► We simulate the wave climate of the NW European shelf seas over a 7year period. ► We apply a high resolution 3rd-generation wave model. ► We quantify spatial patterns of uncertainties in estimating ...the wave power resource. ► Uncertainty is considerably greater over winter months. ► There is a positive correlation between winter wave power and the NAO.
Regional assessments of the wave energy resource tend to focus on averaged quantities, and so provide potential developers with no sense of temporal variability beyond seasonal means. In particular, such assessments give no indication of inter-annual variability – something that is critical for determining the potential of a region for wave energy convertor (WEC) technology. Here, we apply the third-generation wave model SWAN (Simulating Waves Nearshore) at high resolution to assess the wave resource of the northwest European shelf seas, an area where many wave energy test sites exist, and where many wave energy projects are under development. The model is applied to 7years of wind forcing (2005–2011), a time period which witnessed considerable extremes in the variability of the wind (and hence wave) climate, as evidenced by the variability of the North Atlantic Oscillation (NAO). Our simulations demonstrate that there is much greater uncertainty in the NW European shelf wave resource during October–March, in contrast to the period April–September. In the more energetic regions of the NW European shelf seas, e.g. to the northwest of Scotland, the uncertainty was considerably greater. The winter NW European shelf wave power resource correlated well with the NAO. Therefore, provided trends in the NAO can be identified over the coming decades, it may be possible to estimate how the European wave resource will similarly vary over this time period. Finally, the magnitude of wave power estimated by this study is around 10% lower than a resource which is used extensively by the wave energy sector – the Atlas of UK Marine Renewable Energy Resources. Although this can partly be explained by different time periods analysed for each study, our application of a third-generation wave model at high spatial and spectral resolution significantly improves the representation of the physical processes, particularly the non-linear wave-wave interactions.
•We model the influence of waves on tidal kinetic energy in the Fromveur Strait.•Numerical results are compared with field data of waves and currents.•The introduction of waves improve predictions of ...tidal stream power during storm.•Mean spring tidal stream potential is reduced by 12% during extreme wave conditions.•Potential is reduced by 7.8% with waves forces and 5.3% with enhanced friction.
Successful deployment of tidal energy converters relies on access to accurate and high resolution numerical assessments of available tidal stream power. However, since suitable tidal stream sites are located in relatively shallow waters of the continental shelf where tidal currents are enhanced, tidal energy converters may experience effects of wind-generated surface-gravity waves. Waves may thus influence tidal currents, and associated kinetic energy, through two non-linear processes: the interaction of wave and current bottom boundary layers, and the generation of wave-induced currents. Here, we develop a three-dimensional tidal circulation model coupled with a phase-averaged wave model to quantify the impact of the waves on the tidal kinetic energy resource of the Fromveur Strait (western Brittany) - a region that has been identified with strong potential for tidal array development. Numerical results are compared with in situ observations of wave parameters (significant wave height, peak period and mean wave direction) and current amplitude and direction 10m above the seabed (the assumed technology hub height for this region). The introduction of waves is found to improve predictions of tidal stream power at 10m above the seabed at the measurement site in the Strait, reducing kinetic energy by up to 9% during storm conditions. Synoptic effects of wave radiation stresses and enhanced bottom friction are more specifically identified at the scale of the Strait. Waves contribute to a slight increase in the spatial gradient of available mean tidal stream potential between the north-western area and the south-eastern part of the Strait. At the scale of the region within the Strait that has been identified for tidal stream array development, the available mean spring tidal stream potential is furthermore reduced by 12% during extreme waves conditions. Isolated effects of wave radiation stresses and enhanced bottom friction lead to a reduction in spring tidal potential of 7.8% and 5.3%, respectively. It is therefore suggested that models used for tidal resource assessment consider the effect of waves in appropriately wave-exposed regions.
Although tidal stream energy is highly predictable, the distribution of the resource varies over small spatial scales and over tidal-to-decadal time scales, requiring detailed models and accurate ...analysis techniques. The present study investigates the spatial and temporal variability of the tidal stream energy resource around France, using a tidal current harmonic database. The 250 m resolution tidal database covers western Brittany and the western English Channel, two regions that have strong potential for tidal array development. As well as generating a refined resource assessment for the region, a series of metrics are considered to assess resource variability, both spatially and temporally. Particular attention is dedicated to variability over spring-neap time scales (resulting from M2 and S2 compound tides) and current asymmetry (governed by M2 and M4 velocities). A clear contrast in the nature of the resource is found between sites located off the Cotentin Peninsula, which exhibit low spring-neap variability and tidal asymmetry, leading to a more continuous and therefore attractive energy conversion, and sites in western Brittany, with greater variabilities over semi-diurnal and fortnightly time scales.
