G-3-005 Rev 06 Decommissioning Programme - JP additions ......G-3-005 Rev 06 Decommissioning...

PROJECT No. 053256.02

DECOMMISSIONING PROGRAMME REF

No OF SHEETS 43

DOCUMENT No OFFICE CODE 05

PROJECT No

3256 AREA

00 DIS G

TYPE 3

NUMBER 005

06 06/09/10 Re-Issued For Approval KK CS SF RI




02 28/01/10 Issued For Approval CS KK SF RH

01 30/10/09 Issued for Comment CS RH SF RH

REV DATE DESCRIPTION BY CHK ENG PM Client

WAVE HUB

Decommissioning Programme

G-3-005 Rev 06 Decommissioning Programme - JP additions 09-09-10 of 43

TABLE OF CONTENTS

1 INTRODUCTION............................................................................................................................. 4

1.1 Scope .............................................. .................................................................................... 4 1.2 Abbreviations...................................... ............................................................................... 5

2 EXECUTIVE SUMMARY ................................................................................................................ 6

3 BACKGROUND INFORMATION............................. ....................................................................... 7

3.1 General Description ................................ .......................................................................... 7 3.2 Location & layout of Facilities.................... ...................................................................... 8 3.3 Obstructions along Route ........................... ................................................................... 10 3.4 Site Characteristics ............................... .......................................................................... 12

3.4.1 Metocean Data .................................................................................................... 12 3.4.2 Seabed Characteristics...................................................................................... 14

3.5 Fishing Activities................................. ............................................................................ 14 3.6 Shipping ........................................... ................................................................................ 16 3.7 Special Areas of Conservation...................... ................................................................. 18

4 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED............................................................. 19

4.1 Subsea Cables ...................................... ........................................................................... 19 4.2 Subsea Hub......................................... ............................................................................. 21 4.3 Dry-Mate Connectors ................................ ...................................................................... 21 4.4 Subsea Protection Materials ........................ .................................................................. 22 4.5 Navigation Buoys ................................... ......................................................................... 22

5 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES......................................... 25

5.1 General ............................................ ................................................................................. 25 5.2 Subsea Cables ...................................... ........................................................................... 28

5.2.1 Reuse ................................................................................................................... 28 5.2.2 Preservation In-Situ............................................................................................ 28 5.2.3 Removal............................................................................................................... 28 5.2.4 Removal or Disturbance of Overburden .......................................................... 28 5.2.5 Proposed Decommissioning Option ................................................................ 29

5.3 Subsea Hub......................................... ............................................................................. 32 5.4 Dry-Mate Connectors ................................ ...................................................................... 32 5.5 Subsea Protection Materials ........................ .................................................................. 32 5.6 Navigation Buoys ................................... ......................................................................... 33

6 ENVIRONMENTAL IMPACT ASSESSMENT .................... .......................................................... 34

7 CONSULTATIONS WITH INTERESTED PARTIES.............. ....................................................... 36

8 COSTS .......................................................................................................................................... 37

9 FINANCIAL SECURITY................................. ............................................................................... 38

10 SCHEDULE................................................................................................................................... 39

11 SEA-BED CLEARANCE.................................. ............................................................................. 40

12 RESTORATION OF SITE ............................................................................................................. 41

13 POST DECOMMISSIONING MONITORING, MAINTENANCE AND MA NAGEMENT OF SITE 42

14 REFERENCES & SUPPORTING STUDIES................................................................................. 43

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APPENDIX I OFFSHORE APPROACH DRAWING .......................... ...........................................

APPENDIX II HUB STRUCTURAL ASSEMBLY ............................ ...............................................

APPENDIX III CABLE ROUTE........................................ ................................................................

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1 INTRODUCTION

The South West of England Regional Development Agency (SWRDA) is undertaking the development of Wave Hub (see section 3.1), a novel system that will provide the electrical infrastructure to support developers of Wave Energy Converter devices (WECs). When installed, Wave Hub will allow WEC developers the opportunity to test WEC arrays over several years in a fully monitored marine environment, and export their generated electricity to the local grid, via the Western Power Distribution (WPD) substation at Hayle on the north coast of Cornwall.

The development briefly consists of installing approximately 25km of armoured subsea power cable (SPC) from the shore to a subsea hub. The surface WEC’s are connected via sub sea cables from the hub tails.

The SPC will be laid on the seabed and trenched and buried through the near shore area and the first 7km of route. From this point it will be intermittently trenched (where seabed sediments allow) to approximately KP7. Where trenching is not possible between KP 3 and KP7 intermittent rock may be deployed to ensure on-bottom stability.

The remaining length of the proposed cable route comprises mainly bedrock. Accordingly, the cable will be laid directly on top of the bedrock/seabed. To prevent the cable from damage and to ensure that the cable remains in place, cable protection in the form of a continuous rock berm will be provided.

At the transition between the cable emerging from the trench (sand) to the seabed (rock), a suitable length of protection in the form of rock dumping will be provided.

The 300m long Hub Tail cables will be protected by rock dump for the first 150m, thereafter they will be secured by concrete mattresses to the seabed. It should be noted that it will be necessary to roll back the mattresses from time to time to allow connection/disconnection of cables to the wave energy converter devices.

In addition to the SPC rockdumping protection, the hub structure will also require stabilisation with rock placement.

At the landfall the cable will be installed in HDPE conduits under the beach dunes and connected to a block and render construction electrical substation. The substation includes a transformer, switching gear and control and monitoring facilities.

SWRDA are responsible for the development, financing, operation and decommissioning of the Wave Hub project.

SWRDA obtained consent under Section 36 of the Electricity Act 1989 in September 2007 for ‘an offshore renewables wave generating station located approximately 10 Nautical miles offshore from St Ives’. Contained within this consent was the condition that 4 months prior to the start of construction a Decommissioning Programme was to be prepared and submitted to the Secretary of State pursuant to Section 105(2) of the Energy Act 2004.

It is expected that the decommissioning programme will be reviewed throughout the life of the project and where necessary revised to take account of changes in environmental conditions, regulatory requirements as well as advances in technology and working practises.

