The SeaGen tidal turbine was installed in Strangford Narrow, Strangford Lough, Northern Ireland by Marine Current Turbines Ltd (MCT) in 2008 in order to study tidal energy technology through the investigation of engineering, management systems, and environmental impacts.
The SeaGen device consists of two 16 m diameter rotors and generators supported on a crossbeam that is affixed to a central tubular structure with a control unit on top. The device is secured in position using a quadropod foundation fixed on the seabed using drilled pin piles approximately 1 m diameter, 14 m long, and drilled to a depth of approximately 9 m. Each of the quadropod legs is hollow and contains grout and concrete.
MCT was acquired by Atlantis Resources Limited (Atlantis) from Siemens on the 01 July 2015. SeaGen is owned and operated through Sea Generation Ltd. (SGL), a wholly owned subsidiary of MCT, which in turn is now owned by Atlantis. SeaGen is now considered to have served its R&D purpose and Atlantis has taken the decision to decommission the device.
An Environmental Impact Assessment (EIA) was undertaken by Royal Haskoning DHV and completed in June 2005 with the production of an Environmental Statement (ES). The scope of the pre-construction EIA included construction, operation and decommissioning of the device. The decommissioning methods identified in 2005 ES were based upon assumptions concerning the likely methods that would be employed to decommission SeaGen.
An extensive Environmental Monitoring Plan (EMP) was established in order to fulfil the requirements of the conditional Food and Environmental Protection Act (FEPA) marine construction licence. Data collection for the EMP began in 2005 and continued until 2011 when the EMP ceased, SeaGen continued operating until Q4 2015. As part of the EMP, a focused Science Group and a wider Liaison Group were established in order to direct the environmental monitoring undertaken and as a way of reporting the findings to a wider group of stakeholders respectively. Overall, the findings of the EMP provided evidence that SeaGen operated with no likely significant impacts on the marine environment in Strangford Lough.
In 2011, a report produced for MCT by MOJO Maritime Ltd reviewed the potential methods to decommission the SeaGen tidal device. Since 2005, when the pre-construction EIA was undertaken, the range of decommissioning methods has expanded beyond that which was originally considered. As such, further EIA was required in order to cover contemporary decommissioning methodologies not assessed in the pre-construction EIA.
MarineSpace Ltd has been commissioned to prepare an additional EIA to include the decommissioning methods not covered previously. Data used to inform the decommissioning EIA is based upon the evidence gathered during the EMP since the pre-construction EIA.
A scoping study was undertaken by MarineSpace Ltd to identify the key concerns and to consider the revised decommissioning methods. The SeaGen Decommissioning Scoping Report underwent a formal consultation in June 2016 to inform the potential impact pathways that are assessed in the EIA and presented in this Decommissioning ES.
A summary assessment of the residual impacts after appropriate mitigation has been put in place is given below:
- Loss or damage of benthic habitat via use of jack-up or moored barges is assessed to be negligible;
- Loss of designated seabed habitat (Strangford Lough Special Area of Conservation (SAC) and Marine Conservation Zone (MCZ)) via use of jack-up or moored barges is assessed to be negligible;
- Noise and vibration disturbance to fish resources via use of diamond wire cutting tool (DWCT) or abrasive water jet (AWJ) is assessed to be negligible;
- Noise and vibration disturbance to basking shark via use of jack-up or moored barge or DWCT or AWJ is assessed to be negligible;
- Underwater noise disturbance to marine mammals via use of Brocotorch, DWCT, AWJ and vessel noise is assessed to be negligible;
- Collision between marine mammals and vessels involved in the decommissioning work is assessed to be negligible; and
- Obstruction to movement of fishing vessels through use of jack-up or moored barges is assessed to be negligible.
A summary of mitigation measures proposed to minimise the risk of impacts is given below:
- Decommissioning will not take place during common seal pupping season (May to August);
- Undertake decommissioning operations between January and March when abundance of marine mammals is low in order to reduce risk of potential noise disturbance to marine mammals;
- Undertake decommissioning operations between January and March when abundance of marine mammals is low in order to reduce the risk of collision with decommissioning equipment. Maximum vessel speeds to be implemented;
- Reduce potential spread of non-native species through decommissioning activities via DWCT or AWJ; and
- Undertake decommissioning operations between January and March when there is no larval recruitment of Didemnum vexillum in order to reduce the potential risk of introduction of non-native species. No ballast water will be exchanged or discharged within 3 nm of the entrance of the Narrows. No colonies of Didemnum vexillum have been observed on the SeaGen structure throughout operation and in preparation of the site for decommissioning.
Overall, the potential environmental impacts as a result of decommissioning of the SeaGen device have been assessed as follows:
- Short-term and temporary impacts upon benthic communities in Strangford Lough via loss or damage of seabed habitat through use of moored barge or jack-up vessel;
- No adverse effect on site integrity of Strangford Lough SAC and less than 0.01% will experience short-term temporary impacts via loss or damage of designated seabed habitat through use of moored barge or jack-up vessel;
- Short-term and temporary impacts upon fish, including basking shark, pinnipeds and cetaceans, due to noise disturbance through use of DWCT or AWJ;
- Impacts on all other receptors are considered to be negligible;
- No cumulative impacts with commercial fisheries, shipping and the Minesto tidal device; and
- Decommissioning of the SeaGen device is not predicted to result in any medium to longterm environmental impacts.
It is the conclusion of the EIA that following mitigation there will be no major adverse residual impacts either from the project alone or cumulatively with other projects on any environmental receptors within Strangford Lough.
Information has also been provided within the ES to facilitate HRA for the possible impacts of the project upon the nature conservation features of Strangford Lough. It is predicted that the project alone, and in combination with other plans and projects, will result in no likely significant effect on the European sites of Strangford Lough.