Offshore subtidal sands and gravels and ocean quahog aggregations
  1. As outlined in paragraph 173, approximately 100% of the total area of the Firth of Forth Banks Complex MPA is modelled as the offshore subtidal sands and gravels feature, and therefore also represents the extent of supporting habitat for ocean quahog aggregations. For the purposes of this assessment, it is therefore assumed that all the infrastructure which could be placed within the Firth of Forth Banks Complex MPA, as outlined in paragraph 189, could be placed within these features.
Shelf banks and mounds
  1. As outlined in paragraph 173, unlike the offshore subtidal sands and gravels feature, the shelf banks and mounds protected feature does not cover the full extent of the MPA; the shelf banks and mounds feature covers approximately 19.48% of the area of the MPA which overlaps with the Proposed Development, Figure 1.12. Therefore, to adopt the same assumptions outlined in paragraph 189 for offshore subtidal sands and gravels would be unrealistic and would overestimate the maximum design scenario for the shelf banks and mounds feature. For the purposes of this assessment it is therefore assumed that 19.48% of the infrastructure which could be placed within the Firth of Forth Banks Complex MPA could be placed within this feature (e.g. the maximum design scenario for long term habitat loss under foundations assumes that 11 of the 56 foundations for the larger wind turbine scenario which could be installed within the Firth of Forth Banks Complex MPA could be installed within the shelf banks and mounds feature).
Wee Bankie key geodiversity area (moraines)
  1. As outlined in paragraph 173, unlike the offshore subtidal sands and gravels feature, the Wee Bankie Key Geodiversity Area (Moraines) protected feature does not cover the full extent of the MPA; the moraines feature covers approximately 22.17% of the area of the MPA which overlaps with the Proposed Development, Figure 1.12). Therefore, to adopt the same assumptions outlined in paragraph 189 for offshore subtidal sands and gravels would be unrealistic and would overestimate the maximum design scenario for the Wee Bankie Key Geodiversity Area (moraines) feature. For the purposes of this assessment, it is therefore assumed that 22.17% of the infrastructure which could be placed within the Firth of Forth Banks Complex MPA could be placed within this feature (e.g. the maximum design scenario for long term habitat loss under foundations assumes that 12of the 56 foundations for the larger wind turbine scenario which could be installed within the Firth of Forth Banks Complex MPA could be installed within the moraines feature).
  2. Measures Adopted as Part of the Proposed Development As part of the Project design process, a number of measures have been proposed to reduce the potential for impacts on benthic subtidal and intertidal ecology and features of the MPA (see Table 1.36   Open ▸ ). As there is a commitment to implementing these measures, they are considered inherently part of the design of the Proposed Development) and have therefore been considered in the main assessment. These measures are considered standard industry practice for this type of development.

 

Table 1.36:
Designed In Measures Adopted as Part of the Proposed Development

Table 1.36: Designed In Measures Adopted as Part of the Proposed Development

 

