10.12. Cumulative Effects Assessment

10.12.1. Methodology

  1. The CEA assesses the LSE1 associated with the Array together with other relevant plans, projects and activities. Cumulative effects are defined as the combined effect of the Array in combination with the effects from a number of different projects, on the same receptor or resource. Further details on CEA methodology are provided in volume 1, chapter 6.
  2. The plans and projects selected as relevant to the CEA presented within this chapter are based upon the results of a screening exercise (see volume 3, appendix 6.4 of the Array EIA Report). Volume 3, appendix 6.4 further provides information regarding how information pertaining to other plans and projects is gained and applied to the assessment. Each plan or project has been considered on a case-by-case basis for screening in or out of this chapter's assessment based upon data confidence, impact-receptor pathways and the spatial/temporal scales involved.
  3. In undertaking the CEA for the Array, it should be noted that other plans and projects under consideration will have differing potential for proceeding to an operational phase and hence a differing potential to ultimately contribute to a cumulative impact alongside the Array. Therefore, a tiered approach has be adopted which provides a framework for placing relative weight upon the potential for each project/plan to be included in the CEA to ultimately be realised, based upon the project/plan’s current stage of maturity and certainty in the projects’ parameters. The tiered approach which will be utilised within the Array CEA employs the following tiers:
  • tier 1 assessment – Array and Proposed offshore export cable corridor(s) and Proposed onshore transmission infrastructure and all plans/projects which became operational since baseline characterisation, those under construction, and those with consent and submitted but not yet determined;
  • tier 2 assessment – All plans/projects assessed under Tier 1, plus those projects with a Scoping Report; and
  • tier 3 assessment – All plans/projects assessed under Tier 2, which are reasonably foreseeable, plus those projects likely to come forward where an Agreement for Lease (AfL) has been granted.
  1. For consistency with the CEA long list presented in volume 3, appendix 6.4, (which was finalised at the end of March 2024, three months prior to submission of the Array EIA Report), Table 10.52   Open ▸ provides a detailed overview of all screened in projects. However, it is important to note that the cumulative assessment only covers projects and their statuses up to January 2024 (six months prior to submission of the Array EIA Report), as outlined in the Array EIA Scoping Report (Ossian OWFL, 2023) and agreed as part of the Ossian Array Scoping Opinion (MD-LOT, 2023).
  2. The specific projects scoped into the CEA for marine mammals are outlined in Table 10.52   Open ▸ . There will be no cumulative effects with onshore elements (those above MHWS) of the proposed offshore export cable corridor(s) and Proposed onshore transmission infrastructure for marine mammal receptors as all onshore works are above MHWS and there is therefore no receptor-impact pathway. The Proposed onshore transmission infrastructure is therefore screened out of further assessment.
  3. To note, whilst the Proposed offshore export cable corridor(s) is in Tier 1 for the CEA, due to uncertainty in the final grid connection design and location details of the Proposed offshore export cable corridor(s), it was not possible to undertake a full detailed quantitative assessment at the time of writing. However, it is assumed offshore export cables in the vicinity of the Array and would be installed and buried as the primary means of protection.
  4. The range of potential cumulative impacts that are identified and included in Table 10.52   Open ▸ , is a subset of those considered for the Array alone assessment. This is because some of the potential impacts identified and assessed for the Array alone, are localised and temporary in nature. It is considered therefore, that these potential impacts have limited or no potential to interact with similar changes associated with other plans or projects. These have therefore not been taken forward for detailed assessment.
  5. Similarly, some of the potential impacts considered within the Array alone assessment are specific to a particular phase of development (e.g. construction, operation and maintenance or decommissioning). Where the potential for cumulative effects with other plans or projects only have potential to occur where there is spatial or temporal overlap with the Array during certain phases of development, impacts associated with a certain phase may be omitted from further consideration where no plans or projects have been identified that have the potential for cumulative effects during this period.
  6. The CEA screening area for marine mammals initially focussed on projects within the regional marine mammal study area (as described in section 10.3) ( Figure 10.24   Open ▸ ), as agreed with Statutory Nature Conservation Bodies (SNCBs). Spatial and temporal scale of impacts is critical in the CEA and has been considered on an impact by impact basis to ensure a proportionate approach to the CEA and is discussed in detail in section 10.12.2. To note, for piling as a precautionary approach, projects whose construction phase finishes in the two years preceding the commencement of construction phase at the site boundary (2031) were also screened in as the sequential piling at respective projects could lead to a longer duration of effects and whilst are likely to be operational, allows for potential delays in offshore construction (up to two years).
  7. Given the limited data about Tier 3 projects available at the time of writing, projects were screened in initially based on temporal and/or spatial overlap as a precautionary approach. There was limited/no information on the construction/operation dates, nor foundation types proposed, however, with which to undertake any kind of meaningful assessment. Therefore, for potential impacts arising from piling for example which require these more detailed parameters, there is not sufficient information to carry out a full quantitative assessment.
  8. Where ScotWind projects / projects screened into the CEA will receive grid connections as part of Holistic Network Design (HND) and HND Follow-up Exercise (FUE) associated transmission infrastructure is only considered where there is sufficient information in the public domain, i.e. through project Scoping reports, to inform the assessment. Other project where there is a lack of information in the public domain on cable routing, development timescales, and grid connection for the transmission infrastructure has not been considered further within this CEA.

 

Table 10.52:
List of Other Projects and Plans Considered within the CEA for Marine Mammals

Table 10.52: List of Other Projects and Plans Considered within the CEA for Marine Mammals

*Correct as of CEA list freeze on 28 March 2024.

