Publication - Progress report

Draft Sectoral Marine Plans for Offshore Renewable Energy in Scottish Waters - Environmental Report Appendix C: Assessment of Technologies

Published: 25 Jul 2013
Part of:
Marine and fisheries
ISBN:
9781782567462

Appendix C to the SEA Environmental Report of the Draft Sectoral Marine Plans for Offshore Renewable Energy in Scottish Waters.

This appendix contains an assessment of technologies.

50 page PDF

1.3 MB

50 page PDF

1.3 MB

Contents
Draft Sectoral Marine Plans for Offshore Renewable Energy in Scottish Waters - Environmental Report Appendix C: Assessment of Technologies
3 Tidal technology

50 page PDF

1.3 MB

3 Tidal technology

SEA Topic Areas

Horizontal Axis Turbines

Vertical Axis Turbines

Reciprocating Hydrofoils

Emerging Technologies [17]

Device Information [18]

  • Moving blades.
  • Can be suspended as part of a floating array ( i.e. with moorings), or mounted directly on the seabed ( i.e. monopiles).
  • Support structure/moorings may include by gravity/deadweight anchors, monopole, rock anchors or even gravity-base structures.
  • Potentially with surface-piercing components ( i.e. monopole or pontoon support structures).
  • Generating equipment housed in support structure.
  • Marker buoys and other navigational aids are likely required.
  • Moving blades.
  • Can be suspended as part of a floating array ( i.e. with moorings), or mounted directly on the seabed ( i.e. monopiles).
  • Support structure/moorings may include by gravity/deadweight anchors, rock anchors or even gravity-base structures.
  • Potentially with surface-piercing components ( i.e. pontoon support structures).
  • Generating equipment housed in support structure.
  • Marker buoys and other navigational aids are likely required.
  • Hydrofoils.
  • Can be mounted or moored on the seabed ( i.e. monopiles, gravity-based).
  • Support structure/moorings may include by gravity/deadweight anchors, monopole, rock anchors or even gravity-base structures.
  • Potentially with surface-piercing components ( i.e. pontoon support structures).
  • Present in upper, mid or lower water column.
  • Generating equipment housed in support structure.
  • Marker buoys and other navigational aids are likely required.
  • Includes other emerging tidal technologies such as Venturia Effect or Enclosed Tip devices, Archimedes Screw and Tidal kite devices.
  • Can be mounted or moored on the seabed.
  • Support structure/moorings may include by gravity/deadweight anchors, monopole, rock anchors or even gravity-base structures.
  • Present in upper, mid or lower water column.
  • Marker buoys and other navigational aids are likely required.

Biodiversity/flora/ fauna [19]

Summary of key potential effects:

  • Physical disturbance during device installation
  • Noise during construction (particularly piling) and from device operation
  • Risk of collision with operating devices during foraging and feeding/travel ( e.g. migration)
  • Accidental contamination from device failures, vessel collisions and storm damage
  • Habitat exclusion and species displacement due to device presence and operation
  • Increased mink predation due to the creation of islet chains between islands
  • Barriers to movement - due to avoidance reactions to noise and risk of collision
  • Increased suspended sediment/turbidity from seabed disturbance during device installation and cable trenching
  • Smothering from seabed disturbance during device installation and cable trenching
  • Changes in tidal flow and wave regime due to device presence and operation
  • Substratum loss, caused by attaching devices to the seabed
  • Habitat and species loss/disturbance during installation of cables and overhead lines and substation construction from onshore grid connections

Key measures to prevent adverse effects may include: avoidance of sensitive sites; avoidance of sensitive seasons ( e.g. breeding) during installation; use of devices with attachments that cause smaller seabed disturbance such as anchors and clump weights; 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 routeing studies at project level in accordance with 'Holford Rules' best practice guidance on routeing overhead transmission lines; avoid sensitive sites and areas; provide screening (substations)

Fauna:

Noise

Potential for underwater noise impacts on marine fauna during drilling/installation works and operation has been identified. There may be the potential for behavioural impacts to marine fauna ( i.e. seals, cetaceans, otter, basking shark), but there are significant unknowns on disturbance effects (likely site-specific), and noise levels that are actually generated. Acute effects are considered unlikely.

The potential for impacts from above surface noise was identified for marine fauna, during installation works and where floating structures house noise-generating equipment. This potential impact relates to disturbance of species such as seals and otters, and these may be greater for devices located near to the shoreline. There are significant unknowns on disturbance effects (likely site-specific).

Shock Waves

The potential for shock waves was identified from the installation of monopiles and from waves hitting the side of high-profile surface-piercing structures. Hence, this is only applicable for devices with high-profile surface-piercing components. The likely magnitude of any impacts and their effects on these species is unknown, however, the potential for impacts to seals, cetaceans, otter and basking shark has been identified.

Those with low-profile components ( i.e. floating structures) are unlikely to create shock waves.

EMF

While no EMF impacts have been identified from the devices, there is the potential for EMF impacts from underwater cabling and grid connections. Further information is required to determine the potential susceptibility of marine fauna and likely effects associated with this issue.

Physical Barrier

The introduction of new structures in the water column, potentially the whole water column with support structures in place, may disrupt movements or migration of marine fauna. Unknowns over movements and migration routes ( i.e. cetaceans, basking sharks), patterns of movement of other species ( i.e. seals, otters), whether moorings and devices will be perceived or if they will simply alter their movement accordingly. Near-shore devices may restrict movement more than offshore ( e.g. potentially greater alternatives for movement around devices offshore).

Potential for fatal collisions for marine fauna with devices and moorings, particularly with moving turbine blades. Avoidance is likely for some species ( i.e. fish), but impact could be fatal for some species if it were to occur ( i.e. seals, otters, cetaceans, basking shark). Collision with, entanglement or entrapment by mooring lines is also considered possible for larger species ( i.e. cetaceans and basking sharks), particularly in groups of devices or complex mooring arrays. While this may also result in injury or fatality, it is also considered unlikely.

Displacement

Displacement is likely to be site-specific and would depend on a range of other factors (suitable alternative sites, importance of habitat, etc.). It can be due to the presence of devices or structures, or from disturbance in installation, operation or decommissioning ( i.e. noise above and below the water surface, displacement of prey, etc.).

This will also likely depend on what activities are being displaced ( e.g. Basking sharks avoiding of structures or installation/servicing vessel activities may lead to the displacement of foraging activities or courtship behaviour). Others may simply choose alternative sites for foraging or as migratory routes if sufficiently disturbed, and if suitable areas are available.

Fauna:

Noise

Potential for underwater noise impacts on marine fauna, particularly during drilling/installation works. Potential for behavioural impacts to seals, cetaceans, otter and basking shark. But there are significant unknowns on disturbance effects (likely site-specific), and noise levels that are actually generated. Acute effects are considered unlikely.

The potential for impacts from above surface noise was identified for marine fauna, particularly during drilling/piling/installation works and where floating structures house noise-generating equipment. The potential relates to disturbance of species such as seals and otters, and these may be greater for devices near to the shoreline. There are significant unknowns on disturbance effects (likely site-specific).

Shock Waves

The potential for shock waves was identified from the installation of monopiles and from waves hitting the side of high-profile surface-piercing structures. Hence, this is only applicable for devices with high-profile surface-piercing components. The likely magnitude of any impacts and their effects on these species is unknown, however, the potential for impacts to seals, cetaceans, otter and basking shark has been identified.

Those with low-profile components ( i.e. floating structures) are unlikely to create shock waves.

EMF

While no EMF impacts have been identified from the devices, there is the potential for EMF impacts from underwater cabling and grid connections. Further information is required to determine the potential susceptibility of marine fauna and likely effects associated with this issue.

Physical Barrier

The introduction of new structures in the water column may disrupt movements or migration of marine fauna. Unknowns over known movements and migration routes ( i.e. cetaceans, basking sharks), patterns of movement of other species ( i.e. seals, otters), whether moorings and devices will be perceived or if they will simply alter their movement accordingly. Near-shore devices may restrict movement more than offshore ( e.g. potentially greater alternatives for movement around devices offshore).

Potential for fatal collisions for marine fauna with devices and moorings, particularly with moving turbine blades. Avoidance is likely for many species ( i.e. fish), but impact could be fatal for some species if it were to occur ( i.e. seals, otters, cetaceans, basking shark). Collision with or entanglement in mooring lines is also considered possible for larger species ( i.e. cetaceans and basking sharks), particularly in complex arrays. While this may also result in injury or fatality, it is considered unlikely.

Displacement

Displacement is likely to be site-specific and would depend on a range of other factors (suitable alternative sites, importance of habitat, etc.). Can be from presence of devices or structures, or due to disturbance in installation, operation or decommissioning ( i.e. noise, vibration, displacement of prey, etc.).

