km Florida southwest coast, USA, and a 19-km portion of this coast using known values for sand sources, sinks, and longshore transport gradients. Then future shoreline changes are projected for both coasts from 2015 to 2065 and for the southwest coast from 2015 to 2100, using sea level rise projections from the Intergovernmental Panel on Climate Change. Beach nourishment is shown to be a very effective adaptation strategy for sea level rise with shoreline change projections useful to estimate required rates of beach nourishment to counter sea level rise. [ABSTRACT FROM AUTHOR]

In this paper, large-scale experimental data are presented showing the beach profile morphological evolution induced by four different bi-chromatic wave conditions characterized by very similar energy content between them but varying the modulation period. Important differences were observed in the resultant beach profiles as a function of the wave group periods. Larger variability in the profile evolution is generally observed for larger wave group periods and, more importantly, as the wave group period increases the distance between the generated breaker bar and the shoreline increases. The measured primary wave height to depth ratio ( γ ) increases with the wave group period, which is consistent with the observed larger wave height at the breaking location. The primary wave breaking location is also observed at increasing distances with respect to the initial shoreline as the wave group period increases. The variation in γ with wave group period is related to the selective energy dissipation of the higher primary frequency component ( f 1 ) during the wave group shoaling. Broad bandwith conditions (reduced wave group period) lead to larger dissipation of wave heights at the f 1 component relative to f 2 resulting in a reduction in the wave modulation and primary wave height at the breaking location. Suspended sediment fluxes obtained from collocated velocity and sediment concentration measurements in the surf zone showed a consistently larger contribution of the mean return flow to the suspended sediment fluxes compared with the wave group and primary wave components. The distinct beach profile evolution in terms of bar location is interpreted from an increasing distance of the mean breakpoint location and the location of maximum return flow with respect to the shoreline as the wave group period increases. [ABSTRACT FROM AUTHOR]

Beach nourishment on open ocean beaches not bounded by headlands or other structures suffers from high rates of lateral losses of fill volume as the nourished shoreline equilibrates with its surroundings. Estimates of lateral losses are essential for beach nourishment design, these predictions have been made in the last decade utilizing empirical formulations, one line models or lately, process-based coastal morphology models. Coastal morphology models are, however, complex and computationally intensive and in order to maintain a balance between model complexities, computational effort and processing capacity, schematization of model input (input reduction) is necessary. This paper is divided into two main sections. In the first section techniques of wave input reduction for morphological models are evaluated with focus on open ocean wave-dominated coasts. Subsequently, the optimized morphological model is applied to evaluate coastal engineering interventions aimed at reducing volume losses from the Delray Beach nourishment project. Wave input reduction is defined here as the process of reducing the full wave climate of a given coastal region to a set of representative wave-wind conditions, ‘running’ a model with these representative wave conditions in sequence for a smaller time period ( i.e. a few tide cycles) and multiplying its effect on the morphology by a Morfac value, that is related to the frequency of occurrence of that wave condition in nature, or its weight in the overall wave climate. Five different techniques of wave input reduction were tested. Of all the methods of wave climate schematization tested the methods defined as ‘Energy Flux Method’ and ‘Opti Method’ showed best results in terms of representing accurately the sediment transport patterns of the study area. The tests conducted indicate that a number around 12 representative wave cases was enough to represent an annual wave climate compared to a very detailed wave climate used as benchmark. The optimized model was used to evaluate alternative engineering solutions to reduce volumetric losses from the beach nourishment project. Engineering solutions evaluated included a construction of a breakwater field, backfilling all dredge pits located offshore of the project site, construction of a groin field at the downdrift end of the project, and backfilling the deepest dredge pit. These engineering interventions caused a reduction in beach volume losses within the project limits with varying levels of effect on the downdrift beaches. Reduction of the volume loss from the project site is technically feasible and may be economically feasible pending further economic feasibility evaluation. [ABSTRACT FROM AUTHOR]

