19. Archaeology - ABP Southampton O… · · 2012-10-3119. Archaeology Executive Summary: Chapter...

Environmental Statement for Port of Southampton: Southampton Approach Channel Dredge

Updated by Further Information

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19. Archaeology

Executive Summary: Chapter 19. Archaeology Wessex Archaeology was commissioned by Associated British Ports (ABP) Southampton to undertake an archaeological assessment in advance of the widening and deepening of the existing approach channel that runs from the Port of Southampton out to the eastern side of the Isle of Wight by Nab Tower. This chapter follows best-practice in carrying out archaeological desk-based assessments and was undertaken in accordance with the Marine Works (EIA) Regulations 2007. In summary, the Southampton Water and Solent area is likely to have been subject to anthropogenic influences from the time of the earliest human occupation of Britain (c.700,000 BP) and, therefore, the area exhibits a high level of archaeological potential. This not only includes prehistoric archaeology but also more recent shipping and aircraft wrecks, both charted and uncharted. In addition, given the impact of successive rise and fall in sea level since the time of the earliest human occupation of Britain, it is likely that much evidence is now submerged. A study area was established, in respect of which baseline information has been collated. The study area followed the course of the existing dredged approaches to the Port of Southampton and runs from the northern end of Southampton Water and terminates close to the Nab Tower, off the east coast of the Isle of Wight. The study area is larger than the actual areas to be dredged and therefore includes: Areas that will not be affected by the current dredge proposal, for example, because the

existing seabed is sufficiently low to avoid the need to dredge altogether; Areas that will be subject to dredging activities but which have been dredged already under

recent capital and maintenance dredging campaigns, since the 1960s. It is considered that these areas exhibit very limited archaeological potential.

Areas that will be subject to dredging activities and which have not previously been dredged, for example, the areas of the main channel widening between Dock Head and Fawley. It is considered that these areas exhibit the highest level of archaeological potential.

The study area has been subjected to a desk-based assessment for known and potential maritime archaeology and known and charted maritime losses, using information supplied by the UK Hydrographic Office, the National Monuments Record and county and local Historic Environment Records. The study area was subsequently split into 8 separate sub-areas, each of which was surveyed using sidescan sonar, boomer and magnetometer techniques. In order to identify the areas with the highest prehistoric archaeological potential, sub-bottom and bathymetric surveys were conducted within the footprint of the proposed dredge. Borehole and vibrocores logs taken from in and around the proposed dredge areas were also assessed for archaeological potential. The results of these assessments concluded that there are 227 anomalies to be found across the 8 survey sub-areas, of which 125 were assessed of being of archaeological potential. Of those 125 exhibiting archaeological potential, 37 occur outside the area of the current proposed dredge.



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Of the remaining 88 anomalies, 51 occur in areas that have been dredged already under recent capital and maintenance dredging campaigns since the 1960s. It is considered that these anomalies are most likely to be of recent origin and, therefore, exhibit very limited archaeological potential. Finally, there are a residual 37 anomalies that occur within areas that will be subject to dredging activities and which have not previously been dredged. These exhibit the highest level of archaeological potential and, given the extent of the assessment undertaken to date, it is not possible to determine their significance. The majority of these anomalies occur in the areas of channel widening, primarily between Dock Head and Fawley. 1) Potential direct impact Due to dredging activity The impact of the proposed dredge in areas that have previously been subject to capital and maintenance dredging activities is considered to be minor adverse significant, as the 51 recorded anomalies are likely to be of recent origin. The impact of the proposed dredge on maritime archaeology in areas that have not been subject to previous dredging activities is considered to be high. With the implementation of suitable mitigation measures, however, the overall impact of the scheme on these anomalies is likely to be low. The impact of the proposed dredge on prehistoric sediments and any archaeological materials they contain is considered to be high. With the implementation of proposed mitigation measures, the overall impact of the proposed dredge is likely to be low. 2) Potential indirect impacts from changes to sedimentation regime following dredge The physical processes assessment identified changes to sedimentation patterns following the proposed dredge to be small outside the immediate dredge areas and unlikely to be detectable from background variation. The indirect impact of changes to sedimentation regime on archaeological features is considered insignificant. Mitigation In order to mitigate the impact of the dredge, it is proposed to carry out: A further (Stage 3) archaeological assessment of five vibrocore samples displaying

archaeological potential; An archaeological assessment of a number of bulk sediment samples from locations and

depths identified by the project archaeologist; A limited programme of diver ground-truthing of a sample of anomalies, with any significant

results being reported to English Heritage; and The implementation of a Finds Reporting Protocol during dredging operations to ensure that

any finds of significance are reported to the project archaeologist by the dredging team. It is further proposed that these mitigation measures and additional investigations be detailed in a Written Scheme of Investigation (WSI) that is drawn up prior to dredging and which will be subject to the approval of local and national curatorial bodies. The WSI will set out the respective responsibilities of the developer, ABP, dredging contractors and archaeological contractors/consultants, including formal lines of communication between the parties and archaeological curators.



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Conclusion The proposed mitigation measures aim to offset the impact to archaeological features and to further investigate the areas of highest likely archaeological potential. Thus, the overall impact of the Southampton Approach Channel Dredge upon archaeological remains, after mitigation, is assessed as low.

Introduction

19.1 The known and potential archaeological resource within the overall footprint of the proposed Southampton Approach Channel Dredge was established by means of a desk-based assessment (Wessex Archaeology 2008). This included accessing data held by the UK Hydrographic Office (UKHO), the National Monuments Record (NMR), the Sites and Monument/Historic Environment Records held by the Isle of Wight, Southampton and Hampshire Councils and published sources.

19.2 The desk-based work was supplemented with a targeted geophysical survey and the

archaeological assessment of geotechnical core data. The geophysical survey work concentrated upon the areas of new dredge being proposed for the scheme (Western Docks, Fawley, ExxonMobil, Hook and parts of Thorn) and on those areas of the existing dredged channel that will also be impacted by the proposed scheme. The geotechnical analysis comprised the assessment of borehole and vibrocores logs, and sediment samples that have been taken from in and around to the proposed dredge areas.

Legislation and Planning Guidance

19.3 The legislation and planning guidance relevant to the scheme are as follows: 19.4 Under the Protection of Wrecks Act (1973), wrecks and wreckage of historical,

archaeological or artistic importance can be protected by way of designation. It is an offence to carry out certain activities in a defined area surrounding a wreck that has been designated, unless a licence for those activities has been obtained. There are currently no sites designated under this legislation within the study area.

19.5 Within the context of the Merchant Shipping Act (1995), ‘wreck’ refers to flotsam, jetsam,

derelict and lagan found in or on the shores of the sea or any tidal water. It includes a ship, aircraft or hovercraft, parts of these, their cargo or equipment. It may be of antique or archaeological value such as gold coins, or a yacht or dinghy abandoned at sea or items such as drums of chemicals or crates of foodstuffs. The ownership of ‘wreck’ is decided according to procedures set out in the 1995 Act. If any such finds are brought ashore the salvor is required to give notice to the Receiver of Wreck that he/she has found or taken possession of them and, as directed by the Receiver, either hold them pending the Receiver's order or deliver them to the Receiver.

