9.12. Cumulative Effects Assessment
9.12.1. Methodology
301. 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.
302. The projects and plans 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 project or plan 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.
303. In undertaking the CEA for the Array, it should be noted that other projects and plans under consideration will have differing potential for proceeding to an operational stage 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 with 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 when an Agreement for Lease (AfL) has been granted.
304. The specific projects scoped into the CEA for fish and shellfish ecology are outlined in Table 9.30 Open ▸ and presented in Figure 9.10 Open ▸ .
305. The range of potential cumulative impacts that are identified and included in Figure 9.10 Open ▸ , is a subset of those considered for the Array alone CEA assessment. This is because some of the potential impacts identified and assessed for likely significant effects 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.
306. 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.
307. For the purposes of the fish and shellfish ecology assessment of effects, cumulative effects have been assessed within a 50 km buffer of the Array, with the exception to underwater noise during the construction phase, where a larger buffer of 100 km was applied to account for the larger ZoI associated with underwater noise (i.e. behavioural effects to ranges of tens of kilometres from the site boundary).
Table 9.30: List of Other Projects and Plans Considered Within the CEA for Fish And Shellfish Ecology
Figure 9.10: Other Projects/Plans Considered in the Cumulative Effects Assessment for Fish and Shellfish Ecology
9.12.2. Maximum Design Scenario
308. The MDS identified in Table 9.13 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 Project Description (volume 1, chapter 3) (e.g. different wind turbine layout), to that assessed here, be taken forward in the final design scheme.
309. All impacts for the project alone ( Table 9.13 Open ▸ ) have been assessed within the CEA with the exception of increased SSCs and associated deposition during the operation and maintenance phase. This is due to the limited scale of impacts associated with the mooring lines in contact with the seabed during the operation and maintenance phase (each mooring line in seabed contact being of 680 m length (volume 2, chapter 7). Similarly, effects of underwater noise from wind turbine operation were predicted to have a negligible effect on fish and shellfish IEFs due to the highly localised area in which effects could occur. As such, there is no potential for cumulative effects from these impacts.
Table 9.31: Maximum Design Scenario Considered for Each Impact as Part of the Assessment of Likely Significant Cumulative Effects on Fish and Shellfish Ecology
9.12.3. Cumulative Effects Assessment
310. An assessment of the likely significance of the cumulative effects of the Array upon fish and shellfish ecology receptors arising from each identified impact is given below.
Temporary Habitat Loss and Disturbance
311. There is potential for cumulative temporary habitat loss and disturbance because of activities associated with the Array and the other plans and projects. Activities include sand wave and boulder clearance and relocation, cable installation, jack up vessel use, and cable repair and reburial and similar activities associated with the projects considered. For the purposes of this Array EIA Report, this impact has been assessed using the tiered approach outlined in section 9.9. The plans and projects screened into the CEA for this impact and their respective tiers are outlined in Table 9.30 Open ▸ . Cumulative habitat loss and disturbance is not considered for decommissioning as there is insufficient information to determine the decommissioning programme of plans/projects screened into the CEA, however the magnitude of impact is likely to be similar to, or less than, the cumulative effect of construction.
Tier 1
Construction phase
Magnitude of impact
- Proposed offshore export cable corridor(s) ( Table 9.30 Open ▸ ).
313. Currently, there is no EIA Report available for the Proposed offshore export cable corridor(s), though site preparation and construction phase activities for the Proposed offshore export cable corridor(s) are expected to be of a lesser extent than those represented by the MDS for the Array alone, which represented up to 40.41 km2 of temporary habitat loss and disturbance ( Table 9.13 Open ▸ ). Further, (as outlined in paragraph 64 for the Array alone), the impacts of cable installation and seabed preparation are expected to be temporary and reversible following completion of construction operations.
314. Other activities associated with the Array during this phase are not likely to occur within the Tier 1 project, such as jack up vessel use and temporary wet storage. The cumulative magnitude of impact of the Array with the Tier 1 project represents no additional material impact than that defined for the assessment of the Array alone (section 9.11).
