MB MarineSpace concrete center

MarineSpace Ltd in conjunction with

ABPmer and Fjordr

07/09/2012

Version 1.0

AReviewofMarineEnvironmentalConsiderationsAssociatedwithConcreteGravity

BaseFoundationsinOffshoreWindDevelopments

A Review of Marine Environmental Considerations associated with Concrete Gravity Base Foundations in Offshore Wind Developments.

Document Reference: 2012‐6‐1.0

Date Originator Version Action Signature

28 May 2012 Ian Reach 0.1 For client review

04 July 2012 Ian Reach 0.2 Amended following GFIG

workshop and TCC comments

30 July 2012 Ian Reach 0.3 Amended with GFIG and TCC

consultation comments

07 September 2012 Ian Reach 1.0 Amended with further comments

received from GFIG

Cover image: © DONG Energy and The Concrete Centre

Document Produced For:

The Concrete Centre

Project Manager: Andrew Minson

Postal Address: MPA ‐ The Concrete Centre, Riverside House, 4 Meadows Business

Park, Blackwater, Camberley, GU17 9AB

Telephone: 01276 606828

Email: [email protected]

Document Produced By:

MarineSpace Ltd

Project Manager: Ian Reach

Postal Address: Ocean Village Innovation Centre, Ocean Village, Southampton.

SO14 3JZ

Telephone: 02380 381945


Web: www.marinespace.co.uk

A Review of Marine Environmental Considerations Associated with Concrete Gravity Base Foundations in Offshore Wind Developments.

Document Produced In Conjunction With:

ABPmer

Project Manager: Bill Cooper

Postal Address: ABP Marine Environmental Research Ltd, Suite B, Waterside House,

Town Quay, Southampton SO14 2AQ

Telephone: 02380 711840


Web: www.abpmer.co.uk

Fjordr

Project Manager: Antony Firth

Postal Address: Post Office House, High Street, Tisbury, SP3 6LD

Telephone: 01747 873806


Web: www.fjordr.com

This report should be cited as:

Reach, I.S., Cooper, W.S., Firth, A.J., Langman, R.J, Lloyd Jones, D., Lowe, S.A. and Warner, I.C., 2012.

A Review of Marine Environmental Considerations associated with Concrete Gravity Base

Foundations in Offshore Wind Developments. A report for The Concrete Centre by Marine Space

Limited. 160pp.


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TableofContentsEXECUTIVE SUMMARY ............................................................................................................................. i

1 Introduction .................................................................................................................................... 1

1.1 Aims and Objectives ................................................................................................................ 1

1.2 Basis for the Assessment ........................................................................................................ 1

1.3 Assumptions ............................................................................................................................ 4

2 Permitting of Offshore Windfarms in the UK.................................................................................. 6

2.1 Round 1 and 2 Compared to Round 3 ..................................................................................... 6

2.2 Governmental Requirements.................................................................................................. 6

3 Construction Options ...................................................................................................................... 7

3.1 Concrete Gravity Base Foundations ...................................................................................... 10

3.2 Monopiles ............................................................................................................................. 11

3.3 Tripod .................................................................................................................................... 12

3.4 Steel Jacket ............................................................................................................................ 13

3.5 Suction Caissons .................................................................................................................... 14

3.6 Floating Platforms ................................................................................................................. 15

3.7 Comparison between Structures .......................................................................................... 16

4 History of Gravity Bases ................................................................................................................ 17

4.1 Thornton Bank 1 .................................................................................................................... 20

4.2 Rødsand 1 and 2 .................................................................................................................... 23

5 Foreseeable Effects ....................................................................................................................... 26

5.1 Stages of construction and placement ................................................................................. 26

5.2 Effects .................................................................................................................................... 27

5.2.1 Effects relating to the preparation of the ground where the CGBF is to be placed

(if required) ................................................................................................................... 27

5.2.2 Effects relating to the emplacement works associated with the CGBF ........................ 29

5.2.3 Effects associated with the remedial activities required by the CGBF (if required) ..... 30

5.2.4 Effects relating to the settlement of the CGBF following emplacement ...................... 31

5.2.5 Effects of operation of the CGBF .................................................................................. 32

5.2.6 Effects associated with decommissioning of the CGBF (if required) ............................ 33

5.3 Conceptualisation of Effects ................................................................................................. 35

5.3.1 Coastal Processes Study ................................................................................................ 35

5.3.2 Project Design Statement ............................................................................................. 36


6 Physical Receptors ........................................................................................................................ 37

6.1 Introduction: Aims and Scope ............................................................................................... 37

6.2 Physical Receptors ................................................................................................................ 37

6.2.1 Water Column ............................................................................................................... 38

6.2.2 Sub‐seabed Geology ..................................................................................................... 42

6.2.3 Sediment Regime .......................................................................................................... 43

6.2.4 Summary ....................................................................................................................... 49

7 Biological Receptors ...................................................................................................................... 51

7.1 Introduction Aims and Scope ................................................................................................ 51

7.2 Benthic Resources ................................................................................................................. 52

7.2.1 Notable Benthic Receptor Groups ................................................................................ 54

7.2.2 Some Key Aspects of Benthic Habitat and Community Responses to CGBFs ............... 56

7.3 Fish Fauna and Assemblages ................................................................................................. 65

7.3.1 Important Fish Resources ............................................................................................. 66

7.3.2 Important Interactions between Fish Species and Assemblages with CGBFs .............. 67

7.4 Megafauna Resources ‐ Marine Mammals, Turtles and Basking Sharks .............................. 71

7.4.1 Important Megafaunal Resources ................................................................................ 71

7.4.2 Important Interactions between Marine Mammals and Basking Sharks with CGBFs .. 72

7.5 Avifauna ‐ Birds ..................................................................................................................... 76

7.5.1 Important Bird Resources ............................................................................................. 76

7.5.2 Important Interactions between Birds And CGBFs ....................................................... 77

7.6 Noise ..................................................................................................................................... 79

7.6.1 Sensitive Noise Receptors ............................................................................................. 80

7.6.2 Important Interactions between Noise Sensitive Receptors and CGBFs ...................... 82

7.6.3 Summary ....................................................................................................................... 86

7.7 Designated Sites and other Nature Conservation Interests ................................................. 88

7.7.1 Nature Conservation Features ...................................................................................... 88

7.7.2 Important Interactions between Nature Conservation Features and CGBFs ............... 90

7.9 Summary of Biological Receptors ..................................................................................... 94

8 Human Receptors ....................................................................................................................... 105

8.1 Vessel Presence during Emplacement, Ground Preparation, Remediation and Removal of

the CGBF .............................................................................................................................. 105

8.1.1 Secondary Effects ........................................................................................................ 105

8.2 CGBF Presence during Settlement and Operation .............................................................. 106


8.2.1 Secondary Effects ........................................................................................................ 106

8.3 Effects as a Result of Biological Impacts ............................................................................. 106

8.4 Fisheries .............................................................................................................................. 106

8.5 Navigation ........................................................................................................................... 107

8.6 Archaeology and other Historical Uses of the Seabed ........................................................ 107

8.7 Summary ............................................................................................................................. 113

9 Cumulative and In‐combination Effects ...................................................................................... 115

10 Decommissioning .................................................................................................................... 121

11 Discussion ................................................................................................................................ 122

12 Conclusions ............................................................................................................................. 127

13 Observations and Recommendations ..................................................................................... 131

14 References .............................................................................................................................. 133

Appendices .......................................................................................................................................... 143


ListofFiguresFigure 1.1: Images of the Concrete Gravity Base Foundation solutions from members of The

Concrete Centre’s Gravity Foundation Interest Group © various GFIG members ............... 3

Figure 1.2: Figure highlighting the elements of CGBFs and windfarms that are included within this

document and those that are not. ........................................................................................ 5

Figure 3.1: Illustration of various foundation types for use with offshore wind turbines ..................... 7

Figure 3.2: Seabed area interaction with selected foundation types for 5MW turbine. ....................... 9

Figure 3.3: Depth profiles and applicable foundation types. ................................................................. 9

Figure 4.1.1: Bathymetry around Turbine D1 at Thornton Bank, Belgian waters. ............................... 21

Figure 4.1.2: General arrangement of the CGBFs at Thornton Bank, Belgian waters. ......................... 22

Figure 4.2.1: Preparation of the seabed required at Rødsand 2. ......................................................... 23

Figure 4.2.2: Design of the CGBFs utilised at Rødsand 2 ...................................................................... 24

Figure 5.1: Effects arising as a result of ground preparation ................................................................ 27

Figure 5.2: Effects arising as a result of emplacement ......................................................................... 29

Figure 5.3: Effects arising as a result of remedial activities .................................................................. 30

Figure 5.4: Effects arising as a result of settlement .............................................................................. 31

Figure 5.5: Effects arising as a result of operation................................................................................ 32

Figure 5.6: Effects arising as a result of decommissioning ................................................................... 33

Figure 7.1: Benthic habitats and Round 3 offshore windfarm zones................................................... 53

Figure 7.2: Diagrammatic cross‐section of CGBF base, foundation layers and scour protection from

Thornton Bank OWF, Belgian waters. ................................................................................. 58

Figure 7.3: Multi‐purpose barge Thornton 1 depicted in backfill and infill mode. ............................... 64

Figure 9.1: Flow diagram for assessing cumulative impacts. .............................................................. 116

ListofTablesTable 1.1: Details of the technical specifications of the CGBFs considered within this document.. ...... 2

Table 3.1: Comparison between foundation types ................................................................................ 8

Table 3.1.1: Overview of generic effects associated with use of CGBF structure. ............................... 10

Table 3.2.1.: Overview of generic effects associated with use of monopile structure......................... 12

Table 3.3.1: Overview of generic effects associated with use of tripod structure. .............................. 13

Table 3.4.1: Overview of generic effects associated with use of steel jacket structure. ...................... 14

Table 3.5.1: Overview of generic effects associated with use of suction caisson structure. ............... 15

Table 3.6.1: Overview of generic effects associated with use of floating platform structure. ............ 15

Table 3.7.1: Comparison of broad effects between foundation types. ................................................ 16

Table 4.1: Existing Offshore Concrete Structures for Oil and Gas Production ..................................... 18


Table 4.2: Offshore windfarms utilising GBFs to date .......................................................................... 20

Table 6.1: Indicative scour protection parameters for individual turbine locations (excluding

foundation area take). ........................................................................................................ 44

Table 6.2: Total seabed area directly lost to a combination of foundation and scour protection

required for a 5MW turbine. .............................................................................................. 44


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GlossaryandAbbreviations

Abbreviation Description Definition

BCD Below Chart Datum

Beneath the level of water that charted

depths displayed on a nautical chart

are measured from.

Benthic Relating to the seabed or organisms

that live there.

Biotope

An area of uniform environmental

conditions providing a living place for a

specific assemblage of plants and

animals. Biotope is almost synonymous

with the term habitat, but while the

subject of a habitat is a species or a

population, the subject of a biotope is a

biological community.

CCW Countryside Council for Wales The Government’s statutory advisor on

the Welsh natural environment.

CFD Computational Fluid Dynamics

Computational fluid dynamics (CFD)

analyses fluid flows using numerical

methods and algorithms

CGBFs Concrete Gravity Base Foundations

Concrete structures on which wind

turbines can be placed and that stay in

place as a result of their weight

EIA Environmental Impact Assessment

Process by which the effects of a plan

or project on the environment, and its

constituent parts, is determined.

EIA Directive Environmental Impact Assessment

Directive 1997

The Directive from the European

Commission that requires an EIA to be

undertaken for certain projects

Epifauna

Also called epibenthos, are marine

animals that live on the bottom

substratum as opposed to within it,

that is, the benthic fauna that live on

top of the sediment surface at the

seafloor.

Epiphytes

Marine algae and plants that live

attached to other marine algae or

plants (or occasionally animals).

Far Field Beyond the footprint of the primary

and secondary impact zones

Direct Effects Effects resulting from the placement of

the CGBFs on the seabed


Habitat

An ecological or environmental area

that is inhabited by a particular species

of animal, plant, or other type of

organism. It is the natural environment

in which an organism lives, or the

physical environment that surrounds

(influences and is utilized by) a species

population.

Indirect Effects

Effects extending beyond the

boundaries of the direct effects, where

the placement of the CGBF has

changed the natural environment

and/or physical processes that existed

prior to its placement.

Infauna

Benthic organisms that live within the

bottom substratum of a body of water,

especially within the bottom‐most

oceanic sediments, rather than on its

surface.

MCA Maritime and Coastguard Agency

The Government's statutory advisory

body for maritime safety policy in the

UK.

MMO Marine Management Organisation

The executive non‐departmental public

body responsible for most activities

licensed within the marine

environment

MPA Marine Protected Area

Any area of the intertidal or subtidal

terrain, together with its overlying

water and associated flora, fauna,

historical and cultural features, which

has been reserved by law or other

effective means to protect part or all of

the enclosed environment.

MW Megawatt One million Watts of energy

NE Natural England The Government’s statutory advisor on

the English natural environment.

Near Field Within the footprint of the primary and

secondary impact zones

PDS Project Design Statement

The outline engineering description for

the full range of options to be

considered for consent and which

achieves the target generating capacity

for the project.

PIZ Primary Impact Zone The direct footprint of the proposed


development

TCC The Concrete Centre

The Concrete Centre is the central

development organisation for the UK

concrete industry

REA Regional Environmental Assessment

Assessment of marine aggregate

extraction environmental effects at a

regional sea scale considering

cumulative effects. It is a non‐statutory

instrument.

REC Regional Environmental Characterisation

Broadscale description at a regional sea

scale of the environment associated

with marine aggregate extraction

licenses.

Rochdale Envelope

(also known as the

Engineering Envelope)

This approach allows for an EIA to be

completed on a development proposal

for which a degree of flexibility is

required in the final design of that

project at the point of consent

determination. The approach allows

the maximum environmental effects of

a project to be described by defining

the ‘worst case scenario’. This is

premised on the fact that any lesser

development scenario would result in

no greater (and in most cases lesser)

environmental effects than those

described by the ‘worst case scenario’

detailed in the EIA.

SEA Strategic Environmental Assessment

Is a statutory assessment procedure

required by EU Directive 2001/42/EC

(known as the SEA Directive). The SEA

Directive aims at introducing

systematic assessment of the

environmental effects of strategic

related plans and programs.

SIZ Secondary Impact Zone The footprint of effects arising as a

result of the proposed development

SNH Scottish Natural Heritage The Government’s statutory advisor on

the Scottish natural environment.


AcknowledgementsThe following members of The Concrete Centre Interest Group for Gravity Foundations have

provided financial support and expert technical advice for this publication:

Ballast Nedham Offshore B.V. Vici Ventus Construction

Skanska Construction Laing O’Rourke

WindAtBase Vinci Construction UK Ltd

BAM Nuttall Ltd Seatower AS

Strabag Offshore Wind GmbH Sir Robert McAlpine

Hochtief – Costain – Arup Consortium

A full list of The Concrete Centre Interest Group members can be found at:

http://www.concretecentre.com/technical_information/infrastructure/wind_energy/special_interest_group

The Mineral Products Association is the trade association for the aggregates, asphalt, cement,

concrete, dimension stone, lime, mortar and silica sand industries.

The Mineral Products Association (MPA) is the trade association for the aggregates, asphalt, cement,

concrete, dimension stone, lime, mortar and silica sand industries. With the recent addition of The

British Precast Concrete Federation (BPCF) and the British Association of Reinforcement (BAR), it has

a growing membership of 450 companies and is the sectoral voice for mineral products. MPA

membership is made up of the vast majority of independent SME companies throughout the UK, as

well as the 9 major international and global companies. It covers 100% of GB cement production,

90% of aggregates production and 95% of asphalt and ready‐mixed concrete production and 70% of

precast concrete production. Each year the industry supplies £9 billion of materials and services to

the £120 billion construction and other sectors. Industry production represents the largest materials

flow in the UK economy and is also one of the largest manufacturing sectors.

All advice or information from MPA The Concrete Centre is intended only for use in the UK by those

who will evaluate the significance and limitations of its contents and take responsibility for its use

and application. No liability (including that for negligence) for any loss resulting from such advice or

information is accepted by Mineral Products Association or its subcontractors, suppliers or advisors.

