Marine Current Turbines Ltd have constructed the first tidal power turbine in the UK off the coast of Devon, which has been in operation for over two years. A second, larger turbine to be known as “Seagen” is proposed in order to further develop this technology through investigation of its engineering, management systems and environmental impacts. Of several potential locations around the UK, the Strangford Lough Narrows has been chosen due to its wave-sheltered environment, its fast clearly defined directional tidal flows within a small sea level range, and its proximity to excellent services and local technical support. Experience off the Devon coast has shown that it is vital to have easy, frequent and consistent access to the test location, but this has been severely restricted due to weather exposure. This location will provide the opportunity to study the technology more frequently than exposed sites such as Devon, thereby ensuring full knowledge of both technical and environmental impacts is gained before commercial scale ventures are proposed in more remote offshore locations.
Seagen will be a twin turbine system with a mobile cross arm on a single supporting pile 3m in diameter and 9m above the average sea level as illustrated below. 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.
The Seaflow design allows for the cross beam and turbines to be raised above the water for maintenance and inspection. The system will be installed from a barge by drilling a hole in the sea bed and grouting the pile in place, and a location map is provided below. The electricity connection will be made to the national grid by drilling a small hole horizontally from the western side of the Narrows under the shore and sea bed, carefully directing the drill to emerge from the Lough bed within 15m of the turbine base. The system will be removed in approximately 2-5 years once it has successfully addressed all relevant technical and environmental performance requirements, leaving a 3m diameter depression slightly below sea bed level which will naturally fill with cobbles and boulders as a result of tidal flows.
This Environmental Statement has been prepared in support of Marine Current Turbine Ltd’s application to construct Seagen under the Food and Environment Protection Act (1985) in accordance with recognised environmental impact assessment procedures. The assessment involves the application of a standardised process to identify the likely impacts from all relevant issues identified through an initial scoping process and wider consultation with regulators, non-governmental organisations and other interested parties. As the proposed location falls within an area protected under domestic and European law, information considered relevant to a further ‘appropriate assessment’ process has been collected or collated from other sources in order to assist the Environment and Heritage Service as ‘Competent Authority’ in determining if the project is unlikely to damage the protected features.
Strangford Lough hosts internationally important subtidal and intertidal rock, sand and mud habitats and horse mussel beds. The Lough also supports internationally significant wintering waders, breeding terns and important populations of common seals. For these reasons all or parts of the Lough have been recognised as a Special Area of Conservation, Special Protection Area, Ramsar site, Area of Special Scientific Interest, National Nature Reserve and a Marine Nature Reserve. Extensive consultation with regulators, non-governmental organisations and the public has been carried out in order to ensure all relevant issues are considered. This process identified general local support for the project and support from regulators and non-governmental organisations for the need to develop this sustainable technology. It also highlighted concerns that the installation and operation of Seagen should not harm or deter seals, cetaceans or basking shark using the area for feeding or access to breeding areas in the main body of the Lough, nor should it have a detrimental effect on the internationally important breeding tern populations or the subtidal wildlife habitats in Strangford Lough. This was noted as particularly important in relation to recent discoveries on the extent of damage and loss of horse mussel beds.
Modelling of water movement in the Lough was carried out in order to assess the potential impacts of the turbine construction, operation and removal on water speed, the distribution of fine particles and the removal of energy as a result of Seagen. This information was used to predict that it is extremely unlikely that there will be any significant impact on marine life present in the Lough, except out to approximately 4m from the base of the turbine. The overall loss of reef and its marine communities, which will recover once Seagen is removed, is a tiny fraction of the habitat in the context of Strangford Lough and will not add to the justification for its present ‘unfavourable conservation status’ under the EC Habitats Directive.
The potential impacts of operating the turbine on seals have been subject to investigations of historic movement and population observations, extensive discussion with seals experts and academics, surveys and assessment of underwater noise and extensive consultation with experts. Despite this, due to the novel nature of the Seagen design and the lack of knowledge about seal behaviour, it is concluded that enough uncertainty remains over the possible behavioural reaction of seals to Seagen that a definitive assessment cannot be made. The same situation applies to possible impacts on cetaceans and basking shark. In order to ensure that there is an acceptably low risk of damaging these species or affecting their behaviour in ways that may damage their populations in the Lough (in particular common seals protected as part of the Special Area of Conservation) a comprehensive programme of monitoring is proposed alongside monitoring of birds and habitats in the Narrows. This is combined with a formal steering group likely to oversee the programme and a commitment from the developers to work in partnership with regulators and to modify or cease operations if the programme highlights problems or if the regulators and steering group decide it is necessary. This adaptive management approach is in line with recent developments on use of the ‘precautionary principle’ in order to facilitate sustainable development within protected areas such as Strangford Lough. Impacts on other ecological features in the area are considered highly unlikely due to the scale and duration of the commissioning process.
The effect of the project on navigation is likely to be beneficial due to the appropriate marking and lighting of the structure above sea level. The risk to vessels known to use the Narrows posed by operating rotors is generally negligible as the tips will be at least 3m below the lowest astronomical tide level. An area around the turbine may also be noted on charts as an ‘Area To Be Avoided’, providing further security.
Seagen is considered likely to be slightly beneficial to local businesses through increased visitors and workers to the area, and it is considered unlikely to have any effect on commercial fishing in the Narrows due to the current ban on activities that would normally fish the proposed location and the location of the turbine within the deep water of the middle of the Narrows. No impacts on archaeology are anticipated at the proposed turbine location.
It is likely that Seagen will affect the landscape and cause some visual disturbance at all stages of the project as it will be visually obvious from Portaferry and will affect the relatively open seascapes seen from the ferry crossing. The level of this impact is mainly due to the requirement for specific colours and lighting on the superstructure for navigation as there are several similar beacons at various locations through the Narrows. The most significant visual impacts will be intermittent during maintenance periods when the cross arm is raised above sea level.
The project will have a negligible impact on road traffic in the area as most materials will be brought to the site by sea. The main sources of noise above water level will be power generators on board the jack-up barge and in the directional drilling compound during construction. Neither of these are expected to be significant as the noise ratings indicate levels will be low within very short distances from the source.
Impacts on air quality in the area are expected to be negligible in the short and medium term, but it must be recognised that this clean and sustainable energy source represents an opportunity to facilitate long term improvements in air quality and will contribute to the achievement of national and international targets to reduce emissions of gases attributed to accelerating climate change.
In conclusion, Seagen is a critical stage in the development of renewable tidal energy in the UK. Strangford Lough represents an ideal location for this temporary installation the environmental impacts have been assessed and are generally considered unlikely to be significant. Due to the novel nature of the proposed development and the lack of definitive information some uncertainty remains as to its likely impacts on marine mammals and basking shark.