19.10. Measures Adopted as Part of the Array

78. As part of the Array design process, a number of designed in measures have been proposed to reduce the potential for impacts on marine archaeology (see Table 19.14   Open ▸ ). They are considered inherently part of the design of the Array and, as there is a commitment to implementing these measures, these have been considered in the assessment presented in section 19.11 (i.e. the determination of magnitude and therefore significance assumes implementation of these measures). These designed in measures are considered standard industry practice for this type of development.

Table 19.14: Designed In Measures Adopted as Part of the Array

19.10.1. Archaeological Exclusion Zones

79. Best practice favours the preservation in situ of archaeological remains, therefore the ideal preferred mitigation for archaeological remains is avoidance. For the Array, AEZs have been proposed that prohibit development related activities within their extents, which vary depending upon the nature of the site. The final Array layout will take into account these preliminary zones, which may evolve or be removed as the Array progresses, subject to layout designs and additional subsequent surveys that may be required.
80. All AEZs proposed in the outline WSI, will be marked on the Development Specification and Layout Plan (DSLP). If impacts cannot be avoided, measures to reduce, remedy or offset disturbance will be identified where appropriate.
81. In view of the potential archaeological significance of anomalies within the Array, AEZs (either in the form of individual AEZs or clusters) will be placed around the two anomalies classified as being of high archaeological potential that are located within the Array and the 14 anomalies classed as being of medium potential. The third high potential anomaly that was identified in the geophysical survey data has not been assigned an AEZ as it is located more than 100 m from the Array boundary and therefore there is no pathway for direct impact to this receptor. These anomalies have been recommended AEZs based on the size of the anomaly, the extents of any debris, the potential heritage value of the anomaly, the potential impact of the development, and the seabed dynamics within the area.
82. Dependent of the form of the anomaly, AEZs have either been recommended as a ‘radius’ from the centre point of the anomaly or as a distance from the extents. Particularly in the case of shipwrecks, which tend to be longer in length than width, the use of a circle provides unequal protection around the extents. This not only impacts the protection afforded but does not present proportional mitigation, therefore distance from extents is used for proposed AEZs.
83. The proposed AEZs are listed in Table 19.15   Open ▸ and shown in Figure 19.4   Open ▸ . Scope is allowed for their amendment in light of further evidence and with the involvement of consultees. Further details of AEZs and archaeological monitoring is provided in the outline WSI and PAD (volume 3, appendix 19.2). AEZs can be different sizes depending on the size of the archaeological anomaly and the extent to which there is associated debris present on the seabed.
84. The anomalies identified as requiring AEZs have been reviewed against desk based and site-specific data, and as a result of this review, AEZs have been identified of varying sizes according to the size and spread of the individual archaeological receptor. AEZs are presented as either extents or radius; extents indicates the distance proposed from the furthest extents of the archaeological anomaly whilst a radius AEZ is one that is measured as a circumference from the central point of the anomaly.

Table 19.15: Proposed Archaeological Exclusion Zones Within the Array

85. Additionally, TAEZs may be assigned during the construction, operation and maintenance, and decommissioning phases of the Array as anomalies that have been identified in the data do not necessarily represent all of the marine archaeological material that is on the seabed. For example, wooden wrecks can be buried under the seabed and may not appear in the geophysical data. Other previously unknown marine archaeology receptors may be discovered while carrying out construction, operation and maintenance, and decommissioning activities. As set out in The Crown Estate (The Crown Estate, 2021) guidance, AEZs may be altered (enlarged, reduced, moved, or removed) as a result of further data assessment or archaeological field evaluation covering those areas that are subject to AEZs. If new finds of potential archaeological significance come to light during the assessment of marine geophysical data or works associated with the Array during the course of construction, operation, or decommissioning phases, as reported through the PAD, they may be subject to the implementation of a TAEZ. There is no functional difference between an AEZ or TAEZ in any practical sense. A TAEZ will prevent impact to the seabed within their extents but allow activities in other areas to continue. The need for a TAEZ, its position and extent, the implementation of any new AEZs (or the conversion of a TAEZ to a permanent AEZ) or any alterations to existing AEZs will be subject to discussions between the Retained Archaeologist and the Applicant. In consultation with MD-LOT and HES, these will be confirmed with a formal response. Following alteration, a new plan giving details of the AEZs will be drawn up and issued to each relevant party.