Readers should note that the publications from MPA The Concrete Centre are subject to revision

from time to time and should therefore ensure that they are in possession of the latest version.


i

EXECUTIVESUMMARYThe Concrete Centre (TCC) and the Gravity Foundation Interest Group (GFIG) commissioned A

Review of Marine Environmental Considerations Associated with Concrete Gravity Base Foundations

in Offshore Wind Developments. The report investigates the current evidence base for offshore

windfarm foundation structures in a European context and also reviews the use of concrete

structures from other relevant marine sectors such as oil and gas. The review focuses on the use of

Concrete Gravity Base Foundations (CGBFs) and relates the potential environmental footprint of

these structures to other existing types of foundation solution for offshore windfarms.

Specific CGBF designs intended to compete in the UK market have not been compared side‐by‐side

within the report. Rather, the over‐arching environmental effects are considered with a mind to

realistic worst case scenarios.

The review focuses on the possible environmental effects and pathways associated with the various

phases of the lifecycle of concrete gravity base foundations (CGBFs) in the marine environment

including: ground preparation (if required); emplacement on the seabed; scour protection (if

required); operation; and decommissioning. Offshore and underwater effects are considered in

relation to the foundation structure itself: power cables, towers, turbines and rotors are not

reviewed or assessed.

The likely receptor groups and their prominent components are detailed, with an in‐depth review of

the existing evidence base, including: the physical environment and processes (water column,

seabed geology and sediment regime); biological environment (benthos, fish fauna, marine

mammals and other mobile megafauna, birds and nature conservation features); and the human

environment (fisheries, navigation and archaeology, including heritage features). Whilst many of

these effects are not CGBF specific, effects may differ in magnitude from those of other foundation

types that may be deployed within the same environments. The document reviews all known

potential environmental effects, recognising the links between various receptor groups and

considers possible / likely impacts, particularly in relation to the marine environment associated with

Round 3 of the UK’s offshore renewables programme.

The report draws upon the detailed evidence base associated with shallow water use of steel

monopiles to set a baseline context that most developers, engineers, regulators and their statutory /

technical advisors and other practitioners are familiar with in the UK i.e. Round 1 and 2 offshore

windfarms and those installed in Danish and Belgian waters. Evidence associated with concrete

gravity bases, steel jackets and tripods is drawn from existing examples deployed in UK, Danish,

Belgian and German waters.

However, it is widely acknowledged that there will be a requirement for a significant number of

Round 3 projects to consider alternative engineering solutions to monopile foundations, such as

concrete gravity bases, steel jackets, tripods, and suction caissons. The spatial scale of effects and

resultant impacts are anticipated to be different to those associated with Round 1 and 2 arrays.

These are detailed and comparisons are drawn between CGBFs and other deeper water foundation

solutions. Possible cumulative effects are also described where possible.


ii

Many, though not all, of the Round 3 zones are sufficiently distant from coastlines (50‐200km) that

coastal impact studies may require less focus than was required for Round 1 and 2 arrays. Deeper

water at these offshore sites means that an alteration to the local wave climate and subsequent

wave‐induced effects are not likely to impinge upon the seabed or reach the coast. Any local

changes to tidal currents or surface sediment transport pathways are similarly less likely to interface

with coastal systems. Modelling will be required at a project‐specific level to inform an EIA, but

overall blockage effects are expected to be negligible or significantly lower risk than for Round 1 and

2 projects; especially for those solutions with comparable blockage effects to the large monopiles.

CGBFs can have a long‐term surface area footprint (habitat loss and alteration) at the seabed similar

to other deeper water foundation solutions once shadowing of the sediment habitat through ‘halo’

or ‘fringe’ effects associated with the alternative solutions are taken into account. There may be a

short‐term habitat loss associated with seabed preparation and sub‐surface scour protection (if

required). It is anticipated that these impacts may be limited to 6‐24 months for mobile sand

habitats but up to 8 years or greater for consolidated gravel habitats.

In addition, reef effects will occur as a result of the additional hard substrata introduced to the

environment during emplacement for all foundation solutions. This may have effects on the wider

biological composition of the region and interactions at an ecosystem scale.

By far the greatest advantage of CGBFs, over the proven, viable alternatives, is the lack of damaging

underwater noise emissions generated during their installation and emplacement. With increased

requirements for consideration of noise in legislative controls, underwater noise will be a primary

consideration for deep water solutions for Round 3 developments.


1

1 IntroductionThis document has been produced on behalf of The Concrete Centre (TCC) and the Gravity

Foundation Interest Group (GFIG) by MarineSpace Ltd, with specialist input from ABPmer and Fjordr.

MarineSpace are an environmental consultancy with key skills in marine Environmental Impact

Assessment, physical process studies, biological characterisation and conservation review.

Recognising the importance of physical process modelling in understanding the impacts arising from

Concrete Gravity Base Foundations (CGBFs) for windfarms, ABPmer have produced this portion of

the document along with input at other relevant sections. Specialist archaeological advice was also

sought, with Fjordr producing related sections of the document.

1.1 AimsandObjectivesThis document is intended to allow the CGBF engineering/construction industry to demonstrate the

effects associated with a CGBF and set these in relation to alternative foundation solutions; whilst

highlighting any identified benefits associated with the use of CGBFs. Specific consideration of the

cause and effect pathways and footprints described within this document will enable an evidence‐

based, knowledgeable and independent view of CGBFs to be presented by industry and developers.

The specific aims and objectives of this guidance note are to provide The Concrete Centre and the

Gravity Foundation Interest Group with a report that:

Highlights the likely environmental concerns surrounding the permitting of CGBFs in the marine environment;

Identifies other relevant guidance available for other sectors that may be utilised for CGBFs;

Identifies effects and their pathways that may need to be addressed for CGBFs specifically, and also identify effects that can be screened out as not relevant or significant;

Describes possible CGBF‐specific positive and negative effects and applications;

Sets the context for the use of CGBF structures as part of the UK Round 3 initiative; and

Acts as a resource that identifies a CGBF‐specific environmental footprint and provides context for industry, regulators, statutory advisors and wider stakeholders including members of the general public.

1.2 BasisfortheAssessmentThe main suppliers of CGBFs have provided details on the structures representative of the CGBFs

considered in this document. These details were collated by TCC and are presented in Table 1.1

below. These parameters have been used for the basis of this document, although it is important to

note that as a result of design differences and placement within various environmental conditions,

the impacts are likely to be bespoke to each site. A selection of design options are presented in

Figure 1.1.


2

Table 1.1: Details of the technical specifications of the CGBFs considered within this document (Extracted from technical submissions of the Gravity Foundation Solution Providers for the purpose of establishing Rochdale Envelope parameters). (Values quoted are Average and Worst Case respectively).

Parameter Average Values Maximum (Worst Case) Values

35m Depth 5MW Turbine 50m Depth 5MW Turbine

Bedrock Sands Bedrock Sands

PERMANENT INSTALLATION

A.1 External surface area of concrete (extra habitat) (m2)

2,8254,675

2,7394,675

3,421 5,800

3,3385,800

A.2 Elevational area from surface of sea bed to water surface (coastal processes) (m2)

901 1,690

863 1,690

1,201 2,067

1,145 2,067

A.3 Area of concrete footprint at surface level of sea bed (loss of habitat) (m2)

865 1,150

900 1,150

1,000 1,386

1,029 1,386

A.3.b Inferred diameter at seabed (calculated from A.3) (m)

33.238.3

33.938.3

35.7 42.0

36.242.0

A.4 Diameter at water surface (or shape and maximum projected width if not circular) (impact on wave climate) (m)

6.5 8

6.65 8

6.36 7

6.5 7

A.5 Area of scour protection if used (change in habitat) (m2)

Assumed N/A 2,0953,500

Assumed N/A 2,3244,005

A.6 Gradings specification of top layer of scour protection if applicable (nature of new habitat)

Assumed N/A No data supplied

Assumed N/A No data supplied

A.7 Density of wind towers (no/km2) 1

1.23 1

1.23 1

1.23 1

1.23

INSTALLATION

B.1 Area of sea bed preparation (if required) (m2)

Assumed N/A Variable and

project specific Assumed N/A

Variable and project specific

B.2 Depth of sea bed preparation (B.1xB.2 = volume of removals) (m3)




B.3 Area of sea bed impact from installation vessels (numbers and footprint of jack up barge spuds, anchors, and duration) (Foundation only, not including tower and turbine attachment)

~416m2 per jack‐up and assuming one

visit for foundation

emplacement.



emplacement.



emplacement.



emplacement.

B.4 Aggregates for ballast:Tonnage required and preferred material/specification if known (t)

7,250 12,000

8,460 15,000

6,700 12,000

7,400 12,000

B.5 Nature of vessel for delivery of scour protection: side dumping barge, steerable vessel, other (accuracy of placement, known impact area)




REMOVAL

C.1 Area of sea bed impact from Removal Vessels (e.g. barge spuds) (m2)

Typically None Typically None Typically None Typically None

C.2 Duration of removal process (foundation only) and any other details that may have impacts (days)

3.6 7

4.2 7

3.6 7

4.2 7


3

Figure 1.1: Images of the Concrete Gravity Base Foundation solutions from members of The Concrete Centre’s Gravity Foundation Interest Group © various GFIG members

An additional solution is available from Laing O’Rourke


4

1.3 AssumptionsThis document has also made several assumptions which are outlined below:

1 The effects arising as a result of the turbine on the sea surface or the structure in the wider

environment and seascape have not been included within this document. There is already a

significant amount of documentation pertaining to the requirements for this aspect of

windfarm development which is considered inappropriate to reproduce here. The most

relevant document is the Guidance Note for Environmental Impact Assessment in Respect of

FEPA and CPA Requirements produced by Cefas in 2004. This document provides a

comprehensive review of the data, information and scientific evidence that will be required

by the regulator to consent offshore windfarm developments.

2 The materials utilised in the construction of the CGBFs (aggregate and cement) have not

been included. It is assumed that as the production of aggregate and cement requires

consent to operate, these activities have been, or will be, assessed under separate

legislation. It is also assumed that any sediment utilised to infill the structures will also have

been consented under a different regime. Therefore, the impacts arising from the

production, transport, use and construction of the CGBFs is not included within this

document.

3 Shore‐based infrastructure and cable landing are not included within this document. As with

the turbine structure above the sea surface, there is a significant amount of guidance and

information relating to the effects of the landing of the power cable and the infrastructure

required to attach to the national grid.

4 Cables transferring power through the array are also not included within this document. The

methods for laying the cables between the turbines and to the shore are also not included

within this assessment. These effects will be dependent upon the methodologies involved

and the environment through which the cable passes. In addition, significant guidance

already exists for the assessment of the effects of cables and pipelines within the marine

environment.

5 Surveys and their associated impacts are also excluded for consideration under this

document. These require specific licenses to be obtained from the MMO and/or through The

Crown Estate. The MMO provide information on geophysical surveys at

www.marinemanagement.org.uk/protecting/wildlife/geophysical . Geotechnical and

ecological sampling surveys require a Marine Licence obtained through the MMO who

provide a series of guidance notes for applicants to follow. The guidance and application

details can be found at www.marinemanagement.org.uk/licensing/marine.htm. In addition

sampling will require consent from The Crown Estate and should be contacted directly for

details of the process and application forms required.

These assumptions are highlighted in Figure 1.2 which shows the elements included within, and

those excluded from, this document.


5

Figure 1.2: Figure highlighting the elements of CGBFs and windfarms that are included within this document and those that are not.


6

2 PermittingofOffshoreWindfarmsintheUKPermitting of windfarms in the UK requires two separate permits:

1. The commercial agreement between the operator and the land owner (typically The Crown

Estate)

2. The governmental permit that considers the environmental implications for the

development and setting mitigation and monitoring requirements for the development.

2.1 Round1and2ComparedtoRound3The Crown Estate has offered five rounds of tendering for offshore windfarms to date. These include

Round 1, Round 2, Scottish Territorial Waters, Round 1 and 2 extensions and Round 3. The majority

of Round 1, Round 2 and Scottish windfarm sites are located within 12 nautical miles (approximately

22km) of the coastline and are typified by shallow water, sediment seabed habitats and relatively

benign wave conditions.

As a result of the marine environmental conditions experienced at the Round 1 and Round 2

windfarm sites, steel monopiles have been the foundation construction choice for the windfarms

constructed in the UK to date. However, as Round 3 windfarm zones generally occupy deeper water

and more exposed conditions, with a mixture of seabed types which are typically further offshore

than the previous Round 1, Round 2 and Scottish Territorial Waters arrays and at a considerably

larger scale. It is likely that different construction options will need to be considered due to the

different physical environment.

As a result this document is written to address the requirements of the Round 3 sites that are yet to

be constructed and therefore considers deeper water and more exposed conditions experienced at

the proposed Round 3 windfarm sites. Whilst primarily considering Round 3 the findings and

determinations made in this report may also be applicable to those deeper water projects offshore

in Scottish Territorial Waters.

2.2 GovernmentalRequirementsThere are various domestic and international legislation requiring the assessment of environmental

impacts associated with projects including Round 3 developments. More details on the legislative

requirement can be found in Appendix A.

Generally there are two routes for the obtaining of an environmental permit in UK waters:

1. Permits from small projects (less than 100MW) can be obtained through the MMO or the

devolved administrations. The applications are made through the Coastal and Marine

Access Act 2009.

2. Projects of more than 100MW must be made through the Planning Act 2008, which is

administered by the Planning Inspectorate for all sea areas under UK jurisdiction.

More details on the requirements for the environmental permitting routes can be found in

Appendix A.


7

3 ConstructionOptionsThis section of the document has been written to compare and contrast the various options for

foundations used in offshore windfarms in the UK. Foundation options currently deployed in UK

waters or available for use in Round 3 construction are:

Concrete Gravity Base;

Monopile;

Tripod;

Steel Jacket;

Suction Caisson; and

Floating Platform.

Figure 3.1 provides an illustration of the different foundation solutions reviewed in this section.

Figure 3.1: Illustration of various foundation types for use with offshore wind turbines (adapted from STRABAG illustration).

Research presented in Table 3.1 was reported by the Department for Energy and Climate Change

(DECC, 2011a) and provides a comparison between various foundation types detailing basic

parameters such as deployment depth range, seabed types, and structure metrics such as width,

footprint area and weight. Where appropriate the information from Table 3.1 has been used in

conjunction with CGBF‐specific parameters presented by solution providers in Table 1.1 to set the

basis for the sub‐sections that follow.


8

Table 3.1: Comparison between foundation types (from DECC, 2011a)

Structural Form Materials Applicable ranges Structu

re

Width (m

)

Seab

ed

footprin

t1 (m

2)

Weigh

t (to

nnes)

Main Type

Variatio

n

Prim

ary

Other

MSL W

ater

Depth (m

)

Turbine

Size (M

W)

Seabed conditions

Monopile S S, G Up to 25 ‐ 35

3 – 5 Clay/sand/weak rock

4 – 7 12 – 300 400 –750

C2 S, G 35+ 5+ 6+ 20 +

Gravity Base

Conical Caisson

C, S3 S, Sa/Gr/R

0 ‐ >70 Up to 10 Firm clay, med dense sand/gravel, rock

20 – 50 300 – 3,500 3,000 –12,000

Jacket 4‐leg Tripod

S S, G <20 ‐ >70 Up to 10 Sand/silt/clay / weak rock

15 – 50 6 – 500 600 –2,000†

Suction Caisson

S, C < about 50

Up to 10 Clay/sand/open gravel no obstructions, not hard or very dense

15 – 30 175 – 2,000

Floating Catenary S, C4 S, Sa/Gr/R, FRP

>50 Up to 10 All, subject to foundation type5

10 – 80 5 – 1,2006 1,000 –3,000‡

Tension Leg

S, C S, Sa/Gr/R, FRP

>60 Up to 10 All, subject to foundation type5

35 – 60 5 – 1,2006 1,000 –3,000‡

Artificial Island

Sa/Gr R/C/S <20 Up to 10 All but very soft 50 ‐ 250

* S = Steel, C = Concrete, G = Grout, Sa = Sand, Gr = Gravel, R = Rock, FRP = Fibre Reinforced Polymer. † includes piles and transition piece. ‡ Excludes mooring lines and sea bed anchorage. Notes: 1. The range of areas for sea bed footprint includes an allowance for possible scour protection 2. There is insufficient information available for concrete monopiles to estimate the upper end of ranges but they are expected to be higher than for a steel monopile 3. Gravity structures are normally concrete but could be steel 4. Floating structures could be steel or concrete 5. Mooring lines can be fixed to the sea bed by a range of foundations (anchors, piles, gravity and suction caisson) depending on conditions 6. For floating structures, the footprint is the area disturbed by mooring line foundations, rather than the total area of sea bed beneath the structure.