315. The maximum duration of the offshore construction phase for the Array is up to eight years (2031 to 2038), and between 2030 and 2037 for the Proposed offshore export cable corridor(s) ( Table 9.30 Open ▸ ). Therefore, there may be seven years of overlap between the site preparation and construction activities of the Array and the Proposed offshore export cable corridor(s). Given the reversibility of temporary habitat loss and disturbance and the fact that construction operations would only affect a small proportion of the total habitat loss and disturbance footprint at any one time, any cumulative impacts with the Tier 1 project may be of a lesser spatial extent than if the temporal overlap between site preparation and construction activities was longer.
316. Within this phase of development of the Array, site preparation and construction activities are anticipated to occur intermittently; activities will be spread across the full allotted timeframe with only a small proportion of the MDS footprint for this impact being affected at any one time.
Sensitivity of receptor
318. The sensitivities of the fish and shellfish IEFs are as previously described above for the assessment of the Array alone (paragraphs 70 et seq.)
Significance of effect
319. For marine and shellfish species, the cumulative magnitude of the impact is deemed to be low and the sensitivity of most fish IEFs (including herring) is considered to be low. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.
320. For sandeel, the cumulative magnitude of the impact is deemed to be low and the sensitivity is considered to be medium. The effect will, therefore, be of minor adverse significance which is not significant in EIA terms.
321. For diadromous species, the cumulative magnitude of the impact is deemed to be low and the sensitivity of the receptor 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
322. No secondary mitigation is considered necessary because the likely cumulative effect in the absence of further mitigation (beyond the designed in measures outlined in section 9.10) is not significant in EIA terms.
Operation and maintenance phase
- Proposed offshore export cable corridor(s); and
- Eastern Green Link 2 ( Table 9.30 Open ▸ ).
324. Whilst there is currently no EIA Report available for the Proposed offshore export cable corridor(s), the activities and footprints of disturbance associated with its site preparation and construction phase are expected to be similar to those of the Eastern Green Link 2 project (discussed below), given both projects are both HVDC subsea power cables. Site preparation and construction phase activities for the Proposed offshore export cable corridor(s) are expected to be of a lesser extent than those represented by the MDS for the Array alone, which represented up to 51.41 km2 of temporary habitat loss and disturbance ( Table 9.13 Open ▸ ). Further, (as outlined in paragraph 64 for the Array alone), the impacts of operation and maintenance activities (including cable repair and remedial burial) are expected to be temporary and reversible.
325. Site preparation and construction activities at the Eastern Green Link 2 project are planned to occur between 2024 to 2029, so will not overlap with this phase of the Array ( Table 9.30 Open ▸ ). Within the Environmental Appraisal Report for the Eastern Green Link 2, no values were provided for temporary habitat loss and disturbance during its operation and maintenance phase (which coincides with the site preparation and construction phase of the Array). However, it would be substantially lower than the MDS value of 15.2 km2 provided for the site preparation and construction phase ( Table 9.23 Open ▸ ); (National Grid Electricity Transmission and Scottish Hydro Electric Transmission plc, 2022).
326. Other activities associated with the Array during this phase are not likely to occur within the Tier 1 projects, such as jack up vessel use and temporary wet storage. The cumulative magnitude of impact of the Array with the Tier 1 projects represents no additional material impact than that defined for the assessment of the Array alone (paragraphs 63 et seq.).
327. Any operation and maintenance phase activities (e.g. cable repair or cable reburial) will only affect a small proportion of habitats at any one time.
328. The cumulative impact is predicted to be of local spatial extent, long term duration), intermittent, and of high reversibility. It is predicted that the impact will affect the receptors directly. The magnitude is therefore considered to be low.
Sensitivity of receptor
329. The sensitivities of the fish and shellfish IEFs are as previously described above for the assessment of the Array alone (paragraphs 70 et seq.)
Significance of effect
330. For marine and shellfish species, the cumulative magnitude of the impact is deemed to be low and the sensitivity of most fish IEFs (including herring) is considered to be low. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.
331. For sandeel, the cumulative magnitude of the impact is deemed to be low and the sensitivity is considered to be medium. The effect will, therefore, be of minor adverse significance which is not significant in EIA terms.
332. For diadromous species, the cumulative magnitude of the impact is deemed to be low and the sensitivity of the receptor 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
333. No secondary mitigation is considered necessary because the likely cumulative effect in the absence of further mitigation (beyond the designed in measures outlined in section 9.10) is not significant in EIA terms.
