Secondary Mitigation and Residual Effect
  1. No benthic subtidal and intertidal ecology mitigation is considered necessary for the impact of temporary habitat loss/disturbance during the operation and maintenance phase because the likely effects, in the absence of further mitigation (beyond the designed in measures outlined in section 8.10), are not significant in EIA terms.

Decommissioning Phase

Magnitude of Impact

Subtidal Habitat IEFs

  1. The nature and extent of temporary habitat loss/disturbance during decommissioning is likely to be similar or the same as that described for the same activities during the construction phase. However, it should be noted that this approach is considered precautionary as there is no statutory requirement for decommissioned cables to be removed. Therefore, cables may be left buried in place or alternatively partially removed by extracting the cables back out of the ducts. Such details will be included within the Decommissioning Programme which will be developed to minimise environmental disturbance and will be updated throughout the lifetime of the Proposed Development (see Table 8.16   Open ▸ ) to account for changing good practice.
  2. Decommissioning activities within the Proposed Development array area and Proposed Development export cable corridor will lead to temporary subtidal habitat loss/disturbance. The maximum design scenario is for up to 34,571,200 m2 of temporary habitat loss/disturbance during the decommissioning phase ( Table 8.10   Open ▸ ). The decommissioning activities includes jack-up vessels disturbing up to 1,268,000 m2 as well as up to 32,865,000 m2 for the decommissioning of inter-array, interconnector, and offshore export cables, and up to 438,200 m2 from anchor placements during cable removal. This equates to a small proportion (2.38%) of the benthic ecology subtidal and intertidal study area. In the event that cables are left in situ, the extent of temporary habitat disturbance would be reduced.
  3. The impact is predicted to be of local spatial extent, short term duration, intermittent and high reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.

Firth of Forth Banks Complex MPA

  1. The FFBC MPA overlaps with the site boundary for the Proposed Development and therefore some temporary habitat loss/disturbance will occur within the FFBC MPA. The overall figures for the spatial overlap are outlined in paragraph 85 together with the assumptions for the overlap of infrastructure/activities with the FFBC MPA. Based on this percentage of overlap and the maximum design scenario for the decommissioning phase, up to 8,412,661 m2 of temporary habitat loss/disturbance may occur within the FFBC MPA (see Table 8.20   Open ▸ ), which equates to 0.39% of the total area of the FFBC MPA. This can be broken down for the composite parts of the MPA as follows: up to 5,820,638 m2 within the area of Berwick Bank (1.08% of the area of Berwick Bank) and 2,592,023 m2 within the area of Scalp and Wee Bankie (0.31% of the area of Scalp and Wee Bankie). The Montrose Bank will not be affected.
  2. The total area of temporary subtidal habitat loss represents a very small percentage loss (0.001%) of the total area of the OSPAR Region II (Greater North Sea) within which ocean quahog is listed as under threat and/or decline. It also represents a very small percentage (0.39%) of the offshore subtidal sands and gravels feature of the MPA, which is also equivalent to the available supporting habitat for ocean quahog.
  3. The impact is predicted to be of local spatial extent, short term duration, intermittent and high reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.

 

Table 8.20:
Area of FFBC MPA Disturbed by Activities During the Proposed Development’s Decommissioning

Table 8.20: Area of FFBC MPA Disturbed by Activities During the Proposed Development’s Decommissioning

 

Sensitivity of the Receptor

Subtidal Habitat IEFs

  1. The sensitivity of the IEFs is as described previously for the construction phase assessment in paragraphs 91 to 102 and in Table 8.18   Open ▸ .

Firth of Forth Banks Complex MPA

  1. The sensitivity of the IEFs found within the FFBC MPA are as described previously for the construction phase assessment in paragraphs 103 to 107 and in Table 8.19   Open ▸ .
Significance of the Effect

Subtidal Habitat IEFs

  1. For the subtidal sand and muddy sand sediments IEF, the subtidal coarse and mixed sediments IEF, moderate energy subtidal rock IEF, cobble/stony reef outside of an SAC IEF and rocky reef outside an SAC IEF the magnitude of the impact is deemed to be low, and the sensitivity of the receptor is considered to be medium. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.
  2. For the seapens and burrowing megafauna IEF and the Sabellaria reef outside of an SAC IEF the magnitude of the impact is deemed to be low, and the sensitivity of the receptor is considered to be high. The effect will, therefore, be of minor adverse significance because of the intermittent and localised nature of the impact which makes recovery highly likely, which is not significant in EIA terms.