 

Figure 10.24:
Other Projects/Plans Screened into the CEA for Marine Mammals

Figure 10.24: Other Projects/Plans Screened into the CEA for Marine Mammals


10.12.2. Maximum Design Scenario

  1. The maximum design scenarios identified in Table 10.17   Open ▸ have been selected as those having the potential to result in the greatest effect on an identified receptor or receptor group. The cumulative effects presented and assessed in this section have been selected from the details provided in volume 1, chapter 3 of the Array EIA Report as well as the information available on other projects and plans (see volume 3, appendix 6.4), to inform a ‘maximum design scenario’. Effects of greater adverse significance are not predicted to arise should any other development scenario, based on details within the volume 1, chapter 3 (e.g. different wind turbine layout), to that assessed here, be taken forward in the final design scheme.
  2. As discussed in paragraph 594, where there is no spatial or temporal overlap with the activities during certain phases of the Array, impacts associated with other projects listed in Table 10.52   Open ▸ , may be excluded from further consideration.
  3. During the initial screening exercise for marine mammals, projects were considered over the whole of the regional marine mammal study area. Further to this, for each impact, the extent of the cumulative assessment was refined depending on the scale of the potential impact. For the purposes of the marine mammal assessment of effects, cumulative effects have been screened in/out on the following basis per impact:
  • Injury and disturbance from underwater noise generated during piling (construction phase) – the ZoI for piling can extend beyond the boundaries of proposed offshore wind farms and therefore, adopting a precautionary approach, the assessment has screened in projects within the regional marine mammal study area whose construction phases overlap with the construction phase for the site boundary. As a precautionary approach, projects whose construction phase finishes in the two years preceding the commencement of construction phase at the site boundary (two years prior to 2031) were screened in as the sequential piling at respective projects could lead to a longer duration of effect. Where a project finishes offshore construction prior to the two years before construction at the site boundary begins, animals are anticipated to recover fully to baseline levels and therefore these projects are screened out on the basis of no receptor impact pathway.
  • Injury/disturbance to marine mammals from underwater noise during UXO clearance (construction phase) – the ZoI for UXO clearance can extend beyond the boundaries of other proposed offshore wind farms. Therefore, adopting a precautionary approach, the assessment has screened in projects within 100 km of the site boundary (which is greater than the largest disturbance range of ~32 km for the Array alone, and acknowledges that disturbance ranges from other projects may be substantial) whose construction phases (which would include pre-construction UXO clearance) overlap with the construction phase for the site boundary. Projects with completed UXO clearance campaigns are screened out of the assessment. Projects whose construction phase finishes in the year preceding the commencement of construction phase at the site boundary (i.e. one year prior to 2031) were screened in as the sequential UXO clearance at respective projects could lead to a longer duration of effect.
  • Disturbance due to site-investigation surveys (including geophysical surveys) (Construction and operation and maintenance phase) – it is anticipated that the magnitude of the impacts will be of a similar scale to that described for the site boundary (i.e. metres), with the potential to experience disturbance by marine mammal receptors expected to be localised to within the boundaries of the respective projects. Therefore, the cumulative assessment has focussed only on site-investigation surveys for those projects within the close vicinity (up to 50 km buffer) of the site boundary and whose construction phase temporally overlaps with the site boundary. For the construction phase, where surveys are known to have been completed, this impact has been screened out of the CEA.
  • Injury and disturbance to marine mammals from underwater noise due to vessel use and other noise producing activities (all phases) – it is expected that each project will contribute to the increase of vessel traffic and hence to the amount of vessel noise in the environment during the construction, operation and maintenance and decommissioning phases. However, the potential to experience disturbance by marine mammal receptors would be expected to be localised to within the close vicinity of the respective projects (for example the maximum disturbance range from vessels for the Array was 3,259 m) and as such the assessment has focussed only on projects within a 50 km buffer of the Array as a conservative but proportionate approach.
  • Injury of marine mammals due to collision with vessels (all phases) – it is expected that each project will contribute to the increase of vessel traffic and hence to the potential risk of collision during the construction, operation and maintenance and decommissioning phases. However, the potential to experience disturbance by marine mammal receptors would be expected to be localised to within the close vicinity of the respective projects and as such the assessment has focussed only on projects within a 50 km buffer of the Array as a conservative but proportionate approach.
  • Effects on marine mammals due to EMFs from subsea electrical cabling in the water column – the impact of EMF is expected to be localised to within the close vicinity of the respective projects and transient for marine mammals, and as such the assessment has focussed only on projects within a representative 10 km buffer of the Array as a proportionate approach.
  • Injury and disturbance from underwater noise generated during the operation of floating wind turbines and anchor mooring lines (operation and maintenance phase) – this impact is included for which operation and maintenance phase overlaps with the operation and maintenance phase of the Array. However the potential to experience injury and disturbance by marine mammal receptors would be expected to be localised to within the close vicinity of the respective projects (for example the maximum TTS range for the Array was 50 m) and as such the assessment has focussed only on FOW projects within a 50 km buffer of the Array as a conservative but proportionate approach. (Risch et al., 2023b) highlighted the importance of considering the cumulative noise output of large FOW turbine arrays, particular where boundaries overlap, and therefore the wider 50 km buffer captures this wider spatial scale of effect.
  • Effects on marine mammals due to entanglement associated with the Array (operation and maintenance phase) – this impact is included for which operation and maintenance phase overlaps with the operation and maintenance phase of the Array. However, the potential to experience disturbance by marine mammal receptors would be expected to be localised to within the close vicinity of the respective projects and as such the assessment has focussed only on FOW projects within a 50 km buffer of the Array as a conservative but proportionate approach.
  • Effects on marine mammals due to altered prey availability (all phases) – potential cumulative effects on fish and shellfish assemblages, as identified in volume 2, chapter 9, may have indirect effects on marine mammals. For the purposes of the fish and shellfish ecology assessment of effects, cumulative effects have been assessed within a representative 50 km buffer of the Array fish and shellfish ecology study area. This 50 km buffer applies to all impacts considered in the assessment, except underwater noise, where a larger buffer of 100 km has been used to account for the larger ZoI of impacts. Therefore, only the projects considered in volume 2, chapter 9 are considered in the assessment of cumulative indirect impacts due to changes in fish and shellfish communities affecting prey availability.
  1. The assessment of cumulative effects with relevant projects has focussed on information available in the public domain (e.g. where the impact has been identified in the scoping study (Tier 2 projects) or the EIA Report (Tier 1 projects)). In this regard, where an impact has been identified and screened in, there is considered to be a potential for cumulative effects. Therefore, the impact will be considered further in section 10.12.3. Impacts scoped out from individual assessments of respective projects are not considered further.
  2. It should be noted that the CEA presented in this marine mammal chapter has been undertaken on the basis of information presented in the EIA Reports for the other projects, plans and activities, which is based upon the respective MDSs. The level of impact on marine mammal would likely be reduced significantly from those presented here.

