Nil Carrion-Bertran

Low-lying beaches are highly dynamic and vulnerable coastal environments susceptible to flooding and erosion episodes, which will be exacerbated in the context of climate change. Highly complex processes take place during storms, and numerical models are useful tools to assess them. In this study, the XBeach model is applied to an idealised beach to analyse the role of the initial topobathymetry in the formation of washover deposits under an overwash episode caused by a storm event. Initial representative profiles were obtained from real measured 12-year time-lapse topobathymetries, after performing a PCA and a cluster analysis. Alongshore-periodic morphological patterns (mega-cusps, rhythmic dunes, and crescentic bars) of different realistic wavelengths were also included. After running the model with the storm, results of the different scenarios were compared. The washover volume deposited after the overwash event changed when different initial topobathymetries were used and when the morphological pattern wavelength was varied. These outcomes highlight the importance of using real, accurate and up to date topobathymetric data in numerical modeling studies. Also, it is important to consider the possible presence of morphological patterns, since not incorporating them in the initial topobathymetry or misrepresenting their wavelength, could lead to significant changes in washover deposit volumes, and in sediment transport processes in general.

Low‐lying beaches, important ecological and socio‐economic assets, are vulnerable to storm erosion and flooding impacts, which are expected to increase due to climate change. This conceptual study uses the 2DH XBeach model to simulate the influence of the initial topobathymetric shape on the washover deposit formation during a beach overwash caused by an extreme storm, including a quantification of the wave chronology uncertainty. The employed initial alongshore‐uniform (AU) topobathymetries have different cross‐shore profiles, representing the real variability of Mediterranean beaches. The analysis also incorporates the presence of common alongshore‐rhythmic morphological patterns, such as megacusps, rhythmic dunes, and crescentic bars, with varying wavelengths. The results in the AU scenarios show that washover deposits are also periodic alongshore, forming through a 2D self‐organization process that establishes the natural wavelength of the modeled dry beach. The presence of megacusps in the initial topobathymetry can enhance washover deposit volumes up to a factor 4, especially for large initial wavelengths. Rhythmic dunes also influence the spatial distribution of the deposits, while crescentic bars generally have little direct effect on the deposit formation. These findings highlight the importance of using real and up‐to‐date topobathymetric data, including the presence of common alongshore‐rhythmic morphological patterns, in modeling storm impacts on beaches. Furthermore, modeling studies under future climate change scenarios, must consider the uncertainty associated with the unknown shape of the topobathymetry and wave group chronology. The results could also have implications for developing effective coastal management strategies.

Low-lying beaches support a wide range of ecological and socio-economic activities, but their vulnerability to storm and flooding impacts is expected to increase due to climate change. This study uses the 2DH XBeach model to simulate the influence of the initial topobathymetric shape on the washover deposit formation during a beach overwash caused by an extreme storm. Initial alongshore-uniform (AU) topobathymetries can have different cross-shore profiles, extracted from measurements taken on a Mediterranean beach, and can represent the real variability of such environments. In addition, the analysis incorporates the potential presence of alongshore-rhythmic morphological patterns, such as megacusps, rhythmic dunes, and crescentic bars, with varying wavelengths. The results in the AU scenarios show that washover deposits are also alongshore-rhythmic, forming through a 2D self-organization process providing the natural wavelength of the modelled dry beach. Morphological patterns, such as megacusps with specific wavelengths, can enhance washover deposit volumes up to a factor of 4, especially for large initial wavelengths of these morphological patterns. Rhythmic dunes, influence the spatial distribution of the deposits, while crescentic bars generally have little direct effect on the washover deposit formation. These findings highlight the importance of using real and up-to-date topobathymetric data, including the presence of common alongshore-rhythmic morphological patterns, in modelling storm impacts on beaches. Furthermore, when studying storm impacts under future climate change scenarios, it will be essential to consider the uncertainty associated with the unknown shape of the topobathymetry and wave chronology. The results also have implications for developing effective coastal management strategies.

Mediterranean deltaic areas have suffered reduced sediment inputs during the last decades due to dams and coastal structures, resulting into significant losses of wetlands and beaches. To design and develop beach protection strategies for future adaptation of deltaic coasts to climate change impacts, a more comprehensive understanding of the inherent dynamics between the backshore and the nearshore is crucial, especially during extreme events, when these areas become highly vulnerable as they get submerged under the action of waves and surges (Cohn and Ruggiero, 2016). Therefore, this study aims to determine the effect of the topobathymetric variability, on theevolution of the backshore and the nearshore during extreme events. Special attention is given to beach erosion and the formation of backshore sand deposits.

The sensitivity of a 2DH coastal area (XBeach) and a reduced-complexity (Q2Dmorfo) morphodynamic model to using different forcing sources is studied. The models are tested by simulating the morphodynamic response of an embayed beach in the NW Mediterranean over a 6-month period. Wave and sea-level forcing from in situ data, propagated buoy measurements, and hindcasts, as well as combinations of these different data sources, are used, and the outputs are compared to in situ bathymetric measurements. Results show that when the two models are calibrated with in situ measurements, they accurately reproduce the morphodynamic evolution with a “good” Brier skill score (BSS). The calibration process reduces the errors by 65 %–85 % compared with the default setting. The wave data propagated from the buoy also produce reliable morphodynamic simulations but with a slight decrease in the BSS. Conversely, when the models are forced with hindcast wave data, the mismatch between the modelled and observed beach evolution increases. This is attributed to a large extent to biased mean directions in hindcast waves. Interestingly, in this small tide site, the accuracy of the simulations hardly depends on the sea-level data source, and using filtered or non-filtered tides also yields similar results. These results have implications for long-term morphodynamic studies, like those needed to validate models for climate change projections, emphasizing the need to use accurate forcing sources such as those obtained by propagating buoy data.