Firth of Forth Banks Complex MPA

  1. Overall, for the subtidal sands and gravels IEF and the shelf banks and mounds IEF, the magnitude of the impact is deemed to be low, and the sensitivity of the receptor is considered to be medium. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.
  2. Overall, for ocean quahog IEF the magnitude of the impact is deemed to be low, and the sensitivity of the receptor is considered to be high. The effect will, therefore, be of moderate adverse significance in the medium term (i.e. within approximately ten years of completion of construction), with this decreasing to minor adverse significance in the long term as the sediments and ocean quahog populations are predicted to recover. Therefore, minor effects are predicted in the long-term which are not significant in EIA terms.
Secondary Mitigation and Residual Effect
  1. No benthic subtidal and intertidal ecology mitigation is considered necessary for the impact of temporary habitat loss/disturbance during the decommissioning phase because the likely effects, in the absence of further mitigation (beyond the designed in measures outlined in section 8.10), are not significant in EIA terms.

Increased Suspended Sediment Concentrations and Associated Sediment Deposition

  1. Increases of suspended sediments and associated sediment deposition are predicted to occur during the construction, operation and maintenance and decommissioning phases as a result of the installation/removal of foundations, sand wave clearance activities and the installation of inter-array, OSP/Offshore convertor station platform interconnector, and offshore export cables. Increases in suspended sediments and associated sediment deposition are also predicted to occur during the operation and maintenance phase due to inter-array, OSP/Offshore convertor station platform interconnector, and offshore export cables repair and reburial events. Volume 3, appendix 7.1 provides a full description of the physical assessment, including numerical modelling used to inform the predictions made with respect to increases in suspended sediment and subsequent deposition.
  2. The benchmarks for the relevant MarESA pressures which have been used to inform this assessment of effect are described here.
  • Changes in suspended solids (water clarity): the benchmark for which is a change in one rank on the Water Framework Directive (WFD) scale (e.g. from clear to intermediate for one year, caused by activities disturbing sediment or organic particulate material and mobilising it into the water column such as dredging, disposal at sea, cable and pipeline burial).
  • Smothering and siltation rate changes (light): the benchmark for light deposition is up to 5 cm of fine material added to the habitat in a single discrete event.
    1. The benchmarks for the relevant FeAST pressures which have been used to inform this assessment of effect are described below.
  • Water clarity changes: the benchmark for which is a change in one rank on the WFD scale, (e.g. from clear to turbid for one year (ranks are mean suspended particulate matter (SPM) in units of mg/c: >300 - very turbid; 100-300 - medium turbidity; 10-100 - intermediate; <10 - clear)).
  • Siltation changes (low): the benchmark for which is 5 cm of fine material added to the seabed in a single event, or the deposition of fine material over the lifetime of the development.
    1. These pressures correspond to the impacts associated with the installation of wind turbines, OSPs/Offshore convertor station platforms and offshore cables (export, inter-array and interconnector) by drilling and jet trenching respectively.
    2. The Cefas Climatology Report 2016 shows the spatial distribution of average non-algal SPM for the majority of the UK continental shelf. For 1998 to 2005 the largest plumes are associated with large rivers such as the Thames estuary, the Wash and Liverpool Bay, which show mean values of SPM above 30 mg/l. Based on the data provided within this study, the SPM associated with the Proposed Development has been estimated as approximately 0 mg/l to 1 mg/l over the 1998 to 2005 period (Cefas, 2016) (see volume 3, appendix 7.1).
    3. Seabed preparation activities (e.g. sand wave and boulder clearance) will occur in advance of installation of the offshore cables. Dredged material will be disposed of within the Proposed Development array and Proposed Development export cable corridor area.
    4. As discussed in paragraph 40, this assessment has been undertaken on the broad IEFs and separately on the IEFs that comprise features of the FFBC MPA.

Construction Phase

Magnitude of Impact

Subtidal Habitat IEFs

  1. The installation of Proposed Development infrastructure within the Proposed Development array area and Proposed Development export cable corridor will lead to increases in suspended sediment concentrations and associated sediment deposition. Full details of the modelling undertaken to inform this assessment is presented in volume 3, appendix 7.1, including the individual scenarios considered and assumptions within these and full modelling outputs for suspended sediments and associated sediment deposition. For the purposes of this assessment, the following activities have been considered (see Table 8.10   Open ▸ ):

Intertidal Habitat IEFs

  1. The magnitude of the change in the intertidal zone will be on a very small scale, modelling from volume 2 chapter 7 showed that sedimentation at the coastline is predicted to be typically <3 mm.
  2. The impact is predicted to be of local spatial extent, short term duration, intermittent and high reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be negligible.