 

Table 10.53:
Maximum Design Scenario Considered for Each Impact as part of the Assessment of Likely Significant Cumulative Effects on Marine Mammals

Table 10.53: Maximum Design Scenario Considered for Each Impact as part of the Assessment of Likely Significant Cumulative Effects on Marine Mammals

 

10.12.3. Cumulative Effects Assessment

  1. An assessment of the likely significance of the cumulative effects of the Array upon marine mammal receptors arising from each identified impact is given below.

Injury And Disturbance From Underwater noise Generated During Piling

  1. There is potential for cumulative injury and disturbance from underwater noise generated during piling as a result of piling associated with the array and the other plans and projects.
  2. For the purposes of this EIA Report, the likely significance of this effect has been assessed using the tiered approach outlined in section 10.12.1. The plans and projects screened into the CEA for this impact and their respective tiers are outlined in Table 10.52   Open ▸ .

                        Tier 1

Construction phase
Magnitude of impact
  1. There were three Tier 1 projects identified with potential for cumulative effects associated with this impact:
  • the construction and operation and maintenance phases of the Proposed offshore export cable corridor(s);
  • the construction and operation and maintenance phases of Berwick Bank; and
  • the construction and operation and maintenance phases of Hornsea Project Three ( Table 10.52   Open ▸ )
  1. Whilst the construction phase at Green Volt Offshore Wind Farm is anticipated to be completed in 2029 , the Green Volt Offshore Wind Farm EIA (GreenVolt, 2023) states offshore construction is anticipated to take approximately 24 months from Q4 2025 to the end of Q3 2027 and therefore there is no temporal overlap in piling between Green Volt Offshore Wind Farm and the Array. There will be a period of three years between offshore construction at Green Volt Offshore Wind Farm and the Array and therefore animals are anticipated to recover fully in this period and Green-Volt Offshore Wind Farm will not contribute to the cumulative effect with the Array and is excluded from the CEA for piling.
  2. There is no offshore piling during the construction and operation and maintenance phases of the Proposed offshore export cable corridor(s) and therefore will not contribute to the cumulative effect with the Array and is excluded from the CEA for piling.
  3. Piling at each of these projects will occur as a discrete stage within the overall construction phase and therefore the periods of piling may not coincide. These timelines are, however, indicative and may be subject to change. Where cumulative numbers of animals potentially disturbed are presented (e.g. paragraph 627), the calculations consider the timelines of respective projects. Given that Hornsea Project Three completes the construction prior to the commencement of construction activities at the Array (see paragraph 590), animals are likely to recover from the disturbance between piling events and therefore the numbers of animals potentially disturbed at respective projects are not added together. If construction timelines directly overlap (such as between Berwick Bank and Hornsea Project Three), animals could be disturbed during piling for both projects simultaneously and therefore numbers of animals potentially disturbed during piling are summed. Nevertheless, to ensure the most precautionary approach, cumulative iPCoD modelling incorporates numbers of animals affected by all projects throughout construction phases (see paragraph 131 et seq. for more details about iPCoD modelling).
  4. The potential to experience injury in terms of PTS by marine mammal receptors as a result of underwater noise due to piling would be expected to be localised to within the boundaries of the respective projects (assuming similar ranges of effect as presented for the Array). It is also anticipated that standard offshore wind industry construction methods (which include soft starts and visual and acoustic monitoring of marine mammals as standard) will be applied, thereby reducing the magnitude of the impact with respect to auditory injury occurring in marine mammals. Therefore, there is no potential for significant cumulative effects for injury from elevated underwater noise during pilling and the cumulative assessment focuses on disturbance only.
  5. Each project screened into the cumulative assessment has a slightly different approach to assessing behavioural disturbance of cetaceans and pinnipeds. For many years since it was published, Southall et al. (2007) along with Lucke et al. (2009) was widely used to assess the effects of noise on marine mammals, and was used in the assessment of disturbance for Dogger Bank Creyke Beck A, Dogger Bank Creyke Beck B (Forewind, 2014). This represents a fixed-threshold value approach, where it is assumed that all animals within the predicted impact area are to display a behavioural reaction, while none of the animals outside this area will react. However, since then a dose-response curve derived using received noise level and harbour porpoise presence data (Graham et al., 2017) was used to determine the proportion of animals present likely to be displaced in assessments for projects such as Inch Cape (Inch Cape Offshore Limited, 2018), Moray West (Moray West OWF Limited, 2018c) and Hornsea Project Three (Ørsted, 2018), Hornsea Project Four (Ørsted, 2021) and the Array (cetaceans only, see paragraph 105 et seq.). Given that respective projects used different criteria and noise thresholds modelled for marine mammal receptors in their assessments, it is necessary to exercise considerable caution if attempting any comparison between results of these appraisals. There are also variations between projects in the way results are presented. Some projects present the range of area from which animals are excluded and numbers of animals disturbed, whilst others only present number of animals disturbed and no ranges. Various densities were used to derive these numbers of animals (e.g. data from the integrated cetacean analysis (Mackenzie et al., 2012) and combined site-specific density surface and SCANS III Block data at Hornsea Project Three). As these values come from different sources, density details may reflect various densities of respective species throughout the year (i.e. seasonal versus average across the year). Respective projects may also use different reference populations. Therefore, assessment of the potential effects on marine mammals predicted by other wind farms is not always directly comparable to those presented for the Array due to different approaches to assessment taken by other offshore developers, different noise criteria and thresholds used, and differing levels of detail presented in associated EIAs.
  6. Based upon the programme presented in the Berwick Bank Offshore Wind Farm EIA (SSE Renewables, 2022c), the construction phase of Berwick Bank Offshore Wind Farm is expected to run from 2025 to 2032 with the final piling phase in 2031 (SSE Renewables, 2022c), therefore offshore construction may overlap with the construction phase of the Array by two years, and an overlap of piling for one year and therefore lead to cumulative effects from piling. Located 56.84 km south-west from the Array, the MDS for piling at Berwick Bank Offshore Wind Farm assumed that 5.5 m diameter piled jacket foundations will be installed using a maximum hammer energy of 4,000 kJ. The EIA states piling will be required at up to 179 wind turbine foundations and ten OSP/Offshore convertor station platform foundations, with the MDS based on concurrent piling at wind turbine foundations with the largest separation between piling locations as this leads to the MDS for disturbance (piling could occur concurrently at a wind turbine and OSP/Offshore convertor station platform foundation but these locations would be closer together compared to two wind turbine foundations). The maximum number of days (24 hours) within which piling could occur on the basis of two piling operations was 287 piling days (concurrent vessel) for the 179 wind turbines and 85 piling days (single vessel) for the ten OSPs/Offshore convertor station platforms. Piling activity at Berwick Bank Offshore Wind Farm will take place in three campaigns, and an indicative piling schedule was presented in the iPCoD report which give a realistic installation programme (SSE Renewables, 2022b), and this was carried forward to population modelling in this CEA. With mitigation measures in place (MMO2, PAM, ADD for 30 minutes, low hammer initiation, soft start and ramp up, such as those in Table 10.22   Open ▸ ), the residual number of individuals potentially affected by PTS was zero for all species. Numbers of animals disturbed for marine mammal IEFs, as presented in the Berwick Bank Offshore Wind Farm EIA (SSE Renewables, 2022c), is given in Table 10.54   Open ▸ .

