Offshore wind energy - draft sectoral marine plan: strategic environmental assessment

Involves the construction of gravity foundations directly on the seabed.

Gravity base foundations consist of concrete or steel structures, often internally ballasted to create a large mass on the seabed.

May be suitable for depths of 30–60m of water.

Able to be floated and towed out to windfarms and installed without specialist marine equipment with minimum seabed preparation.

Can incorporate scour protection, has low maintenance requirement and can be removed upon decommissioning.

Like typical oil and gas pile designs.

Involves long steel tubes (monopiles) driven into the seabed using a hydraulic piling hammer, assisted by drilling where necessary.

Generally suitable for turbines in shallower waters, although ongoing research into deeper applications (i.e. >25m).

Considered likely to continue to be used in shallow waters in the short-term.

Generally consist of turbines attached to multi-legged structures secured to a series of piles driven into the seabed.

Jackets are mounted on a 3 or 4 legged steel lattice rising out of the sea.

Tripods have a single vertical column above the water, with diagonal braces attaching the turbine mast to a 3-legged structure below the water surface and attached to the seabed.

Jackets in particular are very common in the oil and gas sector, with a number of variations available.

Consists of a structure or suction caisson resembling an upturning bucket placed on a pre-prepared levelled seabed.

Placement is based on a pressure differential attachment to the seabed. The foundations weight combined with the hydrostatic pressure on the caisson when the internal water is pumped out of it provides the force to hold the bucket structure in place.

Can involve use of single or multiple caisson attachments.

Is generally considered a future technique.

Have a variety of types being investigated, including: SPAR and Tension Leg Platform (TLP) such as the 'Hywind' floating device equipped with a cement ballast (used in the first floating wind array (30MW) at Hywind Scotland commissioned in 2017), and 'Windfloat' – a 3 cornered pontoon (installed in Portugal in 2011).

Likely involve attachment to the seabed using anchors (i.e. gravity anchors, moor lines, etc.).

Considered an emergent technology, with no full scale commercial arrays to date.

Summary of key potential effects:

• Physical disturbance during device installation and operation
• Habitat exclusion and species displacement due to device presence and operation
• Potential for creation of artificial habitats underwater and bird aggregation on surface-piercing structures
• Noise and vibration during surveys, unexploded ordnance clearance, construction (particularly piling) and from device operation
• Risk of bird collision with operating devices (e.g. foraging, migration)
• Increased suspended sediment/turbidity from seabed disturbance during device installation and cable trenching
• Substratum loss, caused by placement of devices and attaching support structures and cabling on the seabed

Key measures to prevent adverse effects may include: avoidance of sensitive sites; avoidance of sensitive seasons during installation (e.g. breeding); protocols (such as use of Marine Mammal Observers) to ensure noisy construction activities do not occur when marine mammals are in close proximity; effective device design and project-specific studies to help design appropriate mitigation; carry out detailed routing studies at project level in accordance with 'Holford Rules' best practice guidance on routeing overhead transmission lines onshore.

Marine Mammals and fish

Underwater noise and vibration during installation has the potential to affect marine fauna (e.g. seals, otters, cetaceans, basking sharks and other species of fish potentially sensitive to underwater noise). There is also the potential for cumulative effects from multiple noise sources audible to marine mammals and fish during installation and increased vessel disturbance.

Potential displacement or disturbance of marine fauna through a combination of factors including noise (and multiple noise sources), vibration, visual and light intensity changes, water quality changes, habitat disturbance or the presence of structures and vessels.

Potential for injury with marine mammals during installation period (i.e. risk of injury to seals and dolphins during placement of foundations).

Potential for electro-magnetic field (EMF) effects associated with cabling and grid connection infrastructure.

Cumulative effects may occur, particularly affecting mammals and migratory fish including diadromous fish, from an increased number of barriers affecting movement (i.e. device arrays, construction vessels/equipment, etc.).

Birds

Potential for bird-strike with turbine blades is likely to be site-specific.

Potential for diving bird collisions with support devices (i.e. mooring cables if used). However, this is likely to be site and device-specific, and the likelihood of occurrence is not currently known.

Potential disturbance of diving bird foraging areas due to surface noise, visual and light intensity changes, water quality changes, habitat disturbance or the presence of structures and vessels.

Benthic Habitats

Potential for creation of artificial habitats for marine organisms resulting from the presence of new structures. This may be aided by reductions in commercial fishing (e.g. trawling) in areas where wind farms are sited, as this may enhance biodiversity. These benefits could last for the life of the project, or potentially longer depending on the decommissioning scheme.

Loss of seabed habitat from the placement of gravity foundation directly on/into the seabed, and potential for adverse effects from sourcing of fill or dredged material for use in the gravity-based foundation (i.e. potential risk to marine fauna from dredging activities, turbidity, potential release of contaminated materials, loss of habitat at source, etc.).

Direct adverse effects on benthic habitats, particularly sensitive habitats such as shellfish growing waters, from sediment dispersion and deposition in the construction phase of works (i.e. east of Scotland (e.g. Bell Rock, Inch Cape, Neart na Gaoithe and Forth Array) and west of Scotland (e.g. Argyll Array, Islay and Kintyre) where shellfish waters are prevalent.