Firth of Forth Banks Complex MPA

  1. The magnitude of the change in environmental condition due to the impact of increased suspended sediment concentrations and associated sediment deposition is the same across the Proposed Development including in areas which overlap with the FFBC MPA (see paragraphs 148 and 153).
  2. The impact is predicted to be of local spatial extent, short term duration, intermittent and medium reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.

Berwickshire and North Northumberland Coast SAC

  1. The magnitude of the change in environmental condition due to the impact of increased suspended sediment concentrations and associated sediment deposition is the same across the Proposed Development however at the coast it is particularly low such as at the Berwickshire and North Northumberland Coast SAC (see paragraph 153). Sedimentation at the coastline is predicted to be typically <3 mm. During the sand wave clearance activity in the Proposed Development export cable corridor the sediment plume is expected have a width of 10 km, corresponding with the tidal excursion, with an average concentration of <100 mg/l.
  2. The impact is predicted to be of local spatial extent, short term duration, intermittent and high reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be negligible.
Sensitivity of the Receptor

Subtidal Habitat IEFs

  1. The subtidal sand and muddy sand sediments IEF, subtidal coarse and mixed sediments IEF and moderate energy subtidal rock IEFs have a sensitivity of low or less for the change to suspended solids pressure. Subtidal IEFs overall have a low sensitivity to smothering and siltation rate change but a number of them have been assessed as not sensitive to this pressure ( Table 8.21   Open ▸ ).
  2. The FeAST assesses the subtidal sand and muddy sand sediments IEF to be not sensitive to changes in water clarity and a medium sensitivity to low level siltation change although this can be lowered to low based on the species present ( Table 8.21   Open ▸ ). Within this IEF the biotopes Echinocyamus pusillus, Ophelia borealis and Abra prismatica in circalittoral fine sand (SS.SSa.CFiSa.EpusOborApri) and Nephtys cirrosa and Bathyporeia spp. in infralittoral sand (SS.SSa.IFiSa.NcirBat) were the most sensitive. For both biotopes sensitivity to changes in water clarity is low as an increase in suspended solids would also affect primary productivity. This may alter the availability of food for characteristic filter and suspension feeders in biotopes such as SS.SSa.CFiSa.EpusOborApri. According to Widdows et al. (1979), growth of filter-feeding bivalves may be impaired at SPM concentrations >250 mg/l. However, these characteristic species may have some tolerance to short-term increases in turbidity due to their survival of storms and other events (Tillin, 2016). Additionally the characteristic bivalves and polychaetes of the SS.SSa.CFiSa.EpusOborApri biotope have a low sensitivity to low siltation change due to their ability survive short periods under sediment.
  3. The FeAST assesses the subtidal coarse and mixed sediments IEF to have no sensitivity to water clarity change and medium sensitivity to low level siltation change ( Table 8.21   Open ▸ ) but this can be reduced based on the species involved. The biotope SS.SMx.OMx.PoVen has a low sensitivity to water clarity change because reduced water clarity may impact upon primary production reducing food availability as well as potentially clogging the feeding apparatus of characteristic bivalves, although tolerance over a short period of time is likely. Furthermore, as mentioned in paragraph 93, siltation change can lead to the burial of the characteristic epifauna of some the biotopes of this IEF, however at this benchmark and over a short period of time survival is likely.
  4. The seapens and burrowing megafauna IEF are found by the MarESA to not be sensitive to either of the relevant pressures associated with increases SSC and deposition. This is due to their high recovery rate once SSC returns to normal, as well as their affinity for sheltered muddy habitats which naturally have high sediment accretion rates.
  5. The S. spinulosa reef outside of an SAC IEF is also found by the MarESA to be not sensitive to either of the relevant pressures associated with increases SSC and deposition. This is because they are not reliant on water clarity as they do not photosynthesise. Additionally, S. spinulosa are found in areas of high-water movement which will aid in the quick dispersal of deposited material reducing exposure to potentially damaging conditions, although these are unlikely to be greater than the levels produced by storms which are S. spinulosa regularly survive.
  6. The FeAST at the time of writing has not assessed the moderate energy subtidal rock IEF. The MarESA however identifies a low sensitivity to both pressures. Sensitivity to water clarity change results from changes in the light availability on the seafloor which will reduce the ability of the characteristic oarweed to photosynthesise. Light siltation change in a single incident is unlikely to result in significant mortality before sediments are removed by current and wave action. Adults are more resistant but will experience a decrease in growth and photosynthetic rates (Tillin and Stamp, 2016). A similar effect will occur in relation to the cobble and stony reef outside of an SAC and rocky reef outside an SAC IEFs where smothering could result in the obstruction of the feeding apparatus of some species such as soft coral Alcyonium digitatum. Although smothering may impact specific species, and therefore the overall biological community, the physical habitat of the reef will not be affected allowing for future recovery (De-Bastos and Hill, 2016). Beyond the immediate IEFs, primary production is also considered to be sensitive to suspended sediment concentrations. The rate at which nutrients are converted into phytoplankton biomass via primary production is directly proportional to the quantity of light received (Cole and Cloen, 1987). Increasing suspended sediments can cause a shoaling or narrowing of the euphotic zone, where there is sufficient light for primary production, resulting in a reduction in the in the habitat available for phytoplankton to undergo primary production (Dupont and Aksnes, 2013). Therefore, suspended sediment concentration is a limiting factor for primary productivity in shelf seas (UKMMAS, 2016). However, both Cabré et al. (2015) and Laufkötter et al. (2015) conclude that changing light levels were not a primary driver of changes in net primary production except at the highest latitudes where there were large decreases in sea ice cover.
  7. The moderate energy subtidal rock IEF, cobble/stony reef outside of an SAC IEF, and rocky reef outside an SAC IEF is deemed to be of low vulnerability, medium recoverability, and national value. The sensitivity of the IEF is therefore, considered to be medium.
  8. The subtidal sand and muddy sand sediments IEF and the subtidal coarse and mixed sediments IEF are deemed to be of low vulnerability, high recoverability, and regional value. The sensitivity of the IEFs is therefore, considered to be low.
  9. The seapens and burrowing megafauna IEF, and the Sabellaria reef outside of an SAC IEF are deemed to be not sensitive and of national value. The sensitivity of the IEFs is therefore, considered to be negligible.
  10. Although there is an impact on PMF(s) this will not create significant impact on the national status of these features because of the negligible to low sensitivity of the IEFs and the limited scale of the impact only noticeably impacting habitats in the immediate vicinity of new infrastructure installation.

