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Tidal-stream energy resource can be predicted deterministically, provided tidal harmonics and turbine-device characteristics are known. Many turbine designs exist, all having different characteristics (e.g. rated speed), which creates uncertainty in resource assessment or renewable energy system-design decision-making. A standardised normalised tidal-stream power-density curve was parameterised with data from 14 operational horizontal-axis turbines (e.g. mean cut-in speed was ∼30% of rated speed). Applying FES2014 global tidal data (1/16° gridded resolution) up to 25 km from the coast, allowed optimal turbine rated speed assessment. Maximum yield was found for turbine rated speed ∼97% of maximum current speed (maxU) using the 4 largest tidal constituents (M2, S2, K1 and O1) and ∼87% maxU for a “high yield” scenario (highest Capacity Factor in top 5% of yield cases); with little spatial variability found for either. Optimisation for firm power (highest Capacity Factor with power gaps less than 2 h), which is important for problematic or expensive energy-storage cases (e.g. off-grid), turbine rated speed of ∼56% maxU was found – but with spatial variability due to tidal form and maximum current speed. We find optimisation and convergent design is possible, and our standardised power curve should help future research in resource and environmental impact assessment.

Acoustic telemetry was used to track salmon smolts during river migration and into the open marine coastal zone. We compared migration direction and speed with particle tracking simulations to test the hypothesis that marine migration pathways are defined by active swimming current following behaviour. Habitat-specific survival rates, movement speeds, depths and directions in riverine, estuarine, and coastal habitats were also quantified. Salmon post-smolts did not disperse at random as they entered the unrestricted, coastal zone of the North sea; rather they chose a common migration pathway. This was not the most direct route to marine feeding grounds (ca. 44° N); north in the direction of the prevailing currents. Particle modelling showed that the actual post-smolt migration route was best predicted by active swimming at 1.2 body length.sec.−1 at a bearing of 70° from north but not by current following behaviour. Fish migrating in larger groups and earlier in the migration period had increased migration success. We conclude that: post-smolts have preferred migration routes that are not predicted by the shortest direction to their ultimate destination; they do not simply use the current advantage to migrate; and that they actively swim, occasionally directly against the current prevailing at the time.

The environmental implications of tidal stream energy extraction need to be evaluated against the potential climate change impacts on the marine environment. Here, we study how hypothetical very large tidal stream arrays and a “business as usual” future climate scenario can change the hydrodynamics of a seasonally stratified shelf sea. The Scottish Shelf Model, an unstructured grid three‐dimensional ocean model, has been used to reproduce the present and the future state of the NW European continental shelf. Four scenarios have been modelled: present conditions and projected future climate in 2050, each with and without very large scale tidal stream arrays in Scottish Waters (UK). It is found that where tidal range is reduced a few cm by tidal stream energy extraction, it can help to counter extreme water levels associated with future sea level rise. Tidal velocities, and consequently tidal mixing, are also reduced overall by the action of the tidal turbine arrays. A key finding is that climate change and tidal energy extraction both act in the same direction, in terms of increasing stratification due to warming and reduced mixing, however the effect of climate change is an order of magnitude larger.

The tidal stream energy sector is now at the stage of deploying the world's first pre-commercial arrays of multiple turbines. It is time to study the environmental effects of much larger full-size arrays, to scale and site them appropriately. A theoretical array of tidal stream turbines was designed for the Pentland Firth (UK), a strait between Scotland and the Orkney Islands, which has very fast tidal currents. The practical power resource of a large array spanning the Pentland Firth was estimated to be 1.64 GW on average. The ocean response to this amount of energy extraction was simulated by an unstructured grid three-dimensional FVCOM (Finite Volume Community Ocean Model) and analysed on both short-term and seasonal timescales. Tidal elevation mainly increases upstream of the tidal array, while a decrease is observed downstream, along the UK east coast. Tidal and residual flows are also affected: they can slow down due to the turbines action or speed up due to flow diversion and blockage processes, on both a local and regional scale. The strongest signal in tidal velocities is an overall reduction, which can in turn decrease the energy of tidal mixing and perturb the seasonal stratification on the NW European Shelf.

