23 Offshore and Inter-Tidal Archaeology

23 OFFSHORE AND INTER-TIDAL ARCHAEOLOGY

23.1 Scope of the Assessment

23.1.1 This section of the Environmental Appraisal provides an assessment of the potential impacts to submerged and inter-tidal archaeology during the construction and operational phases of the Hinkley C development. 23.1.2 Figure 23.1 shows the location of the development area and the wider study area considered in this report. 23.1.3 The geographical extent of the development area includes:

 the location of intake/outfall tunnel heads; and  the proposed jetty site located at the western edge of . 23.1.4 Both areas are contained within the box ‘Development Area’ in Figure 23.1. 23.1.5 A detailed description of the proposed development is provided in Volume 2 Chapter 2.

23.2 Objectives of the Assessment

23.2.1 The objectives of the assessment are:

 to identify all known heritage assets within the study area boundary below the Mean High Water Mark (MHWM);  to assess the potential for submerged and buried archaeological remains and their likely level of preservation;  to assess the likely extent of previous impacts on the heritage resource;  to assess the potential impact of the proposed development on the heritage resource; and  to recommend mitigation strategies aimed at reducing the impacts of the proposed development, if necessary.

23.3 Legislation, Policy and Guidance

23.3.1 The proposal site is located within West District. 23.3.2 Aspects of International, European and UK legislation, planning policy and guidance of relevance to the site are presented below. 23.3.3 Other relevant UK legislation, planning policy and guidance of relevance to the historic environment are outlined in Volume 2 Chapter 22. a) United Nations Convention on the Law of the Sea (UNCLOS) 23.3.4 UNCLOS became recognised as international law in 1982 and was ratified by the UK on 25 July 1997. Article 303(1) states that:

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“States have the duty to protect objects of an archaeological and historical nature found at sea and shall cooperate for this purpose.” b) Heritage (Revised) The Valetta Convention, (1992) 23.3.5 The Convention defines archaeological heritage as comprising “all remains and objects and any other traces of mankind from past epochs”. This is said to include “structures, constructions, groups of buildings, developed sites, moveable objects, monuments of other kinds as well as their context, whether situated on land or under water.” 23.3.6 This convention binds the UK to implement protective measures regarding the archaeological heritage within its jurisdiction. In particular, Article 1, which addresses inventorying and protection of sites and Article 2, which requires the mandatory reporting of chance finds and providing for “archaeological reserves” on land or underwater. c) The Protection of Wrecks Act (1973) 23.3.7 Under section one of the Protection of Wrecks Act (1973), wrecks and wreckage of historical, artistic and archaeological importance can be protected via designation. Once a wreck/area is designated it is an offence to carry out certain activities (e.g. survey or excavation) unless a licence is obtained. d) Merchant Shipping Act (1995) 23.3.8 This Act establishes the procedures for determining ownership of flotsam, jetsam, derelict and lagan found in, or on the shores of, the sea or any tidal water. If any such material is encountered and recovered it must be reported to the Receiver of Wreck. e) Protection of Military Remains Act (1986) 23.3.9 This Act automatically protects aircraft that have crashed as a part of military service. The Ministry of Defence may also choose to protect any vessel lost during military service. f) ’s Coastal Heritage: a statement on the management of coastal archaeology 23.3.10 This document sets out principles for the management of coastal archaeology. It promotes the adoption of terrestrial standards to the sub-tidal area and a commitment to in situ preservation of material where possible. g) Planning Policy Guidance Note 20, Coastal Planning (1992) 23.3.11 PPG20 covers the character of the coast, its heritage areas, other designated areas and policies for their conservation.

23.4 Methodology

h) Assessment 23.4.1 The approach adopted for this assessment has been designed to comply with the requirements of the EIA Directive, relevant UK Regulations and various guidance documents detailed in Volume 1 Chapters 3 and 5, in particular, the Guidelines for Environmental Impact Assessment. 23.4.2 The assessment, and all supporting surveys have been conducted in accordance with standards and guidance issued by the Institute for Archaeologists (IfA, formerly Institute of Field Archaeologists), and English Heritage (EH). These bodies have set standards and guidance for all phases of archaeological assessment.

