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Environmental Aspects
Introduction
As part of the planning process of major energy source projects the impact on the environment from the construction process, the operation for the lifetime of the project and the decommissioning of the project have to be considered. Therefore when planning the installation of marine current turbine (MCT’s) farms their potential benefits and threats to the environment have to be taken into account.
Due to the fact that MCT’s are marine based the following general environmental aspects would have to be considered:
- Biological Impacts
- Conflicts of interest
- Ship collision risks
- Visual impacts
There are several areas that an MCT scheme would have an impact positively and negatively on the environmental aspects. These areas are as follows:
Scheme site selection
This area affects all aspects of environmental impact, and they are covered in more detail in other sections, but there are some general considerations that have to be taken into account. These are:
- Is proposed site on or near a designated conservation area? This is to prevent any undue damage to those areas.
- Busy shipping lanes should be avoided.
- Is there in place mechanisms to avoid ships sailing into scheme and causing a collision? This can be remedied by including visual and audio warnings around the site to make ships aware they are entering the schemes boundaries.
- Are there other conflicts of interest for the site such as it is an area used for fishing, there are possible raw material deposits in the ocean bed, or it could be a site of particular interest to marine archaeologists.
- Will the site adversely affect current flow patterns? This could result in sediment transport slowing and possibly falling to the seabed having a smother effect on seabed flora and fauna.
- How visible is the site from shore. There may be public opposition to a site that is regarded to be visually obtrusive within the landscape.
Installation of MCT Scheme
The environmental impacts that would result from an MCT scheme installation would be as follows:
- The laying of cables: When laying the cables a trench would have to be made. This would have an impact on a significant area of the seabed. This involves dredging and possible removal of benthic communities. The trenching of cables would also mobilise sediment, which would increase the schemes impact zone. To combat this due consideration would have to be made into how sensitive the area of seabed would be to these actions, and possible modelling of sediment travel and dispersal could be performed.
- Installation of MCT and substation piles: The process involved in installing the MCT and substation piles would have a couple of major impacts. The first being the driving of monopiles into the seabed. This involves them being hammered into the seabed this hammering action would result in noise being created above and below the water level. The affected parties by this action would be benthic communities and the public that could be disturbed by the extra noise pollution. The second would be the mobilisation of sediment through the boring of holes for monopiles and from the action of driving the monopiles into the seabed. Though, both of these impacts would only be temporary.
- Extra marine activity: This would encompass additional boat, barge and helicopter activity resulting in increased noise pollution and greenhouse gas emissions resulting from these vehicles. This impact would be for a limited period.
- Onshore construction: Impacts would result from the construction/upgrading of ports that would support the supply of materials to the MCT scheme installation site. There would also be additional impacts if road systems have to be constructed or upgraded for access to these ports.
Size of scheme
Dependant on the size of the MCT scheme the level of environmental impact would vary. Therefore larger schemes would have a greater impact:
- Altering of currents: Larger schemes could have a problem of either altering current flows and/or reducing current velocities. Both of these factors would influence the physical processes caused by the current flow. The resulting impacts could be seabed-scouring, changes in seabed morphology and sediment distributions. This could be remedied by the constant monitoring of these impacts as a site was installed and its capacity increased.
- Shipping: With a larger scheme there could be an increased risk of ships or boats entering a schemes perimeter. As mentioned before, due measures would have to be taken to ensure that a scheme was clearly marked to avoid any possible collisions with marine vessels.
Spacing of MCT units within scheme
The potential environmental impacts for MCT unit spacing within a scheme would have some similarities to impacts due to size of scheme and some additional:
- Altering of currents: The closer packing density of a scheme the greater the influence that it will have an impact on the current hydrology and seabed morphology.
- Effects on sea mammals and basking sharks: The greater the packing density the greater the risk the scheme runs of acting as a barrier to the movements of sea mammals (such as whales, porpoises …etc) and basking sharks. This could have possible ramifications on their breeding and feeding habits.
General operation of scheme
The previous environmental impacts dealt with a schemes installation, the following impacts would be due to it operating under normal conditions:
- Dangers to marine benthos communities from blades: Studies carried out for MCT Ltd have shown that the danger posed to fish and marine mammals from the blades would be minimal.
- Noise and vibration: Generally under normal operating conditions majority of noise and vibrations would occur underwater. The impacts would be cause by the rotation of the rotors and gearbox of the MCT unit and any other forces causing a resonance in the monopile construction. If the noise created by the MCT units is greater than the underwater background noise (i.e. ambient noise, especially from ships) then this could have a potential on marine fauna.
- Electromagnetic effects: The electric cables would have the possible effect of changing the surrounding electromagnetic field. This would impact on a range of species but most of all elasmobranches, i.e. sharks, skates and rays. These species are likely to be affected by this due to their use of natural electrical charge to sense other individuals and prey. If the cables were to be laid within an area that these species are prevalent then it could be determined at what depth the cables would have to be buried that would cause minimal impact but also be economically feasible.
- Operational pollution: The most likely cause of operational pollution would be the leaking of gearbox fluid into the sea, but to ensure that this risk would be minimised a non-toxic fluid could be used.
- Operational benefit: There could be a marine environment benefit within the operation of a MCT scheme. Due to a scheme being a exclusion zone to fishing and other marine vessels then it could potentially act as an artificial reef allowing marine benthos communities to feed and spawn without being over fished.
Decommissioning of scheme
The full impacts of removing cables and turbines have to be taken into account when decommissioning a scheme. These would have similar impacts as previous impacts, such as noise, vibration, mobilising of sediment …etc but these would only be temporary.
Conclusions
- MCT farms will have potential impacts on the environment at various levels throughout their lifespan from construction, operation to decommissioning.
- The smaller the scheme the less the environmental impact would be.
- MCT’s could be installed in batches (of 10 up to 20) and this would allow quantative analysis, such as investigations into sediment transport, seabed scouring and effects on marine benthos, to be undertaken into the environmental impacts of increasing capacity at a given site.
- Consideration could be made into developing several different smaller sites to reduce local impacts but also reaching the desired cumulative capacity.
References
www.mct.com
www.offshorewind.com
Wave and marine current energy, DTI report number FES-R-132
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