Triton Knoll Offshore Wind Farm Limited

TRITON KNOLL ELECTRICAL SYSTEM

Environmental Statement

Volume 2

Chapter 2: Marine Physical Environment

April 2015, Revision A Document Reference: 6.2.2.2 Pursuant to: APFP Reg. 5(2)(a) Triton Knoll Offshore Wind Farm Ltd Triton Knoll Electrical System Environmental Statement - Volume 2

Copyright © 2015 Triton Knoll Offshore Wind Farm Triton Knoll Offshore Wind Farm Limited Limited All pre-existing rights reserved. Triton Knoll Electrical System

Environmental Statement Liability In preparation of this document Triton Knoll Offshore Wind Farm Limited (TKOWFL), a joint venture between RWE Volume 2: Chapter 2 – Marine Physical Environment Innogy UK (RWE) and Statkraft UK, subconsultants working on behalf of TKOWFL, have made reasonable efforts to April 2015 ensure that the content is accurate, up to date and complete for the purpose for which it was prepared. Neither TKOWFL nor their subcontractors make any warranty as to the accuracy or completeness of material supplied. Other than any liability on TKOWFL or their subcontractors detailed in Drafted By: ABPmer the contracts between the parties for this work neither TKOWFL or their subcontractors shall have any liability for Approved By: Kim Gauld-Clark any loss, damage, injury, claim, expense, cost or other consequence arising as a result of use or reliance upon any Date of Approval March 2015 information contained in or omitted from this document. Any persons intending to use this document should satisfy Revision A themselves as to its applicability for their intended purpose. Where appropriate, the user of this document has the obligation to employ safe working practices for any activities Triton Knoll Offshore Wind Farm Ltd referred to and to adopt specific practices appropriate to Auckland House local conditions. Great Western Way Triton Knoll Offshore Wind Farm Limited have been awarded Swindon EU TEN-E funding to support the development of the Triton Wiltshire, SN5 8ZT Knoll Offshore Wind Farm Electrical System located in both UK Territorial waters and the UK’s Exclusive Economic Zone. T +44 (0)845 720 090 The funding which is to be matched will support a number of F +44 (0)845 720 050 surveys, engineering reports, and environmental impact I www.rweinnogy.com assessment studies for the Triton Knoll Electrical System. The studies will form part of the formal documentation that will accompany the Development Consent Order which will www.rweinnogy.com/tritonknoll be submitted to the Planning Inspectorate. The sum of €1,159,559 has been granted and the process to reclaim this tritonknoll@rwe.com

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Table of Contents 2 Marine Physical Environment ...... 2-1 Introduction ...... 2-1 Statutory and policy context ...... 2-1 Consultation and scoping ...... 2-4 Scope and methodology ...... 2-10 Existing environment ...... 2-13 Key parameters for assessment ...... 2-19 Environmental assessment: construction phase ...... 2-21 Environmental assessment: operational phase ...... 2-34 Environmental assessment: decommissioning phase ...... 2-36 Environmental assessment: cumulative effects ...... 2-36 Inter-relationships ...... 2-43 Mitigation...... 2-43 Transboundary statement ...... 2-43 Summary of effects ...... 2-43 References ...... 2-45

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2 Marine Physical Environment Regulation 5(2)(l) in relation to the effects of the proposed development that is the subject of the DCO application on statutory and non-statutory sites and features of Introduction nature conservation, habitats of protected species, important habitats or other diversity features. 2.1 This chapter of the Environmental Statement (ES) presents an assessment of the 2.7 The following sections of this chapter include: potential impacts upon the marine physical environment arising from the construction, operation and decommissioning of the offshore components of the proposed Triton • A summary of relevant legislation and planning policy; Knoll Electrical System development, as defined in Volume 2; Chapter 1; Offshore • A description of the methodology for the assessment, including details of the Project Description. The chapter also provides an assessment of the cumulative study area and the approach to the assessment of effects; effects from other developments in the area. • A summary of consultation with stakeholders; 2.2 The proposed offshore development area includes the Triton Knoll Offshore Wind • A review of baseline (existing) conditions; Farm (TKOWF) array area as well as the export cable route corridor (‘the corridor’) beyond the array boundary, up to and including the intertidal zone at Anderby Creek • Details of the measures proposed as part of the project to avoid or reduce (Figure 2-1). For the purposes of the numerical plume model two indicative cable environmental effects, including mitigation and design measures that form part of trenches (route 1 north and route 2 south) are shown in the figure. the project; 2.3 In order to assess the potential effects relative to the baseline (existing) coastal • An assessment of the likely effects for the construction, operation and environment, a combination of analytical assessments of project-specific data, decommissioning phases of the project, taking into account the measures consideration of the existing evidence base, empirical evaluation and detailed proposed; numerical modelling has been used to establish the potential magnitude and • Identification of any further mitigation measures or monitoring required in relation significance of the predicted changes. to likely significant effects; and 2.4 Consideration of the likely changes to the marine physical environment has been • Assessment of any cumulative effects with other proposed developments. made, adopting a number of conservative assumptions based around the ‘worst case’ characteristics of the development. Subsequent impacts upon a series of identified Statutory and policy context marine physical environment receptors have been determined. These receptors include designated seabed/ intertidal areas, the coast and non-designated banks 2.8 The assessment of potential impacts upon marine physical processes has been made (Table 2-10). with specific reference to the relevant National Policy Statements (NPS) and Marine Plans. Those relevant to the project for which development consent is required are: 2.5 The assessment of change to aspects of the marine physical environment are also of relevance to other environmental receptors which are described in the following • Overarching NPS for Energy (EN-1) (July 2011); sections of Volume 2 of the Triton Knoll Electrical System Environmental Statement, • NPS for Renewable Energy Infrastructure (EN-3) (July 2011); and notably: • East Inshore and East Offshore Marine Plans’ (MMO, 2014). • Intertidal and Subtidal Ecology (Chapter 4); 2.9 In undertaking the assessment, the following relevant legislation has been considered: • Fish and Shellfish (Chapter 5); • The Marine and Coastal Access Act (2009); • Commercial fisheries (Chapter 8); and • European Union (EU) Council Directive 92/43/EEC on the conservation of natural • Marine and Coastal Archaeology (Chapter 11). habitats and of wild flora and fauna (the ‘Habitats Directive’); 2.6 The For the purposes of the Infrastructure Planning (Applications: Prescribed Forms • The Offshore Marine Conservation (Natural Habitats, &c.) Regulations 2007 and Procedure) Regulations 2009, Figures 6-1 et seq taken together with this chapter which implement the Habitats Directive and the Birds Directive (Directive (and those matters referred to in Volume 2 Chapter 7), fulfil the requirements of

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2009/147/EC) in relation to marine areas where the UK has jurisdiction beyond Policy Key provisions Section where comment addressed territorial waters (broadly 12 nautical miles to 200 nautical miles); • The Conservation of Habitats and Species Regulations 2010 which implement the coast; the Habitats Directive and the Birds Directive in relation to England and Wales as • The implications of the proposed far as the limit of territorial waters (usually 12 nautical miles) project on strategies for managing 2.10 The planning process for Nationally Significant Infrastructure Projects (NSIPs) is now the coast as set out in Shoreline administered by the Planning Inspectorate (PINS) with the decision on the Management Plans (SMPs)…any Development Consent Order (DCO) being taken by the Secretary of State (SoS). NPS relevant Marine Plans…and capital EN-3 highlights a number of points to be taken into account in that decision making programmes for maintaining flood process (paragraphs 2.6.68 to 2.6.71 and 2.6.75 to 2.6.77); The relevance of the and coastal defences; National Policy Statements with regards to marine physical processes and how these • The effects of the proposed project have been addressed within this assessment are presented in Table 2-1 and Table 2- on marine ecology, biodiversity 2. NPS EN-3 highlights a number of points relating to the judgement of an application and protected sites; and in relation to mitigation; these are summarised in Table 2-3. • The effects of the proposed project on maintaining coastal recreation sites and features; and Table 2-1: Summary of NPS EN-1 & EN-3 policy relevant to physical processes and consideration of the Triton Knoll Electrical System assessment • The vulnerability of the proposed development to coastal change, Policy Key provisions Section where comment addressed taking account of climate change, during the project’s operational life Where relevant, applicants should and any decommissioning period. undertake coastal geomorphological Predictions of the physical impacts that and sediment transfer modelling to The applicant should be particularly NPS EN-1 will result from construction and predict and understand impacts and careful to identify any effects of (Para 5.5.6) operation of the project are presented help identify relevant mitigating or physical changes on the integrity and in paragraph 2.73 to 2.176. compensatory measures (paragraph special features of Marine 5.5.6) Conservation Zones (MCZs), Designated nature conservation areas The ES should include an assessment NPS EN-1 candidate marine Special Areas of have been identified within the list of of the effects on the coast. In (Para 5.5.9) Conservation (cSACs), coastal SACs marine physical environment receptors particular, applicants should assess: and candidate coastal SACs, coastal presented in paragraph 2.61 to 2.68. Special Protection Areas (SPAs) and • The impact of the proposed project potential Sites of Community on coastal processes and Predictions of the physical impacts that Importance (SCIs) and Sites of Special geomorphology, including by will occur at the coast from Scientific Interest (SSSI) NPS EN-1 Potential changes in climate are taking account of potential impacts construction and operation of the NPS EN-1 The resilience of the project to climate (Para 5.5.7) described in Annex 2-1 and are from climate change. If the project are presented in paragraph (Section 4.8) change (such as increased considered alongside predicted effects development will have an impact 2.73 to 2.176. storminess) should be assessed in the described in paragraph 2.73 to 2.176. ES accompanying an application. on coastal processes the applicant

must demonstrate how the impacts In particular, this policy has been

will be managed to minimise considered with regard to potential sea

adverse impacts on other parts of level rise at the landfall (paragraph

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Policy Key provisions Section where comment addressed Policy Key provisions Section where comment addressed

2.122 to 2.133). legs and anchors;

• Increased suspended sediment loads during construction; and • An assessment of the effects of Predicted rates at which the installing cable across the intertidal subtidal zone might recover from zone should include information, where temporary effects. relevant, about: Consideration has been given to Assessment should be undertaken for • potential impacts and associated Any alternative landfall sites that NPS EN-3 all stages of the lifespan of the effects during construction (paragraph have been considered by the (Para proposed wind farm in accordance with 2.73 to 2.150), operation (paragraph applicant during the design phase 2.6.190) the appropriate policy for offshore wind 2.151 to 2.176) and decommissioning and an explanation for the final farm EIAs. Predictions of the physical impacts that (paragraph 2.177 to 2.177). choice; will result from construction and The assessment should include predictions of the physical effect that • Any alternative cable installation operation of the Project are presented Predictions of the physical impacts that NPS EN-3 will result from the construction and methods that have been in paragraph 2.73 to 2.176. will result from construction and (Para operation of the required infrastructure considered by the applicant during operation of the project are presented Details regarding alternative landfall 2.6.194) and include effects such as the NPS EN-3 in paragraph 2.73 to 2.176. the design phase and an sites that have been considered during scouring that may result from the (Para 2.6.81) explanation for the final choice; the design phase and an explanation proposed development. for the final choice is provided in • Potential loss of habitat; Volume 1, Chapter 4 Site Selection • Disturbance during cable and Alternatives. installation and removal (decommissioning); • Increased suspended sediment loads in the intertidal zone during installation; and • Predicted rates at which the intertidal zone might recover from temporary effects. Where necessary, assessment of the effects on the subtidal environment should include: Predictions of the physical impacts that NPS EN-3 • Environmental appraisal of inter- will result from construction and (Para array and cable routes and operation of the Project are presented 2.6.113) installation methods; in paragraph 2.73 to 2.176. • Habitat disturbance from construction vessels’ extendible

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Table 2-2: East Marine Plan Policies of relevance to physical processes 2.11 Other key guidance which is of relevance to the assessment includes: • 'Guidelines for Environmental Impact Assessment' (Institute of Environmental Policy Key provisions Section where comment addressed Management and Assessment (IEMA), 2004); East Inshore Cumulative impacts affecting the • and East ecosystem of the East marine plans 'Coastal Process Modelling for Offshore Wind Farm Environmental Impact Cumulative effects are considered Offshore and adjacent areas (marine, terrestrial) Assessment' (ABPmer and HR Wallingford, 2009) (for COWRIE); within paragraphs 2.161 to 2.218. Marine Plans should be addressed in decision- • 'Review of Cabling Techniques and Environmental Effects applicable to the – ECO1 making and plan implementation. Offshore Wind farm Industry' (BERR, 2008); Any impacts on the overall marine East Inshore protected area (MPA) network must be • 'General advice on assessing potential impacts of and mitigation for human and East taken account of in strategic level Potential effects to designated areas of activities on Marine Conservation Zone (MCZ) features, using existing regulation Offshore measures and assessments, with due seabed are described within paragraph and legislation' (JNCC and Natural England, 2011); Marine Plans regard given to any current agreed 2.73 to 2.176. – MPA1 advice on an ecologically coherent • 'Guidelines for data acquisition to support marine environmental assessments of network. offshore renewable energy projects' (CEFAS, 2011); • 'Dynamics of scour pits and scour protection - Synthesis report and Table 2-3: Summary of NPS EN-3 guidance on PINS decision making with regard to recommendations. (Sed02)' (HR Wallingford et al., 2007); physical processes and consideration in the Triton Knoll Electrical System assessment. • 'Further review of sediment monitoring data (ScourSed-09)' (ABPmer et al., Summary of NPS EN-3 guidance Triton Knoll Electrical System assessment 2010); The direct effects on the physical • 'Potential effects of offshore wind developments on coastal processes' (ABPmer environment can have indirect effects on a The predicted physical effects have been and METOC, 2002); number of other receptors. Where indirect considered in relation to indirect effects on effects are predicted, the IPC should refer to • 'Review of Round 1 Sediment process monitoring data - lessons learnt. (Sed01)' other receptors elsewhere in this ES. relevant sections of this NPS and EN (ABPmer et al., 2007); (paragraph 2.6.195 of NPS EN-3). • 'Advice Note Seven: Environmental Impact Assessment, screening and scoping' The project has proposed designs and The methods of construction, including use installation methods that seek to minimise (The Planning Inspectorate, 2012a); of materials should be such as to reasonably significant adverse effects on the physical minimise the potential for impact on the • 'Advice Note Nine: Using the Rochdale Envelope' (The Planning Inspectorate, environment. Where necessary, the physical environment (paragraph 2.6.196 of 2012b); assessment has set out mitigation to avoid or NPS EN-3). reduce significant adverse effects. • 'Advice Note Twelve: Development with significant transboundary impacts Mitigation measures which the IPC should consultation' (The Planning Inspectorate, 2012c); and expect the applicants to have considered include the burying of cables to a necessary The built-in mitigation relating to cable burial • 'Subsea Power Cables in Shallow Water Renewable Energy Applications'. (DNV, depth and using scour protection techniques and scour are set out in the Project Description 2014). around offshore structures to prevent scour chapter (Volume 2, Chapter 1) of this ES. effects around them. Applicants should Statutory consultees were consulted on the Consultation and scoping consult the statutory consultees on need for and design of any additional mitigation appropriate mitigation (paragraph 2.6.192 of 2.12 As part of the EIA process (both for the TKOWF array and Triton Knoll Electrical NPS EN-3). System), a number of consultations were undertaken with various statutory and non- statutory authorities. A formal scoping opinion (PINS 2014) was sought from the

Planning Inspectorate following submission of the scoping report (RWE, 2014), with

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consultation on the Preliminary Environmental Information (RWE, Sept 2014) undertaken under s42 and s47 of the Planning Act. 2.13 Ongoing consultation has taken place through the development of the Triton Knoll Electrical System EIA Evidence Plan (Evidence Plan) within which agreement has been sought as to the suitability of available evidence, assessment methodologies, and forthcoming guidance where appropriate. Details of the Evidence Plan process are contained in (Application Document 8.16). 2.14 Formal consultation with statutory and non-statutory consultees under Section 42 of the Planning Act 2008, and with community under Section 47 of the Planning Act, on the Preliminary Environmental Information (PEI) took place between 15 October and 19 November 2014. Consultation responses and responses received through the development of the EIA Evidence Plan have been important in informing this Environmental Statement and in the development of the technical supporting annexes. Responses received during consultation on the PEI have been reviewed and analysed to: • Help make sure TKOWFL has properly considered all the potential impacts of the proposal; and • Consider and take account, where appropriate, of feedback and responses received as TKOWFL progresses the proposal towards application submission. 2.15 Further details on consultation are provided in the Consultation Report (Application Document 5.1) with specific details of consultation on site selection and alternatives given in Vol 1, Chapter 4 Site Selection and Alternatives. Responses relating to the physical environment are addressed throughout this chapter. Table 2-4 provides a summary of key points raised, and describes how they have been addressed. This includes consultation responses received as part of the application for the TKOWF, where relevant.

