Beach Profile Model Research Articles

Forecasting coastal evolution on time-scales of days to decades

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

A Coupled Hydrodynamic-Equilibrium Type Beach Profile Evolution Model

An equilibrium beach profile model is developed and coupled with a parametric hydrodynamic model to provide feedback between the evolving morphology and the hydrodynamics. The model is compared to laboratory beach profiles evolving toward equilibrium conditions under constant forcing. The equilibrium model follows the classical approach but uses the bulk sediment transport as the governing model parameter. This approach is coupled with empirically derived and normalised sediment transport functions and a parametric surf zone wave transformation model. The dissipation predicted by the surf zone model controls the cross-shore position of the maxima in the sediment transport functions and hence the cross-shore evolution of the beach profile. Realistic beach profile shapes are generated for both erosive (barred) and accretive (bermed) beach profiles, and predictions of bar and berm position are satisfactory. With more complex normalised sediment transport functions, the model can be applied to conditions with a cyclical wave climate. However, the model concept is better associated with erosive wave conditions and further work is required to improve the link between the modelled dissipation and local transport for accretive conditions.

Effect of Climate Change on Beaches in Japan

Future beach loss in Japan are reported to be more than 90% due to sea level rise in the worst case. Beaches are affected not only by the sea level rise but also by rainfall and wave characteristic changes and others. This paper reviews past and future beach loss in Japan in a national scale and introduces projection method of future beach loss due to sea level rise and rainfall characteristic change. Even past beach loss and sediment budget are not easy to be quantitatively elucidated in coastal catchments in a national scale, then realistic future beach loss projection is much more challenging. Both further past data analysis and beach profile model improvement/development are necessary for better beach loss projections.

Typical equilibrium beach profile models and their significances from different segments of a headland-bay beach

This study introduces three typical models on equilibrium beach profile, and discusses the application limitations of these models. Then this study examines the selections for applying these models on different coastal segments of a headland-bay beach in west Guangdong, South China, and explores the physical significances of those parameters in the models. The results indicate that: (1) Bodge’s model is more in line with the equilibrium beach profile of the tangential or transitional segment, whereas Lee’s model is more consistent with the shadow profile; (2) most of the parameters in three models have clear physical significances in accordance with the actual characteristics of this headland-bay beach; and (3) both the selections for the equilibrium beach profile from different segments and significances of most of the parameters in three models are in essence correlated with the morphodynamic states at various coastal locations.

Equilibrium Beach Profile in the Presence of Beachrocks

Rollnic, M. and Medeiros, C., 2016. Equilibrium Beach Profile in the Presence of Beachrocks In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 452–456. Coconut Creek (Florida), ISSN 0749-0208.Equilibrium Beach Profile (EBP) models are used to estimate sandy beach profiles, they assume the existence of a shoreface shape that represents an equilibrium condition between wave climate and sediments, making it possible to identify erosion/accretion trends. EBP models suit beaches with near homogeneous grain size sediments. However, in subtropical and tropical areas, beachrocks are often found underlying the beach face, such that EBP models may not be suitable as shadowing areas may favour settling of variable grain size sediments. Our goal was to evaluate the Bruun-Dean EBP model for a beach along which beachrocks were at times absent and at times present as onshore or submerged reefs. Eight 1km-long bathymetric profiles were performed from the surf zone to the 10m isobath and sediment samples obtained at 50, 100, 200, 500 and 1000 m from the surf zone. EBP was computed for distinct coefficient (m) values and evaluated as a function of resulting summed square error. A closure depth of 3.97 m was computed using wave characteristics were derived from 1 year radar records. Along the study area the 3.97 m isobath is positioned 140 to 400m offshore, disregarding the quotas of the beachrocks. At the control areas where beachrocks were absent, m=0.67 yielded the best fit. At areas where beachrocks were present, profiles tended to be steeper and m=0.77 results in a better adjustment near the shore. For the more seaward portion of the profiles, the incorporation of a parameter related to the reef high could improve fitting.

New methodology for describing the equilibrium beach profile applied to the Valencia's beaches

Mathematical models used for the understanding of coastal seabed morphology play a key role in beach nourishment projects. These projects have become the fundamental strategy for coastal maintenance during the last few years. Accordingly, the accuracy of these models is vital to optimize the costs of coastal regeneration projects. Planning of such interventions requires methodologies that do not generate uncertainties in their interpretation. A study and comparison of mathematical simulation models of the coastline is carried out in this paper, as well as elements that are part of the model that are a source of uncertainty. The equilibrium profile (EP) and the offshore limit corresponding to the depth of closure (DoC) have been analyzed taking into account different timescale ranges. The results have thus been compared using data sets from three different periods which are identified as present, past and future. Accuracy in data collection for the beach profiles and the definition of the median grain size calculation using collected samples are the two main factors that have been taken into account in this paper. These data can generate high uncertainties and can produce a lack of accuracy in nourishment projects. Together they can generate excessive costs due to possible excess or shortage of sand used for the nourishment.The main goal of this paper is the development of a new methodology to increase the accuracy of the existing equilibrium beach profile models, providing an improvement to the inputs used in such models and in the fitting of the formulae used to obtain seabed shape. This new methodology has been applied and tested on Valencia's beaches.