19.6 Under the Protection of Military Remains Act (1986), all aircraft that have crashed in military

service are protected and the Ministry of Defence (MoD) has powers to protect ships that were



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in military service when they were wrecked. The MoD can designate named vessels as ‘Protected Places’, even if the position of the wreck is not known. In addition, the MoD can designate ‘Controlled Sites’ around wrecks whose position is known. In the case of ‘Protected Places’, the vessel must have been lost after 4 August 1914, whereas in the case of a wreck protected as a ‘Controlled Site’ no more than 200 years must have elapsed since the loss. There is one known, charted aircraft wreck and eight recorded aircraft losses within the study area all of which are protected under this Act.

19.7 Planning Policy Guidance: Coastal Planning (PPG 20) notes that ‘the coastal zone has a

rich heritage both above and below low water mark, which includes buildings and areas of architectural or historic interest, industrial archaeology, scheduled and other ancient monuments and other archaeological sites’ (Para. 2.8). PPG 20 also makes specific references to sites of archaeological and built heritage interest in the information required by local planning authorities in addressing coastal planning (Para. 4.6).

19.8 England’s Coastal Heritage: a statement on the management of coastal archaeology was

published in 1996 by English Heritage and the Royal Commission on the Historical Monuments of England (RCHME) and sets out principles for managing coastal archaeology. The Solent and Southampton Water are identified in the document as ‘Areas of Recognised High Archaeological Potential’.

19.9 The JNAPC Code of Practice for Seabed Developers (2006) is a UK-wide voluntary which

provides a framework for seabed developers similar to the principles found in current policy and practice on land. The aim of the Code is to ensure a best practice model for seabed development. The Code offers guidance to developers on issues such as risk management and legislative implications.

Study Area

19.10 The archaeological impact from the proposed scheme will come from the widening and/or

deepening of the existing dredged approach channel. In order to assess the archaeological potential of the development area in relation to maritime archaeological remains, a study area was established for the collation of information.

19.11 The study area follows the course of the existing dredged channel and runs from the northern

end of Southampton Water into the Solent and along its eastern arm, where it terminates off the east coast of the Isle of Wight, close to the Nab Tower (Figures 19.1-19.4). The study area therefore comprises not only the areas to be directly affected by the proposed scheme but also areas where no dredging operations will take place.

19.12 The main channel approaches to Southampton have been successively dredged for over two

centuries in order to improve access to the Port. More recent dredging activities have included deepening in the area of the Thorn Channel to 12.6m below Chart Datum (CD), carried out in the 1960s, deepening in the vicinity of the container terminal carried out between 1973 and 1978, and a major dredge of the approach channel between Fawley and the container terminal carried out between 1996 and 1997 (see Chapter 8). This latter dredge deepened the approach channel from 10.2m below CD to 12.6m below CD. These relatively recent dredging campaigns



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extend into geological material and would have removed most of the sediment of archaeological interest along the current dredged approaches to Southampton.

19.13 For this reason, this archaeological assessment focuses primarily on locations within the study

area, which were not dredged in previous campaigns. 19.14 Whilst this archaeological assessment also identifies locations of potential archaeological

interest outside the direct impact area of the current proposed dredge, these are considered to be of secondary importance in the context of the proposed dredge, on the basis that they will remain unaffected by the proposal.

Methodology

19.15 The methodology adopted for the preparation of this document reflects best practice in carrying

out archaeological desk-based assessments, as codified by the Institute of Field Archaeologists’ Standards and Guidance for Archaeological Desk-based Assessment (IFA 1999).

19.16 The known and potential archaeology within the area affected by the proposed development

was determined through a search of the local and national databases. The principal sources consulted in this assessment are as follows:

Records of wrecks and obstructions collated by the UK Hydrographic Office (UKHO); Records held in the maritime section of the National Monuments Record (NMR); Records of known maritime archaeological sites held by the Isle of Wight Sites and

Monuments Record (IOWSMR); Records of known maritime archaeological sites held by the Southampton City Council

Historic Environment Record (SCCHER); Records of known maritime archaeological sites held by the Hampshire County

Archaeology and Historic Buildings Record (AHBR); Additional background information was collated from secondary and documentary

sources held in Wessex Archaeology’s library; and Geophysical data from surveys conducted by Wessex Archaeology (2008).

19.17 The records of known maritime sites and casualty positions within the study area were

compiled in a gazetteer and each given a unique WA2000 identification number, before being overlaid on a base map of the development area in a Geographical Information System (GIS).

19.18 In order to supplement this with data concerning potentially older, wooden wrecks within those

areas to be directly impacted by the proposed dredging, a series of geophysical surveys were undertaken. Sidescan sonar and magnetometer surveys were used to search for any, as yet, un-recorded wreck sites.

19.19 In addition to shipwrecks, past changes in sea level mean that there is also some potential for

the presence of submerged prehistoric archaeology within the study area, and reported historical finds from the seabed within Southampton Water and the Solent, close to the scheme footprint, support this. Records of prehistoric archaeological finds and sites, information from



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the White Collection and information drawn from secondary sources were used to suggest patterns of human activity before the final marine transgression.

19.20 In order to identify those areas with the highest prehistoric archaeological potential, sub-bottom

and bathymetric surveys were conducted within those areas to be directly impacted by the proposed dredging. Borehole and vibrocore logs were also assessed and where archaeological potential was identified, sections of core were subject to archaeological recording. This data was used to supplement the existing body of published work into the prehistoric archaeology of the now submerged areas of Southampton Water and the Solent, and in conjunction with the geophysical and desk-based data to identify specific areas of heightened archaeological potential.

19.21 During the geophysical survey all areas were surveyed with sidescan sonar, boomer and

magnetometer. Some areas also had additional lines on which magnetometer data were collected but not sidescan sonar or boomer. Single beam echo sounder data were collected on all lines run.

19.22 The track plots of the sidescan data were plotted in a format suitable for viewing in ArcMAP 9,

where they could be overlaid with information about previously recorded sites and details of the development. The sidescan data was interpreted visually in conjunction with the track plots. All geophysical anomalies identified in the sidescan sonar and magnetometer data were assessed in terms of archaeological potential and classified in terms of anomaly type (e.g. debris, seafloor disturbance, etc.) and each anomaly was assigned a unique WA7000 identification number. Anomalies were then grouped where the same object was seen in more than one line of data or several anomalies form a discrete site.

19.23 Particular attention was paid to the traces in the vicinity of previously recorded sites, and where

magnetic anomalies had been recorded. Additionally, all traces were scanned for ‘new’ anomalies.

Baseline Environment

Results of Desk-based Assessment

Known and Potential Maritime Archaeology

19.24 The potential for wrecks within Southampton Water and the Solent covers all periods from as

far back as the inundation of the area during the period between the Mesolithic and the Iron Age.

19.25 A total of 136 records for all periods were catalogued from desk-based sources. These

demonstrated a heavy bias towards the discovery and plotting of relatively modern, metal wrecks with the majority of these records relating to the period from the 19th to the 21st century.

19.26 By the end of the Mesolithic (c. 4000BC) sea level rise meant that all of the study area is likely

to have been below the Mean High Water mark. Human activity in the study area during the



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Neolithic (4000 – 2400BC) would thus have been maritime in nature. There are no known Neolithic sites or finds within the study area.