 

Table 10.54:
Numbers Predicted to be Disturbed as a Result of Underwater Noise During Piling for Berwick Bank Offshore Wind Farm (SSE Renewables, 2022c)

Table 10.54 Numbers Predicted to be Disturbed as a Result of Underwater Noise During Piling for Berwick Bank Offshore Wind Farm (SSE Renewables, 2022c)

 

  1. The construction of Hornsea Project Three is anticipated to occur until 2030 ( Table 10.52   Open ▸ ), one year prior to the construction of the Array. Therefore, whilst the construction of Hornsea Project Three will be completed prior to commencement of piling at the Array, it could lead to a longer duration of piling operations (i.e. sequential rather than concurrent piling). It must be noted however that Hornsea Three is at the furthest extent of the regional marine mammal study area (a very small overlap therefore was screened in), located 319.38 km from the Array, and therefore cumulative effects are highly unlikely at this distance. The regional study area is a precautionary screening area for assessment to account for the mobile nature of marine mammals, and does not account for the levels of precaution in each respective projects MDS assessment (see paragraph 116 et seq. for examples of conservatism in underwater noise modelling). The cumulative assessment of Hornsea Project Three is based upon the original EIA submitted alongside applications for Development Consent Orders to the Planning Inspectorate (Ørsted, 2018). As detailed in the EIA, piling at Hornsea Three is likely to occur in two short phases (each of approximately one year and a half), with a maximum duration of three years between phases where no piling will occur and it is expected animals will recover in this period.
  2. The MDS for marine mammals for Hornsea Project Three included both a maximum spatial scenario and maximum temporal scenario. The maximum spatial scenario consisted of concurrent piling of 319 monopiles (300 turbine foundations and 19 foundations for other infrastructure and platform foundations) installed over 193.8 days, which comprises 189 days for monopiles over a 2.5 year period (divided into two phases and a gap of up to three years between phases), and 4.8 days for offshore High Voltage Alternating Current (HVAC) booster (over eight months within the 2.5 year piling period, single piling only), with a maximum hammer energy of up to 5,000 kJ (although Ørsted (2018) noted typically the maximum hammer energy will be considerably less than this and would not be required at all locations). The MDS states concurrent piling will occur only for infrastructure located within the Hornsea Three Array Area and not for infrastructure located within the offshore HVAC booster station search area in which only a single vessel scenario is possible.
  3. The maximum temporal scenario for Hornsea Project Three consisted of single piling of 1,848 pin piles (1,200 for jacket foundations and 648 for other infrastructure and platform foundations) over 554.4 days, over a 2.5 year period with two phases and a gap of up to three years between phases, and 28.8 days for offshore HVAC booster over eight months within the 2.5 year piling period), with an absolute maximum hammer energy of up to 2,500 kJ.
  4. The assessment in Hornsea Three was based on the definition of MDS piling parameters for each turbine foundation type (i.e. 5,000 kJ hammer energy for the monopiles and 2,500 kJ for the pin piles), however both a ‘most likely’ ramp up scenario (i.e. maximum hammer energy for most of the piling events = 3,500 kJ hammer energy for monopiles and 1,750 kJ for pin piles) and an overall ‘average’ hammer energy were defined (i.e., average typical hammer energy = 2,000 kJ for monopiles and 1,500 kJ for pin piles). Ørsted (2018) stated the number of animals disturbed under the maximum design scenario is highly precautionary as these hammer energies will not be representative of most of the actual piling activity. Whilst five representative locations were modelled, the highest impact ranges were found at the north-east modelling location within the Hornsea Three array (Hornsea Three NE) and at the south modelling location within the HVAC search area (HVAC S) and therefore used in the assessment for cetaceans. For grey seal, the Hornsea Three north-west (NW) location overlapped with higher seal density areas and therefore used for the assessment for grey seal. For concurrent scenarios, the MDS was modelled for monopiles at locations Hornsea Three NE and NW.
  5. A range of density estimates were used for the assessment of disturbance, as presented in Table 10.55   Open ▸ , alongside the dose-response method, with use of dose-response from Graham et al. (2017) for cetaceans and Russell et al. (2016) for seal species.

