Cross-shore Profile Evolution Research Articles

Cross-shore profile evolution induced by real emergent vegetation in a sandbar-lagoon coast: Laboratory experiments

Pressures from anthropogenic activities and climate change in lagoon ecosystems have increased rapidly in recent years. Coastal vegetation serves as a natural sea defense mechanism and is pivotal in maintaining a robust ecological balance. However, our understanding of how vegetation influences the evolution of typical sandbar-lagoon coasts is limited. To address this gap, a series of mobile-bed flume experiments were conducted within a typical sandbar-lagoon cross-section to investigate the impact of sparse Phragmites spp. planted on the sandbar on wave propagation and the evolution of the cross-shore profile under varying water depths and irregular wave conditions. These findings revealed that vegetation attenuates infragravity and sea-swell waves. Notably, infragravity waves are associated with the formation of a right- or obtuse-angled foredune scarp, whereas sea-swell waves tend to create an acute-angled scarp. Vegetation-induced changes in the local amplitudes of short waves within wave groups and the local mean water level are instrumental in reshaping foredune scarps. Additionally, the cross-shore width of the vegetation had a more pronounced influence on sediment transport within the lagoon than that of the solid volume fraction. Sparse vegetation not only reduces sediment deposition in the lagoon but also enhances offshore sediment transport. These insights significantly advance our understanding of wave-vegetation-sediment dynamics and provide essential scientific support for the implementation of coastal ecological restoration initiatives, particularly in the context of sandbar-lagoon coasts.

Experimental investigation on cross-shore profile evolution of reef-fronted beach

Physical experiments on cross-shore profile evolution of the reef-fronted beach are conducted considering various offshore wave conditions and reef settings. Cross-shore beach profile evolution, sediment transport rate, and waves at the beach toe are analyzed. The reef-fronted beach is found to be resilient to erosion induced by offshore sediment transport. In present cases, the beach evolves from a sloping profile to a reflective profile, and onshore sediment transport leads to the formation of a swash berm. Both the shortwaves and infragravity waves at the beach toe play an important role in forming the beach shape. The berm foreshore slope mainly depends on the wave energy density in the infragravity band at the beach toe. Wave energy density in the shortwave band at the beach toe increases with reef submergences, while wave energy density in the infragravity band at the beach toe increases with offshore wave heights. The temporal evolution of sediment transport rate exhibits two modes, implying complex feedbacks occur between swash flows and beach profile evolution. The bulk transport on the reef-fronted beach is parameterized by the relative height of shortwaves and wave steepness of both shortwaves and infragravity waves at the beach toe. A conceptual model of bulk transport on the beach is proposed that the bulk transport increases with the Gourlay number, indicating that reef-fronted beaches with a well-developed reef flat are resilient to increasing wave exposure.

Modeling cross-shore profile evolution in response to climate change: A case study for the Southwestern Black Sea Coast

Changes in wave climate and sea level as a result of global climate change cause significant effects on coastal morphology. Especially increasing wave heights, more frequent storms, and sea level rise (SLR) significantly alter the morphology of cross-shore profiles and diminish the security of coastal areas. In this study, profile surveys were carried out in two distinct regions along the Western Coast of the Black Sea, and the profile evolutions were analyzed using the XBeach numerical model. The XBeach model was executed using both its default parameters and the parameters derived from on-site measurements. This study was also conducted under the influence of hydrodynamic conditions (wave parameters) that vary according to the RCP4.5 and RCP8.5 climate scenarios, along with the effects of sea level rise (SLR), to analyze the potential impacts of climate change on profile evolution. The results indicated a linear relationship between the upper beach erosion and sea-level rise (SLR). The increased water level in front of the upper beach leads to greater erosion volume. The model results for the scenarios demonstrated moderate sensitivity to variations in offshore wave height, peak wave period, and storm duration, but were predominantly sensitive to accelerated sea level rise (SLR).

