Geomorphological control on boulder transport and coastal erosion before, during and after an extreme extra-tropical cyclone

Extreme wave events in coastal zones are principal drivers of geomorphic change. Evidence of boulder entrainment and erosional impact during storms is increasing. However, there is currently poor time coupling between pre- and post-storm measurements of coastal boulder deposits. Importantly there are no data reporting shore platform erosion, boulder entrainment and/or boulder transport during storm events – rock coast dynamics during storm events are currently unexplored. Here, we use high-resolution (daily) field data to measure and characterise coastal boulder transport before, during and after the extreme Northeast Atlantic extra-tropical cyclone Johanna in March 2008. Forty-eight limestone fine-medium boulders (n = 46) and coarse cobbles (n = 2) were tracked daily over a 0.1 km2 intertidal area during this multi-day storm. Boulders were repeatedly entrained, transported and deposited, and in some cases broken down (n = 1) or quarried (n = 3), during the most intense days of the storm. Eighty-one percent (n = 39) of boulders were located at both the start and end of the storm. Of these, 92% were entrained where entrainment patterns were closely aligned to wave parameters. These data firmly demonstrate rock coasts are dynamic and vulnerable under storm conditions. No statistically significant relationship was found between boulder size (mass) and net transport distance. Graphical analyses suggest that boulder size limits the maximum longshore transport distance but that for the majority of boulders lying under this threshold, other factors influence transport distance. Paired analysis of 20 similar sized and shaped boulders in different morphogenic zones demonstrates that geomorphological control affects entrainment and transport distance – where net transport distances were up to 39 times less where geomorphological control was greatest. These results have important implications for understanding and for accurately measuring and modelling boulde

Assessment of entanglement risk to marine megafauna due to offshore renewable energy mooring systems

This paper defines a methodology to compare different offshore renewable energy (ORE) mooring configurations in terms of the risk of entanglement they present to marine megafauna. Currently, the entanglement of large marine animals is not explicitly considered in environmental impact studies. Recommendations need to be developed, assessing the risk of entanglement of ORE mooring configurations at the beginning of their design process. Physical parameters of the mooring system affecting the relative risk of entanglement have been identified as tension characteristics, swept volume ratio and mooring line curvature. These have been investigated further through six different mooring configurations: catenary with chains only, catenary with chains and nylon ropes, catenary with chains and polyester ropes, taut, catenary with accessory buoys, taut with accessory buoys. Results indicate that the taut configuration has the lowest relative risk of entanglement, while the highest relative risk occurs with catenary moorings with chains and nylon ropes or with catenary moorings with accessory buoys. However, the absolute risk of entanglement is found to be low, regardless of the mooring configuration. This methodology can also be applied to other mooring configurations, arrays or power cables.Scottish National Heritag

Using the CLOX drawing task to educate the public of the effects of hearing loss

We describe a task used to educate the public on the importance of hearing and the experience of hearing loss. During an open day at Nottingham University, participants were presented with verbal instructions (with or without a background masker) and asked to draw the image of a clock face as accurately as possible. Poorest performance was observed when the instructions were presented with a background masker. We suggest that the task could be applied effectively by healthcare professionals who aim to educate younger individuals of the difficulties associated with hearing loss

Cumulative impact assessment of tidal stream energy extraction in the Irish Sea

A cumulative impact assessment of tidal stream developments in the Irish Sea has been conducted on a high-resolution depth-averaged hydrodynamic model, using Telemac2D. Eight sites were investigated, representing the proposed developments at the time of study. These included: Ramsey Sound, Anglesey, Strangford Loch, Mull of Kintyre, Torr Head, Fair Head, Sound of Islay and West of Islay. Only three projects showed array-array interaction: Fair Head, Torr Head and Mull of Kintyre. A smaller model domain was created for further analysis. Results showed Mull of Kintyre had little impact. Fair Head reduced the energy production at Torr Head by 17%, whereas, Fair Head only reduced by 2%. This was caused by the tidal asymmetry whereby the flood was stronger. When operated concurrently, the maximum power-output at Torr Head is 64.5 MW, representing 31% reduction. If Torr Head can still operate commercially in the presence of Fair Head, then the additional environmental impact of Torr Head, such as the change in bed shear stress, is small. Within the Irish Sea, very few of the tidal projects investigated are geographically close to each other. As the industry develops, the risk of interaction to these sites will grow when more intermediary sites are developed

Flowbec

publication-status: UnpublishedThis document provides an overview of the resources available for the description of the natural environment at the Wave Hub site, and surrounding region. It aims to provide the reader with an understanding of the mechanisms that have led to the collection of the data resources, and details on how to access them. Detailed information for key research areas is then presented. The document does not aim to provide results of the data collection and analysis, and the reader is referred to the data sources reviewed.NERC FLOWBE

Modelling the hydrodynamic and morphological impacts of a tidal stream development in Ramsey Sound

