scottish hydro electric power distribution project...

Scottish Hydro Electric Power Distribution

Project Description

Mossbank – Yell

Section ID 150

SHEPD

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Contents Definitions and Abbreviations ................................................................................................................. 3

1. Introduction ................................................................................................................................... 4

2. Background .................................................................................................................................... 5

3. Proposed cable construction ........................................................................................................ 6

4. Pre-installation survey requirements ........................................................................................... 7

5. Project description ...................................................................................................................... 11

5.1. The existing route ................................................................................................................................................... 11

5.2. The proposed route ................................................................................................................................................ 11

5.3. The proposed installation methods ........................................................................................................................ 14

5.4. Proposed cable protection methods ....................................................................................................................... 18

5.5. The proposed delivery programme......................................................................................................................... 18

6. UXO Strategy ............................................................................................................................... 18

7. Appendix A: Existing cable route with bathymetry ................................................................... 20

Appendix B: Proposed cable route ........................................................................................................ 21

Appendix C: Proposed cable RPL ........................................................................................................... 22

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Definitions and Abbreviations

The following definitions are used within this document:

SSEN Scottish and Southern Electricity Networks SHEPD Scottish Hydro Electric Power Distribution plc Cable SHEPD submarine electricity cable network Contractor Submarine cable installation company

The following abbreviations and definitions may be used within this document:

AtoN Aid to Navigation CLV Cable Lay Vessel DSV Dive Support Vessel DWA Double Wire Armoured HDD Horizontal Directional Drilling HVAC High-Voltage Alternating Current kV kilovolt MAIB Marine Accident Investigation Branch MHWS Mean High Water Springs ML Marine Licence MLWS Mean Low Water Springs MSL Mean Sea Level ODN Ordnance Datum Newlyn OHL Overhead Line PAC Pre-Application Consultation PPY Poly Propylene Yarn PSD Particle Size Distribution ROV Remotely Operated Vehicle RPL Route Position List SAC Special Area of Conservation SBP Sub-Bottom Profiler SNH Scottish Natural Heritage SPA Special Protection Area SWA Single Wire Armoured UXO Unexploded Ordnance XLPE Cross Linked Polyethylene

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1. Introduction

1.1. Scottish Hydro Electric Power Distribution plc (SHEPD) proposes to install a replacement 33kV submarine electricity cable from Mossbank to Hoga in Yell within the Shetland Isles.

1.2. This document provides a description of the project, detailing the physical construction of the cable, the proposed routeing, method of installation and operation of the cable.

1.3. This document should be read in conjunction with the:

Marine Licence Application Form Pre-Application Consultation report (appended by Cost Benefit Analysis model) Environmental Supporting Information Fishing Liaison and Mitigation Action Plan (covering all legitimate sea users) Construction Environment Management Plan Operation, Inspection, Maintenance and Decommissioning Strategy

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2. Background 2.1. One of the existing 33kV submarine electricity cables connecting Mossbank to Yell is proposed for

replacement as shown in Figure 1. The cable is rated at 33kV but operated at 11kV on the SHEPD network. The 33kV rating can be utilised during fault situations on the adjacent 33kV submarine cable to restore supplies.

2.2. The existing cable was installed in 1984 and is nearing the end of its operational life. This has been verified through our existing asset records and following recent visual inspections by ROV on the cable. The replacement of this cable is essential to securing SHEPD power supplies to the island of Yell and supports the security of supply to Unst and Fetlar.

Figure 1 - Existing cable route

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3. Proposed cable construction 3.1. Electricity will be transmitted using HVAC submarine cable technology. The typical cable structure is

shown in Figure 2.

3.2. The proposed submarine cable consists of a three core design with copper round compacted stranded conductors, XLPE insulation, copper polyethylene laminated tape, polyethylene sheath, PPY, double galvanized steel wire armour, PPY, with one interstitial armoured optical fibre cable. The cable is rated at 33 kV HVAC, with an outer diameter of 127 mm and weight of 28.8 kg/m in water. The proposed cable construction is shown in Figure 3.

