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Gravel beaches and barriers form a valuable natural protection for many shorelines. The paper presents a numerical modelling study of gravel barrier beach response to storm wave conditions. The XBeach non-hydrostatic model was set up in 1D mode to investigate barrier volume change and overwash under a wide range of unimodal and bimodal storm conditions and barrier cross sections. The numerical model was validated against conditions at Hurst Castle Spit, UK. The validated model is used to simulate the response of a range of gravel barrier cross sections under a wide selection of statistically significant storm wave and water level scenarios thus simulating an ensemble of barrier volume change and overwash. This ensemble of results was used to develop a simple parametric model for estimating barrier volume change during a given storm and water level condition under unimodal storm conditions. Numerical simulations of barrier response to bimodal storm conditions, which are a common occurrence in many parts of the UK were also investigated. It was found that barrier volume change and overwash from bimodal storms will be higher than that from unimodal storms if the swell percentage in the bimodal spectrum is greater than 40%. The model is demonstrated as providing a useful tool for estimating barrier volume change, a commonly used measure used in gravel barrier beach management. [ABSTRACT FROM AUTHOR]

Global climate change drives sea level rise and changes to extreme weather events, which can affect morphodynamics of coastal and estuary systems around the world. In this paper, a 2D process-based numerical model is used to investigate the combined effects of future mean sea level and storm climate variabilities on morphological change of an estuary. Morphodynamically complex, meso-tidal Deben Estuary, located in the Suffolk at the east coast of the UK is selected as our case study site. This estuary has experienced very dynamic behaviors in history thus it might be sensitive to the future climate change. A statistical analysis of future storms around this area, derived from a global wave model, has shown a slight increase of storm wave heights and storm occurrences around the estuary in future as a result of global climate variations under medium emission scenario. By using a process-based model and by combining the forecast 'end-of-century' mean sea level with statistically derived storm conditions using projected storms over a time slice between 2075–2099, we determined hydrodynamic forcing for future morphodynamic modelling scenarios. It is found that the effect of increased sea level combined with future storms can significantly alter the current prevailing morphodynamic regime of the Deben Estuary thus driving it into a less stable system. It is also found that storm waves can be very significant to morphodynamic evolution of this tide-dominated estuary. [ABSTRACT FROM AUTHOR]

• The impacts of arrays of Tidal Energy Converters (TECs) on the sea bed morphology are investigated. • A 3D hydrodynamic and morphodynamic model is set up to study the impacts of TECs. • The Pentland Firth, Inner Sound Channel, UK is used as the test site. • It is proved that TECs installation may have significant impacts on mobile sea bed areas. • TECs impacts depend on array proximity to sea bed areas, array configuration and energy extraction levels. The tidal energy sector is a growing industry in the UK and beyond. Energy developers' interests are progressing towards the deployment of large arrays of tidal energy converters (TECs). Numerous factors will affect decision making related to arrays siting and size. One key factor is the effect that the TEC arrays may have on the natural sediment transport patterns and the sea bottom morphodynamics. The Inner Sound Channel located between the Island of Stroma of Pentland Firth and the Scottish Mainland (UK) has been accredited for a large-scale TEC array installation to be developed in the future. Three morphodynamically active, large sandbanks are located in the Inner Sound channel. This study investigated the impacts of tidal energy extraction from a large array of TECs on the sediment dynamics and morphology of these sandbanks. A large-scale 3D hydrodynamic and morphodynamic Delft3D model was set up to computationally model Pentland Firth, Inner Sound Channel in order to study the impacts of tidal energy extraction from a generic TEC array, on the existing hydrodynamic and morphodynamic regime. A range of hypothetical energy extraction scenarios was modelled. Results reveal that the changes to morphodynamics of these sandbanks as a result of large scale tidal energy extraction far exceeds the morphology change under the natural hydrodynamic regime and that the severity of morphology change depends on the level of energy extraction. [ABSTRACT FROM AUTHOR]