Forecasts of seasonal to inter-annual beach change using a reduced physics beach profile model

Abstract The observed seasonal to inter-annual variability of beach profiles has been investigated using a one dimensional beach profile model. The model used here is developed on the ‘reduced-physics’ modelling approach. The model uses a diffusion formulation as the governing equation and adopts an inverse modelling technique for solving the equation. The model is calibrated and validated against historic measurements of beach profiles at Hasaki Coast, located in the east coast of Japan. The beach is longshore uniform and characterised by a highly dynamic longshore bar-trough system. The model is then used to forecast seasonal to inter-annual scale beach change. The results are compared with beach change determined from measured beach profiles at Hasaki between 2007 and 2011. The simple modelling approach used yields encouraging results of seasonal to inter-annual scale beach change at Hasaki Coast.

Process-based modeling of cross-shore sandbar behavior

A coupled wave–current–sediment transport beach profile model is used to simulate cross-shore sandbar evolution on the time scale from days to months comprising both rapid offshore and slow onshore migrations. The discrimination of four modes of sediment transport driven by velocity and acceleration skewness, mean currents and slope effects allows addressing the dominant hydrodynamic processes governing cross-shore sandbar behavior. Acceleration–skewness-induced transport systematically results in a slow onshore sandbar migration together with a slow bar growth. Velocity–skewness-induced transport can drive onshore and offshore bar migrations with substantially larger rates. Mean–current-induced sediment transport systematically drives an offshore bar migration with either bar growth or decay. Slope effects essentially act as a damping term. The water level above the sandbar crest mainly influences the sandbar migration direction, while wave obliquity regulates the magnitude of the migration rates and is crucial to accurately simulate offshore sandbar migration during energetic obliquely incident waves. The inclusion of acceleration skewness is a necessary requirement to accurately reproduce the onshore migration of shallow sandbars. Detailed inter-site comparison of best-fit model parameters shows large differences meaning that free parameters attempt to compensate some mispecifications of the physics in the model. Although this also applies to other existing beach profile models, this suggests that this model needs further improvements including, for instance, the contribution of the injection of breaking wave turbulence onto the bed to sand stirring.

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...

Beach Profile Model with Size-Selective Sediment Transport. II: Numerical Modeling

AbstractBeach profile evolution is a dynamic phenomenon that often leads to threatening consequences such as severe beach erosion and shoreline retreat. A new comprehensive morphodynamic model is introduced in this study that includes representation of bedload and suspended size-selective sediment transport and cross-shore sediment grain-sorting models. The model is capable of simulating the changes in cross-shore bathymetry and sediment grain size composition observed under laboratory conditions for both erosive- and accretive-type equilibrium beach profiles. The new model is most advantageous for scenarios with poorly sorted sediments or sites with strong cross-shore variability in sediment grain sizes. Information on sediment size composition in the domain and its history is also provided by the new model, which can be useful for engineering, recreational, or biological considerations.

Scale effects in numerical modelling of beach profile erosion

Oliveira, F.S.B.F. and Contente, J., 2013. Scale effects in numerical modelling of beach profile erosion.The beach profile morphodynamic processes can be relatively well reproduced in large scale physical models. However, the cost associated to their use makes this methodology not always practicable. As alternative, it is desirable to explore and apply smaller scales laboratory infrastructures with confidence, despite the different scaling laws, that is, the impossibility to simulate all relevant variables in correct relationship to each other. The combination of physical and numerical modelling can be a methodology to improve the required confidence (HYDRALAB III European Programme). Scale effects in a numerical process-based beach profile model, applied to simulate beach profile evolution under erosive wave conditions, were investigated in the present study. The numerical model was applied at laboratory and prototype scales, first with the default settings and then calibrated. Its performance was evaluated using the Brier Skill Score. The numerical results of the profile evolution in both scales were compared after reducing the results from the prototype scale to the laboratory scale. The profile erosion prediction was overestimated in the laboratory scale and underestimated in the prototype scale. Despite the calibration parameter that causes the largest modifications of the beach profile being the same in both scales, the Gamma2 wave parameter, the most efficient parameter was different. For most of the calibration parameters, the value for the best case was not coincident in both scales. It was concluded that there are scale effects using the Litprof model.

Numerical modelling of erosion and accretion of plane sloping beaches at different scales

The paper focuses on the numerical simulation of erosion of plane sloping beaches by irregular wave attack in three wave flumes of different scales. One of the prime objectives of the tests was to provide a consistent data set for the improvement of numerical beach profile models. A practical application of this research with wave attack on plane sloping beaches is the erosion of the plane beaches after nourishment. Three models (CROSMOR, UNIBEST-TC and DELFT3D) have been used to simulate the flume experimental results focusing on the wave height distribution and the morphological development (erosion and deposition) along the beach profiles. Overall, the model predictions for wave heights show consistent results. Generally, the computed wave heights (H rms and H 1/3) are within 10% to 15% of the measured values for all tests (under-prediction of the largest wave heights close to the shore). The three models can simulate the beach erosion of the wave flume tests (erosive tests) reasonably well using default values of the sand transport parameters. The model performance for the accretive tests is less good than that for the erosive tests. A practical field application of this research is the erosion of nourished beaches, as these beaches generally have rather plane beach slopes immediately after nourishment. Various graphs are given to estimate the beach erosion of nourished beaches.

