Shoreline Change Model Research Articles

Calibration of shoreline change model using an optimization algorithm

As the prediction and preparation for coastline change are regarded as an important social issue, improving the accuracy of the numerical shoreline change model to predict long-term shoreline changes is becoming increasingly important. Most shoreline change models contain several parameters to reflect the local characteristics of the study area, and their performance can be significantly enhanced by calibrating the parameters with the field data. However, as the number of the parameters increases, the model calibration becomes extremely difficult, especially in the model application for a long and complicated shoreline. In the present study, a method for calibrating the parameters of a shoreline change model that uses an optimization algorithm is proposed. Subsequently, its performance is demonstrated by applying the model to the Gangneung littoral cell set on the East Coast of Korea. First, the parameter calibration was performed using the records of 17 years (1980–1996) for all input data, including artificial coastal developments, conservation efforts, wave climate statistics, and the observed shoreline data. Subsequently, the calibrated model was verified using the data of the next 17 years (1997–2013). The results showed that the model calibration using the optimization technique significantly improved the accuracy of the shoreline change model.

The scale of the central beach change processes in the west coast of Nha Trang bay

The central beach in west coast of Nha Trang bay has experienced erosion in recent years. The determination of hydrodynamic regime and causes of this beach fluctuation is still an open problem and is concerned by scientists and managers. This study shows the causes and scales of the shoreline change processes based on the results of shoreline change model and the analysis of remote sensing images of shoreline location.

Impact of model free parameters and sea‐level rise uncertainties on 20‐years shoreline hindcast: the case of Truc Vert beach (SW France)

AbstractShoreline change is driven by various complex processes interacting at a large range of temporal and spatial scales, making shoreline reconstructions and predictions challenging and uncertain. Despite recent progress in addressing uncertainties related to the physics of sea‐level rise, very little effort is made towards understanding and reducing the uncertainties related to wave‐driven shoreline response. To fill this gap, the uncertainties associated with the long‐term modelling of shoreline change are analysed at a high‐energy cross‐shore transport dominated site. Using the state‐of‐the‐art LX‐Shore shoreline change model, we produce a probabilistic shoreline reconstruction, based on 3000 simulations over the past 20 years at Truc Vert beach, southwest France, whereby sea‐level rise rate, depth of closure and three model free parameters are considered uncertain variables. We further address the relative impact of each source of uncertainty on the model results performing a Global Sensitivity Analysis. This analysis shows that the shoreline changes are mainly sensitive to the three parameters of the wave‐driven model, but also that the sensitivity to each of these parameters is strongly modulated seasonally and interannually, in relation with wave energy variability, and depends on the time scale of interest. These results have strong implications on the model skill sensitivity to the calibration period as well as for the predictive skill of the model in a context of future climate change affecting wave climate and extremes. © 2020 John Wiley & Sons, Ltd.

Simulating the Impact of Sea-level Rise and Offshore Bathymetry on Embayment Shoreline Changes

Robinet, A.; Castelle, B.; Idier, D.; D'Anna, M., and Le Cozannet, G., 2020. Simulating the impact of sea-level rise and offshore bathymetry on embayment shoreline changes. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1263–1267. Coconut Creek (Florida), ISSN 0749-0208.LX-Shore is a reduced-complexity shoreline change model driven by cross-shore and longshore processes which can account for man-made or natural non-erodible areas such as groynes and headlands. Here we describe and further test the implementation of two recent developments allowing to account for (i) real and non-erodible offshore bathymetric features such as rocky outcrops and canyons affecting offshore wave transformation and, in turn, shoreline variability and (ii) shoreline retreat due sea-level rise. After a description of the numerical developments, the benefits of these new developments are demonstrated with the application of LX-Shore to an idealized embayed beach exposed to real wave climate during a 10-yr period. Three simulations are conducted to test the impact of an outcrop in the middle of the embayment and of a gradual 1-m sea-level rise on shoreline spatial and temporal modes of variability. Results show that the equilibrium planview shoreline and the shoreline variability are strongly impacted by only slightly modifying the bathymetry and varying the mean sea level. These results show the potential of LX-Shore to better understand and further predict shoreline change along real coasts exhibiting mixed (sandy/rocky) and complex seabed morphologies and undergoing sea-level rise.