It is anticipated that many of the construction and decommissioning effects may be temporary and reversible (i.e. removal of the gravity base structure and rehabilitation of the seabed). However, some effects on biodiversity experienced during operation of wind farms are likely to be permanent and irreversible.

Marine Mammals and fish

Underwater noise and vibration on marine fauna (e.g. seals, otters, cetaceans, basking sharks and other species of fish potentially sensitive to underwater noise) during piling. There is also the potential for cumulative effects from multiple noise sources audible to marine mammals and fish during piling and installation of turbines, and increased vessel disturbance.

Potential displacement or disturbance of marine fauna through a combination of factors including noise (and multiple noise sources), vibration, visual and light intensity changes, water quality changes, habitat disturbance or the presence of structures and vessels.

Potential for injury with marine mammals during installation period (i.e. risk of injury to seals during piling activities). Can likely be mitigated using a variety of techniques (i.e. piling jackets, soft start, etc.).

Potential for EMF effects associated with cabling and grid connection infrastructure.

Cumulative effects may occur, particularly affecting mammals and migratory fish including diadromous fish, from an increased number of barriers affecting movement (i.e. device arrays, construction vessels/equipment, etc.).

Birds

Potential for bird-strike with turbine blades is likely to be site-specific.

Potential for diving bird collisions with support devices (i.e. mooring cables if used). However, this is likely to be site and device-specific, and the likelihood of occurrence is not currently known.

Potential disturbance of diving bird foraging areas due to surface noise, visual and light intensity changes, water quality changes, habitat disturbance or the presence of structures and vessels.

Benthic Habitats

Potential for creation of artificial habitats for marine organisms resulting from the presence of new structures. This may be aided by reductions in commercial fishing (e.g. trawling) in areas where wind farms are sited, as this may enhance biodiversity. These benefits could last for the life of the project, or potentially longer depending on the decommissioning scheme.

Loss of seabed habitat from the installation process for monopiling into the seabed.

Direct adverse effects to benthic habitats, particularly sensitive habitats such as shellfish growing waters, from sediment dispersion and deposition in the construction phase of works (i.e. east of Scotland (e.g. Bell Rock, Inch Cape, Neart na Gaoithe and Forth Array) and west of Scotland (e.g. Argyll Array, Islay and Kintyre) where shellfish waters are prevalent.

It is anticipated that many of the construction and decommissioning effects may be temporary and reversible (i.e. removal of the turbines with the monopole remaining in situ). However, some effects on biodiversity experienced during operation of wind farms are likely to be permanent and irreversible.

Marine Mammals and fish

Underwater noise and vibration during piling and the placement of tripod/jacket structures, with potential effects to marine fauna (e.g. seals, otters, cetaceans, basking sharks and other species of fish potentially sensitive to underwater noise). There is also the potential for cumulative effects from multiple noise sources audible to marine mammals and fish during piling and installation of turbines, and increased vessel disturbance.

Potential displacement or disturbance of marine fauna through a combination of factors including noise (and multiple noise sources), vibration, visual and light intensity changes, water quality changes, habitat disturbance or the presence of structures and vessels.

Potential for injury with marine mammals during installation period (i.e. risk of injury to seals during piling activities). Can likely be mitigated using a variety of techniques (i.e. piling jackets, soft start, etc.).

Potential for EMF effects associated with cabling and grid connection infrastructure.

Cumulative effects may occur, particularly affecting mammals and migratory fish including diadromous fish, from an increased number of barriers affecting movement (i.e. device arrays, construction vessels/equipment, etc.).

Birds

Potential for bird-strike with turbine blades is likely to be site-specific.

Potential for diving birds strike to support devices (support structures, mooring cables if used) is likely to be site-specific, and the likelihood of occurrence is not currently known.

Potential disturbance of diving bird foraging areas due to surface noise, visual and light intensity changes, water quality changes, habitat disturbance or the presence of structures and vessels.

Benthic Habitats

Potential for creation of artificial habitats for marine organisms resulting from the presence of new structures. This may be aided by reductions in commercial fishing (e.g. trawling) in areas where wind farms are sited, as this may enhance biodiversity. These benefits could last for the life of the project, or potentially longer depending on the decommissioning scheme.

Loss of seabed habitat from the installation process for piling into the seabed.

Direct adverse effects to benthic habitats, particularly sensitive habitats such as shellfish growing waters, from sediment dispersion and deposition in the construction phase of works (i.e. east of Scotland (e.g. Bell Rock, Inch Cape, Neart na Gaoithe and Forth Array) and west of Scotland (e.g. Argyll Array, Islay and Kintyre) where shellfish waters are prevalent.

It is anticipated that many of the construction and decommissioning effects may be temporary and reversible (i.e. removal of the turbines and support structures, and piles remaining in situ). However, some effects on biodiversity experienced during operation of wind farms are likely to be permanent and irreversible.