During the development of UK Round 1 and 2 offshore windfarm projects there has been a general

presumption that CGBFs present the worst case scenario regarding total direct area of seabed

contact / loss under the footprint of the foundation structure (see Table 3.1). This relates to a direct

loss of seabed habitats and associated communities, both individually per foundation and

cumulatively; either within an array or between windfarms. However, alteration of the seabed and

loss of sediment habitat is not only a reflection of the structure’s direct footprint but also due to

area covered / ‘over‐shadowed’ by the foundation structure itself – e.g. seabed located beneath the

lattice of a steel jacket but not under one of the feet. When considering the ‘shadowing’ effect, steel


9

jackets and tripods can present a comparable surface area of seabed interaction than CGBFs

(Figure 3.2).

Figure 3.2: Seabed area interaction with selected foundation types for 5MW turbine (adapted from STRABAG, 2012).

Concrete Gravity Base Steel Jacket Tripod Suction Caisson

Footprint –

seabed

habitat loss

1,200 m2 800 m2 1,000 m2 2,000 m2

Water depth and seabed geology has an influence on the engineering parameters required to

provide a stable foundation for turbines – particularly regarding turbines of 5 MW capacity and

above. Different foundation solutions have optimal depth ranges for provision of stability for

turbines along with engineering constraints and cost benefit analyses. Increased water depth will

require greater penetration depths for monopile solutions and the possibility of larger storm wave

loadings means more resilient grouting at the foundation / transition piece connection. This increase

in water depth when factored with likely increased wave energetics will result in a potential shift

from reliance upon monopile foundations to alternative foundation solutions (see Section 3.2 and

Section 5.3.1 for further discussion). Figure 3.3 illustrates the water depth correlation to the

feasibility of various foundation structures and their deployment parameters.

Figure 3.3: Depth profiles and applicable foundation types (adapted from DECC, 2011a).


10

At the end of each of the following sub‐sections, the base structure is compared to CGBFs in

environmental terms, and suitability for use within certain marine environments.

3.1 ConcreteGravityBaseFoundationsConcrete Gravity Base Foundations (CGBFs) are structures made in concrete, and in most cases

ballasted with sand / gravel, that are designed to be held in place by gravity. The tower supporting

the wind turbine is attached to the top of the CGBF which is designed to stand proud of the sea

surface. The structures are typically constructed onshore, transported to site and finally positioned

accurately onto the seabed. There is no piling required so no attendant underwater noise impacts of

the magnitude associated with monopiles, tripods and steel jackets. Transportation and

emplacement time is in the order of 3‐7 days excluding weather downtime.

The design of the CGBF structures will vary depending upon the designer, manufacturer and critically

the conditions experienced at the intended deployment location which may different for any

location within the array. However, whilst their design may vary, the broad parameters of their

design will remain similar across the site as shown in Table 1.1.

As a result of the varied characteristics of the designs proposed and the environment at the

deployment location for CGBFs, the preparation required at a foundation location is likely to vary

from site to site. Some designs are based on the premise of minimising the extent of sea‐bed

preparation whereas others require sea‐bed preparation as part of the construction process. There

are some sites where seabed preparation or mitigation will be inevitable such as areas with large

(2m plus in height) sand waves and areas with exposed rock at the surface. Examples of the potential

preparation and / or mitigation required are shown in Section 4.

Therefore it is possible to generate the table of effects below:

Table 3.1: Overview of generic effects associated with use of CGBF structure.

Parameter CGBFs

Experience 40+ years of use

Water Depth Shallow to deep water

Price Favourable

Availability Favourable

Maintenance required Low

Ground preparation (temp habitat loss) None to high

Emplacement weather / condition window Moderate conditions acceptable

Sound emitted during emplacement Low

Seabed footprint (habitat loss) High

Scour None to Moderate

Blockage effects Moderate to High

Reef effects Moderate to High

Decommissioning Favourable to remove entire structure


11

3.2 MonopilesMonopiles have been the most commonly used foundation method used during the construction of

UK Round 1 and Round 2 offshore windfarms. Monopiles are tubular sections of steel that are

typically driven into the seabed to a suitable depth, ensuring that the transition piece, tower and

turbine placed atop of the structure are stable. Steel monopiles are typically pile‐driven into sandy

seabeds by using a large hammer or a combination of hammering and drilling where sub‐seabed

geology is harder. Strike rates vary depending upon the local seabed conditions but Zucco et al.

(2006) and RPS Energy and RWE NPower Renewables (2011) recorded a range of 20‐40 strikes per

minute for durations between 1.5‐4 hrs per monopile (in sandy seabeds) . The monopiles may take

between 1000‐7000 strikes to install them to operational depth (Zucco et al., 2006). This range

accounts for variations in sub‐surface geology and also differences in monopile diameters (4‐6 m

diameter). Centrica Energy (2010) reports that installation of a turbine foundation typically takes 12

hours with favourable weather conditions and an additional one or two days are required to

reposition the piling vessel / jack‐up barge to the next turbine location. Piling hammers can weigh

225 t and deliver blow forces of 200‐500 kJ per strike (Bailey et al., 2010), with Norro et al. (2010)

reporting piling blow energies of up to 990kJ.

Once the monopile has reached a suitable depth, the transition piece and tower are grouted in place

and the turbine is then secured atop. Monopiles tend to create a greater scour area than the other

structures and take longer to install on site in many cases. In addition, monopile structures are less

suited to deep water depths as they can become unstable due to hydrodynamic stresses including

susceptibility to wave action (Seidel, 2010) and the possibility of larger storm wave loadings means

more resilient grouting at the foundation / transition / tower connection. Taller monopiles are also

less stable when considering the effects of rotor sweep and transmission of rotational forces / cyclic

loading through the tower and foundation making it difficult to meet the requirements for turbine

operation. Increased water depth will require deeper penetration depths for monopile solutions and

resilience results in increased diameter of monopiles and thicker pile walls. These factors mean that

longer piling periods are required with greater sustained hammering using heavier hammers in

comparison to shallow water installation. Therefore noise effects are likely to increase, and will

propagate further in the deep water locations where the Round 3 sites are typically located.

There are also the technical considerations of actually building tall, thick‐walled 6m+ diameter

monopiles and transporting them from fabrication centres to ports (EWEA, 2009). The cost of the

steel required to build these deep‐water size monopile will also be expensive to the point that they

may not be a cost effective solution.

The table below highlights the comparative key facts:


12

Table 3.2.1: Overview of generic effects associated with use of monopile structure.

Parameter Monopiles

Experience Used extensively in current offshore windfarms

Water Depth Shallow to mid water

Price Favourable inshore, high for offshore

Availability Favourable inshore, restricted offshore

Maintenance required High

Ground preparation (temp habitat loss) Low if drilled due to spoil from drill fines

Emplacement weather / condition window Wind and wave sensitive

Sound emitted during emplacement High

Seabed footprint (habitat loss) Low


Scour High

Reef effects Low to moderate

Decommissioning Difficult to remove entire structure

3.3 TripodTripods are three legged structures that are generally secured in place using a pile to secure each

‘foot’ through a pile sleeve to the seabed. There is the ability to use small suction caissons to secure

the ‘feet’ to sandy sediments, though this is not normally the favoured securement option. Tripod

foundations are typically made of steel. The design of the structure allows the weight and loads

generated by the turbine to be transferred as axial loads to the ground, which may be advantageous

in weaker soils (Schaumann and Böker, 2005).

Once in place and secured the tower and wind turbine are added to the foundation and grouted or

swaged in place. Tripods can suffer from fatigue as a result of the complicated joints and have high

construction costs due to complexity of design. However, as a result of their design and nature, the

tripod is considered not to require a significant amount of ground preparation prior to installation

and they are suitable for a variety of ground types.

As for monopiles, piling operations are required for installation including the attendant engineering

technicalities and associated noise impacts. It should be noted that three separate piling operations

per foundation will be required to install the structure. The complete installation time typically

requires between 4‐7 days per foundation, excluding any weather downtime. The underwater noise

impacts associated with tripod installation have been scrutinised as part of the German BARD

Offshore 1 project. The German authorities have imposed restrictions upon the construction of this

project, including periods where cessation of piling operations has been required, to mitigate the

noise‐related impacts on harbour porpoise.

As a result the following parameters can be established:


13

Table 3.3.1: Overview of generic effects associated with use of tripod structure.

Parameter Tripods

Experience Experimental/Test only


Price High cost



Ground preparation (temp habitat loss) None




Scour Moderate



Decommissioning Difficult to remove piles

3.4 SteelJacketSteel jackets work in a similar way to tripods, although their design will vary depending on the site

conditions and manufacturer. Typically the design incorporates 3‐4 legs. The structure supports a

central column to which the tower and turbine is attached and from which the structure dissipates

and transfers the weight and stresses to the ground. The structure is typically secured to the seabed

using multiple piles (one at each of the jacket’s ‘feet’), although suction caissons can also be used.

Steel jackets tend to be corrodible, in spite of corrosion protection paints/coatings, as a result of the

large amount of steel components used in their construction. In addition, they also suffer from

fatigue as a result of the complexity of the structures used and are also complex to manufacture and

often most expensive per tonne of steel used (Schaumann and Böker, 2005). However they can be

designed to meet the required ‘operational life’ specifications for offshore windfarm projects.

Furthermore ground preparation is often required for these structures and piles may not be

completely removed at the end of the structure’s lifespan (Schaumann and Böker, 2005). It is not

known if this incomplete removal of infrastructure at decommissioning of the structures will result in

persistent effects. In recent years these foundations have been used at several offshore windfarms

including Ormonde and Beatrice.

As for monopiles, piling operations are required for installation including the attendant engineering

technicalities and associated noise impacts. It should be noted that 3‐4 separate piling operations

per foundation will be required to install the structure. The complete installation time typically

requires between 4‐7 days per foundation, excluding any weather downtime.

The following can therefore be ascertained:


14

Table 3.4.1: Overview of generic effects associated with use of steel jacket structure.

Parameter Steel Jackets

Experience >40 years’ experience from oil and gas platforms


Price High cost






Seabed footprint (habitat loss) Moderate‐High

Scour Moderate


Reef effects High

Decommissioning Difficult to remove piles

3.5 SuctionCaissonsSuction caissons are comparable to an upturned bucket and work by creating a seal around the base

of the structure. The sediment and water trapped within the caisson is then pumped out forcing the

caisson into the sediment and creating a negative pressure inside once a suitable geological unit is

reached beneath the caisson. Seabed penetration depths of 10‐20 m are typically required for a

stable platform. The hydrostatic pressure created during pumping is usually sufficient to achieve

penetration depth. Due to the need to penetrate the seabed to achieve a hydrostatic seal this

foundation solution is unsuitable for rock or consolidated seabed types.

As with the other solutions, the tower and turbine are attached to the top of the structure which

stands proud of the sea at all states of the tide.

A limited amount of ground preparation may be required to achieve a level seabed surface however

scour and sediment liquefaction are critical because of the importance of maintaining the negative

pressure within the caisson. There is no piling required so no attendant underwater noise impacts of

the magnitude for monopiles, tripods and steel jackets. Installation time is typically about 2 days

excluding weather downtime.

It should be noted that suction caissons have not been used extensively by the offshore renewables

sector within the marine environment, but research by Houlsby et al. (2005) notes that the suction

within the caisson within the examples monitored, have proved to be successful.

As a result, the following can be concluded:


15

Table 3.5.1: Overview of generic effects associated with use of suction caisson structure.

Parameter Suction Caissons

Experience Experimental/Test only


Price Favourable

Availability Low


Ground preparation (temp habitat loss) Moderate


Sound emitted during emplacement Low


Scour Moderate



Decommissioning Favourable to remove entire structure

3.6 FloatingPlatformsFloating platforms are designed to be buoyant within the water column, allowing the windfarm

structure to be attached above the waterline and have been used to a limited extent in the offshore

oil and gas industry. The floating platform is tethered to the seabed using anchors which may be

piles, gravity or suction based. The loading forces placed on the floating structure are transferred to

the seabed via the anchoring cables.

An experimental floating platform at 1:6 scale was deployed off the Norwegian coast in 2011

(Weinhold, 2012). Some technical issues have been encountered in storm conditions but it is

believed that these relate to scale, rather than technical feasibility.

The following table details the paucity of information for this solution type at this time:

Table 3.6.1: Overview of generic effects associated with use of floating platform structure.

Parameter Floating Platforms

Experience Two test beds only

Water Depth Deep water

Price Unknown

Availability None for UK Round 3

Maintenance required Unknown


Emplacement weather / condition window Unknown

Sound emitted during emplacement Low‐Moderate

Seabed footprint (habitat loss) Low

Scour Limited

Blockage effects None

Reef effects None to low

Decommissioning Favourable if anchors only are used, less favourable if piled as difficult to remove piles


16

3.7 ComparisonbetweenStructuresCombining the results from the tables at the end of each section it is possible to create the following

comparative table of effects and uses for each of the foundation types:

Table 3.7.1: Comparison of broad effects between turbine foundation types (adapted from Schaumann and Böker, 2005; STRABAG, 2012; Houlsby et al., 2005; Frederiksen, 2008).

Parameter CGBFs Monopiles Tripods Steel Jackets Suction

Caissons

Floating

platforms

Experience

(No. of foundations

currently installed)

Good

(332)

Good

(1810)

Moderate

(86)

Moderate

(88)

Low

(1)

Trial only

(2)

Water Depth All Shallow All All All Deep

Emplacement

weather window Good Restricted Restricted Restricted Moderate Unknown

Maintenance

required L H H H L Unknown

Price L H H H Unknown Unknown

Availability – UK R3 Fav Unfav† Fav Fav Low None

Environmental Effects/Impacts

Ground

preparation

(temp habitat loss)

L H L L L M Neg L

Sound emitted

during

emplacement

L H H H L L M

Seabed footprint

(habitat loss) H M H H H L

Scour L H L L L L M

Blockage effects H‡ M H‡ H H Neg

Reef effects H M H H H Neg L

Decommissioning L H H H L H

Neg = Negligible, L = Low; M = Moderate, H = High, Fav = Favourable, Unfav = Unfavourable

Environmental Effects / Impacts are relative to baseline of ‘undisturbed’ i.e. no foundations present.

†As deepwater solution

‡Some solutions which do not exceed 9m diameter could be considered as Moderate (M).


17

4 HistoryofGravityBasesThe emphasis of this report is to consider the use of concrete gravity bases as offshore wind turbine

foundations. This section reviews the previous applications of concrete gravity bases in the marine

environment (in a UK context). Whilst other construction materials, most notably steel and in‐

particular steel jackets, have been used extensively as foundation and support structures in the

marine environment, the historical detail of their application is not presented due to the aims and

objectives of this report (see Section 1.1).

Concrete Gravity Bases have been used for offshore for many decades. Concrete structures have a

significant advantage over their traditional steel‐built rivals when placed in the marine environment,

as concrete is not as susceptible to corrosion and require less maintenance. Therefore, marine

concrete structures have been seen as an attractive alternative for the offshore oil and gas industry

for the past 40 years, where tanks, barges and platforms have been constructed using concrete.

Some early examples of concrete structures exist offshore around the UK coast, such as the Nab

Tower (installed in 1920), and also various Naval Forts in the Outer Thames, however these are often

single structures rather than a group of several structures.

The current CGBF solutions have been researched and developed using experience derived primarily

from the oil and gas industry. The first concrete structure utilised by the offshore oil and gas industry

was a tank for storage of oil in the Norwegian sector of the North Sea. Shortly after this in the mid‐

1970s, the first gravity base structures were utilised in by platforms in the North Sea. Beryl A and

Brent B were both large platforms initiated in 1975 in water depths in excess of 100m.

Over 50 major offshore concrete structures have been built worldwide (see Table 4.1). Designs for

up to 300m water depth have been installed, such as Troll, but the majority of recent platforms have

been in water depths more comparable with the Round 3 windfarms. The trend for shallower water

platform installation commenced with the Ravenspurn North platform, installed in 1989 in the

Hornsea zone, and the construction features of these smaller platforms are evident in the CGBFs

now being proposed.