Forecasting the maximum runup height and inundation area caused by a tsunami event has often been done by solving a numerical model describing the physical process. This approach requires data of fault plane parameters and bathymetry. The time required to prepare and execute the numerical model could be substantial. Therefore, it might not be suitable for the purpose of warning tsunami coastal flooding. In this paper we offer an alternative method that provides analytical relationship between the runup height and the fault plane parameters and the characteristic slope of coastal bathymetry. The method uses Okada's linear elastic dislocation model ( Okada, 1985 ) to estimate the coseismic seafloor deformation and the corresponding (initial) sea surface displacement for a given set of fault plane parameters. Once the tsunami waves are generated, Carrier & Greenspan's solution (1958) is adopted to yield analytical expressions for the time histories of shoreline elevation and velocity. Two types of problems are investigated. In the first scenario, the bathymetry is modeled as a constant slope that is connected to a constant depth region, where a seismic event occurs. In the second scenario, the bathymetry is further simplified as a constant slope, on which a seismic event occurs. As far as the Carrier–Greenspan's solution for shoreline movement is concerned, the former is treated as a boundary-value-problem (BVP) and the latter as an initial-value-problem (IVP). For both problems the relationships between dimensionless runup height and dimensionless fault plane parameters are developed and discussed. In addition, since Carrier–Greenspan's approach is valid only for non-breaking waves, expressions limiting the applicability of the present solutions are obtained. Application of the present solutions is demonstrated with two examples: the 2004 Sumatra and 2010 Chile earthquakes. Acceptable agreements are obtained with the field measurements of these events. The present solutions offer a fast way to estimate the runup heights with the simplified beach geometry. [ABSTRACT FROM AUTHOR]

Sandy beaches protected by submerged breakwaters, which have crests below sea level, are assumed to be vulnerable to relative sea level rise (SLR). In this study, the shoreline change due to sea level change and land subsidence along the Niigata West coast in Japan, which is protected by submerged breakwaters, was investigated using field data and a shoreline prediction model assuming that the shoreline change is caused by cross-shore sediment transport. The shoreline movement in the past 10 years was not directly caused by sea level change and land subsidence. However, our model predicts that over the next 100 years, the shoreline will retreat 60 m owing to the increase in the energy flux of incoming waves over the breakwater caused by SLR and land subsidence. These results imply that other sandy beaches protected by low-crested breakwaters as well as those behind coral reefs, which are natural submerged breakwaters, would experience non-negligible erosions caused by future relative SLR. [ABSTRACT FROM AUTHOR]

This paper concerns numerical modelling of the impact on the littoral drift and the shoreline from groynes forming a field of equidistant and identical groynes. The most important effect of a groyne on the shoreline morphology is that the littoral drift is blocked completely or partially. A local reduction in the littoral drift around the groyne introduces alongshore gradients in the alongshore sediment transport and sedimentation and erosion around the groyne which will cause re-orientation of the bed contours towards the prevailing wave direction until an equilibrium is reached. A discussion of this mechanism is presented including effects of scales, e.g. the effect of the relative length of the groynes (compared to the width of the surf zone). The model results indicate a strong dependency of the reduction in littoral drift on the initial geometric bypass ratio (Q geo *), which is defined from the groyne length and the littoral transport on the undisturbed coastline; Q geo * is the transport occurring outside the tip of the groynes divided by the total transport. It is found that the sensitivity of the littoral drift to variations in groyne spacing and the angle, of the approaching waves, is inversely proportional to Q geo *. [ABSTRACT FROM AUTHOR]

Engineered and natural submerged coastal structures (e.g., submerged breakwaters and reefs) modify incident wave fields and thus can alter hydrodynamic processes adjacent to coastlines. Although submerged structures are generally assumed to promote beach protection by dissipating waves offshore and creating sheltered conditions in their lee, their interaction with waves can result in mean wave-driven circulation patterns that may either promote shoreline accretion or erosion. Here, we analyse the mean flow patterns and shoreline water levels (wave runup) in the lee of idealised impermeable submerged structures with a phase-resolved nonhydrostatic numerical model. Waves propagating over submerged structures can drive either a 2-cell mean (wave-averaged) circulation, which is characterised by diverging flows behind the structure and at the shoreline, or 4-cell circulation, with converging flows at the shoreline and diverging flows in the immediate lee of the structure. The numerical results show that the mode of circulation can be predicted with a set of relationships depending on the incoming wave heights, the structure crest level, and distance to the shoreline (or structure depth). Qualitative agreement between the mean flow and proxies for the sediment transport using an energetics approach suggest that the mean flow can be a robust proxy for inferring sediment transport patterns. For the cases considered, the submerged structures had a minimal influence on shoreline wave setup and wave runup despite the wave energy dissipation by the structures due to alongshore wave energy fluxes in the lee. Consequently, these results suggest that the coastal protection provided by the range of impermeable submerged structures we modelled is primarily due to their capacity to promote beach accretion. • A phase-resolved model simulates hydrodynamic interactions with submerged structures. • Waves can drive 2-cell or 4-cell mean circulation and sediment transport patterns. • Bottom shear stresses presented an overall similar pattern to the mean currents. • We develop a predictor for the flow patterns based on wave and structure parameters. • The submerged structures had limited influence on shoreline setup and wave runup. [ABSTRACT FROM AUTHOR]