Tier 2
Construction phase
Magnitude of impact
334. In addition to the Tier 1 projects, there was one Tier 2 project identified with potential for cumulative LSE1 associated with this impact: the site preparation and construction phases of the Morven Offshore Wind Farm ( Table 9.30 Open ▸ ). According to the Morven Offshore Wind Farm Scoping Report, site preparation and construction activities applicable to this impact for the Morven Offshore Wind Farm are expected to be:
- site preparation (sand wave clearance and boulder clearance and relocation);
- cable installation; and
- jack up vessel use for infrastructure installation (Morven Offshore Wind Limited, 2023).
335. Unlike for the Array, there is no offshore temporary wet storage included within the Scoping Report for Morven Offshore Wind Farm (Morven Offshore Wind Limited, 2023). Otherwise, temporary habitat loss and disturbance impacts associated with the Morven Offshore Wind Farm are expected to be similar in nature and extent to the Array. As outlined in paragraphs 155 to 157 for the Array alone, the impacts of site preparation and construction activities are expected to be temporary and reversible. The cumulative magnitude of the Tier 2 assessment represents no additional material impact to that defined for the assessment of the Array alone (paragraphs 63 et seq.)
336. The maximum duration of the offshore construction phase for the Array is up to eight years (2031 to 2038), and between 2027 to 2033 for the Morven Offshore Wind Farm ( Table 9.30 Open ▸ ). Therefore, there will not be significant overlap between the site preparation and construction activities of the Array and Morven Offshore Wind Farm (two years). Given the reversibility of temporary habitat loss and disturbance, and the fact that construction operations would only affect a small proportion of the total habitat loss and disturbance footprint at any one time any cumulative impacts with the Morven Offshore Wind Farm may be of a lesser spatial extent than if the temporal overlap between site preparation and construction activities was longer.
337. The cumulative impact is predicted to be of local spatial extent, medium term duration (between 2031 to 2038), intermittent, and of high reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.
Sensitivity of receptor
338. The sensitivities of the fish and shellfish IEFs are as previously described above for the assessment of the Array alone (paragraphs 70 et seq.)
Significance of effect
339. For marine and shellfish species, the cumulative magnitude of the impact is deemed to be low and the sensitivity of most fish IEFs (including herring) is considered to be low. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.
340. For sandeel, the cumulative magnitude of the impact is deemed to be low and the sensitivity is considered to be medium. The effect will, therefore, be of minor adverse significance which is not significant in EIA terms. This is largely due to the area of unsuitable habitat for sandeel, that sandeel spawning grounds within the fish and shellfish ecology area is of low intensity and because modelling shows the abundance of buried sandeel to be very low.
341. For diadromous species, the cumulative magnitude of the impact is deemed to be low and the sensitivity of the receptor 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
342. No secondary mitigation is considered necessary because the likely cumulative effect in the absence of further mitigation (beyond the designed in measures outlined in section 9.10) is not significant in EIA terms.
Operation and maintenance phase
Magnitude of impact
343. In addition to the Tier 1 projects, there was one Tier 2 project identified with potential for cumulative effects associated with this impact: the operation and maintenance phase of the Morven Offshore Wind Farm ( Table 9.30 Open ▸ ). As with the Array, operation and maintenance activities applicable to this impact for the Morven Offshore Wind Farm are expected to include cable repair and reburial and the use of jack up vessels for operation and maintenance activities (Morven Offshore Wind Limited, 2023). Within the Scoping Report for Morven Offshore Wind Farm, it is stated that the extent of these activities is expected to be lower than that of the site preparation and construction phase (Morven Offshore Wind Limited, 2023).
344. For the Array, up to 51.41 km2 of temporary habitat loss and disturbance may occur due to operation and maintenance activities ( Table 9.13 Open ▸ ) although only a small proportion of this total footprint is likely to be impacted at any one time.
345. The cumulative spatial extent of this impact in the operation and maintenance phase therefore likely to be small in relation to the fish and shellfish ecology study area in which cumulative effects have been considered, although there is the potential for repeated disturbance to the habitats in the immediate vicinity infrastructure and cables. The cumulative magnitude of impact of the Tier 2 assessment represents no additional material impact than that defined for the assessment of the Array alone (paragraphs 63 et seq.)