18

Table 4.1: Existing Offshore Concrete Structures for Oil and Gas Production (adapted from International Federation for Structural Concrete (fib ‐ fédération internationale du béton), 2009)

No Installation

year Original Operator

Field/Unit Platform Type Water depth (m)

Concrete Volume (m3)

Location

1 1973 Phillips Ekofisk Caisson. Jarlan Wall 71 80,000 North Sea

(N)

2 1974 Atlantic Richfield

Ardjuna Field LPG Barge 43 9,200 Indonesia

3 1975 Mobil Beryl A GBS 3 shafts 118 52,000 North Sea

(UK)

4 1975 Shell Brent B GBS 3 shafts 140 64,000 North Sea

(UK)

5 1975 Elf Frigg CDPI GBS 1 shaft. Jarlan Wall 104 60,000 North Sea

(UK)

6 1976 Shell Brent D GBS 3 shafts 140 68,000 North Sea

(UK)

7 1976 Elf Frigg TPI GBS 2 shafts 104 49,000 North Sea

(UK)

8 1976 Elf Frigg MCP‐01 GBS 1 shaft. Jarlan Wall 94 60,000 North Sea

(N)

9 1977 Shell Dunlin A GBS 4 shafts 153 90,000 North Sea

(UK)

10 1977 Elf Frigg TCP2 GBS 3 shafts 104 50,000 North Sea

(N)

11 1977 Mobil Statfjord A GBS 3 shafts 145 87,000 North Sea

(N)

12 1977 Petrobras Ubarana‐Pub

3 GBS caisson 15 15,000 Brazil

13 1978 Petrobras Ubarana‐Pub


14 1978 Pctrobras Uburana‐Pag


15 1978 Shell CormorantA GBS 4 shafts 149 120,000 North Sea

(UK)

16 1978 Chevron Ninian Ccntrnl

GBS 1 shaft. Jarlan Wall 136 140,000 North Sea

(UK)

17 1978 Shell Brent C GBS 4 shafts 141 105,000 North Sea

(UK)

18 1981 Mobil Statfjord B GBS 4 shafts 145 140,000 North Sea

(N)

19 1981 Dome

Petroleum Tarsuit Concrete Island. LWA 16 8,800

Beaufort Sea

20 1982 Phillips Maureen ALC Concrete base artic. LC 92 3,500 North Sea

(UK)

21 1983 Texaco Schwedeneck

A* GBS Monotower 25 3,620

North Sea (D)

22 1983 Texaco Schwcdcneck

B* GBS Monotower 16 3,060

North Sea (D)


19

No Installation

year Original Operator

Field/Unit Platform Type Water

depth (m)

Concrete Volume (m3)

Location

23 1984 Mobil Statfjord C GBS 4 shafts 145 130,000 North Sea (N)

24 1984 Global Marin

Beaufort Sea **

GBS caisson, Arctic 16 14,300 Sakhalin (R)

25 1986 Statoil Gullfaks A GBS 4 shafts 135 125,000 North Sea (N)

26 1987 Statoil Gullfaks B GBS 3 shafts 141 101,000 North Sea (N)

27 1988 Norsk Hydro

Oseberg A GBS 4 shafts 109 116,000 North Sea (N)

28 1989 Statoil Gullfaks C GBS 4 shafts. Skirt

Piles 216 244,000 North Sea (N)

29 1989 Hamilton Bros

N. Ravenspurn

GBS 3 shafts 42 98,000 North Sea

(UK)

30 1989 Phillips Ekofisk P.B Protection Ring 75 105,000 North Sea (N)

31 1996 Elf Congo N'Kossa Concrete Barge 170 26,500 Congo

32 1993 NAM F3‐FB GBS 3 shafts 43 23,300 North Sea

(NL)

33 1992 Saga Snorre CFT Suction anchors,3

cells 310 7,800 North Sea (N)

34 1993 Statoil Sleipner A GBS4 shafts 82 77,000 North Sea (N)

35 1993 Shell Draugen GBS Monotower 251 85,000 North Sea (N)

36 1994 Conoco Heidrun Found

Suction anchor.19 cells

350 28,000 North Sea (N)

37 1996 BP Harding GBS

Foundation/Storage 109 37,000

North Sea (UK)

38 1995 Shell Troll A GBS 4 shafts, Skirt

Piles 303 245,000 North Sea (N)

39 1995 Conoco Heidrun TLP Concrete TLP, LWA 350 63,000 North Sea (N)

40 1995 Norsk Hydro

Troll B Semisub 325 43,000 North Sea (N)

41 1996 Esso West Tuna GBS 3 shafts 61 29,000 Australia

42 1996 Esso Bream B GBS 1 shaft 61 14,000 Australia

43 1996 Ampolex Wandoo GBS 4 shafts 54 28,000 Australia

44 1997 Mobil Hibernia GBS 4 shafts. Ice

Wall 80 165,000 Canada

45 1999 Amerada Hess

South Arne GBS 60 35,000 North Sea

(DK)

46 2000 Shell Malampaya GBS4 shafts 43 34,000 Philippines

47 2005 SEIC Sakhalin LUN‐A

GBS 4 shafts. Arctic 48 35,500 Sakhalin (R)

48 2005 SEIC Sakhalin PA∙B GBS 4 shafts. Arctic 30 28,000 Sakhalin (R)

49 2001 ExxonMobil Adriatic LNG LNG terminal 29 95,000 Adriatic Sea

(I) Notes: * The unit has been removed and demolished

by the end of its life ** Relocated from Benufort Sea to Sakhalin

D Germany NL Netherlands DK Denmark R Russia I Italy UK United Kingdom N Norway


20

The world’s first offshore windfarm was constructed in Denmark in 1991 and was placed on concrete

gravity bases. According to LORC (Lindoe Offshore Renewables Center 2012), 16 offshore windfarms

currently utilise 332 gravity base foundations. These are listed in Table 4.2.

Table 4.2: Offshore windfarms utilising GBFs to date (Lindoe Offshore Renewables Center, 2012)

Name Country Operator Installed Capacity

Number of Turbines

Avedore Holme Denmark DONG Energy 10.8 MW 3

Breitling Demonstration

Germany WIND‐projekt 2.5 MW 1

Donghai Bridge 1 China Shanghai Donghai Wind Power 102 MW 34

Ems Emden Germany ENOVA 4.5 MW 1

Kemi Ajos Finland Innopower 30 MW 10

Lillgrund Sweden Vattenfall 110.4 MW 48

Middelgrunden Denmark DONG Energy 40 MW 20

Nysted 1 Denmark DONG Energy 165.6 MW 72

Pori Offshore 1 Finland Suomen Hyötytuuli 2.3 MW 1

Rodsand 2 Denmark E.ON 207 MW 90

Ronland Denmark Vindenergi/Harboøre Møllelaug + Thyborøn‐Harboøre Vindmøllelaug

17.2 MW 8

Sprogo Denmark Sund & Bælt 21 MW 7

Thornton Bank 1 Belgium C‐Power 30 MW 6

Tuno Knob Denmark DONG Energy 5 MW 10

Vindeby Denmark DONG Energy 4.95 MW 11

Vindpark Vanern Sweden Vindpark Vänern 30 MW 10

Some of these sites are demonstration projects utilising GBFs at a small scale and others are located

in offshore environments significantly different to Round 3 conditions, but several of these examples

are comparable to UK offshore environments, and are therefore described in detail below.

4.1 ThorntonBank1The Thornton Bank windfarm was the first to be developed in Belgian waters. Although only 6 of the

60 turbines planned utilise CGBFs, their location in the southern North Sea provides a reasonable

analogy with the windfarms planned for UK waters.

Thorough geophysical and geotechnical investigations were undertaken at the site, including

Sidescan sonar, multibeam bathymetry, sampling with vibrocore, bore holes for pressure meter

testing and cone penetration tests with the measurement of pore water pressures. After the data

was analysed, foundation pits were dredged to a depth of around 1m compared to the surrounding

sediments. The pits were needed to cater for the large mobile sand waves in the area which

precluded direct placement of the foundations on the seabed.

The dredged material was then deposited at three locations within the array to allow them to be

reutilised for ballast infill during the placement of the structures. On average, 90,000m3 of sediment


21

was removed from each of the foundations of the structures (Peire et al., 2009). Following

preparation of the foundation pit, a bed layer of gravel was placed across the site to ensure stability.

Figure 4.1.1: Bathymetry around Turbine D1 at Thornton Bank, Belgian waters. Note the foundation level is 1.3m below surrounding levels and that the vertical scale is exaggerated by 4 (Peire et al., 2009).

The CGBFs were built in Oostende and constructed to be around 40m in height and weighed around

3,000t. The CGBFs were lifted off the quayside by a Heavy Lift Vessel (HLV) that transported the

CGBFs to their intended location. Once on site, the CGBFs were lowered into position before scour

protection and infill of the CGBF occurred. The sands utilised for backfill and infill were reused from

the ground preparation works described above. In addition to the sands described above, gravel and

crushed rock was also utilised for scour protection and armouring. These were placed up to 15m

from the scour protection layer, which itself extended around 10m from CGBF (Peire et al., 2009).


22

Figure 4.1.2: General arrangement of the CGBFs at Thornton Bank, Belgian waters (Peire et al., 2009).

The Thornton Bank windfarm was constructed in 2008. Since then, a number of monitoring surveys

have been undertaken and reported. Degraer et al. (2010) report the results of the monitoring

undertaken to date can be summarised as follows:

No secondary erosion was noted at the CGBFs;

Sand borrow areas were observed in areas where the fill material was sourced as a result of

the 280,000m3 of sediment that was lost during backfill and infill;

75 taxa were recorded in 2008/9, of which 42 had not been previously recorded at the site.

Whilst the majority of these were subtidal, 13 intertidal species were also observed;

Pouting was the most common fish species observed, inhabiting the scour protection layer.

Each CGBF was estimated to support around 29,000 individuals; and

No overall changes to the epibenthos, demersal fish or pelagic fish were noted, however,

Sole density was noted to be reduced within the impact area and horse mackerel increased.


23

4.2 Rødsand1and2Rødsand 1 and 2 are located in the Danish sector of the Baltic Sea. Rødsand 1 is also referred to as Nysted 1 and as can be seen from Table 4.2, these two offshore windfarms represent the two largest arrays that have been deployed utilising CGBFs.

The CGBFs were designed with an ice cone at the top of the shaft to reduce the potential impacts

from sea ice that forms in the Baltic Sea. Whilst this specific design is unlikely to be utilised in the

regions under consideration in this document, the array design, preparation and array impacts may

be transferrable to the areas under consideration in this document.

The CGBFs utilised for the Nysted and Rødsand windfarms required a footprint of approximately

17m by 17m and required considerable ground preparation and scour protection as outlined in

Figure 4.2.1 and Figure 4.2.2 respectively.

Figure 4.2.1: Preparation of the seabed required at Rødsand 2 (Aarsleff Bilfinger Berger Joint Venture, 2011).

Foundations for the structures were dug until a horizon with sufficient bearing capacity was reached.

Typically around 32,000m3 of sediment was removed; with around 44,000m3 utilised within the

structure for stabilisation and for scour protection, as shown in Figure 4.2.2 below. In total, the

gravity base foundations each occupy around 45,000m2 of the seabed, which represents around

0.2% of the total area of the windfarm site (DONG Energy, 2006).


24

Figure 4.2.2: Design of the CGBFs utilised at Rødsand 2 (Aarsleff Bilfinger Berger Joint Venture, 2011)

The first turbines within the Nysted array were installed in 2001 and since then a number of

monitoring studies have been undertaken to monitor the effects of the windfarm in the wider

region. The physical effects of the structures was predicted to be small and localised as a result of

the small tidal range, low tidal currents, shallow water and small wave exposure. As a result of the

limited predicted effects on the physical environment, no results of the physical monitoring have

been analysed to date (DONG Energy, 2006). Ecological monitoring has shown that the array has

promoted common mussels, barnacles and macroalgae on the concrete structures and scour

protection measures which has in turn attracted associated crustaceans and fish (Boesen and

Andersen, 2005). Any detrimental effects to eel grass beds during construction were noted to have

recovered 2 years after the dredging events. Harbour porpoises were not observed to have changed

in population or behaviour since prior to construction of the windfarm, but the construction traffic

was seen to reduce porpoise sightings during this phase (Boesen and Andersen, 2005). Rødsand is an

important area for both harbour seals and grey seals. During operation of the windfarm, seal

behaviour and populations were seen to be unaffected by the windfarm, indeed populations had

grown by up to 42% 2 years after construction (Boesen and Andersen, 2005). Bird activity was also


25

recorded and avoidance of the windfarm was observed as it is in other windfarm where different

construction methods have been employed.


26

5 ForeseeableEffects

5.1 StagesofconstructionandplacementThe installation and emplacement of concrete gravity base foundations require a range of processes

each of which has the potential to impact the marine environment and other users of the sea. These

impacts will vary in their severity, spatial extent and longevity. There are 6 main phases associated

with Gravity base foundations:

1. Preparation of the ground where the CGBF is to be placed (if required);

2. Emplacement works associated with the CGBF;

3. Remedial activities associated with the CGBF (if required);

4. Settlement of the CGBF in the natural environment following emplacement (if appropriate);

5. Operation of the CGBF; and

6. Decommissioning of the CGBF (if required).

The potential activities and effects associated with each of these stages of development of the

CGBFs in the marine environment are described within the sections below. The receptors which may

be affected by the effects identified are presented within the following Sections 6, 7 and 8.


27

5.2 EffectsThe following section details the potential effects associated with each phase of the placement of

CGBFs identified within Section 0. The various potential CGBF engineering solutions (see

Figure 1.2.1) will require a different combination of the following phases of works and associated

activities e.g. one CGBF solution may require seabed preparation and another may not.

5.2.1 EffectsrelatingtothepreparationofthegroundwheretheCGBFistobeplaced(ifrequired)

Figure 5.1: Effects arising as a result of ground preparation

During preparation of the seabed for emplacement of a CGBF structure several processes will be

required that may result in effects. Effects identified during preparation may include:

a. Dredging. Removal of seabed sediment or rock may be required to level the site. If

undertaken, effects of such works will include;

i. Changes to the bathymetry – effects of tides and waves.

Key: ActivityEffect on the

Human Environment

Effect on the physical

environment

Effect on the biological

environment


28

ii. Removal of seabed sediment/rock ‐ effects on benthic habitat and communities, fish

spawning habitat, fish feeding habitat, bird and mammal feeding habitat,

archaeological sites/artefacts.

iii. Turbidity ‐ effects on benthic habitats and communities, fish spawning habitat and

activities, feeding success of birds and mammals.

iv. Fine sediment deposition ‐ effects on benthic habitat and communities, fish

spawning habitat, fish feeding habitat, bird and mammal feeding habitat.

v. Noise ‐ disturbance/displacement of fish, birds and mammals.

vi. Vessel presence (displacement) ‐ access issues for other users of the sea.

vii. Damage to infrastructure ‐ damage to cables, pipelines and Oil and Gas

infrastructure.

b. Deposition of sub‐structure foundation. The structure may require a more solid foundation

than that provided by natural seabed conditions. Therefore a layer of rock and/or sand may

be required to be placed underneath the structure to act as a foundation for it. The potential

effects arising from this element of the work are likely to be:


ii. Smothering of seabed sediment/rock ‐ effects on benthic habitat and communities,

fish spawning habitat, fish feeding habitat, bird and mammal feeding habitat,









infrastructure.


29

5.2.2 EffectsrelatingtotheemplacementworksassociatedwiththeCGBF Figure 5.2: Effects arising as a result of emplacement

a. Emplacement. Placement of the CGBF on the selected and prepared site, either floated out

to site or placed on site from a barge and backfill of the CGBF (if needed);


ii. Removal of seabed sediment/rock ‐ effects on benthic habitat and communities, fish







v. Additional habitat – effects on benthic habitat and communities, fish, bird and

mammal feeding habitat.

vi. Noise ‐ disturbance/displacement of fish, birds and mammals.

vii. Vessel presence (displacement) ‐ access issues for other users of the sea.

viii. Navigation ‐ obstruction to established shipping routes and hazard to navigation.


Human Environment


environment


environment


30

5.2.3 EffectsassociatedwiththeremedialactivitiesrequiredbytheCGBF(ifrequired) Figure 5.3: Effects arising as a result of remedial activities

a. Scour protection. Placement of the scour protection around the CGBF on the seabed in the

appropriate locations if deemed appropriate for the site;


ii. Removal of seabed sediment ‐ effects on benthic habitat and communities, fish







v. Additional habitat – effects on benthic habitat and communities, fish, bird and

mammal feeding habitat.

vi. Noise ‐ disturbance/displacement of fish, birds and mammals.

vii. Vessel presence (displacement) ‐ access issues for other users of the sea.

viii. Navigation ‐ obstruction to established shipping routes and hazard to navigation.