Assessment of Coastal Morphology on the South-Eastern Baltic Sea Coast: The Case of Lithuania

The Port of Klaipėda, located at the Klaipėda strait, divides the Lithuanian coast into two different geomorphological parts: southern—the coast of the Curonian Spit, and northern—the mainland coast. Port jetties interrupt the main sediment transport path along the South-Eastern Baltic Sea’s coast. Port of Klaipėda reconstruction in 2002 and the beach nourishment project which started in 2014 significantly influenced the northern part of the coast, which led to changes in the coastal zone evolution. The measurements in various periods are essential for cross-shore profile elevation to analyze seabed morphology and sedimentation patterns. These data highlight our understanding of the scale and timing of seabed erosion or sedimentation processes scale and timing. This study evaluates the impact of anthropogenic pressure and natural factors on coastal geomorphology and dynamics. In order to assess the latter changes, the cross-shore profile evolution and sediment budget were analyzed as well as nearshore bathymetry changes. The data illustrated a changing picture of the entire shore profile—on land and underwater.

Experimental and Numerical Simulation of Cross-Shore Morphological Processes in a Nourished Beach

Spyrou, D. and Karambas, T., 2021. Experimental and numerical simulation of cross-shore morphological processes in a nourished beach. Journal of Coastal Research, 37(5), 1012–1024. Coconut Creek (Florida), ISSN 0749-0208. This paper presents the results of an experimental and numerical research carried out to reproduce the cross-shore evolution of nourished sandy beaches. An extensive two-dimensional laboratory investigation was performed to study the cross-shore profile evolution after the application of a beach nourishment method. A 1:20 scale physical model was carried out in the Laboratory of the Department of Hydraulics and Environmental Engineering, Aristotle University of Thessaloniki. The analysis considered only cross-shore sediment transport. Long-shore sediment transport is considered negligible. Consequently, the obtained results are related to the short-term response of the cross-shore profile. Ten different wave combinations were generated in an attempt to reproduce erosive conditions. Experimental results are given in terms of wave parameters, bed slope, and berm height of the nourished beach. An advanced nonlinear wave model was developed to simulate cross-shore morphodynamical processes. The comparison between the experimental and numerical beach profile indicated good agreement. Also, comparisons between Dean's analytical method and the experimental results were made.

An efficient RANS numerical model for cross-shore beach processes under erosive conditions

In this work, a new numerical model for cross-shore beach profile evolution, IH2VOF-SED, is developed. It consists in the bidirectional coupling of a 2D RANS hydrodynamic solver and a sediment transport module. The resulting model is extensively validated against three benchmark cases at different scales, attending to the hydrodynamics, bottom shear stress and bathymetry evolution. Comparisons between experimental and numerical results show a good agreement for both the flow variables and the seabed evolution in all the validation cases without making use of calibration parameters. Additionally, the qualitative analysis of the results is in accordance with previous experimental observations of sediment transport induced by breaking waves. The computational cost is greatly reduced to about 1/10 of other available RANS models. As a novel aspect regarding RANS models, the model is able to simulate the swash zone and changes in the position of the coastline. A good compromise between precision and computational cost is achieved, allowing for an in-depth analysis of the processes leading to the cross-shore profile evolution.

Cross-Shore Profile Evolution after an Extreme Erosion Event—Palanga, Lithuania

We report cross-shore profile evolution at Palanga, eastern Baltic Sea, where short period waves dominate. Cross-shore profile studies began directly after a significant coastal erosion event caused by storm “Anatol”, in December of 1999, and continued for a year. Further measurements were undertaken sixteen years later. Cross-shore profile changes were described, and cross-shore transport rates were calculated. A K-means clustering technique was applied to determine sections of the profile with the same development tendencies. Profile evolution was strongly influenced by the depth of closure which is constrained by a moraine layer, and the presence of a groyne. The method used divided the profile into four clusters: the first cluster in the deepest water represents profile evolution limited by the depth of closure, and the second and third are mainly affected by processes induced by wind, wave and water level changes. The most intensive sediment volume changes were observed directly after the coastal erosion event. The largest sand accumulation was in the fourth profile cluster, which includes the upper beach and dunes. Seaward extension of the dune system caused a narrowing of the visible beach, which has led to an increased sand volume (accretion) being misinterpreted as erosion

