Tidal currents are known to have complex turbulent structures. Whilst the magnitude and directional variation of a tidal flow is deterministic, the characteristics of turbulent flow within a wave-current environment are stochastic in nature, and not well understood. Ambient upstream turbulent intensity affects the performance of a tidal turbine, while influencing downstream wake formation; the latter of which is crucial when arrays of tidal turbines are planned. When waves are added to the turbulent tidal current, the resulting wave-current induced turbulence and its impact on a tidal turbine make the design problem truly challenging. Although some very interesting and useful field measurements of tidal turbulence have been obtained at several sites around the world, only limited measurements have been made where waves and tidal currents co-exist, such as in the PFOW. Also, as these measurements are made at those sites licensed to particular marine energy device developers, the data are not accessible to academic researchers or other device developers. Given the ongoing development of tidal stream power in the Pentland Firth, there is a pressing need for advanced in situ field measurements at locations in the vicinity of planned device deployments. Equally, controlled generation of waves, currents and turbulence in the laboratory, and measurement of the performance characteristics of a model-scale tidal turbine will aid in further understanding of wave-current interactions. Such measurements would provide a proper understanding of the combined effects of waves and misaligned tidal stream flows on tidal turbine performance, and the resulting cyclic loadings on individual devices and complete arrays. The availability of such measurements will reduce uncertainty in analysis (and hence risk) leading to increased reliability (and hence cost reductions) through the informed design of more optimised tidal turbine blades and rotor structures. An understanding of wave-current-structure interaction and how this affects the dynamic loading on the rotor, support structure, foundation, and other structural components is essential not only for the evaluation of power or performance, but also for the estimation of normal operational and extreme wave and current scenarios used to assess the survivability and economic viability of the technology, and to predict associated risks. The proposal aims to address these issues through laboratory and field measurements. This research will investigate the combined effect of tidal currents, gravity waves, and ambient flow turbulence on the dynamic response of tidal energy converters. A high quality database will be established comprising field-scale measurements from the Pentland Firth, Orkney waters, and Shetland region, supplemented by laboratory-scale measurements from Edinburgh University's FloWave wave-current facility. Controlled experiments will be carried out at Edinburgh University's FloWave facility to determine hydrodynamic loads on a tidal current device and hence parameterise wave-current-turbulence-induced fatigue loading on the turbine's rotor and foundation.

The marine renewable energy industry is vital to the future energy security of the UK as climate change necessitates the shift towards low carbon energy sources. Ocean energy represents a vast and largely untapped resource and the shallow seas around the UK represent one the best tidal energy resources globally, accounting for some 10% of the total resource. In consequence, the tidal energy industry is an emerging and steadily growing sector of the UK economy. However, the potentially highest yield tidal environments (i.e. tidal races) are particularly challenging environments for development due to the strong currents and in particular very turbulent flows. Optimum and efficient design of tidal energy convertors (TECs) therefore requires the characterisation of both the flow and turbulence at potential sites for development. The aim of this project is to develop techniques, which are directly applied to enhance the technological capability of oceanographic measurement equipment, for the characterisation of key aspects of turbulence, and hence identification of appropriate turbulence parameters, to aid the design and operation of TECs. The main technical challenge in the development of the marine tidal energy sector is the design, deployment and operation, over the long term, of cost effective in-stream TEC devices which are able to survive the extreme conditions associated with potentially high yield regions (ie. rapid tidal currents). A key requirement in the development of the industry is therefore methodology for site survey which provides characterisation of appropriate turbulent parameters. Measurements demonstrate that turbulent kinetic energy dissipation is strongly linked to tidal current speed, in a confined channel it is highly variable, fluctuating by over an order of magnitude for a given flow speed. However, commonly used acoustic techniques fail to resolve this variability in dissipation, which results from the formation of coherent structures. Furthermore, these measurements do not provide accessible information on the larger scale structure of turbulence, ie. the scales, structure/coherency and stress, which are most likely to compromise the structural integrity of the tidal energy infrastructure and effect power yield. Here we propose to develop and test new methodologies, using measurements from the latest generation of off-the-shelf 5-beam acoustic Doppler current profilers (ADCPs), to provide a more appropriate and comprehensive characterisation of turbulence at length scales directly relevant to the design of tidal stream energy generation infrastructure. The immediate relevance of these developments will be insured through collaboration with our partners, ADCP manufacturer Nortek and marine energy site survey company Partrac. In particular, we will exploit our previous observations that structure function techniques applied to multi-beamed acoustic current profilers can be used to provide a measure of anisotropy of turbulence.

