TIP0028
Natural England written submission to the Environmental Audit Committee - Technological Innovations and Climate Change: Tidal Power Inquiry
Overview
As the Government’s statutory advisor on the natural environment, Natural England’s purpose is to ensure that the natural environment is conserved, enhanced, and managed for the benefit of present and future generations, thereby contributing to sustainable development.
We are pleased to contribute to this important inquiry and would like to offer the following points in relation to the question ‘What are the environmental impacts of tidal schemes and how can these be minimised?’ posed by the Committee.
Climate change represents the most serious long-term threat to the natural environment. Natural England believes that tidal energy developments in our seas, appropriately designed and sited, could play an important part in reducing greenhouse gas emissions and contribute towards a low carbon, more efficient and sustainable energy system, which is needed to tackle climate change. However, as with most developments, tidal energy developments, together with their ancillary infrastructure (transmission lines, substations and access roads) can impact upon the marine and terrestrial environment. The significance of those impacts will vary depending on the sensitivity of the receiving environment in each location.
Tidal energy schemes therefore need to be sensitively located and constructed in ways to ensure marine ecosystems are protected, can recover and where possible can be enhanced. All schemes should aspire to deliver a net gain footprint from development.
1.1 The environmental impacts of tidal range schemes are numerous and diverse and can in some circumstances have very significant ecological consequences. Exactly what kind of impact a project will have on the environment depends on the design of the scheme and its location. No two proposals are likely to have the same effect and some designs and / or locations will result in very different environmental consequences.
1.2 There are various types of tidal range scheme such as lagoons, barrages or fences. They have the same general objective of impounding or restricting the flow of water in order to channel it through electricity producing turbines. This act of impounding or altering tidal flow can reduce how much of the impounded shoreline is exposed at low tide and also reduce the amount of time it is exposed, which can be damaging for wildlife. For example within an estuary or bay the intertidal foreshore of mud and sand is often an important feeding habitat for many types of birds and other organisms. A reduction in the amount of time these intertidal areas are exposed to the air can effectively reduce the amount of food available to animals and birds. Many of these intertidal mud and sand flats are internationally important habitats for birds and other wildlife and protected under environmental designations.
1.3 Reductions in tidal exposure could potentially be addressed by using emerging technologies which can generate electricity using lower hydraulic head i.e. by using slower flows than previous turbine technologies and which produce electricity on both flood and ebb flows. By using low head turbines the water may not need to be impounded for so long to generate the necessary flow strength which could in turn reduce the changes in intertidal exposure.
1.4 Careful design and location can also reduce impacts related to tidal exposure. For example, a tidal lagoon which encircles an area with limited amounts tidal foreshore or lower sensitive intertidal habitats will have a smaller ecological impact (due to tidal exposure changes) when compared with a scheme which impounds a large natural estuary with lots of high value intertidal mud and sand.
1.5 Tidal range schemes have a number of other environmental impacts which are important to note, including:
1.5.1 Fish migration can be effected because coastal areas with a high tidal range often have significant populations of migratory fish such as salmon, lamprey and smelt, some of which are protected under national and international designations. Large structures which impede, restrict or alter the flow of water could significantly hinder or prevent their movement into key estuaries or rivers, which could damage the population. The use of technologies which allow fish passage and prevent fish being injured by the turbines are a possibility but are largely untested on large coastal schemes.
1.5.2 Tidal range schemes often have large scale effects on natural water movement. This can have significant consequences on the movement of sediment e.g. sand into estuaries and along the coast. These changes in sediment movement can starve habitats of required sediment e.g. sand dunes or sand banks or it may cause sediment to accumulate where it could smother existing sensitive habitats such as reef or mussel beds. In addition, the early life stages of many marine organisms see them floating in the water column as plankton before they settle on the seabed or mature into fully grown adults. Large scale alterations in water flow could prevent these young organisms reaching areas they once could. For example cockles and mussels may not be able to settle and grow on beds they historically thrived on.
1.5.3 Lastly, by impounding or restricting the natural flow of water on the coast, tidal range schemes have the potential to significantly affect water quality. For example nutrients, sediments and other elements are transported down river into coastal areas which are then flushed away and diluted by tidal movements. If a tidal scheme is poorly located or designed it may reduce this flushing action and reduce water quality.
1.5.4 An additional consideration for tidal range schemes is that they are large scale permanent structures with design lives of >100 years. This obviously provides benefits for energy security but does mean that if unexpected adverse environmental impacts are observed after construction then options for mitigating or remediating these will be limited.
2.1 The main ecological concerns regarding tidal stream developments are associated with how they interact with wildlife. The presence of turbines can change the behaviour of marine mammals, birds and migratory fish, and in some circumstances can lead to more direct interactions such as collisions. Operational underwater noise can also be a significant impact on some populations. Seabed habitats can also be lost or changed through placement of devices. Tidal stream schemes located in areas of fast water currents, often have high biodiversity interest and support rare species. The impacts of developments could be reduced by locating schemes away from headlands and straits where there are habitats or populations of birds, fish or mammals which are important and sensitive . Feeding and breeding sites in particular for marine mammal species should be avoided when tidal stream sites are selected.
2.2 The environmental consequences of the construction (and decommissioning) of tidal schemes could be similar to other large-scale marine or coastal development projects. Processes would include the operation of heavy lifting barges, increased shipping activity, anchoring, pile driving, leading to the introduction of noise, vibration, disturbance of the seabed, resuspension of sediment, and disturbance to marine organisms. Seasonal and timing restrictions can be used to mitigate effects in part.
2.3 Installation of transmission cables will cause disturbance of the seabed and impacts on benthic habitats. Cables also act as sources of electromagnetic fields (EMF), although mitigation measures, such as burying cables, should reduce the risk of significant impacts. Protection of cables by rock placement can add to habitat loss and disturbance.
3.1 For some schemes there may be significant visible infrastructure above the water surface and there could be significant visual impact on locations designated for their natural beauty.
3.2 There are considerable evidence gaps associated with many of the potential interactions with the natural environment and early prioritisation of research and data collection is needed to establish baselines and provide robust impact monitoring information.
3.3 Investment in alternative technologies which reduce environmental impacts is needed, for example low noise construction technology, low impact cable installation techniques and infrastructure which can be removed on decommissioning.
3.4 Improvements to the grid connection process should be made through strategic consideration of the need for and use of existing and future connection points, taking into account their onshore and offshore environmental impacts and ensuring opportunities for good design are taken to minimise impacts and provide a positive environmental legacy. Consideration of non-linear connections and joint use of cables by multiple asset owners or users could have the potential to reduce environmental impacts.
3.5 Natural England recognises the importance of effective prioritisation of the use of sea space by Government in order to manage the overlap of development with marine protected areas – as such, measures to compensate for (or offset) the impacts on biodiversity can be considered at a strategic planning level and early stage of any tidal energy plan.
3.6 To date there are no schemes producing significant amounts of electricity from tidal range power in the UK. With regard to tidal stream energy there are schemes which produce electricity in Scotland but these have only come on line recently. Therefore, considerable uncertainty exists as to how the potential environmental impacts of tidal energy may manifest in practice.