Sensitivity of receptor
  1. The sensitivities of marine mammals to cumulative disturbance from piling are as previously described above for the assessment of the Array alone (paragraphs 234 to 253) for the construction phase and therefore is not repeated here.
  2. All marine mammals are deemed to have some resilience to behavioural disturbance, high recoverability and high international value. The sensitivity of the receptor is therefore, considered to be medium.
Significance of effect
  1. Overall, the magnitude of the cumulative impact is deemed to be low for harbour porpoise, bottlenose dolphin, white-beaked dolphin, minke whale and grey seal, and the sensitivity of the receptor is considered to be medium. Cumulatively, the effect will therefore be of minor adverse significance, which is not significant in EIA terms.
Further mitigation and residual effect
  1. No marine mammal mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in section 10.10) is not significant in EIA terms.

                        Tier 2

Construction phase
Magnitude of impact
  1. There were 20 Tier 2 projects identified with potential for cumulative effects associated with this impact:
  • Broadshore Hub Offshore Wind Farms
  • Buchan Offshore Wind Farm
  • Caledonia Offshore Wind Farm;
  • Cenos Offshore Wind Farm
  • Dogger Bank South East – RWE Renewables;
  • Dogger Bank South West – RWE Renewables;
  • Marram;
  • Morven BP-EnBW;
  • Muir Mhor Offshore Wind Farm;
  • Salamander Offshore Wind Farm;
  • Stromar;
  • Nordsren I;
  • Nordsren II;
  • Nordsren II vest;
  • Nordsren III;
  • N-10.1;
  • Nordsren III vest;
  • N-10.2;
  • N-9.4; and
  • Ten Noorden van de Waddeneilanden
  1. Broadshore Hub Offshore Wind Farms are located 148.14 km from the Array and includes areas of seabed as part of INTOG leasing rounds to develop the 900 MW Broadshore Offshore Wind Farm Project (the Broadshore Project), the 99.5 MW Sinclair Offshore Wind Farm Project (the Sinclair Project) and the 99.5 MW Scaraben Offshore Wind Farm Project (the Scaraben Project), collectively known as the Broadshore Hub Offshore Wind Farms (Broadshore Offshore Wind Farm Limited et al., 2024). All projects will comprise wind turbines, station keeping systems and inter-array cables. The Broadshore Project will comprise up to 60 wind turbines, whilst the Sinclair and the Scaraben Projects will comprise up to six wind turbines. The Broadshore Hub Offshore Wind Farms Scoping Report (Broadshore Offshore Wind Farm Limited et al., 2024) scoped in underwater noise during impact piling (using hydraulic hammer or vibropiling) of anchors of fixed bottom substructures and/or floating substructures. Anchor driven piles may have up to 12 anchor driven piles per floating substructure estimated at 3.5 m diameter with hammer energy of up to 3,000 kJ. Fixed bottom substructures may comprise either jacket (tripod or quadruped) up to 4 m pile with hammer energy of up to 4,000 kJ, either impact or drill piled, or cable supported monopile with pile diameter of 16 m. The construction phase is expected to begin in 2028 until 2029 and therefore piling will be completed a year prior to the start of the Array, allowing some recovery before piling begins at the Array. Information on the numbers of animals is not available at this time to undertake a quantitative assessment.
  2. Buchan Offshore Wind Farm is located 151.62 km from the Array and is a FOW farm with up to 70 wind turbines and associated supporting structures, including floating foundations, mooring systems and anchors, interarray cables, up to three OSPs and export cable corridor (Buchan Offshore Wind Limited, 2023). The Buchan Offshore Wind Farm scoped in increased underwater noise from pile driving for floating wind turbines, OSPs and Intermediate Reactive Compensation (IRC) platform (if piled foundations are used). The construction phase is expected to begin in 2028 until 2030 and therefore piling may be sequential with the start of the construction of the Array, however the large distance means cumulative effects are unlikely. Information on the numbers of animals is not available at this time to undertake a quantitative assessment.
  3. The Caledonia Offshore Wind Farm is located in the Moray Firth, 157.49 km from the Array, indicatively 75% of the Array Area could be constructed using fixed foundations, and is considering the use of floating foundations for remaining sites (Ocean Winds, 2022). Fixed-foundation types currently being considered include: monopile; fully restrained platform; jacket with pin piles; jacket with suction caissons; Gravity Based Structure (GBS). Floating foundation types include semi-submersible and tension leg platform. A maximum of 150 wind turbine generators will be located within the Array Area, with an estimated split of up to 111 fixed foundations and 39 floating foundations. An indicative spatial distribution on fixed foundations (an area approximately 307 km2 across the north of the Caledonia Array Area) and floating foundations (approximately 122 km2 across the south of the Caledonia Array Area) is presented within the Offshore Scoping Report. The MDS considers up to six OSPs. The final type and design for the foundations will be subject to further site investigations, however jacket with pin piles, jacket with suction caissons, monopile and GBS currently under consideration. The construction phase is expected to begin in 2028 until 2029 and therefore piling will be completed a year prior to the start of the Array, allowing some recovery before piling begins at the Array. Information on the numbers of animals is not available at this time to undertake a quantitative assessment.
  4. Cenos Offshore Wind Farm is located 91.70 km from the Array and is a proposed FOW farm (part of the INTOG leasing process) with up to 1.4 GW and footprint of 333 km2. The Cenos Offshore Wind Farm Scoping Report (Flotation Energy, 2023) gives potential development size of 70 to 100 turbines with floating substructures with 3 to 6 mooring lines/anchor substructures. The Cenos Offshore Wind Farm scoped in underwater noise from percussion piling as a potential impact on marine mammals, but stated no significant effects on marine mammals due to noise are expected (Flotation Energy, 2023). The Cenos Offshore Wind Farm Scoping Report details an indicative schedule from 2027 to 2030 with installation of all the turbines expected to take two to three years, and therefore piling may be sequential with the start of the construction of the Array. Information on the numbers of animals is not available at this time to undertake a quantitative assessment.