Figure 19.4: Archaeological Exclusion Zones in the Marine Archaeology Study Area

19.10.2. Preservation by Record

86. Where preservation in situ is not practicable, disturbance of archaeological sites or material will be mitigated by appropriate and satisfactory measures, also known as ‘preservation by record’. In these circumstances, the effects of the Array will be mitigated by carrying out excavation and recording prior to the impact occurring (COWRIE, 2010).
87. It is possible that previously unknown wrecks, archaeological sites or material may only be encountered during the course of the construction, operation and maintenance and/or decommissioning of the Array. Procedures will therefore be put in place to allow for such eventualities.
88. The Offshore Renewables Protocol for Archaeological Discoveries (The Crown Estate, 2014) has been followed in the production of the PAD specific to the Array (volume 3, appendix 19.2, annex A). This PAD will involve the reporting of archaeological discoveries made during the lifetime of the Array. This protocol covers the reporting and investigating of unexpected archaeological discoveries encountered during construction, operation and maintenance and decommissioning activities, informed by the guidance of a marine archaeologist specialised in working with PADs for offshore wind farm projects. This protocol further makes provision for the implementation of TAEZs around areas of possible archaeological interest, for prompt archaeological advice and, if necessary, for archaeological inspection of important features prior to further construction, operation and maintenance or decommissioning activities in the vicinity. It complies with the Merchant Shipping Act 1995, including notification to the Receiver of Wreck, in accordance with the Code of Practice for Seabed Developers (JNAPC, 2006).
89. As there is potential for the presence of previously unidentified archaeological assets, archaeological monitoring is deemed as appropriate where seabed material is brought to the surface. These proposals may be refined on the basis of the results of any further marine geophysical, geotechnical or ROV surveys.

19.11. Assessment of Significance

90. Table 19.10   Open ▸ summarises the potential impacts arising from the construction, operation and maintenance and decommissioning phases of the Array, as well as the MDS against which each impact has been assessed. An assessment of the likely significance of the effects of the Array on the marine archaeology receptors caused by each identified impact is given below.

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

91. The seabed activities associated with the construction, operation and maintenance, and decommissioning phases of the Array may lead to sediment disturbance and deposition leading to indirect impacts on marine archaeology receptors identified in section 19.7.3. The MDS is for site preparation activities such as sand wave clearance, mooring and anchoring systems, and cable installation. These activities are presented in Table 19.10   Open ▸ .
92. The disturbance of sediment/seabed deposits can result in the exposure of known marine archaeology receptors (i.e. wreck sites) and the exposure of as yet unknown wreck sites and associated materials. Such activities can also result in the burial of known receptors.