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23.4.3 There is, as yet, no standard or guidance published by the IfA or EH specifically relating to EIAs for the historic environment. In the absence of this, guidance on assessing the effects of roads schemes on the historic environment, given in the Design Manual for Roads and Bridges (DMRB) (Ref. 23.1), has been adapted as appropriate to inform the preparation of this chapter. 23.4.4 Assessment of the importance of heritage assets is based upon existing designations, the potential to contribute to the aims of the South West Archaeological Research Framework (Ref. 23.2), the Marine and Maritime Research Framework and the criteria described in Table 23.1, which is based on DMRB (Ref. 23.1). Table 23.1: Criteria Used to Determine the Importance of Heritage Assets

Importance Description

High Ancient monuments scheduled under the Ancient Monuments and Archaeological Areas Act 1979, or archaeological sites and remains of comparable quality, assessed with reference to the Secretary of State’s non-statutory criteria, referred to in PPS5. Sites protected under the Protection of Wrecks Act 1973. Wreckage covered by the Protection of Military Remains Act 1986. Well preserved sites or features not previously detected but considered to be of high importance with reference to relevant research frameworks.

Medium Archaeological sites and remains which, while not of national importance, fulfil several of the Secretary of State’s criteria and are important remains in a regional context.

Low Archaeological sites and remains that are of low potential or minor importance.

Very Low Areas in which investigative techniques have produced negative or minimal evidence for archaeological remains, or where previous large-scale disturbance or removal of deposits can be demonstrated.

Unknown Areas that may contain potential for significant archaeological remains.

23.4.5 The magnitude of impact has been based on the consequences that the proposed development will have upon the heritage resource and has been considered in terms of high, medium and low as shown in Table 23.2 (adapted from DMRB).

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Table 23.2: Criteria Used to Determine the Magnitude of Impact

Magnitude Impact

High Complete removal of an archaeological site. Severe transformation of the setting or context of an archaeological monument or significant loss of key components in a monument group.

Medium Removal of a major part of an archaeological site’s area and loss of research potential. Partial transformation of the setting or context of an archaeological site or partial loss of key components in a monument group. Introduction of significant noise, vibration levels or scour to an archaeological monument leading to changes to amenity use, accessibility or appreciation of an archaeological site. Diminished capacity for understanding or appreciation (context) of an archaeological site.

Low Removal of an archaeological site where a minor part of its total area is removed, but that the site retains a significant future research potential. Minor change to the setting of an archaeological monument.

Very Low No significant physical impact or change. No significant change in setting or context. No impact from changes in use, amenity or access.

i) Sources of Information 23.4.6 Heritage assets were identified through analysis and, where appropriate, modelling of the data sets shown in Figure 23.2. Baseline data used in this assessment was collected between 2008 and 2010. j) Consultation 23.4.7 Consultation has been undertaken with appropriate Statutory Bodies, comprising Somerset County Council and English Heritage. 23.4.8 Meetings were held with the English Heritage Marine Planner and the Regional Scientific Advisor for the South West Region to discuss all stages of the assessment. k) Limitations and assumptions 23.4.9 Detailed designs and construction methodologies for the proposed jetty and the intake/outfall tunnels are still being developed. 23.4.10 Potential impacts have been assessed using the data available at this time and will be revised once the detailed designs are finalised. 23.4.11 Details of dredging requirements are being finalised. Assessment of dredging impacts will be included in the ES to accompany the Development Consent Order (DCO) submission. 23.4.12 Impacts to the settings of heritage assets have not been considered in this assessment. These are considered in Volume 22, Chapter 22.

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23.5 Baseline Environmental Characteristics