3.3. The three core design minimises the resultant electric and magnetic fields produced from the cable during operation. This is further reduced by balancing the loads within each of the cable’s individual phases.

3.4. The proposed DWA construction will provide the cable with additional mechanical protection and will also help reduce the resultant electric and magnetic fields generated during operation of the cable in comparison with SWA cable constructions.

3.5. Fibre optics will be installed integral to the submarine cable for the purpose of cable condition monitoring, control and power system protection.

3.6. The submarine cable conductor specification and power rating has been selected through assessment of historic demand on the existing SHEPD network and with consideration of future customer demand growth on the network.

Figure 2 - Typical XLPE HVAC submarine cable structure

Source: ABB

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1 Copper stranded conductors 2 Semiconductive waterblocking tape 3 Non-metallic screen 4 XLPE insulation 5 Non-metallic screen 6 Semiconductive waterblocking tape 7 Metallic screen 8 HDPE sheath 9 Non-hydroscopic fillers 10 Binding tape 11 PPY separator layer 12 Inner layer of galvanized steel armouring 13 PPY separator layer 14 Outer layer of galvanized steel armouring 15 PPY outer layers 16 Fibre optic

4. Pre-installation survey requirements 4.1. SHEPD previously appointed a Contractor to conduct marine surveys along the proposed cable

route. These surveys were undertaken over a 1000 m wide corridor between September and October in 2015. The main objectives of the marine survey was to identify:

seabed conditions (e.g. sand, rock, mud) to optimise the proposed cable route (avoidance of rock outcrops)

potential geological constraints, such as dykes, rock pinnacles, sand waves, incised channels etc.

locations of potential engineering constraints and/or safety hazards, such as existing pipelines and cables either in service or out of service, wrecks, marine debris, UXO etc.

areas of potential biological and ecological importance (such as biogenic and rocky reefs, priority marine features etc.) to allow habitat mapping and inform the requirement for additional surveys and assessment.

4.2. The surveyed corridor was centred along the existing cable route and was selected following a review of potential cable landing points on Mossbank and Yell, from previous ROV inspections of the existing cable and following an assessment of current and proposed sea user activities in the area. The presence of an existing in-service 33kV cable and island of Samphrey to the east also influenced the positioning for the survey corridor and routeing of the proposed cable.

4.3. The extent of the surveyed corridor was decided in consideration with survey cost, impact on environmental species from the survey equipment and also disruption to sea users from the survey works. Centring the survey corridor on the existing cable provided the ability to route the proposed cable east or west to allow some micro-routing following assessment of the survey data.

Figure 3 – Proposed XLPE HVAC submarine cable construction

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4.4. The bathymetric data acquired along the surveyed route (Figure 4) has highlighted that rock is prevalent throughout the full extent of the surveyed corridor. This is evident from the highly tidal location which has scoured the seabed leaving minimal overlying sediment on the seabed. There is a short section north of Samphrey showing a shallow veneer of sediment, however this is insufficient for cable burial.

4.5. From the Mossbank shoreline, the route gradually increases to a depth of 35 m at an approximate chainage of 800 m before gradually reducing in depth closer to Samphrey. At a chainage of 1500 m from the Mossbank shoreline the water depth reduces to less than 5 m. Beyond Samphrey heading north towards Yell the route levels at a depth of 20 m between chainage 2000 – 2400 m before

Figure 4 - Bathymetric data between Mossbank and Yell

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gradually reducing to a maximum water depth of 50 m from chainage 2800 – 3200 m prior to steadily reducing in depth up to the Yell shoreline.

4.6. From the marine survey data it is evident that with the rocky geology and shallow water depths around Samphrey, this area should be avoided for the proposed cable installation as it may affect cable health and impact on cable stability. The water depths would present significant challenges for the cable installation works with vessel positioning and underkeel clearances. By routeing the proposed cable to the west this also minimises impact on the nearby special area of conservation and site of scientific interest in and around Samphrey.