A NUMERICAL MODEL OF CROSS-SHORE BEACH PROFILE EVOLUTION: THEORY, MODEL DEVELOPMENT AND APPLICABILITY

A practical numerical model was developed to simulate cross-shore profile evolution at two coastal sites in Iran. The model consists of three sub-models for calculating wave and current, sediment transport, and bed level changes. Validation and calibration of the model was carried out using the measured field data on the north and south coasts of Iran, where historic measurements of cross-shore beach profiles and wave conditions have been recorded. The model is formulated for calculating cross-shore sediment transports in and outside the surf zone by the product of time-averaged suspended sediment concentration under three different mechanisms and undertow velocity. The comparisons between the model results and field data show reasonable agreement for both coastal sites and will be capable of applying it to other coastal sites with modifications to the free parameters.

NUMERICAL SIMULATION OF BERM AND DUNE EROSION DUE TO WAVE OVERTOPPING AND SEDIMENT OVERWASH USING OPENFOAM

The present work follows authors’ previous works, published and presented at ICCE 2016 and Coastal Dynamics 2017 conferences (Karagiannis et al. 2016, 2017) and concerns the numerical simulation of berm and dune cross-shore profile evolution due to wave overtopping and sediment overwash through an innovative repetitive approach of coupling a hydrodynamic model, synthesized on the OpenFoam platform with a morphodynamic one, whose origin code is developed in FORTRAN by the authors. The hydrodynamic model is used for the wave propagation, while the morphodynamic one gets the results of the first model and yields the new cross-shore seabed formation. The above process is repeated until the equilibrium profile is achieved.

Study of the evolution of gravel beaches nourished with sand

Coastal erosion is a worldwide problem, so accurate knowledge of the factors involved in the shoreline evolution is of great importance. This study analysed three gravel beaches that were nourished with sand from the same source. However, the evolution of their shoreline was different in each case. For its analysis, different factors were studied such as the shoreline and cross-shore profile evolution, the maritime climate, sedimentology and mineralogy. From the results, it should be noted that Centro beach is the most stable with a loss of surface after the first regeneration of 12.8%, while Carrer de mar is the most instable with a loss of 20.9%. The Posidonia oceanica meadow is one of the factors that make Centro beach the most stable despite being the one that receives the most wave energy. Another factor is its mineralogy and more specifically the composition of the particles that form the sample. Thus, it is observed how the cracking or the formation of particles by different minerals with a fragile union, are factors that make the beaches behave differently against erosion. For this reason, it is concluded that in order for the shoreline to be as stable as possible over time, a previous study of the sediment to be used for nourishment is necessary, as well as its possible effect on the ecosystem, since the future shoreline evolution will depend on it.

Optimizing romanian maritime coastline using mathematical model Litpack

There are many methods and tools to study shoreline change in coastal engineering. LITPACK is a numerical model included in MIKE software developed by DHI (Danish Hydraulic Institute). With this matehematical model we can simulate coastline evolution and profile along beach. Research and methodology: the paper contents location of the study area, the current status of Midia-Mangalia shoreline, protection objectives, the changes of shoreline after having protected constructions. In this paper are presented numerical and graphycal results obtained with this model for studying the romanian maritime coastline in area MIDIA-MANGALIA: non-cohesive sediment transport, long-shore current and littoral drift, coastline evolution, crossshore profile evolution, the development of the coastline position in time.

Wave–dune interaction and beach resilience in large-scale physical model tests

Large-scale laboratory experiments focusing on the main physical processes driving dune erosion have been performed in a wave flume with a sandy dune exposed to a combination of water levels and wave conditions (Tomasicchio et al., 2011b) providing observations of different interaction regimes: collapsing, overwash and breaching (Sallenger et al., 2003).The large set of data has been considered to obtain measurements of beach–dune cross-shore profile evolution, hydrodynamic properties and suspended sediment concentration.Results show that erosion develops faster during the first hundred waves, there is a clear influence of wave period (van Gent et al., 2008) and water depth on the resilience of the beach–dune system, and that sediment concentration at a given transect depends on the bar position.Furthermore, the observed data have been adopted to verify the predictive accuracy of two open source process-based profile numerical models.