a) Geological Background and Marine Environment 23.5.1 The study area lies on the Somerset coast, incorporating the southern and western edges of Bay, and comprising part of the Outer . 23.5.2 The inner and Severn Estuary area is floored by a folded and faulted succession of Carboniferous to Lower Jurassic limestones, mudstones and siltstones (Ref. 23.3). 23.5.3 This part of the Bristol Channel/Severn Estuary system is severely depleted in unconsolidated sediment, with large areas of the seafloor consisting of exposed bedrock (Ref. 23.4). 23.5.4 Within both the intertidal zone and the sub-tidal zone the bedrock can be capped by unconsolidated, muds, sands and gravels of Holocene age. 23.5.5 Inland from along the course of the , the area is characterised as alluvial deposits of the (Ref. 23.5). 23.5.6 This whole area represents a large estuary that developed following the last Glacial Maximum (c. 18,000 BP). It has subsequently been in filled in response to fluctuating sea levels leaving a record of intercalated muds, sands and peats (principally defined in the area as the Wentlooge Formation). 23.5.7 The upper and lower components of the Somerset Levels formation are comprised of marine silts, sands and clays. These relate to periods of marine transgression, first around the time of postglacial sea level rise in the Mesolithic, and then again around the Bronze Age - Iron Age transition. 23.5.8 The middle Formation consists of freshwater and saltwater peat interspersed with alluvium and relates to a period of high inter-tidal and supra-tidal marsh and bog formation running from the late Mesolithic through to the late Bronze Age (Ref. 23.6). 23.5.9 Geographical variations within these peat deposits around the inter-tidal area are due to the influence of local geomorphologic factors. Further inland the middle formation of the levels consists of a single peat bed (Ref. 23.7 and Ref. 23.8). 23.5.10 Inland, this peat deposit began forming around 5,000 BC and was inundated after 2,000 BC (Ref. 23.4). Land reclamation during the Roman period drained inundated areas, before a second period of inundation occurred during the fourth century AD, possibly due to the silting up and erosion of the Roman drainage and land reclamation works (Ref. 23.5). 23.5.11 A third period of flooding took place during the late Medieval period, with the levels becoming completely inundated by up to 3.5 m of water during the flood of 1607. 23.5.12 Work at the Walpole landfill has produced the best understood stratigraphic sequence for sediment deposition within the Parrett Valley (Ref. 23.9). 23.5.13 The earliest dated peat deposits are dated to 7,000-7,900 cal BC, and come from Burnham-on- Sea at the mouth of the Parrett (Ref. 23.10). Younger peat beds, 4-5,000 cal BC, are recorded at Burnham, Stolford and Down (ibid. 43). 23.5.14 These peat deposits below the current high water mark, along with the submerged forest off the Stolford coast, indicate the fluctuations in shoreline position that have taken place during the Holocene. 23.5.15 Bridgwater Bay is notable for its large tidal range between 13.9m and 14.6m and extensive stretching up to 4 kilometres wide.

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23.5.16 The mudflats accrete during periods of calm weather, especially in summer when helped by algal binding (ibid. 8). This forms a blanket or drape of fine sediment over the underlying consolidated Holocene clay pavement. During storm events this surface blanket is eroded away and the fossil clays exposed and they are themselves weathered (Ref. 23.11). 23.5.17 The developmental configuration of the mouth off the Parrett, with its islands and sandbanks, has changed considerably through time (Ref. 23.12, 23.13, 23.14, 23.15, and 23.16). 23.5.18 Between Hinkley Point and the Parrett, Holocene deposits are mostly overlain by storm shingle ridges whilst sand beaches with dune formations stretch northwards from the Parrett up to . b) Geology Offshore of Hinkley Point 23.5.19 The underlying geology of Hinkley Point is Blue Lias overlain by brown silty clay. Blue Lias is formed by a sequence of limestone and shale/mudstone laid down in the late Triassic and early Jurassic between 195 and 200 million years ago (mya). 23.5.20 At Hinkley Point, tidal action has eroded the softer mudstone to leave wide rock platforms of harder Jurassic Limestone extending out from the cliff lines up to 500m offshore. A shingle beach is present at the foot of the cliff, with the main component consisting of eroded limestone and sandstone pebbles (Ref. 23.17). 23.5.21 Continuing offshore, beyond the limestone bedrock platforms the bottom is a thick layer of estuarine sediments, comprising sandy mud and mud. Within this are areas of sandy gravel that form patches, along with outcroppings of underlying bedrock. This Jurassic bedrock is incised with a series of erosion channels that may be tributaries to the palaeo-Severn (Ref. 23.18). 23.5.22 The relatively raised position of Hinkley Point compared to the lower lying ground to the east, combined with the solid nature of the limestone cliffs, has ensured that changes in coastline throughout the late Holocene have had minimal impact upon the immediate area of the present power station. c) Lithological and Stratigraphic Modelling of Deposits 23.5.23 In Winter 2009, 23 boreholes and 64 vibrocores were recovered offshore from Hinkley Point. Data from core logs were entered into the geotechnical utilities package Rockworks 15 in order to carry out lithological and stratigraphic modelling of deposits. 23.5.24 The sequence revealed by the boreholes was relatively consistent across the survey area; c. 1-3 m of surficial sands, gravels or clays, overlying a more consistent clay layer (0.5 - 5 m thick) before reaching claystone bedrock. 23.5.25 The discovery of peat deposits underlying the uppermost superficial deposits in 39 out of 63 vibrocores and organic rich clays in a further six, confirms the widespread presence of buried peats, first identified in the western part of the survey area by EMU (Ref. 23.18 drawing J.1.02.1330.0818). 23.5.26 A relatively straightforward stratigraphic sequence can be reconstructed from the core logs:

1) Upper sands, silts, gravels and clay.