 

Table 10.55:
Sources for Density Estimates used in Hornsea Three Assessment of Piling (Ørsted, 2018)

Table 10.55 Sources for Density Estimates used in Hornsea Three Assessment of Piling (Ørsted, 2018)

 

Harbour porpoise

  1. The assessment for Berwick Bank Wind Farm predicted up to 2,822 animals (based on seasonal peak density) are predicted to experience potential disturbance from concurrent piling at a maximum hammer energy of 4,000 kJ (SSE Renewables, 2022c), which equates to 0.81% of the NS MU population and 7.3% of SCANS III Block R estimated abundance. This was based upon a 1% conversion factor and peak seasonal density of 0.826 animals per km2, assuming all animals are uniformly distributed within all noise contours to provide a precautionary assessment. The EIA stated the duration of piling could potentially affect harbour porpoise over a maximum of five breeding cycles, with the magnitude of the impact having the potential to result in a small but measurable alteration to the distribution of marine mammals during piling only (372 days over 52 months) and may affect the fecundity of small proportion of the population (up to 0.81% of the NS MU at any one time) over the medium term. Results of the iPCoD modelling for Berwick Bank Wind Farm for harbour porpoise against the MU population showed that the median of the ratio of the impacted population to the unimpacted population was 99.9% at 25 years regardless of the conversion factor scenario assessed (SSE Renewables, 2022c) and therefore, it was considered that there is no potential for a long term effect. The magnitude for Berwick Bank Wind Farm, for behavioural impacts from piling, was considered to be low.
  2. The assessment for Hornsea Project Three predicted up to 7,330 porpoises to be exposed to behavioural disturbance during concurrent piling events (monopiles), by combining the site-specific density surface estimates and the SCANS III density data (where impact areas extended beyond the mapped survey area). The NS MU harbour porpoise reference population was used for this assessment (227,298 individuals (Ørsted, 2018)). The effect of disturbance of harbour porpoise from piling was predicted to be of minor adverse significance. Population (iPCoD) modelling of the cumulative assessment for Hornsea Project Three on the North Sea harbour porpoise population as a result of a number of scenarios of offshore wind farm construction in the North Sea was carried out, as presented in Hornsea Project Three EIA (Ørsted, 2018)). The assessment found that even with 15% of the population potentially disturbed due to multiple Tier 2 projects (Dogger Bank Creyke Beck A, Dogger Bank Creyke Beck B, Dogger Bank Teesside A, Dogger Bank Teesside B (Sofia) and East Anglia Three), there was only a small (6%) increase in the risk of an annual population decline of 1% per year and that overall, impacted population trajectories were not significantly different from baseline population trajectories.
  3. Given that Hornsea Project Three completes the construction prior to the commencement of construction activities at the Array, animals are likely to recover from the disturbance between piling events and therefore the numbers of animals potentially disturbed at respective projects are not added together. However, there is the potential overlap of one year of piling with Berwick Bank Wind Farm which may lead to cumulative effects. Up to 11,131 animals may be disturbed at any one time if concurrent piling of wind turbines at Berwick Bank Wind Farm and concurrent piling at the Array occur simultaneously ( Table 10.56   Open ▸ ). However, Berwick Bank Wind Farm is located 56.84 km from the Array, and the likelihood of cumulative effects with projects located at large distances is considered to be reduced; impulsive sound is likely to undergo transition into non-impulsive sound at distance from the sound source (see paragraphs 95 and 121). Furthermore, in reality, it is highly unlikely piling will occur at exactly the same time, and strike at exactly the same rate, therefore this assessment is highly precautionary.
  4. Many projects refer to the North Sea MU as a reference population, which, as presented in the original Seagreen 1 Offshore Array EIA (Seagreen Wind Energy Limited, 2012) stretches across an area of 750,000 km2. The number of harbour porpoise potentially disturbed has been considered for projects located in the marine mammal study area, which means some, including Hornsea Three, lie over 300 km from the Array ( Table 10.52   Open ▸ ). Delineating the spatial extent of cumulative effects is commonly acknowledged as a challenge. Although harbour porpoise is generally rare in waters >200 m depth, the fact that this species utilises such a vast area further complicates a choice of appropriate spatial scale (Clarke Murray et al., 2014). Given the vast extent of available habitat, the fact that harbour porpoise is a wide-ranging species and the low percentage of the NS MU population disturbed as a result of piling at respective projects ( Table 10.52   Open ▸ ), the likelihood of cumulative effects with projects located at large distances (e.g. >100 km) from the Array (i.e. Hornsea Three) is considered to be low.
Table 10.56:
Harbour Porpoise Cumulative Assessment – Numbers Predicted to be Disturbed as a Result of Underwater Noise During Piling for Tier 1 Projects