Human Environment


environment


environment


31

5.2.4 EffectsrelatingtothesettlementoftheCGBFfollowingemplacement(ifappropriate)

Figure 5.4: Effects arising as a result of settlement

a. Settlement. Settlement in this context is the vertical movement of the seabed, due to

consolidation, post‐construction. Changing seabed level following placement of the CGBF

has the potential to cause the following effects;


ii. Changes to the seabed sediment ‐ effects on benthic habitat and communities, fish








Human Environment


environment


environment


32

5.2.5 EffectsofoperationoftheCGBF Figure 5.5: Effects arising as a result of operation

a. Presence. The presence of the CGBF permanently on site has the potential for the following

effects;

i. Changes to the local hydrodynamics – effects of tides and waves.

ii. Increases in wave noise ‐ disturbance/displacement of fish, birds and mammals.

iii. CGBF presence (displacement) ‐ access issues for other users of the sea.

iv. Changes to stratification.

v. Fish aggregation – the array may perform as a fish aggregation device (FAD) acting as

a refuge for fish species. There may also be a positive effect on foraging success

which will also attract certain fish species – both result in an increase of density of

fish.

vi. Ecosystem service ‘cascade’ from FAD effect resulting in attraction of apex predators

(e.g. seals and Harbour Porpoise) – may result in changes at a sub‐population scale.


Human Environment


environment


environment


33

5.2.6 EffectsassociatedwithdecommissioningoftheCGBF(ifrequired) Figure 5.6: Effects arising as a result of decommissioning

a. Remediation. Replacement of seabed sediments following removal of CGBF may be required

in some cases to allow full recovery to occur;


ii. Changes to seabed sediment/rock ‐ effects on benthic habitat and communities, fish









b. Removal of CGBF fill / ballast. Removal of seabed sediment fill may be required to refloat

or remove the CGBF. If undertaken, effects of such works will include;


Human Environment


environment


environment


34


ii. Deposition of fill sediment ‐ effects on benthic habitat and communities, fish









c. Removal of CGBF. The structure will need to be removed once decommissioned. This will

involve removing/refloating the CGBF from its operational location:


ii. Changes to stratification.

iii. Smothering of seabed sediment/rock ‐ effects on benthic habitat and communities,



iv. Turbidity ‐ effects on benthic habitats and communities, fish spawning habitat and


v. Fine sediment deposition ‐ effects on benthic habitat and communities, fish


vi. Fish aggregation – the array may perform as a fish aggregation device (FAD) acting as

a refuge for fish species. There may also be a positive effect on foraging success

which will also attract certain fish species – both result in an increase of density of

fish.

vii. Ecosystem service ‘cascade’ from FAD effect resulting in attraction of apex predators

(e.g. seals and Harbour Porpoise) – may result in changes at a sub‐population scale.

viii. Noise ‐ disturbance/displacement of fish, birds and mammals.

ix. Vessel presence (displacement) ‐ access issues for other users of the sea.

d. Removal of foundation material and/or scour protection. The foundation material and any

scour protection emplaced may need to be removed once decommissioned. This will involve

dredging foundation sediment or scour protection (if used) and disposing of it:


ii. Smothering of seabed sediment/rock ‐ effects on benthic habitat and communities,










35


infrastructure

5.3 ConceptualisationofEffectsAs the majority of effects arising from the use of CGBFs are related to changes to the physical

environment, it is important to model these effects to ensure that the scale and magnitude of

effects are fully understood. The modelling methods employed will change depending upon the local

physical conditions and array design. The section below has been written to provide guidance on the

scope required, depending upon these factors.

5.3.1 CoastalProcessesStudyCoastal process studies form an important part of the environmental impact assessment (EIA) for

any type of proposed offshore development. These studies provide the means to describe the

physical changes that might be expected to occur in the marine environment as a consequence of a

development, including the case of offshore windfarms.

The detailed requirements for a coastal process study related to an offshore windfarm are both site

specific and project specific, however, there are now several publications that offer guidelines for

the main issues of interest and describe appropriate means for investigation, including the use of

numerical modelling.

Chapter 4.7 of Guidelines for data acquisition to support marine environmental assessments for

offshore renewable energy projects (Cefas, 2011), provides generic requirements for physical and

sedimentary process studies. This guidance also refers directly to approaches for physical process

modelling developed for COWRIE (Lambkin et al, 2009). These documents provide as a useful

reference framework for establishing the requirement for EIA for offshore windfarms.

In general terms, the two main themes of interest related to effects of offshore wind development

on coastal processes can be summarised into:

(i) Sediment disturbance issues during construction (and decommissioning) phase; and (ii) Blockage effects during operational phase.

The scales of effects related to these issues inherently vary between projects and due to differences

in foundation types, array layouts and local environmental conditions. The local environmental

conditions also determine the design requirements for these installations in relation to maximising

energy yield, indicating preferred foundation type as well as being used to derive loadings as part of

foundation design.

At the pre‐consent stage it remains important for a developer to retain sufficient flexibility in project

design and not to submit an application with overly specific descriptions of turbine and foundation

type or layout that subsequently constrain the (post‐consent) final design and build contracting.

Instead it is preferred to describe a range of feasible options for the project and document an

outline design in a Project Design Statement (PDS) (see Section 5.3.2 below). The environmental

assessment is then undertaken by considering the realistic worst case scenario (for a specific type of

impact and receptor sensitivity) from across the range of options which the developer wishes their

project to be considered. The premise here is that if consent can be gained for the realistic worst


36

case then by default all lesser options must also be suitable for consent. This approach has now

become the expected norm for offshore wind projects and is generally referred to as the Rochdale

Envelope (DECC, 2011b).

For Round 2 and Round 3 of offshore wind development in the UK there has been a greater

tendency to include gravity base foundations as one of the foundation options, whereas in Round 1

(smaller arrays in shallower water) the main option considered was commonly the monopile case.

There are many reasons why gravity bases have been proposed for Round 3; but the main factor is

that the new sites are further offshore and in deeper water, making it potentially more cost effective

to use gravity bases, compared with larger monopiles with thicker walls required for deep water use.

5.3.2 ProjectDesignStatementA Project Design Statement (PDS) provides, amongst other details, the outline engineering

description for the full range of options to be considered for consent and which achieves the target

generating capacity for the project. A primary parameter for the PDS is the choice of turbine unit.

Here, it is typical that a range of turbine rating capacities is offered with higher capacity units

requiring larger rotor diameters which then influence the necessary spacing between units, the

number of units and hence the overall layout. It is also the case that the new generation of larger

turbines will require larger foundations to withstand a larger overturning moment. The choice of

foundation type may also vary from monopile, steel jacket (e.g. tripod or multiple) or gravity base

depending on site location and sea bed conditions.

The number of possible permutations of layouts and foundation types make it impractical for the EIA

to consider every one. Instead, the Rochdale Envelope approach is applied. The PDS is reviewed to

determine those combinations of design choices which are likely to represent the realistic worst case

in terms of a specific environmental impact. The premise is that if the scale of this impact is not

considered significant and be suitable for consent then all other combinations (which are regarded

to be less than the realistic worst case option) should be permitted for consent.

When considerations are offered on sediment disturbance and blockage related issues the gravity

base option is often selected as the realistic worst foundation case. The main reasons that this

occurs is that, relative to other foundation types, the gravity base option is likely to be larger in scale

through the water column (implying greater blockage) and requires a wider footprint on the seabed,

in‐part due to the presumption that seabed preparation is always required e.g. levelling and

foundation pit excavation (implying the potential for greater volumes of sediment disturbance). This

premise is consistent with Hammer et al. (2010), however is should be noted that some proven CGBF

designs do fall below the thresholds and envelopes presented in Hammer et al. (2010). Therefore,

as detailed in this report, CGBFs do not realistically represent the worst case scenarios in all

instances and certainly when considering underwater noise effects they are the most favourable

proven foundation design to mitigate these impacts.


37

6 PhysicalReceptors

6.1 Introduction:AimsandScopeThe future use of CGBFs is likely to be related to the Round 3 offshore windfarm developments.

These are typically further offshore than those existing and proposed Round 1 and 2 developments.

This section will bring together available information in order to describe the physical receptors and

likely impacts associated with each stage of CGBF deployment, lifespan and decommissioning. Focus

will be given to the scale of effects likely from a single CGBF and particular consideration given to

these effects in relation to monopile solutions. Other foundation solutions will also be discussed,

where data are available.

6.2 PhysicalReceptorsThe placement of CGBFs in the offshore environment has the potential to cause both direct effects

to physical receptors (e.g. by ground preparation (if required) and placement) and indirect effects

(through modifications to the hydrodynamics and associated changes to sediment transport e.g.

scour).

Along with the relevant EIA guidelines, regulatory bodies are seeking developers to demonstrate an

evidence based approach to underpin their applications for consent. A number of relevant reviews

are now available that present existing evidence related to monitoring the effects of offshore

windfarms during construction and early stages of operation, both for the UK sites (Cooper et al.,

2008; Carroll et al., 2009; and Cefas, 2010), and also from elsewhere in Europe (Van de Eynde et al.,

2010).

At the present time the majority of evidence relates to early UK Round 1 and 2 projects. So far the

majority of projects have opted for monopile foundations and it is the pre‐construction, construction

and post‐construction environmental monitoring from these projects that forms the core of the

evidence base. Notable exceptions which have used steel jacket foundations are the Ormonde

Offshore Windfarm and Beatrice Demonstration Site in the UK; Alpha Ventus and BARD Offshore 1 in

Germany; and Thornton Bank in Belgium, utilising or part‐utilising these solutions.

There are no operating UK offshore windfarms yet where gravity bases have been used and the

evidence base for this foundation type is presently limited to other examples around Europe. The

best example to date is Thornton Bank, Belgium, where consent was granted for a 300MW offshore

scheme. Phase 1 of this project has installed a single row of six concrete gravity base structures,

whereas Phase 2 and 3 of the project are now using steel jacket foundations. At present, the

monitoring evidence from this project appears to mainly relate to ecological parameters rather than

any measures of physical processes.

Currently, the evidence base for large arrays of gravity base, steel jacket, tripod, or caisson

structures remains poor by comparison to projects using monopiles. Noting also that monopile

projects remain relatively small, are located closer to the coast and are generally in shallower water.

In the absence of direct monitoring evidence of physical change the substitute evidence remains

largely based on theory. Here too, the understanding of fluid dynamics is strongest for small

cylinders (e.g. monopiles) rather than complex or larger shapes (e.g. multi‐piles or gravity bases). It is


38

evident that each CGBF solution design will have to consider modelling for a single foundation

structure to enable a better understanding of the specific interactions associated with its design.

This research and development has already been conducted by some of the solution providers, for

their designs considered within this report.

The existing evidence can, however, be used to identify three overarching physical receptor groups

that can potentially be affected by the foreseeable effects of CGBFs (see Section 5.2 and the flow

diagrams presented therein):

Water column;

Sub‐seabed geology; and

Sediments regime.

6.2.1 WaterColumnAny structure placed in the marine environment can cause blockage effect. In the context of

offshore wind developments, blockage effects relate to the action of the structure’s cross‐sectional

area placed in the water column blocking the normal passage of flows, waves and sediment

pathways and occur following completion of the construction phase and during the operational

phase. The duration of this phase is generally between 25 to 50 years and accounts for the major

part of the lease period. As such, blockage issues need to consider the long‐term persistence of

these effects, noting that these effects stem from multiple locations within the array at the scale of

each structure. This scale is termed the near‐field.

Blockage effects for a windfarm vary as a function of the number of units, the scale and shape of

each unit, their spacing (cross‐wind and down‐wind) across the array and with respect to the

orientation or path of each process being blocked (e.g. wave direction). A large cross‐sectional area

single unit will generally lead to more interference than a smaller cross‐sectional area unit, but a

project that is considering options with a small number of large units or a large number of small

units may have different levels of blockage when added together, and it is not always immediately

obvious which option has the greater cross‐sectional area blockage cumulatively for the array.

If blockage can be parameterised at the simplest level as the proportional volume that a group of

structures will occupy relative to the volume of water across an array then it is possible to contrast,

at a high‐level, between foundation types and layouts. For all currently known cases this relative

blockage value is extremely small (<<0.1%, i.e. the proportion of water volume in the site taken up

by all structures is much smaller than 0.1%). Of the current commercially viable foundation types

some of the gravity base and suction caisson options are largest and the monopile option smallest;

floating platforms will have the least blockage effect but this technology is unlikely to be

economically proven or available at the scale required, or in time, for Round 3 projects. Between

typically considered gravity base options a flat base foundation almost level with the sea bed has a

smaller blockage effect relative to a conical foundation for the same turbine.

ChangesinWaveConditionsWave‐induced seabed stress is an important driver of seabed sediment transport around much of

the coastline of the United Kingdom. Lambkin et al. (2009) indicate that if turbine foundations

significantly affect the magnitude or direction of wave energy exiting the offshore windfarm site,

then there is the potential for an indirect impact on sensitive receptors e.g. the stability of sandbank


39

systems (Section 6.2.3); scour at the seabed immediately surrounding the turbine location (Section

6.2.3); littoral sediment transport rates at the coastline (Section 6.2.3); or on organisms adapted to a

particular sediment habitat type or wave‐dominated environment (Section 7.2.2). It should be

noted, however, that wave effects on the seabed in deeper offshore waters are relatively small

compared with the shallower UK Round 1 and Round 2 sites.

The impact of monopiles on the wave climate has been investigated by Cefas (2005) who used radar

to monitor wave conditions inshore of the Scroby Sands windfarm. This study found that no

constructive or destructive waves were measurable in the lee of the windfarm, however it should be

noted that the wave conditions during the survey were small when compared with longer‐term

regional data (i.e. no storm wave activity occurred during the survey). Associated modelling carried

out as part of the study showed reductions in significant wave height of 3%, with a relatively small

impact zone (typically to background levels within of 2‐3 turbine spacings), and the majority of wave

changes occurring within the licence boundary of the windfarm.

This research was specific to monopile foundations, and Cefas (2005) noted that different

foundation types may produce different impacts. Cefas (2005) also indicated, however, that while

CGBFs generally have more total cross‐sectional area than a monopile much of this is at the seabed,

and the cross‐sectional areas at the sea surface are similar in both cases. Cefas (2005) therefore

concluded that as wave orbital motions are largest at the surface, CGBFs will tend to have similar

impacts on wave energy to monopiles, if the cross sectional areas at the sea surface are similar.

Empirical evidence for the effects of CGBFs on wave climate is currently poor, however initial

monitoring results from the six CGBFs at the Thornton Bank Offshore Windfarm are available

(Degraer and Brabant, 2009; Degraer et al., 2010). These data appear to indicate no significant

alteration to the hydrodynamics in the first two years of monitoring. No monitoring results from the

jacket foundations at the Beatrice Demonstration Site and Ormonde Offshore Windfarm are

available, but the Environmental Statements for these developments indicate little impact of these

structures on the hydrodynamics (Eclipse Energy Company Limited, 2005; Talisman Energy, 2005).

In addition Lambkin et al. (2009) indicate that since Round 3 sites will tend towards intermediate or

deeper water depths where wave action will reach the seabed less frequently and have a less

dominant effect. Lambkin et al. (2009) does also indicate, however, that some examples of deep but

wave‐dominated sites do exist, e.g. the Celtic Sea, where observed bedforms are aligned to the

dominant storm fetch, rather than the tidal axis; and therefore gravity base structures in Round 3

environments might have the potential to cause wave diffraction effects.

All foundation types, including CGBFs, will have a negligible effect on wave climate during

construction, with these effects relating principally to the legs of jack‐ups used to install the

monopiles, or anchoring of installation vessels. Waves will be affected by sheltering, diffraction and

refraction around the turbine foundations during the operational phase for all foundation types.

Decommissioning of CGBFs, suction caisson and possibly floating platforms involves complete

removal of the structure and following decommissioning there will be no further impacts of the

foundation structure (NB: it is currently unknown if complete removal of anchor piles used with

large‐scale floating platforms is achievable). The removal of monopiles, steel jackets and tripods may

leave some part of the structure above the seabed, and whilst the majority of wave action will not


40

reach the seabed there may be potential for these structures to have a low level of impact on wave

climate following decommissioning.

