Flow and Benthic Ecology 4D (FLOWBEC)

Lead Research Organisation: Queen's University of Belfast
Department Name: Sch of Biological Sciences

Abstract

The strength of currents near the seabed has a major effect on the organisms and communities, that is the benthos, that occur there. The currents may, for example, affect the amount of food supplied to the organisms or they may control the ability of spores and larvae to settle and grow on the seabed. By their very nature, tidal energy devices will disturb the current flow near the seabed with the degree of disurbance depending on the design of the device. In particular a wake will be produced downstream of the body of the device as well as a defined zone of increased turbulence downstream of the blades or rotor. These disturbances to the ambient flow may be expected to have an influence on the benthic communities present on the seabed. Observations of the benthos at three fixed sites downstream of the SeaGen tidal turbine over four years have shown no influence of the device on the benthos; however these observations are very limited spatially. Ultimately there is a need to be able to predict the possible influence of a tidal device or devices on the benthos rather than relying on costly post-installation surveys. One of the main difficulties in being able to make predictions has been the inabiltiy to predict changes in the ambient current flow resulting from tidal energy devices. However recent developments in numerical modelling have the potential to describe at a scale of 1m or better the flowfield downstream from tidal energy devices with early results indicating that there may be localised semi-permanent zones of increased or decreased flow associated with a typical device. Arising from these developments, the proposal intends to carry out detailed benthic surveys downstream of the SeaGen tidal energy device in Strangford Narrows and compare the benthic community distributions with the current field predicted from the high resolution numerical models. The comparison will make a major step in understanding the consequences of flow changes resulting from tidal energy devices on the benthos and also allow predictions to be made for future device deployments.
Queen's University Belfast will oversee the required benthic sampling programme, which will be carried out by personnel from NUI Galway, and will liaise closely with the University of Edinburgh (UoE) who are developing the necessary numerical model within a separate component bid of FLOWBEC. The model will allow current predictions at a spatial scale of 1m or better. Benthic distributions will be characterised by a major series of drop-down video images taken up to 200m downstream of SeaGen during the spring in two consecutive years. The position of each image will be recorded to better than 1m using a precision underwater DGPS system. The video images will be analysed by the University of Galway to quantify the benthos and the nature of the seabed at each sampling point. Statistical analyses will be carried out in close liaison with the UoE team to establish the relationship between the mean velocity and the turbulent velocity component and the distribution of the benthos. Close attention will be paid to assessing an appropriate parameter to describe the turbulent component of the velocity that is appropriate to the biology. The analysis will also consider the interaction between the benthos and the physical nature of the seabed.
The study, which will develop ongoing work establishing the relationship between currents and benthic communities on a coarser spatial scale, is supported by MCT, the developers of SeaGen. The results will be of major value to the marine energy industry as a whole by allowing the prediction of relationships between benthic communities and changes in the ambient current field resulting from the installation of tidal energy devices.

Planned Impact

Given the focus of the study on SeaGen, the tidal turbine deployed in Strangford Narrows in April 2008 By Marine Current Turbines (MCT) and operated on a commercial basis since then by MCT, the immediate beneficiary of the proposed work will clearly be MCT. MCT, which is a fully commercial organisation, will benefit by being able to accurately predict what, if any, influence the flow perturbation associated with one SeaGen device may have on ambient benthic communities. The benthic surveys associated with the SeaGen environmental monitoring programme have been unable to show this. Depending on the development of suitable models of flow perturbation associated with array deployments of SeaGen or equivalent devices, the data to be obtained will also be able to be applied to multiple device deployments. The outcomes of the project will also be of major relevance to national and international marine environmental regulatory bodies by allowing them a firmer base on which to reach decisions on device deployment. Related to this, the presence of firm scientific data confirming what, if any, benthic effects may result from the deployment of a horizontal blade-axis tidal turbine will also provide reassurance for interested public environmental groupings.
Reassurance on possible environmental effects of tidal turbines is an important selling factor for any such device. MCT has a national and international presence and is a clear leader in their field and the ability to reassure their potential customers and associated regulatory bodies of the effects, if any, of the device on the benthos will be a valuable selling point for the SeaGen device. Because of the close commercial involvement of MCT with the proposed project, access to data obtained from the project would be restricted for 15 months after its collection. Following this period, it is expected that the data would be submitted for publication in peer-reviewed journals and would be openly available.