4.7. Rocky areas are present at the intertidal areas around the shore at both Mossbank (Figure 5 and Figure 6) and Yell which was further verified by site visits and site investigations. On Mossbank the rocky coastline extends west and with the nearby jetty and village of Mossbank to the east, a decision was made to re-use the existing landfall location with an offset from the existing cable. Similarly on Yell, the coastline is rocky to the north continuing to the ferry terminal at Ulsta. With the nearby ferry route from Toft to Ulsta this limited cable routeing to the west.

Figure 5 - Mossbank shore line looking west

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4.8. SBP has been utilised to map the seabed surface to allow identification and extent of the sediment types. These survey methods are useful for identifying areas of the surveyed route that may be suitable for direct cable burial within the seabed or help to inform alternative cable protection methods if deemed required.

4.9. Limited geotechnical surveying was carried out along the route as the SBP data from the geophysical surveys indicated a lack of sediment along the extent of the surveyed corridor. The extent of geotechnical surveys was therefore restricted to seabed grab sampling at selected intervals. A number of grab sample attempts during the survey works failed to recover sufficient material due to a lack of sediment.

4.10. The purpose of this sampling was to carry out a benthic characterisation assessment combined with PSD analysis of the material at the seabed surface. The geotechnical sampling methods were intrusive in that there is a physical interaction between the sampling device and the sediments. Further and more intrusive geotechnical surveying would be required where direct cable burial is required along the route. This would provide information on soil conditions and suitability of burial equipment however as there is minimal sediment present, direct cable burial is not achievable. Any cable protection needed would be in the form of rock placement, rock filter bags or concrete mattressing directly over the cable.

4.11. The pre-installation surveys have allowed SHEPD to optimise the cable route within the survey corridor and helped to identify feasible installation and cable protection methods. The routeing has been refined following a review of seabed conditions, bathymetry, stakeholder views, seabed use and any other identified seabed features. In addition to this further marine surveys will be

Figure 6 - Mossbank shore line looking east with jetty in background

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undertaken during the summer of 2018 to better assess the engineering viability and environmental impact of the proposed cable route and installation works.

4.12. As part of this additional survey, drop-down video and imagery surveys will also be undertaken to understand better the range of potential habitats and geographic spread. The methodology in relation to the surveys was developed through discussion with SNH. The survey outputs from the drop-down video surveys will be shared to evidence the habitats and features present along and in the vicinity of the proposed cable.

4.13. To support the marine licence and the proposed cable installation methodology a CBRA and cable stability assessment will be completed to determine the level of protection needed and evaluate the impact of the proposed cable route.

4.14. The additional surveys may influence our cable installation design and routeing to help minimise the impact on the habitats and seabed features present on the route. This will allow identification of mitigation measures in the form of cable re-routing where appropriate, crossing locations for protective habitats, cable burial in areas suitable and also rock bag placement to stabilise the proposed cable to minimise movement along the seabed.

5. Project description

5.1. The existing route

5.1.1. The project is to install a replacement 33kV HVAC cable between Mossbank and Yell. The existing cable route is installed from Mossbank to Hoga on Yell, south of Ulsta across the Yell Sound (Figure 1). At each shore end landfall, the existing land-based network of OHL connects the submarine cable to the SHEPD network.

5.2. The proposed route

5.2.1. Following a review of the marine survey data, an optimum route for the proposed cable has been identified as shown in Figure 7. The proposed cable will be 3.4 km within the marine environment between MHWS limits. However, the ML application length is 4.0 km to allow for obstacle avoidance during cable lay and tolerances with the cable lay operations.

5.2.2. The proposed cable route lies within the survey corridor1 with some micro-routeing selected to avoid areas significant bedrock, boulders and avoid or minimise the impact on sensitive marine features identified from the surveys for the proposed cable.

5.2.3. The proposed cable retains the existing shore end landfall at Mossbank and Yell. Alternative landfall positions were reviewed but discounted due to a number of factors. On Mossbank a nearby jetty constrains the area to the east. The coastline around Yell is rocky and this extends to the ferry terminal at Ulsta.