Shoreline erosion along open water bodies and waterways is a major cause in the conversion of wetlands and uplands to open water habitat. Conventional shoreline protective structures are expensive to construct in these environments, and may impede environmental exchanges essential for connectivity and functionality. The structure, Wave Suppression and Sediment Collection (WSSC) System that contains multiple Wave Robber™ units, is an alternative for shoreline protection that maintains environmental connectivity. The primary goals of this study are to evaluate the wave reduction and sediment collection performance of the unit as well as optimize its design. This study showed that the unit reduces 84 to 90% of the wave energy while collecting and retaining fine-grained sediment. A mathematical model fits the sediment collection data reasonably well with average correlation coefficients of about 0.87. Modeling results show that the sediment collection efficiency of the unit for fine-grained sediment is about 14%. Total area of flow through the unit was determined to be more important than the area distributed among the number and size of pipes. The sensitivity study shows that wave height and initial concentration are the most important factors effecting sediment collection. [ABSTRACT FROM AUTHOR]

Although simpler than process based models, state of the art shoreline evolution models based on the idea of cross-shore equilibrium still depend on at least 4 free-parameters. These dynamic equilibrium models are generally based on a kinetic equation in which shoreline change rate is proportional to the existing disequilibrium. Therefore a link between the model driving forces and their corresponding equilibrium shoreline position is necessary for their implementation. Until now this correlation has been established only empirically adding calibration parameters to the model. In this paper, an analytical correlation between the wave energy and the equilibrium shoreline position (“Equilibrium Energy Function”, EEF) is obtained from known invariant beach physical characteristics according to a theoretical bi-parabolic equilibrium beach profile (EBP). A wave driven shoreline evolution model related to cross-shore processes for the medium and long term is then developed with just one free-parameter as the combination of a kinetic equation simply proportional to the wave energy disequilibrium and the proposed analytical EEF. It is remarkable that, at the particular case of the beach of Nova Icaria, where the model has been calibrated and validated by means of two years of video monitoring, the proposed analytical EEF obtained only as a function of the so called EBP invariants fits shoreline observations as well as a calibrated EEF with precisely shoreline observation. The results at Nova Icaria of the proposed model show the same skills with just one calibration parameter than state of the art models with over 4 free-parameters. Nevertheless, observations in different sites with diverse beach characteristics and wave conditions are needed to widely validate the analytical form of the EEF and the shoreline evolution model proposed in this paper. [ABSTRACT FROM AUTHOR]

The use of variance images for runup and shoreline detection is analyzed in this work. A methodology based on the variance images is first motivated with synthetic time stacks and then confirmed with real images. A total of 55 time stack images from five different cameras at three video stations (in Spain and New Zealand) were digitized and used for the study. These images include different tide and wave conditions. From the time stack images we: 1) obtained the mean shoreline position and maximum runup manually digitizing the water/sand interface and, 2) computed the variance function. The variance function is shown to have a particular cross-shore shape, with two characteristic positions which allow us to satisfactorily recover the mean shoreline position and maximum runup obtained in the first step. Variance images were shown to be useful both for detecting mean shoreline, and for evaluating runup, providing a potential alternative for timex images. The method did not work well when runup occurred within the groundwater seepage face. [ABSTRACT FROM AUTHOR]

Nearshore submerged structures made of sand-filled geosystems are an interesting use for this type of coastal protection technology. These systems have an advantage over more traditional materials such as concrete units or rock, which is the limited and non-permanent impact on natural coastal processes. On top of that are also some important research achievements and improvements at the level of the materials. However, at more exposed hydraulic conditions under high wave energy its application is still hampered by the lack of knowledge about their performance. This paper describes research results based on a series of laboratory measurements of the hydrodynamic and morphodynamic change produced in the vicinity of submerged nearshore structures. An analysis of the different model outputs produced, with respect to sediment transport, wave reflection and wave-induced pressures, has been made and is discussed throughout the paper. Such a comparative analysis provides insights into the efficiency of each defence scheme in maintaining a beach and in protecting the shoreline. The sand-filled geosystems as nearshore submerged structures proved to be efficient in retarding the offshore movement of sediments and in maintaining the shoreline, even if instabilities due to elements' displacement and local scour have been observed. [ABSTRACT FROM AUTHOR]