1.1 Scope

This document presents the decommissioning programme for the Wave Hub Development and is being submitted for approval in accordance with the conditions stipulated in the Energy Act 2004. The decommissioning programme addresses all components of the Wave Hub infrastructure below mean high water springs. Decommissioning requirements for the onshore

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infrastructure fall under the Deemed Planning Permission granted under Section 90 of the Town and Country Planning Act 1990.

1.2 Abbreviations

CSFC - Cornwall Sea Fisheries Committee

EIA - Environmental Impact Assessment

FEPA - Food and Environment Protection Act

HAT - Highest Astronomical Tide

HDPE - High Density Polyethylene

ICES - International Council for the Exploration of the Sea

IP - Intersection Point

KP - Kilometre Point

LAT - Lowest Astronomical Tide

MHWN - Mean High Water Neaps

MLWN - Mean Low Water Neaps

MLWS - Mean Low Water Springs

MSL - Mean Sea Level

ROV - Remotely Operated Vehicle

SPC - Subsea Power Cable

SSSI - Sites of Special Scientific Interests

SWRDA - South West of England Regional Development Agency

SWL - Still Water Level

TSS - Traffic Separation Scheme

WEC(s) - Wave Energy Converter(s)

WGS 84 - World Geodetic System 1984

WEC Developer - Owner of WEC

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2 EXECUTIVE SUMMARY

This document presents the decommissioning programme for the Wave Hub Development and is being submitted as required under condition 3(c) of the project’s Section 36 consent dated 17th September 2007.

The decommissioning programme is supported by the Environmental Statement [Ref. 9], submitted to the regulatory bodies in support of the consent application for the Wave Hub project. The environmental statement provides detailed baseline information for the site and may be downloaded from the Wave Hub website http://www.wavehub.co.uk/.

As detailed within this document, it is proposed to remove all of the subsea infrastructure to shore for re-cycling or disposal except for the rock dump materials and concrete mattresses used for on-bottom stability over the rocky areas of seabed. These will remain in situ on the seabed. SWRDA will assume overall responsibility for decommissioning the Wave Hub site including all devices connected to it.

It is intended that this decommissioning programme is reviewed throughout the project life to reflect any structural changes (newly connected or disconnected devices), technological and regulatory advances.

Section 13 provides details of the supporting documents and references employed in the preparation of this document

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3 BACKGROUND INFORMATION

3.1 General Description

The wave hub system comprises of 4 berths within a 4km x 2km area approximately 10 miles offshore the north coast of Cornwall. The seabed in this region is predominately rock.

Each WEC Developer will connect to the Wave Hub system by means of a subsea (developer installed) cable that will run from the lead device of each WEC array to a connection point on one of four cable tails that run from the Hub. The connections to the tails will be made above water. The details and layout of the WEC arrays are not known at present, these will be subject of separate FEPA licence applications and separate decommissioning plans in due course.

The Hub will be located on the seabed and protected by rock dump. The purpose of the Hub is to provide a watertight connection between the cable tails and the main SPC. Within the Hub, the main cable (which consists of twin 300mm2 33kV power triads and fibre optic cables) will be terminated onto two isolated sections allowing operation as two individual power circuits. Each circuit will service two WEC deployment areas.

The fibre optic cables will be split out from the SPC within the Hub and joined to those running to each WEC via the cable tails and WEC cables.

The SPC runs for 18km on a rocky seabed and then runs 7km on a partially covered sand seabed until the shoreline is reached. The SPC will have continuous rock dump for protection, stabilisation and span correction along the rock seabed section of the route. The cable will be trenched and buried where possible along the sandy section of the route.

The SPC will be trenched and buried across the beach area, and will then be jointed to a pair of 400mm2 33kV onshore cables on the beach

An artist’s impression of the Wave Hub system is shown in Figure 3-1.

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Figure 3-1 Schematic Layout

3.2 Location & layout of Facilities

Table 3-1 shows the approved cable route corridor and Hub deployment area. The WGS (World Geodetic System) 84 coordinates are tabulated in Table 3-2 and Table 3-3 respectively.

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Table 3-1 Cable Route Corridor (Final cable route w ill be advised when built)

UTM 30 N LAT / LONG ID

EASTING NORTHING LONGITUDE LATITUDE KP

IP-0 326,445.43 5,563,127.53 -5 ° 25.899 ' 50 ° 11.692 ' 0.00

IP-1 326,836.12 5,565,003.64 -5 ° 25.622 ' 50 ° 12.710 ' 1,916.37

IP-2 326,719.62 5,565,418.99 -5 ° 25.731 ' 50 ° 12.932 ' 2,347.74

IP-3 326,116.87 5,566,325.65 -5 ° 26.263 ' 50 ° 13.411 ' 3,436.48

IP-4 324,840.45 5,567,318.42 -5 ° 27.363 ' 50 ° 13.923 ' 5,053.53

IP-5 321,573.42 5,567,997.15 -5 ° 30.128 ' 50 ° 14.231 ' 8,390.31

IP-6 321,168.20 5,568,554.32 -5 ° 30.484 ' 50 ° 14.523 ' 9,079.25

IP-7 320,509.73 5,569,780.09 -5 ° 31.073 ' 50 ° 15.172 ' 10,470.69

IP-8 320,074.13 5,571,360.42 -5 ° 31.484 ' 50 ° 16.016 ' 12,109.95

IP-9 319,643.59 5,571,983.44 -5 ° 31.864 ' 50 ° 16.344 ' 12,867.26

IP-10 318,660.95 5,572,560.87 -5 ° 32.707 ' 50 ° 16.638 ' 14,007.00

IP-11 317,911.31 5,573,249.73 -5 ° 33.358 ' 50 ° 16.995 ' 15,025.08

IP-12 316,087.85 5,574,551.47 -5 ° 34.930 ' 50 ° 17.663 ' 17,265.52

IP-13 315,550.94 5,574,860.45 -5 ° 35.391 ' 50 ° 17.819 ' 17,884.98

IP-14 314,595.16 5,575,125.26 -5 ° 36.203 ' 50 ° 17.944 ' 18,876.77

IP-15 313,550.20 5,575,848.16 -5 ° 37.103 ' 50 ° 18.314 ' 20,147.40

IP-16 313,210.28 5,576,348.07 -5 ° 37.404 ' 50 ° 18.577 ' 20,751.93

IP-17 312,904.39 5,578,329.29 -5 ° 37.721 ' 50 ° 19.639 ' 22,756.63

IP-18 312,796.13 5,579,557.28 -5 ° 37.849 ' 50 ° 20.299 ' 23,989.38

IP-19 313,044.00 5,580,181.24 -5 ° 37.658 ' 50 ° 20.640 ' 24,660.78

IP-20 313,567.16 5,580,386.38 -5 ° 37.224 ' 50 ° 20.761 ' 25,222.72

See diagrammatic Representation in Appendix III

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Table 3-2 Coordinates for the approved route corrid or