The coasts and shelf seas that surround us have been the focal point of human prosperity and well-being throughout our history and, consequently, have had a disproportionate effect on our culture. The societal importance of the shelf seas extends beyond food production to include biodiversity, carbon cycling and storage, waste disposal, nutrient cycling, recreation and renewable energy. Yet, as increasing proportions of the global population move closer to the coast, our seas have become progressively eroded by human activities, including overfishing, pollution, habitat disturbance and climate change. This is worrying because the condition of the seabed, biodiversity and human society are inextricably linked. Hence, there is an urgent need to understand the relative sensitivities of a range of shelf habitats so that human pressures can be managed more effectively to ensure the long-term sustainability of our seas and provision of societal benefits. Achieving these aims is not straightforward, as the capacity of the seabed to provide the goods and services we rely upon depends on the type of substrate (rock, gravel, sand, mud) and local conditions; some habitats are naturally dynamic and relatively insensitive to disturbance, while others are comparatively stable and vulnerable to change. This makes it very difficult to assess habitat sensitivities or make general statements about what benefits we can expect from our seas in the future. Recently, NERC and DEFRA have initiated a major new research programme on Shelf Sea Biogeochemistry that will improve knowledge about these issues. In response to this call, we have assembled a consortium of leading scientists that includes microbiologists, ecologists, physical oceanographers, biogeochemists, mathematical modellers and policy advisors. With assistance from organisations like CEFAS, Marine Scotland and AFBI, they will carry out a series of research cruises around the UK that will map the sensitivity and status of seabed habitats based on their physical condition, the microbial and faunal communities that inhabit them, and the size and dynamics of the nitrogen and carbon pools found there. The latest marine technologies will measure the amount of mixing and flow rates just above the seabed, as well as detailed seabed topography. These measurements will allow better understanding of the physical processes responsible for movement and mixing of sediment, nutrient, and carbon. At the same time, cores will be retrieved containing the microbial and faunal communities and their activity and behaviour will be linked to specific biogeochemical responses. Highly specialised autonomous vehicles, called landers, will also measure nutrient concentrations and fluxes at the seabed. Components of the system can then be experimentally manipulated to mimic scenarios of change, such as changing hydrodynamics, disturbance or components of climate change. This will be achieved in the field by generating different flow regimes using a submerged flume or, in the laboratory, using intact sediment communities exposed to different levels of CO2, temperature and oxygen. By measuring the biogeochemical response and behaviour of the microbial and faunal communities to these changes, we will generate an understanding of what may happen if such changes did occur across our shelf seas. We will use all of this information to assess the relative vulnerability of areas of the UK seabed by overlaying the observation and experimental results over maps of various human pressures, which will be of value to planners and policymakers. Mathematical models will test future scenarios of change, such as opening or closing vulnerable areas to fishing or anticipated changes in the factors that control nutrient and carbon stocks. This will be valuable in exploring different responses to external pressures and for deciding which management measures should be put in place to preserve our shelf seas for future generations

THE PROBLEM: Offshore windfarms will be developed at an accelerated schedule under fast-track plans to switch away from fossil fuels. With ever larger offshore windfarms, and the cumulative effects of climate change, we thus urgently need to understand the way the seabed is modified in response and how such changes affect the wider marine ecosystem. When natural currents in the sea deviate around the wind turbines or anchors, the forces acting on the bed enhance, making sediments move and stay in suspension. This reduces the clarity of the water and changes the shape and sediment composition of the seabed, with impacts stretching far beyond the object. The seabed supports ecosystems that deliver a wide range of services incl. fishing, carbon storage, aggregates and coastal protection. The climate crisis will stretch impacts even further and into coastal zones, as future storm waves and rising sea levels will alter the ways energy from the sea is transferred to the seabed. All these changes combined can have wide-reaching impacts for organisms that live on or in the seabed, potentially changing biodiversity (species richness) and the delivery of some of these ecosystem services. The impacts at the seabed extend through the food chain to the water column and beyond as seabed dwelling fish are consumed by seabirds and cetaceans. Aggregations of fish can be strongly associated to particular seabed properties. If displacement or mortality occurs amongst these important prey species, this has knock-on effects for the deep-diving predators that cannot afford to be less efficient in foraging for food, like the seabirds that are protected by legislation. During this pivotal time of energy transition and national security, it is of crucial importance to better understand and unlock the potential of the marine environment for a renewable energy transition with added benefits to the ecosystem. AIM: This proposal sets out a strategy