1 See section 4.2 for justification of how the corridor was selected.

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5.2.4. The proposed cable route is laid adjacent to the west of the existing cable. An offset will be used to allow safe installation, operation, future maintenance and ongoing inspection of the cable(s).

5.2.5. On Mossbank the proposed cable will come ashore at the existing shore end landfall. The cable will then contain a ducted road-crossing and short section of underground cabling onto the existing SHEPD OHL.

5.2.6. The proposed cable route and method of installation has been identified based on a combination of desk studies, marine seabed surveys and stakeholder views. Prior to the cable installation, SHEPD’s appointed contractor will undertake a final review of the marine survey to confirm the seabed conditions and finalise the exact cable within the consented corridor and techniques to be employed.

5.2.7. Further to this, a review of the existing shore end landfall locations and land-based infrastucture was undertaken and verified with site visits on both Mossbank and Yell to confirm the shore end landing points and the method of cable installation above the MLWS limits. This was needed to assess the suitability for site access and the logistical constraints for plant and machinery but also better understand the environmental and landowner contraints.

5.2.8. A shore end cable installation by Horizontal Direction Drilling (HDD) was considered but discounted for a number of reasons namely the route length exceeded engineering capability. The limited public road network would require significant civil improvements. The construction of a temporary or permanent road would be required to permit the large machinery access to the cable landfall area at Yell.

5.2.9. The area around the cable landfall on Yell is composed of difficult, soft boggy terrain mainly peat. For the HDD works a large, level area of approximately 50 m by 50 m is required. The site needs to

Figure 7 - Proposed cable route

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be stable to support the large drilling machinery during the setup and drilling operations. With the unstable ground on Yell, this will require extensive and expensive civil improvement works.

5.2.10. Extensive civil works could be impacted by archaelogical presence in the area. This will require extensive pre-construction surveys with agreements from land owners and tenants but also increases the risk of archaelogical impacting on the works. The additional works will likely increase the difficulty of acquiring the consents to carry out the works.

5.2.11. On Yell, modifications to the land based infrastructure by undergrounding a number of sections of OHL would have operational benefit and improve future access. This would also provide environmental and visual benefits to the local landowners and bird species. The amount of undergrounding may be impacted by the difficult ground conditions.

5.2.12. As it is proposed to re-use the existing shore end landfall positions, the existing AtoN warning beacon locations will be retained. Any ongoing maintenance and inspections associated with the warning beacon will be carried out on a regular basis to ensure they are in good condition for sea user safety. Further details can be found in the Operation, inspection, maintenance and decommissioning strategy.

5.2.13. The proposed cable route and installation method, including associated land based works, have been informed following a review of the marine survey data and cable inspections, stakeholder feedback from consultations and environmental constraints2 whilst balancing SHEPD’s electricity licence obligations. Details of the proposed RPL for the cable route from MHWS limits from Mossbank to Yell is located within Appendix B and Appendix C.

5.2.14. In addition to this, more focussed investigations and studies have been carried out along the proposed cable routes and working areas affected by the works by SHEPD’s archaeological and ecological consultant on both Mossbank and Yell. This has helped to firstly identify archaeological/ecological interests and then to help eliminate and/or mitigate any potential impacts from the proposed works within cultural heritage sites and/or environmentally sensitive locations.

5.2.15. Offshore there are no scheduled archaeological sites or points of interest along the proposed route. Refer to the environmental supporting information within section 6.

5.2.16. Potential impacts on the designated features of the East Mainland Coast pSPA will be mitigated by avoiding the breeding season of red throated diver (April – mid Sept) limiting duration of cable installation and limiting speed of the cable installation vessel to reduce the physical disturbance to sea birds.

5.2.17. Following the otter survey, there are active holts over 100 m from proposed works at Mossbank landfall. Therefore impacts will be limited to a temporary disturbance of commuting and feeding otters in the area. However, at the Yell landfall otter activity was high with three otter holts recorded at 3.25 m, 4m and 23 m to the west of the proposed trenching works. Two of these holts are complex and highly active with numerous holes identified and abundant spraints. The cable route remains flexible so a 100 m wide working corridor in the onshore section of the cable will allow for micro routing and avoidance of holt locations.

