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Renewable energy is the cornerstone of preventing dangerous climate change whilst maintaining a robust energy supply. Tidal energy will arguably play a critical role in the renewable energy portfolio as it is both predictable and reliable, and can be put in place across the globe. However, installation may impact the local and regional ecology via changes in tidal dynamics, sediment transport pathways or bathymetric changes. In order to mitigate these effects, tidal energy devices need to be modelled, to predict hydrodynamic changes. Robust mesh generation is a fundamental component required for developing simulations with high accuracy. However, mesh generation for coastal domains can be an elaborate procedure. Here, we describe an approach combining mesh generators with Geographical Information Systems. We demonstrate robustness and efficiency by constructing a mesh with which to examine the potential environmental impact of a tidal turbine farm installation in the Orkney Islands. The mesh is then used with two well-validated ocean models, to compare their flow predictions with and without a turbine array. The results demonstrate that it is possible to create an easy-to-use tool to generate high-quality meshes for combined coastal engineering, here tidal turbines, and coastal ocean simulations. [ABSTRACT FROM AUTHOR]

We examine the likelihood of early human sea crossings of the southern Red Sea during Pleistocene low sea-level stands, using palaeotopographic reconstruction of coastlines, modelling of palaeo-tidal flows and simulation of passive movements using Lagrangian particles. Existing isotopic and geological data demonstrate that the marine connection between the Red Sea and the Indian Ocean has remained open for at least the past half million years, ruling out the possibility of a land crossing. Many authors have argued for the plausibility of a successful sea crossing during the Pleistocene as a southern route for human dispersal from Africa, especially for the dispersal of Homo sapiens. However, decisive evidence is lacking. Other authors have preferred the default northern route of land-based dispersal via the Sinai Peninsula as the more likely option and viewed the southern sea crossing as a barrier rather than a gateway, especially if tidal flow was much stronger through the narrowed sea channel at low sea levels. We use Fluidity, a finite element modelling procedure, to model tidal flows and assess their validity by comparison with modern tide-gauge data. To model palaeotidal flows, we use reconstructions of palaeoshorelines and coastal palaeotopography extending for 150 km from the Bab al Mandab Strait to the Hanish Sill region, which take account of eustatic, GIA and tectonic effects. We then simulate passive movements using Lagrangian particles and a 4th-order guided search Runge-Katta algorithm. We ran simulations for six days from three different starting points on the African shore and 13 different times in the tidal cycle. We show that crossing distances are much shorter during the Pleistocene than today with clear inter-visibility of the opposing shorelines, but that tidal currents were much stronger. We also show that the highest chances of successful crossing, involving passive rafting or drifting, with a duration of 3–4 days, are in the vicinity of the islands in the Hanish sill region. With directed rafting or swimming, the crossing times would be much shorter. We conclude that sea crossings would be easily accomplished during long periods of the glacial cycle, regardless of hominin status, especially given attractive terrestrial landscapes and environments on both sides of the southern Red Sea. • Palaeotidal modelling shows southern Red Sea could be crossed by drifting alone. • Success rate of crossing is both site and time dependent. • The southern Red Sea was not an impossible barrier to cross for early humans. • The far south point would require powered movement, including swimming. [ABSTRACT FROM AUTHOR]

Tidal energy has the potential to form a key component of the energy production in a number of countries, including the UK. Nonetheless, the deployment of tidal energy systems is associated with potential environmental impacts as prime resource sites often coincide with unique ecosystems inhabited by sensitive organisms. Previous studies have generally focused on the hydrodynamic impact of tidal energy schemes, i.e. how schemes alter the flow dynamics and sedimentary transport processes. Whilst these efforts are key in understanding environmental impacts, there is no straightforward step for translating sediment to faunal changes. Species distribution models offer methods to quantitatively predict certain possible impacts of tidal energy extraction. The River Severn is a distinguished candidate region for tidal energy in the UK featuring sites under stringent ecological protection regulations. We examine the impact of a proposed Severn tidal barrage on 14 species via the linking of hydrodynamic modelling to species distribution models. Through a selection of species that are linked via a simple food web system we extrapolate changes in prey species to the respective predator species. We show that species at lower trophic levels would be adversely affected by the barrage, but higher trophic level organisms increase in possible habitable area. Once food web relationships are acknowledged this increase in habitat area decreases, but is still net positive. Overall, all 14 species were affected, with most gaining in distribution area, and only four losing distribution area within the Severn Estuary. We conclude that a large-scale tidal barrage may have detrimental and complex impacts on species distribution, altering food web dynamics and altering food availability in the Severn Estuary. The methodology outlined herein can be transferred to the assessment and optimisation of prospective projects globally to aide in the sustainable introduction of the technology. Image 1 [ABSTRACT FROM AUTHOR]