Marine Mammals and fish

Underwater noise and vibration during installation has the potential to effect marine fauna (e.g. seals, otters, cetaceans, basking sharks and other species of fish potentially sensitive to underwater noise). There is also the potential for cumulative effects from multiple noise sources audible to marine mammals and fish during installation and increased vessel disturbance.

Potential displacement or disturbance of marine fauna through a combination of factors including noise (and multiple noise sources), vibration, visual and light intensity changes, water quality changes, habitat disturbance or the presence of structures and vessels.

Potential for injury with marine mammals during installation period (i.e. risk of injury to seals and dolphins during placement of foundations).

Potential for EMF effects associated with cabling and grid connection infrastructure.

Cumulative effects may occur, particularly affecting mammals and migratory fish including diadromous fish, from an increased number of barriers affecting movement (i.e. device arrays, construction vessels/equipment, etc.).

Birds

Potential for bird-strike with turbine blades is likely to be site-specific.

Potential for diving bird collisions with support devices (i.e. mooring cables if used). However, this is likely to be site and device-specific, and the likelihood of occurrence is not currently known.

Potential disturbance of diving bird foraging areas due to surface noise, visual and light intensity changes, water quality changes, habitat disturbance or the presence of structures and vessels.

Benthic Habitats

Potential for creation of artificial habitats for marine organisms resulting from the presence of new structures. This may be aided by reductions in commercial fishing (e.g. trawling) in areas where wind farms are sited, as this may enhance biodiversity. These benefits could last for the life of the project, or potentially longer depending on the decommissioning scheme.

Loss of seabed habitat from the placement of foundation directly on/into the seabed.

Direct adverse effects to benthic habitats, particularly sensitive habitats such as shellfish growing waters, from sediment dispersion and deposition in the construction phase of works (i.e. east of Scotland (e.g. Bell Rock, Inch Cape, Neart na Gaoithe and Forth Array) and west of Scotland (e.g. Argyll Array, Islay and Kintyre) where shellfish waters are prevalent.

It is anticipated that many of the construction and decommissioning effects may be temporary and reversible (i.e. removal of the caisson). However, some effects on biodiversity experienced during operation of wind farms are likely to be permanent and irreversible.

Marine Mammals and fish

Underwater noise and vibration during installation (placement of concrete anchors and mooring lines) has the potential to effect marine fauna (e.g. seals, otters, cetaceans, basking sharks and other species of fish potentially sensitive to underwater noise). There is also the potential for cumulative effects from multiple noise sources audible to marine mammals and fish during installation and increased vessel disturbance.

Potential displacement or disturbance of marine fauna through a combination of factors including noise (and multiple noise sources), vibration, visual and light intensity changes, water quality changes, habitat disturbance or the presence of anchors and vessels.

Potential for EMF effects associated with cabling and grid connection infrastructure.

Cumulative effects may occur, particularly affecting mammals and migratory fish including diadromous fish, from an increased number of barriers affecting movement (i.e. device arrays, construction vessels/equipment, etc.).

Birds

Potential for bird-strike with turbine blades is likely to be site-specific.

Potential for diving bird collisions with support devices (i.e. mooring cables, anchors, etc.). However, this is likely to be site and device-specific, and the likelihood of occurrence is not currently known.

Potential disturbance of diving bird foraging areas due to surface noise, visual and light intensity changes, water quality changes, habitat disturbance or the presence of structures and vessels.

Benthic Habitats

Potential for creation of artificial habitats for marine organisms resulting from the presence of new structures (i.e. gravity anchors). This may be aided by reductions in commercial fishing (e.g. trawling) in areas where wind farms are sited, as this may enhance biodiversity. These benefits could last for the life of the project, or potentially longer depending on the decommissioning scheme.

Loss of small discrete areas of the seabed habitat from the placement of gravity anchors into the seabed.

Direct adverse effects to benthic habitats, particularly sensitive habitats such as shellfish growing waters, from sediment dispersion and deposition in the construction phase of works (i.e. east of Scotland (e.g. Bell Rock, Inch Cape, Neart na Gaoithe and Forth Array) and west of Scotland (e.g. Argyll Array, Islay and Kintyre) where shellfish waters are prevalent.

It is anticipated that many of the construction and decommissioning effects may be temporary and reversible (i.e. removal of the gravity anchors and removal of the floating turbine structure). However, some effects on biodiversity experienced during operation of wind farms are likely to be permanent and irreversible.

Summary of key potential effects on population and human health:

• Flicker and noise effects, particularly for near-shore devices
• Displacement of other marine activities (i.e. fishing, recreational, shipping, aquaculture)
• Reductions in the safety of navigation
• Risk of collision by other marine users with turbine structures and installation/maintenance vessels

Key measures to prevent adverse effects may include: siting devices away from spatially constrained areas and areas with high vessel densities; siting devices in open water; making use of industry guidance on assessment of effects and use of aids to navigation; use of notifications such as 'Notices to Mariners', publicising information at marina, and Sailing Directions; and adhering to appropriate safety regulations.

Provision of a new renewable energy supply for the projected increase in the Scottish population for the life of an operating wind farm.