  5. Dogger Bank South Offshore Wind Farms comprise Dogger Bank South East (located 363.35 km from the Array) and Dogger Bank South West (located 499.03 km from the Array). The Project Description (volume 1, chapter 3) allows for up to 150 turbines for each project, and the Scoping Report details a range of foundation options, including monopiles, jackets on pin piles; and jackets on suction buckets (RWE Renewables UK, 2022) (volume 1, chapter 3). Construction of the Dogger Bank Offshore Wind Farms is expected to begin no earlier than 2026, however the programme for construction will depend on the final confirmation of the grid connection date and there is no indication currently of a construction timeline (therefore precautionary it is considered there may be some overlap with the Array construction phase). It is anticipated that the two Dogger Bank projects will be built concurrently and sequentially (RWE Renewables UK, 2022). The large distance between the Dogger Bank South Offshore Wind Farms and the Array (363.35 km to 499.03 km south from the Array) means cumulative effects are unlikely Information on the numbers of animals is not available at this time to undertake a quantitative assessment.
  6. Marram Offshore Wind Farm is located 123.55 km from the Array and is a FOW farm proposed for up to 150 wind turbines at a capacity of 3000 wind turbines (MarramWind Ltd., 2023). Depending on the final wind turbine size selected, Marram Offshore Wind Farm is expected to have in the region of 126 to 225 wind turbines including floating units (platforms and station keeping system). The Marram Offshore Wind Farm Scoping report (MarramWind Ltd., 2023) scoped in increased underwater noise during installation, operation and maintenance, and decommissioning, from anchor piles. The overall duration of construction of the offshore infrastructure is anticipated to be up to eight years, from 2031 to 2038 and therefore may overlap with the construction programme of the Array. Information on the numbers of animals is not available at this time to undertake a quantitative assessment.
  7. The Morven Offshore Wind Project is a proposed large scale fixed-foundation offshore wind farm located 5.50 km from the Array. The Offshore Scoping Report (Morven Offshore Wind Limited, 2023) considers up to 191 wind turbines and up to 11 OSPs. The following foundation types will be considered: monopile foundations, gravity base foundations, piled jacket foundations (three or four legs for wind turbines; three, four or six legs for OSPs), suction bucket jacket foundations (three or four legs for wind turbines; three, four or six legs for OSPs) (Morven Offshore Wind Limited, 2023). The Array Project is estimated to occur over a duration of up to seven years, with construction phase from 2027 to 2033, meaning a potential of three years overlap with the construction phase of the Array. Information on the numbers of animals is not available at this time to undertake a quantitative assessment.
  8. Muir Mhor Offshore Wind Farm is a FOW project located 51.38 km from the Array, comprising up to 67 wind turbine foundations with a spacing of ≥ 1000 m. The turbines will be supported by a floating foundation with associated mooring and anchoring systems to keep the foundation ‘on station’. There are a number of floating foundation types under consideration, which include: semi-submersible, barge, tension leg platform, spar, multi-tower semi- submersible, buoy and semi-spar. The construction of the Muir Mhor Offshore Wind Farm is expected to occur between 2027 and 2030, and therefore whilst there is potential for no direct temporal overlap with the Array construction phase, piling at the Muir Mhor Offshore Wind Farm could lead to a longer duration of piling operations (i.e. sequential piling). Information on the numbers of animals is not available at this time to undertake a quantitative assessment.
  9. Salamander Offshore Wind Farm (Simply Blue Energy (Scotland) Limited, 2023) is located 79.49 km from the Array and is a proposed floating wind farm with an installed capacity of up to 100 MW. Up to seven offshore wind turbines with supporting floating substructures and mooring and anchoring systems, inter-array cables Underwater noise associated with piling activity is scoped in (from potential installation of piles associated with the mooring and anchoring system) in the Salamander Offshore Wind Farm Scoping Report (Simply Blue Energy (Scotland) Limited, 2023). A detailed construction programme with specific construction dates is not given in the scoping report, therefore a potential temporal overlap with construction at the Array cannot be discounted, but an indicative construction programme presents offshore construction from Q2 in year two and year three for six months per time, therefore potential temporal overlap is limited. Information on the numbers of animals is not available at this time to undertake a quantitative assessment.
  10. Stromar is located 170 km away from the Array, with the Stromar Array Area approximately 256 km2 in size. The EIA states up to 71 wind turbines with associate floating wind turbine substructures, with mooring and anchoring systems and inclusion of dynamic and static inter-array/interlink cable and up to three OSPs. Floating substructures may include spar, tension-leg platform, semi-submersible and barge. The indicative programme presented in the EIA Scoping Report assumes Stromar becomes commercially operational between 2030 and 2033 and has an offshore construction programme of six years (7 years construction phase for onshore and offshore). Information on the numbers of animals is not available at this time to undertake a quantitative assessment.
  11. For Nordsren I, Nordsren II, Nordsren II vest, Nordsren III, N-10.1, Nordsren III vest, N-10.2, N-9.4 and Ten Noorden van de Waddeneilanden, whilst scoping reports cannot be obtained, it has been assumed piling is scoped in as a precautionary approach to assessment. However, these projects lie between ~330 km and ~437 km away from the Array and therefore any cumulative effect from piling is highly unlikely given the contours presented for piling for the Array alone (section 10.11.2).
  12. 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. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.
Sensitivity of receptor
  1. The sensitivities of marine mammals to cumulative disturbance from piling are as previously described above for the assessment of the Array alone (paragraphs 234 to 253) for the construction phase and therefore is not repeated here.
  2. All marine mammals are deemed to have some resilience to behavioural disturbance, high recoverability and high international value. The sensitivity of the receptor is therefore, considered to be medium.
Significance of effect
  1. Overall, the magnitude of the cumulative impact is deemed to be low for all receptors, and the sensitivity of the receptor is considered to be medium. Cumulatively, the effect will therefore be of minor adverse significance, which is not significant in EIA terms.
Further mitigation and residual effect
  1. No marine mammal mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in section 10.10) is not significant in EIA terms.