ChangesinTidalCurrentsTidal currents are an important control on sediment transport in many coastal and offshore areas

around the UK, and tidal characteristics are summarised in the Atlas of UK Marine Renewable Energy

Resource (BERR, 2008). Lambkin et al. (2009) indicate that if turbine foundations significantly affect

the magnitude or direction of tidal currents exiting the offshore windfarm site, then there is the

potential for an indirect impact on sensitive receptors e.g. sediment transport onto sandbank

systems (Section 6.2.3) and the coastline (Section 6.2.3); or where sediment changes affect

organisms adapted to a particular sediment types (Section 7.2.2).

Previous research (ETSU, 2002; ABPmer, 2005; reported in Lambkin et al., 2009) has shown that the

effect of monopiles on tidal currents is likely to be minimal. The effect of the monopile on the tidal

flow is to generate a wake around each pile. The piles cause a bifurcation of flow, with flows

accelerating around the edge of each pile, and a reduction in flow velocity directly in the lee of each

pile. Other than in the immediate vicinity of the monopiles modification of tidal currents does not

occur (Cooper, 2010).

Empirical evidence for the effects of CGBFs on tidal currents is currently poor, due to the small

number of CGBFs currently deployed in offshore windfarm sites. Initial monitoring results from the

six CGBFs at the Thornton Bank Offshore Windfarm are available (Degraer and Brabant, 2009;

Degraer et al., 2010) and these indicate no significant alteration to the hydrodynamics in the first

two years of monitoring. These reports do, however, acknowledge that uncertainties still exist on

the possible effects on the hydrodynamics and morphodynamics in the area, and further monitoring

is required.

All foundation types will have a negligible effect on tidal currents during construction, with effects

relating principally to the legs of jack‐ups used to install the monopiles, or anchoring of installation

vessels. Tidal currents may be affected by the turbine foundations during the operational phase of

all foundation types including CGBFs. Decommissioning of CGBFs, suction caisson and possibly

floating platforms involves complete removal of the structure and following decommissioning there

will be no further impacts on tidal currents (NB: it is currently unknown if complete removal of

anchor piles used with large scale floating platforms is achievable). The removal of monopiles, steel

jackets and tripods may leave some part of the structure above the seabed, and in this case there

may be ongoing potential for these structures to have an impact on tidal flows following

decommissioning.

ModellingWaterColumnEffectsCooper and Beiboer (2002) highlight the potential blockage effects on flows and waves and with

particular attention given to the monopile case anticipated for Round 1. Where slender pile theory

remains applicable then drag and inertia forces can be considered as the primary means of scaling

blockage effects on oscillating flows and through the use of expressions such as Morison’s Equation

(this expression assumes the forces apply equally around the slender pile and so diffraction forces

which might vary around a larger structure are not considered). This calculation remains an


41

important step in parameterising the near‐field term which can then be included in a larger scale

coastal process models to investigate both near and far‐field issues.

Coastal process models do not explicitly allow for the effects of small structures or of complex

shapes and neither do they resolve ambient turbulence or the additional turbulence that might be

contained in any wake formed in the lee of a structure. Rather, these models resolve the changes in

the mean flow or phase averaged wave, and often in 2D, by parameterising (up‐scaling) at a sub‐grid

level the ‘effects’ of structures. Typically, the parameterisation simply adds additional friction in the

correct proportions.

Here, the resolution of the model needs to be considered with care as sub‐grid parameterisation

infers the scale of effect is minor in relation to the process being affected over the resolution of the

model at this point. It is also the case that a coarse scale model will diffuse the effect more rapidly

than might occur in practice.

Given these simplifications the application of coastal process models is still considered acceptable

when the objective of the models is to quantify the overall effect of the windfarm array which may

extend beyond the site boundary and across the wider area (far‐field).

Where the consenting process has needed to manage an uncertainty in the assessment of effects,

such as those based on models applied in this way, then monitoring has previously been applied as a

licence condition to help validate the EIA. There are now examples which demonstrate the sub‐grid

parameterisation is sufficient to describe the scale of reductions in the mean flow in the lee of

monopile foundations. As yet this evidence has not extended to gravity base cases.

For very large or complex structures the limits of slender pile theory might be exceeded and

variations of flow will occur around a structure and waves may become diffracted. At this scale the

structure should ideally be resolved in the model or alternate near‐field parameterisation

considered based on detailed computational fluid dynamics (CFD) type models.

At the array scale, the combination of frictional effects can be anticipated to slow mean current

speeds within and behind (downstream of) the array in conjunction with a marginal increase in

speed around the sides of the array. The magnitude of these effects is typically found to be largely

indistinguishable in the field and not practical to measure.

Wave interaction with a structure is more complex and depends on the scale and shape of the

structure (which may vary over depth) and relative to the incident wave length. Wave interactions

with an individual structure include reflection, scattering and diffraction effects, and the waves

which are in contact with the structure are also affected by frictional drag forces. For very long

period waves, the gap between structures can also become relevant to diffraction. Ultimately, these

interactions at the array scale can lead to losses in wave energy in the lee of the windfarm and most

often by affecting shorter period waves. These losses also tend to dissipate quickly such that

patterns of wave energy at the coast are not measurably affected. The research project A1227

(Cefas, 2005) attempted to monitor the change in wave behaviour in the lee of the Scroby Sands

offshore windfarm (comprising 30 monopiles placed on the sandbank) with a wave radar, but results

were inconclusive and did not reveal any noticeable features that were attributed to the windfarm.

Rather, it was the sandbank of the same name which dominated the local wave behaviour.


42

Coastal process models may include a variety of approaches to simulate wave climate and

behaviour. A phase‐average wave model is typically used for EIA in order to cover the large areas

involved; extending from offshore boundaries, across the array and up to the coast with a sufficient

extent to capture different effects from different wave directions. However, these types of wave

model are not appropriate for examining near‐field wave modifications around individual foundation

units, especially where diffraction effects are considered to be important. In this case a more

detailed local phase resolving model is likely to be needed, but these types of model are also limited

to small areas. Good practice is to use the local scale model for near‐field considerations and up‐

scale these effects to the larger scale coastal models which can then investigate the far‐field effects.

Considering the distances for some of the Round 3 zones from the coast then coastal impact studies

are expected to yield negligible to low effects. However, for the reasons described above, there will

be a requirement to conduct these studies as part of the project‐specific EIA considering the lack of

data available to date for design‐specific models; especially at a cumulative array scale.

6.2.2 Sub‐seabedGeologyThe sub‐seabed geology of an offshore windfarm site is controlled by the conditions that previously

existed within the site, often over millions of years. Typically in offshore windfarm Environmental

Statements the sub‐seabed geology is described in terms of the Quaternary deposits (i.e. those laid

down during the Quaternary period – approximately 2.588 million years ago to the present); and the

pre‐Quaternary bedrock. The Quaternary period was characterised by repeated glaciations and

major sea level transgressions and regressions; and also represents the period when early human

first appeared. Quaternary deposits therefore have a potential archaeological value, and impacts on

these units may have an effect on cultural heritage which will be discussed further in Section 8.6 of

this report.

Purely from a physical receptor standpoint different rock types will have different geotechnical

properties and may require different engineering solutions. Of particular importance for this report

is the scale of the direct effects on sub‐seabed geology associated with the CGBF when compared

with alternative solutions such as a suction caisson, steel jackets, tripods and monopiles.

The most commonly used foundation type for offshore windfarms in Europe and the UK is currently

the steel monopile, and is generally engineered for use in water depths of 30m or less, and to date

only fitted with maximum 3.6MW turbines. Monopiles do not generally require any seabed

preparation, such as levelling or excavation. The monopile typically penetrates the seabed by up to

50m, and installation is usually undertaken by using a hydraulic hammer to drive the piles into place.

Seabed drilling may be used as an alternative; however this is dependent on local ground conditions.

Installation of a monopile therefore has a direct effect on the sub‐seabed geology to a maximum

depth of approximately 50m below the seabed surface. Assuming a monopile shaft diameter of 5‐8m

and seabed penetration of 50 m, an estimated volume of approximately 980‐2,513 m3 of sub‐seabed

geology will be directly affected by a single monopile. Piles associated with steel jackets and tripods

(and floating platforms) have 3 or 4 piles of smaller diameters (approximately 3 m) and penetrate to

depths greater than 50 m (60 m cited in RPS Energy and RWE NPower Renewable (2011)).

CGBFs may require some seabed preparation prior to installation, involving dredging or grab

excavation of the seabed to reach the required load bearing strata; and also to provide a level

surface for the CGBF. Estimates of the volumes of material removed can be made using information


43

provided in Table 6.1, which suggests that the footprint of a CGBF at the seabed might vary between

approximately 1,150 m2 and 1,386 m2. Assuming the material being levelled to a depth of two

metres to accommodate the gravity base structure, and assuming that the levelling removes sub‐

seabed material only (i.e. no seabed sediments), then estimated volumes of 2,300‐2,772 m3 of sub‐

seabed geology will be directly affected by a single CGBF. The exact volumes and excavation depths,

however, will depend entirely on each turbine’s location and the depth of load bearing strata, as

with any large building or structure constructed either onshore or offshore.

These impacts to the sub‐seabed geology occur at construction for all foundations types to varying

degrees with the possible exception of floating platforms if surface anchors rather than piles are

used, and no further sub‐seabed effects would be expected during maintenance and

decommissioning. The receptor will not recover following decommissioning, and the effects are

therefore permanent. It should be noted, however, that the sub‐seabed geology is not a sensitive

receptor and the impacts are likely to have a negligible significance, unless that geological sequence

has an additional cultural value or geological rarity (Section 8.6).

6.2.3 SedimentRegimeSeabed sediments can be affected directly by the placement of structures on the seabed, and

indirectly by changes to sediment transport as a result of hydrodynamic alteration. Offshore wind

developments may include installation of foundation units at multiple locations, and a large project

comprising hundreds of turbines may produce effects on the sediment regime over many years.

The environmental risks associated with changes to the sediment regime depend on the proximity

and sensitivity of marine receptors and these risks may be heightened where there are

contaminants contained in the disturbed sediments.

DirectEffectsonSeabedSedimentsMonopiles, steel jackets, tripods and floating platforms do not generally require any seabed

preparation, such as levelling or excavation, prior to piling, therefore their direct effect on the

seabed sediment is restricted to footprint of each pile itself – typically 5‐8m in diameter for a

monopile and 2.5‐4m for each pile used with a steel jacket or tripod foundation (NB: the total

cumulative value for an individual steel jacket foundation will be 3‐4 times the value of each pile per

‘foot’; and for a tripod it will be 3 times the value of each pile per foot).

In addition, this direct impact zone for foundations is extended, in those areas where scour

protection is put in place. Scour is the progressive lowering of the seabed around a structure, in

response to changing hydrodynamics driven by the presence of the installation (Whitehouse, 1998).

Scour pits can jeopardise the integrity of a structure and increase sediment transport (DECC, 2008)

and scour protection is often put in place to resist the locally enhanced flow and turbulence around

the structure (Whitehouse et al., 2011b).

Scour protection types include rock armour placed on the seabed around the foundation;

sandbags/geotextile bags placed on the seabed around the foundation; concrete mattresses placed

on the seabed around the foundation; or frond mats placed on top of concrete mattresses or

anchored directly to the seabed around the foundation (DECC, 2008). Scour protection typically,

therefore, changes the seabed sediments from easily erodible sediments (e.g. fine grained sand) to


44

rock substrate. The scour protection in place around monopiles and CGBFs is therefore a direct

impact on the seabed sediment type.

The Triton Knoll ES has presented indicative scour protection parameters for various foundation

solutions at their site and the data is presented in Table 6.1 below.

Table 6.1: Indicative scour protection parameters for individual turbine locations (excluding foundation area take) (adapted from RPS Energy and RWE NPower Renewable, 2011).

Concept 3.6MW 5MW 8MW

Area of seabed cover per location (excluding foundation area) in m2

Steel monopile 1,636 1,791 1,791

CGBF 1,414 1,571 1,723

Steel jacket (piled) 274 274 431

Tripod (piled) 771 771 1,341

Suction caisson 1,100 943 1,495

These data show that greater amounts of scour protection were suggested as necessary for

monopile foundations compared with a CGBF, however these values exclude the foundation area

itself.

RPS Energy and RWE NPower Renewable (2011) indicate that for the 5MW turbine the steel

monopile would be 8.5m in diameter, while the 5MW CGBF would require a 40m diameter

foundation and a 5MW suction caisson would be 22m. The values in Table 6.1 can therefore be

adjusted, to calculate the total area of direct impact of seabed sediment, of combined footprint and

scour protection for monopiles and CGBFs (Table 6.2).

Table 6.2: Total seabed area directly lost to a combination of foundation and scour protection required for a 5MW turbine (adapted from RPS Energy and RWE NPower Renewable, 2011).

Concept 5MW

Foundation footprint (m2)

Scour protection (m2) Total area (m2)

Steel monopile 57 1,791 1,848

CGBF 1,257 1,571 2,828

Steel Jacket (piled) 57 274 331

Tripod (piled) 305 771 1,076

Suction caisson 380 943 1,323

Armoured scour protection has also been installed around the CGBFs of the Thornton Bank OWF,

Belgium. The maximum diameter of the scour protection layer is reported as 62.5m, which equates

to a seabed area affected of 3,068m2 (Peire et al., 2009).

These direct impacts on the seabed sediment of the placement of foundations and, potentially,

scour protection would occur at construction for all foundation types with the possible exception of

floating platforms, and would persist during the operation of the OWF. Following decommissioning

the foundation and scour protection could be removed (indeed this may be a requirement of the

consent for the project) and there is potential to return the seabed sediment to its pre‐installation


45

state. However, the efficacy of removing scour material from the seabed has yet to be proven for

offshore windfarm developments (MMO, pers. comm.).

IndirectEffectsonSedimentTransportThe indirect effects on seabed sediments will be those which occur as a result of hydrodynamic

changes set up as a result of the presence of a structure in the water column, or because of other

alterations to the seabed causing a far‐field effect, namely:

Scour;

Sediment plumes; and

Alteration of sediment transport pathways.

If these effects overlap with sensitive features, such as subtidal sandbanks or the coastline, then

impacts on these features may occur.

ScourScouring results from the interaction between ambient flows and waves and a blockage posed by

structures at the seabed. These interactions generate flow accelerations and turbulence which can

lead to locally enhanced sediment transport and local erosion around the base of a foundation, i.e.

scour. Scouring initiates as soon as the foundation is in place and continues until an equilibrium

profile is achieved (Whitehouse et al., 2011b).

Where the seabed is comprised of stiff clay or bedrock, or there is a superficial layer of sediment

overlying clay or bedrock; or where the wave and current conditions are not generally strong enough

to cause the seabed sediment to be naturally mobile, scour will be slow or limited. In environments

where scour is likely to occur, however, (i.e. areas of mobile sediment or easily erodible sub‐seabed

geology), scour is likely to occur if no protection is included in the scheme design.

Scour has the potential effect of changing the seabed sediment type at the point of scour, as well as

creating a local source of sediment. It is therefore common that the issue is discussed as part of the

sediment disturbance effects related to the construction phase. Whilst scouring might be allowed

for in the case of a monopile design (i.e. no scour protection is offered in some cases), it remains

unlikely that any gravity base, steel jacket, tripod or suction caisson can be considered on a live bed

without the use of scour protection. Indeed guidance published by DNV (2007) states that gravity

base foundations will “for all locations require some form of scour protection, the extent of which is

to be determined during detailed design.”

The dimensions and rate of scouring depend on the scale and shape of the structure and the

properties of the soil (Whitehouse et al., 2011b). Scour pits may be significant morphological

features and laboratory derived predictive formulae exist for estimating the depth of scour around

cylindrical features (e.g. monopiles). These suggest that the current induced scour depth S, relative

to the cylinder diameter D, varies between S/D = 1.3 (DNV, 2004) and S/D = 1.75 (den Boon et al.,

2004). A review of data from monopiles at five offshore windfarm sites (DECC, 2008) indicated a

maximum depth of scour observed to be S/D = 1.38, at the Scroby Sands OWF, UK. Whitehouse et al.

(2011b) reports that it is usually assumed that a reduction in relative scour depth occurs when the

water depth falls below three to five times the pile diameter.