Potential for flicker and noise effects, particularly if located near-shore.

Potential effects on other marine users (i.e. fishing, recreational, shipping, aquaculture) including the potential displacement of these activities, the risk of collision with turbine structures, and visual effects associated with the presence of the turbines. Upon decommissioning, these effects will likely be reversible.

Potential issues with navigation, although it is noted that this may be managed through the selection of appropriate sites and consultation with the maritime and Coastguard Agency (MCA) to ensure that there are no hazards to shipping.

Provision of a new renewable energy supply for the projected increase in the Scottish population for the life of an operating wind farm.

Potential for flicker and noise effects, particularly if located near-shore.

Potential effects on other marine users (i.e. fishing, recreational, shipping, aquaculture) including the potential displacement of these activities, the risk of collision with turbine structures, and visual effects associated with the presence of the turbines. Upon decommissioning, these effects will likely be reversible.

Potential issues with navigation, although it is noted that this may be managed through the selection of appropriate sites and consultation with the maritime and Coastguard Agency (MCA) to ensure that there are no hazards to shipping.

Potential for commercial effects on the fishing and shipping industries (i.e. loss of access to fishing areas, reduced catches in such areas from displacement of fish populations, collision risk).

Requirement for the installation of new transmission infrastructure to connect the devices to the grid (i.e. cables on the seabed, terrestrial infrastructure) could, in some circumstances, affect recreational and commercial activities. Potential effects are likely to be site and development specific.

Potential for upgrading of nearby port/harbour infrastructure to install and/or maintain turbines.

Provision of a new renewable energy supply for the projected increase in the Scottish population for the life of an operating wind farm.

Potential for flicker and noise effects, particularly if located near-shore.

Potential effects on other marine users (i.e. fishing, recreational, shipping, aquaculture) including the potential displacement of these activities, the risk of collision with turbine structures, and visual effects associated with the presence of the turbines. Upon decommissioning, these effects will likely be reversible.

Potential issues with navigation, although it is noted that this may be managed through the selection of appropriate sites and consultation with the maritime and Coastguard Agency (MCA) to ensure that there are no hazards to shipping.

Potential for commercial effects on the fishing and shipping industries (i.e. loss of access to fishing areas, reduced catches in such areas from displacement of fish populations, collision risk).

Requirement for the installation of new transmission infrastructure to connect the devices to the grid (i.e. cables on the seabed, terrestrial infrastructure) could, in some circumstances, affect recreational and commercial activities. Potential effects are likely to be site and development specific.

Potential for upgrading of nearby port/harbour infrastructure to install and/or maintain turbines.

Provision of a new renewable energy supply for the projected increase in the Scottish population for the life of an operating wind farm.

Potential for flicker and noise effects, particularly if located near-shore.

Potential effects on other marine users (i.e. fishing, recreational, shipping, aquaculture) including the potential displacement of these activities, the risk of collision with turbine structures, and visual effects associated with the presence of the turbines. Upon decommissioning, these effects will likely be reversible.

Potential issues with navigation, although it is noted that this may be managed through the selection of appropriate sites and consultation with the maritime and Coastguard Agency (MCA) to ensure that there are no hazards to shipping.

Potential for commercial effects on the fishing and shipping industries (i.e. loss of access to fishing areas, reduced catches in such areas from displacement of fish populations, collision risk).

Requirement for the installation of new transmission infrastructure to connect the devices to the grid (i.e. cables on the seabed, terrestrial infrastructure) could, in some circumstances, affect recreational and commercial activities. Potential effects are likely to be site and development specific.

Potential for upgrading of nearby port/harbour infrastructure to install and/or maintain turbines.

Provision of a new renewable energy supply for the projected increase in the Scottish population for the life of an operating wind farm.

Potential for flicker and noise effects, particularly if located near-shore.

Potential effects on other marine users (i.e. fishing, recreational, shipping, aquaculture) including the potential displacement of these activities, the risk of collision with turbine structures, and visual effects associated with the presence of the turbines. Upon decommissioning or movement of the array (if undertaken) these effects will likely be reversible.

Potential issues with navigation, although it is noted that this may be managed through the selection of appropriate sites and consultation with the maritime and Coastguard Agency (MCA) to ensure that there are no hazards to shipping.

Potential for commercial effects on the fishing and shipping industries (i.e. loss of access to fishing areas, reduced catches in such areas from displacement of fish populations, collision risk).

Requirement for the installation of new transmission infrastructure to connect the devices to the grid (i.e. cables on the seabed, terrestrial infrastructure) could, in some circumstances, affect recreational and commercial activities. Potential effects are likely to be site and development specific.

Potential for upgrading of nearby port/harbour infrastructure to install and/or maintain turbines.

Summary of key potential effects on geology:

• Disturbance or damage to coastal Geological SSSIs and Geological Conservation Review sites (GCRs) during installation works.
• Changes in coastal processes due to presence of devices in water column.
• Seabed contamination and water quality (including disposal areas) during installation works.

Key measures to prevent adverse effects may include: siting devices away from sensitive and designated areas; using best practice methodologies and technologies to minimise potential effects during installation; adoption of appropriate management planning in installation works.