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Table 2-4: Summary of consultation relating to the marine physical environment Date and consultation phase/ Consultation and key issues raised Section where comment addressed type

Triton Knoll Offshore Wind Farm Array Consultation (2010) September, 2010 ….surveys are all relevant and up to date. Previous data cannot be relied upon. Great Details regarding the data used to characterise the environment can be care should be taken to ensure the assessment is undertaken against a consistent found in paragraph 2.50 to 2.51. (IPC/ MMO scoping opinion) baseline. September, 2010 IPC draws attention to the potential impacts on the coast and foreshore which should be Potential impacts at the coast are identified within paragraph 2.121 to (IPC/ MMO scoping opinion) assessed. 2.133. September, 2010 Cross-reference should be made to the coastal processes section of the ES and the The transport of sediment along the coast has been considered within (IPC/ MMO scoping opinion) consideration of sediment transport. paragraph 2.151 to 2.164.

The transportation of fine grained sediment associated with construction related sediment plumes is considered in paragraph 2.73 to 2.105. September, 2010 Potential impact of the proposed development on the proposed SAC (Inner Dowsing, Race Bank and North Ridge). Potential effects on the Inner Dowsing, Race Bank and North Ridge SCI (IPC/ MMO September, 2010 are considered within paragraph 2.147 to 2.150 and 2.159 to 2.176. September, 2010 ….scour and its associated impacts around export cable …. that have the potential to Scour effects have been considered within paragraph 2.165 to 2.176. become uncovered due to changes in seabed morphology should be fully explored in (IPC/ MMO September, 2010 the ES. September, 2010 … evidence of sediment type that the route traverses. A summary of the surface (and near surface) sediment regime is provided in paragraph 2.40 to 2.60. Further details are contained within (IPC/ MMO scoping opinion) Annex 2-1. September, 2010 An assessment of the predicted levels of suspended sediment concentrations (SSC) An assessment considered potential changes in SSC and associated associated with the export cable route works are required along with an assessment of changes in bed level is provided within paragraph 2.73 to 2.105. (IPC/ MMO scoping opinion) the predicted sediment plume characteristics.

Triton Knoll Electrical System Consultation (2014) April, 2014 It is essential that the potential impacts of all the remedial measures are assessed in the A worst case assessment for the potential impacts of cable protection ES. The MMO advises that an assessment of the quantity and type of cable protection on the marine physical environment has been presented in paragraph (scoping opinion, MMO) that may be required along the export cable routes be provided within the ES. Potential 2.151 to 2.164. impacts on sediment transport and beach profiles should be considered and given in the context of the type (rock protection / mattressing etc.) and positioning of any potential cable protection. April, 2014 … given the dynamic nature of the environment, monitoring is required to verify that Proposed mitigation is set out in paragraph 2.212. buried cables do not become exposed, or even free-spanning. Exposed or free- (scoping opinion, MMO) spanning cables can pose a navigational and safety hazard to other sea users. Further monitoring or mitigation may be required for this potential risk and the MMO will advise what mitigation it considers appropriate once we have reviewed the assessment. April, 2014 The quality standards and assurance methods should be detailed in the individual Where survey reports are included within the PEI appropriate QS/QA survey reports and also included in the documentation submitted for the application detail is provided. (scoping opinion, MMO) process.

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Date and consultation phase/ Consultation and key issues raised Section where comment addressed type May, 2014 Impacts on geology below the maximum burial depth of the cable: N/A

(scoping opinion, Secretary of The Secretary of State (SoS) agrees this can be scoped out from further assessment as State) there is no pathway for impact and on the assumption the assessment will be undertaken in line with the burial depth parameters of the draft DCO.

May, 2014 Elevations in suspended sediment levels in the water column: Elevations in suspended sediment concentrations (SSC) have been considered within paragraph 2.73 to 2.105. (scoping opinion, Secretary of The SoS considers that this information is important for the assessment of impacts on State) receptors including benthic ecology, fish species and impacts on nature conservation sites and as such this information should be presented in the ES. The SoS also refers to and agrees with MMOs comments … which identifies the need for an assessment of the predicted levels of suspended sediment concentration and sediment plume characteristics. The SoS notes jetting is considered to represent the worst case scenario and as such the assessment should be undertaken on this basis. May, 2014 Alteration of bathymetry due to indentations in the seabed from vessel legs and vessel The potential alteration of the bathymetry due to indentations in the anchors: seabed from vessel legs and vessel anchors has been considered as (scoping opinion, Secretary of part of the construction phase in paragraph 2.134 to 2.150. and Volume State) The SoS does not agree this can be scoped out from further assessment on the basis 1: Chapter 11 Nature Conservation. The assessment is limited to the the cable route passes through the Inner Dowsing, Race Bank and North Ridge SCI and construction phase as the operational impacts are considered to be less as the construction vessels to be employed have not yet been determined. severe. May, 2014 Alteration of bathymetry due to the introduction of cable protection: Potential changes to hydrodynamic, wave and sediment transport processes has been considered in paragraph 2.151 to 2.164. and (scoping opinion, Secretary of The SoS notes that elevation of the seabed would be approximately 1m where cable Volume 1: Chapter 13 Shipping and Navigation State) protection is required, however does not agree this can be scoped out from further assessment given that the extent of cable protection has not been defined in the scoping report and as no information has been provided on the potential effects to the surrounding areas. May, 2014 Remobilisation of contaminated sediments: N/A

(scoping opinion, Secretary of The scoping report states that the available evidence on contamination along the cable State) route is sparse, but the likelihood of finding high levels of contamination is considered low given that the sediments are coarse and there is an absence of historic waste disposal sites in proximity to the scoping boundary. The SoS agrees that this can be scoped out from further assessment in the EIA. May, 2014 Operational impacts on geology: N/A

(scoping opinion, Secretary of The SoS agrees that any maintenance works would be local and temporary and that this State) can be scoped out from further assessment. May, 2014 Operational impacts on the tidal regime: Potential changes to hydrodynamic, wave and sediment transport processes have been considered in paragraph 2.151 to 2.164. (scoping opinion, Secretary of The SoS does not agree this can be scoped out from further assessment given that the State) extent of cable protection has not been defined in the scoping report.

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Date and consultation phase/ Consultation and key issues raised Section where comment addressed type May, 2014 The SoS does agree that any impacts are likely to be localised and as such cumulative N/A (scoping opinion, Secretary of impacts during operation can be scoped out from further assessment. State) May, 2014 Operational cumulative and inter-relationship impacts: Potential cumulative impacts due to the presence of the cable and other infrastructure are considered in paragraphs 2.219 to 2.227. (scoping opinion, Secretary of Paragraph 6.5.24 of the scoping report states that potential changes in suspended State) sediment concentrations associated with cable scour will be negligible although earlier states that scour will be assessed in the EIA (paragraph 6.5.17). As such the SoS does not agree this can be scoped out from further assessment. However, the SoS does agree that any impacts are likely to be localised and as such cumulative impacts during operation can be scoped out from further assessment. June 2014 Discussion regarding the scope of issues to be assessed within the marine physical The release of lubricant into the water through HDD operations (or other environment chapter. Request to assess the release of lubricant into the water through trenchless techniques) has been considered in paragraph 2.117 to (CEFAS, MMO, NE) HDD operations. Also request to assess potential alteration of the bathymetry due to 2.120. indentations in the seabed from vessel legs and vessel anchors. The potential alteration of the bathymetry due to indentations in the seabed from vessel legs and vessel anchors has been considered in paragraph 2.134 to 2.150. November, 2014 Request for further details regarding the potential impacts on the designated features of Potential impacts to the designated features of the Inner Dowsing, Race the Inner Dowsing, Race Bank and North Ridge Site of Community Importance (SCI) Bank and North Ridge SCI arising from changes in patterns of sediment (NE Section 42 response) arising from an interruption of sediment transport. This should include discussion transport have been considered within paragraph 2.151 to 2.164 and regarding potential in-combination effects arising from interaction with LID and LINCS paragraph 2.219 to 2.227. OWFs. November, 2014 Reference should be made to Sabellaria spinulosa reefs when evaluating whether there Potential impacts to Sabellaria spinulosa reefs are considered in detail may be any significant effects on Annex 1 habitats associated with the SCI due to within Volume 1, Chapter 8 Subtidal and Intertidal Ecology. However, (NE Section 42 response) changes in physical processes. some brief discussion is also provided within paragraph 2.151 to 2.164.

November, 2014 Further details regarding potential use of cable protection measures (e.g. extent and Potential impacts arising from the use of protection devices are location) as well as any possible impacts: considered within paragraph 2.151 to 2.164. (NE/ MMO Section 42 response) It is stated that the maximum area of cable protection would be 261,189 m2. Details on how this figure was calculated should be included along with the maximum length of cable that may be protected. It would be helpful to include the percentage of predicted cable protection (as provided in the Commercial Fisheries Chapter) to give these figures some relative context.

Until we know which type of protection will be used and where it will be deployed along the route (eg where are the potentially problematic sandbanks and chalk areas that may lead to shallower cable burial?) it is not entirely possible in our view to fully assess whether the impacts will lead to effects on either the Inner Dowsing, Race Bank and North Ridge SCI or Saltfleetby-Theddlethorpe Dunes and Gibraltar point SAC, which may be affected by the placement of cable protection in the near shore area.

We would appreciate further discussion on the likelihood of needing cable protection at

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Date and consultation phase/ Consultation and key issues raised Section where comment addressed type these [chalk] points or when varying cable burial depths to incorporate other boulders. November, 2014 Further details required regarding the effects of decommissioning during cable removal. Decommissioning effects are described within paragraph 2.177 to 2.178. (NE Section 42 response) November, 2014 The impact of bed preparation for cable burial in areas of sand waves should also be The impact of jetting in areas characterised by the presence of assessed. sandwaves is provided within paragraph 2.73 to 2.105. (MMO Section 42 response) November, 2014 Given that the beach re-nourishment work is expected to cease in 2015 all options going Discussion of the shoreline management policy at the landfall is forwards over the lifetime of the project should be considered with EA, LPAs and NE as provided within paragraph 2.121 to 2.133. (NE Section 42 response) the cables may become exposed as an in-direct affect from change in management measures. February, 2015 …[NE’s] preference would be that sand waves are levelled sufficiently to ensure cables The impact of sandwave preparation is discussed in paragraphs 2.106 can be adequately buried and cable protection is only placed where it is absolutely to 2.116. (NE NLSER v.05) essential i.e at cable crossings.

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• Empirical evaluation; and • Scope and methodology Detailed numerical modelling. 2.22 Details regarding the extent of data available for the proposed development Study area environment are provided within the ‘Existing environment’ section (paragraph 2.40 to 2.16 The far-field extent of the study area across which impacts to the marine physical 2.68). This includes project specific geophysical, geotechnical, benthic and metocean environment have been considered is shown in Figure 2-1. This extent has been data along with other publically available datasets. defined using expert judgement, taking into consideration characteristics of the 2.23 Monitoring evidence compiled during the construction and operation of earlier offshore baseline physical environment (e.g. spring tidal excursion ellipse distances) as well as wind farm developments has been used in the assessment. Some of this information is understanding developed from similar infrastructure project assessments. contained within the COWRIE ScourSed-09 publication (ABPmer et al., 2010). 2.17 To aid description, the corridor has been sub-divided into four separate areas 2.24 Numerical modelling has been used to consider the dispersion of sediment plumes (Figure 2-1): associated with cable installation activities. An overview of the numerical models used • Nearshore Area (water depths less than ~ -5m LAT); to inform the assessment is provided later within this section (paragraph 2.29 to 2.3). • Inshore Area (water depths between ~ -5 and -10m LAT); 2.25 The assessment also considers likely naturally occurring variability in, or long-term changes to, physical processes within the project lifetime due to natural cycles and/or • Midshore Area (water depths between ~ -10 and -20m LAT); and climate change (e.g. sea level rise). This is important as it enables a reference • Offshore Area (water depths between ~ -33m LAT and -8m LAT). baseline level to be established against which the potentially modified physical processes can be compared, throughout the project lifecycle. Baseline conditions are 2.18 As previously stated in paragraph 2.2, the proposed offshore development area described in detail within Volume 4 Annex 2.1 and include for the potential effects of includes the TKOWF array area as well as the export cable corridor beyond the array climate change. The baseline description and supporting clarification notes on the boundary, up to and including the intertidal zone at Anderby Creek (Figure 2-1). numerical modelling and associated validation of the models has been agreed as Assessment approach appropriate within the EIA Evidence Plan Offshore Ecology Technical Review Panel (Application Document 8.16). 2.19 The assessment of effects on the marine physical environment has been considered in 2.26 The assessment has been undertaken in accordance with industry best practice, as terms of a source-pathway-receptor model whereby: previously described (paragraph 2.10). • The source is the initiator event; 2.27 The assessment of impacts on the marine physical environment has been considered • The pathway is the link between the source and the receptor impacted by the over two spatial scales. These are: effect (e.g. sediment transport processes); and • Far-field. Defined as the area surrounding the corridor over which remote effects • The receptors are the receiving entities as defined in paragraph 2.61. may occur; and 2.20 A receptor can only be exposed to change if a pathway exists through which an effect • Near-field. Defined as the footprint of the proposed development boundary. can be transmitted between the source activity and the receptor. 2.28 The far-field extent is shown in Figure 2-1. 2.21 In order to assess the potential effects upon the marine physical environment relative 2.29 In terms of temporal scales, the assessment has considered effects associated with to the existing (baseline) coastal environment, a combination of analytical methods the three main phases of development. These are: have been used. These include: • Construction (12 months during a 2 year construction phase); • Qualitative and quantitative assessments of data from the proposed development; • Operation and maintenance; and • Consideration of the existing evidence base; • Decommissioning (as for construction).

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2.35 The value and sensitivity of each receptor has been assessed using expert judgement and described with a standard semantic scale using the terms very low, low, medium, Numerical models high and very high. Definitions for each term are provided in Table 2-5. These expert Hydrodynamic model judgements regarding receptor sensitivity are closely guided by the conceptual understanding of regional-scale marine physical processes, developed during the 2.30 The prevailing baseline hydrodynamic conditions provide the mechanism for baseline characterisation process (Volume 4, Annex 2.1). transporting sediments released by cable installation and define the pathways for sediment movement. The hydrodynamic characteristics across the study area were Table 2-5: Sensitivity/ importance of the environment obtained from the validated models developed as part of the TKOWF array Receptor application. These models were built based on modules from the MIKE21FM suite in sensitivity/ Description/ reason order to resolve the key physical processes over a near-field (corridor) and far-field importance (regional) scale. Model set-up, calibration and validation involved the use of multiple No capacity to accommodate the proposed form of change; and/or field and model datasets, including bathymetric and metocean data from surveys receptor designated and / or of international level importance. Likely to Very high completed within the TKOWF site as well as metocean outputs from the Met Office be rare with minimal potential for substitution. May also be of very high and Admiralty tidal diamonds. These were used to calibrate and validate the water socioeconomic importance. levels and flows throughout the Wash region. Of particular note was the flow data from Very low capacity to accommodate the proposed form of change; three regional tidal diamonds, one of which was located in close proximity, and/or receptor designated and / or of national level importance. Likely High approximately 7km from the cable route. In a regional context this is close enough to to be rare with minimal potential for substitution. May also be of high lend confidence to the models for their application to the particle modelling. socioeconomic importance.

2.31 More detailed information on the hydrodynamic model properties can be found in the Moderate to low capacity to accommodate the proposed form of technical appendices of the TKOWF array DCO application (ABPmer, 2011). change; and/or receptor designated and / or of regional level Medium importance. Likely to be relatively rare. May also be of moderate Particle tracking model socioeconomic importance.

2.32 The particle tracking model was previously applied to the Greater Wash region based Moderate to high capacity to accommodate the proposed form of Low on outputs from the validated hydrodynamic model described above. The model change; and/or receptor not designated but of district level importance. provides a means by which to quantify changes in SSCs and bed level after transport by currents. High capacity to accommodate the proposed form of change; and/or Very low receptor not designated and only of local level importance. 2.33 As a result of the achieved validation (with the adjusted dispersion parameters) the model has been successfully used on many subsequent projects. An example includes 2.36 The magnitude of impact describes the extent or degree of change that is predicted to its application in ScourSed-09 (COWRIE, 2010), in which the model correctly predicted occur. It has been assessed using expert judgement and described with a standard the low SSCs and release from chalk drill arisings during the LINCS OWF construction semantic scale. Definitions for each term are provided in Table 2-6. These expert phase (Centrica, 2007). judgements regarding the magnitude of effect relative to baseline conditions have Identification and assessment of effects and mitigation measures been made by experienced marine physical process specialists and formed following consideration of a range of information sources including: 2.34 This assessment of effects upon marine physical environment receptors is a • Available survey data and supporting reports/ publications described in the systematic process that is determined by taking into account the ‘sensitivity and value baseline (Volume 4 Annex 2.1 ); of the receptor and the ‘magnitude of the impact. These assessment criteria are described in more detail within this section. • The existing evidence base from other offshore wind farms and similar projects; and

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• Detailed numerical modelling outputs. Table 2-7: Significance of potential effects

Table 2-6: Magnitude of impact Magnitude of impact

Magnitude Definition Very High High Medium Low Very Low Permanent changes across the near- and far-field to key characteristics Very high or features of the particular environmental aspect’s character or distinctiveness.

Very High Major Major Moderate Minor Minor Permanent changes, over large parts of the near- and far-field, to key High characteristics or features of the particular environmental aspect’s character or distinctiveness.

High Major Moderate Minor Minor Negligible Noticeable, temporary (for part of the project duration) change, or barely discernible change for any length of time, encountered within the Medium near-field and parts of the far-field, to key characteristics or features of the particular environmental aspect’s character or distinctiveness.