2 Environmental constraints are detailed in Construction environment management plan

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5.2.18. The Yell Sound Coast SAC details restrictions on areas and access. This has been considered within the design by eliminating the works on Samphrey and careful selection of access route on Yell through discussion with landowners and tenants to minimise impact on seal and otter species.

5.2.19. Further information on this can be found in the Construction environment management plan.

5.3. The proposed installation methods

5.3.1. For the cable laying activities, a CLV will be used. Additional smaller support vessels will be required at each of the shallower shore locations; this is likely to be a multicat/DSV. This may require an anchoring system to be laid out prior to and during works in the nearshore region. An anchor handling vessel would be required to lay out the anchors. A guard vessel is also likely to be used during the cable lay operations in order to ensure other vessels remain outside the area of operations to reduce collision risk.

5.3.2. Initially, the proposed submarine cable will be surface laid on the seabed across the length of the route. Due to the strong tidal currents the majority of the proposed cable route will be across rocky seabed with very little overlying sediment. With the limited sediment direct cable burial will not be possible. By initially surface laying the cable this minimises the footprint in these areas however cable mobility on the seabed may increase the footprint and impact on the seabed habit.

5.3.3. To minimise the impact of the cable on the seabed during and after installation, SHEPD plan to lay rock filter bags (each with a seabed footprint of approximately 2.0 m by 2.0 m) or concrete mattresses (each with a footprint of approximately 6.0 m x 3.0 m) in spot locations on the cable to pin the cable to the seabed. Only clean washed stone will be used to fill the rock bags and no cementitious material will be used. Each bag shall be no more than 1.0 m high when installed. The rock filter bags have been proven to provide a habitat for aquatic species and mould to the seabed contours where installed.

5.3.4. Positioning of the rock bags or mattresses will help stabilise the cable. The risk of installing the rock bags or mattresses directly onto the cable could cause subsequent damage from point loading dependant on the seabed and lay of the cable. This may also increase the tension on the cable and potential for cable suspensions either side of the rock bag or mattress positions which increases mariner safety from potential snagging incidents. A post lay inspection of the cable after it is installed will identify the potential risk to placement of the rock filter bag or mattresses directly onto the cable and confirm exact locations to avoid creating suspensions of the cable.

5.3.5. To reduce the risk to mariners in the shallow areas of less than 10m chart datum along the route, rock bags and mattresses will not be installed as this would reduce the chart datum by 5%.

5.3.6. We will be undertaking a cable stability assessment to support our ML application that will help us to inform the cable stability throughout the proposed route with a view of minimising the amount of rock bags or mattresses required to pin the cable whilst ensuring cable stability following the installation. This will help inform the required rock bag or mattress separation.

5.3.7. From Mossbank, rock filter bags or concrete mattresses will be placed on the cable at roughly 50 m intervals within the marine environment. The rock bags or mattresses will help stabilise the cable, thus preventing damage by cable movement on the seabed following installation. Based on the 4.0 km ML application route length, a maximum of 80 rock filter bags or mattresses will be used. As noted above, cable stability assessment and CBRA will be carried out to minimise the number of rock bags or mattresses required to ensure the cable stability.

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5.3.8. In summary we propose to install a maximum of 80 rock filter bags or concrete mattresses along the route depending on our CBRA and cable stability study. Our cable installation and burial methodology is summarised in Table 1.