19.27 During the Bronze Age (2400 – 700BC) the coastline adjacent to the study area was important

as a subsistence resource. Evidence for its use includes a large array of fish traps found on the Isle of Wight coast at Wootton Quay in the eastern Solent. These sites lie below the Mean High Water mark, and others may thus occur elsewhere within submerged parts of the study area which have not been previously subject to dredging

19.28 The Iron Age (700BC – 43AD) heralded the arrival not only of a wetter climate but also of

invaders and traders from Gaul who established bridgeheads along the coast of Wessex. Hillforts and Oppida (trading centres) become the foci for broad networks of rural farming activity during this period. The nearest hillfort to the study area is that of Buckland Rings, near Lymington.

19.29 The Solent can be considered to have been used by shipping for over 2000 years. However, it

was the years between AD 1650 and 1800 that were of vital importance for the region as Portsmouth and Southampton grew and the Solent area acquired a status that was both national and international. The volume of traffic and the congestion caused by the relatively narrow waterway are hazards that can be expected to have caused maritime casualties in the past. In addition to the potential for wrecks consideration must also be given to the potential for stray items, lost or thrown overboard within the Solent through the centuries and which are now of archaeological interest.

19.30 The marine archaeological potential of the study area includes known or charted wrecks and

features, recorded maritime losses and unknown, unrecorded losses.

Known or Charted Wrecks 19.31 Information related to known or charted wrecks and features was supplied by the UKHO, which

lists 21 wrecks, features and anomalies in the study area. Of these, six are classed as ‘dead’, which means that the wreck or feature has not been detected by repeated surveys and is therefore considered to not exist by the UKHO. However, caution should be exercised at these locations as despite the designation of ‘dead’, wreck material may be present on or in the seabed.

19.32 The UKHO lists 15 ‘live’ wrecks, obstructions and features in the study area These are

considered to exist at or near their recorded positions and can be divided into the following categories:

Eight wrecks, which with two exceptions are modern and were lost within the last 40

years. The two exceptions are the wrecks of the Luciston, torpedoed and sunk in 1917 and an aircraft lost in 1940. The wreck of the aircraft is automatically protected under the terms of the Protection of Military Remains Act;

Three unidentified wrecks found by UKHO survey, two of which are classed as ‘dangerous’ (i.e. upstanding and therefore probably metal);

Three features: a tree trunk, a cylindrical navigation buoy fitted with a tripod light and a swamped mooring with ground chains on the seabed.



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19.33 Of these ‘live’ wrecks, obstructions and features only WA2008, a swamped mooring on the eastern edge of the Fawley survey area, is located within an area that will be subject to dredging under the current proposals. ABP reports that this mooring has now been recovered and is in commercial use.

Recorded Maritime Losses

19.34 The records of documented maritime losses in the study area are held by the NMR and the Hampshire AHBR. These records, which are based on historical reports of losses for which no grid reference can be confirmed, are attached in the NMR and AHBR to arbitrary points called Named Locations (NLOs). The co-ordinates of the NLOs are chosen to represent general loss locations, and do not (except by chance) relate to actual wreck positions or seabed remains.

19.35 There are a total of 72 recorded losses at two NLOs within the study area, ranging in date

between 1781 and World War II and it is possible that these wrecks may lie within the study area. It should be noted that eight of the recorded losses are military aircraft, which are automatically protected under the terms of the Protection of Military Remains Act.

19.36 A large proportion of the proposed dredge, however, will deepen areas previously dredged

from the 1960’s onwards. The potential for wrecks being disturbed by the current proposal in these areas is thus likely to be limited.

19.37 The NMR and the Hampshire AHBR together record 20 net fastenings or seabed features

within the study area. These features are net snags reported by fishermen and their nature is not known. They could represent some of the recorded losses at the NLOs, they could be natural, geological features or they could be unrecorded, unknown wrecks (see below).

19.38 The NMR and the Hampshire AHBR together also list six unidentified, undated wrecks within

the study area, for which records exist, but for which no other information is available.

Unknown, Unrecorded Losses 19.39 The long maritime history of the Solent and Southampton Water, going back to at least the Iron

Age, means that there is the potential for unknown, unrecorded wrecks to be found within the study area.

19.40 Nine archaeological find spots are recorded in the Hampshire AHBR, the Isle of Wight SMR

and the Southampton City Council HER within the study area. These include two Bronze Age palstaves (axes), an Iron Age iron axe head and the top of a Spanish, Iron Age, Dressel 20 amphora. More direct evidence comes from the recorded find in 1848 of a large ancient vessel, thought at the time to be a Roman galley. Less than 100m from the recorded location of this vessel, Roman amphora fragments and other remains were dredged from Southampton Water in 1893.

19.41 These finds all come from outside areas to be affected by the current dredge, but demonstrate

the potential for unknown, unrecorded wrecks and related material in areas of new dredge.

Geophysical Anomalies 19.42 A large number of geophysical anomalies were recorded during the geophysical survey of the

areas listed in Table 19.2 below. The majority of these anomalies have been classed as



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‘debris’, the precise nature of which is impossible to ascertain on the basis of the geophysical data. There are also a number of magnetic anomalies, most of which are not associated with visible anomalies on the seabed, but which, by their nature, are likely to be anthropogenic in origin. The geophysical survey located four wrecks: three charted UKHO wrecks, which lie outside areas to be affected by the dredge, and a previously unlocated modern wreck (WA7158) within the proposed Thorn dredge area. Those geophysical anomalies that will be affected by the proposed dredging work are discussed within the context of each survey area below.

19.43 The number of small unidentified seabed objects located during the geophysical survey

suggests that there is a large amount of potentially anthropogenic material within the areas of impact associated with the proposed dredging. To assess the potential for these remains to be archaeologically important is more difficult. However, in general, any features that are on the surface are more likely to have a lower level of archaeological potential, whereas anything that is buried or partially buried is more likely to be older, and therefore more likely to have a higher level of archaeological potential.

Submerged Prehistoric Archaeology

19.44 The known history of human inhabitation of Britain covers at least 700,000 years. Over this period there have been several periods of glaciation, at which times ice sheets covered much of Britain locking up large quantities of water and causing the sea level to drop. The lowest sea level recorded during the last glacial maximum was c.120 metres below its current level. At times of lower sea level areas that are currently submerged would have been inhabitable dry land, and where these areas contained rich natural resources (e.g. river valleys and the coastal zone) they would have been preferred areas of habitation for human populations.

19.45 Following data analysis for the proposed dredging areas it is clear that much or all of the study

area would have been dry land at several times during prehistory, and is therefore likely to have supported animal and human life. The submerged elements of the Solent region are associated with archaeological evidence from the earliest human occupation of Britain during the Lower Palaeolithic (700,000-150,000BP), up until the eventual inundation of the area during the Iron Age. The Solent area is heavily sheltered by the Isle of Wight and was not subjected to the full force of the sea during the transgression, which caused a steady build up of sediments that tended to bury former terrestrial archaeological sites, rather than destroy them. This slow inundation and high level of human activity means that the potential for evidence of submerged archaeological sites within the study area is high.