Controls of local geology and cross-shore/longshore processes on embayed beach shoreline variability

Shoreline variability along the 3.6-km long Narrabeen Beach embayment in SE Australia is investigated over a 5-year period. We apply the one-line shoreline change model LX-Shore, which couples longshore and cross-shore processes and can handle complex shoreline planforms, non-erodible emerged headlands and submerged rocky features. The model skilfully reproduces the three dominant modes of shoreline variability, which are by decreasing order of variance: cross-shore migration, rotation, and a third mode possibly related to breathing. Model results confirm previous observations that longshore processes primarily contribute to the rotation and third modes on the timescales of months to seasons, while cross-shore processes control the shoreline migration on shorter timescales from hours (storms) to months. Additional simulations carried out in simplifying progressively the bathymetry show how the inherent geology strongly modulates the spatial modes of shoreline variability. The offshore central rocky outcrop is found to limit the rotation. In contrast, the submerged rocky platforms that extend from the headlands enhance the shoreline rotation mode and increase alongshore variability of the cross-shore migration mode, owing to increased alongshore variability in wave exposure. Offshore wave transformation across large-scale submerged rocky features and headland shape are therefore critical to contemporary shoreline dynamics.

PROBABILISTIC SHORELINE CHANGE MODELING AND RISK ESTIMATION OF EROSION

Prediction of long-term shoreline changes is a key task in planning and management of coastal zones and regional sediment management. Due to complex natural features of offshore waves, sediments, and longshore sediment transport, quantifying uncertainties of shoreline evolution and risks of extreme shoreline changes (erosion and accretion) is of vital importance for practicing uncertainty- or risk-based design of shorelines. This paper presents probabilistic shoreline change modeling to quantify uncertainties of shoreline variations by using numerical-model-based Monte-Carlo simulations. A shoreline evolution model, GenCade, is used to simulate longshore sediment transport and shoreline changes induced by random waves from offshore. A probability density function with a modified tail distribution is developed to capture stochastic features of wave heights under fair weather and storm conditions. It produces a time series of wave heights including small and extreme waves based on their probabilities (or frequencies of appearance). Probabilistic modeling of shoreline change is demonstrated by computing spatiotemporal variations of statistical parameters such as mean and variance of shoreline changes along an idealized coast bounded by two groins. Maximum shoreline changes in return years with a confidence range are also estimated by using maximum likelihood method. Reasonable results of obtained probabilistic shoreline changes reveal that this model-based Monte-Carlo simulation and uncertainty estimation approach are applicable to facilitate risk/uncertainty-based design and planning of shorelines.

A reduced-complexity shoreline change model combining longshore and cross-shore processes: The LX-Shore model

A reduced-complexity numerical model, LX-Shore, is developed to simulate shoreline evolution along wave-dominated sandy coasts. The model can handle any sandy shoreline geometries (e.g. sand spits, islands), including non-erodible areas such as coastal defenses and headlands, and is coupled with a spectral wave model to cope with complex nearshore wave fields. Shoreline change is primarily driven by the gradients in total longshore sediment transport and by the cross-shore transport owing to variability in incident wave energy. Application to academic cases and a real coast highlights the potential of LX-Shore to simulate shoreline change on timescales from hours (storm) to decades with low computational cost. LX-Shore opens new perspectives in terms of knowledge on the primary mechanisms locally driving shoreline change and for ensemble-based simulations of future shoreline evolution.

A Climate Index Optimized for Longshore Sediment Transport Reveals Interannual and Multidecadal Littoral Cell Rotations