Intertidal Habitat IEFs

  1. The impact of changes in water clarity and smothering/siltation changes for intertidal IEFs are presented in Table 8.21   Open ▸ . With respect to the intertidal rock IEF, the biotope Ulva spp. on freshwater-influenced and/or unstable upper eulittoral rock (LR.FLR.Eph.Ent) has a high tolerance to burial and the shade produced by reduced water clarity, however is sensitive to the abrasion and scouring forces resulting from the deposition and removal of sediment (Tillin and Budd, 2015). Increases in suspended sediment may result in the clogging of the feeding apparatus of filter/deposit feeders in some biotopes such as Corallina officinalis on exposed to moderately exposed lower eulittoral rock (LR.HLR.FR.Coff), however the wave action will reduce accumulation on the algal turf of this IEF (Tillin and Tyler-Walter, 2015a). Some species, such a Fucus serratus within the biotope F. serratus and red seaweeds on moderately exposed lower eulittoral rock (LR.MLR.BF.Fser.R), are likely to experience adverse effects from the loss of light associated with reduced water clarity and smothering (d’Avack and Tyler-Walter, 2015). Similarly, in areas of reduced water clarity, Laminaria species experience significant decrease in growth from the shading of suspended matter and/or phytoplankton (Lyngby and Mortensen, 1996; Spilmont et al., 2009).
  2. The fucus dominated intertidal rock IEF has a higher sensitivity than the intertidal rock IEF as it is more strongly characterised by algal/seaweed communities. Biotopes such as Fucus vesiculosus on mid eulittoral mixed substrata (LR.LLR.F.Fves.X) have a medium sensitivity to changes in water clarity and smothering as these effects reduce the ability of F. vesiculosus to photosynthesise reducing its growth potential however they are likely to rapidly regain photosynthetic capabilities following the return of light levels to the baseline conditions (Perry, d’Avack and Budd, 2015). This level of recovery extends to short periods of smothering; however, spores and juvenile individuals will be more likely to experience mortality (Perry, d’Avack and Budd, 2015). The smothering of algal turf will reduce grazing by littorinids which characterise the Coralline crusts and Corallina officinalis in shallow eulittoral rockpools (LR.FLR.Rkp.Cor.Cor) biotope, however sediments are likely to be removed rapidly by eave action (Tillin and Budd, 2018).
  3. The communities associated with the intertidal sands IEF are characterised by species living in the sediment and are therefore unlikely to be directly affected by an increased concentration of suspended matter in the water column (Ashley, 2020). Additionally, mobile and burrowing species are generally able to reposition following periodic siltation (Ashley, 2020).
  4. The intertidal rock IEF and fucus dominated intertidal rock IEF are deemed to be of medium vulnerability and medium recovery and national value. The sensitivity of the IEFs is therefore, considered to be medium.
  5. The intertidal sands IEF is deemed to be not sensitive and national value. The sensitivity of the IEF is therefore, considered to be negligible.