The Orkney Islands and surrounding waters (known as the Pentland Firth and Orkney Waters Strategic Area, PFOW) contain a significant portion of Scotland's tidal and wave energy resource. This paper forms part of a wider study modelling tidal and wave processes, and planned renewable energy extraction, in PFOW using 3D hydrodynamic and spectral wave numerical models. Such hydrodynamic models require a number of spatial data, i.e. high resolution bathymetry, model boundary conditions and measurements for model validation, which are hard to obtain in extreme environments such as PFOW. This paper examines the characteristics and selection criteria of the data used for the development of the models. Most of these data are freely available, and could form part of an open source marine renewable energy hydrodynamic modelling toolbox. In order to include the planned tidal and wave energy developments in the hydrodynamic models of the wider study, realistic tidal and wave device array scenarios are required. However, there is still considerable uncertainty regarding the type of devices that will be deployed and device array layouts. Here, we describe the process undertaken, in consultation with industry, to develop a small number of generic device types and array scenarios for the PFOW, based on insight provided by documentation submitted by developers as part of the Scottish marine licensing process. For tidal developments, an algorithm was developed to determine the site specific array configuration, taking into account the number of turbines, water depth, tidal current direction and the spatial distribution of mean kinetic energy. The wave development sites did not require such detailed site specific placement of devices, and the generic layouts could simply be constructed in most cases without the need for detailed site specific resource characterisation. It is anticipated that the renewable energy industry will be able to adopt our data selection criteria to ensure models developed for environmental impact assessments satisfy the quality requirements of the regulator. Similarly, the methodologies developed for characterising generic device types and array layouts will be useful to academia and government researchers, who do not necessarily have access to detailed device and site specific information.

Seawater turbidity due to suspended particulate material (SPM) is an important property of a marine ecosystem, determining the underwater light environment and many aspects of biological production and ecology. SPM concentrations are largely determined by patterns of sediment resuspension from the seabed due to shear stress caused by waves and currents. Hence planning for the construction of large scale offshore structures which will alter regional hydrodynamics needs to consider the consequences for SPM concentrations. Here we develop a one-dimensional (vertical) model of SPM dynamics which can be used to scope the effects of changes in wave and tidal current properties at a site. We implement the model for a number of sites off the east coast of Scotland where we have extensive data sets to enable numerical parameter optimisation. The model performs well at simulating fluctuations in turbidity varying from flood-ebb tidal cycles, spring-neap cycles, storm wave events, and an annual cycle of SPM concentration which is attributed to seasonal consolidation of seabed sediments. Sensitivity analysis shows that, for the range of seabed sediment types in the study (water depth 16–50 m; mud content 0.006–0.380 proportion by weight), relatively large (50%) attenuations of tidal current speed are required to produce changes in water column turbidity which would be detectable by observations given the variability in measurements. The model has potential for application to map the large scale sensitivity of turbidity distributions to the installation of wave and tidal energy extraction arrays.

A high spatial resolution three-dimensional (3D) hydrodynamic ocean model of the Orkney Islands is used to investigate the tidal stream resource and physical environmental impact in the Pentland Firth, a high-resource area where the first arrays of tidal stream turbines are likely to be deployed in Scotland. Tidal stream turbines are represented in the model using a momentum sink in order to (1) find an upper bound estimate of the available resource, (2) explore alternative, more realistic scenarios, and (3) estimate their effect on the physical environment. The maximum extractable power scenario (M2 + S2 cycle mean of 5.3 GW) requires a high density of turbines deployed through the channels cross section and has a major impact on the physical environment. More realistic scenarios, with the placement of the turbines constrained by practical factors, resulted in considerably less extractable power but the physical environmental impact was disproportionately reduced. It was also found that a variable thrust coefficient can be used to optimise the performance of tidal arrays. Our work highlights the usefulness of 3D hydrodynamic models for tidal stream resource assessment and impact studies, and illustrates how the design of tidal stream arrays can affect the levels of sustainably harnessed tidal power.

Storm surges are an abnormal enhancement of the water level in response to weather perturbations. They have the capacity to cause damaging flooding of coastal regions, especially when they coincide with astronomical high spring tides. Some areas of the UK have suffered particularly damaging surge events, and the Firth of Clyde is a region with high risk due to its location and morphology. Here, we use a three-dimensional high spatial resolution hydrodynamic model to simulate the local bathymetric and morphological enhancement of surge in the Clyde, and disaggregate the effects of far-field atmospheric pressure distribution and local scale wind forcing of surges. A climatological analysis, based on 30 years of data from Millport tide gauges, is also discussed. The results suggest that floods are not only caused by extreme surge events, but also by the coupling of spring high tides with moderate surges. Water level is also enhanced by a funnelling effect due to the bathymetry and the morphology of fjordic sealochs and the River Clyde Estuary. In a world of rising sea level, studying the propagation and the climatology of surges and high water events is fundamental. In addition, high-resolution hydrodynamic models are essential to forecast extreme events and to prevent the loss of lives, or to plan coastal defences solutions.

