4.2 Data Analyses, Sensitivity of Relevant Receptors and Approach to Modelling

This section aims to document and agree key elements of the benthic ecology, fish and shellfish, and physical processes data analysis for the Proposed Development offshore EIA and HRA. These include the following:

  • approach to assessment of effects (including sensitivity of receptors, method of quantifying impacts and approach to hydrodynamic and hydro-sedimentary modelling); and
  • approach to MPA assessment.
  • Table 4.2   Open ▸ summarises the points of discussion, areas of agreement and areas of outstanding discussion in relation to the benthic ecology, fish and shellfish ecology and physical processes baseline data analysis for the Proposed Development.

 

Table 4.2:
Summary of Discussion and Agreed Position on Benthic Ecology, Fish and Shellfish Ecology and Physical Processes Data Analysis

Table 4.2: Summary of Discussion and Agreed Position on Benthic Ecology, Fish and Shellfish Ecology and Physical Processes Data Analysis

4.2.1           Additional Details on Key Discussions

  • The construction phase is expected to last approximately 8 years. The operation and maintenance phase is 35 years long. Decommission is expected to have similar impacts as the construction phase.

4.2.1.1      General approach to assessment of effects

Benthic ecology and fish and shellfish ecology:

Following the Chartered Institute of Ecology and Environmental Management (CIEEM) Guidelines for EcIA in the UK and Ireland (CIEEM, 2019) and Environmental Protection Agency (EPA) Guidelines on the Information to be Contained in EIA Reports (EPA, 2017), the approach is summarised as follow:

  • identify the IEFs;
  • define the magnitude of the impact (based on the maximum design scenario which is determined by the PDE);
  • define the sensitivity of receptors (considering vulnerability, recoverability and value using the MarESA (benthic ecology only) and FeAST tool, scientific literature and results from other offshore wind farm monitoring programme); and
  • conclusion of significance in EIA terms based on the assessment matrix (magnitude x sensitivity).

CEA for benthic ecology, fish and shellfish, and physical processes:

  • the CEA for benthic ecology and physical processes will take into account the impact associated with the Proposed Development together with other relevant plans, projects and activities (i.e. other offshore wind farm projects, aggregate extraction/disposal areas); and
  • CEA will consider other plans, projects and activities within two tidal excursions (~20 km) of the Proposed Development.

4.2.1.2      MPA assessment

The MPA assessment will:

  • be a stand-alone report accompanying the Offshore EIA Report;
  • consider whether there is, or may be, a significant risk of the Proposed Development hindering the achievement of the conservation objectives of the ncMPA; and
  • draw on the output of other technical chapters such as physical processes, benthic ecology, fish and shellfish and marine mammals.

NatureScot and JNCC requested to see the extent of impacted area for each protected feature, as well as the percentage from the overall ncMPA and each component part of the ncMPA. They requested to see this for each component of the proposed development (e.g. foundations, inter-array/interconnector cabling, export cabling, scour/cable protection), individually and in combination with Seagreen (Seagreen 1 & 1A). They also requested to better understand the extent to which each feature could be protected by the proposed 50 m safety exclusion zone around each wind turbine foundation. From this, they can better evaluate the context of such protection, against the extent that is predicted to be disturbed and permanently lost through the proposed development. The Applicant provided further detail for each of the maximum design scenarios for the assessments presented in the main body of the report to enable calculations to be followed and replicated by the Statutory Nature Conservation Bodies (SNCBs). These changes are actioned for both the project alone assessment and the assessment considering Berwick Bank Wind Farm in combination with Seagreen and Seagreen 1A (including the Seagreen 1A Export Cable Corridor).

The Applicant highlighted that the final wind farm layout is still to be determined and will be informed by more detailed geophysical/geotechnical studies, and engineering design work. The MPA assessment has been based on a series of maximum design scenario related to the proportion of infrastructure that could be installed within the MPA. A map showing the indicative wind turbine layout for the largest wind turbine option (which represents the maximum design scenario for long term habitat loss) is included in the MPA assessment Report, but the Applicant would emphasise that this is only an indicative layout.

4.2.1.3      Long term versus permanent terminology

Habitat lost beneath the wind turbines is considered by the stakeholders to be a long term impact. An effect is permanent to most species if it doesn’t resolve within its lifetime. As to effects following decommissioning, the sediments will recover, however, even if structures are removed, the impact would be permanent. There is also no guarantee that they can be removed. Attempts to remove the mattress can result in significant levels of disturbance. As this cannot be predicted, it should be considered on precautionary basis as a permanent footprint. Although long term may be described as not infinite but persevering in the ecological sense, if the impact is temporary, it was advised to be described as ‘disturbance’, whereas for permanent impacts, to be described as ‘loss’.

4.2.1.4      Modelling approach to physical processes

The material is taken from the peak of the sand waves and running them into the troughs in order to perform the simulation modelling. Dredged materials are not relocated off site but along the route and within the Proposed Development array area.