Table 10.56 Harbour Porpoise Cumulative Assessment – Numbers Predicted to be Disturbed as a Result of Underwater Noise During Piling for Tier 1 Projects

 

  1. Population modelling (see volume 3, appendix 10.3) considered Berwick Bank Wind Farm and Hornsea Project Three alongside the Array, with respective numbers of animals potentially impacted against the MU population ( Figure 10.25   Open ▸ ). The construction phase of Hornsea Project Three ends in 2030, prior to the commencement of the Array construction phase. Furthermore, unsuitable weather conditions in the northern North Sea, particularly during the winter months, are likely to result in forced construction down time, reducing the duration that piling will take place for the Array, thus allowing a further cessation of the impact between the two projects. Results of the cumulative iPCoD modelling for harbour porpoise showed that the median of the ratio of impacted population to unimpacted population approaches a ratio of 1 at all modelled time points. Although there was a difference in the number of animals between the disturbed and undisturbed populations, it was not considered that there is a potential for a long term effect on this species as a result of cumulative piling at the Array and respective Tier 1 projects.


Figure 10.25:
Simulated Harbour Porpoise Population Sizes for Both the Baseline and the Impacted Populations Under the Cumulative Scenario and no Vulnerable Subpopulation

Figure 10.25: Simulated Harbour Porpoise Population Sizes for Both the Baseline and the Impacted Populations Under the Cumulative Scenario and no Vulnerable Subpopulation

 

  1. The cumulative impact (elevated underwater noise arising during piling) is predicted to be of regional spatial extent within the relevant geographic frame of reference, medium-term duration, intermittent and the effect of behavioural disturbance is reversible. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.

Bottlenose dolphin

  1. Bottlenose dolphin was not scoped in as a key species for Hornsea Project Three (Ørsted, 2018) and there is no information available for Proposed offshore export cable corridor(s). However, it was considered in Berwick Bank Wind Farm (SSE Renewables, 2022c) and therefore can be included in the cumulative assessment.
  2. Berwick Bank Wind Farm (SSE Renewables, 2022c) used a dual approach to estimate bottlenose dolphin disturbed, using noise contours overlaid with 2 m to 20 m depth contours and numbers of animals in those areas calculated using a density of 0.197 animals per km2 from Peterhead to Farne Islands and 0.294 animals per km2 for the outer Firth of Tay (where the density is higher). Furthermore, the number of bottlenose dolphins potentially disturbed during piling in offshore areas was calculated using densities from SCANS III Block R data with 0.0298 animals per km2. Up to five bottlenose dolphin are predicted to have the potential to experience disturbance from concurrent piling in coastal waters (2.25% of the CES2 MU population) based upon 1% constant conversion factor and maximum hammer energy of 4,000 kJ. Coastal bottlenose dolphin could also be potentially disturbed during single piling at a wind turbine or an OSPs/Offshore convertor station platform, with up to four (1.49% of the CES2 MU population) animals affected.
  3. Potential effects on the offshore bottlenose dolphin population were also assessed in the EIA for Berwick Bank Wind Farm. During concurrent piling at maximum 4,000 kJ hammer energy, up to 102 individuals occurring in offshore waters have the potential to experience disturbance (5.29% of SCANS III Block R). For the single piling scenario, up to 64 individuals have the potential to experience disturbance offshore, which equates to 3.29% of the SCANS III Block R estimated abundance. The EIA did state the densities were considered to be conservative as these are based on highly precautionary coastal and offshore density estimates. Population modelling for bottlenose dolphin against the MU population showed that the median of the ratio of the impacted population to the unimpacted population was a ratio of 1 at 25 years and there was no potential for a long term effect on this species. The magnitude for Berwick Bank Wind Farm, for behavioural impacts from piling, was considered to be low.
  4. As detailed in paragraph 620, numbers from Hornsea Three are not added together as its construction completes a year prior to the commencement for the Array, but there is the potential overlap of one year of piling at the Array with Berwick Bank Wind Farm which may lead to cumulative effects. Up to ten animals (in the CES2 MU) may be disturbed if concurrent piling of wind turbines at Berwick Bank Wind Farm and concurrent piling at the Array occur simultaneously. However, Berwick Bank Wind Farm is located 56.84 km south-east from the Array, and the likelihood of cumulative effects with projects located at large distances is considered to be reduced; impulsive sound is likely to undergo transition into non-impulsive sound at distance from the sound source (see paragraphs 95 and 121). Furthermore, in reality, it is highly unlikely piling will occur at exactly the same time, and strike at exactly the same rate, therefore this assessment is highly precautionary.

 

Table 10.57:
Bottlenose Dolphin Cumulative Assessment – Numbers Predicted to be Disturbed as a Result of Underwater Noise During Piling for Tier 1 Projects

Table 10.57 Bottlenose Dolphin Cumulative Assessment – Numbers Predicted to be Disturbed as a Result of Underwater Noise During Piling for Tier 1 Projects

1Animals disturbed is based upon the CES2 MU presented in Berwick Bank Wind Farm for comparison with the Array which uses CES2 MU, rather than offshore numbers.