Impacts of storm chronology on the morphological changes of the Formby beach and dune system, UK

Abstract. Impacts of storm chronology within a storm cluster on beach/dune erosion are investigated by applying the state-of-the-art numerical model XBeach to the Sefton coast, northwest England. Six temporal storm clusters of different storm chronologies were formulated using three storms observed during the 2013/2014 winter. The storm power values of these three events nearly halve from the first to second event and from the second to third event. Cross-shore profile evolution was simulated in response to the tide, surge and wave forcing during these storms. The model was first calibrated against the available post-storm survey profiles. Cumulative impacts of beach/dune erosion during each storm cluster were simulated by using the post-storm profile of an event as the pre-storm profile for each subsequent event. For the largest event the water levels caused noticeable retreat of the dune toe due to the high water elevation. For the other events the greatest evolution occurs over the bar formations (erosion) and within the corresponding troughs (deposition) of the upper-beach profile. The sequence of events impacting the size of this ridge–runnel feature is important as it consequently changes the resilience of the system to the most extreme event that causes dune retreat. The highest erosion during each single storm event was always observed when that storm initialised the storm cluster. The most severe storm always resulted in the most erosion during each cluster, no matter when it occurred within the chronology, although the erosion volume due to this storm was reduced when it was not the primary event. The greatest cumulative cluster erosion occurred with increasing storm severity; however, the variability in cumulative cluster impact over a beach/dune cross section due to storm chronology is minimal. Initial storm impact can act to enhance or reduce the system resilience to subsequent impact, but overall the cumulative impact is controlled by the magnitude and number of the storms. This model application provides inter-survey information about morphological response to repeated storm impact. This will inform local managers of the potential beach response and dune vulnerability to variable storm configurations.

Beach Profile Model with Size-Selective Sediment Transport. I: Laboratory Experiment and Sensitivity Study

AbstractThe response of physical models of beach profiles to random breaking waves was studied to investigate size-selective sediment transport and cross-shore profile evolution. Three types of beach profiles with different sediment mixtures were considered and subjected to waves until profiles reached equilibrium. Size-selective sediment transport was evident in the experiments, with the mean sediment size varying up to 20% along the beach profiles. Consistent coarsening and fining of the surface sediment in the experiments revealed size-selective sediment transport governed by cross-shore variations in energy dissipation, affecting important beach profile features such as sandbar structures and offshore and foreshore slopes. The theoretical basis of the transport phenomenon was described by analyzing the relationship between the transport processes and essential wave and hydrodynamic parameters obtained using a new set of numerical models. The results showed that beach profile changes and associated sed...

Modelling gravel beach dynamics with XBeach

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

On the Predictability of Mid-term Cross-shore Profile Evolution

Fernàndez-Mora, À., Calvete, D., Falqués, A., Ribas, F., and Idier, D., 2013. On the Predictability of Mid-term Cross-shore Profile EvolutionThe aim of the present study is to analyse the mid-term beach profile evolution, considering the hypothesis that the alongshore processes can be neglected for the prediction of the mean profile evolution. To this end, a process-based model for the evolution of the cross-shore profile has been used. The model describes feedbacks between waves, rollers, depth-averaged currents and bed evolution, accounting for the effects of wave skewness and asymmetry on sediment transport. Offshore waves and tides conditions and bathymetric profiles measured at the FRF-USACE Duck are used to simulate a mid-term (72 days) onshore sandbar migration event. The model results agree with observed onshore movement and growth of the sandbar due to the inclusion of the intra-wave oscillatory flow with the skewness and asymmetry effects. The best predictions belongs to the averaging of the modelled evolution of individual cross-shore profiles that is better than the evolution of the mean cross-shore profile since. it takes into account the alongshore variability of the cross-shore profiles. These two methods result on better predictions than the individual profiles during the entire event.

