SeaGen is a twin turbine system with a mobile cross arm on a single supporting pile 3m in diameter and 9m above the average sea level. The twin rotors have an 8m radius and will begin to generate electricity once the tide runs faster than 1m/s. At maximum speed the tips move at around 12m/s, approximately 1/3 of the average wind turbine speed.
Strangford Lough, Northern Ireland
The final Environmental Impact Study was submitted to the regulatory authority, the Environment and Heritage Service (EHS) in Northern Ireland in June 2005. The FEPA license for the temporary installation for the SeaGen system for a 5-year duration was first issued in December 2005, revised in February 2007 and again in February 2008. Pre-installation environmental monitoring commenced in May 2004. A baseline report has been completed and was submitted to EHS in August 2006. The environmental impact of SeaGen will be continuously monitored by independent science team throughout the licensed 5-year installation period.
Royal Haskoning Ltd. was appointed in early 2004 to provide support to the EIA process. The scoping consultation was completed in mid-2004, and the EIA commenced late 2004. The final EIA was submitted in July 2005, with the initial FEPA license being granted in December 2006. These were revised to accommodate necessary changes in installation methodology in February 2007, and again in February 2008.
Installation of the moorings for anchoring the SeaGen deployment vessel commenced in February 2008 and was completed in March 2008. The SeaGen structure was positioned on the seabed on April 2, 2008 by the crane barge, Rambiz. Drilling for the pin piles, grouting, and completion of assembly was achieved using the crane barge, Missing Link, which was on location from mid-April to late May 2008.
Commissioning of SeaGen commenced in July 2008, culminating in full 1.2MW power generation to the grid in December 2008. Operation is continuing within the constraints of the FEPA license with the environmental monitoring programme results contributing to an adaptive management strategy where findings are periodically reviewed and improvements to the application of the FEPA restrictions are proposed.
In January 2016, it was announced that Atlantis (the company which now owns MCT) would begin decommissioning the device in summer 2016 after much knowledge had been gained during its operation. Specialist UK-based marine business Keynvor MorLift ltd. (KML) was appointed as the Principal Contractor to carry out the decommissioning engineering, planning and offshore works. The first phase of decommissioning SeaGen started in May 2016 with the removal of the system’s two 600kW powertrains. In August 2018 the topsides and crossbeam were removed, and final works were completed with the successful removal of the remaining tower and subsea structure in July 2019.
Key Environmental Issues
Strangford Lough has been identified as a site which supports internationally important examples of particular marine and coastal habitat and species features and has accordingly been given the dual status of a European Special Area of Conservation (SAC) and a European Special Protected Area (SPA). Three of the site features have been identified as potentially vulnerable to activities and impacts associated with the installation of the SeaGen turbine.
The EIA process identified various levels of uncertainty surrounding potential impacts on key marine species and features within the Strangford Lough Special Area of Conservation (SAC), they include:
- Effects of installation and operation on the integrity of the breeding harbour seal population.
- Collisions of marine mammals, fish and diving birds with the turbine rotors.
- Effects on the abundance, diversity, integrity and extent of the benthic biological communities associated with the submerged rocky reefs.
- Effects of installation and operation on the breeding bird population.
Baseline Assessment: Strangford Lough - MCT (SeaGen)
|Receptor||Study Description||Design and Methods||Results||Status|
|Marine Mammals||Potential impacts to marine mammals (General)||Desk based study and Aerial surveys||No marine mortalities occur consequence of interaction with the turbine rotors. The turbine operates in such a way as to stop when marine mammals are within 50m from the rotors. Relative abundance of marine mammals in Strangford Narrows is not significantly modified by the operation of the SeaGen turbine.||Completed|
|Marine Mammals||Potential impact to Cetacean populations||Desk based study and Aerial surveys||The SeaGen turbine does not displace harbour porpoises from the Strangford Narrows and the adjacent Strangford Lough SAC. The SeaGen turbine does not present a barrier effect to the free passage of harbour porpoises through the Strangford Narrows. Cetaceans not excluded from important foraging habitat or social areas within the Strangford Narrows as a result of the installation and operation of the SeaGen turbine.||Completed|
|Marine Mammals||Potential impact to Harbour Seals||Ariel Surveys, visual surveys, desk based study||The number of harbour seal adults and pups does not decrease significantly as a result of the installation and operation of the SeaGen turbine. The SeaGen turbine does not present a barrier effect to the free passage of harbour seals through the Strangford Narrows. Harbor seals are not excluded from mportant3 foraging habitat or social areas within the Strangford Narrows as a result of the installation and operation of the Seagen turbine.||Completed|
|Marine Mammals||Potential impact of SeaGen to Grey Seal populations||Ariel surveys, visual surveys and desk based studies||The number of grey seal adults and pups does not decrease significantly as a result of the installation and operation of the SeaGen turbine. The SeaGen turbine does not cause a significant change in the use of important grey seal haul out sites within the Strangford Lough SAC. The SeaGen turbine does not present a barrier effect to the free passage of grey seals through the Strangford Narrows. Grey seals are not excluded from important foraging habitat or social areas within the Strangford Narrows as a result of the installation and operation of the SeaGen turbine.||Completed|
|Invertebrates||Potential impacts to Benthic Communities||Desk based study and diver surveys||The installation and operation of the SeaGen turbine will have no significant impact on the abundance, diversity and integrity of the benthic communities within the Strangford Narrows.||Completed|