Tidal range power plants represent an attractive approach for the large-scale generation of electricity from the marine environment. Even though the tides and by extension the available energy resource are predictable, they are also variable in time. This variability poses a challenge regarding the optimal transient control of power plants. We consider simulation methods which include the main modes of operation of tidal power plants, along with algorithms to regulate the timing of these. This paper proposes a framework where simplified power plant operation models are coupled with gradient-based optimisation techniques to determine the optimal control strategy over multiple tidal cycles. The optimisation results inform coastal ocean simulations that include tidal power plants to gauge whether the benefits of an adaptive operation are preserved once their hydrodynamic impacts are also taken into consideration. The combined operation of two prospective tidal lagoon projects within the Bristol Channel and the Severn Estuary is used as an example to demonstrate the potential benefits of an energy maximisation optimisation approach. For the case studies considered, the inclusion of pumping and an adaptive operation is shown to deliver an overall increase in energy output of 20–40% compared to a conventional two-way uniform operation. The findings also demonstrate that smaller schemes stand to gain more from operational optimisation compared to designs of a larger scale. [ABSTRACT FROM AUTHOR]

The ∼8.15 ka Storegga submarine slide was a large (∼3000 km 3 ), tsunamigenic slide off the coast of Norway. The resulting tsunami had run-up heights of around 10–20 m on the Norwegian coast, over 12 m in Shetland, 3–6 m on the Scottish mainland coast and reached as far as Greenland. Accurate numerical simulations of Storegga require high spatial resolution near the coasts, particularly near tsunami run-up observations, and also in the slide region. However, as the computational domain must span the whole of the Norwegian-Greenland sea, employing uniformly high spatial resolution is computationally prohibitive. To overcome this problem, we present a multiscale numerical model of the Storegga slide-generated tsunami where spatial resolution varies from 500 m to 50 km across the entire Norwegian-Greenland sea domain to optimally resolve the slide region, important coastlines and bathymetric changes. We compare results from our multiscale model to previous results using constant-resolution models and show that accounting for changes in bathymetry since 8.15 ka, neglected in previous numerical studies of the Storegga slide-tsunami, improves the agreement between the model and inferred run-up heights in specific locations, especially in the Shetlands, where maximum run-up height increased from 8 m (modern bathymetry) to 13 m (palaeobathymetry). By tracking the Storegga tsunami as far south as the southern North sea, we also found that wave heights were high enough to inundate Doggerland, an island in the southern North Sea prior to sea level rise over the last 8 ka. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Tidal resource assessment is presented for Rathlin Sound, located between Rathlin Island and the north-east coast of Northern Ireland. The flow is simulated in 2D, using the shallow water equations. For an M 2 tide, the natural flow conditions exhibit local spatial mean and maximum flow speeds of 2 and 3 m/s. Upper limits to power extraction are about 298 MW for M 2 and 330 MW for M 2 +S 2 tidal signals (different to undisturbed kinetic power and power naturally dissipated at the seabed). An analytical model of a channel connecting two infinite ocean basins underpredicts maximum power extracted in Rathlin Sound due to changes in head driving the flow and the existence of an alternative flow path. At maximum power extracted, there is substantial reduction in mean flow speeds in the strait and to the south-east of Rathlin Sound. In the strait, maximum power is reduced by 14% and 36% for blockage ratios of 80% and 60%. Power extraction both offshore of the island and in the strait yields higher power generation rates than isolated extraction. Resource assessments for Rathlin Sound are generally in good agreement with those for an idealised strait between an island and landmass. [ABSTRACT FROM AUTHOR]