19.46 There are six known prehistoric find spots within the study area and further material has been

recovered and recorded from Southampton Water and the Western Solent by fisherman Michael White. The majority of prehistoric finds were of flint artefacts. As part of a broad-ranging project to map submerged prehistoric sites, which included consultation with Michael and Stephen White, further information and patterns in the artefact recovery were noted in Southampton Water and the Solent. It was determined that two areas of submerged forests and many of the artefacts came from within peat deposits. Elsewhere in the Solent, Palaeolithic hand axes have been found on the seabed.



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19.47 Within the Solent four of Michael White’s recovery areas are close to or overlap with the study area. These four recovery areas have produced 10 prehistoric finds. These have not been added to the gazetteer as the exact positions from which the finds were recovered are not known. The potential for more of these types of finds to be recovered during any dredging of areas not previously dredged is medium to high. Where dredging has previously taken place in the recent past, however, (as is the case for much of the Southampton approach channel) the potential is low.

Results of Geotechnical Assessment

19.48 The potential submerged land surfaces within and adjacent to the dredge areas were

investigated using a combination of geophysical and geotechnical survey techniques. The aim was to map out areas of surviving pre-transgression land-surface, and to assess the palaeoenvironmental and archaeological potential of the deposits.

19.49 The assessment of the geotechnical logs identified vibrocores within and near the proposed

dredging areas, which may contain sediments of potential archaeological interest. These sediments appear to relate to the known geological sequence of the area including Tertiary bedrock overlain by Pleistocene and Holocene gravels, sands, silts, clays and peats. The geotechnical recording has confirmed four major sedimentary units within the vibrocores, which are presented in the Table 19.1 below. Depth is described in metres below Ordnance Datum (mbOD). Table 19.1 Major sedimentary units identified within the vibrocores

Sedimentary

Unit Depth

(mbOD) Interpretation Date

(Years Before Present)

Unit 4 3.02m to 23.31mbOD Recent estuarine alluvium and seabed sediments

7,000 - Present

Unit 3 19.27 to 22.67mbOD Pleistocene and Holocene alluvium and peat 22,000 – 7,000

Unit 2 9.06m to 24.03mbOD Pleistocene valley gravels 1.8 million - 10,000 Unit 1 14.12to 19.69mbOD Tertiary bedrock 65 – 1.8 million

19.50 Unit 1 (Tertiary bedrock) may in some areas represent the maximum extent of Pleistocene

river valley of the Test. Although the sediment itself is not of archaeological interest, its surface may include glacial features, soil formation and archaeological artefacts.

19.51 Unit 2 may have some archaeological potential. If it represents Pleistocene fluvial activity it

may contain Palaeolithic archaeological material. Given the range of elevation of Unit 2 it is considered that this unit may contain the remnants of more than one gravel terrace.

19.52 Unit 3 contains a sequence of interleaved silts, clays and peats which most likely represent

Holocene sedimentation, in part created by sea level rise. These sediments often contain significant amounts of palaeoenvironmental and potentially archaeological material, which can be investigated using the vibrocore samples not used for geotechnical testing. The peats noted within the vibrocores are of interest as they are dateable units. The depths of these generally



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relate directly to their date i.e. the shallower the younger. Radiocarbon dating of peats at Bouldnor Cliff, Isle of Wight and the English Channel suggest that the elevation of peats recorded within the vibrocores in this study are likely to fall in the date range of circa 8,000 – 6,000 BP (i.e. during the Mesolithic).

19.53 Unit 4 has been distinguished mainly by its very soft texture and its massive depositional

structure. It is considered that where soft alluvial sediments in the region of known dredging activities have been recorded, they are likely to be recent in date. The present depositional environments in and around Southampton Water and the Nab Channel are noted to be not dissimilar to those which caused deposition of the majority of Unit 3 (i.e. salt marsh, estuarine and shallow marine). Unit 4 may in part be analogous in date and environment to the upper part of Unit 3 (i.e. Holocene alluvial sediments). The more recent sediments within Southampton Water and the Nab Channel are of little prehistoric archaeological or palaeoenvironmental interest.

Results of Geophysical Survey

19.54 Eight areas where the maintained channel is to be widened or deepened were surveyed using

sidescan sonar, boomer and magnetometer (Table 19.2 and Figures 19.1-19.4). In some areas additional lines of magnetometer data were collected. Single beam echo sounder data were collected on all lines run. Table 19.2 Component elements of study area

Study Area Description of Area Proposed Dredging Works

Western Docks (WD)

Area in vicinity of Container Terminal to Dock Head

Deepening channel between Berth 207 and Dock Head from -12.6m to -13.6mCD; Widening opposite 106 berth by 30m and deepening to -13.6mCD; Extending the Middle Swinging Ground and deepening to -10.2mCD

Fawley (FAW) Area between Dock Head and Fawley

Widening between Dock Head and Fawley by 100m and deepening to the proposed full channel depth of -13.6mCD, with an exclusion of 150m either side of the pipeline

Esso (ESSO) Area adjacent to ExxonMobil Marine Terminal

Widening of the Fawley Channel off the ExxonMobil Berth #1 from -11.2mCD to the proposed full channel depth of -13.6mCD

Hook (HOOK) Area between the natural deep between Hamble Spit and the northern extent of Thorn Channel

Widening and deepening to -13.6mCD;

Thorn (THORN) Area of the Thorn Channel between Calshot and Bramble Turn,

Deepening from -12.6m CD to a minimum maintained depth of -13.8mCD

Shoal (SHOAL) Central Solent Removal a small number of high spots in the Solent between the Thorn and Nab Channels to give a minimum maintained depth of -15.0mCD

Nab Channel (NAB)

Nab Channel Deepening from -13.3m to a minimum maintained depth of -14.8mCD

Southern Nab Channel (SNAB)

Nab Channel Removal of chalk high spots at the entrance to the Nab Channel to a minimum maintained depth of -14.8mCD



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19.55 The survey areas were defined as the polygons representing the proposed dredge areas

around which a 40m buffer was added in each case. The buffer was to ensure survey coverage of sites located just in- or outside the dredge areas.

19.56 All geophysical anomalies identified in the sidescan sonar and magnetometer data were

assessed in terms of archaeological potential and classified in terms of anomaly type (e.g. debris, seafloor disturbance, etc.). Anomalies were then grouped where the same object was seen in more than one line of data or several anomalies formed a discrete site. Groups of anomalies and individual anomalies of potential archaeological interest were given unique WA7000 identification numbers. Where UKHO records fell within a survey area these were grouped with the geophysical anomalies, where appropriate, or otherwise given their own WA7000 number.

19.57 A total of 360 geophysical anomalies were found across the eight survey areas. Once grouped,

this translated to 227 anomalies, of which 125 were assessed as being of archaeological potential. The 125 anomalies can be further sub-divided as follows:

Anomalies occurring outside the area to be dredged (and, therefore, unaffected by the

current proposal): 37 Anomalies occurring within the current maintained channel (and, therefore, likely to be

of recent origin): 51 Anomalies occurring within an area to be dredged that has not been subject to

previous dredging activities: 37.

19.58 The sites of potential archaeological interest are discussed on an area by area basis below, with particular attention being focussed on anomalies likely to be impacted by the current dredge proposal.

19.59 It is not possible to tell whether features interpreted as dark reflectors, bright reflectors, seafloor

disturbances or small items of debris are of anthropogenic origin. Further investigation would be necessary to define their archaeological potential. Magnetic anomalies, on the other hand, are likely to be of anthropogenic origin.