Receptor sensitivity Receptor Medium Moderate Minor Minor Negligible Negligible Noticeable, temporary (for part of the project duration) change, or barely discernible change for any length of time, restricted to the near- Low field and immediately adjacent far-field areas, to key characteristics or features of the particular environmental aspect’s character or Low Minor Minor Negligible Negligible Negligible distinctiveness.

Very low Changes which are not discernible from background conditions. Very Low Minor Negligible Negligible Negligible Negligible

2.37 The significance of potential effects has been determined by taking into account the sensitivity and value of the receptor and the magnitude of the impact applying to Note: Red shaded cells are defined as significant impacts. construction, operation and decommissioning stages of the project (Table 2-7). 2.38 It is noted here that a distinction is made throughout the assessment between the magnitude, extent and duration of ‘impacts’ and the resulting significance of the ‘effects’ upon marine physical environment receptors. Various actions may result in impacts: for instance, the presence of cable protection causing scour. These impacts may have consequent effects upon receptors: for example, a localised and short-term alteration to the morphology of a designated area of seabed. 2.39 Mitigation is prescribed only to reduce ‘significant’ effects. Under EIA guidelines, ‘Moderate’ and Major’ effects are regarded as being significant (Table 2-7). Mitigation

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measures that were identified and adopted as part of the evolution of the project the southeast of the array where the spring tidal range is 4.5m and the neap tidal design (embedded into the project design) are described separately, in Table 2-11. range is 2.2m (Emu, 2009).

Uncertainty and technical difficulties encountered 2.44 Peak current speeds are greatest during the flood tide with velocities greater than 0.9 m/s experienced across almost the entire array. Peak ebb current velocities are 2.40 The main uncertainty encountered is associated with the assessment of sediment consistently less than this and are commonly between 0.6 and 0.8 m/s. Residual flow plumes and accompanying changes to bed levels. This arises due to uncertainty is spatially variable across the array although generally has a southeasterly regarding how the seabed geology will respond to jetting. The exact volume of material component in the eastern sector of the array and a southwesterly component in the entrained into the water column will be dependent upon a number of factors including western sector of the array (Emu, 2009). the type of cable installation equipment used and the mechanical properties of the 2.45 On the basis of the observational wave data collected from the array, the prevailing geological units. In the absence of detailed information, a series of potential release wave direction is from the north between 345 and 15° N. The largest waves also scenarios have been considered. Together, these scenarios capture the worst case originate from this sector although they become progressively smaller towards the impacts in terms of the highest concentration suspended sediment plumes, the most southeast of the array as they encounter shallower water (Emu, 2009). persistent suspended sediment plumes, the maximum changes in bed level elevation and the greatest spatial extent of change in bed level. 2.46 For the most part, the array is characterised by shallow gradients and reasonably even bathymetry with depths commonly between -15 and -20m LAT. However, two small Existing environment north to south trending trenches are present in the north of the array, each with water depths of around -30m LAT (Osiris, 2009). Several large morphological features are Overview located immediately outside of the array boundary. These are Silver Pit (to the west), 2.41 This section summarises the baseline environment of the TKOWF export cable Triton Knoll sandbank (to the southeast) and the Outer Dowsing Channel (to the east) corridor and array. Triton Knoll Electrical System. This includes the existing baseline 2.47 Analysis of both the seismic survey data collected from the array as well as nearby environment of the corridor is described in detail within Volume 4, Annex 2.1. A BGS borehole records suggests that the array is underlain by five principal technical report (ABPmer, 2011) and ES chapter (Volume 2: Chapter 2 – Physical stratigraphic units, all of which date to the Pleistocene period (~2,6 Ma to 11.5 ka BP). Processes) were produced for the area of the array as part of the applicant in for the In places, these deposits are in excess of 60m thick although the depth of sediment TKOWF. A review of the key findings from that study has been incorporated into the overlying the chalk bedrock is found to be spatially variable (Osiris, 2009). description of the existing environment presented here. These baseline investigations 2.48 These five stratigraphic units have been overlain by a thin (c.1-2m) veneer of describe both the present day existing environment and the future baseline which Holocene sediment. Existing British Geological Survey seabed sampling indicates the would exist in the absence of the project but with anticipated changes in climate taking dominance of gravels across the array although the higher density sampling place. undertaken during the benthic survey reveals a more spatially complex sediment 2.42 It is noted here that the baseline characteristics of the tidal regime (including residual distribution pattern with variability in the dominance of sandy gravel and gravelly sand flow) are of direct relevance to understanding the dispersion of fine grained sediments across the array (BGS, 1990; Osiris, 2009). Most (75%) of the benthic samples were released into the water column during the construction phase. This information is found to have a polymodal distribution and this poor sorting of material is indicative of important for the assessment of impacts on receptors including benthic ecology and low seabed sediment mobility. Drop-down video evidence suggests that in places this fish and shellfish species; see Triton Knoll Electrical System Preliminary gravel deposit may be armoured (i.e. the median grain sizes at the seabed are larger Environmental Information Volume 2; Chapters 4 and 5 respectively. than the median size of grain in the subsurface) (Osiris, 2009).

The array 2.49 The presence of low amplitude, long wave length bedforms along with megaripples identify areas of more active sediment transport and these types of bedforms indicate 2.43 The array is situated in a macro tidal location. The greatest tidal range is experienced that the most active bed areas are generally found in the southeast and east of the in the west of the array where there is a tidal range of approximately 4.8m on spring array. Tentative support for this assertion is provided from an analysis of historic tides and 2.3m on neap tides. Conversely, the smallest tidal range is encountered in charts spanning the past c.100 years with inter-survey comparison revealing localized,

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small-scale change in the positions of the bathymetric contours along both the 2.52 Additional information has also been obtained from other sources to complement that southeastern and eastern margins of the array. obtained from the geophysical, geotechnical, benthic and metocean surveys described 2.50 Information on sediment transport pathways across the array is limited. However, the above. This additional data acquisition has included: available literature suggests that along the southeastern margin of the array sand is • British Geological Survey (BGS) grab samples and vibrocore data; being transported in a northerly direction whilst in the eastern sector of the array, sand • Southern North Sea Sediment Transport Study (SNSSTS, 2002); is being transported to the northwest (Kenyon & Cooper, 2005; Tappin et al., 2011). These observations are in agreement with the orientation of bedform features detected • UKHO admiralty publications; by the high resolution bathymetric survey and suggest an approximate northwest to • Humber Regional Environmental Characterisation (Tappin et al., 2011); southeast axis for sediment transport. • Humber Marine Regional Environmental Assessment (MAREA) (HADA, 2012); The export cable corridor and • Environment Agency beach monitoring datasets. 2.51 In order to support the baseline characterisation and the subsequent impact assessment of the project, from installation through to decommissioning, a number of 2.53 The export cable route occupies a macro tidal setting with the spring tidal range site specific surveys have taken place over the export corridor and surrounding area. increasing towards the coast, away from an amphidrome situated to the northeast of These surveys are detailed in Table 2-8. the array, in the central North Sea (ABPmer et al., 2008). Tidal currents generally follow the orientation of the coastline and flow in a southerly direction during the flood Table 2-8: Recent geophysical and geotechnical surveys undertaken for the Triton Knoll tide and in a northerly direction during the ebb tide. Peak flow speeds are found to be Offshore Wind Farm export cable route in excess of 0.8 m/s and exceed 1.0 m/s in places (Triton Knoll ES Volume 2: Chapter 2 – Physical Processes). Type of survey Year of survey Location Survey methods 2.54 Water depths along the corridor are generally less than -20m LAT although reach a Single and multi-beam echo maximum depth of approximately -33m LAT in the Offshore Area (Gardline, 2009; Initial export cable route sounder, side scan sonar, Geophysical 2009 Osiris, 2013a). With the exception of the Nearshore and Inshore Areas, the shallowest and partial fan area. sub bottom profiler (boomer) water depths are encountered within the Cable Fan Area. Here water depths of and magnetometer. approximately -8m LAT are observed (Gardline, 2009; Osiris, 2013a). Seabed Single and multi-beam echo gradients are generally less than 5° although some localised slopes are reported by Proposed Triton Knoll sounder, side scan sonar, Osiris to be up to 25° in the Midshore Area; these slopes are associated with localised Geophysical 2012 export cable route and sub-bottom profiler (pinger seabed features (Gardline, 2009; Osiris, 2013a). partial fan area. and boomer) and magnetometer. 2.55 Sidescan sonar data and grab samples have been collected along the cable route and these show that the superficial sediments primarily comprise Holocene sands and Proposed Triton Knoll Cone Penetration Tests at gravels (Gardline, 2009; Osiris, 2013a). These sediments are often arranged into Geotechnical 2012 export cable route and 58 locations and vibrocores mobile bedforms and in places large (up to 7m high) sandwaves are found. Frequent fan area. at 18 locations. boulders measuring up to 0.5m are also encountered. This information on the surface and sub-surface geology is directly inputted to numerical models used to consider the characteristics of sediment plumes associated with the construction phase. Initial export cable route Grab sample Particle Size Benthic 2008,2010 2.56 Occasionally clay is found in grab samples and it is possible that this belongs to the and partial fan area. Analysis (PSA) data. underlying Bolders Bank Formation indicating locally thin Holocene cover (Tappin et al., 2011; Osiris, 2013a, b). Sediment mobility is likely to be variable along the cable route and be strongly influenced by variations in seabed substrate and bed morphology. However, given that sandwaves are frequently encountered, it would

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appear that in places the bed is highly mobile. This has important implications for 2.63 Those marine physical environment receptors located either within the near-field or cable burial depth and the extent to which alternative cable protection measures such within one spring tidal excursion of the proposed project have been included within the as rock armouring are required. assessment (Figure 2-2). This is because these areas could (in theory) be affected by 2.57 Maps depicting spatial and temporal variation in surface suspended particulate matter construction, operation and/or decommissioning impacts such as localised changes in (SPM) are available from Dolphin et al. (2011). These maps were compiled from flows and bed level as well as scour. several sources including research cruise databases, a numerical model and the 2.64 Additional receptors were also identified at the coast on the basis of their proximity to Moderate Resolution Imaging Spectroradiometer (MODIS) satellite database. On the the landfall. Indeed, an important consideration within the assessment is the extent to basis of this data, it is found that during winter months surface SPM concentrations are which cable installation activities at the landfall could interrupt longshore sediment typically around 10 mg/l in the Offshore Area of the cable corridor, increasing to ~60 transport. Accordingly, those designated sites within Coastal Sub-cell 2c ‘Donna Nook mg/l in the Inshore/ Nearshore Area. During summer months, SPM concentrations to Gibraltar Point’ (as defined by Motyka and Brampton (1993); see Figure 2-1 for along the corridor are typically in the range of 5 to 10 mg/l. These findings are location) are also included. consistent with the acoustic backscatter measurements of SSC collected during the 2.65 It is important to note that although waves, tides and associated sediment transport site-specific metocean survey. processes may be locally and/or temporally affected by the proposed development, 2.58 It is noted that throughout the year there is a strong east to west gradient in SPM, with these processes represent pathways as opposed to receptors. In terms of the marine the greatest concentrations observed at the coast in Inshore/ Nearshore Areas. physical environment, it is morphological features such as sandbanks and beaches 2.59 The Lincolnshire coastline south of the Humber Estuary is a highly sensitive stretch of which are defined here as the receptors. coast that has suffered from long-term erosion. To counter this erosion and fulfil the 2.66 The majority of receptors identified within Table 2-9 and Figure 2-2 are the 'Hold the Line' shoreline management plan, a major beach renourishment scheme internationally designated conservation sites located both along the Lincolnshire coast (known as 'Lincshore') is in place along the entire coast between Mablethorpe and and in the southern North Sea. Most of these locations are designated for the habitats Skegness (Scott Wilson, 2010). they support, rather than for their geological or geomorphological importance. 2.60 The coastal frontage at Anderby Creek (where the cable makes landfall) is However, the assessments of potential effects to nearby designated sites presented in characterised by the presence of a sandy beach backed by vegetated sand dunes. this chapter focuses upon the potential for significant modification of the naturally Wave exposure characteristics, the shape of the coastline and the offshore geology occurring physical processes that could indirectly impact the habitats they support. determine the sedimentary response of this coastline. The assessment of effects on other EIA topics will be informed by these results, but are reported in other chapters. 2.61 Beach levels along this coastline vary seasonally, with steeper waves during winter transporting sands offshore and less steep waves during summer returning sands to 2.67 The Midshore section of the export cable corridor crosses the Inner Dowsing, Race the beach. The extent of these seasonal as well as longer term (i.e. decadal) scale Bank and North Ridge SCI which is included on the list of physical environment receptors (Table 2-9). The presence of Annex I habitats (‘Sandbanks which are slightly changes is of relevance to determining appropriate design measures at the landfall. covered by sea water all the time’) are a primary reason for selection of this site. Water These include cable burial depth and set back distances for jointing bay infrastructure. depths are generally shallow within the SCI and are typically less than 30m below Marine physical environment receptors chart datum. The area encompasses a variety of highly active sandbank types (banks bordering channels, linear relict banks, sinusoidal banks with distinctive ‘comb-like’ 2.62 Key receptors identified in the study area are described in Table 2-9 and shown in subsidiary banks) and biogenic reef of the worm Sabellaria spinulosa (JNCC, 2015). Figure 2-2. These receptors have been identified on the basis of: The group of banks within the SCI are generally between 15 to 20km long, 1.5 to 3km • Professional judgement, local and regional specialist experience; wide and 7 to 12m high, with crest heights typically less than 5m LAT. The banks comprise fine to medium sands, predominantly originating from coastal erosional • The scoping opinions; processes occurring since the mid Holocene (Cooper et al., 2008). • Outcomes from the consultation process; and 2.68 Non-designated banks are also included in Table 2-9 as these may afford protection to • Reference to best practice guidance. the coast by dissipating wave energy. Triton Knoll Sandbank is also part of the wider

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(designated) Race Bank-North Ridge-Inner Dowsing bank system and is therefore included here. 2.69 During the consultation phase the issue of scour was raised (Table 2-4). Scour is a process which impacts upon the seabed. In those areas where the seabed is considered to be a receptor (e.g. it is designated), the effect significance has been assessed. Table 2-9: Receptors considered in the marine physical environment assessment

Receptor type Receptor designation Receptor name

Inner Dowsing, Race Bank and Offshore SCI North Ridge SAC Humber Estuary Saltfleetby to Theddlethorpe Dunes SAC and Gibraltar Point SAC The Wash and North Norfolk SPA Humber Estuary

SPA Gibraltar Point Designated seabed/ SPA The Wash intertidal areas SSSI Humber Estuary

SSSI Saltfleetby to Theddlethorpe Dunes

SSSI Chapel Point to Wolla Bank

SSSI Gibraltar Point

SSSI The Wash Non-designated N/A Triton Knoll Sandbank banks The coast (Far field area, as (Designated in places – see above) N/A identified in Figure 2-1)

2-16 0°10'0"E 0°20'0"E 0°30'0"E 0°40'0"E 0°50'0"E 1°0'0"E 310000 320000 330000 340000 350000 360000 370000

5940000 Legend: Proposed Development Boundary Triton Knoll OWF Array Boundary Triton Knoll Landfall Far-Field Extent Modelled Cable Route Silver Pit

53°30'0"N Sandwave Crest OS Foreshore 5930000 Donna Nook Inner Dowsing Offshore Wind Farm Cable Route 1 (North) Lincs Offshore Wind Farm Outer Dowsing Bank Lynn Offshore Wind Farm Offshore Race Bank Offshore Wind Farm Cable Fan Area Sheringham Shoal Offshore Protector Bank Wind Farm Lincs Cable Corridor 5920000 Cable Route 2 Triton Knoll Bank Race Bank Cable Corridor (South) Hornsea Export Cable Corridor Aggregates Application Aggregates Licence Mablethorpe Aggregates Option Disposal Site 53°20'0"N Midshore Notes:- This map contains data from the following sources- Osiris (2013) The Crown Estate (2014) Cefas (2014)

Coordinate System: WGS 1984 UTM Zone 31N

5910000 Projection: Transverse Mercator Datum: WGS 1984 Boygrift East Dudgeon Shoal Units: Meter North Ridge Bank

Nearshore

Inshore Inner Dowsing Anderby Creek Source: Global Land Cover Facility, www.landcover.org.