346. The cumulative impact is predicted to be of local spatial extent, long term duration, intermittent and high reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore, considered to be low.
Sensitivity of receptor
347. The sensitivities of the fish and shellfish IEFs are as previously described above for the assessment of the Array alone (paragraphs 70 et seq.)
Significance of effect
348. For marine and shellfish species, the cumulative magnitude of the impact is deemed to be low and the sensitivity of most fish IEFs (including herring) is considered to be low. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.
349. For sandeel, the cumulative magnitude of the impact is deemed to be low and the sensitivity is considered to be medium. The effect will, therefore, be of minor adverse significance which is not significant in EIA terms. This is largely due to the area of unsuitable habitat for sandeel, that sandeel spawning grounds within the fish and shellfish ecology area is of low intensity and because modelling shows the abundance of buried sandeel to be very low.
350. For diadromous species, the cumulative magnitude of the impact is deemed to be low and the sensitivity of the receptor 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
351. No secondary mitigation is considered necessary because the likely cumulative effect in the absence of further mitigation (beyond the designed in measures outlined in section 9.10) is not significant in EIA terms.
Tier 3
Construction phase
Magnitude of impact
352. In addition to the Tier 1 and Tier 2 projects, there were six Tier 3 projects identified with potential for cumulative effects associated with this impact:
- Morven Offshore Export Cable Corridor(s);
- Bellrock Offshore Wind Farm;
- Bowdun Offshore Wind Farm;
- Campion Offshore Wind Farm;
- Eastern Green Link 3; and
- Eastern Green Link 4 ( Table 9.30 Open ▸ ).
353. As these are Tier 3 projects, there are no Scoping Reports in the public domain. Therefore, there is no information available on the impact that these Tier 3 projects will have on fish and shellfish ecology. Temporary habitat loss and disturbance impacts associated the Bellrock, Bowdun and Campion Offshore Wind Farms are expected to be similar in nature and extent to the Array. As outlined in paragraphs 126 to 128 for the Array alone, the impacts of site preparation and construction activities are expected to be temporary and reversible. The impacts of cable installation, seabed preparation, and jack up vessel use are likely to be reversible. The cumulative magnitude of impact of the Tier 3 assessment represents no additional material impact to that defined for the assessment of the Array alone (paragraphs 63 et seq.)
354. Impacts associated with the Morven Offshore Export Cable Corridor(s) and Eastern Green Link 3 and 4 are likely to be similar to those assessed in Tier 1 for the Proposed offshore export cable corridor(s) and Eastern Green Link 2 (see paragraphs 312 et seq.).
355. The maximum duration of the offshore construction phase for the Array is up to eight years (2031 to 2038). There are currently no dates available for the construction phase of various Tier 3 projects. Therefore, there may be minimal overlap between the site preparation and construction activities of the Array and that of the Tier 3 projects ( Table 9.30 Open ▸ ).
356. The cumulative impact is predicted to be of local spatial extent, medium term duration (between 2031 and 2038 for the Array’s site preparation and construction), intermittent, and of high reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.
Sensitivity of receptor
357. The sensitivities of the fish and shellfish IEFs are as previously described above for the assessment of the Array alone (paragraphs 70 et seq.)
Significance of effect
358. For marine and shellfish species, the cumulative magnitude of the impact is deemed to be low and the sensitivity of most fish IEFs (including herring) is considered to be low. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.
359. For sandeel, the cumulative magnitude of the impact is deemed to be low, and the sensitivity is considered to be medium. The effect will, therefore, be of minor adverse significance which is not significant in EIA terms. This is largely due to the area of unsuitable habitat for sandeel, that sandeel spawning grounds within the fish and shellfish ecology area is of low intensity and because modelling shows the abundance of buried sandeel to be very low.
360. For diadromous species, the cumulative magnitude of the impact is deemed to be low and the sensitivity of the receptor 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
361. No secondary mitigation is considered necessary because the likely cumulative effect in the absence of further mitigation (beyond the designed in measures outlined in section 9.10) is not significant in EIA terms.