Densely populated coastal areas of the North Sea are particularly vulnerable to severe wave conditions, which overtop or damage sea-defences leading to dangerous flooding. Around the shallow southern North Sea, where the coastal margin is low-lying and population density is high, oceanographic modelling has helped to develop forecasting systems to predict flood risk. However coastal areas of the deeper northern North Sea are also subject to regular storm damage but there has been little or no effort to develop coastal wave models for these waters. Here we present a high spatial resolution model of northeast Scottish coastal waters, simulating waves and the effect of tidal currents on wave propagation, driven by global ocean tides, far-field wave conditions, and local air pressure and wind stress. We show that the wave–current interactions and wave–wave interactions are particularly important for simulating the wave conditions close to the coast at various locations. The model can simulate the extreme conditions experienced when high (spring) tides are combined with sea-level surges and large Atlantic swell. Such a combination of extremes represents a high risk for damaging conditions along the Scottish coast.

High resolution measurements of the water velocity, bedforms and suspended sediment concentration were made using an Acoustic Doppler Velocimeter, acoustic bedform scanners and an Acoustic Backscatter System, under irregular free-surface waves. The waves were generated in a large scale flume facility above a number of bedform types. These data were analysed in (i) the frequency domain in order to examine the frequency at which sediment suspensions occurred in the oscillatory bottom boundary layer and the free stream; and (ii) the time domain in order to examine the instantaneous entrainment and vertical transport of sediment at intra-wave, wave average and wave group time scales. During the course of the experiments the significant wave height was systematically incremented enabling the character of sediment suspensions to be studied under a number of flow and bedform regimes. Wave groups were identified as an important control over sediment suspensions in both the wave boundary layer and free stream, with fluctuations in the suspended sediment concentration occurring at low, wave group, frequencies. However, the initial entrainment process, within the wave boundary layer, occurred at intra-wave frequencies. In contrast, in the free stream, sediment suspensions were dominated by the vertical transport of sediment at wave group time scales. During wave groups the sediment suspension field was characterised by the upward transport of sediment due to the continual injection of turbulence under a series of waves which generated a wave pumping effect. The character of a wave group is considered to be an important control over sediment suspensions in the free stream. Four distinct types of wave group were identified and the instantaneous sediment suspension field below each type examined. Such comparisons were possible using the high resolution Acoustic Backscatter System which enabled both intra-wave and wave group processes to be resolved up to 0.8 m above the bed.

The 7th UK Young Coastal Scientists and Engineers Conference welcomed 60 scientists and engineers to come together and discuss coastal research. The conference was hosted by the National Oceanography Centre in Liverpool, 30–31 March 2011. Early career practitioners and researchers presented 42 short papers on a range of topics driven by current issues addressed by UK universities, government agencies and consultancies. Although all presentations had a coastal theme, content varied from small-scale processes to regional-scale monitoring and management, covering topics such as structure impact, sediment transport, morphology, waves, currents, ecology, oxygen, estuarine systems, stratification, modelling, observation, ice, renewables and extreme events. This paper presents the keynote lecture and six abstracts considered to be of particular merit by the panel of judges. The conference continues to travel the UK and will be held at Bangor University in 2012.

On 25–26 March 2013, 52 early career scientists and engineers, studying various aspects of coastal science, met at the University of Aberdeen for the ninth Young Coastal Scientists and Engineers Conference. The conference was jointly organised by the School of Engineering, University of Aberdeen, and Marine Scotland Science. Early-career scientists, researchers and practitioners presented 23 oral and 17 poster presentations over the 2-day meeting. The papers all had a coastal theme with a large diversity in the subjects covered, including waves, currents, tidal energy, coastal erosion, sediment transport, fluid mechanics and particle tracking. This briefing paper reports on the conference, and presents the keynote lecture and four papers voted to be of especially high quality by the panel of judges.