Impact Assessment

19.60 Two types of site may be present within the study area: wrecks and associated material,

including aircraft, and drowned prehistoric sites and landscapes. Both these site types are likely to have been subject to disturbance prior to any potential effect arising from this development.

19.61 The process of wreck formation is itself likely to be the main source of previous disturbance to

wrecks, as vessels settling on the seabed are likely to suffer various forms of collapse and decay before stabilising. The main post-depositional processes active in the area are likely to be sand or sediment movement, which may expose and rebury any wrecks, causing periodic instability that leads to physical, biological and chemical decay, and fishing, such as trawling or scallop dredging which may cause direct damage to wreck material.



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19.62 The main processes militating against the survival of prehistoric land-surfaces and any associated sites are the reworking of those deposits during the course of marine transgression and regression. Wave and tidal action are likely to have repeatedly eroded and deposited former terrestrial material, washing out fine sediments, abrading otherwise robust artefacts and exposing organic materials to chemical and biological decay. That sites do survive this process is evidenced by the survival of many peat horizons and drowned forests around the coast of England.

19.63 Following the geophysical assessment a number of anomalies were identified and were

interpreted to gauge their archaeological potential. Where anomalies lie within the maintained approach channel they are likely to post-date the dredging of the channel and are thus probably modern. These anomalies will therefore not be considered further with regard to potential archaeological impacts, except where they are clearly identifiable as archaeological material.

Key Impact Pathways

19.64 The assessment of potential impacts is based on the results of the desk-based assessment,

the assessment of geophysical data and the assessment of geotechnical core material. 19.65 The key impact pathways relating to archaeology are:

Potential direct impact Due to dredging activity; and Potential indirect impacts from changes to sedimentation regime following dredge.

19.66 The numerical modelling that was undertaken for the physical processes assessment identified changes to sedimentation patterns following the proposed dredge to be small outside the immediate dredge areas and unlikely to be detectable from background variation (Chapter 8). The general pattern found was that of increased potential for sedimentation over shallow subtidal and intertidal areas (up to around 0.01m per year), therefore, suggesting a reduction in the potential for erosion from the baseline situation. This rate is likely to be less in reality due to the redistribution of surface sediments by existing ship and wave disturbance. Therefore, the indirect impact of changes to sedimentation regime on archaeological features is considered insignificant and is not considered further in this assessment.

19.67 The geophysical assessment for each survey area is outlined below, along with any

assessment of the archaeological potential for any of these anomalies. The assessment of the prehistoric archaeological potential for each area, based on the results of the geophysical and geotechnical assessments is also included as appropriate to each area.

Western Docks (WD)

19.68 In addition to deepening the existing channel from 12.6m to 13.6m below CD, areas of WD will

be subject to new dredging which will impact on all sediment units (Units 1-4), removing Holocene sediments, which may include peat layers, in the northwest of the survey area. The impact on the sediments to be removed will be high and any sites contained therein will be lost. The geophysical survey has confirmed, however, that these Holocene sediments extend outside the area to be dredged and these areas will not be impacted by the scheme.



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19.69 A total of 31 sidescan sonar anomalies and one magnetic anomaly were observed in the data

collected over this survey area. These were grouped together to produce a total of 20 sites, of which five are of potential archaeological interest.

SSS Anom. Mag Anom. Number of Sites Potential

Archaeological Interest

Outside Dredge Area

Within Maintained

Channel

Impacted by New Dredge

31 1 20 5 3 2 0 19.70 Of the five sites of potential archaeological interest within the survey area three lie outside the

area of impact of the scheme and will thus not be subject to direct impacts by the work. The physical processes assessment (Chapter 8) suggests that the likelihood of indirect or secondary impacts from erosion occurring on these three sites is insignificant.

19.71 No known wrecks or obstructions are present in the area. 19.72 Two sidescan anomalies within the maintained channel, WA7180 (linear debris) and WA7181

(bright reflector), will be subject to direct impact by the proposed works. Their presence in the maintained channel suggests they post-date the dredging of the channel. However, the archaeological nature of WA7181 in particular is not currently known and it is therefore not possible to determine its level of importance

FAW

19.73 The existing dredged channel in the FAW area is maintained to a depth of 12.6m. The proposal

scheme will deepen the channel to 13.6m and widen it in the east by 100m and to the full depth.

19.74 The proposed dredge will remove the Holocene sediments observed in the sub-bottom data on

the eastern bank of Southampton Water. The impact on the sediments to be removed will be high and any sites contained therein will be lost. The assessment of the cross-lines of sub-bottom data, however, has confirmed that these Holocene sediments extend outside the area to be dredged and these areas will not be impacted by the scheme.

19.75 A total of 45 sidescan sonar anomalies and 10 magnetic anomalies were observed in the

geophysical data collected over this survey area. The anomalies were grouped together with the known wrecks and obstructions to produce a total of 45 sites. None of the magnetic anomalies are associated with any sidescan sonar anomalies. Twenty-nine anomalies are of potential archaeological interest.



Outside Dredge Area

Within Maintained

Channel


45 10 45 29 4 14 11

19.76 Four of the sites of potential archaeological interest lie outside the area of impact of the scheme and will thus not be subject to direct impacts by the work. These include one known wreck or obstruction (WA7079). This site is classified by the UKHO as ‘undefined’ and was a wreck observed during routine survey operations in January to February 2006. No further



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details are available and nothing was observed at this location in the new geophysical datasets. The physical processes assessment (Chapter 8) suggests that the likelihood of indirect or secondary impacts from erosion occurring on these sites is insignificant.

19.77 Twenty-five anomalies will be subject to direct impact by the proposed works. However, 14 lie

within the maintained channel and are likely to post-date the dredging of the channel. 19.78 The remaining 11 anomalies (Table 19.3) lie in an area not previously dredged and will be

subject to direct impact by the dredge. The archaeological natures of WA7066-68 (classed as ‘debris’) are not known and it is thus currently impossible to determine their level of importance. Anomalies WA7081-8 are magnetic and are thus likely to be anthropogenic in origin. However, it is currently impossible to determine their level of importance.

Table 19.3 Anomalies of potential archaeological interest in area of new dredge: FAW

WA ID Name / Classification

Easting Northing Description Sources

7066 Debris 445376 106979 Debris (2.2m x 0.2m x 0.1m) 3069 7067 Debris 445735 106683 Linear dark reflector (13.7m x 0.1m x 0m) 3070 7068 Debris 445747 106667 Debris (0.7m x 0.4m x 0.1m) 3071 7081 Magnetic 444651 107541 85.98nT 4021 7082 Magnetic 444543 107648 30.35nT 4022 7083 Magnetic 443965 108174 29.91nT 4023 7084 Magnetic 444355 107863 28.13nT 4024 7085 Magnetic 446264 106338 75.45nT 4025 7086 Magnetic 445058 107314 24.78nT 4027 7087 Magnetic 444640 107573 20.96nT 4028 7088 Magnetic 443911 108171 32.02nT 4029

ESSO

19.79 The existing dredged channel in the ESSO area is maintained to a depth of 12.6m below CD.

The proposal plans to deepen the channel to 13.8m below CD and to widen the channel to the extent of the ESSO study area. Up to 3.6m of sediments will be removed by the dredging. This includes up to 2.4m of Holocene sediments, up to 3.6m of Pleistocene gravel unit and up to 0.5m of the Tertiary bedrock. The impact on the potential prehistoric archaeology in this area will therefore be high as both the Holocene and Pleistocene layers are being affected.