                        Tier 3

Construction phase
Magnitude of impact
  1. There were 14 Tier 3 projects identified within the regional marine mammal study area with potential for cumulative effects associated with this impact:
  • Arven Offshore Wind Farm;
  • Ayre Offshore Wind Farm;
  • Bellrock Offshore Wind Farm;
  • Bowdun Offshore Wind Farm;
  • Campion Offshore Wind Farm;
  • Flora Floating Wind Farm;
  • Aspen;
  • INTOG Site 8: Harbour Energy;
  • Beech;
  • Cedar;
  • INTOG Site 13: Harbour Energy;
  • Yell Sound Array;
  • BP Exploration Operating Company Limited; and
  • Morven BP-EnBW Offshore Export Cable Corridor.
  1. Tier 3 projects are in a pre-application phase and no EIA Scoping Report or EIA Report is available to inform a quantitative assessment. Therefore, a qualitative assessment is provided below.
  2. The construction of the Array, together with construction phase of Tier 1, Tier 2 and Tier 3 projects ( Table 10.52   Open ▸ ) may lead to cumulative injury and disturbance to marine mammals from underwater noise generated during piling.
  3. The data in relation to Tier 3 projects available at the time of writing is limited and it is not possible to carry out a quantitative assessment at this stage. This is particularly the case for INTOG projects, which are a new concept and very little is known about the scale of the potential environmental impacts associated with these projects, though it is likely many will be floating projects. Tier 3 projects were screened in precautionarily based on their location (they lie within the regional marine mammal study area), though there is limited/no information on the construction/operation dates or project design with regards to piling. It should be acknowledged that there is a potential for piling activities to be taking place and therefore projects cannot be discounted, however it is not possible to undertake any kind of meaningful assessment for potential cumulative impacts as a result of elevated underwater noise due to piling with Tier 3 projects to take place intermittently across the North Sea.
  4. The cumulative impact (elevated underwater noise arising during piling) 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. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low for all species.
Sensitivity of receptor
  1. The sensitivities of marine mammals to cumulative disturbance from piling are as previously described above for the assessment of the Array alone (paragraphs 234 to 253) for the construction phase and therefore is not repeated here.
  2. All marine mammals are deemed to have some resilience to behavioural disturbance, high recoverability and high international value. The sensitivity of the receptor is therefore, considered to be medium.
Significance of effect
  1. Overall, the magnitude of the cumulative impact is deemed to be low for all receptors, and the sensitivity of the receptor is considered to be medium. Cumulatively, the effect will therefore be of minor adverse significance, which is not significant in EIA terms.
Further mitigation and residual effect
  1. No marine mammal mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in section 10.10) is not significant in EIA terms.