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this recordA number of sites around the UK are being considered for development of tidal stream energy, one of which is Ramsey Sound off the coast of Pembrokeshire, South Wales. The Sound was used to test the prototype of the Delta Stream by Tidal Energy Ltd. After initial testing, a 10 MW tidal array was proposed at St David’s Head. To investigate any possible environmental impacts of the array due to energy extraction, a case study of the Pembrokeshire coast was performed using a high-resolution depth averaged hydrodynamic model, Telemac2D, to investigate changes to hydrodynamics and morphodynamics. Results show that the proposed array of nine tidal energy converters will cause alterations to eddy propagation leading to changes in the velocity field up to 24km from the tidal array. Changes in morphodynamics are predicted through alterations to the bed shear stress. Changes to the mean and maximum bed shear stress, over a 30-day period, are found to be more localised and extend 12km from the array. These changes indicate that the proposed tidal array will lead to localised sediment accumulation and will act as a barrier to sediment transport, with potential consequences for the benthic ecology of the region.The authors thank Cardiff University for providing ADCP data through Ramsey Sound. The work was funded by the Industrial Doctorate Centre for Offshore Renewable Energy which is funded by the Energy Technologies Institute and the RCUK Energy Programme, grant number (EP/J500847/1). This work was carried out on the High Performance Computing Cluster supported by the Research and Specialist Computing Support service at the University of East Anglia

Wave resource variability: Impacts on wave power supply over regional to international scales

The intermittent, irregular and variable nature of the wave energy resource has implications for the supply of wave-generated electricity into the grid; intermittency of renewable power may lead to frequency and voltage fluctuations in the transmission and distribution networks. This study analyses the wave resource over different spatial scales to investigate the potential impacts of the resource variability on the grid supply. It is found that the deployment of multiple wave energy sites results in a reduction in step changes in power, leading to an overall smoothing of the wave-generated electrical power

Mooring line fatigue damage evaluation for floating marine energy converters: Field measurements and prediction

publication-status: Publishedtypes: ArticleThe vision of large-scale commercial arrays of floating marine energy converters (MECs) necessitates the robust, yet cost-effective engineering of devices. Given the continuous environmental loading, fatigue has been iden- tified as one of the key engineering challenges. In particular the mooring sys- tem which warrants the station-keeping of such devices is subject to highly cyclic, non-linear load conditions, mainly induced by the incident waves. To ensure the integrity of the mooring system the lifecycle fatigue spec- trum must be predicted in order to compare the expected fatigue damage against the design limits. The fatigue design of components is commonly as- sessed through numerical modelling of representative load cases. However, for new applications such as floating marine energy converters numerical models are often scantily validated. This paper describes an approach where load measurements from large- scale field trials at the South West Mooring Testing Facility (SWMTF) are used to calculate and predict the fatigue damage. The described procedure employs a Rainflow cycle analysis in conjunction with the Palmgren-Miner rule to estimate the accumulated damage for the deployment periods and individual sea states. This approach allows an accurate fatigue assessment and prediction of mooring lines at a design stage, where field trial load measurements and wave climate information of potential installation sites are available. The mooring design can thus be optimised regarding its fatigue life and costly safety factors can be reduced. The proposed method also assists in monitoring and assessing the fatigue life during deployment periods

Resource Characterization of Sites in the Vicinity of an Island near a Landmass

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Renewable energy technologies are undergoing rapid development, the global aim being to achieve energy security and lower carbon emissions. Of marine renewable energy sources, tidal power has inherent predictability and large theoretical potential, estimated to exceed 8000 (TW h)a−1 in coastal basins. Coastal sites in the vicinity of an island near a landmass are prime candidates for tidal stream power exploitation by arrays of turbines. This paper characterizes numerically the upper limit to power extraction of turbines installed at such sites. It is demonstrated that the maximum power extracted from the strait is generally not well approximated by either the power dissipated naturally at the seabed or the undisturbed kinetic power of flow in the strait. An analytical channel model [C. Garrett and P. Cummins, “The power potential of tidal currents in channels,” Proc. R. Soc. A Math. Phys. Eng. Sci., vol. 461, no. 2060, pp. 2563–2572, Aug. 2005] provides lower predictions than the present numerical model of available power in the strait due to the analytical model not accounting for changes to the driving head resulting from power extraction and flow diversion offshore of the island. For geometrically long islands extending parallel to the landmass, the numerically predicted extracted power is satisfactorily approximated by the power naturally dissipated at the seabed, and there is reasonable agreement with the estimate by the channel analytical model. It is found that the results are sensitive to choice of boundary conditions used for the coastlines, the eddy viscosity, and bed friction. Increased offshore depth and lower blockage both reduce the maximum power extracted from the strait. The results indicate that power extracted from the site can be maximum if extraction is implemented both in the strait and offshore of the island. Presence of the landmass and increasing island dimensions both enhance power extraction.This work was supported by General Electric Renewable Energy with funding from the ETI and the EPSRC through the Industrial Doctoral Centre for Offshore Renewable Energy (EP/J500847/1). The authors would like to thank the Applied Modelling and Computation Group at Imperial College of London for free access to the software Fluidity and their support

Environmental interactions of tidal lagoons: A comparison of industry perspectives

Tidal lagoons are an attractive renewable energy option that could aid the UK in meeting its ambitious renewable energy targets. One of the main barriers to tidal range development in the UK to date has been regulatory environmental concern. In order for the nascent lagoon industry to move forward into development, the views of the developers and other influential stakeholders such as government bodies, regulators, conservationists and practitioners (herein referred to as 'influencing stakeholders' or 'influencers') need to be aligned. This study is the first of its kind using online questionnaires and semi-structured interviews to present and compare the views of both developers and influencing stakeholders on the environmental interactions of tidal lagoons. We find that, whilst both influencers and developers are working towards the common goal of a good environmental outcome for tidal lagoons, there are mismatches in their views in terms of the priorities given to the key environmental impacts, benefits and potential solution options. The work provides insight into what is at the forefront of developers' and influencers' minds, highlighting the key themes within their views and transforming this information into policy recommendations that will help the industry's development move forward