19.80 A total of 33 sidescan sonar anomalies and two magnetic anomalies were observed in data

collected over this survey area. The observed anomalies were grouped to produce a total of 31 sites, of which 26 are of potential archaeological interest.



Outside Dredge Area

Within Maintained

Channel


33 2 31 26 6 6 14 19.81 Six of the sites of potential archaeological interest lie outside the area of impact of the scheme

and will thus not be subject to direct impacts by the work. The physical processes assessment



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(Chapter 8) suggests that the likelihood of indirect or secondary impacts from erosion occurring on these sites is insignificant.

19.82 Twenty anomalies will be subject to direct impact by the proposed works. However, six lie

within or on the slope of the maintained channel and are therefore likely to post-date the dredging of the channel.

19.83 The remaining 14 anomalies (Table 9.4) lie in an area not previously dredged, and will be

subject to direct impact by the dredge. The archaeological nature of the majority of these anomalies is not known and it is currently impossible to determine their level of importance. However, anomalies WA7054 and WA7055 are magnetic and are thus likely to be anthropogenic in origin although it is currently impossible to determine their level of importance.

Table 19.4 Anomalies of potential archaeological interest in area of new dredge: ESSO



7034 Seafloor disturbance

447142 105076 Seafloor disturbance (16.9m x 8.2m x 0m) 3133

7036 Debris 447104 105127 Debris (1m x 1m x 0.5m) 3136

7037 Seafloor

disturbance 447121 105083 Extends beyond range, area covered

measures 14m x 4.2m x 0m. 3137

7039 Debris 447040 105302 Linear debris (3.8m x 0.2m x 0m) 3139 7040 Debris 447044 105305 Linear debris (6.2m x 0.1m x 0.1m) 3140

7041 Seafloor

disturbance 446906 105345 Seafloor disturbance (6.3m x 5.6m x 0m) 3141

7042 Bright

reflector 446897 105350 Bright reflector (1.4m x 0.5m x 0m) 3142

7043 Bright


7044 Bright


7045 Bright


7047 Debris 446884 105410 Circular debris (1.5m x 1.2m x 0m) 3147 7049 Debris 446809 105494 Debris (2.5m x 0.4m x 0.6m) 3151 7054 Magnetic 446768 105482 93.98nT 4011 7055 Magnetic 446807 105406 157.49nT 4012

Hook

19.84 Geologically this area is similar to the ESSO survey area. Three prominent sedimentary units

were observed in the Hook sub-bottom profiler data. Four vibrocores were acquired in the Hook survey area, and these correlated well with the geophysical data.

19.85 Up to 7.4m of sediments will be removed under the proposals and dredged to a depth of 13.8m

below CD. This will impact all sedimentary units identified in the geophysical data. The impact on the sediments to be removed will be high and any sites contained therein will be lost. The geophysical survey has confirmed, however, that these Holocene sediments extend outside the area to be dredged and these areas will not be impacted by the scheme.



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19.86 A total of 23 sidescan sonar anomalies and 16 magnetic anomalies were observed in the

geophysical data collected over this survey area. Once grouped together this produced a list of 20 sites of which 17 are of potential archaeological interest.



Outside Dredge Area

Within Maintained

Channel


23 16 20 17 5 0 12 19.87 Five of the sites of potential archaeological interest lie outside the area of impact of the scheme

and will thus not be subject to direct impacts by the work. The physical processes assessment (Chapter 8) suggests that the likelihood of indirect or secondary impacts from erosion occurring on these sites is insignificant.

19.88 The remaining 12 (Table 9.5) lie in an area not previously dredged, will be subject to direct

impact by the dredge. The archaeological nature of these anomalies is not known and it is currently impossible to determine their level of importance. However, anomalies WA7103-6 are magnetic, but not associated sidescan sonar anomalies. They are likely to represent buried metal features, which should be assumed to be anthropogenic in origin.

Table 19.5 Anomalies of potential archaeological interest in area of new dredge: Hook



7090 Debris 448283 104305 Debris (3.2m x 1.9m x 0.7m). Possible scour around.

3100

7091 Debris 448457 104066 Debris (1.1m x 0.1m x 0.4m) 3101

7094 Debris 448917 103344 Debris (3m x 0.9m x 0.2m) 3104 3111

7095 Bright


7096 Seafloor

disturbance 448593 103905 Seafloor disturbance (5.8m x 1.1m x 0m) 3106

7097 Dark

reflector 448254 104398

Linear, possibly has height (4.1m x 0.1m x 0m)

3107

7099 Debris 448535 103908 Debris (0.8m x 0.4m x 0.5m) 3109 7100 Debris 448675 103727 Debris (1.6m x 0.4m x 0.2m) 3110 7103 Magnetic 448910 103397.6 41.83nT 4042 7104 Magnetic 449240 102936.8 35.26nT 4043 7105 Magnetic 449251 102943.8 92.33nT 4044 7106 Magnetic 448984 103344.6 22.2nT 4045

Thorn

19.89 The Thorn Channel survey area is an area previously dredged and within the maintained

channel. Maintained to a depth of 12.6m below CD, the proposed work will deepen this area to 13.8m below CD.

19.90 The geophysical survey identified three sedimentary units, the dominant unit comprising a

series of south-west dipping parallel reflectors interpreted as bedrock. Within the western section of the survey area this unit is primarily observed close to the seabed with an overlying



R/3742/8 328 R.2015

veneer of sediments. The overlying sediments thicken in the north-east and east of the survey area where the top of the bedrock is observed up to 6m below the seabed. This is borne out by the results of geotechnical assessments, which indicate the presence of bedrock at the seabed or below a thin veneer of sediment.

19.91 Along the north-westerly half of the channel the dredge will affect the bedrock. In the eastern

half and around the edges of the survey area, Pleistocene gravels will be removed. Only on the extreme north-eastern edge of the area (the western edge of Bramble Bank) will the surface of the Pleistocene gravels and any overlying Holocene sediments be affected by the dredging proposals. Up to 3.2m of Pleistocene gravels and up to 2.5m of Holocene sediments will be removed. The removal of Holocene sediments affects only the edge of the dredging area, and overall impact on these sediments, which extend into Bramble Bank, will be minimal.

19.92 A total of 135 sidescan sonar anomalies and four magnetic anomalies were observed in the

geophysical data collected over the survey area. These were grouped with the known wrecks and obstructions to produce a total of 62 sites, of which 25 are of potential archaeological interest.



Outside Dredge Area

Within Maintained

Channel


135 4 62 25 9 16 19.93 Nine of the sites of potential archaeological interest lie outside the area of impact of the

scheme and will thus not be subject to direct impacts by the work. The physical processes assessment (Chapter 8) suggests that the likelihood of indirect or secondary impacts from erosion occurring on these sites is insignificant.