Operation and maintenance phase
Magnitude of impact
362. In addition to the Tier 1 and Tier 2 projects, there were six Tier 3 projects identified with potential for cumulative effects associated with this impact:
- Morven Offshore Export Cable Corridor(s);
- Bellrock Offshore Wind Farm;
- Bowdun Offshore Wind Farm;
- Campion Offshore Wind Farm;
- Eastern Green Link 3; and
- Eastern Green Link 4 ( Table 9.30 Open ▸ ).
363. As these are Tier 3 projects, there are no Scoping Reports or EIA documents available in the public domain. Therefore, there is no information available on the impact that these Tier 3 projects will have on fish and shellfish ecology. The activities associated with Bellrock, Bowdun, and Campion Offshore Wind Farms are likely to be similar to those of the Array (paragraphs 126 to 128). These activities include cable repair and reburial and use of jack up vessels for infrastructure maintenance. There are currently no dates available for the construction phase of various INTOG projects, though are of small scale (3 MW to 1,350 MW; Table 9.30 Open ▸ ) compared to the Array.
364. For the Array, up to 51.41 km2 of temporary habitat loss and disturbance may occur due to operation and maintenance activities ( Table 9.13 Open ▸ ). Temporary habitat loss and disturbance impacts associated the Bellrock Offshore Wind Farm, Bowdun Offshore Wind Farm, and Campion Offshore Wind Farm are expected to be similar in nature and extent to the Array. As outlined in paragraphs 126 to 128 for the Array alone, the impacts of operation and maintenance phase activities are expected to be temporary and reversible, and only a small proportion of habitat will be affected at any one time, with recovery of sediments occurring following installation of infrastructure.
365. Impacts associated with the Morven Offshore Export Cable Corridor(s) and Eastern Green Link 3 and 4 are likely to be similar to those assessed in Tier 1 for the Proposed offshore export cable corridor(s) and Eastern Green Link 2 (see paragraphs 323 et seq.).
366. The cumulative spatial extent of this impact in the operation and maintenance phase likely to be small in relation to the whole fish and shellfish ecology study area, although there is the potential for repeated disturbance to the habitats in the immediate vicinity infrastructure and cables. The cumulative magnitude of impact for Tier 3 represents no additional material impact to that defined for the assessment of the Array alone (paragraphs 63 et seq.)
367. The cumulative impact is predicted to be of local spatial extent, long term duration, intermittent and high reversibility. It is predicted that the impact will affect the receptors directly. The magnitude is therefore, considered to be low.
Sensitivity of receptor
368. The sensitivities of the fish and shellfish IEFs are as previously described above for the assessment of the Array alone (paragraphs 70 et seq.)
Significance of effect
369. For marine and shellfish species, the cumulative magnitude of the impact is deemed to be low and the sensitivity of most fish IEFs (including herring) is considered to be low. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.
370. For sandeel, the cumulative magnitude of the impact is deemed to be low, and the sensitivity is considered to be medium. The effect will, therefore, be of minor adverse significance which is not significant in EIA terms. This is largely due to the area of unsuitable habitat for sandeel, that sandeel spawning grounds within the fish and shellfish ecology area is of low intensity and because modelling shows the abundance of buried sandeel to be very low.
371. For diadromous species, the cumulative magnitude of the impact is deemed to be low and the sensitivity of the receptor 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
372. No secondary mitigation is considered necessary because the likely cumulative effect in the absence of further mitigation (beyond the designed in measures outlined in section 9.10) is not significant in EIA terms.
LONG TERM Habitat Loss and Disturbance
373. There is potential for cumulative long term habitat loss and disturbance due to infrastructure installed during the construction of the Array and the other plans and projects given in Table 9.30 Open ▸ . This long term habitat loss and disturbance will persist into the operation and maintenance phase as infrastructure is installed, and as such, the construction and operation and maintenance phases have been assessed together. Infrastructure installed includes foundations, scour protection, cable protection, cable crossing protection, junction boxes, mooring lines, and anchors. For the purposes of this Array EIA Report, this impact has been assessed using the tiered approach outlined in 9.12.1. The plans and projects screened into the CEA for this impact and their respective tiers are outlined in Table 9.31 Open ▸ .