Will also depend on what activities are being displaced ( e.g. Basking sharks avoiding of structures or installation/servicing vessel activities may lead to the displacement of foraging activities or courtship behaviour). Others may simply choose alternative sites for foraging or as migratory routes if disturbed, if these are available.

Fauna:

Attraction of Fauna

Potential for fish aggregation during shutdown periods or slack water ( i.e. turbines not moving). There may be a potential risk of physical injury to some species during periods of start-up ( i.e. when the blades start moving), due to this aggregation.

Noise

Potential for underwater noise impacts on marine fauna, particularly during drilling/installation works. Potential for behavioural impacts to seals, cetaceans, otter and basking shark. But there are significant unknowns on disturbance effects (likely site-specific), and noise levels that are actually generated. Acute effects are considered unlikely.

The potential for impacts from above surface noise was identified for marine fauna, particularly during drilling/piling/installation works and where floating structures house noise-generating equipment. The potential relates to disturbance of species such as seals and otters, and these may be greater for devices near to the shoreline. There are significant unknowns on disturbance effects (likely site-specific).

EMF

While no EMF impacts have been identified from the devices, there is the potential for EMF impacts from underwater cabling and grid connections. Further information is required to determine the potential susceptibility of marine fauna and likely effects associated with this issue.

Physical Barrier

The introduction of new structures in the water column may disrupt movements or migration of marine fauna. Unknowns over known movements and migration routes ( i.e. cetaceans, basking sharks), patterns of movement of other species ( i.e. seals, otters), whether moorings and devices will be perceived or if they will simply alter their movement accordingly. Near-shore devices may restrict movement more than offshore ( e.g. potentially greater alternatives for movement around devices offshore).

Potential for fatal collisions for marine fauna with devices and support structures/moorings. Collision with or entanglement in mooring lines is also considered possible for larger species ( i.e. cetaceans and basking sharks), particularly in complex arrays. Avoidance is likely for many species ( i.e. fish), but impact could be fatal for some species if it were to occur ( i.e. seals, otters, cetaceans, basking shark). It is however, considered unlikely.

Displacement

Displacement is likely to be site-specific and would depend on a range of other factors (suitable alternative sites, importance of habitat, etc.). Can be from presence of devices or structures, or due to disturbance in installation, operation or decommissioning ( i.e. noise, vibration, displacement of prey, etc.).

Will also depend on what activities are being displaced ( e.g. Basking sharks avoiding of structures or installation/servicing vessel activities may lead to the displacement of foraging activities or courtship behaviour). Others may simply choose alternative sites for foraging or as migratory routes if disturbed, if these are available.

Fauna:

With similarities in infrastructure and the overall presence of devices in within the water column to that of turbine and hydrofoil devices, many of the potential impacts identified in the columns to the left are likely to be associated with these emerging technologies.

For example, effects such as the potential for attraction of fauna, underwater noise impacts during operation and drilling/installation works, and potential for EMF effects associated with cabling may be applicable for these technologies and their associated infrastructure.

Other effects, such as the potential for behavioural impacts and disturbance ( i.e. displacement of foraging, etc.), possible collision with devices and moorings, have also been identified.

However, as indicated for other tidal energy devices, there are likely to be significant unknowns over such effects.

Birds:

Collision

Potential collision risk with devices within the water column for shallow-diving birds. Collisions have the potential to be fatal for marine birds, which can dive to depths of up to 60m from the water surface ( e.g. common guillemots, long-tailed ducks). This is likely to be of particular concern with the moving blades present on these devices.

Impacts on foraging

Localised changes in turbulence from the presence and operation of devices ( e.g. moving blades, presence of structures in the water column) may have the potential to affect the foraging success of marine birds. However, the potential effects are not currently known and may be difficult to identify a causal link between the two.

Noise

Potential noise risk, both above and below water surface, during installation and decommissioning works in particular ( i.e. during piling, drilling for rock anchors, if used) and operation of blades below the water surface. Significant unknowns around the magnitude of impact, although it has been identified as potentially damaging.

Potential for noise impacts from generators within devices or their support structures for species, particularly for coastal breeding sites if devices are located in near-shore environment. Noise within devices is likely to be low and constant and the effects are unknown, as effects of increased/altered noise levels are not known for birds at present (displacement/avoidance, impacts to foraging success, etc.). It is noted that high energy environments are likely to have high levels of background noise.

Underwater noise from the presence and operation of devices, the importance of hearing underwater for birds and their threshold levels is not currently known. As such the effects of altered underwater noise levels is not known, but potential impacts such as displacement, avoidance, reduction in foraging success, no effect, etc. have been identified.

Disturbance and Displacement

Potential for displacement during installation and operation, but dependant on other factors ( i.e. sensitivity of habitats, availability of suitable alternative habitats) and may only be temporary as fauna become accustomed to the devices. Likely dependant on site-specific including the sensitivity of species and the activities displaced ( i.e. foraging, noise disturbance, etc.).

Potential for visual disturbance if surface-piercing components are present, with the potential for greater impacts if located near-shore and close to coastal breeding sites and moulting sites. In such instances, birds in flight may operate in a broadly similar way and use similar avoidance tactics to those employed when encountering other natural and man-made obstructions ( i.e. by taking alternative flight routes, avoiding obstructions to a greater degree at night).

Birds:

Collision

Potential collision risk with devices within the water column for shallow-diving birds. Collisions have the potential to be fatal for marine birds, which can dive to depths of up to 60m from the water surface ( e.g. common guillemots, long-tailed ducks). Of particular concern if there are moving blades on the device.

Impacts on foraging

Localised changes in turbulence from the presence and operation of devices ( e.g. moving blades, presence of structures in the water column) may have the potential to affect the foraging success of marine birds. However, the potential effects are not currently known and may be difficult to identify a causal link between the two.

Noise

Potential noise risk, both above and below water surface, during installation and decommissioning works in particular ( i.e. during piling, drilling for rock anchors, if used). Significant unknowns around the magnitude of impact, although it could potentially be damaging.

Potential for noise impacts from generators within devices for species, particularly for coastal breeding sites if devices are located in near-shore environment. Noise within devices is likely to be low and constant and the effects are unknown, as effects of increased/altered noise levels are not known for birds at present (displacement/avoidance, impacts to foraging success, etc.). It is noted that high energy environments are likely to have high levels of background noise.

Underwater noise from presence and operation of devices is not known, as is the importance of hearing underwater for birds and threshold levels. As such the effects of altered underwater noise levels is not known, but potential impacts may include displacement, avoidance, reduction in foraging success, no effect, etc.

Disturbance and Displacement

Potential for displacement during installation and operation, but dependant on other factors ( i.e. sensitivity of habitats, availability of suitable alternative habitats) and may only be temporary as fauna become accustomed to the devices. Likely dependant on site-specific including the sensitivity of species and the activities displaced ( i.e. foraging, noise disturbance, etc.).

Potential for visual disturbance if surface-piercing components are present, with potential for greater impacts if close to coastal breeding sites and moulting sites. In such instances, birds in flight may operate in a broadly similar way and use similar avoidance tactics to those employed when encountering other natural and man-made obstructions ( i.e. by taking alternative flight routes, avoiding obstructions to a greater degree at night).

Birds:

Collision

Potential collision risk with devices within the water column for shallow-diving birds. Collisions have the potential to be fatal for marine birds, which can dive to depths of up to 60m from the water surface ( e.g. common guillemots, long-tailed ducks). Blades are likely to be slower moving that other devices ( i.e. horizontal/vertical axis turbines), and as such, may present less of a hazard to diving marine birds.

Impacts on foraging

Localised changes in turbulence from the presence and operation of devices ( e.g. presence of structures in the water column) may have the potential to affect the foraging success of marine birds. However, the potential effects are not currently known and may be difficult to identify a causal link between the two.

Noise

Potential noise risk below water surface, during installation and decommissioning works in particular ( i.e. during piling, if used). Significant unknowns around the magnitude of impact, although it could potentially be damaging.

Underwater noise from presence and operation of devices is not known, as is the importance of hearing underwater for birds and threshold levels. As such the effects of altered underwater noise levels is not known, but potential impacts may include displacement, avoidance, reduction in foraging success, no effect, etc.

Disturbance and Displacement

Potential for displacement during installation and operation, but dependant on other factors ( i.e. sensitivity of habitats, availability of suitable alternative habitats) and may only be temporary as fauna become accustomed to the devices. Likely dependant on site-specific including the sensitivity of species and the activities displaced ( i.e. foraging, noise disturbance, etc.).

Unlikely to have permanent above-water components (other than in installation), and therefore are not considered to create visual disturbance.

Birds:

With similarities in infrastructure and the overall presence of devices in within the water column to that of turbine and hydrofoil devices, many of the potential impacts identified in the columns to the left are likely to be associated with these emerging technologies.