19.94 Sixteen anomalies (Table 19.6) will be subject to direct impact by the proposed works. These

anomalies all lie within the existing maintained channel and are likely to post-date the dredging of the channel. They include WA7158, which is a broken up and widely scattered wreck identified as a wooden day boat sunk in 2005. Also included is an area of foul ground (WA7172), which is classified by the UKHO as ‘dead’. No anomalies were identified in the geophysical data at this position. WA7173 and WA7174 are magnetic, but not associated sidescan sonar anomalies. They are likely to result from buried metal features, which are anthropogenic in origin. The archaeological nature of the remainder of the anomalies is not known and it is thus currently impossible to determine their level of importance.



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Table 19.6 Anomalies of potential archaeological interest in area of deepening: Thorn WA ID Name /

Classification Easting Northing Description Sources Extern

al Ref 7153 Debris 449099 99802 Debris (2.8m x 0.3m x 0.1m) 3208, 3245 7154 Debris 449103 99801 Debris (1.8m x 0.4m x 0.2m) 3209, 3244 7155 Debris 449107 99805 Linear (5.2m x 0.4m x 0.3m) 3210, 3243 7156 Debris 449123 99829 Linear (6.6m x 0.3m x 0.2m) 3211, 3242 7157 Debris 449133 99831 Linear (3.8m x 0.2m x 0.2m) 3241

7158 Wreck 449179 99772

Scattered wreck (112m x 72m x 0m). Many linear pieces of debris and other pieces covering a large area. Debris size ranges from 0.8m x 0.5m x 0.3m up to 13.4m x 0.2m x 0.2m. Two large seafloor disturbances are also contained. These measure 33.9 x 27.2 x 0m and 12.4 x 4.4 x 0m. The wreck is of a wooden day boat that was run down by a container vessel on 02/06/2005.

3212-39, 3249-56, 3262-85, 3333-4

ABP

7160 Debris 449066 99811 Debris (9m x 0.6m x 0.2m). Bit distorted. 3246 7161 Debris 449053 99807 Debris in scour (3m x 1.5m x 0m) 3247 7162 Bright reflector 448424 98581 Patchy bright reflector (15.1m x 3.9m x 0m) 3290 7163 Bright reflector 448651 98753 Bright reflector (2.8m x 2.4m x 0m) 3291 7164 Debris 448657 98759 Debris (1.3m x 0.1m x 0.6m) 3292 7165 Debris 448759 98176 Debris (4.4m x 0.3m x 0.2m) 3295 7171 Debris 449058 98019 Debris (1.4m x 0.1m x 0.3m) 3331

7172 Foul 448388 98235 Foul Ground. Dead. 2100 UKHO 70916

7173 Magnetic 448875 99328 20.72nT 4081 7174 Magnetic 448340 98789 9.92nT 4082

Shoal

19.95 The Shoal survey area is an area previously dredged and within the maintained channel, with

depth varying between 14.8m and 18.7m below CD. The dredging design for this area proposes deepening the shallower portions of this area to 15m below CD. The proposals will thus only affect two small portions of this survey area.

19.96 The dredging will mainly impact the recent seabed sediments that form the sand waves, which

characterise parts of the Shoal area. However, where the sand waves are absent there may be some impact on the Pleistocene gravels. Due to the small sections being impacted by the dredging the impact on prehistoric archaeology in the area can be considered low.

19.97 A total of 20 sidescan sonar anomalies and one magnetic anomaly were observed in the

geophysical data collected over this survey area. These anomalies were grouped with the known wrecks and obstructions to produce a total of 20 sites. Of these, 10 are of potential archaeological interest.



Outside Dredge Area

Within Maintained

Channel


20 1 20 10 6 4 19.98 Six of the sites of potential archaeological interest lie outside the area of impact of the scheme

and will thus not be subject to direct impacts by the work. The physical processes assessment (Chapter 8) suggests that the likelihood of indirect or secondary impacts from erosion occurring on these sites is insignificant.



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19.99 Four anomalies (Table 19.7) will be subject to direct impact by the proposed works. These anomalies all lie within the existing maintained channel and are likely to post-date the dredging of the channel. Because the archaeological nature of these anomalies is not known, it is currently impossible to determine their level of importance.

Table 19.7 Anomalies of potential archaeological interest in area of deepening: Shoal



7140 Bright reflector

456602 96184 Bright reflector (4.5m x 1.3m x 0m). Very bright and nothing similar around.

3175

7144 Bright


7147 Debris 456684 96243 Debris (2.3m x 0.2m x 0.3m) 3182 3186

7148 Debris 456519 96216 Debris (1m x 0.2m x 0.1m).

Possible scour in front. 3183

Nab

19.100 The Nab Channel is an area previously dredged and within the maintained channel. Maintained

to a depth of 13.3m below CD the new scheme proposes deepening this area to a minimum of 14.8m below CD. This dredging will affect the outer edges of the survey area in the south and localised sections of the western edges of the survey area in the north. The dredging will primarily impact the recent seabed sediments (Unit 4) and the upper sediments of Unit 3. The thin layer of Unit 3 overlying the anticline structure in the south will also be impacted.

19.101 A total of 33 sidescan sonar anomalies and four magnetic anomalies were observed in the

geophysical data collected over the Nab survey area. These were grouped with the known wrecks and obstructions in the area to produce a total of 27 sites, of which 13 are of potential archaeological interest.



Outside Dredge Area

Within Maintained

Channel


33 4 27 13 4 9 19.102 Four of the sites of potential archaeological interest lie outside the area of impact of the

scheme and will thus not be subject to direct impacts by the work. The physical processes assessment (Chapter 8) suggests that the likelihood of indirect or secondary impacts from erosion occurring on these sites is insignificant.

19.103 The remaining seven sites (Table 19.8) all lie within the existing maintained channel and will be

subject to direct impact by the proposed works. 19.104 WA7130 represents the position of a UKHO wreck listed within the survey area. This wreck

was not seen in the geophysical data and is a recent loss of small craft. The UKHO position described is unreliable so it is possible that it does not lie within the survey area. WA7130 is the position given for the wreck of the yacht Moody Blue that sank in 1983. This site is now classified by the UKHO as ‘dead’.



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19.105 The other magnetic anomaly (WA7132) is not associated with a sidescan sonar anomaly but is

likely to indicate a buried metal feature of anthropogenic origin. 19.106 Because the archaeological nature of the remaining anomalies is not known, it is currently

impossible to determine their level of importance.

Table 19.8 Anomalies of potential archaeological interest in area of deepening: Nab WA ID Name /

Classification Easting Northing Description Sources Extern

al Ref 7120 Debris 474601 87701 Debris (2.6m x 0.9m x 0.3m) 3371 7121 Debris 474512 88022 Debris (2.8m x 1.1m x 0.2m) 3373 7122 Debris 472788 90589 Debris (1.4m x 0.4m x 0.6m) 3375, 3399 7124 Debris 474013 89305 Debris (1.1m x 0.7m x 0.5m) 3378 7127 Dark reflector 472905 90780 Dark reflector (6.4m x 1m x 0m) 3397

7130 Moody Blue 474144 89519 Yacht that sank on 10/08/1983. Position unreliable. Dead.

2009 UKHO 20201

7132 Magnetic 474414 89195 11.21nT 4063

SNAB

19.107 The SNAB is an area with seabed depths between 14.1m to 20.8m below CD. The dredging proposals are to deepen three shoal patches visible on the bathymetry data to 15m below CD. These shoal patches will need approximately 0.9m of sediments to be removed, and this is likely to comprise only surficial sediments and bedrock.