 

  1. Population modelling (see volume 3, appendix 10.3) considered Berwick Bank Wind Farm alongside the Array (Hornsea Three lies outside of the CES2 MU and did not assess bottlenose dolphin), with respective numbers of animals potentially impacted against the MU population ( Figure 10.26   Open ▸ ). For bottlenose dolphin, the CES2 MU was used as the relevant reference population for cumulative population modelling. Given the importance of the Moray Firth SAC for bottlenose dolphin in this area, the sensitivity of this population and its known ranging behaviour further south towards St Andrews Bay and the Tay Estuary, and inshore in north-east English waters, it is important to capture the potential impact on this important coastal ecotype which may experience potential barrier effects. Whilst there is an abundance estimate for the Greater North Sea MU (2,022 animals (IAMMWG, 2023)) this large MU extends the entire length of the east coast of the UK and east to Scandinavia, so apportioning numbers of the offshore ecotype to the east coast of Scotland is not possible. It is also unlikely that the Array will create significant barrier effects for this offshore ecotype. Therefore, the cumulative modelling assessment for the Array used the CES2 MU as the relevant reference population.
  2. Results of the cumulative iPCoD modelling for bottlenose dolphin showed that the median of the ratio of impacted population to unimpacted population approaches had a ratio of 1 at all modelled time points, with ten fewer animals in the impacted population at 25 years after the start of piling, compared to the impacted population. Therefore, it was not considered that there is potential for a long term effect on this species as a result of cumulative piling at the Array and respective Tier 1 projects. Furthermore, given the population modelling used the CES2 MU, and the Array sits outside of this MU, it is considered further unlikely to have long term effects on the offshore ecotype.

Figure 10.26:
Simulated Bottlenose Dolphin Population Sizes for Both the Baseline and the Impacted Populations Under the Cumulative Scenario and no Vulnerable Subpopulation.

Figure 10.26: Simulated Bottlenose Dolphin Population Sizes for Both the Baseline and the Impacted Populations Under the Cumulative Scenario and no Vulnerable Subpopulation.

 

  1. The cumulative impact (elevated underwater noise arising during piling) is predicted to be of regional spatial extent within the geographic frame of reference, medium term duration, intermittent and high reversibility (with animals returning to baseline levels within hours/days after piling have ceased). It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.

 

White-beaked dolphin

  1. The assessment for Berwick Bank Wind Farm predicted up to 830 animals have the potential to experience disturbance during concurrent piling at a maximum hammer energy of 4,000 kJ (1.89% of the CGNS MU population), based on SCANS III Block R white-beaked dolphin density estimates and 1% constant conversion factor. White-beaked dolphin could also be potentially disturbed within the zone of possible disturbance during single piling at a wind turbine or OSPs/Offshore convertor station platform foundation at a maximum hammer energy of 4,000 kJ, with up to 516 (1.17% of the CGNS MU population) disturbed. The EIA determined the duration of piling could potentially affect white-beaked dolphin over a maximum of five breeding cycles but the area of effect is small in relation to the extensive distribution of the population for this species (CGNS MU, IAMMWG (2021) ). The magnitude for Berwick Bank Wind Farm, for behavioural impacts from piling on white-beaked dolphin, was considered to be low.
  2. The assessment for Hornsea Project Three predicted up to 12 white-beaked dolphin to be exposed to behavioural disturbance during concurrent piling events, by combining the site-specific density surface and the SCANS III density data (Ørsted, 2018). The CGNS MU white-beaked dolphin reference population of 15,895 individuals was used for this assessment (Ørsted, 2018), which is different to the estimate used in Berwick Bank Wind Farm and the Array. The residual effect of disturbance of white-beaked dolphin from piling was predicted to be of negligible adverse significance.
  3. As detailed in paragraph 620, numbers from Hornsea Three are not added together as it finishes construction a year prior to the Array, but there is the potential overlap of one year of piling at the Array with Berwick Bank Wind Farm which may lead to cumulative effects. Up to 2,361 animals (5.37% of the CGNS MU) may be disturbed if concurrent piling of wind turbines at Berwick Bank Wind Farm and concurrent piling at the Array occur simultaneously. However, Berwick Bank Wind Farm is located 56.84 km south-west from the Array, and the likelihood of cumulative effects with projects located at large distances is considered to be reduced; impulsive sound is likely to undergo transition into non-impulsive sound at distance from the sound source (see paragraphs 95 and 121). Furthermore, in reality, it is highly unlikely piling will occur at exactly the same time, and strike at exactly the same rate, therefore this assessment is highly precautionary.

 

Table 10.58:
White-Beaked Dolphin Cumulative Assessment – Numbers Predicted to be Disturbed as a Result of Underwater Noise During Piling for Tier 1 Projects

Table 10.58 White-Beaked Dolphin Cumulative Assessment – Numbers Predicted to be Disturbed as a Result of Underwater Noise During Piling for Tier 1 Projects

 

  1. As discussed in paragraph 131, the current version of iPCoD does not allow modelling for this species and therefore population modelling has not been carried out for this species.
  2. The cumulative impact (elevated underwater noise arising during piling) is predicted to be of regional spatial extent in the context of the geographic frame of reference, medium term duration, intermittent and the effect of behavioural disturbance is reversible (with animals returning to baseline levels within hours/days after piling have ceased). It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.

