Cross-shore Beach Profile Research Articles

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.

Analyses of sea turtle landing behavior based on frequently observed coastal profile data - A case study in Enshu Coast, Japan

This study analyses sea turtle landing behavior along a 10 km sandy beach on the Enshu Coast, Japan, facing the Pacific Ocean. Data for the analysis are sea turtles' landing positions and crawl tracks recorded by a handheld GNSS device from May to September (2011–2016), noting spawning or no-spawning activity simultaneously, supplemented by weekly cross-shore beach profiles surveyed at four locations, satellite images, and other geographical data. At the onset, landing positions on the beach are visualized to determine local concentrations along the beach. Subsequently, we estimate the distance of spawning and no-spawning positions from the waterline during landing and evaluate beach stability through the temporal elevation change standard deviation. The study found that preferred spawning locations are 40–70 m from the waterline, above the intertidal zone, on bare sand, with a standard deviation of 0.1–0.6 m. This study also highlights the impact of beach infrastructure on sea turtle spawning failures and the influence of significant wave height on sea turtle landing.

Experimental study on wave attenuation and beach profile evolution under the protection of submerged flexible vegetation

Coastal protection methods are evolving from hard engineering techniques to natural enhancement approaches. Aquatic vegetation provides an environmentally friendly solution by effectively dissipating waves and resisting erosion. Laboratory flume experiments were conducted to investigate the effect of submerged flexible vegetation on the regular wave attenuation and cross-shore profiles on the artificial plane beach under varying hydraulic conditions. Variations in the waveform, wave spectrum, and wave height were analysed in the vegetation zone. Results show vegetation distorts the waveform and accelerates the attenuation process of the wave energy, and wave height evolution behaves differently from the theoretically obtained attenuation by Mendez and Losada (2004) due to the underestimating vegetation-induced attenuation and neglecting sediment-induced attenuation. Additionally, the formation process of the winter and summer profiles of the vegetated beach was analysed by the screenshots. Regenerated wave breaking becomes more apparent with increasing wave periods. The critical surf similarity parameter of the vegetated beaches was found to be lower than that of a smooth, impermeable slope because of the energy dissipation. Vegetation did not alter the type of the beach profiles, as compared to the final profiles and their characteristic parameters of the unvegetated beaches. Instead, it reduced the erosion depth and brought the eroded area closer to the shoreline. Dimensionless parameters were formulated to characterize the response of the cross-shore beach profile under the shelter of flexible vegetation, and an empirical equation about maximum erosion depth was developed within the scope of the experiment.

Simulation of the Evolution of Cross-Shore Beach Profiles using SBEACH Modelling

Coastal erosion significantly threatens sandy beaches worldwide, impacting coastal communities and ecosystems. This research investigates the application of SBEACH (Storm-induced BEAch Change), a numerical beach modelling computer programme, as a tool for coastal engineers to predict beach profile evolution in response to wave and tidal actions. The study used SBEACH simulations to explore the equilibrium beach profiles under varying conditions, including wave height, wave period, sediment grain size, and beach slope. This study also examined the effects of storm tides on equilibrium profiles and proposed protective sand dunes' dimensions to safeguard against storm surges. This research highlights SBEACH's potential as a valuable tool for assessing and planning coastal erosion mitigation strategies. While SBEACH provides insights into cross-shore beach profile dynamics, combining it with GENESIS offers a more comprehensive approach to coastal management. However, it is crucial to consider real-world engineering experience and safety factors when deciding on beach stabilisation and protection measures. Coastal countries can benefit from such modelling approaches to better manage and protect their sandy beaches, which play a crucial role in coastal defence and maintaining ecosystem integrity.

STUDY OF CROSS-SHORE PROFILES AT SOUTH COASTS OF THE CASPIAN SEA UNDER RAPID CHANGES IN WATER LEVEL

Coastal zone management needs the prediction of the changes in shoreline and coastal profiles, where the fluctuation of sea water level plays an essential role. Climate change and human activities have accelerated the fluctuation/falling of water levels in lakes and enclosed water basins. Using satellite images and cross-shore beach profiles at twelve monitoring stations along the southern coasts of the Caspian Sea, the effect of the rapid fall of water level on the nearshore morphology is studied in this research. Radiometric and atmospheric corrections are made on satellite images, and the NDWI index is used to increase the accuracy of the shoreline extraction. Comparing the accuracy of different methods, it is concluded that the Hands (1984) formula relatively better predicts the shoreline advancement rate due to lowering water level.