50 11.650 N 05 25.833 W

50 12.100 N 05 25.817 W

50 12.750 N 05 25.700 W

50 13.177 N 05 25.017 W

50 13.433 N 05 26.400 W

50 13.733 N 05 26.983 W

50 13.850 N 05 27.833 W

50 14.250 N 05 30.017 W

50 16.300 N 05 31.967 W

50 18.433 N 05 37.117 W

50 20.500 N 05 37.617 W

50 20.750 N 05 37.183 W

Table 3-3 Wave Hub Deployment Area

50 20.700 N 05 37.230 W

50 22.830 N 05 37.760 W

50 20.860 N 05 35.560 W

50 22.980 N 05 36.100 W

3.3 Obstructions along Route

Offshore surveys undertaken have not identified any third party cables or pipelines, either along the route or within the offshore Wave Hub deployment area.

However, there are a number of wrecks within the area, some of which have been designated Protected Wrecks. A wreck has been clearly identified lying within the approved route corridor. A minimum clearance of 50m from the wreck will be maintained to ensure the wreck is undisturbed by construction/removal operations as agreed with English Heritage. The coordinates of the wreckage are listed in Table 3-4. The wreck location and SPC cable route to maintain the minimum clearance are shown in Figure 3-2.

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Figure 3-2 3D Imaging of Seabed at Location of Wre ck

Table 3-4 Wreck Location Coordinates

ID EASTING NORTHING

1 316,959.48 5,573,749.64

2 316,974,.29 5,573,764.97

3 316,990.69 5,573,570.69

4 316,955,13 5,573,701.52

5 316,953.13 5,573,657.10

6 316,909.21 5,573,615.33

7 316,871.12 5,573,590.48

8 316,855.77 5,573,576.74

9 316,840.96 5,573,590.48

10 316,855.77 5,573,606.35

11 316,877.46 5,573,615.86

12 316,922.44 5,573,655.52

13 316,925.61 5,573,701.52

14 316,959.48 5,573,749.64

SPC

Wreck

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3.4 Site Characteristics

3.4.1 Metocean Data

A site specific metocean report has been prepared [Ref. 7]. This shows the Hub site to have the following characteristics:

100 Yr Significant Wave Height 13.7m (Tz 13.4s)

100 Yr Maximum Wave Height 25.1m (Tz 14.1s)

100 yr Current (1m above seabed) 1.05m/Sec

Extreme Water level See Table 3-5

Temperature See Figure 3-4

Salinity See Figure 3-4

Density See Figure 3-4

Table 3-5 Extreme Water levels (at Hub Site)

m LAT m msl

100 year total 24.8 20.7

50 year total 24.0 19.9

100 year +ve swl 8.3 4.2

50 year +ve swl 8.2 4.1

10 year +ve swl 8.1 4.0

1 year +ve swl 7.9 3.8

HAT 7.3 3.2

MHWS 6.8 2.7

MHWN 5.5 1.4

MSL 4.1 0.0

MLWN 2.7 -1.4

MLWS 1.0 -3.1

LAT 0.0 -4.1

1 year –ve swl 0.5 -3.6

10 year –ve swl 0.3 -3.8

50 year –ve swl 0.2 -3.9

100 year –ve swl 0.1 -4.0

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Figure 3-4 Temperature, Salinity & Density Measurem ents

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The depth profile for the route is shown in Figure 3-5 below.

-60

-50

-40

-30

-20

-10

00 5,000 10,000 15,000 20,000 25,000

Route Length (m)

Ele

vatio

n (m

)

Figure 3-5 Depth Profile

3.4.2 Seabed Characteristics

The seabed along the SPC route can in general terms be split into three defined areas.

• KP0 (shore) to KP 3.0 Sandy sediments suitable for cable burial

• KP 3.0 to KP 6.5 Intermittent sediments overlying rock

• KP 6.5 to KP 25.0 Exposed rock seabed

The seabed within the deployment area consists of intermittent sediments overlying rock.

The SPC will be buried where possible and where burial is not possible, rock dumped to assure on-bottom stability.

3.5 Fishing Activities

Fisheries surveillance data was obtained for 29E4 – Sub-Square 1 [Ref 14] for the period 2000-2005 (although 2004 is the last complete year for which data is available). From this data, the following key observations were made.

• Fishing activity is highest in February and March during the sole fishery and lowest in November and December;

• U.K. vessels (47%) and French vessels (43%) account for the majority of sightings of active vessels;

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• The great majority of French vessels are otter trawlers. Almost all of these fish outside the 12 mile limit;

• All the Belgian vessels are beam trawlers. Most sightings of these are outside the 12 mile limit;

• U.K. vessels use a number of different fishing methods in the area, including beam and otter trawling, potting and gill netting. Activity is spread across the whole of ICES rectangle 29E4, Sub-Square 1;

• Beam trawling activity is highest in February and March;

• Otter trawling activity is highest in January and February;

• Potting activity is highest in August and September;

• Gill netting activity is highest from June to October;

• Most of the otter trawling takes place outside of the 12 mile limit

• Much of the beam trawling takes place outside of the 12 mile limit However, some vessels are allowed to work inside the 12 mile limit;

• Much of the potting takes place close to the deployment area;

Figure 3-6 shows the distribution of vessel sightings by gear type. From this figure it can be seen that as expected, the majority of beam trawling occurs in the deeper water (>30m). However there are instances of beam trawlers closer to shore. The sightings are likely to be vessels in transit as rocky seabed is generally considered unsuitable for trawling and national fisheries regulations (reproduced below) place restrictions on fishing in this area.