Beach profile model considering time-space variations of sediment density

Beach profile model taking into account the time-space variations of sediment density has been developed and compared with the movable bed experiments in the laboratory wave flume. Concretely, the conventional sediment transport load using the velocity moments with use the fluid acceleration is revised considering the time-space variations of underwater specific gravity of sand particles in the activation depth based on the X-ray CT scanning. Conducting the numerical experiments, the fluid acceleration (horizontal pressure gradients) is found to have an inverse proportion to the underwater specific gravity of sand particles in the activation depth. Preliminary attempts to parameterize the time-space variations of underwater specific gravity of sands appear promising.

A behavioral template beach profile model for predicting seasonal to interannual shoreline evolution

This contribution presents a simple behavioral template model for beach profile evolution which is calibrated and tested against a 6‐year time series of shoreline position, derived from a coastal imaging system at the Gold Coast, Australia. From a coastal management perspective, the position of the shoreline is arguably one of the most important morphodynamic parameters to be monitored and predicted and therefore forms the focus of this paper. The template model attempts to encapsulate some of the current understanding of coastal dynamics deduced from both scientific investigations and observations. The model framework is based on a simple relaxation model, whereby the profile approaches a template exponentially with time under conditions of constant forcing. The template evolves dynamically in response to incident wave forcing such that when a threshold value of the dimensionless fall velocity (Ω = Hs/wTp, where Hs = offshore significant wave height, Tp = peak wave period, and w = sediment fall velocity) is exceeded, the beach face erodes and flattens, and the shoreline retreats landward, forming an erosional scarp and a breakpoint bar. Conversely, when the Ω falls below threshold, progradation and steepening of the shoreface ensues, accompanied by the evolution of a swash bar and breakpoint step. The Gold Coast data are used to calibrate the threshold value of Ω (≈4.0) which is close to the time series mean (3.8). Testing the calibrated model on unseen data shows that it is able to reproduce the dominant seasonal/interannual shoreline succession observed at this site and up to 77% of the detrended shoreline variability.

N-line Model Considering the Effects of the Beach Nourishment and Sorting of the Mixed Sand due to the Longshore and Cross-Shore Sand Transport

The artificial beach nourishment method has been accepted as one of the protection works from beach erosions. For the long term coastal management, it is need to estimate the coastal changes in the future using the beach profile model. When the beach nourishment is carried out, the characteristics of the injected sands are often different from those of the local sands. In this study, the N-line model considering the effects of the beach nourishment and sorting of the mixed sand due to longshore and cross-shore sand transport is suggested. The transport of the nourished sand is estimated by solving the two-dimensional advection diffusion equation. The change of content rate of each grain size is calculated, the result of the numerical model is compared with experimental data.

Wave reflection on natural beaches: an equilibrium beach profile model

Waves are the most energetic phenomena that control beach morphology. The beach profile mostly depends on the way in which the incident wave energy distributes along the profile, dissipation and reflection being the main mechanisms. While the dissipation phenomena have been widely studied, the effect of wave reflection on the beach profile has attracted much less attention and is still poorly known. In order to evaluate its importance, a new equilibrium profile model that includes reflection is proposed. The model is based on a two-section profile scheme, largely corresponding to the surf and shoaling-dominated zones of the beach profile. The obtained formulations are represented by the expression of two terms. One of the terms accounts for the dissipation effect and coincides with the Dean profile. The other term integrates the reflection process. The model and its coefficients have been calibrated using measured profiles along the Spanish coast. The validation shows a significant improvement of the fitting parameters with respect to the most popular equilibrium profiles model. Moreover, additional empirical expressions that relate morphology and hydrodynamic in the equilibrium profile model are also presented in this study as a novel contribution to this topic.

Equilibrium beach profile model for perched beaches

A beach profile equilibrium model for perched beaches is presented. The model assumes that wave reflection at the seaward and leeward sides of the breakwater is the most important process that modifies Dean's equilibrium profile model for non-perched beaches. The influence of wave breaking over the submerged structure is also discussed. Several laboratory data sets are used to analyze the merit of the proposed model for describing the equilibrium condition of a perched beach. A good comparison is obtained. Results show that if the ratio between the water depth above the submerged structure, d, and the water depth at the toe of the structure, h e, is large, d/ h e>0.5, only minor advance of the shoreline is achieved with the construction of a toe structure. A considerable advance is obtained for d/ h e less that 0.1. In these situations, however, resonant effects may result in an inefficient structure. The proposed model is used to provide an estimation for the required sand volume and the associated beach advance for the case of narrow breakwaters.