Publications

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To Be Decided No publications as yet in To be decided

 
Description We have successfully applied a high resolution flow model to predict the variations in the ambient flow regime, particularly in the region of the seabed, associated with the presence of a tidal energy device in a narrow channel. The modelling programme, which was based on a spatial resolution of 1-5 m, was complemented by two similarly spatially resolved field surveys of the epibenthic communities in the vicinity of the SeaGen tidal device in Strangford narrows. Data from the modelling and field approaches have being integrated and fully analysed.
The outcomes from the analysis indicate that the relationship between the biological and physical environment within the high energy survey area is complex and largely random. As a result it was not possible to predict variation in epifaunal community structure using hydrodynamic parameters, substrate type distribution and positional variables in artificial neural networks.
It was possible, however, to show a variation in biological community structure with distance from the turbine. Within one rotor diameter of the turbine there was a significantly higher variation in community structure than anywhere else in the survey area. The influence was highly localised, only affecting communities found immediately adjacent to the device structure, and suggests that the effects of the device on the benthic communities were related to local scour activity.
Exploitation Route The findings may be used by the tidal energy industry in support of environmental consent applications by giving confidence of minimal impact of ambient flow perturbations associated with a particular tidal device on the adjacent benthic communities.
Although the emphasis of the study was on the SeaGen tidal device, the fundamental design of a horizontally aligned rotor mounted in mid-water column is similar to several tidal devices currently being developed. As such, we believe that the focus on SeaGen will have wider application, although it is recognised that the height of the rotor above the seabed may be critical.
The likely influence of local scour effects on the benthos suggested by the study, hints that the design of the mounting base of tidal energy devices may require detailed consideration in order to reduce local influences on the benthic communities.
Sectors Aerospace, Defence and Marine,Energy,Environment

 
Description A full analysis of the data outputs from the detailed hydrodynamic model of flow perturbation adjacent to the tidal turbine and from the results of the spatially highly resolved dropdown video survey showed complex and largely random relationships between the physical and biological environments. Biological community structure changed with distance from the turbine, but the effects were very localised and restricted to within one rotor diameter of the turbine. Thus it appears that the effects were caused principally by local scour immediately adjacent to the device with no far-field effects being apparent. These findings are of potential value to the tidal energy industry in assisting in the giving of environmental consent to the deployment of tidal devices.
First Year Of Impact 2015
Sector Energy,Environment,Manufacturing, including Industrial Biotechology
Impact Types Economic

 
Description The outcomes will assist in obtaining environmental consent for the deployment of horizontal-axis rotor tidal energy devices in respect of possible influences on adjacent benthic communities.
Geographic Reach Europe 
Policy Influence Type Influenced training of practitioners or researchers
Impact Analysis of the modelling and survey data demonstrate that there are clear indications that the effect of SeaGen type horizontal-axis rotor tidal energy devices have minimal effect on the ambient benthic communities.
 
Title Application of 'fluidity' hydrodynamic model for high resolution flow prediction associated with SeaGen tidal energy device and integration of output with highly spatially resolved data from field surveys in a challenging high velocity environment 
Description To the best of our knowledge, this is the first application of the 'fluidity' hydrodynamic model to a highly spatially resolved inshore location associated with a full-scale commercial tidal energy device and integration of model output with similarly resolved benthic survey data 
Type Of Material Improvements to research infrastructure 
Provided To Others? No  
Impact The output is likely to be of positive assistance to the tidal energy industry by reducing concern about the potential impact of SeaGen-type devices on the ambient benthic structure 
 
Title Local databases as required for purposes of the project 
Description Databases established in respect of outcomes of hydrodynamic modelling and detailed benthic surveys 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact The impacts will arise from integration of the physical and biological databases to allow the objectives of the project to be achieved 
 
Description Development of hydrodynamic model to consider in greater detail the effect of tidal energy device supporting structures on local flow modification 
Organisation ITS United Kingdom
Country United Kingdom 
Sector Private 
PI Contribution The research has focussed on the effects of flow variations arising from the form of the supporting structure of tidal energy devices as based on the model developed for the core FLOWBEC project.
Collaborator Contribution Close liaison was maintained between the modeller (Dr Angus Creech) and IAA to allow incorporation of specific support structure configurations into the basic flow model.
Impact Publication in preparation. Provisional title: "The effects of supporting structures on an actuator line model of a tidal turbine with contra-rotating rotors".
Start Year 2014
 
Title Normal outcomes resulting from academic research. No IP protection expected to be required 
Description Normal outcomes resulting from academic research 
IP Reference  
Protection Protection not required
Year Protection Granted
Licensed No
Impact Preliminary outcomes from analysis of the integrated physical-biological datasets indicate that the influence of SeaGen-type tidal energy devices have minimal impact on the ambient benthic communities
 
Title Application of 'fluidity' hydrodynamic model to predict fine-scale flow in vicinity of SeaGen-type tidal energy device 
Description The established 'fluidity' hydrodynamic was developed to predict the flow pattern adjacent to a SeaGen-type tidal energy device in a highly dynamic environment. The output from the model was integrated with comparable highly resolved data obtained from benthic surveys. 
Type Of Technology Webtool/Application 
Year Produced 2015 
Impact The developments described above indicate that the presence of the tidal energy device forming the basis of the investigation has minimal impact on local benthic communities.