Direct adverse effects to the seabed are likely from preparation of the seabed (i.e. limited dredging) and in the placement of the gravity-base foundation and associated scour protection on the seabed.

Potential alteration of sediment dynamics and tidal flows/fluxes from the presence of gravity-based foundation structures on the seabed and presence of turbine masts and support structures in the water column. Scouring, deposition and abrasion (particularly in the placement of mooring lines, if used) may also occur due to the foundation structures present at the seabed. However, it is assumed that scour protection would be used for such foundation structures and this may alleviate such risks.

Effects from construction and decommissioning works are likely to be temporary and are often reversible. However, effects from seabed preparation works are likely to be permanent.

Sourcing of fill or dredged material for gravity foundations, and potential effects of taking fill from other areas. If terrestrial fill or dredged material is used, potential effects at the source may include: loss of substrata or habitat if taken from suitable undisturbed areas; Potential for release of contaminated materials bonded to dredged sediments; potential for cross-contamination from source areas to windfarm site, particularly if sourced from shipping lanes or harbours; potential effects on hydrodynamics and water flows at the source location from the removal of sediments; reduced water quality and increased turbidity from sediment disturbance during dredging operations; and potential effects for marine fauna and flora, including the disturbance and physical injury risk from dredging operations. If material is sourced from the terrestrial environment it will have effects associated with the removal of material and its transportation.

Potential for direct adverse effects to the seabed during piling operations.

Potential alteration of sediment dynamics and tidal flows/fluxes from the presence of piles and turbine structures into the seabed and presence of the turbine masts and support structures in the water column. Effects such as scouring, deposition, abrasion (during installation of piles only) and vibration may also occur due to the installation and operation of the wind turbines.

Effects from construction and decommissioning works are likely to be temporary and are often reversible.

Potential for direct adverse effects to the seabed during piling operations.

Potential alteration of sediment dynamics and tidal flows/fluxes from the presence of piles and turbine structures into the seabed and presence of turbine masts and support structures in the water column. Effects such as scouring, deposition, abrasion (during installation of piles only) and vibration may also occur due to the installation and operation of the wind turbines.

Effects from construction and decommissioning works are likely to be temporary and are often reversible.

Likely direct adverse effects to the seabed from the preparation of seabed areas (i.e. dredging) and placement of caisson support structures directly on the seabed (e.g. turbidity, sediment disturbance, loss of geology, potential for release of contaminated materials bonded to sediments).

Potential alteration of sediment dynamics and tidal flows/fluxes from the presence of gravity-based foundation structures on the seabed and presence of the turbine masts and support structures in the water column. Effects such as scouring, deposition and abrasion (particularly in the placement of mooring lines, if used) may also occur due to the foundation structures present at the seabed.

However, it is assumed that scour protection would be used for such foundation structures.

Effects from construction and decommissioning works are likely to be temporary and are often reversible. However, effects from seabed preparation works are likely to be permanent.

Potential for direct adverse effects to the seabed from the placement of gravity concrete anchors and moorings directly on the seabed.

Potential alteration of sediment dynamics and tidal flows/fluxes from the presence of anchor structures gravity-based foundation structures on the seabed and presence of moor lines in the water column. Effects such as scouring, deposition and abrasion (particularly in the placement of mooring lines, if used) may also occur due to the foundation structures present at the seabed.

However, it is assumed that scour protection would be used for such foundation structures.

Effects from construction and decommissioning works are likely to be temporary and are often reversible.

Summary of key potential effects on water quality include:

• Disturbance of sediments during device installation and effects to marine fauna, particularly benthic species (e.g. filter feeders)
• Disturbance of contaminated sediments during device installation, e.g. disposal sites (silt, sand, rock and gravel sites, fish wastes and sludge, munitions dumps, and weapons ranges)

Key measures to prevent adverse effects may include: siting devices away from sensitive areas, disposal sites, munitions dumps and weapons ranges; using best practice methodologies and technologies to minimise potential effects during installation; adoption of appropriate management planning in installation works.

Potential effects to water quality from installation of turbine foundations and structures (i.e. turbidity, seabed disturbance from placement of gravity-based supports, contamination from installation equipment and maintenance vessels) and the potential for associated effects on marine biodiversity, particularly those species dependent on existing water conditions. Potential effects to the ability of fish species to spawn, respire and feed, and on shellfish growing waters in the vicinity of windfarm sites are also noted. However, the significance of these effects is currently uncertain.

Construction and decommissioning effects are temporary and may be reversible.

Potential for cross-contamination in the use of excavated fill material or dredging material as ballast in gravity-based foundations.

Potential effects to water quality from installation of turbine monopiles (i.e. turbidity, seabed disturbance from piling works, contamination from installation equipment and maintenance vessels) and the potential for associated effects on marine biodiversity, particularly those species dependent on existing water conditions. Potential effects to the ability of fish species to spawn, respire and feed, and on shellfish growing waters in the vicinity of windfarm sites are also noted, However, the significance of these effects is currently uncertain.

