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This study investigates the impacts of global climate change on the future wave power potential, taking Sri Lanka as a case study from the northern Indian Ocean. The geographical location of Sri Lanka, which receives long-distance swell waves generated in the Southern Indian Ocean, favors wave energy-harvesting. Waves projected by a numerical wave model developed using Simulating Waves Nearshore Waves (SWAN) wave model, which is forced by atmospheric forcings generated by an Atmospheric Global Climate Model (AGCM) within two time slices that represent “present” and “future” (end of century) wave climates, are used to evaluate and compare present and future wave power potential around Sri Lanka. The results reveal that there will be a 12–20% reduction in average available wave power along the south-west and south-east coasts of Sri Lanka in future. This reduction is due mainly to changes to the tropical south-west monsoon system because of global climate change. The available wave power resource attributed to swell wave component remains largely unchanged. Although a detailed analysis of monthly and annual average wave power under both “present” and “future” climates reveals a strong seasonal and some degree of inter-annual variability of wave power, a notable decadal-scale trend of variability is not visible during the simulated 25-year periods. Finally, the results reveal that the wave power attributed to swell waves are very stable over the long term.

Beach profile evolution under storm sequence forcing presents an emerging research topic that has only been investigated at a limited number of sites. The occurrence and effects of storm sequencing on beach profile evolution are studied at Hasaki Beach, Japan, using weekly beach profile and two-hourly offshore wave measurements. During the 25-year study period, the supratidal beach at Hasaki is subjected to long-term accretion and steepening while the shoreline shows a long-term oscillation. In addition, oscillations of the supratidal beach volume and the shoreline at semi-annual and annual intervals are identified, which are largely controlled by the variability of the wave height. Hasaki Beach is subjected to frequent storms that often cluster in sequences, especially during the extra-tropical cyclone season (January to March). The majority of storms and sequences generate erosion of the beach above the low water level but some also lead to recovery. Despite a tendency for storms and storm sequences with larger power to cause more erosion, the present data does not demonstrate increased beach erosion by storm sequences. Following these findings, the tendency of the beach to evolve towards equilibrium and the importance of the antecedent beach morphology are demonstrated., We gratefully acknowledge the Ministry of Land, Infrastructure, Transport and Tourism of the Japanese Government and the Marine Information Group of the Port and Airport Research Institute (PARI) for providing the offshore wave data and the staff from the Hazaki Oceanographical Research Station (HORS) for performing the beach profile measurements. SE acknowledges funding from the Department of Civil and Environmental Engineering, Imperial College London. HK acknowledges the support by the UK Research Councils under Natural Environment Research Council award NE/N013573/1, Title CoastWEB: Valuing the contribution which COASTal habitats make to human health and WEllBeing, with a focus on the alleviation of natural hazards. Finally, we would like to thank the two reviewers for their comments that helped to improve the manuscript., Peer Reviewed, Postprint (published version)

This paper presents the results of a sensitivity study investigating beach/dune response to offshore wave boundary forcing. The modelling study was based on the convex-shape Sefton coast, UK which has a complex nearshore morphology with ridge-runnel patterns and foreshore frontal dunes. Simulations were performed using a cascade of nested grids to transform offshore waves up to a high resolution nearshore XBeach model of the Sefton coast in which the beach/dune response was modelled. Two storm events representing low and high severity were simulated using uniform and varying wave boundary conditions at the offshore model boundary for both cases. The uniform boundary always resulted in higher storm waves in the XBeach domain. There were differences along the coast based on the coastline orientation and the local morphology, indicating different localised sensitivities to the wave boundary type. Bed level change within the tidal regions (sub-, inter- and supra-tidal) indicated landward decrease of the wave boundary effect. Volume change within the sub-tidal area showed the highest sensitivity to the space varying wave boundary forcing. Applying a uniform wave boundary for the XBeach domain exacerbated the wave impacts in the model domain. Our study suggests that application of a spatially varying wave boundary condition for the XBeach domain was able to correctly capture sediment transport and hence the beach/dune response of Sefton coast.

This paper reviews and discusses the current research status, trends, and future needs in the field of beach morphodynamics under the influence of storm sequences. The paper reviews how the three main research methods, field investigations, numerical modelling, and physical modelling, have been used to study beach morphodynamics during storm sequences. Available quantitative definitions of storm sequences at different sites are presented and discussed. It is shown that the definition of storm sequences is site-specific and requires knowledge of the storm climate, beach characteristics, and the temporal scale of beach recovery. Subsequently, the paper brings together currently available approaches aimed at describing the effect of storm sequences on beach erosion in a general way. The importance of storm chronology and the effects of an extreme storm within a sequence of storms are highlighted. Following that, the more poorly studied aspect of beach recovery in between storms within a sequence is discussed. Three indicators for defining beach recovery, namely the shoreline location, sediment volumes, and the beach state, are identified and compared. Finally, important research needs, including the need for detailed physical modelling, are identified., Peer Reviewed, Postprint (published version)

Two-dimensional numerical simulations were used to investigate the impacts of storm clustering on the beach/dune evolution of the Sefton coast, Liverpool Bay, UK. A storm cluster consisting of a series of closely spaced seven events was identified using observed wave and surge data during the 2013/2014 winter period. First event in this cluster is regarded as exceptionally intense and the occurrence of seven storms within a very short time period, is unique. The XBeach coastal area model was used to simulate beach change from 1) the storm sequence (Clustered events) and 2) the same storms considering them as isolated events. Offshore metadata was transformed to the nearshore area using the Delft3D and SWAN models. Resulting evolution was first compared with the available post-storm profiles measured at a number of locations along the Sefton coast. Analysis of the Clustered and Isolated simulations showed the effect of clustering on the Sefton beach/dune system when compared to the impact of isolated events occurring on a fully recovered beach system. Morphological change occurred during each storm in the Cluster was influenced by the preceding storm(s), such that the evolution is not proportional to the storm power of the event, as it would be for Isolated events. Both storm cases resulted in heavy erosion at Formby Point (i.e. central of the Sefton coast) and accretion in the north and south. The Cluster prevented system recovery with the area of erosion continually extending south along the coast compared with that in Isolated events. The initial storm within the Cluster caused large bed level changes in the nearshore ridge-runnel system, enabling the subsequent storms to penetrate further south. The local convex geometry of the Sefton coast is found to have more influence on the beach/dune morphodynamics than the clustering effect. This study enhances the understanding beach/dune response to storm clusters, to interpret observed morphological changes and to devel