2) Upper Peats and Upper Organic clays.

3) Thin veneers of sands, silts, gravels and clay.

4) Very thin intercalated peats (not always present).

5) Mid sands, silts, gravels and clay.

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6) Basal Peat.

7) Lower sands, gravels, silts and clay.

8) Lower Clay.

9) Claystone/Limestone Bedrock.

23.5.27 Figure 23.3 shows a stratigraphic cross section moving offshore from Hinkley Point. Within the stratigraphic model, the shallowly shelving nature of the relict peat land surface is clear. Figures 23.4 and 23.5 show the full model with stratigraphic layers being sequentially removed. 23.5.28 It would appear that the peat occurrences relate to extensive, largely intact, yet thin, palaeo- landsurface deposits. 23.5.29 In 35 out of the 39 occurrences of peat only a single layer is observed. The remaining four provide evidence of multiple peat horizons in the following sequence; a basal peat deposit overlain by sands or clays, very thin intercalated peats, sand or gravel, before a final upper peat. This is redolent of sequences described for the local terrestrial record. 23.5.30 The basal peat deposit sits between -15mOD and -12mOD, which indicates a date in the range of 7-8,000 cal. BP, when compared to Long et al’s RSL curve (Ref. 23.4). However, this should only be considered a rough estimate as neo-tectonic factors may well have changed the altitude of deposits. d) Archaeological and Historical Background 23.5.31 The heritage resource along shorelines, estuary river banks and within and below the tidal zone falls into three broad categories:

 sites exposed above MHWM;  submerged terrestrially deposited archaeology; and  wrecks.

23.5.32 A foreshore survey (undertaken in June 2010) confirmed that there are no surviving archaeological remains above MHWM (Ref. 23.34). 23.5.33 No confirmed submerged archaeological remains have been identified from the assessment of the survey data (Figure 23.2), although a potential wreck site has been noted (25.5.36, below). Basal peat layers, with the potential to address research questions relating to the terrestrial heritage resource have been identified and are described above. i) Wrecks 23.5.34 The Hydrographic Office (UKHO) wreck record for the study area contains 14 sites, all of which are classified as ‘live’. These are listed in Figure 23.6. 23.5.35 No protected wrecks were identified in the development area. 23.5.36 One wreck site (ID 67535), located c. 750m east of the area of proposed works, relates to a ‘diffuser’ associated with the Hinkley Point power station. 23.5.37 One potential wreck (ID 1), identified from sidescan anomalies (Ref. 23.18), lies 116m northwest of the edge of the area designated for construction work Figure 23.5. This is shown in Figure 23.7. 23.5.38 It is not possible to offer a definitive interpretation of the type of wreck or wreckage that this feature represents.

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23.5.39 Further assessment will be undertaken when construction and installation methodologies have been finalised. e) Period Summaries 23.5.40 The period summaries below, summarised from the DBA (Ref. 23.35), provide the broader context for the Hinkley Point study area to determine archaeological potential below the MHWM. 23.5.41 Throughout the Quaternary (1,806 mya – present) fluctuations in relative sea-level have repeatedly transformed Britain from a peninsula into an island, and vice versa. 23.5.42 Thus, parts of the now submerged study area have variously been close to ice margins, submerged under proglacial lakes, or exposed as dry land in the past. 23.5.43 When considering the potential of the heritage resource, it is essential to carefully account for the submerged, terrestrially deposited, record. This allows for an assessment of the probability of encountering evidence for early hominin activity offshore. f) Palaeolithic (c.700,000 - 10,000BC) 23.5.44 The earliest evidence for hominin activity in the British Isles is currently dated to c.700,000 BP (Ref. 23.19). At no point in the past did ice sheets fully cover the entire study area. However, Bridgwater Bay and any associated Lower Palaeolithic deposits prior to 480,000 BP are likely to have been reworked by the impact of Anglian glacial activity. 23.5.45 There are no recorded Palaeolithic remains in the study area. However, recent work highlighted the potential for primary context, or minimally moved material, to be recovered from fluvial gravels in areas which have previously been considered of ‘very low potential’ for Palaeolithic archaeology (Ref. 23.20). g) Mesolithic (10,000- c.4,000 BC) 23.5.46 Sea level changes between 7,000 BC and 5,000 BC affected the upper Severn estuary, with marine transgression drowning the coastal woodlands and low lying landscape (Ref. 23.6). This is identifiable as a sequence of clay and sand deposits, interspersed with peat and forest remains (Ref. 23.21). 23.5.47 These depositional sequences are indicative of a landscape changing between saltwater estuary, reed beds and a drier bog forming environment within which Mesolithic populations existed and adapted (Ref. 23.13). 23.5.48 The flats, comprising deep deposits of alluvium and freshwater peat, and the Stolford Submarine Forest, are closely associated with a small amount of Mesolithic archaeological material. 23.5.49 Mesolithic flint scatters are recorded to the west of Hinkley Point and also to the south of Stolford. Portions of the off shore peat deposits and submerged forest date to the late Mesolithic. h) Neolithic (c. 4,000- 2,000BC) 23.5.50 During the early Neolithic extensive coastal organic peat deposits were formed and preserved beneath the silty clays of subsequent mid-holocene flooding events. These peat deposits and the environmental information contained with them are given a high priority for archaeological investigation (Ref. 23.6, 23.10, 23.22).

