Appendix 13 Marine Archaelogy– Baseline Environment
13.1 Desktop Study
- An initial desk-based review of literature and data sources to support this Offshore EIA Scoping Report has identified a number of baseline datasets. These are summarised at Apx. Table 13. 1 Open ▸ .
Apx. Table 13. 1: Summary of Key Desktop Reports
13.2 Site Specific Survey Data
- A geophysical survey was undertaken across the Offshore Wind Farm Proposed Development Array Area and part of the ECC. Magnetometer, Sidescan Sonar (SSS), Sub-Bottom profiler (SBP) and Multibeam Bathymetry (MBES) survey data were collected by Fugro between August and October 2019 (Fugro 2019, Fugro 2020a and 2020b), the primary purpose of which was to provide baseline information to inform the EIA (Figure 3.3). The data collected varied in specification however is considered comparable and appropriate to allow for the characterisation of the marine archaeological potential of the development sites.
- Line spacing within the two survey areas varied: within the Proposed Development Array Area the specification was set at 200 m for mainlines (running NNW/SSE) with crosslines (running WSW/ENE) at 1000 m; whilst within the proposed ECC mainlines were specified at 75 m with crosslines at 1000 m.
- The data was collected to a specification appropriate to achieve the following interpretation requirements:
- magnetometer: identification of contacts > 5 nT;
- SSS: ensonfication of contacts > 0.3 m;
- SBP: penetration > 10 m; and
MBES: ensonification of contacts < 1.0m.
- Following data delivery, an initial review of the dataset was undertaken to gain an understanding of the geological and topographic make-up of the survey area. Within the survey area, the potential for variations in the seabed are high and can affect the interpretation of contacts. However, the towed sensors, SSS and magnetometer, used an Ultra Short Baseline (USBL) positioning system to ensure positional accuracy of the sensors throughout the survey. Positional accuracy is further increased through the correlation of SSS and Magnetometer datasets with the MBES dataset.
- SSS is considered the best tool for the identification of anthropogenic contacts on the seabed through its ability to ensonify small features and so forms the basis of any archaeological data assessment.
- Magnetometer data indicate the presence of ferrous and thus usually anthropogenic material both on, and under the seabed, and where line spacing allows. The survey line spacing for the Proposed Development offshore wind farms geophysical surveys ranges between 75 m and 200 m which is too great for the accurate positioning of magnetic anomalies, but can indicate areas of archaeological potential. A magnetic anomaly position can only be determined from directly below the sensor, or where lines are run close together to position an anomaly seen on two, or more lines. Where possible, significant magnetic anomalies were correlated with contacts visible on the seabed.
- Whilst SBP and MBES are useful tools for archaeological assessment, their primary use, outside of seabed and palaeo-landscape characterisation, is in the corroboration of contacts identified in the SSS and magnetometer data. As such, all contacts of potential anthropogenic origin were assessed for archaeological potential, primarily alongside the magnetometer data, with SBP and MBES data used to corroborate identified contacts.
- The archaeological potential was assigned to each contact based on the criteria outlined in Apx. Table 13. 2 Open ▸ . Where uncertainty existed as to the identification or archaeological potential of a contact the provided dataset was imported into point cloud visualisation software such as Cloud Compare in order to view the un-gridded data.
Apx. Table 13. 2: Criteria for Assigning Archaeological Potential
- Contacts assessed as having low, medium and high archaeological potential were then compiled into a gazetteer and a shapefile created for further assessment alongside known features such as wrecks, mooring buoys, third party assets such as cables and pipelines, and other seabed structures. The data was subsequently assessed against known anomalies of no archaeological interest to remove contacts of no archaeological importance.
- As well as identifying surface contacts of potential archaeological interest the geophysical and hydrographic survey data was reviewed to assess the potential survival of palaeo-landscapes within the limits of the Proposed Development.
- Sub-surface data acquired from SBP and seismic surveys is key to understanding the palaeo-landscape potential of the study area. Sedimentary horizon grids and geological maps derived from the interpretation of sub-surface data and the current seabed derived from MBES data were assessed. Sedimentary deposits were correlated with geological formations, and the depositional context and make-up of the deposits presented. The results inform the characterisation of the palaeo-environmental and archaeological potential included in this report.
- The MASA was submerged during the late glacial/early Holocene and prior to this it was covered in a succession of ice sheets. During periods of glaciation the MASA would have been uninhabitable but during inter-glacial periods there is a potential for periglacial occupation at times when the seabed would have formed dry land. The zones of highest potential for the survival of archaeological material are likely to be those on the edges of channels and floodplains, where old ground surfaces and organic remains are most likely to survive. These deposits often lie beneath relatively thin layers of seafloor sediment and may be vulnerable to exposure.