Race Bank Bathymetry (m LAT) <-30 -29.99 to -27.5 5900000 -27.49 to -25.0 00 06/03/2015 Second Draft AJB NKD ?? Ingoldmells -24.99 to -22.5 Rev Date Description Drn Chk App -22.49 to -20.0 Triton Knoll Electrical System -19.99 to -17.5 Docking Shoal Bank

53°10'0"N -17.49 to -15.0

-14.99 to -12.5 Skegness -12.49 to -10.0 TITLE: -9.99 to -7.5 Figure 2-1 Marine Physical Environment

5890000 -7.49 to -5.0 Study Area -4.99 to -2.5 0 3 6 -2.49 to 0.0 Kilometres / 0.99 to 2.5 Gibraltar Point SCALE: 1:200,000 @ A3 REV 00 Document Path:Y:\4105_Triton_Knoll_3\GIS\002ass_Fig2_1_Study_Area.mxd

© Crown copyright, All rights reserved. 2014 License No. EK001-20140601. Contains Ordnance Survey data © Crown copyright and database right 2014. Not to be used for navigation. 0°10'0"E 0°20'0"E 0°30'0"E 0°40'0"E 0°50'0"E 1°0'0"E 310000 320000 330000 340000 350000 360000 370000

5940000 Legend: Proposed Development Boundary Triton Knoll OWF Array Boundary Triton Knoll Landfall Offshore SCI SAC 53°30'0"N SPA

5930000 SSSI Humber Estuary SAC & SPA & SSSI Non-Designated Banks OS Foreshore Spring Tidal Excursion Ellipses 5920000 Saltfleetby-Theddlethorpe Dunes and Gibraltar Point SAC

Saltfleetby-Theddlethorpe Dunes SSSI 53°20'0"N

Notes:- This map contains data from the following sources- © Natural England and JNCC copyright [2014] ABPmer et al. (2008)

Coordinate System: WGS 1984 UTM Zone 31N

5910000 Projection: Transverse Mercator Datum: WGS 1984 Units: Meter

Inner Dowsing, Race Bank and North Ridge SCI

Source: Global Land Cover Facility, www.landcover.org.

Chapel Point to Wolla Bank 5900000

00 06/03/2015 Second Draft AJB NKD ??

Rev Date Description Drn Chk App

Triton Knoll Electrical System 53°10'0"N

Saltfleetby-Theddlethorpe Dunes and Gibraltar Point SAC TITLE: Figure 2-2 Gibraltar Point SPA & SSSI Marine Physical

5890000 Environment Receptors The Wash and North Norfolk Coast SAC 0 3 6 The Wash SPA & SSSI Kilometres / SCALE: 1:200,000 @ A3 REV 00 Document Path:Y:\4105_Triton_Knoll_3\GIS\002ass_Fig2_2_Receptors.mxd

© Crown copyright, All rights reserved. 2014 License No. EK001-20140601. Contains Ordnance Survey data © Crown copyright and database right 2014. Not to be used for navigation. Triton Knoll Offshore Wind Farm Ltd Triton Knoll Electrical System Environmental Statement - Volume 2

Key parameters for assessment Potential effect Maximum adverse scenario assessed Justification

2.70 This section identifies the maximum adverse scenario from the marine physical constituent particles. in the largest bed level environment, defined by the project design envelope (Volume 2, Chapter 1). The changes (albeit over a Trenching will be used to install the cable in small spatial extent). method adopted is in accordance with the requirements of the Rochdale Envelope areas where chalk is present. A conservative approach to environmental assessment as set out in the PINS Advice note nine: assumption has been made that this will result The longest export cable ‘Using the Rochdale Envelope’ (PINS, 2012b). In essence, the design envelope is a in 50% disaggregation of material into route has been considered series of projected maximum extents to the project for which the significant effects are constituent particles. since this provides the assessed. The detailed design of the project can then vary within this envelope greatest potential for without rendering the EIA inadequate. Thus, this approach also provides a Up to six export cables may be installed sediment plumes to arise. conservative method to understanding the potential worst case effects of the proposed although only two would be installed simultaneously. project. The offshore work will take ~<12 months to Design envelope assessed complete. However, there is potential for this work to be spread over a 2 year construction 2.71 The maximum adverse scenarios assessed for the marine physical environment are window. described in Table 2-10. It is noted that only variations in those design parameters detailed under each specific impact in Table 2-10 have the potential to influence the Sandwave crest level preparation significance of the effect described. Therefore, if a particular design parameter is not Where necessary, sandwave crests will be resulting in a temporarily swept aside to clear a 15m wide discussed, then any change to that parameter is considered not to have a material change in the The lowering of the path, for the width of the crest, to enable bearing on the outcome of the assessment. local sandwave crest by up to deeper cable burial and therefore reduce the hydrodynamic, 3m represents a localised likelihood of secondary protection being wave and lowering of the seabed. required. Sandwave crests may be lowered by Table 2-10: Design envelope scenario assessed sediment up to 3m in this process. transport Potential effect Maximum adverse scenario assessed Justification processes Release of Construction sediment and lubricant through Maximum length for the export cable of 66km. Jetting through The total volume of material released would be HDD operations. unconsolidated fine- approximately 44m3. (Other potential Cable burial to a depth of 1.5m below the grained material has the Based on a theoretical installation seabed surface in areas where chalk is absent potential to cause the most A total volume of ~0.5m3 of drilling mud may be maximum drill length of Elevations in techniques exit and 1.0m below the seabed in areas where persistent suspended released into the beach pit excavation for each 500 m, a maximum bore suspended above Mean chalk is present. sediment plumes and the HDD. diameter of 0.75m and sediment levels High Water greatest spatial extent of assuming that 20% of the and associated Springs and Cable trench width of 0.5m. effect in terms of any All released material will be contained and drill cuttings are small-scale therefore fall associated changes in bed removed on completion of the bore. discharged. changes in bed outside this Cable installation at a rate of 150m/hr. level. levels assessment of

Jetting will be used to install the cable in areas Installation of cables into offshore physical where chalk is absent. A conservative coarse grained and/or processes.) assumption has been made that this will result consolidated substrates in 100% disaggregation of material into has the potential to result

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Potential effect Maximum adverse scenario assessed Justification Potential effect Maximum adverse scenario assessed Justification Use of trenchless techniques to install cables The depth and extent of beneath the dunes/ sea defences, with a Introduction of scour will be limited in plough and/or back hoe dredger then used to scour due to the proportion to the diameter Up to six export circuits with voltage in the cut a trench into the beach and seabed across Cable trenching across the exposure of of the individual material range of 132 kV to 220 kV. Each circuit would Changes to Nearshore and Inshore Areas out to a depth of beach/ shallow subtidal export cables as used. Accordingly, the consist of one three-phase High Voltage beach -10m LAT. areas represents the well as the greatest diameter cable Alternating Current offshore export cable, morphology realistic worst case presence of and largest potential approximately 0.275m in diameter. resulting from The HDD option is the only technology that scenario as unlike HDD, it cable protection dimensions of cable installation of results in an exit pit either above or below could (in theory) result in measures protection have been the export cable MHWS (all other options exit above MHWS) interaction with considered in the at the landfall and intertidal works will be undertaken over a hydrodynamic, wave and assessment. longshore sediment period of weeks. Installation of a trench box & The potential impacts of maintenance activities include indentations in the seabed from vessel HDD punch out is estimated at 12 hours/cable. transport processes. legs and vessel anchors and increases in SSC due to remedial cable burial. However, Re-excavation of the trench box, trench down associated effects are anticipated to be no greater than those previously described during the beach & cable installation also estimated at 12 construction phase and so have not been considered further). hours/cable. The realistic worst case vessel footprint would For the purposes of assessment the worst case assumption with regards to remedial cable Alteration of the be caused by jack up barges with a maximum The greatest alterations to burial is 12 repair operations during the lifetime of the project. The combined total length of bathymetry due of 6 legs per barge (with total area of seabed the seabed would be cable lifted/replaced/reburied is 6km for the 12 repair operations. to indentations in disturbance for each leg of 4 m2). caused by the largest jack Decommissioning the seabed from up barge legs and vessel legs and The maximum vessel anchor dimensions are anchors. These have been (Potential effects are considered to be similar to or less than those assessed for the vessel anchors assumed to be 4.45 x 3.56m. considered within the construction phase) assessment.

Cumulative effects Operation Potential cumulative effects of the construction/operational phases and other offshore In general terms, the larger activities are also assessed in detail within section 2.179 et seq. Introduction of the cable protection (in The worst case scenario for the dimensions of rock armour terms of height from the the proposed cable protection is an elevation of and/or concrete bed), the greater the Embedded mitigation approximately 1.5m off the bed and a width of mattresses potential for interaction 11m. For general secondary protection away resulting in a with local hydrodynamic, 2.72 Mitigation measures that were identified and adopted as part of the evolution of the from pipeline asset crossings, the width of the change in the wave and sediment project design (embedded into the project design) and that are relevant to the marine cable protection would be 10m. local transport processes. As physical environment are listed in Table 2-11. General mitigation measures, which hydrodynamic, such, the greatest The maximum total area covered via would apply to all parts of the electrical transmission works, are set out first. Thereafter wave and diameter cable and largest secondary cable protection would be 61,200m2 mitigation measures that would apply specifically to marine physical environment sediment potential dimensions (in per cable/ 367,200m2 in total (six cables). See issues associated with the cable route are described separately. transport terms of height and width) Volume 2, Chapter 1; Table 1-4 for further processes of cable protection have details. 2.73 Full details of the mitigation referred to within this table and associated with this been considered in the chapter are set out within section 2.2 of the Mitigation Strategy (Document 8.15). assessment. That strategy also shows where this mitigation will be secured within any consent granted for the Electrical System.

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Table 2-11: Embedded mitigation relating to the marine physical environment concrete mattresses for cable protection will be investigated, based on (inter alia) the seabed current data at the location of Parameter Mitigation measures embedded into the project design interest and the assessed risk of impact damage.

General Environmental assessment: construction phase Careful routing of the offshore cable route to avoid areas of designated seabed. Elevations in suspended sediment levels and associated small-scale changes in bed levels

Of particular relevance to the assessment of effects to the marine Overview physical environment is the position of the landfall. This has been micro-sited to avoid the Chapel Point-Wolla Bank SSSI - a 2.74 The impact of cable burial operations mainly relates to a localised and temporary re- Project design nationally important geological site for its intertidal sediments, suspension of sediments (BERR, 2008), with the exact nature of this disturbance which record the evidence of early Holocene sea level change determined by the soil conditions along the cable route, the length of installed cable, (Natural England, 2014). the burial depth and burial method. 2.75 According to the source-pathway-receptor model: • Re-suspension of sediment whilst installing (burying) cables is considered as the source of potential changes to SSCs in the water column; Construction • Tidal currents initiate sediment mobility and act as the pathway for transporting The cable route has been selected to avoid sandwaves where the suspended sediment; and possible, and the cable route will be optimised further to avoid • The receptor is a feature potentially sensitive to any increase in suspended sandwave features. However where sandwaves are unavoidable, sediments and consequential deposition. temporarily lowering the sandwave crests, by up to 3m, by ploughing prior to trenching will increase burial depth through the 2.76 The main issues resulting from any increases in SSC relate to potential effect on sandwaves, minimising the potential for exposure and the pelagic species and marine mammals whilst those resulting from accumulations in requirement for external cable protection and disturbance. sediment and changes to sediment type relate to, for example, smothering or modification of benthic habitats. The potential effects on these receptors are described Offshore cable Within areas characterised by the presence of chalk at the elsewhere in the ES. It is noted here that marine physical environment receptors will seabed, ploughing or mechanical trenching rather than jetting be entirely insensitive to changes in SSC. techniques will be used to install the cable. This will minimise 2.77 Sediment release scenarios have been informed by the project engineering design levels of chalk held in suspension within the water column. details (Volume 2, Chapter 1). Seabed sediments and underlying geology have been informed by a range of evidence which are summarised in Table 2-8. Duration of time between trench excavation, cable lay and trench backfill operations at the landfall is to be kept to a minimum (i.e. Conceptual understanding of impact to be undertaken within one tidal cycle) so as to limit disruption to 2.78 The main cable installation methodologies available are ploughing, jet trenching and coastal processes. mechanical trenching and are described in Volume 2, Chapter 1. The installation methodology applied may vary according to water depth and seabed geology, with the Operation possibility for a combination of the three installation methods depending on the ground Where burial depth cannot be achieved, cable armouring will be conditions. However, jetting typically results in sediment suspension introducing a Offshore cable implemented (e.g. concrete mattressing, rock dump, protective potential for mobilisation over a wider area than for other cable laying techniques aprons or frond matting). The suitability of installing rock or which may be employed during construction. As such, jetting is considered to

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represent the realistic worst case scenario in those areas in which the nature of the 2.81 In terms of sediment plumes, jetting typically represents a realistic worst case scenario seabed substrate permits jetting to be undertaken. since this has the potential to fluidise material, causing it to enter suspension (BERR, 2008; ABPmer et al., 2010). This introduces potential for mobilisation over a wider 2.79 Key input parameters used in the assessment are as follows: area than for other cable laying techniques that may be employed during construction. • Cable burial to a depth of 1.5m below the seabed surface in areas where chalk is By contrast, other cable installation techniques are expected to introduce only a very absent; small amount of material into the water column. Due to the spatial variation in • Cable burial to 1.0m below the seabed in areas where chalk is present; geotechnical properties of the underlying geology within this region, it is considered very unlikely that jetting will be possible along the entire corridor. Instead, a • Cable trench width of 0.5m; combination of techniques is likely to be used. • Cable installation at a rate of 150m/hr (~13 days (315 to 320 hours) per cable in 2.82 The preparation of the sandwave crests (considered in the following section), will be total); undertaken prior to cable installation by jetting or ploughing. The preparation will push • Jetting will be used to install the cable in areas where chalk is absent and will the sandy seabed material aside, minimising suspension into the water column and also be used in areas where sandwaves occur. A conservative assumption has thus retain the sand on site. The preparation ploughing will mobilise some sediment been made that this will result in 100% disaggregation of material into constituent into the water column albeit at a greatly reduced rate compared to the cable particles. The released material will comprise clay (2µm), silt (20µm) and fine installation by jetting. Therefore, plume formation by the sandwave crest preparation is sand (125µm); not considered further. • Sandwave crests will be temporarily lowered with a plough by up to 3m prior to 2.83 The seabed and near seabed geology along the corridor is complex. In places, all of the installation of the cable by jetting. Sand will be pushed aside so that it is the disturbed material will be coarse grained sand and gravels whereas elsewhere, retained on-site and suspension is minimal. The total width of the ploughed path much of the released material may potentially comprise finer grained particles through a sandwave crest, for each cable, including the spoil berms, will be no associated with the Bolders Bank Formation. Coarse grained sediments will behave more than 15m. differently to fine grained sediments when released into the water column. Cable • Trenching will be used to install the cable in areas where chalk is present (see installation into coarse grained, unconsolidated material is likely to give rise to high Annex 2.1; Figure 8). A conservative assumption has been made that this will SSCs in the vicinity of the cable trench, but the released material is likely to settle out result in 50% disaggregation of material into constituent particles. The released of suspension very quickly (e.g. order of seconds to minutes) and any sediment material will comprise calcite (10µm); plumes are likely to be highly localised. By contrast, any fine grained material released into the water column will remain in suspension for a much longer period of time (order • Up to six export cables may be installed although only two would be installed of hours to days), potentially resulting in an increase in SSC over a wide area as the simultaneously; and material disperses from the original release location. Similar differences are expected • The total volume of material displaced for each cable trench is approximately when considering any ensuing bed level changes, with the release of coarse material 48,500m3. giving rise to greater but more localised changes in bed levels than for the release of 2.80 Two alternative export cable routes have been considered in this assessment; one fine grained material which may give rise to very small changes (order of mm’s or less) which connects to the consented wind farm at the northern end of the Cable Fan Area in bed levels over a wide area. ('Cable Route 1') and one which connects to the wind farm at the southern end of the 2.84 Due to the key differences in plume characteristics, the release of fine and coarse Cable Fan Area ('Cable Route 2') (Figure 2-1). It is noted here that the export cable grained sediments has been considered separately: will connect to the offshore platforms (OSPs) which will be located inside the array. • The release of fine grained sediments has been considered using a numerical However, their exact position has yet to be determined. The effects of cable particle tracking model, since this material is likely to remain in suspension for a installation (in terms of elevated levels of SSC and associated bed level changes) period of hours to days and will be influenced by patterns of tidal asymmetry and inside the array will be subordinate to the effects of foundation installation, already residual circulation across the far-field. The particle tracking model is informed by considered for the array ES (Volume 2: Chapter 2 – Physical Processes). the tidal current flow fields derived from the numerical tidal model developed to