 

Minke whale

  1. The assessment for Berwick Bank Wind Farm (SSE Renewables, 2022c) predicted up to 132 animals have the potential to be disturbed as a result of concurrent piling at a maximum hammer energy of 4,000 kJ (based on SCANS III Block R minke whale density estimates) (equating to 0.66% of the CGNS MU). Minke whale could also be potentially disturbed within the zone of possible disturbance during single piling at a wind turbine or an OSPs/Offshore convertor station platform at a maximum hammer energy of 4,000 kJ with up to 82 (0.41% of the CGNS MU population) animals affected. The EIA determined the duration of piling could potentially affect minke whale over a maximum of five breeding cycles, with magnitude of the impact resulting in a small but measurable alteration to the distribution of marine mammals during piling only. However, population modelling showed that the median of the ratio of the impacted population to the unimpacted population was 0.989 at 25 years and it was considered that there was no potential for a long term effect on this species from Berwick Bank Wind Farm. The magnitude for Berwick Bank Wind Farm, for behavioural impacts from piling on minke whale, was considered to be low.
  2. The assessment for Hornsea Project Three predicted 51 minke whales could be exposed to noise levels that could result in behavioural disturbance during concurrent piling events, by using SCANS III density data (Ørsted, 2018). The CGNS MU minke whale reference population was used for this assessment (23,528 individuals). The effect of disturbance on minke whale from piling was predicted to be of minor adverse significance.
  3. As detailed in paragraph 620, numbers from Hornsea Three are not added together as it finishes construction a year prior to the Array, but there is the potential overlap of one year of piling at the Array with Berwick Bank Wind Farm which may lead to cumulative effects. Up to 495 animals may be disturbed if concurrent piling of wind turbines at Berwick Bank Wind Farm and concurrent piling at the Array occur simultaneously (2.46% of the CGNS MU). However, Berwick Bank Wind Farm is located 56.84 km south-west from the Array, and the likelihood of cumulative effects with projects located at large distances is considered to be reduced; impulsive sound is likely to undergo transition into non-impulsive sound at distance from the sound source (see paragraphs 95 and 121). Furthermore, in reality, it is highly unlikely piling will occur at exactly the same time, and strike at exactly the same rate, therefore this assessment is highly precautionary.
  4. Population modelling (see volume 3, appendix 10.3) considered Berwick Bank Wind Farm and Hornsea Project Three alongside the Array are not available at this stage), with respective numbers of animals potentially impacted against the MU population ( Figure 10.27   Open ▸ ). Results of the cumulative iPCoD modelling for minke whale showed that the median of the ratio of impacted population to unimpacted population was 1 at all modelled time points, with a difference of one animal between the impacted and unimpacted population 25 years after the start of piling. Therefore, it was considered that there is no potential for a long term effect on this species as a result of cumulative piling at the Array and respective Tier 1 projects.

Table 10.59:
Minke Whale Cumulative Assessment – Numbers Predicted to be Disturbed as a Result of Underwater Noise During Piling for Tier 1 Projects

Table 10.59: Minke Whale Cumulative Assessment – Numbers Predicted to be Disturbed as a Result of Underwater Noise During Piling for Tier 1 Projects

Figure 10.27:
Simulated Minke Whale Population Sizes for Both the Baseline and the Impacted Populations Under the Cumulative Scenario and no Vulnerable Subpopulation

Figure 10.27: Simulated Minke Whale Population Sizes for Both the Baseline and the Impacted Populations Under the Cumulative Scenario and no Vulnerable Subpopulation

 

  1. The cumulative impact (elevated underwater noise arising during piling) is predicted to be of regional spatial extent in the context of the geographic frame of reference, medium term duration, intermittent and the effect of behavioural disturbance is reversible (with animals returning to baseline levels within hours/days after piling have ceased). It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.

Grey seal

  1. The assessment for Berwick Bank Wind Farm (SSE Renewables, 2022c) predicted up to 1,358 animals were predicted to have the potential to be disturbed from concurrent piling at a maximum hammer energy of 4,000 kJ (3.19% of the East Scotland plus North East England MUs population), based upon Carter et al. (2020) maps. Grey seal could also be potentially disturbed within the zone of possible disturbance during single piling at a wind turbine or an OSPs/Offshore convertor station platform at a maximum hammer energy of 4,000 kJ with up to 705 (1.66% of the East Scotland plus North East England MUs population) animals disturbed. In the EIA population modelling for grey seal against the MU population showed that the median of the ratio of the impacted population to the unimpacted population was 100% at 25 years and it was considered that there is no potential for a long term effect on this species. The magnitude for Berwick Bank Wind Farm, for behavioural impacts from piling on grey seal, was considered to be low.
  2. The assessment for Hornsea Project Three predicted 53 grey seal to be exposed to behavioural disturbance during concurrent piling events (monopiles), based upon noise contours overlain on grey seal at-sea density surfaces from Russell et al. (2017). Given that Hornsea Project Three completes the construction prior to the commencement of construction activities at the Array, animals are likely to recover from the disturbance between piling events and therefore the numbers of animals potentially disturbed at respective projects are not added together.

 

Table 10.60:
Grey Seal Cumulative Assessment – Numbers Predicted to be Disturbed as a Result of Underwater Noise During Piling for Tier 1 Projects

Table 10.60: Grey Seal Cumulative Assessment – Numbers Predicted to be Disturbed as a Result of Underwater Noise During Piling for Tier 1 Projects

 

  1. Population modelling (see volume 3, appendix 10.3) considered Berwick Bank Wind Farm and Hornsea Project Three alongside the Array, with respective numbers of animals potentially impacted against the MU population. Results of the cumulative iPCoD modelling for grey seal showed that the median of the ratio of impacted population to unimpacted population was 1 at all modelled time points, and there was no difference in the mean size of the impacted and unimpacted populations at all time points. Therefore, it was considered that there is no potential for a long term effect on this species as a result of cumulative piling at the Array and respective Tier 1 projects.


Figure 10.28:
Simulated Grey Seal Population Sizes for Both the Baseline and the Impacted Populations Under the Cumulative Scenario and no Vulnerable Subpopulation

Figure 10.28: Simulated Grey Seal Population Sizes for Both the Baseline and the Impacted Populations Under the Cumulative Scenario and no Vulnerable Subpopulation

 

  1. The cumulative impact (elevated underwater noise arising during piling) is predicted to be of regional spatial extent in the context of the geographical frame of reference, medium term duration, intermittent and the effect is reversible (with animals returning to baseline levels within hours/days after piling have ceased). It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.