AbstractA recent 35‐year endpoint shoreline change analysis revealed significant counterclockwise rotations occurring in north‐central Oregon, USA, littoral cells that extend 10s of kilometers in length. While the potential for severe El Niños to contribute to littoral cell rotations at seasonal to interannual scale was previously recognized, the dynamics resulting in persistent (multidecadal) rotation were unknown, largely due to a lack of historical wave conditions extending back multiple decades and the difficulty of separating the timescales of shoreline variability in a high energy region. This study addresses this question by (1) developing a statistical downscaling framework to characterize wave conditions relevant for longshore sediment transport during data‐poor decades and (2) applying a one‐line shoreline change model to quantitatively assess the potential for such large embayed beaches to rotate. A climate INdex was optimized to capture variability in longshore wave power as a proxy for potential LOngshore Sediment Transport (LOST_IN), and a procedure was developed to simulate many realizations of potential wave conditions from the index. Waves were transformed dynamically with Simulating Waves Nearshore to the nearshore as inputs to a one‐line model that revealed shoreline rotations of embayed beaches at multiple time and spatial scales not previously discernible from infrequent observations. Model results indicate that littoral cells respond to both interannual and multidecadal oscillations, producing comparable shoreline excursions to extreme El Niño winters. The technique quantitatively relates morphodynamic forcing to specific climate patterns and has the potential to better identify and quantify coastal variability on timescales relevant to a changing climate.

A model integrating longshore and cross‐shore processes for predicting long‐term shoreline response to climate change

AbstractWe present a shoreline change model for coastal hazard assessment and management planning. The model, CoSMoS‐COAST (Coastal One‐line Assimilated Simulation Tool), is a transect‐based, one‐line model that predicts short‐term and long‐term shoreline response to climate change in the 21st century. The proposed model represents a novel, modular synthesis of process‐based models of coastline evolution due to longshore and cross‐shore transport by waves and sea level rise. Additionally, the model uses an extended Kalman filter for data assimilation of historical shoreline positions to improve estimates of model parameters and thereby improve confidence in long‐term predictions. We apply CoSMoS‐COAST to simulate sandy shoreline evolution along 500 km of coastline in Southern California, which hosts complex mixtures of beach settings variably backed by dunes, bluffs, cliffs, estuaries, river mouths, and urban infrastructure, providing applicability of the model to virtually any coastal setting. Aided by data assimilation, the model is able to reproduce the observed signal of seasonal shoreline change for the hindcast period of 1995–2010, showing excellent agreement between modeled and observed beach states. The skill of the model during the hindcast period improves confidence in the model's predictive capability when applied to the forecast period (2010–2100) driven by GCM‐projected wave and sea level conditions. Predictions of shoreline change with limited human intervention indicate that 31% to 67% of Southern California beaches may become completely eroded by 2100 under sea level rise scenarios of 0.93 to 2.0 m.

Cause Analysis of Erosion-Induced Resort Washout on Cua Dai Beach, Vietnam

ABSTRACT Hung, N.T.; Vinh, B.T.; Nam, S.Y., and Lee, J.L., 2017. Cause analysis of erosion-induced resort washout on Cua Dai Beach, Vietnam. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 214–218. Coconut Creek (Florida), ISSN 0749-0208. On an eroding beach, high waves can completely wash out beaches, swimming pools, and resorts. Cua Dai shore, which is located immediately north of Thu Bon river mouth in central Vietnam, has eroded on the order of hundreds of meters in beach width. The present study estimated the erosion rate of sediment volume into the estuary through the Thu Bon river mouth by using recent satellite images, and utilized a shoreline change model to reproduce the erosion of shoreline near the river mouth. Results are in good agreement with observed data. The numerical model is modified by including the equilibrium angles that were obtained from a static shoreline ...

Observations and 3D hydrodynamics-based modeling of decadal-scale shoreline change along the Outer Banks, North Carolina

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 60km 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 1.5m/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(105m3/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 (∼−1m/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 (<0.1m/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.

A method for using shoreline morphology to predict suspended sediment concentration in tidal creeks

Improving mechanistic prediction of shoreline response to sea level rise is currently limited by 1) morphologic complexity of tidal creek shorelines that confounds application of mechanistic models, and 2) availability of suspended sediment measurements to parameterize mechanistic models. To address these challenges we developed a metric to distinguish two morphodynamic classes of tidal creek and tested whether this metric could be used to predict suspended sediment concentration. We studied three small tidal creeks in North Carolina, U.S.A. We collected suspended sediment at one non-tidal and two tidal sites in each creek and measured the wetland and channel width using a geographic information system. In each creek, tidal harmonics were measured for one year, sediment accretion on the salt marsh was measured for three years, and shoreline erosion was measured from aerial photographs spanning 50years. Additional total suspended solids measurements from seven creeks reported in a national database supplemented our analysis. Among the three intensively studied creeks, shoreline erosion was highest in the most embayed creek (having a wider channel than the width of adjoining wetlands) and lowest in the wetland-dominated creek (having a channel narrower than the width of adjoining wetlands). Wetland sediment accretion rate in the wetland-dominated creek was four times higher than the accretion in the embayed creek. The wetland-dominated tidal creek had over twice the suspended sediment as the most embayed creek. Based on these results, we conclude that our metric of embayed and contrasting wetland-dominated creek morphology provides a guide for choosing between two types of morphodynamic models that are widely used to predict wetland shoreline change. This metric also allowed us to parse the 10 tidal creeks studied into two groups with different suspended sediment concentrations. This relationship between suspended sediment concentration and creek morphology provides a method to estimate sediment concentration for individual tidal creek shorelines from spatial data alone, enabling more accurate parameterization of shoreline change models.