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inform the assessment of marine physical processes in the Triton Knoll Wind • Peak depth-averaged SSCs are encountered when the installation of the cable is Farm ES (Triton Knoll ES Volume 2: Chapter 2 – Physical Processes); and taking place in shallow (i.e. < -10m LAT) water depths. Here, concentrations of up • The local (near-field) disturbance of coarse grained materials has been to a few 10s mg/l above background levels may be experienced within ~5km from considered using a desk-based assessment which (amongst other things) takes the corridor, although these concentrations are not anticipated to persist for more into consideration the settling velocity for the released particles and indicative than a few hours; flow conditions. • In Offshore and Midshore Areas of the corridor (where water depths are generally 2.85 These two assessments are complementary: the plume dispersion modelling results deeper than -10m LAT), elevations in SSC are very low and typically less than 8 may be used to consider change over the wider study area (far-field) whereas the desk mg/l away from the immediate release location; and based assessment should be used to consider change in the immediate vicinity of the • After a period of several days (and on completion of the export cable installation corridor (i.e. near-field). The results from the two assessments have been considered activities), any fine grained material remaining in the water column will have fully alongside information contained within the existing evidence base, derived from other dispersed as a result of advection and diffusion; and similar developments. • Following completion of the cable installation activity, fine grained material held in 2.86 It is noted here that for the numerical modelling of far-field effects a highly suspension could theoretically be transported and deposited up to tens of conservative approach has been adopted whereby two cables are installed kilometres from the release locations (Figure 2-5 and 2-6). However, the simultaneously and immediately adjacent to one another. This has the potential to dispersion of these fine sediment fractions is so great that any deposits at this cause an additive effect whereby SSCs in the combined plumes are potentially double distance from the corridor will generally be less than ~0.750mm in thickness (i.e. that expected to occur in a single plume. Conversely, within the near-field it is not measureable in practice and indeterminable from background levels). considered extremely unlikely the concentrations of material in the water column would 2.90 Previous monitoring of SSC levels during similar cable installation works (reviewed by be additive as the two cable installation devices would not be operating close enough ABPmer et al., 2010) are consistent with the general results provided by the numerical to one another for this to occur. However, bed level changes across the near-field modelling approach described above. The results presented in Figure 2-3 to 2-6 are could (at least in theory) be additive since material from an initial installation operation also consistent with numerical modelling results for similar cable installation activities could settle to the bed and subsequently be overlain by material from a second undertaken to inform the nearby Hornsea Project One OWF (SMart Wind, 2013). (adjacent) installation operation. 2.91 Residual flow will control the net transport of suspended sediments. Along much of the Numerical modelling of fine sediment release corridor residual flow is generally in a northerly direction. The exception to this general 2.87 Results from the numerical plume modelling analysis for the installation of two pattern is close to the coast within the Inshore and Nearshore Areas, where residual trenches in the vicinity of Cable Route 1 and Cable Route 2 are shown separately, in flow is to the south. Figures 2-3 to 2-6. The figures show changes in SSC and bed level and are based on 2.92 It is possible that local meteorological conditions (in particular, strong winds) could a moving sediment release (position indicated by the red marker) for the full distance cause any fine grained sediment plume to travel further, causing higher SSCs than of cable installation. described above. However, under such conditions, it is probable that wind-waves will 2.88 Assuming a jetting rate of 150 m/hr, cable installation takes approximately 13 days per also disturb the bed, resulting in elevated background levels of SSC. It should be cable. This time interval is close to the length of a full spring-neap cycle (~15 days). noted that in order to ensure the most conservative assessment of elevations in SSC Each figure includes six 'windows'. Each window shows an instantaneous moment relative to background levels, waves have not been included in the modelling analyses (snapshot) in the evolution of the released sediment plume. The time of each snapshot undertaken here. shown in each window is not fixed between different figures. The snapshot is chosen 2.93 It should also be noted that the residual plume concentrations shown in Figure 2-3 and on the basis of a notable moment in the evolution of the plume, such as a high SSC, 2-4 are likely to be overly conservative since the plume dispersion model takes into the distribution of the suspended sediment or the spatial excursion of the plume. consideration the potential for re-mobilisation of the sediment arisings into the water 2.89 Figures 2-3 to 2-6 show that: column once they have settled to the bed. However, any released sand sized material is predicted to quickly settle out of suspension persisting in the water column for no

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more than a few tens of minutes. Once this material has settled to the bed, it would quickly be incorporated into the natural mobile bed regime. 2.94 Finally, it is noted here that within the Nearshore Area potential outcrops of peat have been identified at the seabed. These areas of peat are found to be of very limited spatial extent (< ~100m2) and as such, have not been considered within the plume modelling sediment release scenarios described above. 2.95 Peat units are likely to be of weak strength and low density and as such, will readily disaggregate if subjected to jetting/ trenching. Given its low density, the disturbed peat material is likely to float and it may well therefore be washed ashore by wave action. 2.96 Peat material not washed ashore may well persist in the water column for a relatively long period of time. Tidal flow velocities within the Nearshore Area are of moderate strength, with peak flows typically around 0.5 m/s (see Annex 2.1). Any disturbed peat is therefore likely to be dispersed over a relatively large distance. Indeed on the basis of available tidal excursion ellipse information (Figure 2-2), the disturbed material would travel a distance of approximately 9km in a north-northwesterly direction during an ebb spring tide and in a south-southeasterly direction during a flood spring tide. 2.97 The flood flows are more dominant than the ebb, resulting in residual flow to the south. Accordingly, over longer time-scales (period of days to weeks), any peat material remaining in suspension would be expected to be transported in a general southerly direction. However, prevailing winds may drive persistent surface currents, interrupting this generalised pattern.

2-24 ￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

Rev Date Description Drn Chk App

Triton Knoll Electrical System

￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ / ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿ ￿￿￿￿￿￿ ￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

Rev Date Description Drn Chk App

Triton Knoll Electrical System

￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ / ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿ ￿￿￿￿￿￿ ￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿ ￿￿￿￿￿￿￿￿￿￿ Legend: Changes in Bed Levels after ~13 days resulting from Installation of Cable Route 1 Designated Sites Changes in Bed Level (mm) Above 8.0 6.0 - 8.0 4.0 - 6.0 2.0 - 4.0 1.5 - 2.0 0.75 - 1.5 0.375 - 0.75 Below 0.375

Notes:- This map contains data from the following sources- ABPmer (2014)

Coordinate System: WGS 1984 UTM Zone 31N Projection: Transverse Mercator Datum: WGS 1984 Units: Meter

Source: Global Land Cover Facility, www.landcover.org.

00 06/03/2015 Second Draft AJB NKD ??

Rev Date Description Drn Chk App

Triton Knoll Electrical System

TITLE: Figure 2-5 Changes in Bed Levels Resulting from Installation of Cable Route 1 / SCALE: NOT TO SCALE REV 00 Document Path:Y:\4105_Triton_Knoll_3\GIS\002ass_Fig2_5_Bed_Level_Cable1.mxd

© Crown copyright, All rights reserved. 2014 License No. EK001-20140601. Contains Ordnance Survey data © Crown copyright and database right 2014. Not to be used for navigation. Legend:

Designated Sites Change in bed level (mm) Above 8.0 6.0 - 8.0 4.0 - 6.0 Changes in Bed Levels after ~13 days resulting from Installation of Cable Route 2 2.0 - 4.0 1.5 - 2.0 0.75 - 1.5 0.375 - 0.75 Below 0.375

Notes:- This map contains data from the following sources- ABPmer (2014)

Coordinate System: WGS 1984 UTM Zone 31N Projection: Transverse Mercator Datum: WGS 1984 Units: Meter

Source: Global Land Cover Facility, www.landcover.org.

00 06/03/2015 Second Draft AJB NKD ??

Rev Date Description Drn Chk App

Triton Knoll Electrical System

TITLE: Figure 2-6 Changes in Bed Levels Resulting from Installation of Cable Route 2 / SCALE: NOT TO SCALE REV 00 Document Path:Y:\4105_Triton_Knoll_3\GIS\002ass_Fig2_6_Bed_Level_Cable2.mxd

© Crown copyright, All rights reserved. 2014 License No. EK001-20140601. Contains Ordnance Survey data © Crown copyright and database right 2014. Not to be used for navigation. Triton Knoll Offshore Wind Farm Ltd Triton Knoll Electrical System Environmental Statement - Volume 2

Desk based assessment of coarse grained sediment release 2.101 Table 2-12 shows that: 2.98 The available benthic and geophysical data reveals that the ratio of sands to gravels Medium to coarse sand and gravels are likely to settle out of suspension in close within the seabed and near seabed sedimentary units varies both horizontally and proximity (metres or tens of metres) to the corridor; vertically along the corridor. Since it is impractical to capture this heterogeneity in • Within this zone, SSCs are likely to temporarily exceed natural background detail within the context of this assessment, a series of realistic worst case 'end- levels. However, elevations in SSCs above background levels are only likely to member' assessments have been presented for the coarse grained sediment releases. persist for a short period (i.e. order of minutes to tens of minutes); and These represent the full potential range of change both in terms of the duration, spatial extent of effect and maximum bed thickness changes. • Bed level changes are likely to be highly localised. Smothering in the order of tens of centimetres may occur within approximately 10m of the cable trench. 2.99 These realistic worst case assessment scenarios are: However, regardless of the released material type, smothering of more than 50 • Scenario 1: The release of 100% granule gravel (4,000µm) sized material from a mm is not expected to occur at a distance of more than ~20 to 30m from the U-shaped trench measuring 1.5m depth by 0.5m width; corridor. • Scenario 2: The release of 100% medium/ coarse sand (500µm) sized material Assessment of significance from a U-shaped trench measuring 1.5m depth by 0.5m width; and 2.102 From the perspective of the marine physical environment, all of the receptors identified • Scenario 3: The release of 100% fine sand (125µm) sized material from a U- in Table 2-9 will be entirely insensitive to elevated levels of SSC. However, some shaped trench measuring 1.5m depth by 0.5m width. receptors could (in theory) be affected by changes in bed level and sediment type. 2.100 Results from these three scenarios are summarised in Table 2-12. Both jetting and 2.103 The following receptor types have been considered in the assessment of effects ploughing techniques will be used to install the cable, although only jetting has the resulting from changes in bed levels due to cable jetting and/or ploughing: capacity to entrain large volumes of material into the water column. • Designated seabed/ intertidal areas (listed in Table 2-9); and Table 2-12: Summary of near-field impacts associated with the disturbance of coarse • Non-designated banks (Triton Knoll Sandbank). grained material during export cable installation 2.104 Using the receptor sensitivity/ importance criteria presented in Table 2-5, all of the Height of Distance Indicative Bed designated seabed receptors are considered to be of very high or high Ejection Duration of Sediment Travelled (m)* Level Changes sensitivity/importance. This is because although the receptors would have high into Water Effect (s)* (mm) capacity to accommodate the anticipated impact, they are of either international or Column (m) national importance. In contrast, non-designated banks are assigned a very low Granule gravel 1 4 2 300 sensitivity/importance score as they have high capacity to accommodate the (4,000µm) anticipated impact and are of local level importance only. 5 20 10 60 2.105 At all receptor locations the magnitude of impact is predicted to be low. This Medium/ coarse sand 1 14 7 85 assessment is based on the fact that in most areas the anticipated changes will not be (500µm) discernible from background levels which themselves are constantly changing over 5 71 36 35 short, medium and long-term timescales. Where change is likely to be observed, it will 1 87 43 30 be of temporary duration only and restricted to near-field/ immediately adjacent far- Fine sand (125µm) field areas, as demonstrated in Figure 2-5 and Figure 2-6, as well as Table 2-12. 5 435 217 5 2.106 The overall level of effect significance has been assessed according to the EIA *Based on representative flow speed of 0.5m/s and indicative settling velocities methodology set out earlier in this chapter and in Chapter 3. Effect significance has described in Soulsby (1997) been determined by combing the assigned ratings for receptor sensitivity/ importance and impact magnitude, as shown in Table 2-7. Overall, the effect on all receptors is

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adverse but temporary, and experienced at a local level for a short period of time. For crossings per cable x 6 cables = 1,800m, or 1.8km. This represents a small seabed the designated seabed/ intertidal areas the level of significance is Minor whereas for disturbance considering the scale of the sandwaves some of which are longer than the non-designated banks (i.e. Triton Knoll Sandbank) the level of significance is total width of the cable fan’s widest point of approximately 9km. The total volume of Negligible. sand material temporarily displaced by this operation is 81,000m3.

Sandwave crest level preparation resulting in a change in the local 2.111 The width of the lowered portion of the ploughed path, at 6m – 6.5m, for each cable hydrodynamic, wave and sediment transport processes represents a very small aperture considering the total width of the sandwave field which stretches for the entire width of the cable fan area. Therefore, the effect upon Overview tidal flows and waves is expected to be minimal considering the net effect of the total 2.107 Prior to cable installation by jetting, the crests of sand waves will be levelled off by the sandwave field upon the passage of currents and waves, in conjunction with the use of a plough (or similar device). The plough will push sand aside so that a flatter temporary nature of the operation. path of 6m – 6.5m wide is created for the subsequent passage of the jetting tool, or Assessment of significance installation plough thus enabling deeper burial of the cable. The total width of the path 2.112 The following receptor types have been considered in the assessment of changes to will be 15m including the adjacent spoil berms. To complete the installation through the local hydrodynamic, wave and sediment transport processes resulting from sand the sandwave crests, a bed-levelling plough will be used to return the spoil berms to wave levelling: the furrow such that the sandwave crest resembles the pre-ploughed condition as close as is practically possible. • Inner Dowsing, Race Bank and North Ridge Offshore SCI; Conceptual understanding of impact • Saltfleetby to Theddlethorpe Dunes and Gibraltar Point SAC; 2.108 The majority of the sandwaves on the cable route are located in the fan area and are • Triton Knoll Sandbank; generally orientated W-E and have wavelengths in the range 40 – 400m. The highest • The coast of sub-cell 2c 'Donna nook to Gibraltar Point'; and of these has a crest tip of 7m above the surrounding seabed. The elevation of this • crest is 11.5m LAT. At the neck of the fan area another group of sandwaves stand Wolla Bank to Chapel Point SSSI. between 2m – 3m height. All of these sandwaves are covered with megaripples 2.113 Using the receptor sensitivity/ importance criteria presented in Table 2-5, the Inner (heights between 0.1m – 3m) some of which are near-perpendicular to the sandwaves Dowsing, Race Bank and North Ridge Offshore SCI as well as Saltfleetby to themselves. Isolated small sandwaves or small patches of sandwaves are present Theddlethorpe Dunes and Gibraltar Point SAC are considered to be of very high along the remainder of the route but are orientated longitudinally relative to the cable sensitivity/importance. This is because despite the banks being very active and having route itself and do not transverse the entire cable corridor. As such, avoidance of high capacity to accommodate the anticipated impact, the receptors are of these sandwave features in these locations is possible. international importance. 2.109 Where the plough is pulled through a sandwave the crest will be lowered by up to 3m. 2.114 Triton Knoll Sandbank is considered to be of low sensitivity/importance. This is This represents a localised deepening of the bathymetry which is limited in extent to because the receptor is of local level importance and has high capacity to the sandwave crest only, in a path up to 6m – 6.5m wide but only until the bed- accommodate the proposed form of change. levelling plough is drawn through post-jetting. The spoil berms temporarily represent 2.115 The coast at the Triton Knoll landfall is considered to be of medium an elevated bed level of approximately 1m above the bed, which is smaller than the sensitivity/importance. This is because it is of regional importance and has moderate size of the megaripples observed to cover the sandwaves (which are up to 3m in to high capacity to accommodate the proposed form of change. The Chapel Point to height). Wolla Bank SSSI is considered to be of high sensitivity/importance. This is because 2.110 Each of the 6 cables will transverse between 16 - 20 sandwave crests, all of which will the receptor is of national level importance, despite having high capacity to be located in, or at the neck of, the cable fan. The geophysics surveys of Osiris accommodate the proposed form of change. (2013a) indicate that the crests of the sandwaves are approximately 15m wide. Therefore, the total length of prepared sandwave crest will be 15m x 20 crest

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2.116 At all receptors, the magnitude of impact is expected to be low, with changes that are proposed form of change. The magnitude of change is expected to be very low, with a barely discernible, temporary and restricted to the near-field and immediately adjacent noticeable change to beach morphology only apparent for a very short period of time. far-field areas. Any changes to longshore sediment transport would be undetectable. 2.121 The overall level of effect significance has been assessed by combining the assigned 2.117 The overall level of effect significance has been assessed by combing the assigned ratings for receptor sensitivity/ importance and impact magnitude, as shown in Table ratings for receptor sensitivity/ importance and impact magnitude, as shown in Table 2-7. The effect on the coast at the landfall is adverse but temporary, and experienced 2-6. Overall, the effect on all receptors is adverse and temporary and experienced at a at a local level for a short period of time. The level of effect significance is Negligible. local level. It is found that for the coast, the Wolla Bank to Chapel Point SSSI, the Inner Dowsing, Race Bank and North Ridge Offshore SCI and the Saltfleetby to Changes to beach morphology resulting from installation of the export cable at the landfall Theddlethorpe Dunes and Gibraltar Point SAC receptor, the level of effect significance is Minor. For Triton Knoll Sandbank, the level of effect significance is Negligible. Overview Release of sediment and lubricant through HDD operations 2.122 TKOWFL has identified a preferred landfall area just north of Anderby Creek, Lincolnshire (see Figure 2-1). Reference to Annex 2.1 reveals that coastal erosion Overview rates on the Lincolnshire coastline are significant and a beach replenishment 2.118 The following section discusses HDD only as it is this methodology that may result in programme (managed by the Environment Agency (EA)) is undertaken on a regular exit pits within the intertidal. HDD involves the drilling of an initial pilot hole, followed by basis. reaming to enlarge the bore to the required diameter of the cabling duct. The drilling Conceptual understanding of impact activity utilises a viscous drilling fluid (a mixture of water and bentonite - a non-toxic, 2.123 In order to minimise disruption to the shoreline the preferred construction method to naturally occurring clay mineral), which is continuously pumped to the drill head cross the sea defences is to use HDD techniques. Starting landwards of the sea assisting in the removal of drill cuttings, stabilising the walls of the bore, and cooling defences, a drill would pass under the defences and emerge on the seaward side, and lubricating the drill string. above MLWS. The cable would then be buried under the beach using either an Conceptual understanding of impact excavator or a typical subsea cable burial plough pulled by a tractor or the cable laying 2.119 The volume of sediment and drill fluid released during the HDD process is related to vessel, out to deeper water. the volume of drilling fluid in the bore, the hydrostatic head balance (dependant on the 2.124 A typical installation by HDD would involve the following: location, length and angle of the bore) and the nature of the release. Taking into • Drilling a pilot hole from landward of the sand dunes and sea defences down to consideration a theoretical maximum drill length of 500 m, a maximum ream diameter the beach; of 0.75m and (conservatively) assuming that 20% of the drill arisings are discharged, the maximum volume of sediment released would be approximately 44m3. A total • Reaming (to make the hole bigger); 3 volume of approximately 0.5m of drilling mud may also be released into the beach pit • Installation of a trench box at the HDD exit point; excavation for each HDD. However, all released material would be contained and removed on completion of the bore. No material would be left on the beach and there • Pulling a ducting pipe through the reamed hole: and would be no opportunity for this material to enter into the suspension within the water • Pulling of the offshore export cable through the conduit by the cabling barge. column since punch-out would not take place when the tide is above the level of the 2.125 It is anticipated that the area excavated for the installation of the trench box may be up beach pit excavation. to 25m2 and a maximum depth of 4.5m. This corresponds to a total area of disturbance Assessment of significance of 150m2 for six cables, with an associated volume of sediment of 675m3. The 2.120 Using the receptor sensitivity/ importance criteria presented in Table 2-5, the coast at installation of each cable circuit within the inter-tidal zone will be completed within a the Triton Knoll landfall is considered to be of medium sensitivity/importance. This is single tidal cycle, i.e. a period of up to 12 hours, with trench box installation and HDD because it is of regional importance, despite having high capacity to accommodate the punch-out taking up to 36 hours. Other cable installation options such as micro-boring