46

Monitoring of the scour pit evolution at Scroby Sands has shown the pits to reach 5m in depth and

100m in diameter (OSPAR Commission, 2006). Scour pits of this diameter affect approximately

7,854m2 of sea bed. This is significantly greater than the values indicated in Table 6.2 for a CGBF

with scour protection (if used).

There is also some evidence for development of secondary scouring effects away from the

foundation unit (e.g. observed scour tails at Scroby Sands OWF, Cooper et al. (2008)). The

mechanisms creating these effects are not well understood and were not predicted by the EIA.

Scouring around slender piles tends to be fairly symmetrical in form, whereas scour around gravity

bases may tend to occur at discrete locations around the base, especially if the gravity base has a

complex shape or abrupt corners. Whitehouse (2004) reports the results of laboratory‐based testing

which indicated that a conical structure produced deeper scour than a flat topped structure, for the

same forcing conditions.

SedimentPlumesSediment plumes are generated when sediment is introduced into the water column and

subsequently transported by the local and regional hydrodynamics.

Sediment plumes may be generated during the construction phase of OWFs by:

Resuspension of bed sediment through bed preparation (dredging) if required;

Interaction with the seabed of construction equipment;

Piling/drilling for monopiles;

Emplacement of foundations;

Backfill and ballasting of CGBFs (if required); and

Emplacement of scour protection (if used).

Further sediment resuspension may be generated during the operational phase by alteration of

hydrodynamics – particularly if scour of the seabed occurs. Finally, further sediment plumes will be

generated during the decommissioning process, as infrastructure is removed from the seabed.

Any interactions between equipment, OWF infrastructure, or scour protection material (if deployed)

with the seabed will result in local resuspension of sediment. Any sediment released into the water

column will be dispersed laterally and vertically by waves, tides and gravitational settling, and

transported by tidal currents as a sediment plume. The extent of the plume is largely controlled by

the amount of sediment re‐suspended, the grain size of the released sediment, and the local

hydrodynamic regime. Large particles will settle quickly to the seabed, with finer particles potentially

travelling further. When particles settle back to the seabed they have the potential to change the

local baseline seabed sediment composition.

The processes by which sediment is introduced into the water column during marine dredging

operations are well understood, and described in detail in Appendix E of this report. In summary,

however, sediment is released by dredging into the water column via the following routes (Tillin et

al., 2010):

The physical disturbance of seabed sediments by the drag head;


47

From the dredger overflow, whilst the vessel is loading; and

Deliberate screening of the dredged material, although this mechanism is unlikely during

seabed preparation works, and where screening is not used, the plume effects may be

confined to the dredge area (Newell et al., 2004; Tillin et al., 2010).

Significant dredging for bed preparation would not be expected for monopile wind turbines,

however CGBFs will often require some measure of bed preparation before deployment to ensure a

stable and level installation and include a prepared seabed of gravel beds and filter layers to spread

the load evenly and to protect the structure from scour. Some soils may also be unsuitable for

gravity base solutions (e.g. clays which may deform unevenly under load).

Where a large diameter base is considered and the area for scour protection may also need to be

prepared, then levelling may be required over a more extensive area of the seabed. As an example

(which may not be appropriate at all sites); extensive seabed dredging occurred as part of the

Thornton Bank OWF deployment, where six foundation pits were dredged and involved levelling

over an area of 50m by 80m and to a depth of 7m below the normal seabed level. Peire et al. (2009)

reported that, on average, approximately 90,000m3 of sediment was dredged for each site, noting

that the actual volume of material removed from each turbine location also varied as a function of

local sand waves.

If required, the dredging for ground preparation for CGBFs differs from standard marine aggregate

dredging in that the sediments dredged as part of the ground preparation may be retained within

the development area or on barges and later reused as fill and/or ballast material. The Thornton

Bank development provides an example of this, where the dredged sediments were deposited

within the footprint of the OWF area and later re‐dredged to supply ballast material for the CGBFs

and backfill material to restore the foundation pits to reference seabed levels (Peire et al., 2009).

Each of these activities will generate a sediment plume, extending the impact footprint of the

ground preparation, and increasing the potential to affect the baseline seabed sediment type

through settling of plume sediments along the local and regional transport paths.

Comparison can be made with sediment plumes generated by monopile installation techniques,

which typically involve pile driving or drilling. During piling monopiles are driven into the seabed

from a jack‐up barge using a hydraulic hammer, and this method is preferred where the seabed is

sufficiently soft to allow pile penetration, as it is quicker and more efficient (Centrica Energy Ltd,

2010). Drilling is used where the rock or soil is hard, and piling is not feasible. Drilled piles create

arisings which might potentially be equivalent to the full depth of the pile, which for large monopiles

could be in excess of 50m soil depth and diameters greater than 7m. The type of sediment may vary

over depth with soil stratigraphy and drilling methods.

Preliminary information for the Triton Knoll EIA (RPS Energy and RWE NPower Renewable, 2011)

indicates that for a single steel monopile a volume of sediment of between 1,925 and 2,838m3

would be generated as a result of installation.

Piles used to situate steel jackets and tripods may also conceivably need drilling if the sub‐surface

geology necessitates this. It is expected that the drill arisings will be smaller in volumes per ‘foot’

due to the smaller diameter of the pile. However, consideration to the total volume of such arisings

is needed when considering the cumulative effect of 3‐4 arisings per foundation structure. RPS


48

Energy and RWE NPower Renewable (2011) predicted total spoil arisings (for a 5MW turbine

scenario) per foundation as 1,166m3for a tripod and 1,697m3 for a steel jacket. The figure for a

concrete gravity base was cited as 7,389m3 and 2,268m3 for a suction caisson foundation.

Management of the drill arisings may include direct discharge onto the seabed or collecting the

material in a barge before agreed disposal elsewhere at sea (usually a licensed disposal site).

Arisings as a result of drilling of chalk have tended to be a focus of interest for nature conservation

bodies and are discussed further in Section 7.7.

AlterationofSedimentTransportPathwaysIt may be necessary, as part of an EIA, to demonstrate that any natural sediment transport that

occurs through the OWF area is not disrupted as a result of the development, particularly if

sediment transport pathways feed offshore sandbanks or the coastline.

A large number of studies have been conducted during the past decades investigating sediment

transport around the UK shelf. These range from site‐specific studies undertaken to investigate the

results of marine aggregate dredging to larger scale regional sediment transport mapping (e.g.

Kenyon and Stride, 1970, HR Wallingford et al., 2002).

In UK Round 3 sites CGBFs are likely to be deployed in water depths greater than 30m, where bed

sediments are unlikely to be mobile except under extreme wave and tidal conditions. There is

therefore a reduced possibility that CGBFs, suction caissons, steel jackets and tripods will interfere

with natural sediment transport pathways when compared with structures placed in shallower

water. In addition, as the UK Round 3 sites are located further offshore than Round 1 and 2 sites,

the possibility of effects generated by Round 3 sites interacting with the coastline is much less likely.

ModellingSedimentRegimeEffectsCoastal process models can help understand the fate of disturbed sediments and appraise the likely

temporary and localised increases to suspended sediment concentrations through the water column

(e.g. to inform risk of interference to pelagic or benthic receptors) and identify the locations and

levels for any subsequent deposition (e.g. to inform risk of smothering of benthic receptors). The

construction details required to quantify sediment inputs is defined by the PDS and the

environmental data from the baseline surveys (e.g. geophysical and benthic surveys, in particular).

Nevertheless, certain assumptions will always be necessary when defining some model inputs and in

the fundamental design of the models themselves which may, in turn, introduce additional

uncertainties. These uncertainties can be managed by a combination of sensitivity analysis and

retaining a conservative approach.

The scouring process is not described in a coastal process model directly; rather standard empirical

tools are used to define the likely degree of scour at equilibrium and these estimates are then

applied to the model as potential source terms for any sediment disturbance issues if scour

protection is not offered in the design.

Blockage effects also have the potential to alter a sediment transport pathway due to modifications

to wave and tidal processes which drive the transport process along the pathway. Consequently, the

greater the scale of change to waves and currents the greater there is a potential to modify a

sediment pathway affected by these changes. It may be the case that a highly modified pathway is


49

not sensitive to such changes if no sediment is available to move along the path; similarly, a small

change to an active pathway onto a designated feature (e.g. sub‐tidal sandbank) may be a greater

concern over time if the sediment budget is affected. Coastal process models can be used to help

predict the potential transport rates for various sediment grades and determine changes to these

rates to help inform the consideration of the long‐term effects but the levels of uncertainty at this

stage of assessment remain relatively high.

6.2.4 SummaryA comparison of the relative magnitude of effects, between a single CGBF and alternative foundation

types, is presented considering the evidence reviewed in this section. Note that the effects of a large

number of small foundations, compared with a smaller number of larger foundations, is not yet well

understood. Also note that this table makes no estimation of the significance of an effect.

Key

I Installation (including any ground preparation and remedial works required) O Operation (including any settlement) D Decommissioning

Receptor Sub‐receptor

Description Phase effect detected

Relative effect

Scale Significance

Physical Waves Structure blocks the normal passage of waves

O CGBF similar to or greater than other Round 3 solutions in most cases

Likely to be low given distances offshore

Tidal current Structure blocks the normal passage of tidal currents


Likely to be low given distances offshore

Sub‐seabed geology

Removal of sub‐seabed geology by piling/drilling or seabed preparation (If required)

I CGBF similar to other Round 3 solutions

Likely to be low due to limited area of impact

Seabed sediments

Direct impact on the sediment of placement of foundation only

I / O CGBF similar to or greater than other Round 3 solutions in most cases



50

Direct impact on the sediment of placement of foundation plus scour protection (if required)



Sediment transport

Scour around base of structure due to changes in local hydrodynamics caused by the structure

I / O CGBF similar to or less than other round 3 solutions in most cases


" Generation of sediment plumes by ground preparation for CGBF (if required), monopile drilling and removal

I / D CGBF similar to or greater than other Round 3 solutions in most cases


" Alteration of sediment transport pathways

O CGBF similar to other round 3 solutions



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7 BiologicalReceptors

7.1 IntroductionAimsandScopeThe near‐future market for the use of CGBF will be associated with Round 3 offshore windfarm

development areas. These zones are generally located on areas of seabed dominated by sediment

habitats and can be considered more distant from the coastal and nearshore environments

associated with existing, and proposed, Round 1 and 2 arrays. These offshore environments contain

a wide variety of benthic habitats and communities and can support diverse ecosystems utilised by

fish species, seabirds and marine mammals. For these reasons some of these areas are also the

current focus for designation of a series of marine protected areas (MPAs).

This section will describe the various effect pathways (ways that effects can interact with receptors)

and likely impacts associated with each stage of CGBF deployment, lifespan and decommissioning as

described in Section 5.2 (detailed in the flow diagrams, Figure 5.1‐Figure 5.6). Particular focus will be

given to the scale of effects likely from a single CGBF and consideration given to these effects in

relation to other foundation solutions.

Available information, focussed where possible on recent use of CGBFs in OWFs has been brought

together in this report to identify:

The likely sensitivity to and possible adverse effects on marine species and benthic biotopes,

mobile megafauna, birds and fish fauna as a result of CGBFs;

The considerations required for existing and proposed designated nature conservation sites

(MPAs) and for which measures should be taken to ensure they are not adversely affected

by CGBFs; and

Possible positive effects associated with CGBFs and their interaction with biological

receptors.

Identification of discrete biological receptor groups has been ascribed from those that are routinely

considered within production of an EIA. Information regarding the assessment of sensitivity is drawn

from general accepted EIA toolkits including MarLIN (2012) and the Genus Trait Handbook (MES,

2008) etc. Receptor‐specific sensitivity thresholds will be sign‐posted rather than listed individually

within this guidance as these will be presented and considered at a project‐specific EIA level.

Of particular importance is the scale of effects that may be associated with a CGBF when compared

to alternative solutions such as steel jackets, tripods and monopiles and specifically any use of scour

protection and generation of underwater energy (noise and pressure waves) (for any foundation

considered). Direct effects (such as habitat removal) upon face value may appear to be greater for

CGBF solutions when compared with alternative foundation solutions. However, consideration of

steel jacket and tripod foundations shows that CGBFs have a comparable seabed footprint when

accounting for ‘shadowing’ and reef effects. Indirect effects such as those related to an absence of

noise disturbance and creation of refugia for fish species, due to the engineering and installation

techniques associated with a CGBF, may result in positive effects (when compared with current

foundation solutions). These issues are discussed in the receptor‐specific sub‐sections below.


52

7.2 BenthicResourcesThis section is intended to provide an overview of benthic habitats and fauna likely to interact with

CGBFs in UK waters and likely effects and associated impacts. Detailed information on distribution of

biotopes and sensitivity information can be drawn from several sources at a regional and sub‐

regional seas scale; along with project‐specific information derived from site‐specific

characterisation and baseline surveys conducted to support EIA and Environmental Statements.

Section 5.2 has identified Benthos as a receptor to activities and effects associated with each phase

of the lifespan of a CGBF considered in this report. Benthos consists of many sub‐receptors that can

be described in various ways. This section will consider the benthic sub‐receptors under several

broad descriptors dependent upon life strategies and biological traits. Ostensibly the sub‐receptors

can be identified as those living within the seabed sediment habitats – infauna; those living attached

to the seabed coarse sediments and rock – sessile epifauna; and mobile or errant species able to

move across the seabed. Each of these broad sub‐receptor groups may have different sensitivities to

impacts from a CGBF and are considered below.

In the case of Round 3 offshore windfarm developments, the most likely benthic habitats and

biotopes to be present are those associated with surficial sediments such as sands and gravels. The

distribution and location of Round 3 areas predominately occupy sediment habitat types (Figure

7.1), although there are localised areas of bedrock, and bedrock with sediment veneers, in some of

the regions and associated areas (especially along the South Coast and Bristol Channel). The range of

communities and biotopes are generally represented by burrowing infauna associated with mobile

sediments such as sands and gravelly sands. More stable sediments consisting of larger particle sizes

such as sandy gravels, gravels, pebbles and cobbles tend to support epifaunal communities growing

on the sediment surface with some infauna associated with any pockets of finer particle size. In

undisturbed conditions these epifauna can actually consolidate to form ‘bio‐mattresses’ which may

further stabilise the coarse and mixed sediment habitat. Biogenic reef habitat created by species

such as the bivalve molluscs Modiolus modiolus or Mytilus edulis and the polychaete worm

Sabellaria spinulosa can exist across a suite of sediment habitat types.


53

Figure 7.1: Benthic Habitats and Round 3 Offshore Windfarm Zones (Source: JNCC, 2010a; The Crown Estate data).


54

7.2.1 NotableBenthicReceptorGroupsHiscock et al. (2002) presents a comprehensive list and description of biotopes expected to be

distributed within areas associated with Round 1 and 2 offshore windfarm developments. These are

likely to be representative of biotopes expected to occur further offshore and interact with the

intended use of CGBFs. Further reference to the various mapping data associated with Round 3

zones will identify the full suite of benthic habitats and biotopes likely to interact with the proposed

arrays.

The general descriptions and statements for the broad benthic receptor groups (detailed below) are

drawn from various literature including: Hiscock (1998); Hiscock et al. (2002); Connor et al. (2004);

Thorson (1971); and Nybakken and Bertness (2004).

InfaunalSpeciesandCommunities/BiotopesSediment biotopes tend to consist predominantly of species which burrow beneath the surface of

the sediment. The species typically represented are burrowing and tube‐building polychaete worms;

burrowing bivalve molluscs; tube‐dwelling and burrowing crustaceans; and echinoderms such as

brittlestars and burrowing urchins.

Energy exposure (related to water depth, wave climate, tidal streams and nearbed sediment

transport) and sediment particle size are two physical environmental factors that greatly influence

the cohesion and consolidation of surficial sediment habitats (see Section 6). These natural physical

pressures exert a great environmental force on the biology associated with the sediment habitat

resulting in different communities and biotopes in similar sediment particle sizes dependent upon

energy exposure.

Medium‐fine sands in high energy environments (such as the crests of subtidal sandbanks) tend to

be mobile and non‐cohesive. As a result the infaunal biotopes are dominated by species which are

able to rapidly re‐burrow themselves and move through the mobile upper layers of sand. These

species tend to be motile and do not construct permanent burrow structures. They are represented

by mobile polychaete worms, small bivalve molluscs and burrowing amphipod crustaceans.