The following U.K. national fishery regulations apply between 6 miles and 12 miles from land in the study area [Ref.8]:

• No beam trawlers allowed to fish with engine capacity of >221 kw;

• No foreign vessels without clear historical fishing rights and quota (in this area this includes mainly Belgian beam trawlers and French otter trawlers).

Cornwall Sea Fisheries District (CSFD) regulations apply to waters from the coast out as far as the 6 mile limit; the following byelaws are relevant:

Shellfish fishing:

No vessels greater than 16.46 m overall length may fish for shellfish, except that between 3 and 6 miles from land any shellfish vessel who had fished in this area prior to 6th August 1997 may (under registration with CSFD) continue to do so.

Trawling:

No vessels of greater than 18.28 m overall length or with an engine power of > 221 kw can trawl inside 6 miles, except that between 3 and 6 miles from land, any trawler under this category who had fished in this area prior to 6th August 1997 may (under registration with CSFC) continue to do so.

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Figure 3-6 Fishing Vessel Sightings by Gear Type 20 02-2004 [Ref. 8]

The information presented in Figure 3-6 is based on a total of 221 patrols of Subsquare 29E4/1 between 2002 and 2004. It shows that for Subsquare 29E4/1 as a whole, the main gear types sighted were beam trawlers (38%), unspecified trawlers (38%) and potters (21%).

3.6 Shipping

A navigation and shipping study was performed [Ref. 8]. The results shown in Figure 3.7 and Figure 3.8 present a cumulative picture of shipping data over a 28 day survey period (20TH May – 3rd June 2005 and 29th July – 12th August 2005). It is clear from this study that large vessels may traverse the cable route however, these marine surveys were carried out before the extension to the TSS off Land’s End was introduced (From 1st July 2009 the north-south TSS between Land’s End and the isles of Scilly will be extended northwards by 12 nautical miles). Hence it is likely that the movements are now likely to be significantly different as vessels will enter and leave the TSS further north than previously stated.

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Figure 3-7 Shipping Types

Figure 3-8 Shipping Track results

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3.7 Special Areas of Conservation

No special areas of conservation exist within the boundaries of the Wave Hub development. However, the project is situated in fairly close proximity to two Sites of Special Scientific Interest (SSSI). The location of these is shown as the shaded areas in Figure 3-9.

Figure 3-9 Boundaries of Sites of Special Scientifi c Interest (SSSI) in the vicinity of the Wave Hub Landfall

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4 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED

4.1 Subsea Cables

Two different sizes of cable will be employed subsea, the main export cable (SPC) and the smaller ‘hub tail’ cables

Table 4-1 and Table 4-2 illustrate in detail the mechanical properties of the offshore cables. The cable designs are shown pictorially in Figure 4-1and Figure 4-2

Table 4-1 Subsea Power Cable Mechanical Properties

6 core x 300mm2 CU, 18/30(36)kV SUBMARINE POWER CABLE

Parameter Description/Input

Outer Sheath Diameter 160mm +/- 3mm

Outer Sheath Material Extruded Polyethylene

Outer Sheath Colour Black + Yellow stripe

Sheath reinforcement Material Galvanised Steel Wire

Static Minimum Bend Radius 1600mm

Weight in Air 50,950 kg/km

Weight in Seawater-Unflooded 30,340 kg/m

Weight in Seawater-Flooded 32,590 kg/m

Minimum Breakload 125 kN

Umbilical Max Safe Working Load 500 kN

Cable Impact Energy 918kJ/m2

Figure 4-1 SPC Layout

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Table 4-2 Hub Tail 3 core of 120mm 2 33kV Submarine Power Cable Mechanical Properties

3 Core of 120mm2 33 kV SUBMARINE POWER CABLE

Parameter Description/Input

Outer Sheath Diameter 104mm +/- 3mm

Outer Sheath Material Polyethylene

Outer Sheath Colour Black + Yellow stripe

Sheath reinforcement Material Galvanised Steel Wire

Static Minimum Bend Radius 1040 mm

Weight in Air 20,200 kg/km

Weight in Seawater 11,490 kg/m

Minimum Breakload 390 kN

Umbilical Max Safe Working Load 97.5 kN

Figure 4-2 Hub Tail Layout

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4.2 Subsea Hub

The Hub is a subsea connection unit, providing electrical and fibre optic connection between the SPC and hub tails. It is a steel structure containing electrical and fibre optic cable joints. (For details of the Hub’s weight and dimensions see Appendix II). The hub does not require any foundation and will be placed directly onto the seabed. It will be protected by rock dumping.

Figure 4-3 Hub Representation

4.3 Dry-Mate Connectors

The dry mate connectors are situated at the WEC end of the four no. hub tails. One half will be fitted to the cable tail and the other half free issued to the WEC developers, the dry-mate connectors are rated for 11kV as no proven system rated to 33kV currently exists. In the event the system is ever required to be rated to the higher voltage, these components will need to be replaced by a cable splice. They provide electrical and fibre optic connection for the hub tail power cables to the WEC installed cables.

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Figure 4-4 Dry Mate Connector [Ref 13]

4.4 Subsea Protection Materials

The SPC will be continuously rock dumped along the route where the cable traverses rocky seabed conditions.

The hub will also be rock dumped. Furthermore, concrete mattresses may be deployed to provide protection along the Hub Tails and for the dry mate connectors as well as being employed to provide additional stability to the rock berm. The Offshore Approach Drawing, 05-3256-00-U-0-002, shows the protection requirements for the Hub and Hub Tails in terms of both rock dump and mattress deployment.

For a continuous rock berm covering the whole cable length, the target rock grading is as follows:

4.5 Navigation Buoys

The WEC deployment area shall be marked using 6 navigation buoys. The extremities of the area to each be marked by a Special Mark buoy Total 6 (six) buoys. The special marks will be on the 4 corners and one each in the mid point of the 4km length. The buoys to be established, one in each of the following positions:

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1. Latitude 50 deg 22'.833N Longitude 05 deg 37'.767W 2. Latitude 50 deg 22'.983N Longitude 05 deg 36'.100W 3. Latitude 50 deg 20'.866N Longitude 05 deg 35'.567W 4. Latitude 50 deg 20'.700N Longitude 05 deg 37'.233W 5. Latitude 50 deg 21’.765N Longitude 05 deg 37’.495W 6. Latitude 50 deg 21’.920N Longitude 05 deg 35’.830W Two Cardinal Marks are also to be deployed at the following positions:

North Cardinal - Latitude 50 deg 23'.057N Longitude 05 deg 38'.251W

South Cardinal - Latitude 50 deg 20'.644N Longitude 05 deg 35'.082W

The special marks conform with the requirements of the IALA Maritime Buoyage System and have the characteristics as described below:

Table 4-3: Specification for the Navigation Special Marks

No. of Buoys Required 6 No.