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and pipe jacking will exit the beach above the MHWS mark, offering less opportunity to stretch of coastline is ‘hold the line’ and this strategy is recommended for the next 50 interact with beach processes. years (Halcrow, 2004). 2.126 HDD is generally considered to cause minimal direct disturbance to the existing Assessment of significance coastline and is an appropriate form of mitigation to avoid damage, particularly in the 2.131 The following receptors have been considered in the assessment of changes to beach intertidal and landfall areas where habitats may be more sensitive (BERR, 2008). This morphology resulting from installation of the export cable at the landfall: methodology has been successfully adopted at the export cable landfalls of a number of Round 1 and Round 2 OWF developments with minimal environmental impact. • The coast at the Triton Knoll landfall; and Provided that the cable remains buried beneath the dunes there is no possibility for it • Chapel Point to Wolla Bank SSSI. to interact with, or have any impact on them. 2.132 Using the receptor sensitivity/ importance criteria presented in Table 2-5, the coast at 2.127 As stated, a trench is likely to be excavated across the Nearshore and Midshore Area. the Triton Knoll landfall is considered to be of medium sensitivity/importance. This is The realistic worst case for coastal processes would involve excavation of the trench because it is of regional importance and has moderate to high capacity to with a plough, resulting in a heap either side of the trench of approximately 0.8 to 0.9m accommodate the proposed form of change. The Chapel Point to Wolla Bank SSSI is in subtidal areas although possibly >1m in intertidal areas. This is because the trench considered to be of high sensitivity/importance. This is because the receptor is of across the beach is likely to be deeper (approximately 3m compared with 1.5m for national level importance, despite having high capacity to accommodate the proposed sub-tidal areas), in order to take into consideration the anticipated inter- and intra- form of change. annual vertical changes in beach elevation. The excavated heaps would subsequently 2.133 At the Triton Knoll landfall, the magnitude of change is expected to be low with be used to backfill the trench once the cables had been laid. noticeable but temporary change to beach morphology observed during the 2.128 It is expected that the excavated material from the trench will be side-cast and will construction period. At the Chapel Point to Wolla Bank SSSI (which is located partially infill on the next tide. Full reinstatement will be completed on the next low tide. approximately 2km downdrift from the landfall), changes to beach morphology are not Accordingly, heaps would only be present on the seabed/ beach for a very short period expected to be discernible from background conditions. Accordingly, the magnitude of of time (i.e. matter of hours). Given that the heaps would only be present for a very effect is considered to be very low. short period of time, any effects on coastal morphology would be temporary and of low 2.134 The overall level of effect significance has been assessed by combing the assigned magnitude. ratings for receptor sensitivity/ importance and impact magnitude, as shown in Table 2.129 The current ‘hold the line’ shoreline management strategy for this section of coast is 2-7. Overall, the effect on all receptors is adverse but temporary, and experienced at a implemented via the Lincshore beach replenishment programme. The present phase local level for a short period of time. At both the Triton Knoll landfall and at Chapel of beach re-nourishment is expected to cease in 2015 although it is assumed that the Point to Wolla Bank SSSI, the level of effect significance is Negligible. coastline will continue to be protected in accordance with the existing ‘hold the line’ Shoreline Management Plan. Accordingly, if beach re-nourishment stops, alternative Alteration of the bathymetry due to indentations in the seabed from vessel legs shoreline management measures (such as recycling) will most likely be considered. It and vessel anchors is possible that these alternative management measures may lead to local changes in Overview beach morphology although the extent to which this could occur is not possible to assess in the absence of detailed management plans. However, these would be 2.135 Some of the vessels used during the construction and operation phase of the project available well before the anticipated start date of construction (2018) and would be may potentially impact the seabed. This is particularly the case for those vessels that considered within the cable burial studies undertaken to inform engineering use jack-up legs to hold station and to provide stability for the working platform. requirements. Where legs and vessel anchors have been inserted into the seabed and then removed, there is the potential for an indentation proportional to the dimensions of the 2.130 Climate change is likely to lead to mean sea level rise which in many areas is object to remain. The volume and dimensions of the depression may reduce over time expected to lead to an increased rate of beach erosion and shoreline retreat. However, in proportion to the rate of sediment transport through the area. The presence of such as stated in the previous paragraph the current shoreline management policy for this a feature does not necessarily imply a difference in sedimentary environment in the

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area of the effect, but this would depend upon the nature and depth of the sub-surface 2.142 The degree of interaction between the anchor and seabed would vary depending upon sediments. the particular design of anchor used. The anchor would initially fall to the seabed under its own weight, causing minimal impact disturbance in its own footprint (up to Conceptual understanding of impact: jack-up leg indentations approximately 16m2 for larger ‘pull ahead’ anchors). The anchor would then be pulled 2 2.136 A single jack-up barge leg could have a footprint of approximately 4m , with a total of horizontally across the seabed for some distance to allow the flukes and crown to up to 6 legs per vessel. The typical estimated penetration depth of a leg is anticipated penetrate the seabed. This may result in a short, shallow furrow. Once embedded in to be very small, i.e. order of a few decimetres. Precise depths would be highly the seabed, a sediment ridge would arise in front of the anchor in the direction of pull, dependent on the nature of the surficial sediments and underlying geology. partially accumulated from the furrow and partially pushed up by the horizontal 2.137 As the leg is inserted, the already partially consolidated seabed sediments would pressure on the bed from the anchor pull. primarily be compressed downwards and then displaced laterally sideways. This may 2.143 To release the anchor, the connecting wire or chain is tensioned vertically, levering the cause the seabed around the inserted leg to be raised in a series of concentric flukes out of the sediment. The anchor is then retrieved through the water column, pressure ridges. The seabed response is dependent upon the actual dimensions of either to the main vessel or by an anchor handling vessel for redeployment. The act of the leg and the local geotechnical properties of the soils. removing the anchor in this way would redistribute much of the accumulated sediment 2.138 As the leg is subsequently retracted, the force which is holding the sediments laterally back to the seabed around or into any remaining hole. would be reduced. Some of the material that has been previously pushed sideways 2.144 The footprint of the disturbance remaining soon after an anchor’s removal would be would return to the hole via mass slumping under gravity. Any loose sediment would approximately similar to the size of the anchor (4.45 by 3.56m). The character of the avalanche back into the depression until a maximum stable slope angle is achieved. disturbance may be highly variable (chaotic ridges and depressions) within the 2.139 The frequency with which sediments are mobilised by the prevailing hydrodynamic footprint of effect. In the worst case, the maximum depth of depression would be up to conditions normally experienced within the corridor has been presented in Annex 2.1. approximately 1m. It is likely that any depressions left by the jack-up barges would be infilled over short to 2.145 For the most part, the sedimentary texture of the disturbed surface is likely to be medium timescales (i.e. months to years). This assertion is supported by field similar to that of the surrounding seabed because no sediment is introduced or evidence available from post construction scour monitoring undertaken at several removed by the anchor. However, where the surficial sediment veneer is thin, it is Round 1 and Round 2 wind farm sites: possible that small quantities of the underlying sub-soil material may become exposed • In areas characterised by high rates of sand transport (such as at Scroby Sands at the seabed. OWF), the seabed has recovered quickly; and 2.146 In time, the disturbed surface would be reworked and flattened to a baseline condition • Where depressions have occurred in clay-type soils (such as at Kentish Flats by the action of currents. Where surficial sediment is present, it is expected that this OWF), they have persisted for much longer periods i.e. months to years. would occur over a period of several months. In areas where surficial sediment is absent and the scar is within the underlying Bolders Bank formation, they would 2.140 Seabed characteristics similar to Scroby and Kentish flats are variously found within essentially become permanent features. However, no potential to intercept regional different sections of the corridor and it is anticipated that recovery times for the seabed sediment transport is expected because the sediment is essentially only locally would therefore be spatially variable. redistributed in a small footprint. Conceptual understanding of impact: anchor scars 2.147 The frequency with which sediment is mobilised as a result of tidal currents and wave 2.141 As for jack-up barges, the exact type of cable installation vessel to be used remains stirring of the bed has been discussed within Annex 2.1. Here it is shown that, due to unknown at this stage. However, it is typically the case that an array of four to six tidal control, superficial sediment is regularly mobilised. It is therefore considered that anchors may be used by work vessels to both hold position and provide stability during in most locations, any pits would be in filled relatively quickly (order of weeks to operations. It is assumed that, for one anchor, the length of the main body is up to months). 4.45m. Assessment of significance

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2.148 The following receptors have been considered in the assessment of changes to • Bagged solutions, (including geotextile sand containers, rock-filled gabion bags or bathymetry due to indentations in the seabed from vessel legs and vessel anchors: nets, and grout bags, filled with material sourced from the site or elsewhere). • Inner Dowsing, Race Bank and North Ridge Offshore SCI; and 2.153 Protection measures may be placed alone or in combination, and may be secured to • Triton Knoll Sandbank. the seabed where appropriate. Where appropriate, cable clips (also known as cable anchors, or anchor clamps) may also be utilised to secure cables to the seabed. 2.149 Using the receptor sensitivity/ importance criteria presented in Table 2-5, the Inner Dowsing, Race Bank and North Ridge Offshore SCI is considered to be of very high 2.154 The requirement for these protection devices is limited in maximum extent (Table 2- sensitivity/importance. This is because despite having high capacity to accommodate 10) as adequate cable burial is anticipated for the majority of the route. However, the anticipated impact, the receptor is of international importance. The Triton Knoll where burial cannot be achieved and protection material is subsequently added to the Sandbank is considered to be of very low sensitivity/importance. This is because the seabed environment, there would be a target maximum reduction in navigable depth of receptor is of local level importance and has high capacity to accommodate the no more than 10 per cent. It is considered that the maximum height of protection that proposed form of change. would be required could result in a local elevation of the seabed profile by up to 1.5m. 2.150 At both receptors, the magnitude of impact is expected to be low, with noticeable but 2.155 The protection devices would be placed onto the seabed surface above the cable and temporary change observed within the near-field. therefore could, in theory, interact with the coastal process regime in two ways: • 2.151 The overall level of effect significance has been assessed by combing the assigned The protection measures could locally trap sediment, potentially impacting ratings for receptor sensitivity/ importance and impact magnitude, as shown in Table downdrift locations; and 2-7. Overall, the effect on all receptors is adverse but temporary, and experienced at a • Cable protection measures could, in theory, modify the transmission of waves local level for a short period of time. It is found that for the Inner Dowsing, Race Bank across the Nearshore/ Inshore Area, influencing patterns of longshore sediment and North Ridge Offshore SCI receptor, the level of effect significance is Minor transport locally. whereas for Triton Knoll Sandbank it is . Negligible 2.156 These potential impacts are discussed further below. Environmental assessment: operational phase Conceptual understanding of impact

Introduction of rock armour and/or concrete mattresses resulting in a change in 2.157 Following installation and under favourable conditions, an initial period of sediment the local hydrodynamic, wave and sediment transport processes accumulation would be expected to occur, creating a smooth slope across any rock armour. Based on the relatively high rates of sediment mobility in this region (and Overview especially within shallow Inshore/ Nearshore Areas), this process may take place over 2.152 There may be a requirement for the remedial protection of cables should adequate a period of a few months or less. Sandy sediments are transported in two modes: burial not be achieved or if cables subsequently become exposed as a consequence bedload and saltation. Saltation is the process by which sands are moved up into the of sandwave migration or as a result of anthropogenic activity. Protection measures water column. These suspended sands would be expected to move freely over the top that might be deployed onto unburied sections of cable may include one or a of the armour, regularly becoming deposited upon it. Saltation is expected to be largely combination of the following options: unaffected by the presence of the rock armour such that existing transport process will remain unaffected. Bedload is the process by which sands move while still in contact • Rock or gravel burial; with the seabed. Bedload will be temporarily affected up until such time that the • Concrete mattresses; armour is covered by sand. This is expected to occur relatively quickly due to saltation, • Flow energy dissipation devices (used to describe various solutions that dissipate flow and the region’s high rates of transport. Once covered bedload will continue because energy and entrap sediment, and including options such as frond mats, and mats of the slope angle presented by sections of protected cable would (at most) be in the large linked hoops); order of 15 to 20º which is within the natural range of bed slope angles associated with bed forms mapped within the corridor. Accordingly, for all areas in which cable • Protective aprons or coverings (solid structures of varying shapes, typically protection is used (including where sand waves are present), it is not expected that the prefabricated in concrete or high-density plastics), and;

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presence of the cable protection devices will affect patterns of sediment transport to high capacity to accommodate the proposed form of change. The Chapel Point to following the initial period of accumulation. It follows that any changes on seabed Wolla Bank SSSI is considered to be of high sensitivity/importance. This is because morphology away from the protection devices will also be very small and any the receptor is of national level importance, despite having high capacity to associated impacts on ecological receptors (especially Sabellaria spinulosa) will be accommodate the proposed form of change. similarly limited. 2.164 At all receptors, the magnitude of impact is expected to be low, with changes that are 2.158 Some secondary scour may occur as a result of turbulence caused by the protection barely discernible and restricted to the near-field and immediately adjacent far-field devices. However, the action of the (upstream) scour will be to actively re-suspend areas. Any changes to longshore sediment transport would be extremely small and and transport sediment over the obstacle, therefore not causing any impact in relation undetectable at locations downdrift of the landfall in sub-cell 2c (i.e. between Anderby to sediment transport. Creek and Gibraltar Point). 2.159 In terms of the potential for the cable protection measures to modify the wave regime, 2.165 The overall level of effect significance has been assessed by combing the assigned it is considered that any interruption of Inshore/ Nearshore wave processes would be ratings for receptor sensitivity/ importance and impact magnitude, as shown in Table minimal and highly localised. The extent of interaction would probably be analogous to 2-6. Overall, the effect on all receptors is adverse and permanent, although that of a surface mounted outfall pipe at the coast. Indeed, the cable protection experienced at a local level. It is found that for the coast, the Wolla Bank to Chapel measures would likely occupy a low profile within the water column (i.e. <1m in height Point SSSI, the Inner Dowsing, Race Bank and North Ridge Offshore SCI and the off the bed) and be orientated perpendicular to the shore, thereby presenting a Saltfleetby to Theddlethorpe Dunes and Gibraltar Point SAC receptor, the level of minimal cross section of interference to the passage of incoming waves. effect significance is Minor. For Triton Knoll Sandbank, the level of effect significance is . Assessment of significance Negligible 2.160 The following receptor types have been considered in the assessment of changes to Introduction of scour due to the exposure of export cables as well as the the local hydrodynamic, wave and sediment transport processes resulting from the presence of cable protection measures introduction of rock armour and/or concrete mattresses: Overview • Inner Dowsing, Race Bank and North Ridge Offshore SCI; 2.166 Cables are normally buried to reduce the risk of snagging or other direct damage and • Saltfleetby to Theddlethorpe Dunes and Gibraltar Point SAC; therefore present no scour risk. However, in areas containing mobile bedforms (such • Triton Knoll Sandbank; as within the Cable Fan Area – Figure 2-1), it is possible that cables may become exposed, potentially resulting in scouring of nearby sediments. • The coast of sub-cell 2c ‘Donna nook to Gibraltar Point’; and 2.167 Where cable burial is not possible due to seabed conditions or at crossing points with • Wolla Bank to Chapel Point SSSI. pipeline infrastructure, scour protection measures are typically used to mitigate the risk 2.161 Using the receptor sensitivity/ importance criteria presented in Table 2-5, the Inner of scour and other damage, and so will largely prevent scour developing. Protection Dowsing, Race Bank and North Ridge Offshore SCI as well as Saltfleetby to measures that might be deployed onto unburied sections of cable have previously Theddlethorpe Dunes and Gibraltar Point SAC are considered to be of very high been described in Volume 2, Chapter 1 and include concrete mattresses as well as sensitivity/importance. This is because despite the banks being very active and having rock dump. However, the presence of cable protection such as rocks or mattressing high capacity to accommodate the anticipated impact, the receptors are of can result in a change in the water movements within the immediate vicinity of the international importance. infrastructure, resulting in secondary scour (localised seabed erosion) around the structures. 2.162 Triton Knoll Sandbank is considered to be of very low sensitivity/importance. This is because the receptor is of local level importance and has high capacity to 2.168 The extent and depth of scour may vary over time and may be limited under certain accommodate the proposed form of change. physical conditions. However, a conservative approach (based on the methods of Whitehouse (1998)) has been applied in this section to calculate the maximum 2.163 The coast at the Triton Knoll landfall is considered to be of medium expected dimensions of scour, independent of other factors. sensitivity/importance. This is because it is of regional importance and has moderate