•The spatio-temporal variability of tidal stream power resource around France is investigated.•A 250 m tidal current harmonic database is exploited with specific technical methods.•Particular attention is made to spring-neap tidal variability and semi-diurnal asymmetry.•Such variabilities reduce power consistency over daily-to-fortnightly time scales.•A contrast is exhibited between sites off the Cotentin Peninsula and in western Brittany.
UK estuarine environments are regulated by inter-acting physical processes, including tidal, wave, surge, river discharge and sediment supply. They regulate the fluxes of nutrients, pollutants, ...pathogens and viruses that determine whether coastlines achieve the Good Environmental Status (GEnS) required by the EU's Marine Strategy Directive. We review 20th century trends and 21st century projections of changes to climatic drivers, and their potential for altering estuarine bio-physical processes. Sea-level rise will cause some marine habitats to expand, and others diminish in area extent. The overall consequences of estuarine morphodynamics to these habitat shifts, and vice-versa, are unknown. Increased temperatures could intensify microbial pathogen concentrations and increase public health risk. The patterns of change of other climatic drivers are difficult to predict (e.g., river flows and storm surges). Projected increased winter river flows throughout UK catchments will enhance the risks of coastal eutrophication, harmful algal blooms and hypoxia in some contexts, although there are spatial variabilities in river flow projections. The reproductive success of estuarine biota is sensitive to saline intrusion and corresponding turbidity maxima, which are projected to gradually shift landwards as a result of sea-level rise. Although more-frequent flushing events in winter and longer periods of drought in summer are predicted, whereby the subsequent estuarine mixing and recovery rates are poorly understood. With rising estuarine salinities, subtidal species can penetrate deeper into estuaries, although this will depend on the resilience/adaptation of the species. Many climate and impact predictions lack resolution and spatial cover. Long-term monitoring and increased research, which considers the catchment-river-estuary-coast system as a whole, is needed to support risk predicting and mitigatory strategies.
Tidal Energy Converter (TEC) arrays are expected to reduce tidal current speeds locally, thus impacting sediment processes, even when positioned above bedrock, as well as having potential impacts to ...nearby offshore sand banks. Furthermore, the tidal dissipation at potential TEC sites can produce high suspended sediment concentrations (turbidity maxima) which are important for biological productivity. Yet few impact assessments of potential TEC sites have looked closely at sediment dynamics beyond local scouring issues. It is therefore important to understand to what extent exploitation of the tidal energy resource will affect sedimentary processes, and the scale of this impact is here assessed in relation to natural variability. At one such site in the Irish Sea that is highly attractive for the deployment of TEC arrays, we collect measurements of sediment type and bathymetry, apply a high resolution unstructured morphodynamic model, and a spectral wave model in order to quantify natural variability due to tidal and wave conditions. We then simulate the impacts of tidal-stream energy extraction using the morphodynamic model. Our results suggest that the sedimentary impacts of ‘first generation’ TEC arrays (i.e. less than 50 MW), at this site, are within the bounds of natural variability and are, therefore, not considered detrimental to the local environment. Yet we highlight potential environmental issues and demonstrate how impact assessments at other sites could be investigated.
•Detailed study of sedimentary impacts of tidal-stream energy extraction.•Impact assessment based on natural variability of tide/wave induced shear stress.•Observational and modelling case study at potential TEC array in the Irish Sea.•Impact of first-generation TEC arrays on sediment processes will be ‘insignificant’.•Impact of TEC arrays on sediment processes is site-specific.