Injury and disturbance from underwater noise generated during Unexploded Ordnance (UXO) clearance

                        Tier 1

Construction phase
Magnitude of impact
  1. There were two Tier 1 projects within the 100 km buffer identified with potential for cumulative effects associated with this impact:
  • the construction phases of the Proposed offshore export cable corridor(s); and
  • the construction phases of Berwick Bank Wind Farm ( Table 10.52   Open ▸ ).
  1. Potential impacts of underwater noise from UXO detonations on marine mammals include mortality, physical injury or auditory injury. The risk of injury in terms of PTS to marine mammal receptors as a result of underwater noise during UXO clearance would be expected to be localised to the vicinity around the boundaries of the respective projects. It also is anticipated that standard offshore wind industry mitigation methods (which include visual and acoustic monitoring of marine mammals as standard and additional mitigation in form of ADDs and/or soft start charges) will be applied based on UXO specific risk assessment and if any residual risk of injury remains it will be mitigated further post-consent, thereby reducing the magnitude of the impact with respect to auditory injury occurring in marine mammals. However, the potential for a residual risk of injury was investigated based on the UXO clearance technique and mitigation proposed for each project.
  2. As previously presented for the Array alone in paragraph 267 et seq. (which uses TTS as a proxy for disturbance), the duration of effect for each UXO detonation is less than one second and behavioural effects are therefore considered to be negligible in this context.
  3. Projects screened in for this cumulative assessment are expected to involve similar construction activities to those described for the Array alone, including UXO clearance activities. It is anticipated that, for all projects, impacts associated with these activities will require additional assessment under EPS licensing, however such applications are not yet available in the public domain.
  4. Berwick Bank Wind Farm based their assessment on 14 UXOs requiring clearance (SSE Renewables, 2022c) ( Table 10.61   Open ▸ ) (up to 70 UXOs are likely to be found within the Berwick Bank Array Area and the Berwick Bank Proposed offshore export cable corridor(s), however, only 14 of these will require clearance based upon experience at Seagreen Wind Energy Ltd (2021)) and noise modelling was undertaken for UXO clearance (both low order and high order detonation) using the methodology described in Soloway and Dahl (2014). The EIA did state the precise details and locations of potential UXOs was unknown at the time of assessment. For the purposes of the UXO assessment, it was assumed that the maximum design scenario is UXO size up to 300 kg, and the maximum frequency would be up to two detonations within 24 hours. Berwick Bank Wind Farm stated low order techniques will be applied as the intended methodology for clearance of UXO (in which case cumulative effects would be further reduced) however highlighted there is a small risk that a low order clearance could result in high order detonation of UXO, and some UXOs may need to be cleared with high order methods and therefore whilst both low and high order clearance was assessed, the MDS was based upon high order clearance (300 kg).

 

Table 10.61:
UXO Clearance Parameters for the Array and Berwick Bank Wind Farm

Table 10.61 UXO Clearance Parameters for the Array and Berwick Bank Wind Farm

 

Auditory injury (PTS)

  1. For a given marine mammal hearing group, exceedance of the threshold for the onset of PTS may result in a permanent hearing loss which in turn could inhibit ecological functioning, such as communication, foraging, navigation and predator avoidance. The inability to continue with these important activities could eventually lead to a decline in vital rates of an individual, including growth, reproduction and subsequently survival. Depending on the type of detonation and size of UXO, UXO clearance activities may have residual effects in respect to marine mammals and PTS injury. In November 2021, the UK Government published a joint interim statement advising to use low noise alternatives to high order detonations where possible and it is anticipated that future developments will follow this guidance (JNCC, 2010b).
  2. For the Array alone, with measures adopted as part of the Array applied there was predicted to be a small residual effect of PTS based on accidental high order detonation of UXOs. The residual magnitude for all species, except for harbour porpoise, was determined to be low. For harbour porpoise, it is expected that small, nominal number of animals could be exposed to PTS threshold. Given that details about UXO clearance technique to be used and charge sizes will not be available until after the consent is granted, it is not possible to quantify the effects of UXO detonations and therefore the residual number of animals is not presented within this chapter. At a later stage, when details about UXO sizes and specific clearance techniques to be used become available, it will be possible to tailor the secondary mitigation to specific UXO sizes and species in order to reduce the risk of injury. Therefore, prior to the commencement of UXO clearance works, an EPS licence will be sought as required based on the detailed information on UXOs available at the time and with the application of appropriate secondary mitigation measures as a part of the MMMP (volume 4, appendix 22). It is therefore anticipated that following the application of secondary mitigation (volume 4, appendix 22), the residual magnitude of this effect will be reduced to low.
  3. The assessment for Berwick Bank Offshore Wind Farm determined harbour porpoise were likely to be the most sensitive species to potential injury from high order UXO clearance. The EIA found that the maximum injury (PTS) range estimated for harbour porpoise using the SPLpk metric is 10,630 m for the high order detonation of charge size of 300 kg. Conservatively, the number of harbour porpoise that could be potentially injured during each high order detonation of UXO was up to 293 individuals (0.08% of the NS MU population and 0.76% of SCANS III Block R). Using the SEL metric, to the predicted number of animals potentially affected was 38. In the assessment, up to 16 grey seals had the potential to be injured during each high order detonation of the UXO (0.04% of the East Scotland plus North East England MUs). Less than one individual has the potential to be injured for all other species considered in the assessment (bottlenose dolphin, white-beaked dolphin, minke whale).
  4. The Berwick Bank Wind Farm EIA (SSE Renewables, 2022c) detailed designed in measures will be adopted as part of a MMMP (volume 4, appendix 22) to reduce the potential of experiencing injury. However, the mitigation zones required of 10 km are considerably larger than the standard 1,000 m mitigation zone recommended for UXO clearance (JNCC, 2010b). Visual surveys note that there is often a significant decline in detection rate with increasing sea state (Embling et al., 2010, Leaper et al., 2015). Therefore, the EIA details additional mitigation will be applied in the form of soft start charges and ADDs to minimise residual risk of injury. The assessment therefore determined that with the application of secondary mitigation measures (following receipt of more detail regarding size and number of UXO post-consent as part of the EPS licence supporting information for UXO clearance), the magnitude of this impact will be reduced to low. Therefore, Berwick Bank EIA assessed the residual effect of auditory injury as minor adverse, with the residual magnitude as low following application of secondary measures (the unmitigated magnitude was medium based upon high order UXO clearance).