Statistical modeling of interannual shoreline change driven by North Atlantic climate variability spanning 2000–2014 in the Bay of Biscay

Modeling studies addressing daily to interannual coastal evolution typically relate shoreline change with waves, currents and sediment transport through complex processes and feedbacks. For wave-dominated environments, the main driver (waves) is controlled by the regional atmospheric circulation. Here a simple weather regime-driven shoreline model is developed for a 15-year shoreline dataset (2000–2014) collected at Truc Vert beach, Bay of Biscay, SW France. In all, 16 weather regimes (four per season) are considered. The centroids and occurrences are computed using the ERA-40 and ERA-Interim reanalyses, applying k-means and EOF methods to the anomalies of the 500-hPa geopotential height over the North Atlantic Basin. The weather regime-driven shoreline model explains 70% of the observed interannual shoreline variability. The application of a proven wave-driven equilibrium shoreline model to the same period shows that both models have similar skills at the interannual scale. Relation between the weather regimes and the wave climate in the Bay of Biscay is investigated and the primary weather regimes impacting shoreline change are identified. For instance, the winter zonal regime characterized by a strengthening of the pressure gradient between the Iceland low and the Azores high is associated with high-energy wave conditions and is found to drive an increase in the shoreline erosion rate. The study demonstrates the predictability of interannual shoreline change from a limited number of weather regimes, which opens new perspectives for shoreline change modeling and encourages long-term shoreline monitoring programs.

NEMOS (Nearshore Modelling of Shoreline Change) Model for Abrasion Mitigation at the Northern Coast of Ambon Bay

The Northern coast of Ambon Bay was suffered degradation in the form of abrasion. The research aims to analyse factors that causing abrasion and mitigation prevention. The research was done to measurement of NEMOS modeling use of GENESIS (Generalized Model for Simulating Shoreline) with three scenarios i.e existing conditions without protection, with groin series, and groin and seawall combination protection. Results obtained that sediment transport in the areas is 89 227 843 m3, it means that Northern coast had abrasion. NEMOS model with series of groins simulation will reduce to 60 259 673 m3. Simulation with groins and seawall, transport sedimen will reduced to 49 361 749 m3.

Long-Term Shoreline Change at Kailua, Hawaii, Using Regularized Single Transect

ABSTRACT Anderson, T.R.; Frazer, L.N., and Fletcher, C.H., 2015. Long-term shoreline change at Kailua, Hawaii, using regularized single transect. Traditional long-term (decadal) and large-scale (hundreds of kilometers) shoreline change modeling techniques, known as single transect, or ST, often overfit the data because they calculate shoreline statistics at closely spaced intervals along the shore. To reduce overfitting, recent work has used spatial basis functions such as polynomials, B splines, and principal components. Here, we explore an alternative to such basis functions by using regularization to reduce the dimension of the ST model space. In our regularized-ST method, traditional ST is an end member of a continuous spectrum of models. We use an evidence information criterion (EIC = −2 times the log of the prior predictive distribution) to select the optimal value of the regularization parameter, instead of the usual L-curve method, because the EIC can also be used to evaluate basis function models...

Current Characteristics and Shoreline Change at Pondok-Bali, North Coast-West Java of Indonesia

Numerical model of shoreline change by GENESIS (Generalized Model for Simulating Shoreline Change) and some field surveys were performed in the Pondok-bali Subang Distric of Indonesia. The objective of this investigation is to learn the cause of shoreline retreat that happen in Pondok-bali and its surrounding area in ten years nowadays. Based on field observation and the study result, we found that the waves occurred in East-wind monsoon, rip current and inundation due to water level raised have the significant contribution on an impact to shoreline retreat in Pondok -Bali.