Analysis of the mechanics of breaker bar generation in cross-shore beach profiles based on numerical modelling

In this work, a recently developed numerical model, capable of solving the hydro- and morphodynamics of the cross-shore beach profile, is used to gain insight into the relevant processes driving the generation of a breaker bar. The bedload and suspended sediment transport contributions are analysed separately. It has been shown that the bedload transport tends to accumulate sediment on the onshore side of the undertow detachment point, at a distance that depends on the skewness of the waves and the magnitude of the friction velocity, shaping the onshore face of the breaker bar. In contrast, the suspended transport contributes to the growth of the offshore side of the breaker bar. Besides, a comparison between the sediment transport rates produced by different types of breakers shows a faster bathymetric evolution and an offshore displacement of the position of the breaker bar for high Iribarren numbers. Differences are consistent with the proposed mechanisms driving the evolution of the beach profile. The findings of this work provide a better understanding of the processes driving the formation of breaker bars, how they interact with each other and the relative importance of bedload and suspended sediment transport at each location of the cross-shore profile.

Subaqueous and Subaerial Beach Changes after Implementation of a Mega Nourishment in Front of a Sea Dike

Sandy nourishments can provide additional sediment to the coastal system to maintain its recreational or safety function under rising sea levels. These nourishments can be implemented at sandy beach systems, but can also be used to reinforce gray coastal infrastructure (e.g., dams, dikes, seawalls). The Hondsbossche Dunes project is a combined shoreface, beach, and dune nourishment of 35 million m3 sand. The nourishment was built to replace the flood protection function of an old sea-dike while creating additional space for nature and recreation. This paper presents the evolution of this newly created sandy beach system in the first 5 years after implementation based on bathymetric and topographic surveys, acquired every three to six months. A significant coastline curvature is created by the nourishment leading to erosion in the central 7 km bordered by zones with accretion. However, over the five-year period, net volume losses from the project area were less than 5% of the initial nourished sand volume. The man-made cross-shore beach profile rapidly mimics the characteristics of adjacent beaches. The slope of the surfzone is adjusted within two winters to a similar slope. The initially wide beaches (i.e., up to 225 m) are reduced to about 100 m-wide. Simultaneously, the dune volume has increased and the dune foot migrated seaward at the entire nourished site, regardless of whether the subaqueous profile gained or lost sediment. Our results show that the Hondsbossche Dunes nourishment, built with a natural slope and wide beach, created a positive sediment balance in the dune for a prolonged period after placement. As such, natural forces in the years after implementation provided a significant contribution to the growth in dune volume and related safety against flooding.

Surf and Swash Dynamics on Low Tide Terrace Beaches

Low tide terrace (LLT) beaches are characterised by a moderately steep beach face and a flat shallow terrace influencing the local hydro-morphodynamics during low tide. The upper beachface slope (β) and the terrace width (Lt) are the main morphological parameters that define the shape of LTT cross-shore beach profiles. This work aims at better understanding the behaviour of β and Lt and their link with the incoming wave forcing. For this purpose, our results are based on 3.5 years times series of daily beach profiles and wave conditions surveys at two different microtidal LTT beaches with similar sediments size but different wave climate, one at Nha Trang (Vietnam) and the other one at Grand Popo (Benin). While they look similar, two contrasting behaviour were linked to two sub-types of LTT regimes: the first one is surf regulated beaches (SRB) where the swash zone is highly regulated by the surf zone wave energy dissipation on the terrace, and the second is swash regulated beaches (SwRB) acting in more reflective regime where the terrace is not active and the energy dissipation is mainly produced in the swash zone, the terrace becomes a consequences of the high dynamics in the swash zone. Finally, extending the common view of an equilibrium beach profile as a power law of the cross-shore distance, the ability of a simple parametrized cubic function model with the Dean number as unique control parameters is proposed and discussed. This simple model can be used for the understanding of LLT environments but it can not be extended to the whole beach spectrum.