                        All phases

                        Magnitude of impact

93. The site-preparation activities and installation of infrastructure within the Array may lead to increased suspended sediment concentrations (SSCs) and associated deposition. Although the impact is proposed to be scoped out for physical processes due to effects arising from the Array being so slight as to be considered insignificant (see volume 2, chapter 7). However, marine archaeology receptors are of high sensitivity and suspended sediment will still occur and can still cause indirect damage to marine archaeology receptors. The MDS for sand wave clearance is a total clearance volume of 7,104,614.74 m3.
94. The MDS is for the drilled installation of 265 semi-submersible wind turbine foundations each with driven pile anchor systems shared between wind turbines; up to 10% of piles require drilling with total drill arisings volume of 131,122.22 m3. For the installation of OSPs, drill arisings volume totals 43,260 m3. The MDS for drilled installation of piles is a total volume of 181,592.22 m3.
95. For the installation of inter-array cables (1,222.4 km) and interconnector cables (236 km), the MDS for sediment clearance volume from trenching is 8,750,400 m3.
96. The MDS for the operation and maintenance phase is for reburial up to 61.12 km of inter-array and 11.8 km of interconnector cable annually. The mooring lines have the potential for movement along the seabed with a total of 795,600 m of mooring line with the potential to be in contact with the seabed for the whole of the Array or 830,700 m of mooring line during a one in 50 year AEP storm, for the whole of the Array.
97. Total removal of all infrastructure has been assumed during the decommissioning phase.
98. The implementation and adherence to the WSI and PAD as a mitigation measure, described in section 19.10, will require that any exposure of any as yet unknown marine archaeology receptors will be properly reported and impact mitigated through the establishment of a TAEZ. The burial of marine archaeology receptors could also occur and would have a beneficial impact as this would afford them more protection. Provision will also be made for the recording of any new discoveries through the PAD. These measures will ensure preservation by record and reduce the magnitude of the impact on as yet unknown marine archaeology receptors to low.
99. Sediment disturbance and deposition leading to indirect impacts on marine archaeology receptors as discussed in section 19.8.1 during the construction, operation and maintenance, and decommissioning of the Array would result in some measurable change in attributes, quality or vulnerability, minor loss of, or alteration to, one (maybe more) key characteristics, features or elements. It is predicted that the impact will affect marine archaeology indirectly. The magnitude of impact is therefore considered to be low.

                        Sensitivity of the receptor

100. The marine archaeology baseline presented in section 19.7 above indicates that this sub-region of the North Sea has historically been an area with a moderate intensity of maritime activity. The number of known shipwrecks, seabed anomalies in the geophysical data with medium potential, and recorded losses associated with the area indicate some potential for more discoveries to arise. However, the potential and as yet unknown marine archaeology receptors identified in section 19.7.3 are vulnerable sites that can be exposed further by disturbance activities. There is a low potential to encounter human-occupied palaeolandscapes within the marine archaeology study area. There does, however, remain the potential of submerged formerly terrestrial landforms which could provide crucial insights into the timing of glacial retreat and marine transgression in this area of the North Sea. Palaeoenvironmental evidence is so rare that any discoveries are considered important.
101. The marine archaeology study area retains several anomalies of archaeological potential and some identified wrecks, some of which were previously unknown before the site-specific surveys were undertaken. This indicates that there is potential for more discoveries to arise with the site preparation and construction works proposed. Shipwrecks are regarded as being important as they add to our understanding of ship construction, maritime routes, and movements of their period. Shipwrecks are also vulnerable sites that can be exposed by disturbance activities.
102. As there is potential for the discovery of currently unknown archaeological receptors, a precautionary approach is applied here. All marine archaeology receptors are therefore deemed to be of high vulnerability, no recoverability and high value. The sensitivity of the receptor is therefore, considered to be high.

                        Significance of the effect

103. Overall, the magnitude of the impact 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 effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

                        Secondary mitigation and residual effect

104. No marine archaeology mitigation is considered necessary because the likely effect in the absence of mitigation is not significant in EIA terms.

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

105. Direct damage to marine archaeology receptors may arise through the construction, operation and maintenance and decommissioning phases of the Array. Activities that have the potential to directly impact archaeological material include the installation of the mooring and anchoring systems, OSP foundations, inter-array cables, interconnector cables and any installation and maintenance vessel anchoring and jack-up activities associated with these. The MDS for direct damage to marine archaeology receptors is presented in Table 19.10   Open ▸ .