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i) Bronze Age (2,000 to 700BC) 23.5.51 The offshore peat deposits may date to the Bronze Age. These deposits are an important source of information regarding the changing local environment, and the impact upon and subsequent responses of coastal people. 23.5.52 A large amount of Bronze Age material, including partial remains of Bronze Age boats, has been recorded within the inter-tidal area along the Welsh side of the Severn Estuary (Ref. 23.32). This spatial bias reflects intensive surveys on the Gwent Levels (Ref. 23.6). Similar remains could be expected within deposits of this date on the English side of the estuary. 23.5.53 Remains, probably from Bronze Age wreck sites, have been located off Moor Sands and Langdon Bay on the south Devon coast (Ref. 23.23, 23.24, 23.25). This points to the very low background potential for ephemeral, secondary context, prehistoric material. j) Iron Age (700BC-AD43) 23.5.54 Marine transgression during the Iron Age means that much of the low lying study area was flooded saltmarsh (Ref. 23.4). Occupation was located on raised ground associated with outcrops of underlying geology (Ref. 23.5). The local area contains three large hillforts, one at Cannington to the south, Brent Knoll behind Burnham-on-sea, and at Brean Down to the north. 23.5.55 An Iron Age log boat was recovered from the Somerset levels at Shapwick. k) Roman (AD43-450) 23.5.56 There is extensive evidence for Roman occupation of the site and surrounding study area. Two possible Romano-British farmsteads have been identified on the site of the proposed Hinkley Point C (see Volume 2, Chapter 22). 23.5.57 A thin accumulation of intercalated sands and muds at the western margin of the Bridgwater Bay is believed to have been deposited, below wave base, in response to human management of the adjacent Somerset Levels since the Roman period (Ref. 23.4). l) Early medieval (450-1066 AD) 23.5.58 Bridgwater Bay, especially the Steart Point mudflats, contains a large number of wooden stake fish weirs, some of which have been dated by dendrochronology to the end of the Early medieval period (Ref. 23.26). m) Medieval (1066 - 1540AD) 23.5.59 Fish weirs continued to be used on the inter-tidal mudflats during the medieval period (Ref. 23.27). n) Post-medieval (1540-1899 AD) 23.5.60 Water meadows were constructed in low lying areas to increase the productivity of pasture land. This was coupled with the increased use of fertilizers from the later 16th Century onwards. This had an increasing effect on the local area as coal was imported from Wales in order to fuel the lime kilns necessary for fertilizer production. 23.5.61 Lime kilns dot the coastline. The remains of a lime kiln, and a possible coal landing points at Burton Quay are located to the east of the Hinkley Point C site (Volume 2, Chapter 22). 23.5.62 The Severn estuary became a major shipping channel as trade with Europe, and later the New World flourished. 23.5.63 Ten wrecks dating from this period are recorded within Bridgwater Bay; Auckland, Edward, Endeavour, Favourite, Friends, Frances & Mary, Hope, Halcyon, Merioneth and Molly.

