19.12. Cumulative Effects Assessment

19.12.1. Methodology

135. 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.
136. 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.
137. 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 been 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 projects which became operational since baseline characterisation, those under construction and those with consent application(s) submitted but not yet determined;
• tier 2 assessment – All plans/projects assessed under Tier 1, plus those projects with a Scoping Report;
• 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.

138. The specific projects scoped into the CEA for marine archaeology, are outlined in Table 19.16   Open ▸ and presented in Figure 19.5   Open ▸ .
139. The range of potential cumulative effects that are identified and included in Table 19.18   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. The impact of direct damage to deeply buried marine archaeology receptors (submerged prehistoric receptors e.g. palaeolandscapes and associated archaeological receptors) has 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.
140. 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.
141. For the purposes of this Array EIA Report, a 2 km screening buffer around the Array was used to identify other plans and projects to be included within the CEA. This buffer is considered appropriate and precautionary as all of the screened-in impacts considered within the CEA will be localised in extent.

Table 19.16: List of Other Projects and Plans Considered within the CEA for Marine Archaeology

Figure 19.5: Other Projects/Plans Screened into the Cumulative Effects Assessment for Marine Archaeology

19.12.2. Maximum Design Scenario

142. The maximum design scenarios identified in Table 19.17   Open ▸ have been selected as those having the potential to result in the greatest impact 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.
143. Of the impacts set out in Table 19.10   Open ▸ , the following have not been included in the CEA for any phase, as the Proposed offshore export cable corridor(s) does not contain infrastructure that will impact deeply buried deposits:

• direct damage to deeply buried marine archaeology receptors – submerged prehistoric receptors (palaeolandscapes and associated archaeological receptors).

144. Of the impacts set out in Table 19.10   Open ▸ , the following have not been included in the CEA for the construction and decommissioning phases due to the fact that it is the presence of infrastructure on the seabed which has the potential to alter sediment transport regimes, so only the phase where this occurs is assessed:

• alteration of sediment transport regimes.

145. This is due to the fact that it is the presence of infrastructure on the seabed which causes the impact, therefore there is no impact-receptor pathway outside of the operations and maintenance phase.

Table 19.17: Maximum Design Scenario Considered for Each Impact as part of the Assessment of Likely Significant Cumulative Effects on Marine Archaeology

19.12.3. Cumulative Effects Assessment

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

Sediment disturbance and deposition leading to indirect impacts on marine archaeology receptors (the exposure or burial of receptors)

                        Tier 1

147. The Proposed offshore export cable corridor(s) together with the Array has the potential to produce cumulative effects that may indirectly impact marine archaeology receptors through sediment disturbance and deposition.

                        All phases

Magnitude of impact

148. The construction phase of the Array is due to occur simultaneously with the construction phase of the Proposed offshore export cable and therefore has the potential to increase sediment disturbance and deposition leading to a cumulative indirect impact on marine archaeology receptors. Construction activities may result in increased suspended sediment concentration, and therefore increased disturbance or deposition of sediment, however these activities would be of limited spatial extent and frequency and are unlikely to interact with sediment plumes from the Array.
149. The operation and maintenance phase of the Array is due to occur simultaneously with the operation and maintenance phase of the Proposed offshore export cable and therefore activities such as cable repair and reburial activities, any associated jack-up vessel and vessel anchoring have the potential to increase sediment disturbance and deposition leading to a cumulative indirect impact on marine archaeology receptors.
150. Measures adopted as part of the Array (section 19.10) include the implementation and adherence to the WSI and PAD, as described in section 19.10, so that any exposure of any as yet unknown marine archaeology receptors will be properly mitigated and reported. A separate, project-specific WSI and PAD would be produced and implemented for the Proposed offshore export cable. The burial of marine archaeology receptors could also occur and would have a beneficial impact as this would afford them more protection. Establishment of AEZs where appropriate and necessary, around new discoveries will protect the archaeological resource.
151. The cumulative effect is predicted to be of local spatial extent, short term duration, intermittent and low reversibility. It is predicted that the impact will affect the receptor indirectly and result in some measurable change in attributes, quality or vulnerability, minor loss of, or alteration to, one (maybe more) key characteristics, features or elements. The magnitude is therefore considered to be low.

Sensitivity of receptor

152. The sensitivities of marine archaeology receptors are as previously described above for the assessment of the Array alone (see section 19.11).
153. The receptors are deemed to be of high vulnerability, no recoverability and high value. The sensitivity of the receptor is therefore, considered to be high.

Significance of effect

154. Overall, the magnitude of the cumulative effect is deemed to be low and the sensitivity of the receptor is considered to be high. Based on professional judgement and implementation of designed in measures it is considered that the cumulative effect will, therefore, be of minor adverse significance, which not significant in EIA terms.

Further mitigation and residual effect

155. No further marine archaeology mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in section 19.10) is not significant in EIA terms.

Direct damage to marine archaeology receptors (e.g. wrecks, debris, submerged prehistoric receptors (palaeolandscapes and associated archaeological receptors))

                        Tier 1

156. The Proposed offshore export cable corridor(s) together with the Array has the potential to produce cumulative effects that may directly impact marine archaeology receptors through direct damage.