Sand waves

Dynamically active:

The physical processes assessment modelled different scenarios (specific tides, waves & storm events) to examine the potential for change and determined that the physical processes underpinning the marine environment would be maintained with little change after the project was built. This modelling can also be used to indicate sediment transport patterns for particular scenarios, however, the study was not designed or intended to examine the detailed sand wave mobility and longer-term morphology. Sand wave mobility and migration studies usually involve a combination of multiple geophysical surveys (i.e. current and historic) recorded over a reasonably long period, sometimes supplemented with very high resolution computational modelling. Such an assessment would be much more focussed than the comparative modelling implemented within the context of an EIA. However, the baseline modelled scenarios undertaken for the offshore EIA do indicate seabed sediment activity. Similarly, a study of bedform migration undertaken using historic geophysical surveys within the Seagreen 1 development area (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 the Applicant suggests that sand wave recovery would be expected to occur gradually over a period of 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. However, the Applicant's commitment to pre and post construction monitoring will provide important information on this hypothesis both in terms of the recovery of the MPA features but also in terms of providing a more robust dataset relating to the impact of offshore developments in areas of sand waves and seabed features more generally.

Risk of re-exposure of cables:

The Project Design Envelope (PDE) prescribes the provision of cable and scour protection and defines the required cable burial depths to account for coastal recession. The cable installation strategy will be designed to avoid free spanning (i.e. through the derivation of seabed clearance parameters and, armouring). The risk of cable exposure is therefore managed through project design (as with the justification of the scour protection depths/extents etc.). These parameters were precautionary and have been developed based on experience. A full cable burial risk assessment (CBRA) will be developed with the aim of avoiding areas of extensive sand waves where they are present along the offshore export cable route, and if this cannot be achieved, by setting a burial depth that will prevent any de-burial of the cable over the lifetime of the project whilst maintaining the electrical integrity of the cable.

NatureScot and JNCC reiterated that any armouring of the cable through areas of sand waves/megaripples (whether at installation or in response to future re-exposure) could disrupt the hydrodynamics that underpin the ncMPA features. Therefore, the CBRA should not rely solely on armouring as an expected method of cable protection.

4.2.2           Summary Statement of Final Position

The approach to assessment of effects suggested by the Applicant for each effect were undertaken as agreed with the stakeholders as in Table 4.2   Open ▸ with regards to the following agreed points:

  • the FeAST tool was used, in addition to the Applicant’s proposed approach, for the assessment of the sensitivity of the fish and shellfish ecology receptors; and
  • further details and clear figures requested in Table 4.2   Open ▸ for the MPA assessment and for the physical processes assessment were provided in the respective chapters

4.3 Approach to EIA and HRA

This section aims to document and agree key topics associated with the realistic maximum design scenarios assessed in relation to the benthic ecology, fish and shellfish ecology and physical processes assessments for Proposed Development offshore EIA and HRA. These include the following:

  • initial findings of assessment of effects appropriate mitigation and monitoring; and
  • initial findings of the MPA assessment.
  • Table 4.3   Open ▸ summarises the points of discussion, areas of agreement and areas of outstanding agreements in relation to the approach to offshore EIA for the Proposed Development.

 

Table 4.3:
Summary of Discussion and Agreed Position on Benthic Ecology, Fish and Shellfish Ecology and Physical Processes Approach to EIA

Table 4.3: Summary of Discussion and Agreed Position on Benthic Ecology, Fish and Shellfish Ecology and Physical Processes Approach to EIA

 

4.3.1    Additional Details on Key Discussions

4.3.1.1      Boulder and sand waves clearance

The Applicant clarified that boulder and sand waves clearance is more a redistribution. Therefore, with physical processes maintained in the area, sand waves are predicted to recover together with associated sediments and benthic communities. PDE assumes that up to 20% of the offshore export cables and 30% of the inter-array cables will require sand wave clearance, and 20% of all cables that will require boulder clearance. Material is removed during this clearance and deposited along the seabed that will cause temporary habitat loss. The volume of the material to be cleared is assumed to be deposited over an area up to a depth of 0.5 m. This “mound” will likely disperse over time. As engineers are able to refine the final design parameters pre-construction, the habitat loss figures will change. Maximum design scenario assumed a dredging-disposal technique but could create a less intense construction plume with plough dredging. In addition, the deposition of the sand wave clearance material is assessed as temporary habitat loss rather than in the assessment of suspended sediments and sediment deposition because of the scale of the activity/depth of deposition.

4.3.1.2      Maximum design scenario used in the assessment of effects

Temporary habitat disturbance/loss (construction) – benthic ecology:

  • PDE assumes that up to 20% of the offshore export cables and 30% of the inter-array cables will require sand wave clearance and 20% of all cables that will require boulder clearance;
  • cable installation: 1,225 km of inter-array cables, 94 km of interconnector and 872 km of offshore export cables (total of 42,948,000 m2);
  • anchor footprint: 438,200 m2;
  • jack-up footprint: up to four jack-up locations per wind turbine and OSPs/Offshore convertor station platform; and
  • the deposition of the sand wave clearance material is assessed as temporary habitat loss rather than in the assessment of suspended sediments and sediment deposition because of the scale of the activity/depth of deposition.