to assess the seabed response to the combination of accelerated windfarm expansion and accelerated climate change, and to quantify the implications for (1) biodiversity, (2) ecosystem services, (3) habitats, and (4) interactions between seabird populations and their food. We ultimately seek to help identify opportunities that benefit the conservation of species and increase biodiversity around windfarms. We will help windfarm developers design their monitoring strategies long beyond the life-span of our project. SUMMARY OF METHODS AND OUTPUTS: Via a multi-proxy study using observations, laboratory experiments and models, we will assess and map, under different climate predictions, how the stresses on the bed will be modified by 2050, how the distribution of seabed habitats and biodiversity will change, and how that drives changes to ecosystem services and the foraging success of deep-diving seabirds. We will design relevant scenarios, where we consider offshore windfarm size, scour mitigation strategies, predator behaviour and the ecosystem's vulnerability to change due to the combined effect of accelerated windfarm expansion and climate change. We will use the Eastern Irish Sea area as case study, as it is the home of a variety of seabird species with specific predator-prey relationships, of diverse seabed types and of considerable windfarm expansion nearby existing windfarms. To help all developers of windfarms in the UK, UK-scale maps will be made of the vulnerability of the seabed to change, and a new seabird vulnerability index will be developed. Our quantification of how these processes from seabed to seabirds interact can directly inform/feed into existing and future decision support tools. We will provide a tool where stakeholders can run their own simulations anywhere around the UK and for any given model/data resolution to quantify uncertainty levels of bed stress caused by windfarms, with cascading effects of uncertainty in habitat and biodiversity distribution and ecosystem services.

Estuaries are more than simply areas of mud and marsh that represent the transition zone between rivers and the ocean. They play a vital role in our economy as sites of leisure and commercial activities, such as fishing and boating. In addition, they are important nursery grounds for many species of economically important fish that later migrate to the open sea. As approximately 40% of the world's population live within 100 km of the coast, estuaries are also some of the most vulnerable sites for impact from man's activities. Not only can they suffer from activities occurring within the estuary itself, but they also mark the point where pollutants gathered by rivers from large areas of the interior can accumulate. One of the major pollution concerns in estuaries arises from the excess river borne concentrations of phosphate and nitrate. These can be derived from a variety of sources, such as run off from fertilised fields and discharge (accidental or purposeful) from sewage treatment plants. Regardless of their source, they can cause severe problems, such as stimulating the growth of excess algal growth that can deplete the water in oxygen and causing widespread fish kills, or causing the growth of poisonous algal species (red tides) that cause shell fish fisheries to be closed. Although this problem has been recognised for some time, and monitoring activities by bodies such as the Environment Agency and water companies play an important role in keeping pollution in check, there are still major gaps in our knowledge. In particular, it is apparent that a large proportion of the flux of nitrate and phosphate are delivered to estuaries by sudden storm events, but most monitoring takes place at fixed times that are spaced too far apart to capture these events. This is a major gap in our knowledge that will become more important as the intensity and frequency of storms are likely to increase due to climate change. Additionally, the phosphate and nitrate load of rivers can take many forms - dissolved and particulate, organic and inorganic - and relatively little is known about the concentrations of these different forms varies throughout the seasons and during storm events. Only if we are able to fully understand these processes will we be able to take the necessary steps to identify and control polluting sources of nitrate and phosphate to estuaries. Our research seeks to address this gap in our knowledge by carrying out detailed monitoring of the many forms of phosphate and nitrate that enter Christchurch Harbour estuary (Dorset) from both the rivers and the sea over the course of a year. We will be using state-of-the-art technology (much of it developed by ourselves) that will allow us to monitor they key parameters at intervals of every 30 minutes. Hence, we will be able to capture the effects of sudden and short-lived storms that have eluded previous studies and routine monitoring practices. We will then use the results of our study to examine how these sudden storm events affect the distribution of phosphate and nitrate within the estuary. In particular, we will examine what happens when sediments are stirred up in the estuary by storms - do they remove or add phosphate and nitrate to the system? We will also examine the effects of these sudden storms on the biological activity in the estuary. Again, do they increase or decrease the growth of algae, and what difference is there if the storm happens in the summer or the winter? The various threads of our study will be drawn together into a powerful statistical model that will allow us to better understand the transfer of phosphate and nitrate from rivers, through estuaries and into the coastal seas, and the role that storms play in this process. Our results will then allow policy makers to make more informed decisions about how we can seek to reduce pollution of estuaries by nitrate and phosphate.