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Conceptual understanding of impact Sandbank is considered to be of very low sensitivity/importance. This is because the 2.169 Up to six export circuits could be required to transmit the power to the onshore receptor is of local level importance and has high capacity to accommodate the substation via the Intermediate Electrical Compound. The voltage will be determined proposed form of change. by detailed studies, but is likely to be in the range of 132 kV to 220 kV. Each circuit 2.176 At both receptors, the magnitude of impact is expected to be low, with noticeable but would consist of one three-phase HVAC offshore export cable, approximately 0.275m highly localised change observed within near-field areas only. in diameter. 2.177 The overall level of effect significance has been assessed by combing the assigned 2.170 A conservative estimate for the potential dimensions of cable scour is provided by ratings for receptor sensitivity/ importance and impact magnitude, as shown in Table Whitehouse (1998), as follows: 2-7. Overall, the effect on all receptors is adverse and (potentially) permanent, although experienced at a local level. It is found that for the Inner Dowsing, Race Bank • Maximum depth of between one and three times the cable diameter (i.e. in the range 0.3m to 0.8m); and and North Ridge Offshore SCI receptor, the level of effect significance is Minor whereas for Triton Knoll Sandbank it is Negligible. • Maximum horizontal extent of up to fifty times the cable diameter (i.e. up to ~14m). Environmental assessment: decommissioning phase 2.171 It follows from the information above that any depression created will not necessarily 2.178 Should the cable system require removal at the end of its operational life, it will be be steeply sided. In predominantly sandy areas, the surface of the scour pit will have a removed through the same soils and sediments disturbed during installation. This similar character to the surrounding seabed. In more gravelly areas, a gravel lag process could result in short-term elevations in SSC and localised changes in bed veneer may initially form as finer sands are preferentially winnowed, but may then level (i.e. within the near-field). It is anticipated that the working areas for removal will become buried with predominantly sandy material following recovery of the seabed if also be restricted to the area used for installation. If the cables are left in the seabed at self-burial occurs. As no exposure is expected, a specific length of exposure cannot be the end of the proposed development, impacts will be the same as those described realistically proposed and so no further calculations of total area or volume are made. above for the operation phase. 2.172 The worst case scenario for the dimensions of the proposed protection is an elevation 2.179 Impacts upon tidal, wave and sedimentological regimes as a consequence of this of approximately 1.5m off the bed and a maximum width of 11 m. The maximum total phase will be comparable (or subordinate) to those identified for the construction area covered via cable protection would be 61,200m2 per cable/ 367,200m2 in total. phase. Given that during the construction phase, the level of effect significance for all 2.173 The raised profile of the protection may cause a limited amount of localised secondary marine physical environment receptors is found to be negligible to minor, it is scouring at the edges of the protection in line with the dominant flow or wave direction. anticipated that the same would hold true for the decommissioning phase. However, the depth and extent of scour will be limited in proportion to the diameter of the individual material used which may be reduced by embedment or settling over Environmental assessment: cumulative effects time. 2.180 Cumulative effects refer to effects upon receptors arising from the Triton Knoll Assessment of significance Electrical System when considered in addition to those arising from other proposed 2.174 As described above, the extent of any scour effects will be confined to (sub-tidal) developments and activities and any other reasonably foreseeable project(s). In this areas within the near-field. Accordingly, the only receptors that could be affected are: context the term project(s) is considered to refer to any past, present or reasonably forseeable project, programme or plan that could result in an additive impact with the • Inner Dowsing, Race Bank and North Ridge Offshore SCI; and Triton Knoll Electrical System. • Triton Knoll Sandbank. 2.181 The approach to cumulative assessment for the Triton Knoll Electrical System takes 2.175 Using the receptor sensitivity/ importance criteria presented in Table 2-5, the Inner into account the Cumulative Impact Assessment Guidelines issued by RenewableUK Dowsing, Race Bank and North Ridge Offshore SCI is considered to be of very high in June 2013, together with the PINS ‘Advice Note 9: Rochdale Approach’, comments sensitivity/importance. This is because despite having high capacity to accommodate made in response to other renewable energy developments within the Southern North the anticipated impact, the receptor is of international importance. The Triton Knoll Sea, and relevant National policy. Full details of the approach to cumulative

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assessment is provided within the accompanying annex (Volume 1; Annex 3.1 ) 2.189 Tier 3 projects comprise those for which a developer has notified the relevant planning entitled “Approach to Cumulative and Inter-relationships Impact Assessment for the authority in writing that they intend to submit an application in the future. This includes Triton Knoll Electrical System”, which should be read alongside this ES chapter. projects where a scoping report may be available, but where data presented is limited 2.182 There can be some uncertainty in terms of the status of some projects as it is often and / or data confidence is low. very difficult to establish whether a development has been lawfully implemented and 2.190 The Tier 3 assessment would consider the potential effects arising from the Triton determining construction stages and timescales may not always be achievable due to Knoll Electrical System together with impacts and effects arising from projects included a lack of available information. For this reason the status of each project is based on in Tiers 1, 2 and 3. However, the lack of information for projects categorised as Tier 3, reasonable assumptions, as described in Annex 3.1. All relevant projects/ plans with attendant low data confidence, prevents a meaningful assessment of such considered cumulatively alongside the Triton Knoll Electrical System have been projects to be undertaken and therefore no detailed Tier 3 assessment has been allocated into ‘Tiers’, reflecting their current stage within the planning and development presented. It should be noted that where scoping reports have provided sufficient process. detail, such projects have been elevated to Tier 2 to ensure that a comprehensive 2.183 The proposed tier structure that is intended to ensure that there is a clear cumulative assessment, commensurate with the level of information available, has understanding of the level of confidence in the cumulative assessments provided in been provided for the Electrical System application. the Triton Knoll Electrical System EIA is as follows: 2.191 The specific projects scoped into this cumulative impact assessment, and the tiers into Tier 1 which they have been allocated are presented in Table 2-13. The operational projects included within the table are included due to their completion/ commission subsequent 2.184 Tier 1 projects comprise those other projects / plans currently under construction and/ to the data collection process for the Triton Knoll Electrical System and as such not or those consented but not yet implemented, and/ or those submitted but not yet included within the baseline characterisation. determined where data confidence for the projects falling within this category is high. 2.192 Each project, plan or activity has been considered and scoped in or out on the basis of 2.185 Built and operational projects are included within the cumulative assessment where effect–receptor pathway, data confidence and the temporal and spatial scales they have not been included within the environmental characterisation survey, i.e. they involved. For the purposes of assessing the impact of the Triton Knoll Electrical were not operational when baseline surveys were undertaken, and/ or any residual System on the marine physical environment, professional judgement has been used in impact may not have yet fed through to and been captured in estimates of ‘baseline’ order to create a shortlist of projects for assessment for this topic. The ‘Approach to conditions or there is an ongoing effect. Cumulative and Inter-relationships Impact Assessment’ annex provides further detail 2.186 The Tier 1 assessment considers the potential effects arising from the Triton Knoll about the projects proposed for consideration in this ES chapter. Electrical System together with impacts and effects arising from relevant projects / 2.193 The specific projects scoped into this cumulative impact assessment that are relevant plans categorised as Tier 1 projects. to the marine physical environment and the tiers into which they have been allocated, Tier 2 are presented in Table 2-13 below. 2.187 Tier 2 projects comprise those projects/ plans that are consented but not yet implemented and/ or submitted applications not yet determined and / or where detailed scoping reports are available where data confidence for the projects falling into this category is medium. This includes projects that are expected to be submitted over a similar timeframe to that of the Triton Knoll Electrical System. 2.188 The Tier 2 assessment considers the potential effects arising from the Triton Knoll Electrical System together with impacts and effects arising from projects included in Tier 1 and those categorised as Tier 2 projects. Tier 3

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Table 2-13: Projects for cumulative assessment Shortest Overlap with TK Overlap with TK Distance from Dates of Offshore Electrical Electrical System Tier Phase Project/Plan Triton Knoll Details Construction/operation System (Construction Electrical (as applicable) (Operation phase) System phase) Offshore Wind Farms 75 turbines

Up to 60,640m2 of remedial cable protection works. Construction phase completed in 2013. Operational Lincs 5.2km   Expected life 20 years Secondary protection up to 70m in length (3m wide, 1m high) at 150 cable ends leaving/entering foundations 54 turbines

Up to 51,540m2 of remedial cable protection works Construction phase completed in 2009. Operational LID 6.7km   Expected life 25 years Inter-array cable protection at discrete locations, the greatest of which is 264m in length, 3m wide and 1m high to a Tier total of 1,049m length 1 Under Race Bank Offshore Wind 0.5km 88-206 turbines 2014-2017 (plus operational lifetime)   construction Farm

Triton Knoll Offshore Wind Consented X 50-96 turbines 2017-2021 (plus operational lifetime)   Farm Hornsea Project One Submitted 2.1km Up to 360 turbines 2015-2019 (plus operational lifetime)   Offshore Wind Farm Aggregate Extraction Areas Humber Estuary (106/1) 2.5 3.94km2 Operational until end 2029   Humber Estuary (106/2) 8 3.20km2 Operational until end 2029   on - Humber Estuary (106/3) 2.25 35.36km2 Operational until end 2029  

Off Saltfleet (197) 4.5 26.18km2 Operational until end 2029   106 East (480) 2.25 9.84km2 Operational until end 2023   Inner Dowsing (481/1) 3.25 6.07km2 Operational until end 2023   Inner Dowsing (481/2) 6.25 1.93km2 Operational until end 2023   Outer Dowsing (515/1) 0 52.81km2 Operational until end 2020   Operational (with (with Operational effects) going

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Shortest Overlap with TK Overlap with TK Distance from Dates of Offshore Electrical Electrical System Tier Phase Project/Plan Triton Knoll Details Construction/operation System (Construction Electrical (as applicable) (Operation phase) System phase) Disposal Sites Wash Bank dredge disposal Operational 2.25 0.25km2 (Unknown)   (HU114)

Triton Knoll Offshore Wind Consented N/A 145km2 2017-2021   Farm disposal site Aggregate Extraction Areas

Application for operation sought up to end North Dowsing (400) 2.25 14.25km2   2029 Tier 2 Application for operation sought up to end Inner Dowsing (439) 0.5 26.28km2   2029 Application for 15 years operation Humber Overfalls (493) 3.5 12.21km2   submitted 07 June 2012 Application

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2.194 The cumulative Rochdale Envelope considered in the assessment is summarised in Table 2-14. Impact scenarios relate to the potential for sediment plume interaction Interaction of sediment plumes as a result of the combined activities of export cable installation and other industrial activities during the construction phase and potential modification of the hydrodynamic and sedimentary processes during the operational phase. Any potential changes in SSCs Overview associated with cable scour will be very minor. 2.195 Meaningful sediment plume interaction generally only has the potential to occur if: Table 2-14: Cumulative Rochdale Envelope • The activities generating the sediment plumes are located within one spring tidal excursion ellipse from one another; Impact Scenario Justification • The activities occur either simultaneously or shortly after one another; and The intensity of aggregate • Fine sediment is released which has the potential to remain in suspension during extraction is anticipated to remain ebb/ flood tides. broadly similar to that presently Interaction of occurring. 2.196 In terms of potential cumulative effects, it is primarily the potential for sediment plumes sediment arising from other wind farm construction activities, aggregate extraction and dredge Triton Knoll Electrical System The types of aggregate vessel plumes as a disposal operations to combine with any plumes arising from export cable installation result of the being used are not expected to 2 wind farms activities that is most relevant. The risk of the interaction creating a greater effect than combined be significantly greater than the activities of 19 aggregate sites (noting that some of Arco Dijk, an H-Class Trailer either solitary activity has been assessed. these sites are in fact licence renewals) Suction Hopper Dredger owned export cable 2.197 As previously stated, the main concerns resulting from any increases in SSC relate to Installation and by Hanson Aggregates Marine 1 dredge disposal site impacts on pelagic species and fisheries whilst those resulting from accumulations in other industrial Ltd. (The Arco Dijk represents activities one of the largest dredgers in the sediment and changes to sediment type relate to, for example, smothering or UK aggregate fleet, with a modification of benthic habitats. The potential significance of these issues are reported capacity of approximately elsewhere in this ES. 4,800m3) Conceptual understanding of impact Changes in 2.198 Spring tidal excursion ellipses show the approximate path that a body of water would hydrodynamic The presence of infrastructure at conditions and Triton Knoll Electrical System follow over the course of a mean spring tide and have been used here to identify the the seabed (i.e. turbine associated potential for sediment plume interaction between export cable installation and: foundations and cable protection) sediment has the greatest potential to • Aggregate extraction operations; processes 3 wind farms (Race Bank, Lincs and influence hydrodynamic resulting from LID) • Triton Knoll OWF construction; conditions and sediment the presence of transport processes. • cable protection Race Bank OWF construction (including cable corridor); measures • Hornsea Project One OWF export cable installation; • Lincs and LID remedial cable burial activities; and • Dredge disposal activities. Aggregate dredging 2.199 Reference to Figure 2-1 and Table 2-13 reveals that there are 19 aggregate areas (either already licensed, under application or options) located within a distance of one spring tidal excursion ellipse from the corridor.

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2.200 In terms of aggregate extraction, the target material at these sites is sands and gravels from the export cable works acting cumulatively with any of the construction works (HADA, 2012). Characteristically, the aggregate deposits in this region contain 1 to 3% within the TKOWF site is regarded as low and as such of negligible significance (Triton fines (silt and clay) in situ and, therefore, the concentrations of this fraction in the Knoll array ES chapter (Volume 2: Chapter 2 – Physical Processes). Accordingly, overflow from the dredging vessels are relatively low. The predicted footprint of fine potential effects have not been considered further. sediment plumes arising from aggregate dredging in this region has previously been Race Bank OWF construction (including cable corridor) considered for the Humber Regional Environmental Assessment (MAREA) using plume dispersion modelling. The spatial extent of the zones around the aggregate 2.206 The Race Bank OWF, as well as the offshore section of the adjoining export cable areas experiencing elevated levels of SSC in excess of 20 mg/l above background corridor is located within one tidal excursion of the Triton Knoll Electrical System. In levels remains localised (i.e. within 1 to 2km) to the marine aggregate areas. the vicinity of the corridor tidal excursion ellipses are orientated in a general north to south direction (Figure 2-2). This means that in terms of cumulative impacts with the 2.201 The interaction between sediment plumes generated by export cable installation and Race Bank OWF and the Race Bank export cable, plume interaction has the potential those from nearby aggregate dredging and dredge disposal could occur in two ways: to occur when export cable installation within the TKOWF cable fan area and Offshore • Where plumes generated from the two different activities meet and coalesce to Area of the corridor is taking place. Further inshore the two cable corridors diverge form one larger plume; or such that they are separated by more than one spring tidal excursion. • Where a dredge barge is dredging (or discharging material) within the plume 2.207 On the basis of the above, it is possible that the plumes associated with the two generated by cable installation activities (or vice versa). separate projects may coalesce to cover a slightly larger geographical area and, for a 2.202 For two or more separately formed plumes that meet and coalesce, the physical laws very short period of time, locally exhibit higher concentrations than shown in Figure 2-3 of dispersion theory mean concentrations within the plumes are not additive but and Figure 2-4. However, the period over which higher SSCs may occur would not last instead a larger plume is created with regions of potentially differing concentration for more than a few hours. representative of the separate respective plumes. In contrast, in the case of plumes Hornsea Project One OWF cable corridor formed by a dredging vessel operating within the plume created by cable installation 2.208 At its closest point, the Hornsea Project One OWF export cable corridor is located (or vice versa), the two plumes would be additive, creating a plume with higher SSC approximately 7.5km from the Triton Knoll Electrical System (Figure 2-1). In terms of (HR Wallingford, 2010). cumulative impacts, plume interaction only has the potential to occur when export 2.203 It is anticipated that the most common form of plume interaction during the cable installation within the cable fan area is taking place. construction phase will be associated with the coalescing of separate plumes. This 2.209 As for the situation described above for Race Bank, it is theoretically possible that the scenario may result in a combined plume of slightly larger extent than shown in Figure plumes associated with the two separate projects may coalesce to cover a slightly 2-3 or 2-4. larger geographical area and, for a very short period of time, locally exhibit higher 2.204 In the (extremely unlikely) event that dredgers are operating immediately adjacent to concentrations than shown in Figure 2-3 and Figure 2-4. However, the period over the corridor at the same time as two cables are being simultaneously installed, it is which higher SSCs may occur would not last for more than a few hours. possible that any fine sediment plumes from the respective activities would be Lincs and LID remedial cable burial additive, giving rise to higher concentration plumes than shown in Figure 2-3 or 2-4. However, these higher concentration plumes would not be expected to persist for 2.210 At the closest point, the Lincs and LID OWFs are located 5.2km and 6.7km much longer than a few hours. respectively from the Triton Knoll Electrical System (Figure 2-1). If inter-array cables at Lincs and LID OWF were to become exposed during the operational lifetime of the Triton Knoll OWF construction developments remedial cable burial may be required, resulting in short term and 2.205 It is likely that installation of the offshore parts of the export cables would coincide with localised sediment plumes. If this were to take place at the same time as export cable the construction of the TKOWF foundations and installation of the inter-array cables. installation in the Inshore/ Midshore Area, it is theoretically possible that plume The potential for cumulative effects has previously been considered in the Triton Knoll interaction could occur. OWF ES. It was found that the likelihood and magnitude of plume interaction arising