The sensitivity of a 2DH coastal area (XBeach) and a reduced-complexity (Q2Dmorfo) morphodynamic models to using different forcing sources is studied. The models are tested by simulating the morphodynamic response of an embayed beach in the NW Mediterranean over a 6-month period. Wave and sea level forcing from in-situ data, propagated buoy measurements, hindcasts as well as combinations of these different data sources are used and the outputs are compared to in-situ bathymetric measurements. Results show that when the two models are calibrated with in-situ measurements, they accurately reproduce the morphodynamic evolution with a "Good" BSS (Brier Skill Score). The wave data propagated from the buoy also produces reliable morphodynamic simulations but with a slight decrease in BSS. Conversely, when the models are forced with hindcast wave data the mismatch between the modelled and observed beach evolution increases. This is attributed to a large extent to biased mean directions in hindcast waves. Interestingly, in this small tide site the accuracy of the simulations did not depend on the sea-level data source, and using filtered or non-filtered tides also yielded similar results. These results have implications for long-term morphodynamic studies, like those needed to validate models for climate change projections, emphasizing the need of using accurate forcing sources such as those obtained by propagating buoy data.

The sensitivity of a 2DH coastal area (XBeach) and a reduced-complexity (Q2Dmorfo) morphodynamic models to using different forcing sources is studied. The models are tested by simulating the morphodynamic response of an embayed beach in the NW Mediterranean over a 6-month period. Wave and sea level forcing from in-situ data, propagated buoy measurements, hindcasts as well as combinations of these different data sources are used and the outputs are compared to in-situ bathymetric measurements. Results show that when the two models are calibrated with in-situ measurements, they accurately reproduce the morphodynamic evolution with a "Good" BSS (Brier Skill Score). The wave data propagated from the buoy also produces reliable morphodynamic simulations but with a slight decrease in BSS. Conversely, when the models are forced with hindcast wave data the mismatch between the modelled and observed beach evolution increases. This is attributed to a large extent to biased mean directions in hindcast waves. Interestingly, in this small tide site the accuracy of the simulations did not depend on the sea-level data source, and using filtered or non-filtered tides also yielded similar results. These results have implications for long-term morphodynamic studies, like those needed to validate models for climate change projections, emphasizing the need of using accurate forcing sources such as those obtained by propagating buoy data.

The sensitivity of a 2DH coastal area (XBeach) and a reduced-complexity (Q2Dmorfo) morphodynamic models to using different forcing sources is studied. The models are tested by simulating the morphodynamic response of an embayed beach in the NW Mediterranean over a 6-month period. Wave and sea level forcing from in-situ data, propagated buoy measurements, hindcasts as well as combinations of these different data sources are used and the outputs are compared to in-situ bathymetric measurements. Results show that when the two models are calibrated with in-situ measurements, they accurately reproduce the morphodynamic evolution with a "Good" BSS (Brier Skill Score). The wave data propagated from the buoy also produces reliable morphodynamic simulations but with a slight decrease in BSS. Conversely, when the models are forced with hindcast wave data the mismatch between the modelled and observed beach evolution increases. This is attributed to a large extent to biased mean directions in hindcast waves. Interestingly, in this small tide site the accuracy of the simulations did not depend on the sea-level data source, and using filtered or non-filtered tides also yielded similar results. These results have implications for long-term morphodynamic studies, like those needed to validate models for climate change projections, emphasizing the need of using accurate forcing sources such as those obtained by propagating buoy data.

The sensitivity of a 2DH coastal area (XBeach) and a reduced-complexity (Q2Dmorfo) morphodynamic models to using different forcing sources is studied. The models are tested by simulating the morphodynamic response of an embayed beach in the NW Mediterranean over a 6-month period. Wave and sea level forcing from in-situ data, propagated buoy measurements, hindcasts as well as combinations of these different data sources are used and the outputs are compared to in-situ bathymetric measurements. Results show that when the two models are calibrated with in-situ measurements, they accurately reproduce the morphodynamic evolution with a "Good" BSS (Brier Skill Score). The wave data propagated from the buoy also produces reliable morphodynamic simulations but with a slight decrease in BSS. Conversely, when the models are forced with hindcast wave data the mismatch between the modelled and observed beach evolution increases. This is attributed to a large extent to biased mean directions in hindcast waves. Interestingly, in this small tide site the accuracy of the simulations did not depend on the sea-level data source, and using filtered or non-filtered tides also yielded similar results. These results have implications for long-term morphodynamic studies, like those needed to validate models for climate change projections, emphasizing the need of using accurate forcing sources such as those obtained by propagating buoy data.

The sensitivity of a 2DH coastal area (XBeach) and a reduced-complexity (Q2Dmorfo) morphodynamic models to using different forcing sources is studied. The models are tested by simulating the morphodynamic response of an embayed beach in the NW Mediterranean over a 6-month period. Wave and sea level forcing from in-situ data, propagated buoy measurements, hindcasts as well as combinations of these different data sources are used and the outputs are compared to in-situ bathymetric measurements. Results show that when the two models are calibrated with in-situ measurements, they accurately reproduce the morphodynamic evolution with a "Good" BSS (Brier Skill Score). The wave data propagated from the buoy also produces reliable morphodynamic simulations but with a slight decrease in BSS. Conversely, when the models are forced with hindcast wave data the mismatch between the modelled and observed beach evolution increases. This is attributed to a large extent to biased mean directions in hindcast waves. Interestingly, in this small tide site the accuracy of the simulations did not depend on the sea-level data source, and using filtered or non-filtered tides also yielded similar results. These results have implications for long-term morphodynamic studies, like those needed to validate models for climate change projections, emphasizing the need of using accurate forcing sources such as those obtained by propagating buoy data.