Main assessment

Temporary Habitat Disturbance

Construction phase
  1. Direct temporary disturbance of subtidal habitat may occur within the Firth of Forth Banks Complex MPA during the construction phase as a result of the installation of inter-array cables, interconnector cables, offshore export cables and wind turbine foundation installation activities (including site preparation works such as sand wave and boulder clearance, anchor placements and vessel jack-ups).
  2. For the purposes of this assessment, temporary habitat disturbance refers to the impact of activities and events which will produce effects which are temporary within the environment. After the cessation of the activities associated with this impact a shift toward the original baseline of the environment will occur via the recovery of the sediments themselves and the associated communities. Temporary impacts to sediments and benthic communities has been considered separately from long term habitat loss (see paragraph 291 et seq.) which considers the footprint of seabed which will be occupied by the Proposed Developments infrastructure (e.g. wind turbines and scour protection) over its 35 year lifetime. Finally, where there is the potential for cable and scour protection to remain on the seabed following the decommissioning process and to remain in perpetuity, this is referred to, and has been assessed, as permanent habitat alteration (see paragraph 0 et seq.) on the basis that this habitat will be recolonised over time.
  3. This assessment is equivalent to the following pressures identified by JNCC's Advice on Operations for the Firth of Forth Banks Complex MPA for ‘Renewable Energy: offshore wind’ and ‘Power cables: laying burial and protection’ (JNCC,2018c):
  • Abrasion/disturbance of the substrate on the surface of the seabed;
  • Penetration and/or disturbance of the substratum below the surface of the seabed, including abrasion;
  • Habitat structure changes - removal of substratum (extraction); and
  • Siltation rate changes (high), including smothering (depth of vertical sediment overburden).
    1. Table 1.37   Open ▸ presents the maximum design scenario for temporary habitat disturbance within the Firth of Forth Banks Complex MPA during the construction phase.
    2. On the basis of the assumptions outlined in paragraph 189, there may be up to 24.70 km2 of temporary habitat disturbance within the Firth of Forth Banks Complex MPA during the construction phase, equating to 1.16% of the total area of the MPA. Of this total, up to 7.61 km2 may occur within the Scalp and Wee Bankie section of the MPA[9] (0.36% of the total area of the MPA or 1.92% of the area of the Scalp and Wee Bankie section of the MPA) and up to 17.09 km2 within the Berwick Bank part of the MPA[10] (0.8% of the total area of the MPA or 3.16% of the area of the Berwick Bank section of the MPA). This assessment considers the effects of construction activities resulting in temporary habitat disturbance on the attributes and targets for the offshore subtidal sand and gravels, shelf banks and mounds, ocean quahog aggregations and moraines representative of the Wee Bankie key geodiversity area features and therefore the assessment has been subdivided according to these feature types.

 

Table 1.37:
Maximum Design Scenario for Temporary Habitat Disturbance within the Firth of Forth Banks Complex MPA During the Construction Phase

Table 1.37:  Maximum Design Scenario for Temporary Habitat Disturbance within the Firth of Forth Banks Complex MPA During the Construction Phase

1 For the purposes of replicating the calculations in this table, 31.33% is calculated as 316.5 km2/1010.2 km2 (i.e. overlap between Proposed Development array area / total Proposed Development array area).

2 For the purposes of replicating the calculations in this table, 13.08% is calculated as 114.08 km/872 km (i.e. proportion of total length of export cables that could occur within the part of the Proposed Development export cable corridor that overlaps with the MPA).

 

Offshore subtidal sands and gravels

  1. On the basis of the assumptions outlined in paragraph 190, all of the temporary habitat disturbance predicted within the MPA (i.e. 24.70 km2) could occur entirely within the offshore subtidal sands and gravels feature of the MPA. This would equate to temporary habitat disturbance of up to 1.16% of the offshore subtidal sands and gravels feature within the MPA (see Table 1.38   Open ▸ ). Of this temporary habitat disturbance up to 7.6 km2 could occur within the Scalp and Wee Bankie part of the MPA9 (0.92% of the offshore subtidal sands and gravels feature within the MPA) and up to 17.09 km2 could occur in the Berwick Bank part of the MPA10 (0.8% of the feature within the whole MPA) (see Table 1.38   Open ▸ ).

Table 1.38:
Summary of the Extent of Temporary Habitat Disturbance within the Firth of Forth Banks Complex MPA (as a Whole, and for the Component Sites) during the Construction Phase

Table 1.38: Summary of the Extent of Temporary Habitat Disturbance within the Firth of Forth Banks Complex MPA (as a Whole, and for the Component Sites) during the Construction Phase

1 Calculated as 30.81% of the 24.7 km2 total on the basis of the overlap with the Scalp and Wee Bankie (see paragraph 170).

2 Calculated as 69.19% of the 24.7 km2 total on the basis of the overlap with the Berwick Bank (see paragraph 188).

3 Calculated as 43.82% of total 7.61 km2 of disturbance within the Scalp and Wee Bankie section (i.e. 43.82% of the total area of Scalp and Wee Bankie that overlaps with the Proposed Development and contains the shelf banks and mounds feature).