Construction and decommissioning effects are temporary and may be reversible.

Potential effects to water quality from installation of turbines and associated structures (i.e. turbidity, seabed disturbance from piling works and placement of support structures on the seabed, contamination from installation equipment and maintenance vessels) and the potential for associated effects on marine biodiversity, particularly those species dependent on existing water conditions. Potential effects to the ability of fish species to spawn, respire and feed, and on shellfish growing waters in the vicinity of windfarm sites are also noted, However, the significance of these effects is currently uncertain.

Construction and decommissioning effects are temporary and may be reversible.

Potential effects to water quality from installation of turbine, caisson and seabed preparation activities (i.e. turbidity, seabed disturbance from preparation/levelling of seabed, potential placement of concrete foundations, placement of caisson and support structures, contamination from installation equipment and maintenance vessels) and the potential for associated effects on marine biodiversity, particularly those species dependent on existing water conditions. Potential effects to the ability of fish species to spawn, respire and feed, and on shellfish growing waters in the vicinity of windfarm sites are also noted. However, the significance of these effects is currently uncertain.

Construction and decommissioning effects are temporary and may be reversible.

Potential effects to water quality from installation of mooring anchors (i.e. turbidity, seabed disturbance from placement of gravity anchors, potential for contamination from installation equipment and maintenance vessels) and the potential for associated effects on marine biodiversity, particularly those species dependent on existing water conditions. Potential effects to the ability of fish species to spawn, respire and feed, and on shellfish growing waters in the vicinity of windfarm sites are also noted. However, the significance of these effects is currently uncertain.

Construction and decommissioning effects are temporary and may be reversible.

Benefits through contribution to decarbonisation of electricity generation through the long-term operation of the wind farms (i.e. displacement of non-renewable power generation).

Benefits through contribution to decarbonisation of electricity generation through the long-term operation of the wind farms (i.e. displacement of non-renewable power generation).

Benefits through contribution to decarbonisation of electricity generation through the long-term operation of the wind farms (i.e. displacement of non-renewable power generation).

Benefits through contribution to decarbonisation of electricity generation through the long-term operation of the wind farms (i.e. displacement of non-renewable power generation).

Benefits through contribution to decarbonisation of electricity generation through the long-term operation of the wind farms (i.e. displacement of non-renewable power generation).

Summary of key potential effects on marine and coastal historic environment include:

• Direct disturbance, damage, or destruction of submarine archaeological remains and wrecks during device installation and cable trenching.
• Direct disturbance, damage or destruction of coastal archaeological remains during cable trenching (effects of grid connections are considered separately below).
• Disturbance, damage or loss of archaeological remains and sites during installation of cables and overhead lines and substation construction from onshore grid connections.

Key measures to prevent adverse effects may include: avoid sites of interest and exclusion zones for protected sites; follow Crown Estates 2007 JNAPC Code of Practice for seabed developers; carry out seabed surveys and walkover surveys prior to installation; carry out detailed routing studies at project level in accordance with 'Holford Rules' best practice guidance on routeing overhead transmission lines.

Potential for placement of gravity-based foundations and scour protection on known and designated historic sites and their exclusion zones, World Heritage Sites, coastal listed buildings such as lighthouses, scheduled monuments and other unknown, submerged or non-designated archaeological assets features or paleo-landscapes to create adverse effects.

The potential scouring, siltation and deposition around these important sites located in the vicinity of such devices or arrays may also occur.

However, adverse effects are likely to be avoided through careful siting of individual device foundations and arrays, although this may be more difficult for larger gravity bases or arrays of bases.

Potential for piling operations on or close to known and designated historic sites and their exclusion zones, World Heritage Sites, coastal listed buildings such as lighthouses, scheduled monuments and other unknown, submerged or non-designated archaeological assets features or paleo-landscapes to create adverse effects.

Adverse effects are likely to be avoided through careful siting of device monopiles and arrays.

Potential for piling operations on or close to known and designated historic sites and their exclusion zones, World Heritage Sites, coastal listed buildings such as lighthouses, scheduled monuments and other unknown, submerged or non-designated archaeological assets features or paleo-landscapes to create adverse effects.

Adverse effects are likely to be avoided through careful siting of device piles and arrays.

Potential for placement of foundations and caisson structures directly on the seabed in the vicinity of known and designated historic sites and their exclusion zones, World Heritage Sites, coastal listed buildings such as lighthouses, scheduled monuments and other unknown, submerged or non-designated archaeological assets features or paleo-landscapes to create adverse effects.

The potential scouring, siltation and deposition around these important sites located in the vicinity of such devices or arrays may also occur.

However, adverse effects are likely to be avoided through careful siting of individual device foundations and arrays, although this may be more difficult for larger gravity bases or arrays of bases.

Potential for placement of concrete gravity anchors directly on the seabed, and installation of mooring lines in the vicinity of known and designated historic sites and their exclusion zones, World Heritage Sites, coastal listed buildings such as lighthouses, scheduled monuments and other unknown, submerged or non-designated archaeological assets features or paleo-landscapes to create adverse effects.