|Physical Environment||Alterations to Hydrodynamics||Desk based study, modelling and video footage.||The installation and operation of the SeaGen turbine will not impede or modify the flow dynamics, scour patterns or turbulence character of the Narrows in such a way that will cause a change to benthic community structure.||Completed|
Post-Installation Monitoring: Strangford Lough - MCT (SeaGen)
|Stressor||Receptor||Study Description||Design and Methods||Results||Status|
|Collision||Marine Mammals||Carcass post mortem||A programme of shoreline surveillance covering key areas which were predicted to be hotspots for stranding based on local advice and hydrodynamics. It was agreed by the Science Group that these surveys were no longer required. Plans were in place for any carcasses discovered to be subjected to a post-mortem by a Vet Pathologist to determine whether the cause of death has potential to have resulted from collision with the SeaGen turbine.||No major impacts on marine mammals have been detected across the 3 years of post-installation monitoring.||Completed (2010)|
|Collision||Marine Mammals||Active sonar||An active Sonar monitoring and mitigation system has been in operation on SeaGen since the turbine was commissioned in 2008. This system provided real time subsurface sonar imagery of large objects within 80m of the turbine whilst it is operating.||Overall the seals transited at a relatively higher rate during periods of slack tide, indicating avoidance but also this slack water window when the turbine is not operating or is moving very slowly, ensures that there is always an opportunity for transit past the turbine.||Completed (2010)|
|Collision||Marine Mammals||Harbour seal telemetry||Thirty six seals were fitted with electronic tags. These instruments were glued to the animals’ fur meaning that they detached during the annual moult. They captured location data and information on animals’ diving and haulout behaviour. The 3 deployments took place in 2006 (April-July, pre-installation), 2008 (March – July, during installation and commissioning) and in 2010 (April-July, operation). The seals were captured at sites in Strangford Narrows and the southern islands in Strangford Lough. The three groups of animals tagged contained similar mixes of ages and sexes.||Overall the seals transited at a relatively higher rate during periods of slack tide, indicating avoidance but also this slack water window when the turbine is not operating or is moving very slowly, ensures that there is always an opportunity for transit past the turbine.||Completed (2010)|
|Noise||Marine Mammals||Underwater noise monitoring||Underwater noise measurements were undertaken in Strangford Lough on 23th April 2008 between 09:00 and 21:00 during drilling operations. Background underwater noise measurements were also carried out during periods when no drilling was taking place in order to determine the pre-existing noise levels in the Strangford Lough region.||No major impacts on marine mammals have been detected across the 3 years of post-installation monitoring. |
Findings are described in more detail in the EMP
|Habitat Change||Invertebrates||Benthic hard communities||Four relocatable sample stations were established by installing Ultra Short Baseline (USBL) transceivers. Three stations were placed in line with the rotational axis of the east turbine at 20m, 150m and 300m down/upstream to the south-east (approx.) of the||The data collection and analysis are robust in determining that the changes observed appear to be gradual and in line with natural variation. Colonisation of the device since its installation has replaced the community lost at the device foundations during construction.||Completed (2010)|
|Displacement||Marine Mammals||Shore based survey||Observations carried out between May 2005 and December 2010 from a fixed point on the east shore of the Narrows 10m above Mean High Water. Observations of birds and mammals were recorded along with their location using laser range finding binoculars. During each month a total of 8x3-hour watches were carried out under different tidal states and at different times of the day.||Porpoise activity declined during installation; however there have been no long term changes in abundance of either seals or porpoises which can be attributed to the presence or operation of the device.||Completed (2010)|
|Displacement||Marine Mammals||Passive acoustic monitoring (T-PODs)||The TPOD (‘Timing Porpoise Detector’) is a self-contained submersible unit that includes a hydrophone element, an amplifier, analogue electronic filters and a digital processor, as well as a battery pack and memory. worked by logging the start and end of echolocation clicks of porpoises and dolphins. The basic metric they generated was expressed at detection positive minutes (DPM) which consists of any minute in which a porpoise click train was detected. TPODS logged continuously 24 hours a day.||Seals and porpoises regularly transit past the operating turbine, clearly demonstrating a lack of any barrier effect.||Completed (2010)|
|Displacement||Marine Mammals||Aerial survey||Aerial surveys of seal haul out sites along the Northern Ireland coast between Carlingford Lough and Belfast Lough, including Strangford Lough were carried out annually by SMRU. Surveys were carried out from a helicopter using a thermal imaging camera.||No major changes have been observed in the distribution of haul out and breeding sites.||Completed (2010)|
|Displacement||Birds||Shore based observations||Observations carried out between May 2005 and December 2010 from a fixed point on the east shore of the Narrows 10m above Mean High Water. Observations of birds and mammals were recorded along with their location using laser range finding binoculars. During each month a total of 8x3-hour watches were carried out under different tidal states and at different times of the day.||While some fine scale displacement of birds had been recorded in the immediate vicinity of the device, the overall numbers in the Narrows remained stable.||Completed (2010)|
|Changes in Flow||Physical Environment||Hydrodynamics||Vessel- or bottom mounted ADCP measurement of upstream and downstream flow character and turbulence signature. Diver video survey for scour effects.||The data showed no evidence of significant change to the ambient velocity or flow direction within the Lough, subsequent to the installation of the turbine. The findings show that it is unlikely that marine traffic between Strangford town and Portaferry has been affected. The wake which can be observed on the water surface is not propagated into the water column.||Completed (2010)|