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o) Modern (1900-present day) 23.5.64 The twentieth century saw a change in landscape use and substantial appropriation of the area for military and energy generation purposes. 23.5.65 Large offshore areas at Hinkley Point and Stolford are used by the military. A number of magnetic anomalies were identified across the wider survey area through analysis of bathymetric and side scan sonar data. These are likely to relate to buried ferrous material, or potential unexploded ordnance. 23.5.66 Thirteen aircraft crash sites are located within the area of Bridgwater Bay. The majority consist of military target aircraft from the offshore firing range. 23.5.67 One of the wreck remains just offshore at Hinkley Point relates to the nuclear plant’s outfall diffuser (see above). 23.5.68 Five modern wrecks are recorded in the wider Hinkley area on the mud banks of Bridgwater Bay; Providence, Diana, Borderdene and two unidentified craft. 23.5.69 Steart Flats is the last site in England where Mudhorse fishing is practiced. Some of the linear wooden staked features recorded on the flats relate to this continued practice (Ref. 23.27). p) Previous Impacts 23.5.70 Previous impacts include dredging for shellfish (trawl marks visible on side-scan sonar), military use of the area and borehole/vibrocore surveys carried out for this project.

23.6 Assessment of Impacts during Construction

23.6.1 This section describes the impacts on the offshore heritage resource that will arise as a result of activities during the construction of the inlet/outlet tunnel heads and the proposed jetty. 23.6.2 Details of construction methods had not been finalised at the time of this assessment. A full assessment of impacts to the offshore heritage resource will be included in the ES to accompany the DCO submission. a) Potential Construction Phase Impacts 23.6.3 Work offshore of Hinkley Point will see the construction of two intake tunnels drilled through bedrock, with three intake/outfall pipes, protruding from the surface. Construction of the tunnels will not impact directly on deposits of interest. However, it is likely that construction of the intake/outfall heads will impact on the basal peat and associated deposit. 23.6.4 The basal peat deposit is tentatively dated to 7-8,000 cal. BP. It has the potential to illuminate the nature of Holocene environmental change, and people’s relationship to it. As such, it is of high importance. 23.6.5 Impacts arising from construction are currently uncertain. It is likely that a minor part of the basal peat will be lost. This would constitute a low magnitude of impact on an asset of high importance, resulting in an overall impact of moderate adverse significance. 23.6.6 There are a number of known wrecks within Bridgwater Bay. None of these are located within the area proposed for construction. There is the potential for more wrecks to remain buried by the area’s changing sediment regime (Ref. 23.28).

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23.6.7 The potential wreck site (ID 1) is located in close proximity to the boundary of the area designated for the north western outfall pipe. Potential impacts arising from construction are uncertain. b) Mitigation Measures during Construction 23.6.8 Mitigation of impacts has been discussed with English Heritage. 23.6.9 It has been agreed that the most appropriate form of mitigation would comprise additional analysis and research to gain increased knowledge of the buried surfaces offshore of Hinkley Point. 23.6.10 Analysis will focus on deposits contained within the stored cores derived from the recent offshore geotechnical site investigations for the cooling water works and the jetty. 23.6.11 Given the uncertainty of survival of palaeo-environmental proxies, a phased investigative approach is proposed. 23.6.12 A more detailed assessment of the cores will be undertaken. A small selection (determined after consultation with English Heritage Regional Scientific Advisor) will be sampled for radiocarbon dating, macrofossil and pollen analysis in advance of the DCO submission. 23.6.13 Based upon the results of this report more extensive sampling of retained cores may be required to generate detailed Holocene palaeo-environmental and palaeo-geographic models. 23.6.14 The buried peat horizons below the soft sediments offshore of Hinkley Point power station are believed to be a relict Mesolithic landscape. The peat deposits may contain paleo- environmental data such as pollen, macrofossil, insect remains and radiocarbon datable organics. These could be used to reconstruct the local Mesolithic environment and produce a high resolution record of local change (SWARF research aim 18a). 23.6.15 This would allow comparison against a large body of existing work from the Somerset Levels (Ref. 23.29), more recent summary by Straker et al (Ref. 23.10), sequences from Portlock Bay (Ref. 23.30) and Burnham-on Sea (Ref. 23.31). 23.6.16 The archaeological potential of offshore deposits is recognised and targeted within SWARF research aims 23c and 23d10. The Rapid Coastal Zone Assessment has also highlighted the need to target peat deposits and submerged land surfaces in order to obtain this information (Ref. 23.6). 23.6.17 The investigation of change is prioritised by SWARF research aim 1610, specifically the desire to investigate key transitions between the Mesolithic and Neolithic, and the effects of sea level change upon populations and their subsequent relationships with the sea and coastal landscape. 23.6.18 These themes are also noted to be of key research significance within the Maritime and Marine Research Frameworks for the Mesolithic, Neolithic and Early Bronze Age (Ref. 23.32 and 23.22). 23.6.19 Appropriate protocols for investigation and recording of suspected archaeological artefacts recovered during the construction phase, will be agreed with English Heritage prior to the DCO submission. 23.6.20 The establishment of a 50 m exclusion zone around the potential wreck site (ID1) is considered an appropriate means of mitigating impact during construction.