Table 10.62:
Number of Animals with the Potential to Experience PTS During UXO Clearance at Tier 1 Projects prior to any mitigation, and residual magnitude assessed in the EIA

Table 10.62 Number of Animals with the Potential to Experience PTS During UXO Clearance at Tier 1 Projects prior to any mitigation, and residual magnitude assessed in the EIA

1 Detailed mitigation to be agreed post-consent to fully mitigate injury.

 

  1. Although development of the Proposed offshore export cable corridor(s) will also be undertaken by the Applicant, UXO surveys have not yet been completed and the HND approach dictates that its development will be informed by that of the Array. Therefore, there is currently no information by which to determine if UXO is scoped in or out of the impact assessment. Furthermore, there is uncertainty of the final design and location details of the Proposed offshore export cable corridor(s) and therefore it is not possible to provide any sort of quantitative assessment of UXO clearance. It can be reasonably assumed, however, that the extent of the impacts for the Proposed offshore export cable corridor(s) are expected to be of a similar extent than those represented by the MDS for the Array alone, since 698 kg represents a large munition size for the North Sea. As outlined in paragraphs 283 to 284, the magnitude of impact is predicted to be of local (for all species except harbour porpoise) to regional (harbour porpoise) spatial extent, very short term duration, intermittent and, although the impact itself is reversible (i.e. the elevation in underwater sound only occurs during the detonation event), the effect of injury on sensitive receptors is permanent.
  2. UXO clearance at each of these projects will occur as a discrete stage within the overall construction phase and therefore will not coincide continuously over the duration of temporal overlap. Furthermore, each clearance event results in a very short duration of sound emission (seconds) so the impact will be short in duration and therefore the overlap is unlikely. For example, whilst there is uncertainty in the final grid connection design and location details of the Proposed offshore export cable corridor(s), the Proposed offshore export cable corridor(s) is predicted to begin construction one year prior to the Array construction phase (as per the volume 3, appendix 6.4 of the Array EIA Report) and therefore there is potential for some overlap of UXO clearance associated with the Array and Proposed offshore export cable corridor(s), however, this is expected to be minimal and of very short duration.
  3. Given that the risk of injury will be reduced by the appropriate standard industry measures at respective projects to minimise the risk of PTS to marine mammal receptors, the cumulative risk of injury is expected to be reduced further. At the Array with designed-in measures applied ( Table 10.22   Open ▸ ) it is anticipated that all species except harbour porpoise would be deterred from the injury zone and therefore the likelihood of PTS and population-level effects would be unlikely. However, following the application of secondary mitigation as described in paragraph 318 et seq. and more detail regarding size and number of UXO, the magnitude of this cumulative impact is considered to be low, as a reduction in impact to a non-significant level will reduce the project’s contribution to any cumulative impact on harbour porpoise in the North Sea MU (i.e., the cumulative assessment takes into account the project alone commitments to reducing the potential for significant auditory injury to a non-significant level). Therefore, with the residual magnitude for harbour porpoise for both the Array alone and Berwick Bank Wind Farm as low, and the residual magnitude for other marine mammal receptors as negligible, it is anticipated that the cumulative impact will be reduced to a non-significant level.
  4. The cumulative impact (high order detonation) is predicted to be of local (for all species except harbour porpoise) to regional (harbour porpoise) spatial extent in the context of the relevant geographic frame of reference, very short term duration, intermittent and the effect of injury is permanent. It is predicted that the impact will affect the receptor directly. With the adoption of secondary mitigation for the Array, as detailed in paragraph 318 et seq., the magnitude is therefore considered to be negligible for bottlenose dolphin, white-beaked dolphin, minke whale, humpback whale and grey seal.
  5. For harbour porpoise the ranges of effect are large for high order clearance, and it is likely that following designed in mitigation measures there will be a residual risk of PTS to a small number of individuals. With the adoption of secondary mitigation for the Array, as detailed in paragraph 318 et seq., the magnitude is therefore considered to be low.