Approximate diameter of buoy body 3m

Hull Material Steel

Paint Colour BS 381C 356

Focal Plane Height of Light 4m

Light Sequence flashing every 5 seconds (FL Y 5s)

Light Colour Yellow

Nominal range of Light 5nm

Topmark X [1]

Mooring System To be determined

Weight of ‘Sinker’ To be determined

Sinker Material Cast Iron

Design Life 25 Years

Water Depth Range 45m-70m

Seabed Type Sand/Rock

Radar Reflector Required

No. of lifting eyes 4 No. Per Buoy (each rated to lift the

whole weight of buoy & riser)

No. of mooring eyes 2 No. Per Buoy

Notes: 1 the arms of the 'X' should be diagonally contained within a square with length of side of about 33% of the buoy diameter at the waterline. The width of the arms of the 'X' to be about 15% of the length of side of the square

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The cardinal marks conform with the requirements of the IALA Maritime Buoyage System and have the characteristics as described below:

Table 4-4: Specification for the Navigation Cardina l Marks

No. of Buoys Required 1 No. North Cardinal

Pillar Buoy 1 No. South Cardinal

Pillar Buoy

Approximate diameter of buoy body 3m 3m

Hull Material Steel Steel

Colour black above yellow yellow above black

Focal Plane Height of Light 6m 6m

Light Sequence Very Quick (VQ)

flashing VQ(6) + LFl 10s

Light Colour White White

Nominal range of Light 7nm 7nm

Topmark 2 black cones, one

above the other, points upward

2 black cones, one above the other, points

downwards Mooring System To be determined To be determined

Weight of ‘Sinker’ To be determined To be determined

Sinker Material Cast Iron Cast Iron

Design Life 25 Years 25 Years

Water Depth Range 45m-70m 45m-70m

Seabed Type Sand/Rock Sand/Rock

Radar Reflector Required Required

No. of lifting eyes 4 No. Per Buoy (each rated to lift the whole

weight of buoy & riser)

4 No. Per Buoy (each rated to lift the whole

weight of buoy & riser)

No. of mooring eyes 2 No. Per Buoy 2 No. Per Buoy

Additional Requirements This buoy should be provided with AIS as an AtoN to identifying the wave hub site.

None

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5 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES

5.1 General

Sections 105 to 114 of the Energy Act 2004 introduce a decommissioning scheme for offshore marine energy installations. Offshore infrastructure is defined as that beyond Mean Low Water.

The Energy Act does not cover the inter-tidal zone (area between high & low water). Decommissioning of any infrastructure within this zone will be carried out in accordance with relevant legislation.

The Guidance Notes for Industry [Ref. 1] start from a general presumption in favour of the whole of all disused installations being removed and subsequently taken back to land for reuse, recycling, incineration with energy recovery or disposal at a licensed site. However, reference is made to the IMO Standards [Ref. 5] in which other solutions may be considered. The situations where an installation may be left in place or only partially removed are:

• The installation or structure will serve a new use;

• Entire removal would involve extreme cost;

• Entire removal would involve unacceptable risk to personnel;

• Entire removal would involve an unacceptable risk to the environment;

• The installation or structure weighs more than 4000 Tonnes in air or is standing in more than 100m of water and could be left wholly or partially in place without causing unjustifiable interference with other users of the sea.

The guidance notes [Ref. 1] set out some examples where solutions other than complete removal may be possible. Three cases are potentially applicable to Wave Hub:

• Structures which will be reused for renewable energy generation – where infrastructure such as cabling is intended to be reused for new renewable energy devices it is likely to be preferable to leave the infrastructure in place. This may be the case, for example at a test site for wave and tidal energy devices. i.e. there is no need to remove the cable if the site is empty for a few years but other devices are expected in the future. However the infrastructure will have to be removed when the site eventually becomes ‘disused’;

• Cables buried at a safe depth below the sea-bed – where cables remain buried at a safe depth below the sea-bed there may be a case for leaving them there, given the potential for impact on the marine environment, as well as the financial costs of removal….where it is proposed to leave cables in place, cable burial depth should be monitored over and beyond the life of the installation to assess the risk of cables becoming exposed after decommissioning;

• Scour protection materials – where scour protection materials have been used, there may be a case for leaving them there to preserve any marine habitat established over the life of the installation, where they do not have a detrimental impact on the environment, conservation aims, the safety of navigation and other users of the sea.

As decommissioning activities will inevitably lead to the production of controlled waste, under the Environmental Protection Act 1990, SWRDA will have a duty of care to ensure that when waste is transferred, it is only transferred to an authorised person (e.g. a registered waste carrier or someone who holds a license to recover or dispose of waste) and that there is a written description of the waste on a waste transfer note.

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Table 5-1 presents the criteria employed in reviewing the various decommissioning options available for the Wave Hub infrastructure.

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Table 5-1 – Assessment Criteria Definitions

Weighting Technical Complexity and Challenges

Risks to Personnel Cost and Timescale Effect on Other Users of the Sea

1 The method is very simple, is used on a regular basis and poses few technical challenges.

The method proposed involves a very low risk of injury to personnel

The method is very cost effective and can be performed within a very short timescale.

The is no effect on other users of the sea as a result of this method/activity

2 The method is simple or is regularly used and poses some technical challenges.

The method proposed involves a low risk of injury to personnel

The method is cost effective and can be performed within a short timescale.

The effects, on other users of the sea is minimal as a result of this method/activity

3 The method is moderately complex, is sometimes used and poses some technical challenges.

The method proposed involves a low to medium risk of injury to personnel

The method is only moderately cost effective and can be performed within a moderate timescale.