Coastal communities are currently facing the challenge of climate change and coastal retreat. While scientists are moving towards ensemble-modelling approaches to address uncertainties on shoreline evolution predictions, they rarely account for the stochastic nature of wave conditions across a variety of temporal scales (e.g., daily, weekly, seasonal, and interannual). In this contribution, we investigate the effects of the inherent variability of wave conditions on past and future multi-decadal shoreline evolution at the cross-shore transport dominated beach of Truc Vert (France). Using a climate-based wave emulator and variance decomposition method, we address the relative impacts of uncertain wave chronology, sea-level rise and model free parameters on modelled shoreline change, while accounting for possible correlations and interactions among the input variables. This work is done for two different wave-driven equilibrium models. The results show that the equilibrium shoreline models respond differently to the ensemble wave forcing, so that the choice of the modelling approach is critical to long-term modelled shoreline variations and the related uncertainties. We find that the modelled shoreline variance is primarily driven by the uncertain wave chronology until mid-21st century, while the uncertainties on future sea-level rise become dominant after 2060 in all the simulated scenarios. We also found that interactions and correlations among the uncertain variables can affect the estimation of shoreline predictions uncertainties. Finally, we provide a perspective on the application of non-stationary wave-related model parameters as a future research avenue for understanding uncertainties in modelled shoreline position. • Uncertain future variability of wave forcing strongly affect shoreline projections. • Interactions and correlation among uncertain inputs contribute to model uncertainty. • Onset of sea-level rise dominance on uncertain model prediction occurs after 2060. • Dynamic model parameters alter shoreline models response to waves variability. [ABSTRACT FROM AUTHOR]

Nowadays there are numerous computational tools to forecast the evolution of the shoreline position in sandy coast environments. However, few studies have waited for the time horizon of the predictions to actually check the accuracy of the forecasted scenarios. Thus, this work proposed to assess the accuracy of medium-term predictions made with Long-Term Configuration (LTC) and GENEralised model for SImulating Shoreline change (GENESIS) numerical models for the time horizon of 15-year and evaluate the models' performance in forecasting the actual status of a complex sandy coastal stretch in 2018, the targeting year. The projection premises were already presented in Baptista et al. (2014) on which observational data used to calibrate and blind hindcast future scenarios of shoreline development was discussed. The case study focused on an area located downdrift of Poço da Cruz groin, on the northwest Portuguese coast, and considered two beach sectors in accordance with Baptista et al. (2014): sector AC, about 3.5 km long, and sector AB, about 2.4 km long and included in the first one. The whole coastal stretch is composed of sandy beaches, and past trends highlight erosion downdrift of Poço da Cruz groin due to the interruption of sediment transport. A monitoring program performed by the University of Aveiro between 2003 and 2018 (corresponding to the period of simulation presented in Baptista et al., 2014), including six topographic surveys, was considered for comparison with the projections previously made. An additional topographic survey performed in 2018, within COSMO programme, was also considered. Simulations results have proved divergent performances of LTC and GENESIS models, despite the equity of inputs parameters and modelling processes. It is concluded that GENESIS and LTC, considering the typical (TYP) wave climate (randomly generated to represent the typical frequencies of wave height and direction during five years), create an envelope (GENESIS below and LTC above) to the real average results. For TYP, GENESIS underestimates the mean retreat rates up to 23 m in sector AB and up to 23 m in AC; LTC overestimates the retreat up to 33 m in sector AB and up to 13 m in AC. Conversely, observed (OBS) wave climate (shorter characterisation period but maintaining the registered data sequence) projections overestimate the shoreline retreat in both coastal stretches, suggesting that a larger characterisation period should be more important than maintaining the sequence of recorded waves. For OBS, the models overestimate the mean retreat rates in both sectors: GENESIS overestimates up to 90 m in sector AB and up to 51 m in AC; LTC overestimates up to 60 m in AB and up to 60 m in AC. Also, the consideration of the artificial nourishment operations executed during the simulation period leads to better results in the LTC, which was overestimating the erosion rate. This showed that if all man-made interventions could be anticipated, the average retreat in the main sector, AC, would only be up to 5 % different from the projections made by Baptista et al. (2014) with LTC model and TYP wave climate. • Checked accuracy of 15-year forecasts. • Checked performance of LTC and GENESIS shoreline evolution models. • The wave sampling period used in calibration has relevant impact on forecasts made. • LTC and GENESIS create an envelope to the real average retreat surveyed. • Better projections would be achieved if planed interventions were known in advance. [ABSTRACT FROM AUTHOR]