Behavioural disturbance (TTS as proxy)

  1. For this impact TTS is applied as a proxy for strong disturbance although noting that TTS onset could potentially result in a temporary loss in hearing. Whilst some behaviours (e.g. feeding, communication, socialisation) could be inhibited in the short term due to disruptions in ecological function (including a temporary hearing shift), these are reversible and therefore not considered likely to lead to any long term effects on the individual. As discussed in paragraph 267, the duration of effect for each UXO detonation is less than one second and therefore behavioural effects are considered to be negligible in this context.
  2. For Berwick Bank Wind Fam, the maximum range across which animals have the potential to experience disturbance (using TTS as a proxy) due to high order detonation of a 300 kg charge (as the MDS) was assessed for minke whale as approximately 34 km. Harbour porpoise could potentially experience disturbance within a maximum of ~19 km from the source. The disturbance ranges for HF cetaceans (bottlenose dolphin and white-beaked dolphin) as well as seals are relatively small with a maximum of approximately 1 km and 6 km, respectively.
  3. Production of underwater sound during detonation of UXOs as a part of the cumulative projects as well as the Array have the potential to cause disturbance (TTS) in marine mammal receptors, however, this effect will be very short-lived (during detonation only) and reversible. A spatial maximum design scenario would occur where UXO clearance activities occur concurrently at the respective projects considered in the cumulative assessment. Sequential UXO clearance at respective projects could lead to a longer duration of effect. However, as described in paragraph 685, each clearance event results in a very short duration of sound emission (seconds) so the impact will be short in duration and therefore the overlap is unlikely, particularly given the construction phases of Hornsea Three, Berwick Bank Wind Farm and Proposed offshore export cable corridor(s) is likely to be completed several years (as due to safety reasons the UXO clearance activities takes place before other construction activities commence (JNCC, 2023a)) before the construction phase of the Array begins.
  4. Since each clearance event results in no more than a one second ensonification event and since animals are anticipated to recover quickly, the potential for cumulative effects with respect to disturbance is considered to be very limited. Furthermore, Berwick Bank Wind Farm lies over ~50 km away from the Array and therefore (given the maximum effect range was 32.7 km for minke whale, using SELcum metric) it is unlikely to lead to cumulative behavioural effects.
  5. The cumulative impact (high order detonation) is predicted to be of regional spatial extent in the context of the geographic frame of reference, very short term duration, intermittent and both the impact itself (i.e. the elevation in underwater noise during detonation event) and effect of disturbance is reversible (onset of TTS represents a non-trivial disturbance but not permanent injury). It is predicted that the impact will affect the receptor directly. The cumulative magnitude is therefore considered to be low for all species.
Sensitivity of receptor

Auditory injury

  1. The sensitivities of marine mammals to cumulative auditory injury from UXO are as previously described above for the assessment of the Array alone (paragraphs 293 to 300) for the construction phase and therefore is not repeated here.
  2. Therefore, all receptors, are deemed to have limited resilience to PTS, low recoverability and adaptability and are of high international value. The sensitivity of the receptor is therefore, considered to be high.

Behavioural disturbance (TTS as a proxy)

  1. The sensitivities of marine mammals to cumulative disturbance from UXO are as previously described above for the assessment of the Array alone (paragraphs 301 to 312) for the construction phase and therefore is not repeated here.
  2. All marine mammals are deemed to have some resilience to behavioural disturbance, high recoverability and adaptability, and high international value. The sensitivity of the receptor to cumulative disturbance is therefore, considered to be low.
Significance of effect

Auditory injury

  1. Considering that only up to 29 UXOs cumulatively from Tier 1 projects ( Table 10.61   Open ▸ ) require clearing and with low order techniques being prioritised, it is expected that UXO clearance would not manifest to population-level effects due to the small proportion of the North Sea MU potentially affected. In addition, as discussed in the Array alone assessment (paragraph 318) the project will apply further mitigation to reduce the project’s contribution to the cumulative effect assessment.
  2. Overall, for bottlenose dolphin, white-beaked dolphin, minke whale, humpback whale and grey seal, the magnitude of the cumulative impact (auditory injury from UXO clearance) is deemed to be negligible and the sensitivity of all receptors is considered to be high. The effect will therefore be of minor adverse significance, which is not significant in EIA terms.
  3. Overall, for harbour porpoise, the magnitude of the impact is deemed to be low and the sensitivity of the receptor is considered to be high. The effect will therefore be of minor adverse significance, which is not significant in EIA terms.