SHOREWARD SAND TRANSPORT OUTSIDE THE SURFZONE, NORTHERN GOLD COAST, AUSTRALIA

To date, no suitable theoretical basis has been derived to predict with reliable accuracy the shoreward sand transport under waves in the deeper water outside the surf zone. This is important for understanding the rate of recovery of beaches after major storm erosion and, in some circumstances, to quantify net shoreward supply of sand to the shoreline from the active lower shore-face below the depth of storm erosion bar development. Even a relatively low rate of long term shoreward net supply may contribute to shoreline stability where it offsets a gradient in the longshore sand transport that would otherwise lead to recession. This paper outlines the results of analysis of a 41 year dataset of beach and nearshore profile surveys to quantify annual average rates of shoreward net sand transport in 6-20m water in an area where the profiles are not in equilibrium due to the existence of a residual river mouth ebb delta bar lobe. Additionally, an empirical adaptation of the sheet flow relationship of Ribberink and Al-Salem (1990) to provide for the effects of ripples has been derived from large wave flume data and correlates well with the measured Gold Coast transport rates. These have been applied to a new coastline modelling system developed as part of research into the long term evolution of Australia’s central east coast region in response to sea level change and longshore sand transport processes, which combines the one-line concept of shoreline profile translation within the zone of littoral sand transport with cross-shore profile evolution across the deeper shore-face profile below that zone. It demonstrates the importance of providing for both the shoreward supply from the continental shelf and the varying profile response time-scale across the shore-face in predicting shoreline evolution.

Critical storm thresholds for morphological changes in the western Black Sea coastal zone

Storms are one of the phenomena determining the short-term evolution of coasts by influencing the erosion and accretion patterns of the beaches. Some severe storms could cause loss of beach sediments, partial or complete destruction of coastal structures and even threaten human life and occupation. Bearing this in mind, it is essential to comprehend, which storms could evoke transient, although in some instances, significant morphological changes, and which could be considered as hazardous and result in catastrophic damage. This issue implies establishment of a set of critical thresholds for storm impact on coastal morphology.The paper presents a regional scale analysis of the near-shore morphological response of five beaches to storms of varying intensity. The analysis is accomplished by coupling of offshore wave and cross-shore profile data obtained for the Bulgarian Black sea coast. The historical storm pattern is reconstructed through hindcast using a coupled wave model system, while resulting morphological changes, such as shoreline alteration and cross-shore profile evolution, are estimated by analysis of long-term series of coastal measurements performed in 1970–1977 and 2008–2010.The storm impact thresholds are set in terms of integral wave energy taking into account both storm pattern and duration. It was found that the morphological response to storm impact is site specific and single-value thresholds are difficult to be established even at regional scale. Nevertheless, a range of critical storm thresholds is proposed. Thus, storms with integral wave energy varying within threshold values 0.4–0.7×106Jm−2 are regarded as capable of significant morphological changes, while less energetic events are supposed to influence predominately the seasonal beach dynamics. Furthermore, storms with integral wave energy higher than 0.7×106Jm−2 represent potentially destructive events that can change irreversibly the beach pattern or damage impact.

Analyzing wave breaking in a barred beach using wavelet

In this paper, a cross-shore profile evolution model, Uniform Beach Sediment Transport-Time-Averaged Cross-Shore (UNIBEST-TC), is used. The model was developed at WL/Delft hydraulic laboratory in the Netherlands. The model is used to predict wave height in a barred beach (Egmond site, The Netherlands) and the results show that there is a good agreement between the measured and predicted values by the model. In the present study, Morlet wavelet is used to distinguish the breaking waves; it is integrated over frequency to provide the temporal variation of localized total energy. The study shows that the local peaks of the energy densities correspond to the events of wave breaking in the predicted–wave time series. Furthermore, the wave energy distribution shows a tendency to decrease in the off-shore direction of the inner bar.

ON MODELLING BEACH PROFILE EVOLUTION

Behaviour-oriented beach evolution models are normally applied in a prognostic fashion, with model parameters and boundary conditions estimated from previous experience, other forecasts or from historic measurements. Here, we use observations of beach profiles to solve a cross-shore beach profile evolution equation in an inverse manner to determine key model parameters, cross-shore sediment diffusion coefficient and a time-varying source function. The data used to demonstrate the method are from Christchurch Bay in Dorset, United Kingdom. It was found that there is a significant contribution from diffusive processes to the morphodynamic variability of the beach profiles and that the development and disappearance of cross-shore coastal features such as upper beach berms and inter- and sub-tidal bars are well captured by the time-varying source function in the governing equation.