Location along the cable route Installation type Length of

cable (m) No rock filter

bags/concrete mattresses

From termination point with OHL to Mossbank shoreline

Onshore cable burial by open-cut trench from termination point with OHL through

field and local road 40 0

From Mossbank shoreline to MLWS

Cable lay with up to 100 m of cast iron split pipe protection 100 0

From MLWS on Mossbank to MLWS on Yell

Rock filter bags or concrete mattresses installed directly on cable 3,800 80

From MLWS to Yell shoreline

Cable lay with up to 100 m of cast iron split pipe protection 100 0

From Yell shoreline to termination point with OHL

Onshore cable burial by open-cut trench from termination point with OHL through

field 1,000 0

Total (marine cable length) 4,000 m 80

Table 1 - Cable installation, burial and protection

5.3.9. Due to the suitability of the existing shore end landfall locations and following assessment of alternative areas, the proposed cable will be installed adjacent to the existing cable at both Mossbank and Yell.

5.3.10. It is proposed to install the cable by using an open-cut trench method of installation inshore from the MLWS tidal limits at both shore end landfall locations. An open cut trench will be excavated to install and bury the cable. This will utilise traditional terrestrial based plant including excavators at low tide. The typical underground cable trench is illustrated below in Figure 8. To allow for micro-routing during cable installation, the landfall excavation works will take place within 100 m either side of the cable landfall positions shown.

5.3.11. At the Mossbank landfall, the marine cable will be installed by an open cut trench method above the MLWS limit. The marine cable will installed within a ducted conduit (Figure 9) through the nearby road.

5.3.12. At Mossbank, to complete the shore end installation works there will be some underground cabling from the transition joint location with the marine cable and minor modifications to the existing 33kV overhead line.

5.3.13. The trench will be excavated alongside the existing cable using a terrestrial-based mechanical excavator during low spring tide. The excavated material will be placed to one side of the trench for later reinstatement. Using a mechanical winch and cable rollers, the cable will be manoeuvred into the bottom of the trench and then covered with the excavated material using the mechanical excavator. The trench width will be minimised where possible however will be dependent on ground stability but will typically be 1 m wide. The target depth of the trench will be 1.25 m. Temporary trench shoring may be required to prevent collapse of the trench wall. The footprint of the excavator may be up to 5 m, and a working width, including for the temporary storage of removed material, would be in the order of 10 m.

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5.3.14. On either shore where sufficient burial cannot be achieved, cast iron split pipe will be fitted around the cable for additional protection in the event of exposure (Figure 9). This will be installed down to MLWS mark. We propose to install a maximum of 100 m of split pipe protection on each shore from MWHS to MLWS in the event that we can’t achieve sufficient cable burial to protect the cable. The split pipe is an articulated cast iron shell design that locks around the cable and fixed with bolted end clamps. There are a number of suppliers with differing shell designs and weights. As a guide each shell has an 8 mm wall thickness, with an effective length of 391 mm and combined weight in air of 39.96 kg/m.

Figure 8 - Open cut cable trench cross section inshore of MWS limit

Figure 9 - Open cut trench section through road on Mossbank

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5.3.15. The intertidal cable will be connected to the terrestrial cable in a transition joint pit buried in the ground located above the MHWS limit at each end. At the Mossbank end, from MHWS limit the cable will be buried onshore for approximately 40 m through the road and connect into the existing OHL. On the Yell shore, from the MHWS limit the cable will be buried for approximately 1000 m through the field and connect in to the OHL. This will permit the dismantling of 12 spans of existing OHL.

5.3.16. On completion of jointing and cabling works, spoil material will be backfilled into the trenches and the shore will be reinstated; grassed areas will be left to re-seed naturally. The upper surface layer will be stripped and stockpiled separately to allow a quicker reinstatement.

5.3.17. At each shore landfall location, to facilitate the onshore works and ensure compliance with the Construction (Design and Management) Regulations 2015, a temporary site area will be required, approximately 30 m x 30 m in size, to provide welfare facilities and parking during the works. To minimise ground disturbance, ease reinstatement and recovery, the area will be covered with a membrane material and levelled with rock chippings.