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2.211 The plumes associated with the two separate projects may coalesce to cover a slightly 2.218 At all receptor locations the magnitude of impact is predicted to be either low or very larger geographical area and, for a very short period of time, locally exhibit higher low. This assessment is based on the fact that in most areas the anticipated changes concentrations than shown in Figure 2-3 and Figure 2-4. However, the period over will not be discernible from background levels. Where change is likely to be observed, which higher SSCs may occur would not last for more than a few hours. it will be of temporary duration only and restricted to near-field/ immediately adjacent Dredge disposal far-field areas, as demonstrated in Figure 2-5 and Figure 2-6, as well as Table 2-12. 2.212 Reference to Figure 2-1 and Table 2-13 reveals that there are two active dredge 2.219 The overall level of effect significance has been assessed by combining the assigned disposal site located within a distance of one spring tidal excursion ellipse from the ratings for receptor sensitivity/ importance and impact magnitude, as shown in Table 2-7. Overall, the effect on all receptors is adverse but temporary, and proposed development. experienced at a local level for a short period of time. For the designated seabed/ 2.213 One of these disposal sites is the Triton Knoll array disposal site, consented for the intertidal areas the level of significance is Minor whereas for non-designated banks 3 disposal of up to 1,058,968 m of inert material of natural origin produced during the (i.e. Triton Knoll Sandbank) the level of significance is Negligible. drilling installation of monopiles or jacket pin foundations. The potential for cumulative interaction with disposal activities at this site has previously been considered within Cumulative changes to hydrodynamic conditions and sediment transport paragraph 2.204. processes arising from the presence of seabed infrastructure

2.214 It is possible that sediment plume interaction could occur when export cable Overview installation within the Midshore Area of the corridor is taking place at the same time as 2.220 During consultation, a concern was raised that the presence of cable protection disposal operations at the Wash Bank dredge disposal site. In theory, plumes devices at the seabed associated with the Triton Knoll Electrical System could alter associated with the two separate projects may combine to cause a plume of slightly hydrodynamic conditions and associated sediment transport processes. These greater spatial extent and (temporally) of higher concentration. However, these higher changes could then cumulatively interact with those caused by other wind farm project concentration plumes would not be expected to persist for much longer than a few infrastructure (namely turbine foundations and cable protection devices), potentially hours. impacting the Inner Dowsing, Race Bank and North Ridge Offshore SCI. Assessment of significance 2.221 On the basis of Figure 2-1, it is the cumulative effects associated with Race Bank, 2.215 As previously stated, from the perspective of the marine physical environment, all of Lincs and LID OWFs with the Triton Knoll Electrical System that would have the the receptors identified in Table 2-9 will be entirely insensitive to elevated levels of greatest potential to result in cumulative changes to hydrodynamic conditions in the SSC. However, some receptors could (in theory) be affected by changes in bed level. vicinity of the Inner Dowsing, Race Bank and North Ridge Offshore SCI. Because any 2.216 The following receptor types have been considered in the assessment of effects changes will be very small and localised, other more distal wind farms in the study resulting from changes in bed levels due to cable jetting and/or ploughing: area (i.e. Sheringham Shoal) have been scoped out of the assessment. • Designated seabed/ intertidal areas (listed in Table 2-9); and 2.222 This assessment considers the potential for morphological changes to the Annex I sandbank features within the SCI. Potential impacts on ecological features within the • Non-designated banks (Triton Knoll Sandbank). SCI (especially Sabellaria spinulosa reefs) are discussed within Volume 1, Chapter 8 2.217 Using the receptor sensitivity/ importance criteria presented in Table 2-5, all of the Subtidal and Intertidal Ecology. designated seabed receptors are considered to be of very high or high Conceptual understanding of impact sensitivity/importance. This is because although the receptors would have high capacity to accommodate the anticipated impact, they are of either international or 2.223 Any cumulative effects to hydrodynamic conditions arising from the presence of national importance. In contrast, non-designated banks are assigned a very low seabed infrastructure are expected to be extremely small, localised and immeasurable sensitivity/importance score as they have high capacity to accommodate the in practice. This is primarily because the cable protection measures will occupy a low anticipated impact and are of local level importance only. profile within the water column in relation to overall water depth and therefore any effects related to flow blockage will be small. Associated modifications to the bedload

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transport regime resulting from changes in the percentage of time during which Transboundary statement sediment is mobilised would also therefore be extremely small. 2.231 Following completion of a transboundary screening matrix and in agreement with 2.224 Any cumulative blockage effects on bedload transport would also be very minor. This PINS, it is considered that transboundary impacts are not likely to arise as a result of is because the slope angle presented by sections of protected export/ inter-array this development (see Volume 1 Annex 3.2). Transboundary effects are therefore not cables would (at most) be in the order of 15 to 20º which is within the natural range of considered further. bed slope angles associated with bed forms mapped within the corridor. These localised and very minor changes in sediment transport would have extremely limited Summary of effects potential to overlap and adversely affect either the gross morphology of the Annex I sandbanks or the Sabellaria spinulosa reefs within the SCI. 2.232 This chapter has investigated potential effects on marine physical environment receptors arising from the Triton Knoll Electrical System. The range of potential Assessment of significance impacts and associated effects considered has been informed by scoping responses 2.225 The following receptors have been considered in the assessment of effects resulting (Table 2-4) as well as reference to existing policy and guidance. Those impacts from alterations to hydrodynamic conditions and associated changes in sediment considered include changes to the marine physical environment brought about directly transport: (by the presence of infrastructure at the seabed), as well indirectly (through a • Inner Dowsing, Race Bank and North Ridge Offshore SCI. modification to physical process pathways). Potential impacts considered in this chapter are listed below. 2.226 Using the receptor sensitivity/ importance criteria presented in Table 2-5, the Inner Dowsing, Race Bank and North Ridge Offshore SCI receptor is considered to be of 2.233 During the construction/decommissioning phases: very high sensitivity/importance. This is because although the receptor would have • Short-term elevations in suspended sediment levels during the installation of high capacity to accommodate the anticipated impact, it is of international importance. cables and associated small-scale changes in bed levels; 2.227 At the receptor location the magnitude of impact is predicted to be very low. This • Temporary modification of bathymetry during pre-installation preparation of assessment is based on the fact that in most areas the anticipated changes will not be sandwave crests; discernible from background levels. • Release of sediment and lubricant through HDD operations at the landfall; 2.228 The overall level of effect significance has been assessed by combing the assigned • Localised changes to beach morphology resulting from installation of the export ratings for receptor sensitivity/ importance and impact magnitude, as shown in Table cable at the landfall; and 2-7. Overall, the effect on the Inner Dowsing, Race Bank and North Ridge Offshore SCI receptor is adverse and permanent, and experienced at a local level. The level of • Alteration of the bathymetry due to indentations in the seabed from vessel legs significance is Minor. and vessel anchors. 2.234 During the operation phase: Inter-relationships • Armour and/or concrete mattresses resulting in a long-term change in the local 2.229 Volume 2, Chapter 12: Inter-relationships should be referred to for a summary of all hydrodynamic, wave and sediment transport processes potential inter-related effects associated with the proposed development. • Introduction of local scour due to the exposure of export cables as well as the Mitigation presence of cable protection measures 2.235 Cumulative impacts were also considered and an assessment was carried out looking 2.230 All of the potential effects to marine physical environment receptors are identified as at the potential for interaction of sediment plumes as a result of the combined activities Not Significant in terms of the EIA Regulations (Chapter 3). Accordingly, no mitigation of export cable installation and other industrial activities in the study area. These has been put forward as there are no significant effects which require mitigation. include aggregate extraction operations, construction of the Race Bank and Hornsea

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Project One OWFs, remedial cable burial activities at Lincs and LID OWFs, as well as Description of Possible mitigation Effect Residual impact dredge disposal activities. impact measures 2.236 These potential impacts to the marine physical environment have been investigated anchors using a combination of methods including analytical techniques, the existing evidence base and numerical modelling. In accordance with the requirements of the Rochdale Envelope approach to EIA, the worst case characteristics of the proposed Operation development have been considered thereby providing a highly conservative Introduction of rock assessment. armour and/or 2.237 Even adopting the conservative assessment approach described above, it has been concrete mattresses resulting in a change No mitigation found that for all of the marine physical environment receptors included in this Minor/ Negligible Minor/ Negligible in the local measures necessary assessment (Table 2-9), the level of effect significance is either Negligible or Minor hydrodynamic, wave (Table 2-15). Accordingly, all of the potential effects to marine physical environment and sediment receptors are therefore Not Significant in terms of the EIA Regulations. transport processes Introduction of scour Table 2-15: Summary of predicted effects of the Triton Knoll Electrical System due to the exposure Description of Possible mitigation of export cables as No mitigation Effect Residual impact Minor/ Negligible Minor/ Negligible impact measures well as the presence measures necessary of cable protection Construction measures Elevations in Decommissioning suspended sediment No mitigation levels and associated Minor/ Negligible Minor/ Negligible Potential effects are considered to be similar to or less than those assessed for the measures necessary small-scale changes construction phase in bed levels Sandwave crest level Cumulative effects preparation resulting in a change in the No mitigation Interaction of Minor/ Negligible Minor/ Negligible local hydrodynamic, measures necessary sediment plumes as a result of the wave and sediment No mitigation combined activities of Minor/ Negligible Minor/ Negligible transport processes measures necessary Release of sediment export cable No mitigation and lubricant through Negligible Negligible installation and other measures necessary HDD operations industrial activities Cumulative changes Changes to beach to hydrodynamic morphology resulting No mitigation conditions and Minor Minor from installation of Minor/ Negligible No mitigation Minor/ Negligible measures necessarys sediment transport the export cable at measures necessary processes the landfall Alteration of the bathymetry due to No mitigation indentations in the Minor/ Negligible Minor/ Negligible measures necessary seabed from vessel legs and vessel

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References • Fugro (2009). Triton Knoll Offshore Wind Farm Geotechnical Site Investigation. 1260pp. • ABPmer (2011). Triton Knoll Offshore Wind Farm: Physical Processes Technical • Report. ABP Marine Environmental Research Ltd, Report R.1788. Gardline (2009). Triton Knoll Offshore Wind Farm Geophysical Survey: Fan and cable route to the shore survey report. Report 8078.2. • ABPmer, HR Wallingford & CEFAS (2010). Further review of sediment monitoring • Halcrow (2004). Lincshore Sea Defence Strategy. Mablethorpe to Skegness. data’. (COWRIE ScourSed-09). ABP Marine Environmental Research Ltd, HR Wallingford Ltd & Centre for Environment, Fisheries and Aquaculture Science, for • HR Wallingford, (2010). South Coast Dredging Association MAREA: High-level plume COWRIE. studies to establish footprints of aggregate dredging activities, Technical Note DDR4323-03. • ABPmer and HR Wallingford (2009). Coastal Process Modelling for Offshore Wind farm Environmental Impact Assessment (for COWRIE). • HR Wallingford, CEFAS & ABPmer (2007). Dynamics of scour pits and scour protection - Synthesis report and recommendations. (Sed02). For DTI. November • ABPmer, CEFAS & HR Wallingford (2007). Review of Round 1 sediment process 2007. monitoring data - lessons learnt. (Sed01) ABP Marine Environmental Research Ltd, Centre for Environment, Fisheries and Aquaculture Science & HR Wallingford Ltd, for • Humber Aggregate Dredging Association (HADA) (2012). Marine Aggregate regional BERR. November 2007. Environmental Assessment of the Humber and Outer Wash. • ABPmer, Met Office and POL (2008). Atlas of UK Marine Renewable Energy • Institute of Environmental Management and Assessment (IEMA) (2004). Guidelines for Resources: Atlas Pages. A Strategic Environmental Assessment Report, March 2008. Environmental Impact Assessment. BP Marine Environmental Research Ltd. Produced for BERR. Report and associated • JNCC (2015). Inner Dowsing, Race Bank and North Ridge. GIS layers available at: http://www.renewables-atlas.info/ http://jncc.defra.gov.uk/protectedsites/sacselection/sac.asp?EUCode=UK0030370. • ABPmer & METOC (2002). Potential effects of offshore wind developments on coastal Accessed on 06/01/2015. processes. ABP Marine Environmental Research Ltd and METOC, for DTI (now • JNCC, Natural England (2011). General advice on assessing potential impacts of and DECC). mitigation for human activities on MCZ features, using existing regulation and • BERR (2008). Review of Cabling Techniques and Environmental Effects applicable to legislation. Advice from the Joint Nature Conservation Committee and Natural England the Offshore Wind farm Industry. Technical Report, Department for Business to the Regional MCZ Projects. Enterprise and Regulatory Reform (BERR), in association with Defra, 164pp. • Kenyon NH.,Cooper WS. (2005). Sand banks, sand transport and offshore wind farms. • British Geological Survey (BGS) (1990). Spurn 53N 00 sea bed sediments, 1:250,000 Report for DTI. geological map. • Motyka, J.M. & Brampton, A.H. (1993). Coastal management. Mapping of littoral cells. • CEFAS (2011). Guidelines for data acquisition to support marine environmental Unpublished report to the Ministry of Agriculture, Fisheries and Food, Report no. SR assessments of offshore renewable energy projects. ME5403, CEFAS, 98pp. 328. • Centrica (2007). Lincs Offshore Windfarm Environmental Statement. • Natural England (2014). Chapel Point – Wolla Bank SSSI citation details. http://www.sssi.naturalengland.org.uk/Special/sssi/sssi_details.cfm?sssi_id=2000261 • Cooper, W.S., Townend, I.H., & Balson, P.S. (2008), „A synthesis of current Accessed 09/07/2014 knowledge on the genesis of the Great Yarmouth and Norfolk Bank Systems. The Crown Estate, 69 pages. • Osiris (2013a). Triton Knoll Offshore Wind Farm Export Cable Route Survey Volume 2a: Results Report. Report C12033. • DNV (2014). Subsea Power Cables in Shallow Water Renewable Energy Applications. • Osiris (2013b). Triton Knoll Offshore Wind Farm Export Cable Route Survey Volume 3: • EMU (2009). Greater Wash Hydrodynamic Measurement Campaign. Operational Geotechnical Report. Report C12033. Report, Deployment 1 and 2.

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• Osiris, (2009). Triton Knoll Offshore Wind Farm Hydrographic & Geophysical Surveys. Survey Report Volume 1 and 2. • PINS (2014). Scoping Opinion: Proposed Triton Knoll Electrical System. http://infrastructure.planningportal.gov.uk/projects/east-midlands/triton-knoll-electrical- system/ • RWE (2014) Triton Knoll Offshore Wind Farm Electrical System Environmental Impact Assessment Scoping Report http://infrastructure.planningportal.gov.uk/projects/east- midlands/triton-knoll-electrical-system/ • Scott Wilson (2010). Humber Estuary Coastal Authorities Group Flamborough Head to Gibraltar Point Shoreline Management Plan. Prepared for Humber Estuary Coastal Authorities Group. • Smart Wind (2013). Hornsea Offshore Wind Farm Project One. Environmental Statement Vol. 5 – Offshore Annexes. Annex 5.1.6 Cable Burial Plume Assessment. PINS Document Reference: 7.5.1.6. • Southern North Sea Sediment Transport Study (SNSSTS) (2002). Southern North Sea Sediment Transport Study Phase 2: Sediment Transport Report. Report No. EX4526, August 2002. • Tappin, D R, Pearce, B, Fitch, S, Dove, D, Gearey, B, Hill, J M, Chambers, C, Bates, R, Pinnion, J, Diaz Doce, D, Green, M, Gallyot, J, Georgiou, L, Brutto, D, Marzialetti, S, Hopla, E, Ramsay, E, and Fielding, H. (2011). The Humber Regional Environmental Characterisation. British Geological Survey Open Report OR/10/54. 357pp. • The Planning Inspectorate (2012a). Advice Note Seven: Environmental Impact Assessment, screening and scoping. 9pp. • The Planning Inspectorate (2012b). Advice note nine: Using the Rochdale Envelope. 10pp. • The Planning Inspectorate (2012c). Advice Note Twelve: Development with significant transboundary impacts consultation. 12pp. • Whitehouse, R. (1998). Scour at Marine Structures. Thomas Telford, London, 198pp.

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