The potential for effects such as collision risk with devices and their associated structures ( e.g. moorings), behavioural impacts ( e.g. foraging) and disturbance from underwater noise on diving birds has been identified (see left).

Benthic Habitats:

Habitat Changes

The presence of these devices in the water column and their supporting structures ( i.e. moorings, monopole structures, etc.) has the potential to contribute to habitat changes in a number of ways. In general, impacts on seabed habitats from the devices themselves are likely limited to changes in tidal flows, fluxes and turbulence due to the presence of these devices and associated structures in the water column.

Other impacts, such as scouring, deposition/siltation, abrasion, smothering and the potential for loss of habitat are likely to be associated with the placement of supports ( i.e. gravity and rock anchors, etc.) on the seabed and mooring lines in the water column. Direct seabed impacts such as changes in sediment dynamics, scouring, deposition/siltation and abrasion from supports and moorings have the potential to affect benthic habitats in a range of ways. These can include the introduction of variations and shifts in grain size of sediments affecting habitat character and species distribution; shading or smothering of benthic areas, changes in species distribution via interference with filter feeders ( i.e. interference with feeding, inhibiting respiration, smothering, reproduction, loss of habitat, affecting species distribution, reducing food sources for other species, etc.), and leading to wider changes in ecosystem composition.

In some instances, this may also result in changes to changing in coastal character/profile.

Sediment Dynamics, Scour, deposition and Smothering

Changes in sediment dynamics due to the presence of moorings for these devices (gravity anchors, gravity base structures, monopiles, rock anchors and mooring lines) may occur, with the potential for associated impacts such as scouring, deposition/siltation and smothering. The potential for significant change to habitats has been identified. While likely site specific, this may present a potential risk to BAP species such as mussel beds, M. edulis, and filter feeders initially with secondary impacts up the food chain ( i.e. affecting predatory species that feed on them). The potential for impacts in a range of BAP habitats has been identified:

  • Changes in sediment dynamics, increased scour and sediment deposition in High energy littoral rock (including BAP habitat Tidal Swept Channels) if F. distichus is present.
  • Changes in sediment dynamics, increased scour, and the deposition of sediment during high tide in Moderate energy littoral (including BAP habitat Under boulder communities) if under boulder communities are present. Deposition may reduce photosynthesis for algae (i.e . F. serratus, F. vesticulosus, M. stellatus).
  • Changes in sediment dynamics, increased scour, and deposition of sediment during high tide in Littoral biogenic reefs (including BAP habitat blue mussel beds) and interference with filter feeders ( i.e. M. edulis, S. alveolata). Impacts are unlikely, but potential noted if blue mussel beds are present. Potential for changing the character of this habitat.
  • Changes in sediment dynamics, increased scour and deposition of sediment in features of littoral sediment (including BAP habitat blue mussel beds) and interference with filter feeders ( i.e. M. edulis). Impacts are unlikely in small arrays, but may change the habitat character, with potential impacts noted if blue mussel beds are present.
  • Changes in sediment dynamics, and associated increased scour, deposition and smothering in Sublittoral coarse sediment (including BAP habitats subtidal sands and gravel, blue mussel beds). Impacts unlikely for small arrays, although potential for interference with filter feeders ( i.e. M. modiolus, A. digitatum, A. fragilis) and potential impacts identified if A. fragilis, C. cruoriaeformis, D. Montagnei, E. timida or horse mussel beds are present.
  • Changes in sediment dynamics, and associated increased scour, deposition and smothering in Sublittoral sand (including BAP habitat sub-tidal sands and gravel, blue mussel beds). Impacts are unlikely for small arrays, although potential for interference with filter feeders ( i.e. M. edulis, A. fragilis) and potential impacts identified if A. fragilis, E. timida, A. sarsi or blue mussel beds are present
  • Changes in sediment dynamics, and associated increased scour, deposition and smothering in Sublittoral mixed sediments (including BAP habitat Horse mussel beds, file shell beds). Impacts are unlikely for a small array, although there may be the potential for interference with filter feeders ( i.e. M. modiolus, A. digitatum, A. fragilis) and potential impacts have been identified if A. fragilis, D. Montagnei, E. timida, horse mussel beds or file shell beds are present.
  • Changes in sediment dynamics, and associated increased scour, deposition and smothering in Sublittoral macrophyte-dominated sediment (including BAP habitats maerl beds, tidal swept channels, horse mussel beds, blue mussel beds). Impacts are unlikely for a small array, although there may be the potential for interference with filter feeders ( i.e. M. modiolus, A. digitatum, M. edulis, A. fragilis) and potential impacts have been identified if A. fragilis, C. cruoriaeformis, D. Montagnei, P. calcareum, L. corallioides, horse mussel beds, blue mussel beds of maerl beds are present
  • Changes in sediment dynamics, and associated increased scour, deposition and smothering in Sublittoral biogenic reefs (including BAP habitats horse mussel beds, cold-water coral reefs and blue mussel beds). Impacts are unlikely for a small array, although there may be the potential for interference with filter feeders ( i.e. M. modiolus, A. digitatum, M. edulis) and potential impacts have been identified if horse mussel beds, cold-water coral reefs or blue mussel beds are present.
  • Changes in sediment dynamics in Atlantic and Mediterranean high energy infralittoral rock (including BAP habitat Tidal Swept Channels). Smothering may affect filter feeders ( S. pallida, U. feline, A. digitatum, B. schlosseri, H. panacea) from feeding and growth, while photosynthesis by algae may be compromised. Potential for impacts on S. pallida, as even small impacts may have important influences on UK populations.
  • Changes in sediment dynamics in Atlantic and Mediterranean moderate energy infralittoral rock (including BAP habitat Tidal Swept Channels and S. spinulosa reefs). Smothering may affect filter feeders ( S. pallida, U. feline, A. digitatum, B. schlosseri, H. panacea) from feeding and growth, while photosynthesis by algae may be compromised. Potential for impacts on A. dohrnii and S. pallida, as even small impacts may have important influences on UK populations.
  • Changes in sediment dynamics in Atlantic and Mediterranean high energy circalittoral rock (including BAP habitat Tidal Swept Channels). Smothering may affect filter feeders ( S. pallida, U. feline, A. digitatum, B. schlosseri, H. panacea) from feeding and growth, while photosynthesis by algae may be compromised. Potential for impacts on S. pallida, as even small impacts may have important influences on UK populations.
  • Changes in sediment dynamics in Atlantic and Mediterranean moderate energy circalittoral rock. Potential for smothering impacts on A. dohrnii and S. pallida, as even small impacts may have important influences on UK populations.
  • Changes in sediment dynamics and deposition in features of circalittoral rock may hinder filter feeders ( i.e. respiration, feeding and growth). While characteristic species are common and widespread, potential for impact is noted since this habitat is seldom recorded.

Loss of Habitat/Abrasion

The direct placement of offshore or near-shore devices, and/or their moorings on the seabed can result in damage to benthic habitats, or their loss in extreme instances ( e.g. seabed structures, piling, drilling and anchoring, subsea cable placement).

This could also include additional damage such as the abrasion of marine habitats and sessile/sedentary species ( i.e. BAP species such as mussel and file shell beds) from the installation of technology ( i.e. mooring cables dragging during installation) and subsea cabling ( i.e. placement and dragging during installation and operation). The potential for impacts in a range of BAP habitats has been identified:

  • Loss of habitat and Abrasion from foundation/mooring systems in Atlantic and Mediterranean high energy infralittoral rock (including BAP habitat Tidal Swept Channels), particularly if S. pallida populations is present. Even small amounts of abrasion may impact on these populations.
  • Loss of habitat and abrasion from foundation/mooring systems in Atlantic and Mediterranean moderate energy infralittoral rock (including BAP habitat Tidal Swept Channels and S. spinulosa reefs), particularly if S. pallida and A. dohrnii populations are present. Even small amounts of abrasion may impact on these populations.
  • Loss of habitat and abrasion from foundation/mooring systems in Atlantic and Mediterranean high energy circalittoral rock (including BAP habitat Tidal Swept Channels), particularly if S. pallida populations is present. Even small amounts of abrasion may impact on these populations.
  • Loss of habitat and abrasion from foundation/mooring systems in Atlantic and Mediterranean moderate energy circalittoral rock, particularly if S. pallida and A. dohrnii populations are present. Even small amounts of abrasion may impact on these populations.
  • Loss of habitat and abrasion from foundation/mooring systems in Sublittoral coarse sediment (including BAP habitats subtidal sands and gravel, horse mussel beds). Impacts are considered unlikely for small arrays, although the potential for effects on A. fragilis, C.cruoriaeformis, D. Montagnei, E. timida or horse mussel beds are present.
  • Loss of habitat and abrasion from foundation/mooring systems in Sublittoral sand (including BAP habitat sub-tidal sands and gravel, blue mussel beds). Impacts are considered unlikely for small arrays, although the potential for effects on A. fragilis, E. timida, A. sarsi or blue mussel beds are present.
  • Loss of habitat and abrasion from foundation/mooring systems in Sublittoral mixed sediments (including BAP habitat Horse mussel beds, file shell beds). Impacts are considered unlikely for small arrays, although the potential effects A. fragilis, D. Montagnei, E. timida, A. sarsi, horse mussel beds or file shell beds are present.
  • Loss of habitat and abrasion from foundation/mooring systems in Sublittoral macrophyte-dominated sediment (including BAP habitats maerl beds, tidal swept channels, horse mussel beds, blue mussel beds). Impacts are considered unlikely for small arrays, although the potential effects A. fragilis, C.cruoriaeformis, D. Montagnei, P. calcareum, E. timida, A. sarsi, horse mussel beds or file shell beds are present.
  • Loss of habitat and abrasion from foundation/mooring systems in Sublittoral biogenic reefs (including BAP habitats horse mussel beds, cold-water coral reefs and blue mussel beds). Impacts are considered unlikely for small arrays, although the potential effects horse mussel beds, cold water coral beds or blue mussel beds are present.