The potential scouring, siltation and deposition around these important sites located in the vicinity of such anchors may also occur.

However, adverse effects are likely to be avoided through careful siting of these anchors and installation of mooring cables.

Summary of key potential effects on land/seascape include:

Key measures to prevent adverse effects may include: maximising the distance of devices from shore; reducing the height of devices above the water surface; reducing the area of sea occupied by the devices; and modifying the position and layout of devices to suit characteristics of the local seascape; carry out detailed routing studies at project level in accordance with 'Holford Rules' best practice guidance on routeing overhead transmission lines; provide screening for substations.

Potential for turbines and supporting infrastructure (i.e. additional platforms, construction, maintenance or decommissioning vessels and equipment) to adversely affect sensitive receptors (i.e. designated or valued landscapes/seascapes). In general, greater effects are likely for near-shore devices than those located further offshore.

Field observations of offshore wind facilities in the United Kingdom revealed that the facilities may be visible at distances of 26 mi (42 km) in daytime and 24 mi (39 km) in night-time views. They may be a focus of visual attention at distances of up to 10 mi (16 km).

Potential onshore effects from supporting grid infrastructure and interconnectors with terrestrial grid, although these will likely depend on siting and surroundings (i.e. proximity to valued or sensitive landscapes/seascapes).

The potential for landscape effects at the source of excavated terrestrial fill material, or from dredging areas for use as ballast in gravity-based foundations has also been identified.

Potential for turbines and supporting infrastructure (i.e. additional platforms, construction, maintenance or decommissioning vessels and equipment) to adversely affect sensitive receptors (i.e. designated or valued landscapes/seascapes). In general, greater effects are likely for near-shore devices than those located further offshore.

Field observations of offshore wind facilities in the United Kingdom revealed that the facilities may be visible at distances of 26 mi (42 km) in daytime and 24 mi (39 km) in night-time views. They may be a focus of visual attention at distances of up to 10 mi (16 km).

Potential onshore effects from supporting grid infrastructure and interconnectors with terrestrial grid, although these will likely depend on siting and surroundings (i.e. proximity to valued or sensitive landscapes/seascapes).

Potential for turbines and supporting infrastructure (i.e. additional platforms, construction, maintenance or decommissioning vessels and equipment) to adversely affect sensitive receptors (i.e. designated or valued landscapes/seascapes). In general, greater effects are likely for near-shore devices than those located further offshore.

Field observations of offshore wind facilities in the United Kingdom revealed that the facilities may be visible at distances of 26 mi (42 km) in daytime and 24 mi (39 km) in night-time views. They may be a focus of visual attention at distances of up to 10 mi (16 km).

Potential onshore effects from supporting grid infrastructure and interconnectors with terrestrial grid, although these will likely depend on siting and surroundings (i.e. proximity to valued or sensitive landscapes/seascapes).

Potential for turbines and supporting infrastructure (i.e. additional platforms, construction, maintenance or decommissioning vessels and equipment) to adversely affect sensitive receptors (i.e. designated or valued landscapes/seascapes). In general, greater effects are likely for near-shore devices than those located further offshore.

Field observations of offshore wind facilities in the United Kingdom revealed that the facilities may be visible at distances of 26 mi (42 km) in daytime and 24 mi (39 km) in night-time views. They may be a focus of visual attention at distances of up to 10 mi (16 km).

Potential onshore effects from supporting grid infrastructure and interconnectors with terrestrial grid, although these will likely depend on siting and surroundings (i.e. proximity to valued or sensitive landscapes/seascapes).

Potential for turbines and supporting infrastructure (i.e. additional platforms, construction, maintenance or decommissioning vessels and equipment) to adversely affect sensitive receptors (i.e. designated or valued landscapes/seascapes). In general, greater effects are likely for near-shore devices than those located further offshore.

Field observations of offshore wind facilities in the United Kingdom revealed that the facilities may be visible at distances of 26 mi (42 km) in daytime and 24 mi (39 km) in night-time views. They may be a focus of visual attention at distances of up to 10 mi (16 km).

Potential onshore effects from supporting grid infrastructure and interconnectors with terrestrial grid, although these will likely depend on siting and surroundings (i.e. proximity to valued or sensitive landscapes/seascapes).

Includes offshore AC substations and AC/DC substations.

Common designs are based upon experience in offshore oil and gas industry.

Common designs consist of a 'topside' component housing the main equipment, and a foundation structure (e.g. steel jacket, monopile, gravity based structure)

Cables to transfer the power from the AC substation or the offshore AC/DC convertor station to the shore.

Installed from a ship or barge, using installation tools to plough, jet or excavate a trench for placement, followed by backfilling of the trench.

Designed to bring the subsea cables to shore, and connect to buried onshore cables or overhead power lines.

Can be undertaken from a number of methods (e.g. Horizontal Directional Drilling (HDD), trenching) or a combination of them, using drilling rigs or trenching equipment.

Marine Mammals and fish

Noise from survey, unexploded ordnance clearance, construction from piling (e.g. behavioural response, lethal effects, displacement from natural habitat and possible feeding areas, physical injury to hearing organs).