Bay beaches are common coastal landforms along the world's coastlines and have frequently been used as equilibrium coastal systems to mitigate erosion problems and stabilize coasts. Throughout the literature, several formulae can be found to obtain the static equilibrium planform (SEP) of such beaches on the leeward sides of single protruding headland structures. However, equations used to define SEP behind breakwater gaps are rare and based on a limited number of studies, especially when the obliquity angle (β) is large. This paper proposes a new formula for modelling the SEP of bay beaches that includes cases with planform shapes characterized by large obliquity angles (β > 75°) for which the SEP is almost quasi-semicircular. The formula represents a general form of the parabolic bay shape equation (PBSE) with modified coefficients to alter the planform's curvature to be quasi-semicircular, mimicking the behavior of such bays in nature. The coefficients are expressed as functions of both the obliquity angle (β) and the curvature-adjustment angle (φ), which was determined based on field observations of the best-fitting SEP of 26 bay beaches with (β > 75°) along the coasts of Spain, Portugal and Brazil. Additionally, 32 beach cases characterized by smaller obliquity angles (β < 70°) were included in the derivation of the curvature adjustment angle, which was expressed as a function of (β). The model showed good results in modelling the SEP, with an RMSE of 0.90° obtained when estimating the planform's curvature-adjustment angle (φ) to obtain quasi-semicircular planform shapes for the prototype cases, confirming its utility as a valuable tool for engineering applications. • Static equilibrium planforms (SEPs) characterized by large obliquity angles are modelled. • A new formula was derived to plot the (SEP) of bay beaches behind gaps when (β > 75°). • A curvature-adjustment angle is used to alter the SEP's curvature based on field cases. • The SEP is quasi-semicircular for pocket beaches behind breakwater gaps when (β > 75°). • The curvature-adjustment angle is directly proportional to the obliquity angle (β). [ABSTRACT FROM AUTHOR]

Analysis of shoreline change is fundamental to a broad range of investigations undertaken by coastal scientists, coastal engineers, and coastal managers. Multispectral Satellite Imagery (MSI) provides high resolution datasets that allow coastlines to be monitored more frequently and on a global scale. The Landsat and Sentinel-2 MSI datasets are free for public use, which has increased the frequency of studies focusing on coastal change using satellite imagery. However, despite access to global and free satellite imagery, a method has yet to be developed to monitor different shoreline types and indicators globally, as not all shorelines are sandy beaches, and the waterline cannot be representative of all shoreline changes. The review paper introduces different techniques used currently to extract shoreline features, including water indexing, Machine Learning (ML) and segmentation methods. We presented here a comprehensive review of range of the methods available for shoreline extraction from MSI and discuss why some shoreline features have been identified using multispectral satellite imagery and others not. This approach helps to signal where the gaps are on the current methods for shoreline extraction and provides a roadmap of the key challenges that prevents MSI to be used for understanding shoreline changes at a global scale. • Assessing shoreline indicators and their extraction through the use of Multispectral Satellite Imagery (MSI). • There is a no "one size fits all" technique to monitor different shoreline types and indicators globally. • Machine Learning can reduce the number of options for shoreline extraction for all temporal and spatial scales. [ABSTRACT FROM AUTHOR]

Background The curved shoreline shape of embayed beaches is one of its most notable characteristics and can be described using the parabolic bay shape equation (PBSE). Wave diffraction in and around the shadow zone is often regarded as the primary forcing mechanism leading to the prominent curvature of the shoreline. However, wave climate variables (wave direction, directional spreading and wave height) are shown to be influential in redistributing wave energy throughout the bay and in the shadow zone. Methods In this study, a process-based morphological model (Delft3D) is used for hydrodynamic and morphodynamic simulations of a schematic embayed beach. Wave forcing conditions are systematically varied between a mixture of time-invariant and time-varying cases. Results The role of diffraction is shown to be dominant only when the wave conditions are both narrow-banded (< 20°) and when the PBSE angle β is high (> 30°). Otherwise, as little as 6% variation in wave direction within a 90° range can account for the shoreline curvature in and around the shadow zone. Conclusion The degree to which wave direction and directional spreading vary through time therefore has a large effect on the equilibrium orientation and shoreline planform of the bay. [ABSTRACT FROM AUTHOR]