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c) Residual Impacts during Construction Phase 23.6.21 Table 23.3 presents a summary of the potential impacts to the offshore and intertidal heritage resource during the construction phase. The table presents potential impacts, proposed mitigation and the subsequent residual impacts. Table 23.3: Construction Phase Impacts

Site Importance Potential Magnitude Significanc Proposed Residual Description Impact of Impact e of Impact Mitigation Impact (prior to mitigation)

Basal peat High Minor loss Low Moderate Analysis to Minor deposits of research Adverse address Adverse potential National through and construction Regional activities Research Aims

Potential Uncertain Uncertain Uncertain Uncertain 50 m None Wreck site exclusion (ID 1) zone around potential wreck site

Archaeologi Uncertain Uncertain Uncertain Uncertain Protocols to Uncertain cal artefacts be agreed within the with EH construction area

23.7 Assessment of Impacts during Operation

a) Potential Operational Phase Impacts 23.7.1 Details of the operation of the intake and outfall pipes and jetty have yet to be confirmed. As such, operational impacts to the heritage resource cannot be fully assessed at this time. Therefore they are uncertain. 23.7.2 However, the report submitted by BEEMS (Ref. 23.33) suggests that outfall structures will be positioned furthest offshore and will potentially create scour pits c. 2.2m in depth while the intake structures located close to shore will scour to a depth of 0.6m, extending down to 2m in silty areas. 23.7.3 Once an exact location has been determined for these structures it will be possible to predict the potential impact of this depth of scour on the heritage resource more accurately. 23.7.4 The site of geophysical anomaly ID 1, an object of roughly similar dimensions to the outfall structures (c. 12m wide by 4m high for ID 1 as opposed to 9.4m wide and 5m high for the outfall structures), has caused an east-west scour footprint of c. 100m and a north-south scour of 48m.

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23.7.5 As such, a similar footprint can be suggested for northerly proposed construction areas. Precise coordinates for the structures will be required to assess potential impact on geophysical anomaly ID 1, although at present it would appear unlikely that the scour pits of the two objects would merge. 23.7.6 The scour assessment for the jetty suggests that depths of up to 1.3m will be reached around piles. 23.7.7 Given that clay with rootlets was recorded at 1.13m below the seabed surface in one of the vibrocores (VCJ15), it is possible that there will be low level impact on this strata. However, it should be noted that in all other cores organic rich components occur beyond the depth of anticipated scour. b) Mitigation Measures during Operation 23.7.8 The mitigation measures for the operational impacts on the offshore heritage assets are the same as those identified for the construction phase. c) Residual Impacts during Operational Phase 23.7.9 The residual impacts for the operational phase on the heritage assets are the same as those identified for the construction phase and are included in Table 23.3.

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References

23.1 Highways Agency (2007). ’Design Manual for Roads and Bridges (DMRB), Volume 11: Environmental Assessment, Section 3, Part 2, Cultural Heritage’. 23.2 Webster, C.J. (ed.) (2008). ‘The Archaeology of : South West Archaeological Research Framework Resource Assessment and Research Agenda’. 23.3 Evans, C.D.R., The geology and superficial sediments of the inner Bristol Channel and Severn estuary, in . 1982, Thomas Telford: London. p. 25-42. 23.4 Long, A.J., et al., The Holocene and recent evolution of Bridgwater Bay and the Somerset Levels, in Unpublished Report to North Devon & Somerset Shoreline Management Group, West Somerset District Council. 2002, University of Durham Environment Research Centre: Durham. 23.5 Rippon, S., The Severn Estuary: Landscape Evolution and Wetland Reclamation. 1997, London: Leicester University Press. 23.6 Mullin, D., R. Brunning, and A. Chadwick, Severn Estuary Rapid Coastal Zone Assessment. 2009, English Heritage. 23.7 Kidson, C. and A. Heyworth, 1976. The Quaternary Deposits of the Somerset Levels. Quaternary Journal of Engineering Geology, 1976. 9: p. 217-235. 23.8 Haslett, S.K., et al., Holocene stratigraphy of the northern coastal plain of the Somerset Levels. Proceedings of the Cotteswold Naturalists Field Club, 2001. XLII(1): p. 78-88. 23.9 Holinrake, C. and N. Holinrake, Parrett Banks Strategy Study, Linden Farm to Rose Cottage, Archaeological Investigation. Unpublished report No: 275. 2002, Held under HER file PRN 29303. 23.10 Webster, C.J., ed. The Archaeology of South West England: South West Archaeological Research Framework Resource Assessment and Research Agenda. 2009, Somerset County Council. 23.11 Kirby, R., Distinguishing accretion from erosion-dominated muddy coasts. 2000, UNESCO (Scientific Committee for Ocean Research) Working Group 106 p. 1061-1077. 23.12 Carr, A.P., Coastal Changes at Bridgwater Bay: 1956-64. . Proceedings of the Bristol Naturalists Society, 1971. 31: p. 91-100. 23.13 McDonnell, R., Preliminary archaeological assessment of Bridgwater bay: gore sands and Steart flats. Archaeology in the Severn Estuary, 1993. 4: p. 41-46. 23.14 McDonnell, R., Bridgwater Bay: a summary of its geomorphology, tidal characteristics and inter- tidal cultural resource. Archaeology in the Severn Estuary, 1995. 5: p. 87-114. 23.15 McDonnell, R., Island evolution in Bridgwater bay and the Parrett Estuary: an historical geography. Archaeology in the Severn Estuary, 1996. 6: p. 71-84.