Potential habitat loss or disturbance, especially to bottom dwelling species such as sand eels, which are important prey species for birds, marine mammals and fish.

Potential collision risk with submerged structures and associated cabling (if any).

Potential for increased suspended solids during construction and sediment deposition affecting respiration in bottom dwelling and spawning species (e.g. sand eel).

Potential for EMF effects during operation as part of cable distribution.

Potential creation of artificial rocky habitats due to the presence of submerged infrastructure.

Seabirds

Potential displacement due to disturbance during construction from offshore feeding sites to other areas (e.g. Herring Gull, Great Cormorant, etc.).

Potential loss of feeding grounds for on-passage (migrating) species due to presence of structures (e.g. dunlin, knot, etc.) and associated with loss of prey species (e.g. sand eel for migratory species such as Arctic Tern).

Marine and Coastal Habitats

Potential loss or disturbance to especially sensitive/ designated habitats from construction (e.g. reefs and associated species which may take time to recover).

Potential for increased suspended solids and sediment deposition associated with construction site, and associated effects for epibenthic species, especially filter feeders.

Marine Mammals and fish

Potential habitat loss or disruption to seabed communities during installation.

Potential temporary displacement to other areas and potential collision risk during installation.

Potential EMF from the cable distribution, and potential for changes in behaviour and migratory patterns of some fish and mammal species.

Seabirds

Potential loss of prey species in offshore feeding grounds from installation activities.

Marine and Coastal Habitats

Installation can lead to potential increases to suspended solids and deposition, leading to smothering of seabed communities.

Potential habitat loss or disruption to benthic communities during installation.

Potential habitat disturbance due to maintenance and repair activity.

Marine Mammals and fish

Potential habitat loss or disruption to inshore seabed communities from installation.

Potential temporary displacement to other areas during installation.

Potential EMF from the cable distribution, and potential changes in behaviour and migratory patterns of some fish and mammal species.

Seabirds

Possible effects from proximity of landfall sites to protected areas for breeding or wintering birds (e.g. oystercatcher.)

Potential for loss of prey species in feeding grounds.

Marine and Coastal Habitats

Potential habitat loss or disruption to inshore seabed communities from installation activities.

Potential disruption to intertidal habitats and benthic species.

Potential increase in suspended solids and smothering (deposition) during installation works.

Potential disturbance to seabed and intertidal areas due to maintenance and repair activity.

Construction vessels and helicopter flights may cross other user's transit routes (e.g. dredging, oil and gas operations and freight).

Potential for increased collision risk, effects on navigation and displacement of other marine users (e.g. shipping, recreation, etc.) during construction and maintenance activities.

Potential for displacement of some marine users during construction (e.g. safety exclusion areas during construction) and operation (e.g. fishing activities with potential gear interactions with permanent seabed structures).

Potential for collision with cable excavation vessels in transit during installation.

Potential for displacement of other marine users during construction and maintenance activities (e.g. shipping, recreation, etc.) and operation al periods (e.g. fishing activities with potential gear interactions with submerged structures, etc.).

Potential interference with communications due to EMF.

Potential for collision with cable excavation vessels in transit during construction.

Potential for displacement of other marine users during construction and maintenance activities (e.g. shipping, recreation, etc.) and operation al periods (e.g. fishing activities with potential gear interactions with submerged structures, etc.).

Scour from seabed foundations (e.g. piles) and sediment deposition during construction and operation phases have the potential to alter physical processes and sediment structure.

Sediment disturbance during construction has the potential to alter physical processes and sediment structure.

Sediment disturbance during construction has the potential to alter physical processes and sediment structure at landfall.

Potential re-suspension of sediments and associated hazardous substances during construction.

Potential for accidental spillage from construction vessels and structures during operation.

Potential re-suspension of sediments and hazardous substances due to excavation during installation and during major repair activity.

Potential for accidental spillage from construction and cable repair vessels during operation.

Potential re-suspension of sediments and release of hazardous substances due to excavation.

Potential for accidental spillage from construction equipment.

Construction vessel emissions have the potential to affect air quality and contribute to greenhouse emissions.

Construction vessel emissions have the potential to affect air quality and contribute to greenhouse emissions.

Construction vessel and vehicle emissions have the potential to affect air quality, and subsequently human health, and contribute to greenhouse emissions.

Potential loss of or damage to known and unknown buried heritage in construction activities.

Potential damage to known and unknown buried heritage from maintenance/repair activities (e.g. vessels anchoring).

Potential loss of or damage to known or unknown buried heritage due to corridor excavation by ploughing or trenching during installation.

Potential damage to known and unknown buried heritage from maintenance/repair activities (e.g. vessels anchoring).

Potential loss of or damage to known or unknown buried heritage due to corridor excavation by ploughing or trenching during installation.

Potential damage to known and unknown buried heritage from maintenance/repair activities (e.g. vessels anchoring).

Potential for the seascape to change.

Potential issues of lighting during construction and operation.

Potential issues of temporary lighting during construction.

Potential effects on landscape/seascape during construction.