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.

MODELING OF BERM FORMATION AND EROSION AT THE SOUTHERN COAST OF THE CASPIAN SEA

Cross-shore beach profile data from field measurements performed at six locations on the southern coast of the Caspian Sea are used to investigate bathymetry change due to various wave conditions. Beach profile measurements are analyzed and subsequently compared with the results of a berm formation and erosion model. The model comprises distinct empirical sediment transport equations for predicting the cross-shore sediment transport rate under various wave conditions. To yield a berm formation and erosion model, empirical cross-shore sediment transport equations are combined with the mass conservation equation. Simulations results obtained from the model compared well with the measurements, proving the capability of the model in simulating berm formation and erosion evolution.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/FTgAr73h5rA

Coastal Flooding Process: Comparing Different Coastal Typologies Response to Extreme Hydrodynamic Conditions

Freire, P.; Oliveira, F. S. B. F. and Oliveira, J. N., 2020. Coastal flooding process: Comparing different coastal typologies response to extreme hydrodynamic conditions. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 797–802. Coconut Creek (Florida), ISSN 0749-0208.To upgrade the response capability to coastal flood events, hazard predictions need to be improved through integrating the effect of the coastal morphological variability in the nearshore-foreshore-backshore hydromorphological processes induced by waves-tide-wind-atmospheric pressure. In order to evaluate the short-term morphological response of different coastal typologies to potential flood conditions (spring high tide level, storm surge, high wave height), field data acquired in 2019 in three sites in the West coast of Portugal with past flooding episodes are presented and discussed. The preliminary results point out that under the same forcing conditions the short-term response of the cross-shore beach profile that controls the flooding levels is dependent on the beach typology, namely: the nature of the lower and upper limits of the beach face, profile gradient and its alongshore context. This knowledge can be used to develop robust and validated flood prediction tools contributing to improve mitigation and adaptation management strategies.

Beach scarp dynamics at nourished beaches

Beach scarps are nearly vertical seaward facing sandy cliffs within the cross-shore beach profile. These features are often associated with eroding (nourished) coastlines and can reach heights of O(2–3 m). An analysis of a six-year dataset of beach scarp presence at the nourished Sand Engine beach shows that the formation of beach scarps at the nourishment is linked to mildly erosive (summer storm) conditions, whereas destruction is often related to extremely erosive (winter storm) conditions. Additional experiments were carried out showing the formation, migration, and destruction of scarps from artificially constructed mounds with linear slopes. The field experiments show that steep initial slopes are more susceptible to beach scarp formation. Video observations at these experiments show that the scarp toe level, where the vertical slope meets the gently sloping beach, is related to the high wave runup events. The commonly used 2% exceedance wave runup estimates can therefore be used to predict the final elevation of the scarp toe. The strong connection of maximum runup elevation with the scarp toe elevation provides a direct relation between the final scarp height through nourishment platform height and hydrodynamic conditions. High platform nourishments will promote the formation of beach scarps and steep initial profiles increase the speed at which scarps form. This study suggests that by adjusting the design of beach nourishments, beach scarp formation and persistency can be limited by regulating the natural destruction of these features.

Short-term observations of beach Morphodynamics during seasonal monsoons: two examples from Kuala Terengganu coast (Malaysia)