There is a small effect on other users of the sea as a result of this method/activity

4 The method is complex or is very rarely used and poses significant technical challenges.

The method proposed involves a medium to high risk of injury to personnel

The method is costly and may be performed over an extended timescale.

There are moderate effects on other users of the sea as a result of this method/activity

5 The method is very complex or has never been tried and poses major technical challenges.

The method proposed involves a high risk of injury to personnel

The method is very costly and is expected to be very slow.

There are significant effects on other users of the sea as a result of this method/activity

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5.2 Subsea Cables

The submarine power cable will be laid on the seabed and trenched and buried through the near shore area and the first 7km of route. From this point it will be intermittently trenched (where seabed sediments allow) to approximately KP7. Where trenching is not possible between KP 3 and KP7 intermittent rock may be employed to ensure on-bottom stability. From KP 7 onwards the cable will be laid directly on the seabed and stabilised with flexible concrete mattresses and continuous rock. The cable will terminate at the subsea Hub unit. Four smaller cables (Tails) will emanate from the hub unit and terminate in dry mate connectors.

The options currently available for decommissioning the offshore infrastructure include:

• re-use;

• preservation in-situ;

• removal.

5.2.1 Reuse

Re-use is generally the preferred option and the 33kV rating of the cable (although initially operated at 11kV) allows for a wide range of possible additional users. However, there will come a time when the cable will eventually be redundant and will have to be decommissioned.

5.2.2 Preservation In-Situ

The simplest decommissioning option is to leave the infrastructure in place to decay over time. However, this will present a continued liability to SWRDA and may also involve maintenance of the rock berm over time.

5.2.3 Removal

There are various methods available for the removal of the subsea cables. These consist of the reversal of the installation process along with other methods specific to removal such as cutting the cable into sections, then lifting each section to a barge on the surface. Alternatively, the cable may be cut into sections and then towed to shore instead of retrieval to a barge.

5.2.4 Removal or Disturbance of Overburden

Each of the above mentioned removal activities will require disturbance of the overburden (backfill, mattresses and rock dump) prior to recovery in order to gain access to the cable. Exposure of the cable may be necessary in order to prevent any dynamic stresses or build-up of tension in the cable during recovery operations. It may also be performed for example to allow access for installation of cutting equipment, buoyancy aids, etc.

The duration between uncovering the cable and removing it should be as short as possible in order to minimise any potential reburial. Several methods of cover removal are available. These are summarised below. Decommissioning of the rock dump is discussed in Section 5.5.

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5.2.5 Proposed Decommissioning Option

An evaluation of the various decommissioning options is shown in Table 5-2. From this it can be seen that removal of the cable by the reverse reeling method is considered as the preferred option. SWRDA are proposing to adopt this option. Once removed the cable would be taken to shore for processing at a re-cycling/scrapping facility.

Jetting Sled: A sled straddles the cable and a high pressure pump directs jets of water onto the cover material.

Plough: The plough share runs beneath the cable lifting it while the plough carrier rides over or straddles it.

Mechanical Trencher:

A tracked vehicle straddles the cable, removing the cover material through a combination of cutting and suction.

Jet Pump: Opposite to the principal of the suction pump, seabed excavation is achieved by jetting large volumes of water onto seabed material. No limitation on depth of water and is most efficient on non-cohesive soils.

Suction Pump: Similar to the hopper suction dredger except a high volume, low pressure pump is fitted to the lower end of the suspended pipe which discharges cover material into the hopper.

Surface Grab: A grab mechanism is suspended from a barge-mounted jib and removes rock or cohesive soil from the pipeline, depositing to one side or recovering to surface.

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Table 5-2 Subsea Cable Decommissioning Appraisal

Method Technical Complexity and

Challenges Risks to Personnel Cost and Timescale Effect on Oth er Users of the Sea Total Score

1 Leaving In-Situ

No Remedial Work

Although this is the most cost effective and safer option due to the nature of the seabed along the route, should the cable be left in situ without maintenance of the rock berm it may become exposed and present a snagging hazard with continued liability for SWRDA, therefore this option is not considered suitable unless SWRDA are prepared to fund an ongoing monitoring programme for the cable and any liabilities that arise from its continual presence on the seabed. However in the nearshore area where the cable is buried it may be possible to allow the cable to remain in-situ. The feasibility of this option should be re-assessed as the project progresses and details are gained as to the behaviour of the sediments in the nearshore region.

5 1A

Score 0 0 0 5

With Remedial Work

Selective Trenching

High technical risk, selective trenching of any exposed or unstable sections of cable into the rock seabed

Low risk of injury to personnel as trenching can be controlled by procedures.

Expected to be costly and slow Cable will remain on seabed in trenched condition and will be overtrawlable.

13 1B

Score 5 1 5 2

With Remedial Work

Selective rock dumping

Low to Medium technical risk, selective burial of any exposed or unstable sections. Using rock placement.

Low risk of injury to personnel as rock placement can be controlled by procedures.

A significant quantity of rock will be required, likely to be expensive.

Cable will remain on seabed in rock dumped condition and will be overtrawlable.

10 1C

Score 2 1 4 3

With Remedial Work

Selective Removal

Medium technical risk due to cutting operations, selective removal of any exposed or unstable sections.

Medium risk of injury to personnel as cutting may be performed by divers. If fully automated risk may reduce to low. However risk remains in lifting/handling of cut sections

Moderately costly method and can be performed moderately quickly.

Some of the cable will remain on seabed in rock dumped condition and will be overtrawlable.

12 1D

Score 4 3 3 2

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Method Technical Complexity and Challenges Risks to Personnel Cost and Timescale Effect on Other Users of the Sea Total

Score

2 Removal and Recovery

2A Reverse reel method

Technically feasible, may require removal of continuous rock placement and mattresses, this is considered a moderate technical risk method.

Low risk of injury to personnel as rock removal and reeling can be controlled by procedures and performed without divers. Note if mattresses are recovered to the surface, this can be an extremely hazardous operation.

The method is costly and would be slow. However the scrap value of the cable could be offset against these costs

Cable removed therefore no long term effect on other users of the sea. (There will be a temporary impact during removal operations)

14

Score 3 5 4 1

2B Cut and lift method Technically feasible, however, as the cable is trenched and covered consciously with rock the operation will be complex and slow i.e. de-bury, cut into sections, lift sections onto vessel.