Change in Tidal Flows and Fluxes

Changes, predominantly decreases in tidal flows associated with device supports or mooring systems may have adverse effects on benthic areas, although these are largely expected to be site and habitat specific:

  • Changes in tidal flows and fluxes in Sublittoral coarse sediment (including BAP habitats subtidal sands and gravel, horse mussel beds) due to moorings (offshore). on filter feeders ( i.e. M. modiolus, A. digitatum and A. fragilis) from reduced food supplies and siltation. Strong flows may detach weakly attached organisms. Changes in the overall habitat, through changing grain size in sediments may also occur. While many species are present in a variety of tidal flow conditions, impacts are unlikely. However, the potential may exist for impacts if C. cruoriaeformis, D. Montagnei, E. timida, A. sarsi or horse mussel beds are present.
  • Changes in tidal flows and fluxes in Sublittoral sand (including BAP habitat sub-tidal sands and gravel, blue mussel beds) due to moorings (offshore). on filter feeders ( i.e. M. modiolus, A. digitatum and A. fragilis) from reduced food supplies and siltation. Strong flows may detach weakly attached organisms. Changes in the overall habitat, through changing grain size in sediments may also occur. While many species are present in a variety of tidal flow conditions, impacts are unlikely. However, the potential may exist for impacts if A. fragilis, E. timida, A. sarsi or blue mussel beds are present.
  • Changes in tidal flows and fluxes in Sublittoral mixed sediments (including BAP habitat Horse mussel beds, file shell beds) due to moorings (offshore). on filter feeders ( i.e. M. modiolus, A. digitatum and A. fragilis) from reduced food supplies and siltation. Strong flows may detach weakly attached organisms. Changes in the overall habitat, through changing grain size in sediments may also occur. While many species are present in a variety of tidal flow conditions, impacts are unlikely. However, the potential may exist for impacts if A. fragilis, E. timida, A. sarsi, horse mussel beds or file shell beds are present.
  • Changes in tidal flows and fluxes in Sublittoral macrophyte-dominated sediment (including BAP habitats maerl beds, tidal swept channels, horse mussel beds, blue mussel beds) due to moorings (offshore). on filter feeders ( i.e. M. modiolus, A. digitatum and A. fragilis) from reduced food supplies and siltation. Strong flows may detach weakly attached organisms. Changes in the overall habitat, through changing grain size in sediments may also occur. While many species are present in a variety of tidal flow conditions, impacts are unlikely. However, the potential may exist for impacts if A. fragilis, C. cruoriaeformis, D. Montagnei, P. calcareum, L. corallioides, horse mussel beds or blue mussel beds or maerl beds present.
  • Changes in tidal flows and fluxes in Sublittoral biogenic reefs (including BAP habitats horse mussel beds, cold-water coral reefs and blue mussel beds) due to moorings (offshore). on filter feeders ( i.e. M. modiolus, A. digitatum and A. fragilis) from reduced food supplies and siltation. Strong flows may detach weakly attached organisms. Changes in the overall habitat, through changing grain size in sediments may also occur and increase competition between kelp species ( i.e. A. esculenta) associated with changing flow rates. While many species are present in a variety of tidal flow conditions, impacts are unlikely. However, the potential may exist for impacts if horse mussel beds, cold coral reefs or blue mussel beds if present.

Benthic Habitats:

Habitat Changes

The presence of these devices in the water column and their supporting structures ( i.e. moorings, monopole structures, etc.) has the potential to contribute to habitat changes in a number of ways. In general, impacts on seabed habitats from the devices themselves are likely limited to changes in tidal flows, fluxes and turbulence due to the presence of these devices and associated structures in the water column.

Other impacts, such as scouring, deposition/siltation, abrasion, smothering and the potential for loss of habitat are likely to be associated with the placement of supports ( i.e. gravity and rock anchors, etc.) on the seabed and mooring lines in the water column. Direct seabed impacts from these systems, such as changes in sediment dynamics, scouring, deposition/siltation and abrasion from supports and moorings have the potential to affect benthic habitats in a range of ways. These can include the introduction of variations and shifts in grain size of sediments affecting habitat character and species distribution; shading or smothering of benthic areas, changes in species distribution via interference with filter feeders ( i.e. interference with feeding, inhibiting respiration, smothering, reproduction, loss of habitat, affecting species distribution, reducing food sources for other species, etc.), and leading to wider changes in ecosystem composition.

In some instances, this may also result in changes to changing in coastal character/profile.

Sediment Dynamics, Scour, deposition and Smothering

Changes in sediment dynamics due to the presence of moorings for these devices (gravity anchors, gravity base structures, monopiles, rock anchors and mooring lines) may occur, with the potential for associated impacts such as scouring, deposition/siltation and smothering. The potential for significant change to habitats has been identified. While likely site specific, this may present a potential risk to BAP species such as mussel beds, M. edulis, and filter feeders initially with secondary impacts up the food chain ( i.e. affecting predatory species that feed on them). The potential for impacts in a range of BAP habitats has been identified:

  • Changes in sediment dynamics, increased scour and sediment deposition in High energy littoral rock (including BAP habitat Tidal Swept Channels) if F. distichus is present.
  • Changes in sediment dynamics, increased scour, and the deposition of sediment during high tide in Moderate energy littoral (including BAP habitat Under boulder communities) if under boulder communities are present. Deposition may reduce photosynthesis for algae ( i.e. F. serratus, F. vesticulosus, M. stellatus).
  • Changes in sediment dynamics, increased scour, and deposition of sediment during high tide in Littoral biogenic reefs (including BAP habitat blue mussel beds) and interference with filter feeders ( i.e. M. edulis, S. alveolata). Impacts are unlikely, but potential noted if blue mussel beds are present. Potential for changing the character of this habitat.
  • Changes in sediment dynamics, increased scour and deposition of sediment in features of littoral sediment (including BAP habitat blue mussel beds) and interference with filter feeders ( i.e. M. edulis). Impacts are unlikely in small arrays, but may change the habitat character, with potential impacts noted if blue mussel beds are present.
  • Changes in sediment dynamics, and associated increased scour, deposition and smothering in Sublittoral coarse sediment (including BAP habitats subtidal sands and gravel, blue mussel beds). Impacts unlikely for small arrays, although potential for interference with filter feeders ( i.e. M. modiolus, A. digitatum, A. fragilis) and potential impacts identified if A. fragilis, C. cruoriaeformis, D. Montagnei, E. timida or horse mussel beds are present.
  • Changes in sediment dynamics, and associated increased scour, deposition and smothering in Sublittoral sand (including BAP habitat sub-tidal sands and gravel, blue mussel beds). Impacts are unlikely for small arrays, although potential for interference with filter feeders ( i.e. M. edulis, A. fragilis) and potential impacts identified if A. fragilis, E. timida, A. sarsi or blue mussel beds are present
  • Changes in sediment dynamics, and associated increased scour, deposition and smothering in Sublittoral mixed sediments (including BAP habitat Horse mussel beds, file shell beds). Impacts are unlikely for a small array, although there may be the potential for interference with filter feeders ( i.e. M. modiolus, A. digitatum, A. fragilis) and potential impacts have been identified if A. fragilis, D. Montagnei, E. timida, horse mussel beds or file shell beds are present.
  • Changes in sediment dynamics, and associated increased scour, deposition and smothering in Sublittoral macrophyte-dominated sediment (including BAP habitats maerl beds, tidal swept channels, horse mussel beds, blue mussel beds). Impacts are unlikely for a small array, although there may be the potential for interference with filter feeders ( i.e. M. modiolus, A. digitatum, M. edulis, A. fragilis) and potential impacts have been identified if A. fragilis, C. cruoriaeformis, D. Montagnei, P. calcareum, L. corallioides, horse mussel beds, blue mussel beds of maerl beds are present
  • Changes in sediment dynamics, and associated increased scour, deposition and smothering in Sublittoral biogenic reefs (including BAP habitats horse mussel beds, cold-water coral reefs and blue mussel beds). Impacts are unlikely for a small array, although there may be the potential for interference with filter feeders ( i.e. M. modiolus, A. digitatum, M. edulis) and potential impacts have been identified if horse mussel beds, cold-water coral reefs or blue mussel beds are present.
  • Changes in sediment dynamics in Atlantic and Mediterranean high energy infralittoral rock (including BAP habitat Tidal Swept Channels). Smothering may affect filter feeders ( S. pallida, U. feline, A. digitatum, B. schlosseri, H. panacea) from feeding and growth, while photosynthesis by algae may be compromised. Potential for impacts on S. pallida, as even small impacts may have important influences on UK populations.
  • Changes in sediment dynamics in Atlantic and Mediterranean moderate energy infralittoral rock (including BAP habitat Tidal Swept Channels and S. spinulosa reefs). Smothering may affect filter feeders ( S. pallida, U. feline, A. digitatum, B. schlosseri, H. panacea) from feeding and growth, while photosynthesis by algae may be compromised. Potential for impacts on A. dohrnii and S. pallida, as even small impacts may have important influences on UK populations.
  • Changes in sediment dynamics in Atlantic and Mediterranean high energy circalittoral rock (including BAP habitat Tidal Swept Channels). Smothering may affect filter feeders ( S. pallida, U. feline, A. digitatum, B. schlosseri, H. panacea) from feeding and growth, while photosynthesis by algae may be compromised. Potential for impacts on S. pallida, as even small impacts may have important influences on UK populations.
  • Changes in sediment dynamics in Atlantic and Mediterranean moderate energy circalittoral rock. Potential for smothering impacts on A. dohrnii and S. pallida, as even small impacts may have important influences on UK populations.
  • Changes in sediment dynamics and deposition in features of circalittoral rock may hinder filter feeders ( i.e. respiration, feeding and growth). While characteristic species are common and widespread, potential for impact is noted since this habitat is seldom recorded.