4 Calculated as 8.64% of total 17.09 km2 of disturbance within the Berwick Bank section (i.e. 8.64% of the total area of Berwick Bank that overlaps with the Proposed Development and contains the shelf banks and mounds feature).

5 Calculated as 71.59% of total 7.61 km2 of disturbance within the Scalp and Wee Bankie section (i.e.71.59% of the total area of Scalp and Wee Bankie that overlaps with the Proposed Development and contains the moraines feature).

6 Calculated as 0.16% of total 17.09 km2 of disturbance within the Berwick Bank section (i.e. 0.16% of the total area of Berwick Bank that overlaps with the Proposed Development and contains the moraines feature).

 

  1. Activities resulting in temporary habitat disturbance will occur intermittently throughout construction period of up to 96-months, with only a proportion of the total maximum area of temporary habitat disturbance occurring at any one time. Following these activities, the sediments would be expected to recover to their baseline state through wave and tidal action, allowing the associated communities to recover into these areas. A recent study reviewed the effects of cable installation on subtidal sediments and habitats, drawing on monitoring reports from over 20 UK offshore wind farms (RPS, 2019). This review showed that sandy sediments recover quickly following cable installation, with trenches infilling quickly following cable installation and little or no evidence of disturbance in the years following cable installation. It also presented evidence that remnant cable trenches in coarse and mixed sediments were conspicuous for several years after installation. However, these shallow depressions were of limited depth (i.e. tens of centimetres) relative to the surrounding seabed, over a horizontal distance of several metres and therefore did not represent a large shift from the baseline environment (RPS, 2019). It has been reported that benthic communities associated with soft sediments (e.g. muds, sands and gravels) readily recover into areas if the sediment type is reflective of the baseline environment (RPS, 2019). Similarly, a study of bedform migration undertaken using historic geophysical surveys within Seagreen 1 (HR Wallingford 2012) also indicated that seabed sediments are mobile and prone to accretion although the underlying bedforms were stable. Thus, from the limited amount of available data it would suggest that any sand-based habitat and sand waves are likely to recover over several years. Evidence for other industries and regions suggests that sand based sediments can recover over shorter periods. For example, Newell et al. (2004) reports recovery times of months to one or two years.
  2. The effects of temporary habitat disturbance during the construction phase will be temporary and cease following completion of the construction activities. Whilst flora and fauna will be affected, recoverability in most cases is likely to be medium, as a result of passive import or larvae and active migration of juveniles and adults from adjacent non-affected areas. Evidence from the marine aggregates industry suggests that recovery on sandy sediments will happen over a relatively short time scale (e.g. months to one or two years; Newell et al., 2004), and coarse, gravelly and mixed sediments showing longer recovery timescales, usually within five years (Desprez, 2000; Newell et al., 1998), but in some cases, recovery has been reported as taking up to nine years following cessation of dredging (Foden et al., 2009).
  3. Based on the information presented above, the following can be concluded with respect to the physical attributes of the protected features of the Firth of Forth Banks Complex MPA:
  • Extent and distribution of the offshore subtidal sands and gravels feature will be maintained in the long term following the completion of the construction phase, with only a small proportion of the total extent of this feature within the MPA affected (1.16%). These effects are limited to the northern half of the Berwick Bank section of the MPA (affecting up to 17.09 km2 which equates to 0.80% of the total extent of this feature within the MPA) and the southern/central section of Scalp and Wee Bankie (affecting up to 7.61 km2 which equates to 0.36% of the total extent of the feature within the MPA). In addition, any effects on the offshore subtidal sands and gravels feature will be temporary and reversible with recovery of sediments occurring following the completion of construction. Recovery of the sand waves within this feature will be monitored at a representative number of locations where sand wave clearance activity has taken place as part of wider Project pre- and post-construction geophysical surveys (monitoring commitments are detailed in Table 1.59   Open ▸ ). This is consistent with the ‘conserve’ objective of the extent and distribution attribute for this feature.
  • The activities associated with the cable installation, jack-up events and anchor placements are not expected to impact upon the hydrodynamic regime of the area as no permanent structures are needed to complete these works. The fine scale features of this site include relict banks and mounds which are part of the Wee Bankie Key Geodiversity Area feature and do not rely on hydrodynamics as they were formed during the last glacial period. Sand ripples are also found in the MPA which are formed by the prevailing hydrodynamic regime from the dominant sediment type. There is likely to be little to no effect on fine scale topographic features as the associated processes which they rely on will be maintained throughout this phase. This is consistent with the ‘recover’ objective of the structure and function attribute for this feature.
  • The sediment composition of the offshore subtidal sands and gravels protected feature is unlikely to be affected by the temporary habitat disturbance impact. Whilst sand wave clearance will temporarily remove sediment, it will be deposited locally, and the high rate of sedimentation will ensure rapid redistribution of material (sand wave recovery will be monitored as part of designed in monitoring commitments, see Table 1.59   Open ▸ ). Boulder clearance activities may result in a redistribution of boulders and cobbles within discrete areas and could potentially concentrate these in the areas either side of the cleared corridor. Since no sediment/substrate is being removed and given the existing patchiness of the distribution of cobbles and boulders in the offshore environment, this is considered unlikely to represent a significant shift in the baseline situation. Additionally, the limited change to the hydrodynamic regime is unlikely to lead to any change in the prevailing sediment composition. This is consistent with the ‘recover’ objective of the structure and function attribute for this feature.