 

Table 8.21:
Sensitivity of the Benthic Subtidal and Intertidal IEFs to Increased Suspended Sediment Concentration and Associated Sediment Deposition

Table 8.21: Sensitivity of the Benthic Subtidal and Intertidal IEFs to Increased Suspended Sediment Concentration and Associated Sediment Deposition

Firth of Forth Banks Complex MPA

  1. The FeAST determines that the subtidal sands and gravels IEF is not sensitive to changes in water clarity and has medium sensitivity to light smothering and siltation rate change ( Table 8.22   Open ▸ ). Although siltation change can be reduced to low depending on species present. The MarESA determines the subtidal sands and gravels IEF which occurs within the FFBC MPA to have a low sensitivity to the pressures associated with increased suspended sediment concentration and associated sediment deposition ( Table 8.22   Open ▸ ). Paragraph 162 describes how the biotope SS.SSa.CFiSa.EpusOborApri is tolerant to both pressures, which also applies to the other sensitive biotope SS.SSa.CFiSa.ApriBatPo.
  2. The shelf banks and mounds IEF has the same sensitivity as the subtidal sands and gravel IEF as it is represented by the same biotopes.
  3. The FeAST and the MarESA determine that the ocean quahog IEF is not sensitive to water clarity light smothering and siltation rate change ( Table 8.22   Open ▸ ). This is due to their ability to unbury themselves (paragraph 105) at this level of siltation (maximum of 0.5 m to 0.75 m of as well as their insensitivity to light. Ocean quahog occur in silty sediments in sheltered to wave exposed conditions, where the surface of the sediment is probably regularly mobilised, and where accretion rates are moderate to high. Therefore, increase in turbidity (suspended sediments) may not adversely affect the species, especially as it can avoid sudden changes by burrowing for several days (Tyler-Walter and Sabatini, 2017).
  4. The subtidal sands and gravel IEF and the shelf banks and mounds IEF are deemed to be of low vulnerability, high recoverability, and national value. The sensitivity of the IEFs is therefore, considered to be low.
  5. The ocean quahog IEF is deemed to be not sensitive and of national value. The sensitivity of the IEF is therefore, considered to be negligible.

 

Table 8.22:
Sensitivity of the Benthic Subtidal IEFs found within the FFBC MPA to Increased Suspended Sediment Concentration and Associated Sediment Deposition

Table 8.22:  Sensitivity of the Benthic Subtidal IEFs found within the FFBC MPA to Increased Suspended Sediment Concentration and Associated Sediment Deposition

 

Berwickshire and North Northumberland Coast SAC

  1. The FeAST determines that tide swept coarse sands, which are representative of the mudflats and sandflats not covered by seawater at low tide IEF, are not sensitive to light smothering or siltation rate change (see Table 8.23   Open ▸ ). The MarESA largely identifies mudflats and sandflats to be low to not sensitive to water quality changes, however the seagrass Zostera noltii can be found in the SAC which has a high sensitivity as high suspended sediments can reduce light availability and therefore inhibit photosynthesis. Similarly, biotopes which are of medium sensitivity to smothering and siltation rate change site the same reason for their sensitivity as well as other fauna such as common mussel Mytilus edulis being unable undergo suspension and filter feeding due to higher-than-normal levels of suspended sediment.
  2. Reefs (subtidal and intertidal rocky reefs within the SAC) are not assessed within the FeAST as it is not an MPA protected feature in Scotland. The MarESA however identifies that the biotopes which represent these habitats are of medium sensitivity to smothering and siltation rate change and water quality changes on reefs is due to the inability of organisms to feed until the sediment is dispersed. The impact on intertidal reefs in particular is likely to be very small due to their distance from the Proposed Development array area as well as the small scale of the works in the nearshore zone which could result in increased suspended sediments in the intertidal zone.
  3. Submerged or partially submerged sea caves IEF are not assessed within the FeAST as it is not an MPA protected feature in Scotland. The MarESA finds the effects of increased siltation and changes in water quality to have a varying impact on component biotopes. The effect can either be a reduction in suspension feeding by characteristic species or many encrusting sponges, for example, prefer these conditions, and will have no problem operating in these conditions over short periods. This captures the range of fauna in these habitats.
  4. The large shallow inlets and bays IEF doesn’t have any specific biotopes associated with it, although the feature consists of the following sub-features: intertidal sand and muddy sand; subtidal coarse sediment; subtidal sand; subtidal mud, subtidal mixed sediment, and saltmarsh habitat. The sensitivity of the component habitats is therefore likely to be as described previously for equivalent IEFs.
  5. The Berwickshire and North Northumberland Coast SAC site is located 4.12 km from the Proposed Development export cable corridor, therefore the effects resulting from changes to water quality and light smothering and siltation rate change are likely to be reduced due to dilution.
  6. The mudflats and sandflats not covered by seawater at low tide IEF are deemed to be of low vulnerability, high recoverability and international value. The sensitivity of the IEF is therefore, considered to be low.
  7. The reefs (subtidal and intertidal rocky reef) IEF is deemed to be of medium vulnerability, medium recoverability and international value. The sensitivity of the IEF is therefore, considered to be medium.
  8. The submerged or partially submerged sea caves IEF is deemed to be of medium vulnerability, medium recoverability and international value. The sensitivity of the IEF is therefore, considered to be medium.
  9. The large shallow inlets and bays IEF is deemed to be of low vulnerability, high recoverability and international value. The sensitivity of the IEF is therefore, considered to be low.