PREDICTION OF FUTURE SHORELINE CHANGE WITH SEA-LEVEL RISE AND WAVE CLIMATE CHANGE AT HASAKI, JAPAN

We developed a shoreline change model considering the effects of the wave regime, sea level, and time heterogeneity. The model predicts the shoreline change under changing global climate conditions: sea-level rise and wave climate change. The model predicted the future shoreline positions from 2008 to 2095 at the Hasaki coast on Japan’s Pacific coast. The simulation results showed that the shoreline would retreat approximately 20 m by the end of this century owing to the rise in sea level; nevertheless, the wave climate change would not cause a worsening of the beach erosion, but would cause only a slight increase in the variation of the shoreline position.

Assessment of a Measure for Water Exchange Strengthening of Artificial Headland Bays Based on Shoreline Change and Flushing Time

ABSTRACT Pan, Y.; Kuang, C.; Gu, J.; He, L.; Zhang, Y.; Yang, Y.; Qiu, R., and Zhang, J., 2014. Assessment of a measure for water exchange strengthening of artificial headland bays based on shoreline change and flushing time. Artificial headlands are used around the world to form headland bays to contain beach materials. However, the artificial headland would weaken the water exchange in the bay and in some cases would make the water quality deteriorate. In this paper, we propose reserving a tidal channel in the landward end of the artificial headland, thus enabling the tidal current to pass through the channel, as a solution. The effects of the tidal channel on the weakening of beach protection and the strengthening of water exchange were investigated via numerical studies based on a beach nourishment project. A shoreline change model was set up to investigate the weakening of the beach protection. Four project schemes were simulated, and the results indicated that weakening of the beach protection is ac...

An OpenMI-based combined model for alongshore sediment transport and shoreline change

This paper describes the extension of a state-of-the-art one-line model in terms of alongshore sediment transport rate by linking with a cross-shore profile model through the OpenMI-based Pipistrelle interface. In order to combine these two models, three additional modules (Drift Interpolation module, Vector-to-Scalar module and Orientation Updating module) need to be developed, so that the two models which are based on different assumptions, coordinate systems and set-ups can be linked seamlessly. The existing two models and the three new modules are able to work together as a whole composition (i.e. the combined model) based on the OpenMI standard. This combined model aims to improve the one-line model in terms of alongshore sediment transport and beach morphological response predictability. It adopts both the modified Coastal Engineering Research Centre, USA (CERC) formula and the Energetics approach to calculate the alongshore sediment transport. Tests at a real curved coast demonstrate that the model is numerically stable, effective in computing and able to give reasonable predictions of shoreline change. It demonstrates that further research on linking existing models is promising.

Application of Empirical Orthogonal Function Models to Analyze Shoreline Change at Bangkalan Madura

Bangkalan’s shoreline, especially on the opposite side of Surabaya, has been evaluated to determine the morphological changes due to wave attack, near-shore current, long-shore sediment transport and coastal configuration. This research aims to determine the dominant patterns of variation of Bangkalan’s shoreline change, expressed by Eigen-function in empirical orthogonal function (EOF) models. That was started with data collection such as oceanographic data (wave and tidal), bathymetry and topographic map and sediment data. All data was used for forecasting two-monthly shoreline. Coordinate of two-monthly shoreline was used as input of EOF model. The first Eigen mode is a profile of shoreline equilibrium. The second Eigen mode shows pivot point that separates the different behaviors, which indicates a positive balance of shoreline from the direction of the dominant force. The models execution based on 1986’s shoreline show the shoreline change significantly at some cells e.g. around Suramadu bridge (cell 1-40), Batuporon (cell 70-100), Jungdima (cell 142-170) and at Kamal port (cell 230-250). The model of shoreline change using EOF was validated with the One-line model and data of 1995’s map’s shoreline. The E.O.F. value of model RMSE, 0.02, is less than the root mean square error (RMSE) value of One-line model, 0.04, which shows that the EOF model performance better than One-line models.