Loss of Habitat/Abrasion

The direct placement of offshore or near-shore devices, and/or their moorings on the seabed can result in damage to benthic habitats, or their loss in extreme instances ( e.g. seabed structures, piling, drilling and anchoring, subsea cable placement).

This could also include additional damage such as the abrasion of marine habitats and sessile/sedentary species ( i.e. BAP species such as mussel and file shell beds) from the installation of technology ( i.e. mooring cables dragging during installation) and subsea cabling ( i.e. placement and dragging during installation and operation). The potential for impacts in a range of BAP habitats has been identified:

  • Loss of habitat and Abrasion from foundation/mooring systems in Atlantic and Mediterranean high energy infralittoral rock (including BAP habitat Tidal Swept Channels), particularly if S. pallida populations is present. Even small amounts of abrasion may impact on these populations.
  • Loss of habitat and abrasion from foundation/mooring systems in Atlantic and Mediterranean moderate energy infralittoral rock (including BAP habitat Tidal Swept Channels and S. spinulosa reefs), particularly if S. pallida and A. dohrnii populations are present. Even small amounts of abrasion may impact on these populations.
  • Loss of habitat and abrasion from foundation/mooring systems in Atlantic and Mediterranean high energy circalittoral rock (including BAP habitat Tidal Swept Channels), particularly if S. pallida populations is present. Even small amounts of abrasion may impact on these populations.
  • Loss of habitat and abrasion from foundation/mooring systems in Atlantic and Mediterranean moderate energy circalittoral rock, particularly if S. pallida and A. dohrnii populations are present. Even small amounts of abrasion may impact on these populations.
  • Loss of habitat and abrasion from foundation/mooring systems in Sublittoral coarse sediment (including BAP habitats subtidal sands and gravel, horse mussel beds). Impacts are considered unlikely for small arrays, although the potential for effects on A. fragilis, C.cruoriaeformis, D. Montagnei, E. timida or horse mussel beds are present.
  • Loss of habitat and abrasion from foundation/mooring systems in Sublittoral sand (including BAP habitat sub-tidal sands and gravel, blue mussel beds). Impacts are considered unlikely for small arrays, although the potential for effects on A. fragilis, E. timida, A. sarsi or blue mussel beds are present.
  • Loss of habitat and abrasion from foundation/mooring systems in Sublittoral mixed sediments (including BAP habitat Horse mussel beds, file shell beds). Impacts are considered unlikely for small arrays, although the potential effects A. fragilis, D. Montagnei, E. timida, A. sarsi, horse mussel beds or file shell beds are present.
  • Loss of habitat and abrasion from foundation/mooring systems in Sublittoral macrophyte-dominated sediment (including BAP habitats maerl beds, tidal swept channels, horse mussel beds, blue mussel beds). Impacts are considered unlikely for small arrays, although the potential effects A. fragilis, C.cruoriaeformis, D. Montagnei, P. calcareum, E. timida, A. sarsi, horse mussel beds or file shell beds are present.
  • Loss of habitat and abrasion from foundation/mooring systems in Sublittoral biogenic reefs (including BAP habitats horse mussel beds, cold-water coral reefs and blue mussel beds). Impacts are considered unlikely for small arrays, although the potential effects horse mussel beds, cold water coral beds or blue mussel beds are present.

Change in Tidal Flows and Fluxes

Changes, predominantly decreases in tidal flows associated with device supports or mooring systems may have adverse effects on benthic areas, although these are largely expected to be site and habitat specific:

  • Changes in tidal flows and fluxes in Sublittoral coarse sediment (including BAP habitats subtidal sands and gravel, horse mussel beds) due to moorings (offshore). on filter feeders ( i.e. M. modiolus, A. digitatum and A. fragilis) from reduced food supplies and siltation. Strong flows may detach weakly attached organisms. Changes in the overall habitat, through changing grain size in sediments may also occur. While many species are present in a variety of tidal flow conditions, impacts are unlikely. However, the potential may exist for impacts if C. cruoriaeformis, D. Montagnei, E. timida, A. sarsi or horse mussel beds are present.
  • Changes in tidal flows and fluxes in Sublittoral sand (including BAP habitat sub-tidal sands and gravel, blue mussel beds) due to moorings (offshore). on filter feeders ( i.e. M. modiolus, A. digitatum and A. fragilis) from reduced food supplies and siltation. Strong flows may detach weakly attached organisms. Changes in the overall habitat, through changing grain size in sediments may also occur. While many species are present in a variety of tidal flow conditions, impacts are unlikely. However, the potential may exist for impacts if A. fragilis, E. timida, A. sarsi or blue mussel beds are present.
  • Changes in tidal flows and fluxes in Sublittoral mixed sediments (including BAP habitat Horse mussel beds, file shell beds) due to moorings (offshore). on filter feeders ( i.e. M. modiolus, A. digitatum and A. fragilis) from reduced food supplies and siltation. Strong flows may detach weakly attached organisms. Changes in the overall habitat, through changing grain size in sediments may also occur. While many species are present in a variety of tidal flow conditions, impacts are unlikely. However, the potential may exist for impacts if A. fragilis, E. timida, A. sarsi, horse mussel beds or file shell beds are present.
  • Changes in tidal flows and fluxes in Sublittoral macrophyte-dominated sediment (including BAP habitats maerl beds, tidal swept channels, horse mussel beds, blue mussel beds) due to moorings (offshore). on filter feeders ( i.e. M. modiolus, A. digitatum and A. fragilis) from reduced food supplies and siltation. Strong flows may detach weakly attached organisms. Changes in the overall habitat, through changing grain size in sediments may also occur. While many species are present in a variety of tidal flow conditions, impacts are unlikely. However, the potential may exist for impacts if A. fragilis, C. cruoriaeformis, D. Montagnei, P. calcareum, L. corallioides, horse mussel beds or blue mussel beds or maerl beds present.
  • Changes in tidal flows and fluxes in Sublittoral biogenic reefs (including BAP habitats horse mussel beds, cold-water coral reefs and blue mussel beds) due to moorings (offshore). on filter feeders ( i.e. M. modiolus, A. digitatum and A. fragilis) from reduced food supplies and siltation. Strong flows may detach weakly attached organisms. Changes in the overall habitat, through changing grain size in sediments may also occur and increase competition between kelp species ( i.e. A. esculenta) associated with changing flow rates. While many species are present in a variety of tidal flow conditions, impacts are unlikely. However, the potential may exist for impacts if horse mussel beds, cold coral reefs or blue mussel beds if present.