19.108 Two sidescan sonar anomalies were observed in the geophysical data collected over this area.

No magnetic anomalies were observed and there are no known wrecks or obstructions. Of the sidescan anomalies, one was located outside the area and the other was interpreted as fishing gear or other rope/cable caught on an upstanding rocky area and is thus likely to be of low archaeological importance.

Summary of Impacts

19.109 Holocene and Pleistocene sediments, with a high potential, particularly in Southampton Water,

to contain prehistoric archaeological sites and material will be removed in areas of new dredge. The impact of the scheme on these sediments and any archaeological materials they contain will be high as these sites and material will be lost. However, geophysical data indicates that these sediments continue beyond the area of impact.

19.110 With suitable mitigation undertaken, the overall impact of the scheme on the prehistoric

archaeology is likely to be low. 19.111 The scheme will impact on 51 anomalies within the maintained channel. These are assumed to

post-date the dredging of the channel and therefore likely to be modern, although this cannot be stated with certainty on the basis of the current data. Because the scheme is likely to remove these anomalies from the seabed the impact on individual anomalies will be high. However, the significance of the impact to anomalies is likely to be minor adverse significant, if these anomalies represent modern material.



R/3742/8 332 R.2015

19.112 Thirty-seven anomalies, the archaeological nature of which are not known, have been identified

within areas of the proposed scheme that have not been subject to previous dredging activities. Fourteen of these are magnetic anomalies and should be assumed to represent metal objects of anthropogenic origin. Because the scheme will remove these 37 anomalies from the seabed the impact is considered to be high. However, given the extent of the assessment undertaken to date, it is not possible to determine the significance of the impact. With the implementation of suitable mitigation measures, however, the overall impact of the scheme on these anomalies is likely to be low.

Mitigation and Residual Impact

19.113 Archaeological best practice favours in situ preservation of archaeological material and

avoidance of archaeological remains. Where this is not possible the effects of the scheme can be offset with mitigation measures.

19.114 The following measures, which will be set out in detail in a Written Scheme of Investigation

(WSI) (see below), are designed to mitigate the impact of this development upon known sites, and to establish the presence of unknown sites within the areas subject to dredging. Where there is a clearly identified archaeological potential the proposed mitigation aims to further investigate the deposits that may contain, or anomalies that may represent archaeology.

Submerged Prehistoric Archaeology

19.115 In order to clarify the situation with regard to the potential for the presence of submerged land-

surfaces, possibly containing archaeological sites, it is proposed that further (Stage 3) archaeological assessment of five vibrocore samples displaying archaeological potential will be undertaken by a suitably qualified archaeologist. This analysis of the vibrocore material will establish the palaeo-environmental importance of the submerged sediments and whether Stage 4 assessment will be required.

19.116 In addition, a programme of bucket sampling, the exact nature of which will be set out in the

WSI, will be undertaken prior to or during the dredging programme. Bulk sediment samples from locations and depths identified by the project archaeologist will be taken for archaeological assessment, the aim of which will be to identify and record the presence of any prehistoric archaeological material.

19.117 With the implementation of the mitigation measures outlined above, and taking into account the

recorded presence of these sediment layers beyond the area of impact of the dredge, the residual impact of the scheme on the prehistoric archaeology is likely to be low.

Maritime Archaeology

19.118 The significance of any anomaly that is considered to have archaeological potential depends

on the actual nature of the anomaly. It is however not always possible to determine the precise nature of an anomaly from geophysics alone. The level of archaeological importance of the anomalies with archaeological potential identified within the areas that have not previously



R/3742/8 333 R.2015

been dredged is, therefore, unknown, although it can be assumed that the 14 magnetic anomalies are anthropogenic in origin.

19.119 In order to learn more about the nature of the geophysical anomalies, a programme of diver

ground-truthing of a sample of the anomalies in the new dredge areas is proposed, the details of which will be set out in detail in the WSI. The net result of the diver surveys will be to achieve parity between the recorded anomalies and their archaeological potential. Any that are determined of archaeological importance will be reported to English Heritage and further mitigation may be proposed, as appropriate, based on the results of the diver survey.

19.120 The nature of the proposed scheme means that a programme of archaeological watching briefs

during dredging operations is not considered an appropriate mitigation strategy. Instead, a Finds Reporting Protocol (see below) will be implemented during dredging operations. This will establish mechanisms for contractors to report finds of archaeological interest to the project archaeologist and the Curator/s and for archaeological access to and monitoring of material recovered from the dredge head. Specific methodologies will be presented in detail in the WSI.

19.121 With the implementation of the mitigation measures outlined above the residual impact of the

scheme on the maritime archaeology is likely to be low.

Written Scheme of Investigation 19.122 It is proposed that all mitigation measures proposed above will be detailed within a Written

Scheme of Investigation (WSI) that is drawn up prior to construction. In addition to detailed methodologies for proposed mitigation, the WSI will also set out procedures for dealing with any features that appear to be of archaeological importance which are discovered in the course of construction. The WSI would ensure compliance with the relevant legislation.

19.123 The WSI will:

Set out the respective responsibilities of the developer, main contractors, and archaeological contractors/consultants, including contact details and formal lines of communication between the parties and with archaeological curators;

Ensure that any further geophysical and geotechnical investigations associated with the project are subject to archaeological input, review, recording and sampling;

Provide for archaeological involvement in any pre-dredge obstruction surveys, such as grapple runs, that may be undertaken;

Detail the programme of measures for mitigating effects upon known and unknown archaeological material, both prior to and during the construction phase of the scheme;

Establish the reporting, publication, conservation and archiving requirements for the archaeological works undertaken in the course of the scheme.

19.124 The WSI will be subject to the approval of local and national curatorial bodies.

Reporting Protocol 19.125 In order to cater for the possibility of chance finds made during the course of dredging a Finds

Reporting Protocol (to be included within the WSI) will be prepared. The Protocol will make



R/3742/8 334 R.2015

provision for prompt reporting of archaeological material, the institution of temporary exclusion zones around areas of possible archaeological interest, prompt archaeological advice and, if necessary, for archaeological inspection of important features prior to further dredging in the vicinity.

19.126 The Protocol will also provide for the reporting of archaeological discoveries to the English

Heritage and the Hampshire and Isle of Wight Sites and Monuments Records. It will comply with the Merchant Shipping Act 1995, including the requirement for notifying the Receiver of Wreck of recoveries, and accord with the JNAPC Code of Practice for Seabed Developers.

Monitoring

19.127 Measures for monitoring of the effectiveness of and reporting on the mitigation measures will

be detailed in the WSI.

Conclusions 19.128 This assessment has identified a large number of geophysical anomalies, of which a subset is

within the footprint of the dredge (i.e. will be directly impacted), and some of which are likely to be of archaeological interest. A small number of known maritime sites and the potential for the presence of submerged prehistoric sites have also been identified. The proposed mitigation aims to offset impact to the known sites and to further investigate the areas of highest likely archaeological potential. Thus, the overall impact of the Southampton Approach Channel Dredge upon archaeological remains, after mitigation, is assessed to be low.

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