- However, based on the available evidence whilst potential palaeo-landscape features have been recorded within the limits of the Proposed Development including kettle holes, palaeo-channels, incised valleys and relict glacial lakes, the proglacial environments in which they are likely to have been formed are not likely to have been attractive locations for human habitation. In other areas such features would have formed foci for human activity following climatic amelioration, however, sea level rises are likely to have submerged these features within the site relatively rapidly further demonstrating the limited archaeological potential of the area.
- Consequently, it is considered unlikely that evidence of in situ Palaeolithic and Mesolithic activity will be found within the limits of the Offshore Wind Farm Proposed Development Array Area due to the effects of repeated glaciations, marine transgressions and associated fluvial activity. There is however some paleoenvironmental potential within the Aberdeen Ground Formation. Within the ECC there is some potential for late Palaeolithic/Mesolithic deposits in the near shore area although due to the effects of erosion redeposited material is more likely than in situ evidence. In addition, the localised presence of peat buried in the Quaternary deposits within the ECC could suggest a good palaeo-environmental potential and where these sediments are present there is a good potential for organic preservation of remains such as fish traps, associated with prehistoric exploitation of the coastal margins. The future archaeological assessment of the results of pre-construction geotechnical investigations within the limits of the offshore development will provide further information on the presence or absence of peat and the palaeo-environmental and archaeological potential of this area.
- A summary of the known archaeological features is provided below:
- there are no protected areas or statutory designations in relation to submerged landscapes within the limits of the Proposed Development;
- there is one designated wreck within the limits of the Proposed Development (U 12 SSS_2020_0165 – a designated war grave, Apx. Figure 13. 1 Open ▸ ) which falls within the protection of the Protection of Military Remains Act.
- A total of 20 wrecks have been recorded by the project specific geophysical survey within the limits of the Offshore Wind Farm Proposed Development Array Area, 4 of which are known; Oswin, Kitty, Burnstone and U12 (discussed above). Of the remaining 16 wrecks, 14 are also recorded as UKHO data. The remaining 2 wrecks may represent one of the 16 wrecks recorded on the NRHE as potentially lying within the Proposed Development Array Area (although none of their positions have been verified). In addition 10 wrecks included within the UKHO data were not identified during the survey and their positions have been recorded as ‘Dead (Apx. Figure 13. 1 Open ▸ ).
- No wrecks were recorded within the limits of the ECC during the project specific geophysical survey (although the survey did not cover the full extent of the ECC). There are eight wrecks and obstructions recorded on the UKHO that lie beyond the extent of the survey and so their locations must still be assumed at this stage (UKHO 2873, UKHO 2875 Sharon Vale, UKHO 2884, UKHO 2890, UKHO 2892, UKHO2904 Cradock, UKHO 3101 Obstruction, UKHO 63948) (Apx. Figure 13. 1 Open ▸ ).
• In addition 43 unconfirmed anomalies of medium archaeological potential and 119 large magnetic anomalies of archaeological potential were recorded within the limits of the proposed development. Some of these anomalies may be associated with wrecks recorded on the UKHO or NRHE that have no known position or they could represent anomalies of as yet unknown archaeological interest (Apx. Figure 13. 1
- There is also an absence of charted wrecks pre-dating the 19th century within the limits of the offshore Proposed Development. The known shipwrecks are predominantly iron and steel vessels dating from the 19th and 20th centuries. The preponderance of iron and steel wrecks in the record could potentially mask the presence of earlier shipwrecks, which are of potentially greater archaeological interest. Compared to iron and steel wrecks, wooden shipwrecks tend to be older, smaller and to have carried less ferrous material. They also tend to break up more quickly than iron and steel wrecks and are thus more likely to be scattered, dispersed and have a generally lower physical profile on the seabed. Consequently, they are less likely to be located by geophysical survey
- These earlier wrecks are potentially the most archaeologically important and there will be an on-going recognition of the potential to encounter currently unknown or unrecorded shipwrecks, and mechanisms put in place to ensure the prompt reporting and avoidance of undue damage to any such discoveries.
- There is therefore a generally moderate to good potential for unexpected remains to be discovered within the limits of the Proposed Development.
Apx. Figure 13. 1: The Position of UKHO and NRHE Records with the Proposed Development