The evolution of beaches in response to the incident wave conditions has long attracted the attention of researchers and engineers. A popular mathematical model describing the change in the position of a single height contour on the coastline assumes that the beach profile is stable and the plan shape evolves due to wave-driven long-shore transport. Extensions of this model include more contours and allow for beach profile alteration through cross-shore transport of sediment. Despite this advantage, models with multiple contours remain relatively underused. In this paper we examine the stability of this class of model for the cases of one to three contours. Unstable modes may exist when there is more than one contour. These include short waves whose growth rate is strongly dependent upon wavenumber. For the case of three contours an additional long wave instability is possible. A necessary, but not sufficient, condition for instability is found. It requires a reversal of transport direction amongst the contours. The existence of these instabilities provides a possible explanation for the difficulties found in implementing computational multi-line models, particularly where structures alter the natural longshore transport rates so they satisfy, locally, the condition for instability. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a simple approximation for assessment of the alongshore sediment transport rate on dissipative weakly curvilinear coasts. The approximation considers spatial variations in the wave angle and energy, sediment size, beach slope and type of wave breaking inside the surf zone. Similar approaches were employed in the past for coasts forced by high oblique waves where shoreline undulations frequently develop. With our approach, we can analyze more realistic situations, i.e., alongshore relations between the sediment size and the beach slope. The general expression for alongshore sediment transport is made explicit using a simple model for wave propagation. The solution is used to examine the implications of the behavior of alongshore sediment transport on shoreline evolution. After the analysis of the effects of variations in the wave conditions, the alongshore beach slope distribution and the shoreline geometry, three different shoreline tendencies were obtained for undulating shorelines: migration for changes in deep-water wave angle; amplitude growth for increases in wave height or period and changes in shoreline geometry; and wavelength changes and asymmetries for coasts with alongshore changes in beach slope. Our results also indicate that wave setup may enhance the formation of undulating shoreline features. [Copyright &y& Elsevier]

Abstract: In this paper we address the question of estimating the average position of a beach and its inherent variability about this mean. It is demonstrated how, even in a much simplified situation, the ensemble average of beach plan shape involves cross-correlation of the beach position and wave conditions. This renders the governing equations inimical to analytical treatment. A new analytical expression for the mean beach plan shape and its variation are derived for the case of a single groyne exposed to waves varying in direction only. This demonstrates that ‘beach memory’ is directly related to the autocorrelation of wave direction. For more general conditions a semi-analytical expression for the ensemble average of the shoreline position is derived. This solution is estimated with site specific wave conditions using Monte Carlo simulations. The characteristics of the solution are investigated and it is demonstrated that, for this case at least, the terms involving the wave direction are virtually uncorrelated with the terms that do not. It is concluded that, in an ensemble sense, the morphodynamic impact of wave direction is decoupled from that due to wave height and period. [Copyright &y& Elsevier]

Abstract: Edge waves generated by moving atmospheric disturbances parallel to the shoreline are investigated. Following a standard transformation method, an analytical expression of the surface elevation is derived, which consists of an infinite number of modes. Each mode is expressed as the sum of three singular integrals. Using the contour integration method, these singular integrals are converted to regular integrals, which are evaluated by numerical integration methods. The numerical results of two atmospheric pressure distributions studied by Greenspan (1956) are presented, and the resonance conditions are discussed. [Copyright &y& Elsevier]

Abstract: The non-hydrostatic wave model SWASH is compared to flume observations of infragravity waves propagating over a plane slope and barred beach. The experiments cover a range of infragravity wave conditions, including forcing by bichromatic and irregular waves, varying from strongly dissipative to strongly reflective, so that model performance can be assessed for a wide range of conditions. The predicted bulk wave parameters, such as wave height and mean wave period, are found to be in good agreement with the observations. Moreover, the model captures the observed breaking of infragravity waves. These results demonstrate that SWASH can be used to model the nearshore evolution of infragravity waves, including nonlinear interactions, dissipation and shoreline reflections. [Copyright &y& Elsevier]