This paper describes the morphodynamic changes that took place along Kuala Terengganu coastline over daily periods during seasonal monsoons (onset of Northeast Monsoon in October 2014 and during Southwest Monsoon in May 2015). Cross-shore beach profiles had been determined and foreshore sediments were sampled from two selected beaches; north of Kuala Terengganu at Pengkalan Maras (PM) and another to the south at Kuala Ibai (KI). Based on the beach classification scheme, PM appeared to be a spilling breaker type beach (ξb) with an Intermediate state (Ω), whereas KI belonged to the plunging breaker type (ξb) with Intermediate-Dissipative state (Ω). The beaches were dominated by coarse and fine sands at PM and KI, respectively. The wave hydrodynamics on the southern beach (KI) was characterised by higher Hb values, when compared to that in the north (PM). This study investigated the impact of morphodynamic changes during seasonal monsoons, regardless of the presence of coastal defence structures. Without any coastal defence structure (revetment), the PM beach exhibited attainment of equilibrium state, when compared to the KI beach. Therefore, coastal structures, such as revetments, directly modified the morphodynamics at KI beach. The PM beach displayed the tendency for occurrence of erosion during the Northeast Monsoon, while exhibited accretion during the Southwest Monsoon. This scenario differed from that noted at the KI beach, which signified erosion during both seasonal monsoons. The study outcomes may assist in formulating an effective coastal zone management plan for monsoon-dominated coasts, particularly sandy beaches.

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.

Modelling the cross-shore beach profiles of sandy beaches with Posidonia oceanica using artificial neural networks: Murcia (Spain) as study case

This paper presents a model of the cross-shore beach profile taking into account the presence of the seagrass Posidonia oceanica whose ultimate objective is to reduce the volume of sand used in beach nourishment. The methodology describes the training, validation, testing and application of models of artificial neural networks (ANN) for computing the cross-shore beach profile of sandy beaches in the province of Murcia (Spain). Eighty ANN models were generated by modifying both the input variables and the number of neurons in the hidden layer. The input variables consist of wave and sediment data and data concerning the Posidonia oceanica. To select and evaluate the performance of the optimal model, the following parameters were used: R2, absolute error, mean absolute percentage error and percentage relative error. The results show a mean absolute error of 0.22 m (0.21 m in training and 0.28 m in test), representing an improvement of 85.1% compared to models that do not use the Posidonia oceanica and 69.8% against those that consider it. Although the ANN was developed for beaches with P.oceanica, it could be used in areas with other seagrass able to reduce wave energy and consolidate the sand such as Syringodium filiforme, Thaalassia testudinum, Laminaria hyperborea, Halodule wrightii and Zostera marina.

Laboratory study on tsunami erosion and deposition under protection of rigid emergent vegetation

Devastating tsunami waves can change the coastal morphology considerably. The effects of vegetation to coastal morphodynamics have been of primary interest for decades, because of their role in coastal protection and ecological environment. The damping of wave and impact of beach evolution are the two significant contributions on emerged vegetation. However, the laboratory study of tsunami erosion and deposition under protection of coastal vegetation was less understood compared to tsunami run-up and tsunami inundation. A set of laboratory experiments were reported in this study on changes of size-selective sandy beach profile under the protection of rigid emergent vegetation. The total of fifteen experiments was carried out in a wave flume including two initial profiles (with vegetation and none vegetation), three different wave conditions and four forest densities. The experiments show that rigid emergent vegetation changes the depth and location of tsunami deposition and erosion in sandy beach. The dimensionless numbers were derived to characterize the cross-shore beach profile response under the protection of rigid emergent vegetation. These parameters were written as a dimensionless group, and based upon this present experimental datum, the empirical equations were developed. The study reveals the internal connection among tsunami deposition and erosion, wave height and forest density. The findings of this study have the potential to assist the tsunami hazards prevention and mitigation.

Depth of closure: New calculation method based on sediment data

Obtaining depth of closure (DoC) in an accurate manner is a fundamental issue for coastal engineering, since good results for coastal structures and beach nourishment depend mainly on DoC. Currently, there are two methods for obtaining the DoC, mathematical formulations and profile surveys. However, these methods can incur important errors if one does not take into account the characteristics and morphology of the area, or if one does not have a sufficiently long time series. In this work the DoC is obtained from the break in the trend of the sediment with the depth, that is, in general with the increase of the depth a decrease in the size of the sediment takes place. However, at one point this tendency changes and the size increases, and then decreases again. When comparing the point where the minimum sediment size occurs before the increase, it is observed that the error incurred is small compared to other methods. If the Standard Deviation of Depth Change (SDDC) method is considered as the most accurate method, the error incurred by the proposed method is less than 7%. In addition, it can be seen that the dispersion of the sediment method always occurs outside the zone of bar movement. Whereas in the methods of profiles survey (using 2cm precision profiles), sometimes the DoC is obtained within the active zone of bar movement. In addition, where the relative minimum of the median sediment size is found, and the sizes of 0.063 and 0.125mm predominate in the composition of the sample. Therefore, this new method allows the precise location of the DoC to be obtained in a fast and simple way. Furthermore, this method has the advantage that it is not affected by the modifications that may be experienced by both the study area and the cross-shore beach profile.