 

Shelf banks and mounds

  1. On the basis of the assumptions outlined in paragraph 191, and for the purposes of this assessment it is assumed that 19.48% of the maximum temporary habitat disturbance from the construction of the Proposed Development within the MPA could occur in this feature, equating to 4.81 km2 or 1.82% of the shelf banks and mound feature within the MPA. Of this temporary habitat disturbance, up to 3.33 km2 could occur within Scalp and Wee Bankie (1.26% of the feature within the whole MPA) and 1.48 km2 could occur in the Berwick Bank part of the MPA (0.56% of the feature within the whole MPA) (see Table 1.38   Open ▸ ).
  2. Activities resulting in temporary habitat disturbance will occur intermittently throughout construction period of up to up to 96 months, with only a proportion of the total maximum area of temporary habitat disturbance occurring at any one time. Following these activities, sediments would be expected to recover to their baseline state through wave and tidal action (volume 2, chapter 7 of the Offshore EIA Report), allowing the associated communities to recover into these areas. Further detail is provided in paragraph 200. As outlined in Table 1.59   Open ▸ , the Applicant is committed to the monitoring of the recovery of sand waves within the MPA via pre- and post-construction geophysical surveys to validate the predictions of this assessment.
  3. Effects of temporary habitat disturbance during the construction phase will be temporary and cease following completion of the construction activities. Whilst flora and fauna will be affected, recoverability in most cases is likely to be medium, as a result of passive import or larvae and active migration of juveniles and adults from adjacent non-affected areas. These predictions are similar to those made for offshore subtidal sands and gravels as they are characterised by the same biotopes.
  4. Based on the information presented above, the following can be concluded with respect to the physical attributes of the protected features of the Firth of Forth Banks Complex MPA:

Ocean quahog aggregations

  1. On the basis of the assumptions outlined in paragraph 190, and for the purposes of this assessment, it is assumed that all of the temporary habitat disturbance predicted within the MPA (i.e. 24.70 km2) could occur entirely within supporting habitat for ocean quahog aggregations. This would equate to temporary habitat disturbance of up to 1.16% of the supporting habitat for ocean quahog within the MPA (see Table 1.38   Open ▸ ).
  2. Activities resulting in temporary habitat disturbance will occur intermittently throughout construction period of up to up to 96 months, with only a proportion of the total maximum area of temporary habitat disturbance occurring at any one time. Following these activities, the sediments would be expected to recover to their baseline state through wave and tidal action (volume 2, chapter 7 of the Offshore EIA Report), allowing the associated benthic communities, including ocean quahog, to recover into these areas.
  3. Effects of temporary habitat disturbance during the construction phase will be temporary and cease following completion of the construction activities. Ocean quahog are vulnerable to physical abrasion, but damage is related to their body size. Thorarinsdottir and Jacobson (2005) and Thorarinsdottir et al. (2010) noted that ocean quahog are vulnerable to impacts resulting in abrasion and disturbance of the sediment due to its long lifespan, slow growth, uncertain recruitment, low productivity, and poor estimates of stock biomass and capture efficiency. This damage can increase the mortality of ocean quahog either through the damage itself, increased vulnerability to predation or high intensity pressures such as the use of hydraulic dredges (Thorarinsdottir et al., 2009). Currently, within the Firth of Forth Banks Complex MPA, demersal trawling is highest in Wee Bankie, which during 2016 recorded a total of over 2,500 hours of dredge fishing, a practice which is known to damage ocean quahog (JNCC, 2018b). Damage of this nature can also be attributed to the effect of penetration and disturbance of the substratum as ocean quahog live at the surface of the sediment while feeding but burrows to depths of 14 cm periodically (Strahl et al., 2011) where penetrative activities could damage individuals or lead to mortalities.
  4. The recovery of ocean quahog to the pressures exerted by this impact is, in most cases likely to be slow (Tyler-Walters and Sabatini, 2017), and a full recovery from activities such as dredge fishing which penetrate the seabed may take decades (Ragnarsson et al., 2015). Recovery of ocean quahog populations is also dependant on the age of sexual maturity at which population expansion can begin. Ocean quahogs reach sexual maturity at between 5 and 11 years and may be dependent upon growth rate and locality (Thorarinsdóttir, 1999).
  5. Heavy smothering or siltation rate change is likely to result in negligible effects to ocean quahog as they are able to burrow back to the surface. A study by Powilleit et al. (2006) deposited a till and sand/till mixture up to 1.5 m deep on to existing sediment and found the resident ocean quahogs were ‘almost’ unaffected and the population structure was similar two years later. After initial deposition, 78% and 26% reached the surface under the ‘till’ and ‘sand/till’ mixtures respectively. Finally, the removal of substratum to a depth of 30 cm will remove the substratum occupied by ocean quahog together with any other species in the assemblage (Tyler-Walters and Sabatini, 2017).
  6. It is worth noting that the presence of the infrastructure associated with the Proposed Development may also have some beneficial effects on ocean quahog by facilitating recovery following disturbance. Whilst there will be no safety zones enforced during the operation and maintenance phase (except during maintenance events), a 50 m safe passing distance for logistical and safety reasons (i.e. to account for the offset/drifting of fishing gear that happens as a result of the tide) can be assumed for fishing vessels in the vicinity of wind turbines. The effect of this may be that trawling activity could potentially be reduced within the Proposed Development array area, in localised areas around the wind turbine/OSP-Offshore convertor station platforms foundations. As a result, ocean quahog in the vicinity of the offshore infrastructure may potentially experience a reduced level of disturbance from commercial fishing in the long term (i.e. over the operational lifetime of the Proposed Development and potentially beyond), which may aid with the recovery of the wider population to the impact of temporary habitat disturbance. As outlined in Table 1.59   Open ▸ , the Applicant is committed to engaging in discussions with Marine Scotland and the SNCBs to identify, and implement, appropriate and collaborative strategic monitoring of temporary habitat disturbance to sensitive features of the Firth of Forth Banks Complex MPA features (e.g. ocean quahog) in conjunction with other offshore wind farm developers in the Firth of Forth in order to validate the predictions in this assessment.
  7. The predictions for the ocean quahog supporting habitat are similar to those made for offshore subtidal sands and gravels feature (see paragraph 203 and 204).
  8. Based on the information presented above, the following can be concluded with respect to the physical attributes of the ocean quahog aggregations feature of the Firth of Forth Banks Complex MPA:

Wee Bankie key geodiversity area (moraines)