Medium risk of injury to personnel as cutting may be performed by divers. If fully automated risk may reduce to low. However risk remains in lifting/handling of cut sections

This method would be moderately cost effective but would be slower than re-reeling.

As 2A. 11

Score 4 3 3 1

2C Float and tow method

Slow complex process with increased technical risk. Would require cutting the cable into reasonable (~1km) lengths initially

As 2B. This would be a costly operation, supply and fitting of floatation

devices would incur costs. Cutting equipment is still required along

with potentially additional vessels for towing etc.

As 2A. 14

Score 5 3 5 1

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5.3 Subsea Hub

The subsea hub will be removed from the seabed unless it can be shown that leaving the rock dump surrounding the hub in place preserves a marine habitat. Until surveys of the rock dump are undertaken over the life of the hub it is not possible to know if this is likely to occur. However, due to the high hydrodynamic loads in the area, the presence of the rock dump is likely to provide a sheltered area for marine life which otherwise would not be found in the vicinity.

Removal of the hub would take the form of:

• exposing the hub and cables by displacing the rock dump;

• cutting the cables attached to the hub;

• recovering the cable tails to the surface (for the main submarine cable see Section 5.2);

• recovering the hub and transporting to shore for re-cycling.

It is not possible to remove the rock material associated with the hub from the seabed without incurring excessive cost and personnel risk (see Section 5.5) and in accordance with Reference 1 it is envisaged that the rock material would remain.

5.4 Dry-Mate Connectors

The dry mate connectors will be removed from the seabed and taken ashore for re-cycling or disposal. The dry mate connectors are attached to the cable tails so will be lifted with them.

5.5 Subsea Protection Materials

The main subsea protection material will be rock dump placed to provide stability against hydrodynamic loads for both the subsea cable and the hub. In addition to the rock dump a number of concrete mattresses will be deployed as temporary construction aids as well as to provide stability to the cable tails and provide protection to the dry mate connectors.

The rock dump provided to stabilise the cable will be continuous along the 18km of cable route that runs over rocky seabed. This will have to be partially displaced in order to recover the cable; however recovery of the rocks to the surface is impractical, posing an unacceptable risk to personnel where divers are employed. Furthermore, the opportunities for the re-use of the rock material would be limited and the materials gathered would need to be disposed of elsewhere. As the seabed is predominantly rock in the regions where the rock dump is to be employed, the residual rock will not significantly impair the future use of the seabed. In order to ensure an overtrawlable profile, the rock dump may be dispersed over the seabed if necessary.

The concrete protection mattresses may be removed from the seabed and returned to the shore for re-cycling or disposal. However, it is recommended that these are left in place as recovery presents a significant risk as lifting aids may well have degraded over the lifetime of the project. Furthermore, lifting the mattresses out of the water would result in a sudden increase in loading on the connecting elements (polypropylene rope) as the sudden loss of buoyancy force would impart the full weight of the blocks onto the connecting ropes.

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Each mattress edge shall be tapered thus minimising the risk of snagging. The individual mattress elements are only 300mm in height, so smaller than some of rock dump materials that will remain on the seabed. Jetting round the mattresses could be an option to lower them into the seabed (should sufficient sediment exist). Should a mattress be lifted from the seabed and then fail during the lift, the resulting uncontrolled pile of mattress elements on the seabed would be much more likely to present a snagging hazard than a properly aligned, tapered mattress laying flat on the seabed.

Figure 5-1 ‘Massivmesh’ and ‘Flexiweight’ Concrete Mattresses Note: The mattresses employed for this project will have a tapered edge.

5.6 Navigation Buoys

The navigation buoys and their moorings will be removed and taken ashore for refurbishment or disposal.

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6 ENVIRONMENTAL IMPACT ASSESSMENT

An environmental impact assessment was prepared as part of the consents applications under Section 36 of the Electricity Act, the Coastal Protection Act and the FEPA licence.

The EIA process for Wave Hub considered the likely impacts of the scheme through the construction, operation and decommissioning phases of the project. The different environmental impacts were assessed for the worst case and the typical case scenarios, in order to establish impact thresholds for the different receptors and provide an envelope of potential environmental impacts. The worst case scenario for each receptor assumed the entire site was taken up by the type of WEC having the greatest impact on that particular receptor, while the typical cases assumed a mix of different WECs being deployed

Various actions led to the preparation of the Wave Hub EIA, including:

• an Environmental Scoping Study to determine the context and extent of the information to be covered by the EIA;

• WEC assessment to collect sufficient data about the WEC devices from developers;

• surveys and specialist investigations to establish current baselines and assess likely impacts of the development on:

o Coastal processes

o Water, sediment and soil quality

o Terrestrial ecology

o Ornithology

o Marine ecology

o Fish resources and commercial fisheries

o Navigation

o Landscape and views

o Cultural heritage and archaeology

o Noise and air quality

o Others;

• use of a stepped procedure to identify, predict and assess the environmental impacts, to devise impact mitigation measures where necessary, and to consider uncertainty about the impact assessment; and

• Consultation with stakeholders and interested parties to understand their opinions and share information and to gain their input into impact identification, surveys and specialist investigations.

The results of the assessment work were brought together in an Environmental Statement [Ref. 9], submitted to the regulatory bodies in support of the consent application for the Wave Hub project. It is proposed that the existing Environmental Statement is reviewed throughout the life of the project with a final review proposed prior to decommissioning to ensure the impact of the decommissioning measures has been adequately assessed.

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The final review will:

• Identify and assess potential impacts on the environment including exposure of biota to contaminants associated with the installation, other biological impacts arising from physical effects, conflicts with the conservation of species, with the protection of their habitats, or with mariculture, and interference with other legitimate users of the sea.

• Identify and assess potential impacts on amenities, the activities of communities and on future uses of the environment

• Describe the measures envisaged to avoid, reduce and, if possible remedy any significant adverse effects indicated.

The use of explosives is not proposed during the decommissioning process.

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7 CONSULTATIONS WITH INTERESTED PARTIES

The submission of the consent application to the regulatory bodies (DTI and DEFRA) on 23 June 2006, was followed by an open consultation period. The purpose of this consultation process was to enable stakeholders and members of the public to review the publicly available Environmental Statement (See Section 6) and present their concerns regarding all phases of the project.