Temporary habitat disturbance/loss (operation and maintenance) – benthic ecology:

  • cable repair and reburial (inter-array and interconnector 450,000 m2 for repair and 150,000 m2 for reburial) = 720,000 m2;
  • jack-up footprint (used for all component repairs) = 269,000 m2; and
  • total = 989,000 m2.

Long term habitat loss – benthic ecology:

  • cable protection (15% of each cable type) = 5,470,500 m2;
  • foundations and scour protection (179 wind turbines and ten OSP/Offshore convertor station platform foundations) = 2,265,776 m2; and
  • total = 7,798,856 m2.

Colonisation of hard structures – benthic ecology:

  • cable protection (15% of all cables) = 6,442,200 m2;
  • OSP/Offshore convertor station platform foundations and scour protection (ten OSP/Offshore convertor station platforms foundations, and associated scour protection);
  • wind turbine foundations and scour protection (307 wind turbine foundations); and
  • total = 10,198,971 m2.

MPA assessment:

Temporary habitat disturbance/loss:

  • sand wave and boulder clearance 6,306,405 m2;
  • assuming clearance occur within a 25 m wide corridor within which the cables are subsequently buried;
  • sand wave and boulder clearance deposition 13,762,343 m2;
  • temporary habitat disturbance/loss from the placement of dredged material to a uniform thickness of 0.5 m as a result of sand wave clearance placed on the seabed within the Firth of Forth Banks Complex MPA;
  • cable installation 4,126,083 m2;
  • assumes a maximum of 31.33% of the total temporary habitat disturbance/loss from 612.5 km of inter-array cables, and 47 km of substation interconnector cables, as well as 13.08% of the total temporary habitat disturbance/loss from 872 km of offshore export cables, affecting a corridor of up to 15 m width;
  • jack-up events 397,270 m2;
  • assumes maximum of 31.33% of total temporary habitat disturbance/loss from jack-up placements within the Proposed Development array area and export cable corridor;
  • anchoring during cable installation 105,466 m2;
  • assumes maximum of 31.33% of total temporary habitat disturbance/loss from anchor placement across the Proposed Development array area and Proposed Development export cable corridor; and
  • total 24,697,555 m2 (equates to 1.32% of the total area of the MPA).

Underwater noise magnitude – fish and shellfish ecology:

  • installation of up to 179 piled jacket foundations: 1,432 piles;
  • maximum hammer energy of 4,000 kJ, but realistic max hammer energy 3,000 kJ;
  • up to 10 hours piling per pile (up to 8 hours for OSPs/Offshore convertor station platforms)
  • maximum number of days when piling may occur: 372 days;
  • up to 14 UXO clearances may be required – assumed 5% of detonations will be higher order (due to unsuccessful deflagration), with the remaining detonated by deflagration, or microsited around if possible; and
  • all other noise sources (e.g. cable installation, foundation drilling etc.) have much smaller injury ranges than predicted for piling operations.

4.3.2           Summary Statement of Final Position

The initial findings for the assessment of effects and the MPA assessment as presented by the Applicant in Table 4.3   Open ▸ were agreed by the stakeholders and maintained with regards to the following agreed points:

  • sand waves and boulder clearance maintained as temporary habitat disturbance/loss;
  • monitoring of sand waves recovery in the Firth of Forth Banks Complex MPA;
  • additional details regarding the workings of the values and for significance of impact from small impact footprint included in the MPA assessment;
  • impact of EMF on benthic invertebrates included in the MPA assessment;
  • calculation for determining the maximum design scenario for wind turbine and OSPs/Offshore convertor station platform included in the MPA assessment;
  • the use of percentage of suitable habitat that would be disturbed or permanently lost to assess the degree of mortality for ocean quahog in the MPA assessment; and
  • overall belief that conservations objectives of the Firth of Forth Banks Complex MPA are unlikely to be hindered.

5 Areas of Agreement and Outstanding Non-Alignment

Table 5.1   Open ▸ summarises the position following completion of the Road Map process for benthic ecology, fish and shellfish ecology and physical processes at the point of Application submission. This forms the basis of the offshore EIA and HRA assessments presented within the offshore EIA Report and RIAA for the Proposed Development.

 

Table 5.1:
Areas of Agreement and Outstanding Non-Alignment Following Completion of the Road Map Process for Benthic Ecology, Fish and Shellfish Ecology and Physical Processes

Table 5.1: Areas of Agreement and Outstanding Non-Alignment Following Completion of the Road Map Process for Benthic Ecology, Fish and Shellfish Ecology and Physical Processes

 

6 Conclusion

The aim of the Benthic Ecology, Fish and Shellfish Ecology and Physical Processes Road Map was to ensure that the final consent Application submitted provides MS-LOT and its statutory advisors with sufficient information with which to make a determination. This document has set-out the meetings, agreements and areas of outstanding discussion that have been achieved in relation to the benthic ecology, fish and shellfish ecology and physical processes topics for the offshore EIA, and benthic ecology and fish and shellfish ecology topics for the offshore HRA.

7 References

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[1] By the Conservation of Habitats and Species Amendment (EU Exit) Regulations 2019