5.3.18. SHEPD’s Cost Benefit Analysis Methodology3 is used as evidence that the solution proposed in this project description represents a best value4 installation method of this submarine electricity cable route. The modelling recommended that rock placement (or rock bags) should be used to reduce the risk to marine users, stablise the cable and balance the views of the different stakeholders who we engaged with. The final CBA recommendation suggested that up to 400m of rockplacement should be installed to achieve these objectives. The current solution for the Mossbank – Yell cable is:

Initially surface lay the cable along the sea bed Install a maximum of 80 rock filter bags or concrete mattresses directly over the cable Install a maximum of 200 m of cast iron shells This solution would be able to achieve the same objective, outlined by the CBA model, but at a higher projected societal value and lower disruption to the marine environment by reducing the level of rock bags. It is therefore proposed to deviate from the CBA final recommendation.

5.3.19. A summary of the Cost Benefit Analysis model can be found in the Pre-Application Consultation report.

3 http://news.ssen.co.uk/media/147004/4731-ssepd-submarine-cables-doc-july-2016_06.pdf 4 Which we define as best balancing the health and safety, environmental, socio-economic, wider-engineering and economic considerations whilst meeting regulatory obligation.

Figure 9 – Diagram of split pipe protection

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5.4. Proposed cable protection methods

5.4.1. The cable installation method within the marine environment from each MLWS location will initially be surface laid across the length of the route. The proposed installation methods are less intrusive and allow for quicker installation duration. Due to the strong tidal currents along the route, rocky seabed and to minimise impact on protected habitats, it is planned to lay rock filter bags or concrete mattresses in spot locations on the cable at intervals along the route to pin the cable to the seabed ensuring stability.

5.4.2. By routeing the cable to the west of the existing cable we have avoided the need for any cable crossings within the marine environment.

5.4.3. As evidenced form the marine surveys due to a lack of sediment, we are not proposing to bury the cable in the marine environment however at the intertidal areas at both shore end landfall locations it is proposed to use an open cut trench method to install the cable down to the MLWS tidal limits.

5.4.4. On either shore above the MLWS limit, where sufficient cable burial cannot be achieved, cast iron split pipe will be fitted around the cable for additional protection in the event of exposure. On both Mossbank and Yell we propose to install a maximum of 100 m of split pipe protection to the cable.

5.4.5. This change to the cable design methodology follows consideration of comments and/or objections received at the PAC events as detailed in the Pre-Application Consultation report.

5.5. The proposed delivery programme

5.5.1. Due to the potential for seals and otters present close to the proposed cable installation activities, SHEPD propose to programme the cable installation works to avoid the sensitive periods from June to August.

5.5.2. SHEPD propose to complete the submarine cable and onshore connection works during the months of October 2018 – March 2019 or before if the necessary consents have been secured. The planned duration of the works is no greater than 30 days, exclusive of weather.

5.5.3. The onshore cabling works on both Mossbank and Yell will be completed prior to the main submarine cable installation works. This will include the ducted road crossing on Mossbank situated between the shore line and the existing OHL in the nearby field. The minor modifications required to the existing OHL networks will be carried out during commissioning of the submarine cable to the SHEPD network. Replacement of the existing AtoNs will also be undertaken during the OHL works.

5.5.4. Following successful commissioning of the proposed cable onto the SHEPD network, the OHL dismantling works down to the existing cable landfall on Yell will be undertaken and disposed of from site.

6. UXO Strategy

6.1.1. The Contractor appointed by SHEPD shall undertake an initial desktop study to assess the risk of UXO within the area of the cable route. In addition, if the desktop study identifies a high risk, a UXO survey along the cable route will be completed to detect any objects potentially UXO related. The results shall be used to inform cable routing within the consented corridor such that significant targets are avoided. If it is not possible to avoid a target, it shall be identified using an ROV or drop

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down camera. Alternatively where a UXO is encountered that cannot be avoided, a specialist Contractor shall be engaged to clear, recover or remove the target from the working area.

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7. Appendix A: Existing cable route with bathymetry

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Appendix B: Proposed cable route

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Appendix C: Proposed cable RPL

Position Name UTM30N

KP Latitude

Longitude

0.00 6704229.91 N 599871.24 E 0.04 6704262.34 N 599887.99 E 3.44 6707168.18 N 601601.59 E 4.44 6730063.66 N 611194.41 E

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