Menai Strait Crossing Report (2016)
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DOCUMENT 9.6 Menai Strait Crossing Report (2016) National Grid (North Wales Connection Project) Regulation 5(2)(q) of the Infrastructure Planning (Applications: Prescribed Forms and Procedure) Regulations 2009 First published September 2016 Application Reference EN020015 September 2018 Page intentionally blank North Wales Connection Project Menai Strait Crossing Report (Document 2.3) National Grid National Grid House Warwick Technology Park Gallows Hill Warwick CV34 6DA September 2016 North Wales Connection Project Menai Strait Crossing Report Page intentionally blank North Wales Connection Project Menai Strait Crossing Report Table of Contents 1. INTRODUCTION 1 1.1 Background 1 1.2 Purpose of Report 4 1.3 Structure of the Report 4 1.4 Outcome 5 2. NATIONAL GRID DUTIES AND POLICIES 6 2.1 Introduction 6 2.2 Duty to Provide a Connection 6 2.3 Economic Duties 7 2.4 Duty to Protect the Environment 7 2.5 Stakeholder, Community and Amenity Policy 8 2.6 Transmission Line Design and Routeing 8 3. CONTEXT FOR THE APPRAISAL 9 3.1 Factors in Appraising Options 9 3.2 Statutory Duties 9 3.3 Planning Act 2008 9 3.4 National Policy Statements 10 4. OVERVIEW 15 4.1 Introduction 15 4.2 Landscape 15 4.3 Historic Environment 15 4.4 Ecology 16 4.5 Marine Ecology 17 4.6 Local Economy 17 4.7 Transport 17 4.8 Hydrology and Flood Risk 18 4.9 Geology 18 4.10 Topography and Bathymetry 19 4.11 Seabed Morphology 19 5. CONSTRUCTION CONSIDERATIONS – NEW NATIONAL GRID INFRASTRUCTURE 26 5.1 Introduction 26 5.2 Overhead Line 26 5.3 Cable Sealing End Compounds 27 5.4 Underground Cables 28 5.5 Crossing Techniques for the Menai Crossing 30 September 2016 North Wales Connection Project Menai Strait Crossing Report 5.6 Initial Preference 45 6. CONSTRUCTION CONSIDERATIONS – OTHER INFRASTRUCTURE 46 6.1 Introduction 46 6.2 Consultation Feedback 46 6.3 Installation on the Britannia Bridge 46 6.4 Disused Pipeline Across the Lavan Sands 55 6.5 Third Menai Crossing 55 6.6 Outcome 56 7. OVERHEAD LINE ROUTE CORRIDORS 57 7.1 Introduction 57 7.2 Consultation Feedback 57 7.3 Description of Options 59 7.4 Consideration of Options 83 7.5 Initial Preference 86 8. IDENTIFICATION OF SEALING END COMPOUND SITING AREAS 87 8.1 Introduction 87 8.2 Considerations for Siting 87 8.3 Consultation Feedback 88 8.4 Description of Options 90 8.5 Consideration of Options 130 8.6 Initial Preference 136 9. UNDERGROUND CABLES 138 9.1 Introduction 138 9.2 Consultation Feedback 139 9.3 Description of Options 139 9.4 Consideration of Options 144 9.5 Initial Preference 148 10. MENAI CROSSING 149 10.1 Introduction 149 10.2 Consultation Feedback 150 10.3 Crossing Techniques 151 10.4 Crossing Zone 1 151 10.5 Crossing Zone 2 153 10.6 Crossing Zone 3 156 10.7 Crossing Zone 4 158 10.8 Consideration of Options 159 September 2016 North Wales Connection Project Menai Strait Crossing Report 10.9 Initial Preference 174 11. PENTIR SUBSTATION 178 11.1 Introduction 178 11.2 Option 1 179 11.3 Option 2 181 11.4 Option 3 182 11.5 Consideration of Options 184 11.6 Outcome 185 12. END-TO-END’ OPTIONS CONSIDERED 187 12.1 Introduction 187 12.2 Description of options 187 12.3 Consideration of ‘end to end’ options 189 12.4 Cost 218 12.5 Consideration of Options 219 12.6 Outcome 223 13. PROPOSED DESIGN 226 13.1 Introduction 226 13.2 Overhead Line Alignment Anglesey. 226 13.3 Crossing Zone 228 13.4 Overhead Line Alignment Gwynedd. 232 14. NEXT STEPS 233 14.1 Introduction 233 14.2 Stage 3 (Statutory) Consultation 233 14.3 The DCO Application and timeline 233 September 2016 North Wales Connection Project Menai Strait Crossing Report Page intentionally blank North Wales Connection Project Menai Strait Crossing Report 1. INTRODUCTION 1.1 Background 1.1.1 National Grid owns and operates the national electricity transmission system in Wales and England – the network of cables and pylons that connects the UK’s power stations to homes and businesses. This connecting role puts National Grid at the centre of solving the UK energy industry’s major challenge: delivering low carbon energy in an affordable, secure and sustainable way. 1.1.2 The North Wales Connection is a proposed new connection for the Wylfa Newydd nuclear power station on Anglesey. There is an existing line in North Wales, but an additional, new connection is required to get the amount of power from the new station to the homes and businesses that need it. The new connection is a crucial part of providing reliable low carbon power and unlocking the investment the new power station will bring for North Wales. 