 

Table 8.23:
Sensitivity of the Benthic Subtidal and Intertidal IEFs found within the Berwickshire and North Northumberland Coast SAC to Increased Suspended Sediment Concentration and Associated Sediment Deposition

Table 8.23: Sensitivity of the Benthic Subtidal and Intertidal IEFs found within the Berwickshire and North Northumberland Coast SAC to Increased Suspended Sediment Concentration and Associated Sediment Deposition

* The mudflats and sandflats not covered by seawater at low tide habitat is approximately 12 km from the Proposed Development.

 

Significance of the Effect

Subtidal Habitat IEFs

  1. For the cobble/stony reef outside of an SAC IEF, the rocky reef outside an SAC IEF and the moderate energy subtidal rock IEF, the magnitude of the impact is deemed to be low and the sensitivity of the receptors is considered to be medium. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms, because of the high likelihood of recovery for these IEF to this short-term impact.
  2. For the subtidal sand and muddy sand sediments IEF, and the subtidal coarse and mixed sediments IEF the magnitude of the impact is deemed to be low and the sensitivity of the receptors is considered to be low. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms, because of the high likelihood of recovery for these IEF to this short-term impact.
  3. For the seapens and burrowing megafauna IEF, and the Sabellaria reef outside of an SAC IEF, the magnitude of the impact is deemed to be low and the sensitivity of the receptors is considered to be negligible. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms, because of the high likelihood of recovery for these IEF to this short term impact.

Intertidal Habitat IEFs

  1. For the intertidal rock IEF and the fucus dominated intertidal rock IEF, the magnitude of the impacts is deemed to be negligible and the sensitivity of the receptors is considered to be medium. The effect will, therefore, be of negligible adverse significance, which is not significant in EIA terms because of the high likelihood of recovery for these IEF to this short-term impact.
  2. For the intertidal sands IEF, the magnitude of the impact is deemed to be negligible and the sensitivity of the receptors is considered to be negligible. The effect will, therefore, be of negligible adverse significance, which is not significant in EIA terms.

Firth of Forth Banks Complex MPA

  1. For the subtidal sands and gravels IEF and the shelf banks and mounds IEF, the magnitude of the impact is deemed to be low and the sensitivity of the receptors is considered to be low. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms, because of the high likelihood of recovery for this IEF to this short-term impact.
  2. For the ocean quahog IEF, the magnitude of the impact is deemed to be low, and the sensitivity of the receptors is considered to be negligible. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms because of the high likelihood of recovery for these IEFs to this short-term impact.