Benthic Habitats:

Habitat Changes

The presence of these devices in the water column and their supporting structures ( i.e. moorings, monopole structures, etc.) has the potential to contribute to habitat changes in a number of ways. In general, impacts on benthic habitats from the devices themselves are likely limited to changes in tidal flows, fluxes and turbulence due to the presence of these devices and associated structures in the water column.

Other impacts, such as scouring, deposition/siltation, abrasion, smothering and the potential for loss of habitat are likely to be associated with the placement of supports ( i.e. gravity and rock anchors, etc.) on the seabed and mooring lines in the water column. Direct seabed impacts such as changes in sediment dynamics, scouring, deposition/siltation and abrasion from supports and moorings have the potential to affect benthic habitats in a range of ways. These can include the introduction of variations and shifts in grain size of sediments affecting habitat character and species distribution; shading or smothering of benthic areas, changes in species distribution via interference with filter feeders ( i.e. interference with feeding, inhibiting respiration, smothering, reproduction, loss of habitat, affecting species distribution, reducing food sources for other species, etc.), and leading to wider changes in ecosystem composition.

Sediment Dynamics, Scour, deposition and Smothering

Changes in sediment dynamics due to the presence of moorings for these devices (gravity anchors, gravity base structures, monopiles, rock anchors and mooring lines) may occur, with the potential for associated impacts such as scouring, deposition/siltation and smothering. The potential for significant change to habitats has been identified. While likely site specific, this may present a potential risk to BAP species such as mussel beds, M. edulis, and filter feeders initially with secondary impacts up the food chain ( i.e. affecting predatory species that feed on them). The potential for impacts in a range of BAP habitats has been identified:

  • Changes in sediment dynamics, increased scour and sediment deposition in High energy littoral rock (including BAP habitat Tidal Swept Channels) if F. distichus is present.
  • Changes in sediment dynamics, increased scour, and the deposition of sediment during high tide in Moderate energy littoral (including BAP habitat Under boulder communities) if under boulder communities are present. Deposition may reduce photosynthesis for algae ( i.e. F. serratus, F. vesticulosus, M. stellatus).
  • Changes in sediment dynamics, increased scour, and deposition of sediment during high tide in Littoral biogenic reefs (including BAP habitat blue mussel beds) and interference with filter feeders ( i.e. M. edulis, S. alveolata). Impacts are unlikely, but potential noted if blue mussel beds are present. Potential for changing the character of this habitat.
  • Changes in sediment dynamics, increased scour and deposition of sediment in features of littoral sediment (including BAP habitat blue mussel beds) and interference with filter feeders ( i.e. M. edulis). Impacts are unlikely in small arrays, but may change the habitat character, with potential impacts noted if blue mussel beds are present.
  • Changes in sediment dynamics, and associated increased scour, deposition and smothering in Sublittoral coarse sediment (including BAP habitats subtidal sands and gravel, blue mussel beds). Impacts unlikely for small arrays, although potential for interference with filter feeders ( i.e. M. modiolus, A. digitatum, A. fragilis) and potential impacts identified if A. fragilis, C. cruoriaeformis, D. Montagnei, E. timida or horse mussel beds are present.
  • Changes in sediment dynamics, and associated increased scour, deposition and smothering in Sublittoral sand (including BAP habitat sub-tidal sands and gravel, blue mussel beds). Impacts are unlikely for small arrays, although potential for interference with filter feeders ( i.e. M. edulis, A. fragilis) and potential impacts identified if A. fragilis, E. timida, A. sarsi or blue mussel beds are present
  • Changes in sediment dynamics, and associated increased scour, deposition and smothering in Sublittoral mixed sediments (including BAP habitat Horse mussel beds, file shell beds). Impacts are unlikely for a small array, although there may be the potential for interference with filter feeders ( i.e. M. modiolus, A. digitatum, A. fragilis) and potential impacts have been identified if A. fragilis, D. Montagnei, E. timida, horse mussel beds or file shell beds are present.
  • Changes in sediment dynamics, and associated increased scour, deposition and smothering in Sublittoral macrophyte-dominated sediment (including BAP habitats maerl beds, tidal swept channels, horse mussel beds, blue mussel beds). Impacts are unlikely for a small array, although there may be the potential for interference with filter feeders ( i.e. M. modiolus, A. digitatum, M. edulis, A. fragilis) and potential impacts have been identified if A. fragilis, C. cruoriaeformis, D. Montagnei, P. calcareum, L. corallioides, horse mussel beds, blue mussel beds of maerl beds are present
  • Changes in sediment dynamics, and associated increased scour, deposition and smothering in Sublittoral biogenic reefs (including BAP habitats horse mussel beds, cold-water coral reefs and blue mussel beds). Impacts are unlikely for a small array, although there may be the potential for interference with filter feeders ( i.e. M. modiolus, A. digitatum, M. edulis) and potential impacts have been identified if horse mussel beds, cold-water coral reefs or blue mussel beds are present.
  • Changes in sediment dynamics in Atlantic and Mediterranean high energy infralittoral rock (including BAP habitat Tidal Swept Channels). Smothering may affect filter feeders ( S. pallida, U. feline, A. digitatum, B. schlosseri, H. panacea) from feeding and growth, while photosynthesis by algae may be compromised. Potential for impacts on S. pallida, as even small impacts may have important influences on UK populations.
  • Changes in sediment dynamics in Atlantic and Mediterranean moderate energy infralittoral rock (including BAP habitat Tidal Swept Channels and S. spinulosa reefs). Smothering may affect filter feeders ( S. pallida, U. feline, A. digitatum, B. schlosseri, H. panacea) from feeding and growth, while photosynthesis by algae may be compromised. Potential for impacts on A. dohrnii and S. pallida, as even small impacts may have important influences on UK populations.
  • Changes in sediment dynamics in Atlantic and Mediterranean high energy circalittoral rock (including BAP habitat Tidal Swept Channels). Smothering may affect filter feeders ( S. pallida, U. feline, A. digitatum, B. schlosseri, H. panacea) from feeding and growth, while photosynthesis by algae may be compromised. Potential for impacts on S. pallida, as even small impacts may have important influences on UK populations.
  • Changes in sediment dynamics in Atlantic and Mediterranean moderate energy circalittoral rock. Potential for smothering impacts on A. dohrnii and S. pallida, as even small impacts may have important influences on UK populations.
  • Changes in sediment dynamics and deposition in features of circalittoral rock may hinder filter feeders ( i.e. respiration, feeding and growth). While characteristic species are common and widespread, potential for impact is noted since this habitat is seldom recorded.

Loss of Habitat/Abrasion

The direct placement of offshore or near-shore devices, and/or their moorings on the seabed can result in damage to benthic habitats, or their loss in extreme instances ( e.g. seabed structures, piling, drilling and anchoring, subsea cable placement).

This could also include additional damage such as the abrasion of marine habitats and sessile/sedentary species ( i.e. BAP species such as mussel and file shell beds) from the installation of technology ( i.e. mooring cables dragging during installation) and subsea cabling ( i.e. placement and dragging during installation and operation). The potential for impacts in a range of BAP habitats has been identified:

  • Loss of habitat and Abrasion from foundation/mooring systems in Atlantic and Mediterranean high energy infralittoral rock (including BAP habitat Tidal Swept Channels), particularly if S. pallida populations is present. Even small amounts of abrasion may impact on these populations.
  • Loss of habitat and abrasion from foundation/mooring systems in Atlantic and Mediterranean moderate energy infralittoral rock (including BAP habitat Tidal Swept Channels and S. spinulosa reefs), particularly if S. pallida and A. dohrnii populations are present. Even small amounts of abrasion may impact on these populations.
  • Loss of habitat and abrasion from foundation/mooring systems in Atlantic and Mediterranean high energy circalittoral rock (including BAP habitat Tidal Swept Channels), particularly if S. pallida populations is present. Even small amounts of abrasion may impact on these populations.
  • Loss of habitat and abrasion from foundation/mooring systems in Atlantic and Mediterranean moderate energy circalittoral rock, particularly if S. pallida and A. dohrnii populations are present. Even small amounts of abrasion may impact on these populations.
  • Loss of habitat and abrasion from foundation/mooring systems in Sublittoral coarse sediment (including BAP habitats subtidal sands and gravel, horse mussel beds). Impacts are considered unlikely for small arrays, although the potential for effects on A. fragilis, C.cruoriaeformis, D. Montagnei, E. timida or horse mussel beds are present.
  • Loss of habitat and abrasion from foundation/mooring systems in Sublittoral sand (including BAP habitat sub-tidal sands and gravel, blue mussel beds). Impacts are considered unlikely for small arrays, although the potential for effects on A. fragilis, E. timida, A. sarsi or blue mussel beds are present.
  • Loss of habitat and abrasion from foundation/mooring systems in Sublittoral mixed sediments (including BAP habitat Horse mussel beds, file shell beds). Impacts are considered unlikely for small arrays, although the potential effects A. fragilis, D. Montagnei, E. timida, A. sarsi, horse mussel beds or file shell beds are present.
  • Loss of habitat and abrasion from foundation/mooring systems in Sublittoral macrophyte-dominated sediment (including BAP habitats maerl beds, tidal swept channels, horse mussel beds, blue mussel beds). Impacts are considered unlikely for small arrays, although the potential effects A. fragilis, C.cruoriaeformis, D. Montagnei, P. calcareum, E. timida, A. sarsi, horse mussel beds or file shell beds are present.
  • Loss of habitat and abrasion from foundation/mooring systems in Sublittoral biogenic reefs (including BAP habitats horse mussel beds, cold-water coral reefs and blue mussel beds). Impacts are considered unlikely for small arrays, although the potential effects horse mussel beds, cold water coral beds or blue mussel beds are present.