1.1.3 In 2012 National Grid presented information for public consultation which identified a common area within which the new connection would approach and cross the Menai Strait and continue to the existing 400kV substation at Pentir (see Figure 1.1 below)1. Figure 1.1 1 Extract from National Grid: Wylfa to Pentir Initial Route Corridor Report (October 2012) 1 September 2016 North Wales Connection Project Menai Strait Crossing Report 1.1.4 In January 2015, National Grid announced a preferred route corridor for the development of the new electricity transmission line connection between Wylfa and Pentir. At the same time, National Grid also announced that overhead lines would not be used to cross the Anglesey Area of Outstanding Natural Beauty (AONB) and the Menai Strait. ‘You also told us that the Menai Strait is particularly sensitive, so we’ve decided to place the cables underground here, to minimise the impact on the views both at the Menai Strait and in the Anglesey Area of Outstanding Natural Beauty (AONB)’2. 1.1.5 Further work was undertaken to review the common area in order to ascertain whether it continued to be a suitable search area for the routeing of the underground cables that would now be required3. 1.1.6 In summary, the search area was defined at the eastern end by the edge of the built-up area of Menai Bridge and at the western end, by Moel-y-Don on Anglesey and Port Dinorwig on the mainland as: it was not felt necessary to consider routeing underground cables beneath or through residential areas in this instance, given the geography of the search area. Y Felinheli occupies a long length (approximately 1.8km) of the Gwynedd foreshore from Port Dinorwig westwards, so a significant extension of the search area westwards would have been required to avoid the settlement; the technical constraints west of Y Felinheli imposed by the mobile sediments and rapidly changing bed profiles associated with this part of the Menai Strait and the length of the crossing that would be required (as noted in the Preferred Route Corridor Selection Report); the risk of potential adverse effects of skylining panoramic views of Snowdonia from the north due to extending the overhead line and cabling connections through the Dinorwig Registered Landscape of Outstanding Historic Interest west of Pentir (as noted in the Preferred Route Corridor Selection Report); and a route south of Y Felinheli would represent a longer connection (connecting the Orange Route Corridor to the north-west of Llanfairpwllgwyngyll and Pentir Substation). This longer route length would result in risk of greater adverse effects upon communities that would otherwise be largely unaffected, such as Y Felinheli and Bethel, and other environmental and socio-economic receptors, such as Greenwood Forest Park. 2 Extract from National Grid, North Wales Connection; Project News January2015 3 National Grid: Wylfa to Pentir Route Options Report (October 2015) 2 September 2016 North Wales Connection Project Menai Strait Crossing Report 1.1.7 In October 2015 National Grid undertook its Stage 2 Consultation identifying the area around the Menai Strait as ‘Section 5’ of the Project. In order for the connection to go underground cable sealing end compounds would be required, both on Anglesey and in Gwynedd, to make the change from an overhead line to an underground cable. Five search areas were identified, three on Anglesey and two on Gwynedd. All of the search areas are outside of the Anglesey AONB and avoid Plas Newydd and the Vaynol Registered Parks and Gardens. 1.1.8 Five proposed overhead line route options (5A–5E) were identified to reach the sealing end compound search areas on Anglesey and three proposed overhead line route options (5F–5H) from the sealing end compound search areas in Gwynedd to the existing substation at Pentir (see Figure 1.2 below). Figure 1.24 Overhead Line Route Corridors and CSEC Search Areas (October 2015) 4 Extract from Project News: North Wales Connection (National Grid Autumn 2015) 3 September 2016 North Wales Connection Project Menai Strait Crossing Report 1.2 Purpose of Report 1.2.1 This Report identifies National Grid’s the preferred option for crossing the Menai Strait with a new 400 kV connection. 1.2.2 This report provides information as to the work National Grid has undertaken since the Stage 2 Consultation for Section 5 of the project, the options that have been developed and considered. The Report identifies the preferred option for the connection through this Section that is being taken forward to statutory consultation prior to an application being made for a DCO. 1.3 Structure of the Report 1.3.1 As Section 5 potentially includes a number of elements (overhead line, cable sealing end compounds, underground cable. Menai Crossing) these have been considered individually and initial preferences expressed.