Berwickshire and North Northumberland Coast SAC

  1. For the mudflats and sandflats not covered by seawater at low tide IEF, the magnitude of the impact is deemed to be negligible and the sensitivity of the receptor is considered to be low. The effect will, therefore, be of negligible adverse significance, which is not significant in EIA terms, because of the high likelihood of recovery from this impact and the large distance between this IEF and any potentially active construction activities.
  2. For the reefs (subtidal and intertidal rocky reef) IEF, the magnitude of the impact is deemed to be negligible and the sensitivity of the receptor is considered to be medium. The effect will, therefore, be of negligible adverse significance, which is not significant in EIA terms, because of the high likelihood of recovery for this IEF and the large distance between this IEF and any potentially active construction activities.
  3. For the submerged or partially submerged sea caves IEF, the magnitude of the impact is deemed to be negligible and the sensitivity of the receptor is considered to be medium. The effect will, therefore, be of negligible adverse significance, which is not significant in EIA terms because of the high likelihood of recovery for these IEFs to this short-term impact and the large distance between this IEF and any potentially active construction activities.
  4. For the large shallow inlets and bays IEF, the magnitude of the impact is deemed to be negligible and the sensitivity of the receptor is considered to be low. The effect will, therefore, be of negligible adverse significance, which is not significant in EIA terms.
Secondary Mitigation and Residual Effect
  1. No benthic subtidal and intertidal ecology mitigation is considered necessary for the impact of increases in SSC and associated sediment deposition during the construction phase because the likely effects in the absence of further mitigation (beyond the designed in measures outlined in section 8.10), are not significant in EIA terms.

Operation and Maintenance Phase

Magnitude of Impact

Subtidal and Intertidal Habitat IEFs

  1. Maintenance activities within the Proposed Development benthic subtidal and intertidal Proposed Development array area may lead to increases in suspended sediment concentrations and associated sediment deposition over the operational lifetime of the Proposed Development. The maximum design scenario for inter-array and OSP/Offshore convertor station platform interconnector cables is for cable repair for up to 30,000 m and reburial of up to 10,000 m. The maximum design scenario for offshore export cables is for cable repair of up to 4,000 m and reburial of up to 4,000 m of offshore export cables over the Proposed Developments lifetime (35 years), using similar methods as those for cable installation activities.
  2. For the inter-array cables in each case the length of the repair or reburial activity may be up to 2% of the length of cable installed in the construction phase; therefore, the magnitude of the impacts would be a fraction of those quantified for the construction phase. In the case of the offshore export cables the total length of works would be approximately 0.4% of the length assessed for the construction phase with events being undertaken over the Proposed Developments lifetime. The sediment plumes and sedimentation footprints would be dependent on which section of the cable is being repaired however for the purposes of this assessment, the impacts of the operation and maintenance activities (i.e. cable repair and reburial) are predicted to be no greater than those for construction.
  3. The removal of encrusted growth from offshore structures may also occur during the operation and maintenance phase; however, no quantitative assessment can be made as the volume of encrusting material that may be removed is not known. An investigation conducted at the research platform Forschungsplattformen in Nord- und Ostsee 1 FINO 1 in the southwestern German Bight in the North Sea reported that yearly, 878,000 single shell halves from Mytilus edulis sink onto the seabed from the FINO 1 platform, thereby greatly extending the reef effects created by the construction of the offshore platform structure (Krone et al., 2013). Although recent monitoring from Beatrice offshore wind farm found no M. edulis colonised its structures reducing the amount of debris reaching the seabed (APEM, 2021).
  4. Removal of marine growth from the wind turbine foundations may cause debris to fall within the vicinity of the wind turbine foundation and smother benthic communities within the impact zone. It is likely that seaweed/algal material would disperse into the water column, with heavier material (e.g. mussels) being deposited within 10 m to 15 m of the foundation (Vattenfall Wind Power Ltd, 2018). The discharge of the fine material generated as a result of the use of high pressure jet washing to remove the encrusting fauna into the marine environment may result in a short‐term increase in suspended organic material in the water column. This material would be expected to be rapidly dispersed on the following tides and under the prevailing hydrodynamic conditions. The study by Mavraki et al. (2020) of gravity-based foundations in the Belgian part of the North Sea found that higher food web complexity was associated with zones where high accumulation of organic material such as soft substrate or scour protection which begins to describe the potential reef effect that can be found at these hard structures and is explored further in paragraphs 319 and 321.
  5. The impact is predicted to be of local spatial extent, short term duration, intermittent and of high reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be negligible.

Firth of Forth Banks Complex MPA

  1. The magnitude of the change in environmental condition due to the impact of increased suspended sediment concentrations and associated sediment deposition is the same across the Proposed Development including in areas which overlap with the FFBC MPA (see paragraphs 202 to 205).
  2. The impact is predicted to be of local spatial extent, short term duration, intermittent and medium reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be negligible.

Berwickshire and North Northumberland Coast SAC

  1. The magnitude of the change in environmental condition due to the impact of increased suspended sediment concentrations and associated sediment deposition which may affect the Berwickshire and North Northumberland Coast SAC, should it extend to the coast, is the same as described in see paragraphs 202 to 205.
  2. The impact is predicted to be of local spatial extent, short term duration, intermittent and medium reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be negligible.
Sensitivity of the Receptor

Subtidal Habitat IEFs

  1. The sensitivity of the subtidal IEFs is as described previously for the construction phase assessment in paragraph 161 to 170 and in Table 8.21   Open ▸ .