Global climate variabilities have the potential to impact many coastlines around the world, and can have detrimental effects on the stability of coastlines and their function as natural coastal defenses. This paper investigates the impacts of future extreme storms and sea level rise on morphodynamics of the macro-tidal Sefton Coast, UK, taking a process-based model as a tool to simulate a snap-shot of future beach change during storms. Sefton Coast represents one of the largest dune systems in the UK, where frontal dunes function as a natural barrier against extreme conditions. Future storm conditions were determined from global predictions of future waves at the end of the twenty first century. Future sea levels were determined based on climate change allowances set by the UK Environment Agency (EA), while future surge conditions were determined based on the guidelines also provided by EA. A nested numerical modelling approach, that combined a regional scale model with a local scale model with high resolution, is used. The modelling suite was first validated against measured waves, water levels and beach change, before using it to simulate morphodynamic change from numerous statistically significant 'future' storm conditions. Future storm-induced morphodynamic change of the Sefton coast was then compared with that from the present storms. The results reveal that this beach will experience significant climate change driven impacts where dune retreat during storms will be considerably higher in future. The results also reveal that due to the shape of the beach and its orientation to predominant wave approach direction, there will be a strong longshore variability of morphodynamic response to storms. It was also found that the water level in front of the dune (and hence surge and future sea level rise) is the most critical factor that determines beach erosion during a storm. • Storm impacts on a macro-tidal beach were investigated. • Water level is more significant than the storm wave height for erosion of the dune face. • Dune retreat during storms will be considerably higher in future due to climate change. [ABSTRACT FROM AUTHOR]

The tidal energy sector attracts developers' interest worldwide. For potential tidal energy deployment sites, numerous factors will impact decision making process related to siting and size of the tidal energy converter (TEC) farms. A key factor is the effect that TECs may have on the natural coastal hydrodynamic and morphodynamic environment. In this paper a Delft3D hydro-morphodynamic model was used to investigate potential impacts of TEC deployment on coastal morphology. The Inner Sound channel in Pentland Firth located between the Scottish Mainland and the Island of Stroma (UK), a site licensed for a large marine energy development, was used as a test site. The proposed tidal farm lies in close proximity to three large sandbanks located in the Inner Sound channel. This study investigates the impacts of tidal energy extraction from a TEC farm on the morphodynamics of these sandbanks. A range of hypothetical energy extraction scenarios was modelled to understand sandbanks morphodynamic response to each level of extraction from a hypothetical TEC array. This is an extremely useful technique to gain preliminary insights into the impacts of large-scale tidal energy extraction since field or large-scale laboratory investigations are hardly possible to investigate impacts of TECs on coastal morphodynamics. Same modelling techniques can be adopted and applied to undertake similar studies worldwide where tidal energy resource exploitation is possible. [ABSTRACT FROM AUTHOR]

Impacts of storm clustering on beach/dune morphodynamics were investigated by applying the state-of-the-art numerical model XBeach to Formby Point (Sefton coast, UK). The adopted storm cluster was established by analysing the observed winter storms from December 2013 to January 2014 using a storm threshold wave height. The first storm that occurred during this period is regarded as exceptionally intense, and the occurrence of such a cluster of events is very unusual. A 1D model was setup for the highly dynamic cross-shore at Formby Point. After initial calibration of the model parameters against available post-storm profile data, the model was used for the simulation of the storm cluster. It was assumed that no beach recovery occurred between adjacent storms due to the very short time intervals between storms. As a result, the final predicted post-storm profile of the previous storm was used as the pre-storm profile of the subsequent storm. The predicted evolution during each storm was influenced by the previous storms in the cluster. Due to the clustering effect, the bed level change is not proportional to the storm power of events within the cluster, as it would be in an individual storm case. Initially, the large storm events interact with the multi-bared foreshore enabling the subsequent weaker storms to influence the upper beach and lower dune system. This results in greater change at the dune toe level also during less severe subsequent storms. It is also shown that the usual water level threshold used to define dune erosion is over predicted by about 1 m for extreme storm conditions. The predicted profile evolution provides useful insights into the morphodynamic processes of beach/dune systems during a storm cluster (using Formby Point as an example), which is very useful for quantifying the clustering effects to develop tools for coastal management. [ABSTRACT FROM AUTHOR]