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23.16 Hartland Point to Brean Down: Summary of Existing Knowledge of Coastal Trends and Stability. Report to North Devon, Somerset and South Avon Coastal Group. 1996, Ravensrodd Consultants Ltd. 23.17 Kidson, C., The Shingle complexes of Bridgwater Bay. Transactions and Papers (Institute of British Geographers), 1960. 28: p. 75-87. 23.18 Simmons, N., Offshore investigations for Hinkley Site. 2009, EMU. 23.19 Parfitt, S.A., et al., The earliest record of human activity in northern Europe. Nature, 2005. 438: p. 1008 – 1012. 23.20 Hosfield, R.T., et al., The Palaeolithic Rivers of South-West Britain. English Heritage Project Report (Project No. 3847). 2007. 23.21 Heyworth, A., Submerged Forests, in Aberystwyth. 1985, The University of Wales. 23.22 Sturt, F. and R. Van-de-Noort, The Neolithic and Early Bronze Age; Draft resource assessment for the Marine and Maritime Research Framework. 2010. 23.23 Muckelroy, K., Two Bronze Age cargoes in British waters. Antiquity, 1980. 54: p. 100-109. 23.24 Muckelroy, K., Middle Bronze Age trade bettween Britain and Europe. Proceedings of the Prehistoric Society, 1981. 47: p. 275-297. 23.25 Needham, S. and C. Gardino, from Sicily to Salcombe: a mediterranean Bronze Age object from British coastal waters. Antiquity, 2008. 82: p. 60-72. 23.26 Groves, C., C. Locatell, and N. Nayling, Tree Ring Analysis of Oak Samples from Stert Flats Fish Weirs, Bridgwater Bay. 2004, English Heritage Centre for Archaeology Report: London. 23.27 Brunning, R., A Millennium of fishing structures in Steart Flats. Archaeology in the Severn Estuary, 2008. 18: p. 67-83. 23.28 Merritt, O., D. Parham, and D.M. McElvogue, Enhancing our understanding of the marine historic environment: Navigational Hazards project. 2007, Bournemouth University. 23.29 Coles, J.M., The Somerset Levels Project 1973-89. Somerset Levels Papers, 1989. 15: p. 5-13. 23.30 Jennings, S., et al., The role of relative sea-level rise and changing sediment supply on Holocene gravel barrier development: the example of Porlock, Somerset, UK. The Holocene, 1998. 8(2): p. 165-181. 23.31 Druce, D., Late Mesolithic and Early Neolithic Environmental Change in the Central Somerset Levels: Recent Work at Burnham-on-Sea. Archaeology in the Severn Estuary, 1999. 9: p. 17-30. 23.32 Bell, M. and G. Warren, The Mesolithic: Draft resource assessment for the Marine and Maritime Research Framework 2010. 23.33 BEEMS, Hinkley Jetty Scour Assessment. 2010. 23.34 Chadwick, A, Hinkley Point Foreshore Survey, Gloucester CC Archaeology Service 2010 23.35 Sturt F and Dix JK, Intertidal and Offshore Archaeology at Hinkley Point 2010

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