This review provides a critical, multi-faceted assessment of the practical contribution tidal stream energy can make to the UK and British Channel Islands future energy mix. Evidence is presented that broadly supports the latest national-scale practical resource estimate, of 34 TWh/year, equivalent to 11% of the UK’s current annual electricity demand. The size of the practical resource depends in part on the economic competitiveness of projects. In the UK, 124 MW of prospective tidal stream capacity is currently eligible to bid for subsidy support (MeyGen 1C, 80 MW; PTEC, 30 MW; and Morlais, 14 MW). It is estimated that the installation of this 124 MW would serve to drive down the levelized cost of energy (LCoE), through learning, from its current level of around 240 £ / MWh to below 150 £ / MWh , based on a mid-range technology learning rate of 17%. Doing so would make tidal stream cost competitive with technologies such as combined cycle gas turbines, biomass and anaerobic digestion. Installing this 124 MW by 2031 would put tidal stream on a trajectory to install the estimated 11.5 GW needed to generate 34 TWh/year by 2050. The cyclic, predictable nature of tidal stream power shows potential to provide additional, whole-system cost benefits. These include reductions in balancing expenditure that are not considered in conventional LCoE estimates. The practical resource is also dependent on environmental constraints. To date, no collisions between animals and turbines have been detected, and only small changes in habitat have been measured. The impacts of large arrays on stratification and predator–prey interaction are projected to be an order of magnitude less than those from climate change, highlighting opportunities for risk retirement. Ongoing field measurements will be important as arrays scale up, given the uncertainty in some environmental and ecological impact models. Based on the findings presented in this review, we recommend that an updated national-scale practical resource study is undertaken that implements high-fidelity, site-specific modelling, with improved model validation from the wide range of field measurements that are now available from the major sites. Quantifying the sensitivity of the practical resource to constraints will be important to establish opportunities for constraint retirement. Quantification of whole-system benefits is necessary to fully understand the value of tidal stream in the energy system.

The vast majority of advanced numerical ocean models in use today, while performing extremely well, especially for certain classes of problem, do not necessarily take full advantage of current trends in numerical analysis and scientific computing. Here, a three-dimensional finite-element model is presented for use in oceanic simulations. The main aim is to fully exploit the use of unstructured meshes in both the horizontal and vertical directions, in order to conform well to topography and coastlines, and also to enable the straightforward use of dynamic variable mesh resolution reflecting fluid flow. In addition, the model should be accurate and efficient under typical oceanographic conditions, and not make the hydrostatic approximation. For simplicity here however the model does assume the presence of a rigid lid. To cope with inherent instabilities present in finite-element simulations of incompressible flow, caused by the Lagrange multiplier role that pressure plays in satisfying incompressib... Abstract The vast majority of advanced numerical ocean models in use today, while performing extremely well, especially for certain classes of problem, do not necessarily take full advantage of current trends in numerical analysis and scientific computing. Here, a three-dimensional finite-element model is presented for use in oceanic simulations. The main aim is to fully exploit the use of unstructured meshes in both the horizontal and vertical directions, in order to conform well to topography and coastlines, and also to enable the straightforward use of dynamic variable mesh resolution reflecting fluid flow. In addition, the model should be accurate and efficient under typical oceanographic conditions, and not make the hydrostatic approximation. For simplicity here however the model does assume the presence of a rigid lid. To cope with inherent instabilities present in finite-element simulations of incompressible flow, caused by the Lagrange multiplier role that pressure plays in satisfying incompressib...

Research into the use of unstructured mesh methods in oceanography has been growing steadily over the past decade. The advantages of this approach for domain representation and non-uniform resolution are clear. However, a number of issues remain, in particular those related to the computational cost of models produced using unstructured mesh methods compared with their structured mesh counterparts. Mesh adaptivity represents an important means to improve the competitiveness of unstructured mesh models, where high resolution is only used when and where necessary. In this paper, an optimization-based approach to mesh adaptivity is described where emphasis is placed on capturing anisotropic solution characteristics. Comparisons are made between the results obtained with uniform isotropic resolution, isotropic adaptive resolution and fully anisotropic adaptive resolution.

Coastal response to anthropogenic climate change is of central importance to the infrastructure and inhabitants in these areas. Despite being globally ubiquitous, the stability of rock coasts has been largely neglected, and the expected acceleration of cliff erosion following sea-level rise has not been tested with empirical data, until now. We have optimised a coastal evolution model to topographic and cosmogenic radionuclide data to quantify cliff retreat rates for the past 8000 years and forecast rates for the next century. Here we show that rates of cliff retreat will increase by up to an order of magnitude by 2100 according to current predictions of sea-level rise: an increase much greater than previously predicted. This study challenges conventional coastal management practices by revealing that even historically stable rock coasts are highly sensitive to sea-level rise and should be included in future planning for global climate change response.