                        All phases

Magnitude of impact

157. The construction phase of the Array is due to overlap with the construction phase of the Proposed offshore export cable corridor(s) and therefore have the potential to result in direct damage to marine archaeology receptors. Construction activities likely to be required for the Proposed offshore export cable corridor(s) include seabed preparation activities such as sand wave and boulder clearance, and cable installation have the potential to damage known and as yet unknown archaeological assets.
158. The operation and maintenance phase of the Array is due to overlap with the operation and maintenance phase of the Proposed offshore export cable corridor(s). Activities such as cable repair and reburial activities, and any associated jack-up vessel and vessel anchoring have the potential to cause direct damage and lead to a cumulative direct impact on marine archaeology receptors.
159. The decommissioning phase of the Array is due to overlap with the decommissioning phase of the Proposed export cable corridor(s) and therefore activities associated with the removal of infrastructure have the potential to interact with the seabed and therefore cause a cumulative direct impact on marine archaeology receptors.
160. Pre-construction site investigation surveys will be reviewed by the Retained Marine Archaeologist to inform the refined layout of infrastructure around any newly identified archaeological constrains. Provision will also be made for the recording of any new discoveries via the WSI and PAD. Establishment of AEZs where appropriate and necessary, around new discoveries will protect the archaeological resource.
161. The cumulative impact is predicted to affect the receptor directly and result in very minor loss or detrimental alteration to one (maybe more) characteristics, composition, or attributes. It is predicted that the impact will affect the receptor indirectly. Through avoidance by the establishment of AEZs and TAEZs, the possibility of direct damage to known marine archaeology receptors is effectively removed. The establishment of the PAD provides the mechanism by which previously unknown archaeological receptors are recorded and protected. The magnitude is therefore, considered to be negligible.

Sensitivity of receptor

162. The sensitivities of marine archaeology receptors are as previously described above for the assessment of the Array alone (see section 19.11).
163. Overall, marine archaeology resource is deemed to be of high vulnerability, no recoverability, and high value. The sensitivity of the receptor is therefore, considered to be high.

Significance of effect

164. Overall, the magnitude of the cumulative effect is deemed to be low and the sensitivity of the receptor is considered to be high. Based on professional judgement and implementation of designed in measures, it is considered that the cumulative effect will, therefore, be of minor adverse significance, which not significant in EIA terms.

Further mitigation and residual effect

165. No further marine archaeology mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in section 19.10) is not significant in EIA terms.

Alteration of sediment transport regimes

                        Tier 1

166. The Proposed offshore export cable corridor(s) together with the Array has the potential to produce cumulative effects that may indirectly impact marine archaeology receptors through alteration of sediment transport regimes.

                        Operation and maintenance phase

Magnitude of impact

167. The operation and maintenance phase of the Array is due to occur during the operation and maintenance phase of the Proposed offshore export cable corridor(s). Presence of infrastructure on the seabed (e.g. cable protection) could influence sediment transport and therefore impact marine archaeology receptors. The burial of marine archaeology receptors would have a beneficial impact as this would afford them more protection. Volume 2, chapter 7 has assessed the magnitude of the Array alone to be low, anticipated to occur only during extreme storm conditions. Low sediment transport rates will ensure any disturbed native materials are redeposited locally after a short period of suspension, thus not impacting significantly on seabed morphology or the overall sediment transport regime. Although physical processes modelling has not been undertaken for the Proposed offshore export cable corridor(s), we can reasonably assume that there will be less infrastructure present on the seabed as a result of this development and therefore less potential for the alteration of sediment transport regimes. Should these two projects work in combination to increase the alterations to sediment transport regimes it is considered that this increase would be minor.
168. Measures adopted as part of the Array (as described in section 19.10) include the implementation and adherence to the WSI and PAD will ensure that any exposure of any as yet unknown marine archaeology receptors will be properly mitigated and reported. A separate, project-specific WSI and PAD would be produced and implemented for the Proposed offshore export cable corridor(s). The burial of marine archaeology receptors could also occur and would have a beneficial impact as this would afford them more protection. Where exposed, establishment of AEZs where appropriate and necessary, around new discoveries will protect the archaeological resource.
169. The cumulative effect is predicted is to be of local spatial extent, long term duration, intermittent and low reversibility. It is predicted that the impact will affect the receptor indirectly and result in very minor loss or detrimental alteration to one or more characteristics, composition, or attributes. The magnitude is therefore considered to be negligible.

Sensitivity of receptor

170. The sensitivities of marine archaeology receptors are as previously described above for the assessment of the Array alone (see section 19.11).
171. Overall, marine archaeology resource is deemed to be of high vulnerability, no recoverability, and high value. The sensitivity of the receptor is therefore, considered to be high.

Significance of effect

172. Overall, the magnitude of the cumulative effect is deemed to be negligible and the sensitivity of the receptor is considered to be high. Based on professional judgement and implementation of designed in measures, it is considered that the cumulative effect will, therefore, be of minor adverse significance, which not significant in EIA terms.

Further mitigation and residual effect

173. No further marine archaeology mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in section 19.10) is not significant in EIA terms.