Previous results from one-dimensional model studies have demonstrated that large-scale exploitation of the tidal stream resource could have a significant impact on large-scale sediment dynamics. In ...this research, we model the impact that such exploitation would have on the dynamics of headland sand banks. Such sand banks, formed by the large eddies generated by strong tidal flow past headlands, have an important role in natural coastal protection, since they cause waves to refract and dissipate energy. Therefore, a tidal energy converter (TEC) array developed in the vicinity of a headland could alter this natural form of coastal protection. Here, we investigate the impact of TEC array operation on idealised headland sand bank formation, followed by a case study, the Alderney Race: a strait of water between the island of Alderney (Channel Islands) and Cap de la Hague (France). This is achieved through the application of a morphological model that incorporates TEC device operation as an additional bed friction source term in the three-dimensional hydrodynamic module. Through a series of model experiments, we demonstrate the impact that a full-scale (300 MW) TEC array would have on sediment dynamics when sited near a headland. This modelling study demonstrates that a 300 MW TEC array located in the vicinity of a headland could lead to a considerable change in the maintenance of headland sand banks over a spring-neap cycle. If the scale of this change is demonstrated to be significant compared to the natural range of inter-annual and inter-seasonal sand bank variability, then developers of TEC arrays would be advised to examine ways in which they could reduce the environmental impacts of TEC arrays sited near headlands. The most obvious of these is to limit the scale of the array, but if we assume that developers wish to exploit the tidal energy resource to its maximum, the alternative is to site the array strategically (within the bounds of economic feasibility) such that it will not interfere with the natural morphodynamics of the headland system.
► Headland sand banks affect wave energy, and so are important for coastal protection. ► We model the impact of tidal energy converter (TEC) array operation on sand bank dynamics. ► TEC array operation could alter these sand banks. ► TEC arrays should be strategically sited in the vicinity of headlands.
Assessing how natural environmental drivers affect biodiversity underpins our understanding of the relationships between complex biotic and ecological factors in natural ecosystems. Of all ...ecosystems, anthropogenically important estuaries represent a 'melting pot' of environmental stressors, typified by extreme salinity variations and associated biological complexity. Although existing models attempt to predict macroorganismal diversity over estuarine salinity gradients, attempts to model microbial biodiversity are limited for eukaryotes. Although diatoms commonly feature as bioindicator species, additional microbial eukaryotes represent a huge resource for assessing ecosystem health. Of these, meiofaunal communities may represent the optimal compromise between functional diversity that can be assessed using morphology and phenotype-environment interactions as compared with smaller life fractions. Here, using 454 Roche sequencing of the 18S nSSU barcode we investigate which of the local natural drivers are most strongly associated with microbial metazoan and sampled protist diversity across the full salinity gradient of the estuarine ecosystem. In order to investigate potential variation at the ecosystem scale, we compare two geographically proximate estuaries (Thames and Mersey, UK) with contrasting histories of anthropogenic stress. The data show that although community turnover is likely to be predictable, taxa are likely to respond to different environmental drivers and, in particular, hydrodynamics, salinity range and granulometry, according to varied life-history characteristics. At the ecosystem level, communities exhibited patterns of estuary-specific similarity within different salinity range habitats, highlighting the environmental sequencing biomonitoring potential of meiofauna, dispersal effects or both.
Tidal energy is one of the most predictable forms of renewable energy. Although there has been much commercial and R&D progress in tidal stream energy, tidal range is a more mature technology, with ...tidal range power plants having a history that extends back over 50 years. With the 2017 publication of the “Hendry Review” that examined the feasibility of tidal lagoon power plants in the UK, it is timely to review tidal range power plants. Here, we explain the main principles of tidal range power plants, and review two main research areas: the present and future tidal range resource, and the optimization of tidal range power plants. We also discuss how variability in the electricity generated from tidal range power plants could be partially offset by the development of multiple power plants (e.g. lagoons) that are complementary in phase, and by the provision of energy storage. Finally, we discuss the implications of the Hendry Review, and what this means for the future of tidal range power plants in the UK and internationally.
•Tidal range power plants have a history that extends back over 50 years.•We review the present and future tidal range resource.•We review optimization of tidal range power plants.•90% of the global tidal range resource is distributed among just five countries.•Development of multiple lagoons would minimise variability in power output.
As the marine renewable energy industry evolves, in parallel with an increase in the quantity of available data and improvements in validated numerical simulations, it is occasionally appropriate to ...re-assess the wave and tidal resource of a region. This is particularly true for Scotland - a leading nation that the international community monitors for developments in the marine renewable energy industry, and which has witnessed much progress in the sector over the last decade. With 7 leased wave and 17 leased tidal sites, Scotland is well poised to generate significant levels of electricity from its abundant natural marine resources. In this state-of-the-art review of Scotland's wave and tidal resource, we examine the theoretical and technical resource, and provide an overview of commercial progress. We also discuss issues that affect future development of the marine energy seascape in Scotland, applicable to other regions of the world, including the potential for developing lower energy sites, and grid connectivity.
•Scotland has been at the forefront of global marine energy developments.•We examine the theoretical and technical wave and tidal resource of Scotland.•We examine past and current commercial developments in Scotland.•In parallel with energetic sites, we suggest that less energetic sites be developed.
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