Artificial neural network modeling of cross-shore profile on sand beaches: The coast of the province of Valencia (Spain)

ABSTRACTThe paper describes the training, validation, testing, and application of models of artificial neural networks (ANN) for computing the cross-shore beach profile of the sand beaches of the province of Valencia (Spain). Sixty ANN models were generated by modifying both the input variables as the number of neurons in the hidden layer. The input variables consist of wave data and sedimentological data. To select and evaluate the performance of the optimal model, the following parameters were used: R2, absolute error, mean absolute percentage error, and percentage relative error. Finally, the results are compared with the numerical model proposed by Aragonés et al. (2016b) for the equilibrium profile in the study area. The results show a mean absolute error of 0.21 m compared to 0.33 m Aragones’ model, significantly improving the results of the numerical model in the bar area around de Valencia Port. In addition, when comparing the results with other methods currently used (Dean’s or Vellinga formulation), the errors of these compared to ANN are of the order of 167 and 1538% higher, respectively.

An available formula of the sandy beach state induced by plunging waves

Laboratory experiments are performed to explore the response rule of a sandy beach profile under plunging wave on a non-uniform sediment-bed slope. The initial beach slope of combination of 1/10 and 1/20 is exposed to regular waves and cnoidal waves respectively. The free surface elevation, process of wave propagation, wave breaking, uprush and backwash and the change of a cross-shore beach profile are measured and recorded. The beach profile under the regular waves action exhibits two parts: a sandbar profile and a beach berm profile, and only one typical profile transformation under the cnoidal waves action is obtained, which is the beach berm profile. In the laboratory experiments, it is found that the beach states under wave action related to the previous factors. In addition, they are related to the characteristic of breaking waves such as the breaking intensity of the plunging wave. A concept about the characteristic angle of the plunging wave has been put forward through the observation and analysis of the phenomenon of the laboratory experiment. A qualitative analysis about the sediment transport carrying by currents generated from the plunging wave and the state of beach profile under the wave action has been done. The quantitative analysis about the relationship between the characteristic angle and Irribarren number has been done. An available formula of equilibrium states for the sandy beach induced by the plunging wave has been established based on the relationship between Irribarren number and the beach profile. By fitting these experimental results and others' experimental results to three lines, the three fitting coefficients can be calculated in their formula respectively. The recommended empirical formulas can divide three states of a beach morphology profile obviously, which include a depositive beach, an erosive beach and an intermediate beach.

Automatic super-resolution shoreline change monitoring using Landsat archival data: a case study at Narrabeen–Collaroy Beach, Australia

Long-term monitoring of shoreline changes is of significant importance for coastal erosion prediction and coastal planning. This paper presents the use of the Landsat archival dataset over 29 years to monitor shoreline changes at Narrabeen–Collaroy Beach, Australia. For each scene of Landsat data, a vector-based shoreline at subpixel level was automatically extracted by employing the super-resolution border segmentation method. Monthly cross-shore beach profile surveys at five locations along the beach are used as ground truth data to assess the results. The experimental results show that after the correction of tidal effects the RMSEs of the time-series shorelines at the five locations are all less than 10 m; RMSEs of annual mean shorelines are within 5.7 m. These results were achieved within the context that the Narrabeen–Collaroy Beach has been observed to vary in width by up to 80 m during this same period. In addition, the observed variabilities in shoreline change at different locations along the 3.6-km long embayment are also clearly observed from Landsat-derived results. The results indicate the feasibility of Landsat data for long-term shoreline change monitoring.