  1. On the basis of the assumptions outlined in paragraph 192, and for the purposes of this assessment, it is assumed that 22.17% of the maximum temporary habitat disturbance from the Proposed Development within the MPA could occur within this feature. This equates to 5.47 km2 or 0.73% of this feature within the MPA and of this, 5.45 km2 (0.73% of the area of this feature across the MPA) could occur within Scalp and Wee Bankie and 0.03 km2 (0.004% of the area of this feature across the MPA) could occur in the Berwick Bank part of the MPA (see Table 1.38   Open ▸ ).
  2. Activities resulting in temporary habitat disturbance will occur intermittently throughout construction period of up to 96 months, with only a proportion of the total maximum area of temporary habitat disturbance occurring at any one time. Following these activities, the sediments would be expected to recover to their baseline state through wave and tidal action (volume 2, chapter 7 of the Offshore EIA Report), allowing the associated communities to recover into these areas.
  3. Based on the information presented above, the following can be concluded with respect to the physical attributes of the Wee Bankie Key Geodiversity Area feature of the Firth of Forth Banks Complex MPA:
  • All impacts to the seabed associated with construction activities will be temporary in nature and no sediment will be permanently removed from the system during the construction phase. Whilst material will be removed during sand wave clearance activities, it will be deposited locally such that there will be no overall loss of the feature’s extent or distribution. Furthermore, the scale of the potential temporary impacts to this feature are predicted to be very small, affecting only 0.73% of the total extent of the Wee Bankie Key Geodiversity Area feature in the MPA. This is consistent with the ‘conserve’ objective of the extent and distribution attribute for this feature.
  • The structure of the moraines in the MPA are defined by their height above the surrounding seabed (~20 m), their steep western edges, gradually sloping eastern edges and large scale (Wee Bankie has a width of ~20 km and length of ~70 km). The temporary and localised sediment disturbance associated with construction activities are unlikely to result in large scale changes to this feature as the extent of disturbance is predicted to be small (0.73%) in the context of the wider area of the feature. There will be no permanent removal of material and any mounds of material deposited during sand wave clearance will gradually erode over time and displaced material will re-join the natural sedimentary environment, gradually reducing the size of the mounds. This is consistent with the ‘conserve’ objective of the structure and function attribute for this feature.
  • The function of the Wee Bankie Moraine protected feature is as a valuable site of scientific study as it marks an ice limit at some point during the ice retreat of the British-Irish Ice Sheet, during the Last Glacial Maximum. Additionally, the moraines provide habitat that is an integral part of the offshore subtidal sands and gravel protected feature, supplying substrate to the sedimentary biological communities. As the hydrodynamic regime of the site will not be impacted by the construction phase activities the supply of sediment to surrounding habitats is unlikely to be affected. Any disturbance to sediment during the construction phase will be temporary, localised and very small in the context of the wider extent of this feature (i.e. 0.73%) and will not affect the functions provided by this geodiversity feature. The feature will continue to be an integral part of the offshore subtidal sands and gravels protected feature, supplying substrate that supports the sedimentary biological communities, and it will continue to provide habitat for the ocean quahog aggregations feature. This is consistent with the ‘conserve’ objective of the structure and function attribute for this feature.
    1. Based on the information presented here, it can be concluded that temporary habitat disturbance during the Proposed Development construction phase will not lead to a significant risk of hindering the achievement of the overall conservation objective (i.e. “maintain in favourable condition”) for the Wee Bankie Key Geodiversity Area feature of the Firth of Forth Banks Complex MPA for the following reasons:
  • Temporary habitat disturbance is predicted to affect a very small proportion (0.73%) of the total extent of the protected feature within the MPA during the construction phase. Therefore, its extent, component elements and integrity as a relict feature will be maintained;
  • The structure and function will remain unimpaired by the activities as only a small proportion of the feature will be affected, and the temporary nature of the impact will not result in any long term changes to the feature; and
  • The surface of the feature will remain sufficiently unobscured during the construction phase.