Intertidal Habitat IEFs

  1. The sensitivity of the intertidal IEFs is as described previously for the construction phase assessment in paragraphs 171 to 175 and in Table 8.21   Open ▸ .

Firth of Forth Banks Complex MPA

  1. The sensitivity of the IEFs is as described previously for the construction phase assessment in paragraphs 176 to 180 and in Table 8.22   Open ▸ .

Berwickshire and North Northumberland Coast SAC

  1. The sensitivity of the IEFs is as described previously for the construction phase assessment in paragraphs 181 to 189 and in Table 8.23   Open ▸ .
Significance of the Effect

Subtidal Habitat IEFs

  1. For the cobble/stony reef outside of an SAC IEF, the rocky reef outside an SAC IEF and the moderate energy subtidal rock IEF, the magnitude of the impact is deemed to be negligible, and the sensitivity of the receptors is considered to be medium. The effect will, therefore, be of negligible adverse significance, which is not significant in EIA terms, because of the very small magnitude and intermittent nature of this impact in this phase.
  2. For the subtidal sand and muddy sand sediments IEF, and subtidal coarse and mixed sediments IEF, the magnitude of the impact is deemed to be negligible, and the sensitivity of the receptors is considered to be low. The effect will, therefore, be of negligible adverse significance, which is not significant in EIA terms because of the very small magnitude and intermittent nature of this impact in this phase.
  3. For the seapens and burrowing megafauna IEF, and Sabellaria reef outside of an SAC IEF, the magnitude of the impact is deemed to be negligible, and the sensitivity of the receptors is considered to be negligible. The effect will, therefore, be of negligible adverse significance, which is not significant in EIA terms.

Intertidal Habitat IEFs

  1. For the intertidal rock IEF and fucus dominated intertidal rock IEF, the magnitude of the impact is deemed to be negligible, and the sensitivity of the receptors is considered to be medium. The effect will, therefore, be of negligible adverse significance, which is not significant in EIA terms because of the very small magnitude and intermittent nature of this impact in this phase and therefore high likelihood of recovery.
  2. For the intertidal sands IEF, the magnitude of the impact is deemed to be negligible, and the sensitivity of the receptors is considered to be negligible. The effect will, therefore, be of negligible adverse significance, which is not significant in EIA terms.

Firth of Forth Banks Complex MPA

  1. For the subtidal sands and gravels IEF and the shelf bank and mound IEF, the magnitude of the impact is deemed to be negligible, and the sensitivity of the receptors is considered to be low. The effect will, therefore, be of negligible adverse significance, which is not significant in EIA terms, because of the very small magnitude and intermittent nature of this impact in this phase.
  2. For the ocean quahog IEF, the magnitude of the impact is deemed to be negligible, and the sensitivity of the receptors is considered to be negligible. The effect will, therefore, be of negligible adverse significance, which is not significant in EIA terms.

Berwickshire and North Northumberland Coast SAC

  1. For the mudflats and sandflats not covered by seawater at low tide SAC IEF, the magnitude of the impact is deemed to be negligible, and the sensitivity of the receptors is considered to be low. The effect will, therefore, be of negligible adverse significance, which is not significant in EIA terms, because of the very small magnitude and intermittent nature of this impact in this phase as well as the large distance between this SAC and the Proposed Development.
  2. For the reefs (subtidal and intertidal rocky reef) IEF, the magnitude of the impact is deemed to be negligible, and the sensitivity of the receptors is considered to be medium. The effect will, therefore, be of negligible adverse significance, which is not significant in EIA terms, because of the very small magnitude and intermittent nature of this impact in this phase as well as the large distance between this SAC and the Proposed Development, which is not significant in EIA terms.
  3. For the submerged or partially submerged sea caves IEF, the magnitude of the impact is deemed to be negligible, and the sensitivity of the receptors is considered to be medium. The effect will, therefore, be of negligible adverse significance, which is not significant in EIA terms, because of the very small magnitude and intermittent nature of this impact in this phase as well as the large distance between this SAC and the Proposed Development.
  4. For the large shallow inlets and bays IEF, the magnitude of the impact is deemed to be negligible, and the sensitivity of the receptors is considered to be low. The effect will, therefore, be of negligible adverse, which is not significant in EIA terms, significance because of the very small magnitude and intermittent nature of this impact in this phase as well as the large distance between this SAC and the Proposed Development.