                        All phases

                        Magnitude of impact

106. The MDS for the construction phase comprises site preparation activities; installation of up to 265 semi-submersible wind turbines with associated mooring and anchoring systems and six OSPs, with associated scour protection; the installation of inter-array, interconnector and associated cable protection; and any associated jack-up vessel and vessel anchoring activities with a total of 45,016,619.62 m2 of seabed disturbance.
107. For the purposes of this assessment, the impacts of operation and maintenance and decommissioning activities are predicted to be no greater than those for construction As the construction phase represents the maximum design scenario, any assessment of effect for the operation and maintenance and decommissioning phases would be lesser than or equal to the effects arising from the construction phase, as such these phases are presented together.
108. The activities described above have the potential to directly and permanently impact upon marine archaeology receptors and areas of archaeological potential that lie concealed within seabed sediments. These activities also have the potential to expose previously unrecorded marine archaeology receptors.
109. As described in section 19.10, measures adopted as part of the Array account for preservation, by record, of submerged prehistoric archaeology through data acquired from geotechnical surveys. The results of these surveys will be reviewed by the Retained Marine Archaeologist and the findings will be communicated to HES. The implementation and adherence to the PAD for any prehistoric discoveries, requires preservation by record, reducing the magnitude of the impact on submerged prehistoric archaeology to low.
110. AEZs will be established around each archaeological anomaly identified to be of high or medium potential and within which no activities will take place unless agreed by HES. This will reduce the magnitude of the impact on known marine archaeology receptors to ‘no change’.
111. 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 constraints. Provision will also be made for the recording of any new discoveries via the PAD. These measures will preserve by record and reduce the magnitude of the impact on as yet unknown marine archaeology receptors to low.
112. In summary, direct damage to marine archaeology receptors would result in the loss of the resource and/or severe damage to key characteristics, features or elements. It is predicted that the impact will affect the receptor directly. Due to the AEZs that will be implemented through the measures adopted as part of the Array (section 19.10), the pathway for direct impact to known archaeological receptors is removed and the establishment of the PAD will provide the necessary measures for the reporting and protection of any as yet unknown archaeological material (including submerged prehistoric archaeology) that may be encountered during the construction, operation and maintenance and decommissioning of the Array. The magnitude is therefore considered to be negligible for known marine archaeology receptors, and low for previously unknown marine archaeology receptors.

                        Sensitivity of the receptor

113. The marine archaeology study area retains several anomalies of archaeological potential and some identified wrecks, some of which were previously unknown before the site-specific surveys were undertaken. This indicates that there is potential for more discoveries to arise with the site preparation and construction works proposed. Shipwrecks are regarded as being important as they add to our understanding of ship construction, maritime routes, and movements of their period.
114. There is very low potential for submerged prehistoric archaeological material to survive in relation to palaeolandscapes within the marine archaeology study area. However, if any discoveries were made they are so rare and have the potential to enhance the understanding of the prehistory of the North Sea. All marine archaeology receptors are therefore deemed to be of high vulnerability, no recoverability and high value. The sensitivity of the receptor is therefore considered to be high.

                        Significance of the effect

115. Overall, the magnitude of the impact is deemed to be negligible for known marine archaeology receptors, and low for previously unknown marine archaeology receptors (including submerged prehistoric archaeology), 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 effect will, therefore, be of minor adverse significance for both known and previously unknown marine archaeology receptors, which is not significant in EIA terms.

                        Secondary mitigation and residual effect

116. No marine archaeology mitigation is considered necessary because the likely effect in the absence of mitigation is not significant in EIA terms.

Direct damage to deeply buried marine archaeology receptors – submerged prehistoric receptors (e.g. palaeolandscapes and associated archaeological receptors)

117. The seabed activities associated with the construction phase of the Array have the potential to directly damage palaeolandscapes and associated archaeological material deeply buried within the marine archaeology study area. This impact would only occur during the construction phase of the project, as it is assumed that there is unlikely to be an impact to deeply buried receptors during the operational phase. The direct damage to deeply buried submerged prehistoric receptors is an unavoidable impact that occurs in the construction phase (but is mitigated through the preservation by record of the archaeological resource (see section 19.10.2)). Therefore, direct damage is scoped out for the decommissioning phase.