Behavioural disturbance (TTS as a proxy)

  1. Overall, for all species the magnitude of the impact (behavioural disturbance) is deemed to be low and the sensitivity of all receptors is considered to be low. The effect will therefore be of minor adverse significance, which is not significant in EIA terms.
Further mitigation and residual effect

Auditory injury

  1. No marine mammal mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in section 10.10 is not significant in EIA terms.

Behavioural disturbance (TTS as a proxy)

  1. No marine mammal mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in section 10.10) is not significant in EIA terms.

                        Tier 2

Construction phase
Magnitude of impact
  1. There were four Tier 2 projects identified in the 100 km buffer of the Array within regional marine mammal study area with potential for cumulative effects associated with this impact:
  • Cenos Offshore Wind Farm;
  • Morven BP-EnBW;
  • Muir Mhor Offshore Wind Farm; and
  • Salamander Offshore Wind Farm.
  1. The Cenos Offshore Wind Farm (Flotation Energy, 2023) included removal of UXO in construction impacts and stated if UXO is found, an underwater noise assessment specific to the UXO (the current presence and characteristics of UXO cannot be predicted) found will be completed to inform mitigation and EPS application. The dates of construction at Cenos Offshore Wind Farm are unknown, but potential overlap is unlikely given the short timescales of UXO clearance, and in combination with the distance from the Array (approximately 91.70 km) means that there is minimal spatial overlap from PTS and behavioural disturbance ranges and therefore potential for cumulative effects are unlikely.
  2. The Morven Offshore Wind Project scoped in injury and disturbance from UXO clearance (Morven Offshore Wind Limited, 2023). The Scoping Report detailed that a range of UXO sizes and clearance methodologies will be explored to develop the MDS (e.g. largest and most likely size/type of UXO, number of possible UXOs requiring clearance, high order vs low order/low yield clearance methodologies). Construction at Morven begins in 2027, and therefore it is likely that UXO clearance will have been undertaken four years before UXO clearance will begin at the Array and therefore there is no potential for cumulative effects.
  3. The EIA Scoping Report for Muir Mhor Offshore Wind Farm (Fred Olsen Seawind and Vattenfall, 2023) proposed that noise related impacts associated with construction activities resulting in auditory injury (i.e. PTS) and behavioural disturbance is scoped into the EIA, and included UXO clearance. The impact assessment of the risk of auditory injury scoped in as a result of UXO clearance operations will include an assessment for both high order detonations and low order detonations, whilst aligning with recent recommendations and position statements on UXO clearance for similar offshore wind farm developments in the area. Construction at Muir Mhor Offshore Wind Farm is planned from 2027 to 2030, and any UXO clearance is likely to be undertaken prior to the construction phase, therefore it is unlikely there will be overlap of UXO clearance with the Array as it will be carried out prior to the Array construction phase. This, in combination with the distance from the Array (approximately 51.38 km north) means that there is minimal spatial overlap from PTS and behavioural disturbance ranges and therefore potential for cumulative effects are unlikely.
  4. The EIA Scoping Report for Salamander Offshore Wind Farm (Simply Blue Energy (Scotland) Limited, 2023) stated while UXO clearance will be subject to a separate Marine Licence application, an indicative assessment of the potential for noise impacts to marine mammals from UXO clearance during the construction phase will be included in the EIA, and therefore scoped in UXO clearance. The underwater noise assessment will likely include a quantitative assessment of the risk of injury and disturbance (using TTS-onset as a proxy) to all species scoped-in as a result of UXO clearance operations, based on indicative example UXO sizes supported by noise propagation modelling. The Salamander Offshore Wind Farm Scoping Report states the MMMP will be implemented for UXO clearance if needed. The dates of construction at Salamander Offshore Wind Farm are unknown, but potential overlap is unlikely given the short timescales of UXO clearance, and in combination with the distance from the Array (approximately 79.49 km) means potential for cumulative effects are unlikely.
  5. It is expected than given that the risk of injury will be reduced by standard industry measures (including visual and acoustic monitoring) at respective projects, the cumulative risk of injury is expected to be reduced further. As discussed in paragraph 686, the cumulative assessment considers the Array’s commitments to reducing any potential significant auditory injury to a non-significant level by implementation of designed-in measures described in Table 10.22   Open ▸ (i.e. soft starts to piling and UXO clearance, deployment of ADDs up to 30 mins prior to commencement of piling or UXO clearance, application of low-order deflagration of UXO (where practicable) and implementation of an outline MMMP) and secondary mitigation measures discussed in section 10.11.2 (i.e. deployment of ADDs beyond 30 mins for prior to UXO clearance).

Auditory injury

  1. The cumulative impact (high order clearance) is predicted to be of local (for all species except harbour porpoise) to regional (harbour porpoise) spatial extent in the context of the geographic frame of reference, very short term duration, intermittent and the effect of injury is permanent. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be negligible for bottlenose dolphin, white-beaked dolphin, minke whale, humpback whale and grey seal.
  2. For harbour porpoise, the magnitude of the cumulative impact for harbour porpoise is considered to be low (as a reduction in impact to a non-significant level (see paragraph 709) will reduce the Array’s contribution to any cumulative impact on harbour porpoise in the North Sea MU).