Change in Tidal Flows and Fluxes

Changes, predominantly decreases in tidal flows associated with device supports or mooring systems may have adverse effects on benthic areas, although these are largely expected to be site and habitat specific:

  • Changes in tidal flows and fluxes in Sublittoral coarse sediment (including BAP habitats subtidal sands and gravel, horse mussel beds) due to moorings (offshore). on filter feeders ( i.e. M. modiolus, A. digitatum and A. fragilis) from reduced food supplies and siltation. Strong flows may detach weakly attached organisms. Changes in the overall habitat, through changing grain size in sediments may also occur. While many species are present in a variety of tidal flow conditions, impacts are unlikely. However, the potential may exist for impacts if C. cruoriaeformis, D. Montagnei, E. timida, A. sarsi or horse mussel beds are present.
  • Changes in tidal flows and fluxes in Sublittoral sand (including BAP habitat sub-tidal sands and gravel, blue mussel beds) due to moorings (offshore). on filter feeders ( i.e. M. modiolus, A. digitatum and A. fragilis) from reduced food supplies and siltation. Strong flows may detach weakly attached organisms. Changes in the overall habitat, through changing grain size in sediments may also occur. While many species are present in a variety of tidal flow conditions, impacts are unlikely. However, the potential may exist for impacts if A. fragilis, E. timida, A. sarsi or blue mussel beds are present.
  • Changes in tidal flows and fluxes in Sublittoral mixed sediments (including BAP habitat Horse mussel beds, file shell beds) due to moorings (offshore). on filter feeders ( i.e. M. modiolus, A. digitatum and A. fragilis) from reduced food supplies and siltation. Strong flows may detach weakly attached organisms. Changes in the overall habitat, through changing grain size in sediments may also occur. While many species are present in a variety of tidal flow conditions, impacts are unlikely. However, the potential may exist for impacts if A. fragilis, E. timida, A. sarsi, horse mussel beds or file shell beds are present.
  • Changes in tidal flows and fluxes in Sublittoral macrophyte-dominated sediment (including BAP habitats maerl beds, tidal swept channels, horse mussel beds, blue mussel beds) due to moorings (offshore). on filter feeders ( i.e. M. modiolus, A. digitatum and A. fragilis) from reduced food supplies and siltation. Strong flows may detach weakly attached organisms. Changes in the overall habitat, through changing grain size in sediments may also occur. While many species are present in a variety of tidal flow conditions, impacts are unlikely. However, the potential may exist for impacts if A. fragilis, C. cruoriaeformis, D. Montagnei, P. calcareum, L. corallioides, horse mussel beds or blue mussel beds or maerl beds present.
  • Changes in tidal flows and fluxes in Sublittoral biogenic reefs (including BAP habitats horse mussel beds, cold-water coral reefs and blue mussel beds) due to moorings (offshore). on filter feeders ( i.e. M. modiolus, A. digitatum and A. fragilis) from reduced food supplies and siltation. Strong flows may detach weakly attached organisms. Changes in the overall habitat, through changing grain size in sediments may also occur and increase competition between kelp species ( i.e. A. esculenta) associated with changing flow rates. While many species are present in a variety of tidal flow conditions, impacts are unlikely. However, the potential may exist for impacts if horse mussel beds, cold coral reefs or blue mussel beds if present.

Benthic Habitats:

With the presence of tidal energy devices within the water column and the likelihood of seabed disturbance during installation, many of the potential impacts identified in the columns to the left are likely to be associated with these emerging technologies.

In general terms, the potential for impacts on benthic habitats from the devices themselves is likely limited to loss of benthos from the installation of a device and its seabed mounting, ( i.e. anchors, piling, etc.) to changes in tidal flows, fluxes and turbulence due to the presence of these devices and associated structures in the water column.

The potential for associated effects ( e.g. sediment deposition, scouring, smothering, abrasion, etc.) during the operational phase of a project has also been identified for a range of habitats (see left).

Population and human health [20]

Summary of key potential effects on population and human health:

  • Displaced/increased shipping density.
  • Reductions in the safety of navigation.
  • Risk of collision of recreational or commercial shipping with installation vessels and operational devices, particularly for devices and vessels that are low in the water and in high waves.
  • Access restrictions - the presence of devices in the water may restrict or reduce access to key recreational sailing areas or other water sports.

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. Consideration of device types that are fully submerged and allow shipping to pass over the top of them could reduce effects, but guidance would need to be sought on a case-by-case basis on the level of clearance required.

The potential for vessel collisions with above water device components, or components at shallow depths in the water column, has been identified and may have the potential for serious injury.

However, navigational warnings ( i.e. marker buoys, navigational aids, lighting) are likely to be required on such devices for navigational purposes.

The potential for vessel collisions with above water device components, or components at shallow depths in the water column, has been identified and may have the potential for serious injury.

However, navigational warnings ( i.e. marker buoys, navigational aids, lighting) are likely to be required on such devices for navigational purposes.

The potential for vessel collisions with device components at shallow depths in the water column has been identified and may have the potential for serious injury.

However, navigational warnings ( i.e. marker buoys, navigational aids, lighting) are likely to be required on such devices for navigational purposes.

As for other tidal devices, the potential for vessel collisions with device components at shallow depths in the water column, has been identified and may have the potential for serious injury.

However, navigational warnings ( i.e. marker buoys, navigational aids, lighting) are likely to be required on such devices for navigational purposes.

Water and marine environment [21]

Summary of key potential effects on water quality include:

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.

Potential for impacts from local changes in water quality during installation ( i.e. turbulence, turbidity) and due to the presence of these devices in the water column ( i.e. water turbulence, changes in tidal flows/fluxes) with localised impacts. Additional impacts ( i.e. changes to sediment dynamics, scouring, deposition, smothering and water turbulence) may be associated with the installation and presence of support cables and structures on the seabed ( i.e. gravity anchor and mooring).

Potential for installation impacts such as water turbidity and contamination risks associated with installation and operation ( e.g. leakage from vessels or equipment).

See Biodiversity section.

Potential for impacts from local changes in water quality during installation ( i.e. turbulence, turbidity) and due to the presence of these devices in the water column ( i.e. water turbulence, changes in tidal flows/fluxes) with localised impacts. Additional impacts ( i.e. changes to sediment dynamics, scouring, deposition, smothering and water turbulence) may be associated with the installation and presence of support cables and structures on the seabed ( i.e. gravity anchor and mooring).

Potential for installation impacts such as water turbidity and contamination risks associated with installation and operation ( e.g. leakage from vessels or equipment).

See Biodiversity section.

Potential for impacts from local changes in water quality during installation ( i.e. turbulence, turbidity) and due to the presence of these devices in the water column ( i.e. water turbulence, changes in tidal flows/fluxes) with localised impacts. Additional impacts ( i.e. changes to sediment dynamics, scouring, deposition, smothering and water turbulence) may be associated with the installation and presence of support cables and structures on the seabed ( i.e. gravity anchor and mooring).

Potential for installation impacts such as water turbidity and contamination risks associated with installation and operation ( e.g. leakage from vessels or equipment).

See Biodiversity section.

Potential for impacts from local changes in water quality during installation ( i.e. turbulence, turbidity) and due to the presence of these devices in the water column ( i.e. water turbulence, changes in tidal flows/fluxes) with localised impacts. Additional impacts ( i.e. changes to sediment dynamics, scouring, deposition, smothering and water turbulence) may be associated with the installation and presence of support cables and structures on the seabed ( i.e. gravity anchor and mooring).

Potential for installation impacts such as water turbidity and contamination risks associated with installation and operation ( e.g. leakage from vessels or equipment).

See Biodiversity section.

Climatic factors [22]

Contribution to renewable generation and reduction in GHG emissions ( i.e. displacement of energy generated from non-renewable sources).

Contribution to renewable generation and reduction in GHG emissions ( i.e. displacement of energy generated from non-renewable sources).

Contribution to renewable generation and reduction in GHG emissions ( i.e. displacement of energy generated from non-renewable sources).