                        Construction phase

                        Magnitude of impact

118. The MDS for the construction phase comprises seabed installation of up to 265 wind turbines with an anchoring system comprising six driven piles per wind turbine that have a seabed penetration depth of up to 40 m. Three large OSPs and twelve small OSPs are also to be constructed on jacket foundations with 12 legs per large foundation, 6 legs per small foundation, to a penetration depth of up to 70 m. These activities have the potential to directly and permanently impact palaeolandscapes locations that might lie deeply buried below the covering seabed sediment.
119. The measures adopted as part of the Array, as described in section 19.10, account for preservation by record of submerged prehistoric archaeology through data acquired from geotechnical surveys. The results of these surveys will be reviewed by the Retained Archaeologist and the findings communicated to HES. Implementation and adherence to the PAD will require preservation by record of any prehistoric or palaeoenvironmental discoveries, reducing the magnitude of the impact on submerged prehistoric archaeology to low.
120. Direct damage to deeply buried marine archaeology receptors would result in some measurable change in attributes, quality or vulnerability, minor loss of, or alteration to, one (maybe more) key characteristics, features or elements. It is predicted this would impact the receptors directly. Due to measures which include preservation by record the magnitude is therefore considered to be low.

                        Sensitivity of the receptor

121. There is very limited potential for submerged prehistoric archaeological material in relation to palaeolandscapes to survive within the marine archaeology study area. However, if any discoveries were made, they are so rare and have the potential to enhance the understanding of the prehistory of the North Sea they would be considered valuable. All marine archaeology receptors are therefore deemed to be of high vulnerability, no recoverability and high value. The sensitivity of the receptor is therefore, considered to be high.

                        Significance of the effect

122. Overall, the magnitude of the impact 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 effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

                        Secondary mitigation and residual effect

123. No marine archaeology mitigation is considered necessary because the likely effect in the absence of mitigation is not significant in EIA terms.

Alteration of sediment transport regimes

                        Operation and maintenance phase

124. The presence of infrastructure on the seabed during the operation and maintenance phase of the Array has the potential to alter sediment transport regimes. As a result changes in sediment may indirectly impact archaeological material present in the marine archaeology study area through burial or exposure.

                        Magnitude of impact

125. The physical processes baseline environment presented in volume 2, chapter 7 of this EIA Report illustrated that due to the smaller-scale footprint of the anchoring structures when compared to fixed-foundation designs, there will only be minimal disruption to sediment transport and sediment transport pathways. OSP jackets are fixed-foundation and by being installed in the water column have the potential to alter sediment transport regimes.
126. Any alteration of sediment transport pathways could impact upon marine archaeology receptors. The implementation and adherence to the WSI and PAD as described in section 19.10, will require that the exposure of any as yet unknown marine archaeology receptors will be properly mitigated and reported. The burial of marine archaeology receptors would have a beneficial impact as this would afford them more protection.
127. AEZs will be established around each archaeological anomaly identified to be of high or medium potential and within which no activities will take place unless agreed by HES.
128. 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 constraints. Provision will also be made for the recording of any new discoveries via the PAD.
129. Alteration of sediment transport regimes would result in some measurable change in attributes, quality or vulnerability, minor loss of, or alteration to, one (maybe more) key characteristics, features or elements. It is predicted this would impact the receptors indirectly. Due to measures which include the establishment of the PAD will provide the necessary measures for the reporting and protection of any as yet unknown archaeological material that may be encountered in the course of the Array the magnitude is considered to be negligible.

                        Sensitivity of the receptor

130. The marine archaeology study area lies in a wider area that retains a number of shipwrecks and the potential for more to be discovered. Shipwrecks are vulnerable sites that can be exposed or buried by significant alteration of the sediment transport regimes.
131. While the potential for palaeolandscapes and associated submerged prehistoric archaeology is extremely low, if and where they do exist, the activities associated with the Array have the potential to directly impact marine archaeology receptors and any material of this nature is so rare that any discoveries would be considered important.
132. Although the potential to discover currently unknown receptors is low, a precautionary approach is applied here. All marine archaeology receptors are therefore 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

133. Overall, the magnitude of the impact 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 effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

                        Secondary mitigation and residual effect

134. No marine archaeology mitigation is considered necessary because the likely effect in the absence of mitigation is not significant in EIA terms.