TTS (proxy for disturbance)

  1. The cumulative magnitude of disturbance resulting from a high order detonation is predicted to be of regional spatial extent, very short term duration, intermittent and both the impact itself (i.e. the elevation in underwater noise during detonation event) and effect of disturbance is reversible (TTS represents a non-trivial disturbance but not permanent injury). It is predicted that the impact will affect the receptor directly, however, for all species a small proportion of the relevant MUs is predicted to be affected by strong behavioural disturbance. As such, whilst there may be effects at an individual level, these are not predicted to be at a scale that would lead to any population-level effects. The cumulative magnitude is therefore considered to be low for all species.
Sensitivity of receptor

Auditory injury

  1. The sensitivities of marine mammals to cumulative auditory injury (PTS) from UXO are as previously described above for the assessment of the Array alone (paragraphs 293 to 300) for the construction phase and therefore is not repeated here.
  2. All marine mammals are deemed to have limited resilience to auditory injury (PTS), low recoverability and adaptability and are of high international value. The sensitivity of the receptor is therefore, considered to be high.

Behavioural disturbance

  1. The sensitivities of marine mammals to cumulative disturbance from UXO are as previously described above for the assessment of the Array alone (paragraphs 301 to 312) for the construction phase and therefore is not repeated here.
  2. All marine mammals are deemed to have some resilience to behavioural disturbance, high recoverability and adaptability, and high international value. The sensitivity of the receptor to cumulative TTS is therefore, considered to be low.
Significance of effect

Auditory injury

  1. Overall, for bottlenose dolphin, white-beaked dolphin, minke whale, humpback whale and grey seal, the magnitude of the impact (auditory injury) is deemed to be negligible and the sensitivity of all receptors is considered to be high. The effect will therefore be of minor adverse significance, which is not significant in EIA terms.
  2. For harbour porpoise only, overall, the magnitude of the impact is deemed to be low and the sensitivity of all receptors is considered to be high. The effect will therefore be of minor adverse significance, which is not significant in EIA terms.

Behavioural disturbance (TTS as a proxy)

  1. Overall, for all species the magnitude of the impact (behavioural disturbance) is deemed to be low and the sensitivity of all receptors is considered to be low. The effect will therefore be of minor adverse significance, which is not significant in EIA terms.
Further mitigation and residual effect

Auditory injury

  1. No marine mammal mitigation for all receptors is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in section 10.10) is not significant in EIA terms.

Behavioural disturbance (TTS as a proxy)

  1. No marine mammal mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in section 10.10) is not significant in EIA terms.

                        Tier 3

Construction phase
Magnitude of impact
  1. There were eight Tier 3 projects identified in the regional marine mammal study area with potential for cumulative effects associated with this impact:
  • Bellrock Offshore Wind Farm;
  • Bowdun Offshore Wind Farm;
  • Campion Offshore Wind Farm;
  • Flora Floating Wind Farm;
  • Aspen;
  • Cedar; and
  • Morven BP-EnBW Offshore Export Cable Corridor.
  1. Tier 3 projects are in a pre-application phase and no EIA Scoping Report or EIA Report is available to inform a quantitative assessment. Therefore, a qualitative assessment is provided below.
  2. The construction of the Array, together with construction phase of Tier 1, Tier 2 and Tier 3 projects ( Table 10.52   Open ▸ ) may lead to cumulative injury and disturbance to marine mammals from underwater noise generated during UXO clearance. Tier 3 projects screened into the assessment within the regional marine mammal study area include: Bellrock Offshore Wind Farm, Bowdun Offshore Wind Farm, Campion Offshore Wind Farm, Flora Floating Wind Farm, Aspen, Cedar and Morven BP-EnBW Offshore Export Cable Corridor.
  3. As described in paragraph 669, the data in relation to Tier 3 projects available at the time of writing is limited, this is particularly the case for INTOG projects which as a new concept very little is known about the scale of the potential environmental impacts associated with these projects, though it is likely they will be largely floating projects. Tier 3 projects were screened in precautionarily based on their location within 100 km of the Array within the regional marine mammal study area (noting this is a highly precautionary screening area for UXO clearance), though there is limited/no information on the construction/operation dates or project design with regards to UXO clearance. It should be acknowledged that there is a potential for UXO clearance activities to be taking place at these Tier 3 projects, and therefore cumulative effects cannot be discounted. However, at this point in time, is not possible to undertake any kind of meaningful assessment for potential cumulative impacts as a result of underwater noise generated during UXO clearance from the Array and other Tier 3 projects.
  4. The cumulative impact of behavioural disturbance with respect to marine mammal IEFs is predicted to be of regional spatial extent in the context of the geographic frame of reference, medium term duration, intermittent and the effect is reversible. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.