Contribution to renewable generation and reduction in GHG emissions ( i.e. displacement of energy generated from non-renewable sources).

Marine geology and coastal processes [23]

Summary of key potential effects on geology:

  • Disturbance or damage to coastal Geological SSSIs and GCRs.

Changes in coastal processes due to energy extraction Seabed contamination and water quality (including disposal areas): key issues.

As detailed in Biodiversity section, the potential may exist for changes to flows in the boundary layer, and localised reductions in tidal flows from the devices themselves.

Other impacts may occur from the placement of support structures or moorings for these devices on the seabed, including increased scouring, deposition/siltation from changes to coastal processes ( i.e. sediment dynamics and tidal fluxes) associated with the during operation, benthic disturbance during installation ( i.e. loss of habitat), abrasion of marine geology in installation of technology and subsea cabling ( i.e. damage to habitats, particularly to sensitive habitats ( BAP)).

As detailed in Biodiversity section, the potential may exist for changes to flows in the boundary layer, and localised reductions in tidal flows from the devices themselves.

Other impacts may occur from the placement of support structures or moorings for these devices on the seabed, including increased scouring, deposition/siltation from changes to coastal processes ( i.e. sediment dynamics and tidal fluxes) associated with the during operation, benthic disturbance during installation ( i.e. loss of habitat), abrasion of marine geology in installation of technology and subsea cabling ( i.e. damage to habitats, particularly to sensitive habitats ( BAP)).

As detailed in Biodiversity section, the potential may exist for changes to flows in the boundary layer, and localised reductions in tidal flows from the devices themselves.

Other impacts may occur from the placement of support structures or moorings for these devices on the seabed, including increased scouring, deposition/siltation from changes to coastal processes ( i.e. sediment dynamics and tidal fluxes) associated with the during operation, benthic disturbance during installation ( i.e. loss of habitat), abrasion of marine geology in installation of technology and subsea cabling ( i.e. damage to habitats, particularly to sensitive habitats ( BAP)).

As detailed in Biodiversity section, the potential may exist for changes to flows in the boundary layer, and localised reductions in tidal flows from the devices themselves.

Other impacts may occur from the placement of support structures or moorings for these devices on the seabed, including increased scouring, deposition/siltation from changes to coastal processes ( i.e. sediment dynamics and tidal fluxes) associated with the during operation, benthic disturbance during installation ( i.e. loss of habitat), abrasion of marine geology in installation of technology and subsea cabling ( i.e. damage to habitats, particularly to sensitive habitats ( BAP)).

Historic Environment [24]

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 routeing studies at project level in accordance with 'Holford Rules' best practice guidance on routeing overhead transmission lines; avoid sensitive sites and areas; provide screening (substations).

There is the potential for placement of device moorings ( i.e. gravity-base, anchors, etc.) on known and designated historic sites, and on unknown sites ( i.e. wrecks). The potential may also exist for adverse effects on historic sites located nearby or downstream during operation ( i.e. scouring, deposition/siltation or abrasion from moorings; deposition/siltation from the presence of devices).

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

Pre-construction impacts can result from intrusive site investigation.

Construction effects as a result device installation, in particular from moorings, chains and cables. In particular as a result of piling and preparation of the seabed disturbing historic features.

Secondary effects from construction might arise from vessels anchoring and from temporary visual impacts on the setting of historic features

Associated cables and grid could directly impact on archaeological features on the seabed.

Operational effects are more limited Mooring requires lengthy chains and cables that rest on the sea bed and these can cause damage to heritage assets.

Changes to sediment processes and associated coastal erosion might cause impacts on some resources but may also help to reduce energy reaching shore and some erosion related heritage impacts.

Visual impacts for the setting of historic features during operation, construction and decommissioning

There is the potential for placement of device moorings ( i.e. gravity-base, anchors, etc.) on known and designated historic sites, and on unknown sites ( i.e. wrecks). The potential may also exist for adverse effects on historic sites located nearby or downstream during operation ( i.e. scouring, deposition/siltation or abrasion from moorings; deposition/siltation from the presence of devices).

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

Pre-construction impacts can result from intrusive site investigation.

Construction effects as a result device installation, in particular from moorings, chains and cables. In particular as a result of piling and preparation of the seabed disturbing historic features.

Secondary effects from construction might arise from vessels anchoring and from temporary visual impacts on the setting of historic features

Associated cables and grid could directly impact on archaeological features on the seabed.

Operational effects are more limited Mooring requires lengthy chains and cables that rest on the sea bed and these can cause damage to heritage assets.

Changes to sediment processes and associated coastal erosion might cause impacts on some resources but may also help to reduce energy reaching shore and some erosion related heritage impacts.

Visual impacts for the setting of historic features during operation, construction and decommissioning

There is the potential for placement of device moorings ( i.e. gravity-base, anchors, etc.) on known and designated historic sites, and on unknown sites ( i.e. wrecks). The potential may also exist for adverse effects on historic sites located nearby or downstream during operation ( i.e. scouring, deposition/siltation or abrasion from moorings; deposition/siltation from the presence of devices).

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

Pre-construction impacts can result from intrusive site investigation.

Construction effects as a result device installation, in particular from moorings, chains and cables. In particular as a result of piling and preparation of the seabed disturbing historic features.

Secondary effects from construction might arise from vessels anchoring and from temporary visual impacts on the setting of historic features

Associated cables and grid could directly impact on archaeological features on the seabed.

Operational effects are more limited Mooring requires lengthy chains and cables that rest on the sea bed and these can cause damage to heritage assets.

Changes to sediment processes and associated coastal erosion might cause impacts on some resources but may also help to reduce energy reaching shore and some erosion related heritage impacts.

Visual impacts for the setting of historic features during operation, construction and decommissioning

There is the potential for placement of device moorings ( i.e. gravity-base, anchors, etc.) on known and designated historic sites, and on unknown sites ( i.e. wrecks). The potential may also exist for adverse effects on historic sites located nearby or downstream during operation ( i.e. scouring, deposition/siltation or abrasion from moorings; deposition/siltation from the presence of devices).

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

Pre-construction impacts can result from intrusive site investigation.

Construction effects as a result device installation, in particular from moorings, chains, cables and installation of supports such as piling (if required).

Secondary effects from construction might arise from vessels anchoring and from temporary visual impacts on the setting of historic features

Associated cables and grid could directly impact on archaeological features on the seabed.

Operational effects are more limited Mooring requires lengthy chains and cables that rest on the sea bed and these can cause damage to heritage assets.

Changes to sediment processes and associated coastal erosion might cause impacts on some resources but may also help to reduce energy reaching shore and some erosion related heritage impacts.

Visual impacts for the setting of historic features during operation, construction and decommissioning

Landscape/Seascape [25]

Summary of key potential effects on land/seascape include:

  • For linear structures, with devices at up to 5km from the coastline, effects may occur for all seascape types. The further from the coast, the less the effect becomes, and beyond 10km the effects are typically minor.
  • For point structures, 8 out of the 10 seascape types are of high sensitivity to these types of device, with potential effects occurring at 0-10km from coastline. Moderate effects may also occur at distances over 10km.
  • Submerged structures are likely to have negligible effects on seascape (although marker buoys and lighting may be required).
  • Fixed coastal structures may have moderate effects depending on their design and location.
  • Landscape and visual intrusion from substations and overhead lines as onshore grid connections.

Key measures to prevent adverse effects may include: maximising the distance of devices from shore; reducing the height of devices above the 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 routeing studies at project level in accordance with 'Holford Rules' best practice guidance on routeing overhead transmission lines; avoid sensitive sites and areas; provide screening (substations).

Potential for visual issues identified if surface-piercing structures are present and during installation and maintenance periods ( i.e. monopiling equipment, etc.). This may result in an alteration of aesthetic character of the coastline, particularly if positioned near shore, which may be viewed by some as negative impacts.

No shore based infrastructure is anticipated, hence only impacts considered are those from devices in coastal waters.

Potential for visual issues identified if surface-piercing structures are present and during installation and maintenance periods ( i.e. monopiling equipment, etc.). This may result in an alteration of aesthetic character of the coastline, particularly if positioned near shore, which may be viewed by some as negative impacts.

No shore based infrastructure is anticipated, hence only impacts considered are those from devices in coastal waters.

Potential for visual issues identified during installation and maintenance periods ( i.e. monopiling equipment, etc.). This may result in an alteration of aesthetic character of the coastline, particularly if positioned near shore, which may be viewed by some as negative impacts.

No shore based infrastructure is anticipated, hence only impacts considered are those from devices in coastal waters.

Potential for visual issues identified during installation and maintenance periods ( i.e. vessels and installation equipment). This may result in an alteration of aesthetic character of the coastline, particularly if positioned near shore, which may be viewed by some as negative impacts.

No shore based infrastructure is anticipated, hence only impacts considered are those from devices in coastal waters.


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