The results of this consultation process were included in an Environmental Action Plan [Ref. 10], which sets out the project’s proposed mitigation, monitoring and liaison proposals for Wave Hub during construction, operation and decommissioning.

It is proposed that (as with the Environmental Impact Assessment) a final series of consultations with interested parties is undertaken prior to decommissioning. It is expected that opinion will be sought from the following organisations, however this list may be reviewed over the life of the project:

• Centre for Environment, Fisheries and Aquaculture Science

• Joint Nature Conservation Committee

• Natural England

• The Environment Agency

• English Heritage

• The Maritime and Coastguard Agency

• Trinity House Lighthouse Service

• National Federation of Fishermen’s Organisations

• Royal Yachting Association

• Hayle Harbour Authority

• British Chamber of Shipping

• Cornwall Council

• Local fishing organisations

• Cornwall Sea Fisheries Committee (CSFC)*

*From April 2011, Cornwall Sea Fisheries Committee (CSFC) will become The Cornwall Inshore Fisheries and Conservation Authority (as per Marine and Coastal Access Act 2009)

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8 COSTS

At current market prices of approximately £2500/tonne for copper, the scrap value of the cable is likely to be around £1Million. This may be offset against the costs of retrieval of the cable and hub. The offshore works may take up to one month to perform (including mobilisation and unloading/demobilisation). With current market rates of £80,000 per day for an appropriate offshore vessel of reasonable size, the total cost is likely to be in the order of £2.4 million. Taking into account mobilisation, demobilisation costs and disposal changes onshore along with the residual scrap value of the cable, the estimated potential liability will be approximately £1.4 million.

It is expected that any pre-decommissioning survey requirements could be provided by the general inspection surveys undertaken over the life of the project with a final post-decommissioning survey performed to re-map the seabed once the infrastructure has been removed.

A fully detailed cost estimate will be prepared prior to decommissioning once the final decommissioning methodology has been established. SWRDA are aware of their obligation to fund any decommissioning activity (see Section 9 for details).

As the decommissioning proposal is to remove all infrastructure from the seabed except the rock dump and mattresses, no post-decommissioning monitoring is envisaged. However should the option to leave the nearshore buried section of the cable in place be employed, a suitable monitoring scheme will be established.

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9 FINANCIAL SECURITY

Under the Energy Act decommissioning provisions it is left for the responsible person to determine what form of security they propose to provide. SWRDA is a statutory body funded by the UK Government and cannot become insolvent.

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10 SCHEDULE

It is expected that decommissioning will not commence before year 25 (approximately 2037) coinciding with the end of the design life of the offshore infrastructure. It is expected that the decommissioning process will follow the following outline schedule:

• Engineering, planning and contracting 6 months

• Offshore works (including mobilisation/demobilisation) 1 month

• Dismantling and disposal onshore 1 month

It is proposed that formal reviews of the decommissioning programme are undertaken throughout the life of the project at the following intervals:

• 2 years following commissioning



• Final review in year 23 to incorporate the activities as described in Sections 6 and 7 as well as detailing the decommissioning provisions and finalising the cost estimate and schedule of works.

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11 SEA-BED CLEARANCE

As discussed earlier within this document, SWRDA proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this.

Following decommissioning, surveys will be carried out to show that the site has been cleared. These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Wave Hub development and which may pose a risk to navigation, other users of the sea or the marine environment. It is currently intended that side scan sonar will be used to identify debris, with an ROV deployed to investigate and recover any potential hazards identified.

The area to be covered will be the 500m cable corridor along with the entire deployment area surveyed along with an additional 500m around the outside of the deployment area.

It is noted that a wreck exists along the cable route and an exclusion area will be set up around this wreck to ensure only debris associated with the Wave Hub project is removed.

In order to ensure impartiality and independence of data it is envisaged that the final survey results will be made publicly available.

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RESTORATION OF SITE

As discussed in the preceding sections, SWRDA propose the removal of all subsea infrastructures except the concrete mattresses and rock dump materials employed to provide on-bottom stability. In order to return the project site, as far as reasonably practical, to the condition that it was in prior to the construction of the Wave Hub project.

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12 POST DECOMMISSIONING MONITORING, MAINTENANCE AND MANAGEMENT OF SITE

As SWRDA are proposing to fully remove all of the subsea infrastructure except that of the mattresses and rock dump materials which will gradually become an integral part of the seabed, it is not envisaged that any post decommissioning monitoring, maintenance or management will be required. Should the decision be taken to leave the nearshore buried section of the cable in situ, or indeed the entire rock dumped length of the cable a full monitoring programme will have to be established to ensure the cable does not become exposed or present a hazard to other users of the sea.

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13 REFERENCES & SUPPORTING STUDIES

1. Decommissioning of Offshore renewable Energy Installations under the Energy Act 2004. Guidance Notes for Industry. DTI 2006

2. Coast Protection Act 1949

3. Food & Protection Act (FEPA) 1985

4. The Energy Act 2004

5. Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone IMO 10 October 1989

6. Environmental Protection Act 1990

7. SW Wave Hub – Metocean Design Basis METOC Report No. 2056

8. Navigation Risk Review SW Wave Hub Development Anatek 20 Nov 2008. A1988-HA-RA-1

9. Wave Hub Environmental Statement June 2006 [No Document Number]

10. Wave Hub Environmental Action Plan March 2007 [No Document Number]

11. Wave Hub Website : www.wavehub.co.uk

12. South West Of England Regional Development Agency’s website 2009 [online], [Accessed 30th September 2009] Available from World Wide Web: http://www.wavehub.co.uk

13. Hub End Termination Arrangement for The Hub Tail Cable (CAF1464), document number 11622-GA-011.

14. Wave Hub Development Area Commercial Fisheries Study, Appendix J to the Environment Statement. June 2006. Halcrow

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G-3-005 Rev 06 Decommissioning Programme - JP additions 09-09-10

APPENDIX I OFFSHORE APPROACH DRAWING

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APPENDIX II HUB STRUCTURAL ASSEMBLY

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APPENDIX III CABLE ROUTE

G-3-005 Rev 06 Decommissioning Programme - JP additions ......G-3-005 Rev 06 Decommissioning...

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