Muddy sands can exist in moderate‐low energy‐exposed seabed types. Species associated with these

habitats tend to be represented by medium‐large size bivalve molluscs, burrowing urchins,

brittlestars, and polychaete worms. As the sediment habitat is relatively stable then burrows can be

built and occupied.

Subtidal muds are found in low energy environments such as deeper waters distant from tidal

streams. These habitats are stable and cohesive and are colonised by tube‐builders and dwellers

such as burrowing megafauna (such as burrowing shrimp), large bivalve molluscs and echinoderms

and seapens.

Gravels and coarse sands in high energy habitats such as tide‐swept sandbank troughs, tend to

support robust medium‐large sized infauna such as large bivalve molluscs, burrowing anemones, and

polychaete worms. These infaunal biotopes may have low species diversity but a moderate‐high

biomass due to the large size of the few different species.


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Subtidal mixed sediments consist of gravels, sands and muds and can exists under a range of energy

exposures. The variable matrix of sediment particle sizes tends to stable habitats with a range of

ecological niches available to infauna. These habitats support a wide range of burrowing fauna such

as polychaete worms and tube‐dwelling species such as: Sabellaria spinulosa and Lanice conchilega;

small‐medium sized bivalve molluscs; burrowing anemones; echinoderms including ophiuroids

(brittlestars); and holothurians (sea cucumbers).

EpifaunalCommunities/BiotopesBenthic habitats composed of the larger particle sized sediments and geogenic structures such as

gravels, pebbles and cobbles, along with bedrocks and boulders, support species which attach to the

outside of these habitats. The epifauna consists of a wide and varied diversity of phyla which have

evolved to take advantage of the numerous ecological niches associated with hard substrata.

Subtidal coarse (gravels) and mixed sediments (gravels, sands and muds) can support a high diversity

of species. Most of these epifauna form complex mosaics of biotopes and grow as encrustations and

turfs across the supporting hard habitat. In undisturbed situations, with plentiful recruitment and

abundant food supply, these biotope mosaics can ‘mesh’ together, consolidating the coarse

sediments that support them to further increase the stability of the substrata. This ‘bio‐armouring’

effect may increase the overall sensitivity of the biotope matrices to certain removal and abrasion

impacts; as recovery to pre‐impact status may take considerable time (>8 years) or never be

achieved.

Species associated with coarse and mixed sediment biotopes are represented by: encrusting and

tube‐building polychaete worms such as Sabellaria spinulosa and Pomatoceros spp.; barnacles,

colonial ascidians (sea squirts); anemones; ophiuroids (brittlestars); encrusting and erect sponges;

encrusting and erect bryozoans (sea mats) and erect hydroids (sea firs). The mats and turfs created

by these communities add to the physical complexity of the habitat creating ecological niches and

allowing small‐medium sized mobile species refugia. These niches are utilised by predators such as

crustaceans (squat lobsters, prawns and crabs), gastropod molluscs (snails), starfish and small fish

species.

These biotopes / biotope complexes can have a high biodiversity which may be further increased for

areas of mixed sediments which can also support high numbers of infaunal species.

Biogenic reef habitats are generally associated with coarse and mixed sediment habitats and can

support epifaunal communities due the alteration of the local habitat through additional structural

complexity. They are known to support communities of encrusting polychaetes; ascidians, erect

sponges, bryozoans and hydroids; brittlestars; and predators such as squat lobsters, prawns, shrimp

and crabs. Geogenic reefs associated with the mussel species Modiolus modiolus and Mytilus edulis

along with the polychaete worm Sabellaria spinulosa are those most likely to interact with CGBFs

associated with Round 3 projects. Due to the life‐strategies of the reef‐building species then the

sensitivity to various impacts from CGBFs may be different e.g. M. modiolus reef may be more

sensitive to smothering impact than S. spinulosa reef (Holt et al., 1998; Last et al., 2011; Pearce et

al., 2011).

Geogenic reef habitats such as pebbles and cobble (stony) reefs, boulders and bedrock generally

support high diversity communities and biotopes in areas that are not influenced by near seabed


56

sediment transportation resulting in scouring effects (Connor et al., 2004). The biotopes supported

by these hard substrata habitats range from algal dominated in the upper water column photic

zones to those dominated by epifauna in the aphotic circalittoral zone. Most CGBF locations are

likely to interact with the circalittoral, animal‐dominated communities. Again, as with sediment

biotopes, differences in geogenic biotopes are dependent upon energy exposure. The higher energy

habitats (tidal streams, high wave exposure) support erect and branching forms of life such as large

sponges, octocorals (sea fans and dead man’s fingers), bryozoans (sea mats) and hydroids (sea firs)

with carpets of anemones and colonial ascidians (sea squirts).

Lower energy systems tend to more silty conditions and support diverse turfs of encrusting sponges,

bryozoans, hydroids, ascidians with anemones.

Certain of the geogenic biotopes consist of long‐lived, slow‐growing, low recruitment species and are

susceptible (sensitive) to many anthropogenic impacts.

Mobile/ErrantSpeciesMobile benthic species tend to be predators and scavengers derived from phyla such as crustaceans,

molluscs (gastropod snails), echinoderms (sunstars and starfish) and pisceans (fish). Species from

these phyla prey upon the infauna and epifauna and use the ecological niches, associated with the

more structurally complex coarse and mixed sediment and geogenic habitats and associated

epifaunal communities, for refugia. Whilst sensitive to direct impacts such as habitat removal these

species are generally less sensitive to indirect effects due to their mobility. This allows them to

relocate to less / unimpacted areas avoiding or recovering from impacts more easily than sessile

organisms.

Brittlestars are generally suspension feeders with a limited mobility and are thus sensitive to both

direct and indirect impacts likely from CGBFs.

7.2.2 SomeKeyAspectsofBenthicHabitatandCommunityResponsestoCGBFs

EffectsofaCGBFonBenthicHabitatsandCommunitiesBenthic community sensitivity (to the effects discussed in this section) is very much determined by

the habitats that support them. As a general rule, high energy‐exposed sediments are more mobile

and thus support infaunal species evolved to opportunistically respond to disturbance events – the

species are mobile, fast‐growing, short‐lived and able to reproduce rapidly ‐ r‐selected or

opportunistic species (Nybakken and Bertness, 2004). Species associated with more stable habitats

such as low energy‐exposed, stable mixed or coarse sediment (gravels and pebbles) are generally

less tolerant to disturbance – the species are sessile, slow‐growing, long‐lived with a slower

reproductive rate (than opportunistic species) – K‐selected or equilibrium species (Nybakken and

Bertness, 2004). Therefore pathways associated with physical environment effects are of paramount

importance for the biological environment. Effects from changes to bathymetry affecting tidal

currents, sediment transport and wave climate; removal / alteration of habitat; resuspension /

deposition of sediments; and noise and pressure will result in direct and indirect effects and possible

impacts on benthos.

The tolerance, adaptability and recoverability (sensitivity) of species to the natural processes they

are adapted to have a relationship to the sensitivity to those anthropogenic activities resulting in


57

similar pressures. For example higher energy systems exert greater disturbance / turbation forces on

the species living in them, than do low energy systems, and this can reflect their sensitivity to

anthropogenic pressures resulting in disturbance.

Impacts resulting in physical loss and damage to benthic biotopes are associated with all phases and

activities of CGBFs considered in this report as detailed in Section 5.2. These interactions and

possible impacts are described below.

PhysicalLossofHabitatIf required, the seabed / ground preparation through dredging (see Appendix E for detailed

consideration of this activity) will directly remove the surface layer of the seabed, which has a direct

impact on the benthic communities within the dredging area, including the removal of infauna and

epifauna. Physical loss of habitat during extraction operations could also result from the settlement

of suspended particles mobilised during dredging i.e. smothering. The deposition of these fine

sediments can locally change the nature of the surface substratum, making it finer and potentially

altering the benthic communities where these changes occur. Also, fine sediments settling onto the

seabed can (subject to prevailing environmental conditions) be transported on or near the seabed

further away from the dredging area by tidal currents and waves, extending the potential area of

seabed / community changes and potential smothering of sessile benthic communities beyond the

boundaries of a dredging area.

The in situ lifespan of the CGBF can have two levels of direct impact (seabed surface layer removal)

dependent upon whether seabed / ground preparation is required, or not. If the particular solution

means that no ground preparation is required then the initial direct removal of the seabed surface

layer will relate to the direct footprint extent of the CGBF structure itself (plus any scour protection

if needed). Where ground preparation is required then the initial extent of seabed removed will be

related to the excavation footprint. It is expected that the dredge or grab area will recover to pre‐

excavation conditions within the in situ lifespan of the CGBF (so long as infill fines are of same

particle size distribution as pre‐excavation), but the area beneath the concrete structure will

effectively be removed from the sediment habitat system; until after the CGBF has been

decommissioned and removed from the seabed.

Most infaunal species occupy the top 0.5m of the sediment habitat (Thorson, 1971; Hiscock et al.,

2002; EMU Ltd, 2010a). Therefore any activities which remove this biologically critical habitat

resource are likely to result in impacts to the communities / biotopes. Research (Hill et al., 2011) has

shown that high energy environments with medium‐fine sediment biotopes can be expected to

recover within a period of 6‐24 months. Coarse and mixed sediment biotopes may not show

recovery within a period less than 8 years and >15 years in some cases (Cooper et al.; 2011; Hill et

al., 2011). Therefore the habitat type, duration of habitat removal / alteration and potential

recovery periods are important when considering the magnitude of effects and different activities

will result in varying levels of impact. It can be summarised that benthic assemblages in regions of

high natural disturbance and low gravel content appear to be less sensitive to changes in particle

size distribution (Cooper et al., 2011). The longest biological recovery times occur within less

dynamic and energetic environments, such as gravels and coarse sediments associated with low

wave exposure and tidal streams (Hill et al., 2011).


58

From the two scenarios presented above it is evident that so long as the CGBF is expected to remain

in situ for longer than 10 years the main consideration of habitat loss should be the direct footprint

of the CGBF structure (including any scour protection if used) and not necessarily the full extent

ground preparation footprint (if this is also required) e.g. dredging associated with ground

preparation will result in loss of an area of biotopes, but it would be expected that these biotopes

may recover to pre‐dredge conditions during the lifespan of the windfarm; so long as similar

sediment particle size is used to back fill the dredge pit. However seabed habitat lost beneath the

base of the foundation itself will effectively be removed from the environment for the duration of

the windfarm operation (and for a recovery period following decommissioning and removal). Seabed

habitat ‘over‐shadowed’ by a steel jacket or tripod structure (but not directly beneath the ‘feet’ and

any scour protection) can also be in an altered state due to localised changes in water flow,

sediment transport, shading and nutrification. These factors affecting an indirect physical loss of

habitat are described in more detail later in this section. These can result in equivalent footprints to

CGBF direct habitat loss and are effective for the in situ lifespan of the structure on the seabed.

It is also necessary to consider the nature of the foundation base‐layer upon which the CGBF rests. In

most cases the foundation‐layer consists of gravel or crushed rock (Piere et al., 2009) which may be

a very different particle size compared with the naturally‐occurring sediments. As discussed in the

previous sub‐sections, particle size and sediment type has a great effect upon the communities able

to colonise the habitat. Also, as the biological zone tends to penetrate to a depth generally not

exceeding 0.5m from seabed surface (EMU Ltd, 2010a; Thorson, 1971; Hiscock ed., 1998), then the

burial depth of the foundation layer is important. Figure 7.3: presents a diagrammatic cross‐section

of a CGBF base at Thornton Bank OWF, Belgium. This shows that foundation layer resides at

approximately 4m below reference seabed level. There is no pathway for biological zone alteration

due to the foundation layer being deeper than 0.5m below seabed level. It is proposed that so long

as the foundation layer or the load‐bearing layer is always deeper than a precautionary depth of 1m

below reference seabed level, and that backfill is used of the same grain size (as pre‐excavation),

then impacts associated with removal of benthic habitat will be mitigated (so long as scour material

is not deposited on the sediment surface).

Figure 7.2: Diagrammatic Cross‐Section of CGBF base, Foundation Layers and Scour Protection from Thornton Bank OWF, Belgian waters (From Peire et al., 2009).


59

Physical loss of benthic habitats and shifts in macrobenthic communities can also result from effects

associated with changes to hydrography (Hiscock et al., 2002; Coates et al., 2010; Zucco et al., 2006).

The alteration of the physical environment can lead to scour pit evolution which may require

mitigation through the addition of scour protection solutions. Impacts on benthic biotopes can

manifest due to changes in sediment particle size within scour pits (Whitehouse et al., 2011a, 2011b;

Hiscock et al., 2002; Coates et al., 2010; Zucco et al., 2006). Different infaunal species and

communities are evolved to occupy different sediment types and a coarsening of the sediment

(through winnowing of fines) will effectively remove pre‐installation habitat. Therefore

consideration of scouring, based upon project‐specific models (see Sections 5.3, 6.2.1. and 6.2.3), is

a very important factor of any site‐specific EIA. Similarly, the addition of scour protection (if

deployed) will result in: a loss of sediment habitat below the protection footprint; and also in

colonisation by epifaunal communities naturally associated with rocky / geogenic reefs. This will

result in potential alterations to the ecosystem and these are discussed later in this sub‐section. The

important factor is that both scour pits and mitigation solutions will likely alter the naturally

occurring distribution of sediment biotopes present at the pre‐installation baseline by replacing

sediment habitat with hard habitat.

As presented in Table 1.1 the worst case scenario footprint of CGBF structure at seabed surface level

is 36.2m diameter equivalent to an area of 1,029m2 (5MW turbine at 50m below chart datum on

sand) (based on data provided by the Gravity Foundation Interest Group members). Where scour

protection is required, then the area of seabed habitat loss (the removal of pre‐installation habitat),

increases from 1,029 m2 to 2,324 m2 (worst case). Monitoring of scour pit evolution from monopile

foundations at Scroby Sands OWF, UK, has been recorded to 5m depth and 100m diameter (OSPAR

Commission, 2006; Rees, 2005). Therefore the largest scour pits were demonstrated to effect

approximately 7,850 m2 of sea bed, an area considerably greater than the worst case scenario

seabed area take for CGBF. Steel jacket and tripod foundations have a relatively large seabed

footprint which increases to comparable or greater area than CGBFs when considering the structure

footprint on the seabed as a whole (see Table 3.2). The construction surface area is will result in pre‐

installation habitat loss due to a combination of ‘over‐shadowing’ or ‘shading’ effects and ‘reef

effects’ (discussed in detail later below). The ‘shading’ effects are likely arise due to sediment

particle size alteration from scouring and changes to beneath foundation water flow. ‘Reef effects’

will interact with the sediment communities within the construction area due to changes to organic

nutrification and likely predation events from mobile predators attracted to the artificial structure

(Zucco et al., 2006; Hiscock et al., 2002).

Suction caisson foundations can have a direct footprint of up to 2,000 m2 which will result in some

cases to comparable seabed habitat loss to CGBFs (but greater than some CGBF design solutions)

(DECC, 2011a). Table 3.2 cites a slightly lower seabed footprint, including scour protection, of

1,323 m2 (RPS Energy and RWE NPower Renewable, 2011).

The UK Round 2 Triton Knoll OWF Environmental Statement (RPS Energy and RWE NPower

Renewable, 2011) presents a modelling study examining the potential introduction of scour resulting

from turbine foundations. The study concluded that the maximum adverse environmental scenario

concerning scour of sand and finer sediments would be found in the surficial sediment layer of

approximately 1m depth and up to a 23m radius from the foundation for monopile foundations. For

CGBF scour pits were modelled as 5‐10m additional radius around the foundation base. Estimated


60

maximum volumes of material that might be released by scour were approximately 1100m3 per

gravity base foundation compared with approximately 92m3 for monopile foundations. For either

solution the model showed that “scour material would be dispersed away in the same way that

material released during construction is predicted to be dispersed.”

The Triton Knoll ES presented indicative scour protection parameters for various foundation

solutions. These data are presented in Table 6.1 and Table 6.2. It is evident from these data that

greater amounts of scour protection were indicated necessary for monopile foundations than for a

CGBF solution. It should be noted that Table 6.1 presents the values for scour material alone, whilst

Table 6.2 presents the cumulative extent of scour material and the foundation area take. For a 5MW

turbine scenario then an 8.5m diameter monopile is predicted necessary with a seabed footprint of

57m2. These values for the same scenario for CGBF were determined as 40m diameter with 1,257m2

seabed area take. Therefore adjusted total seabed area take per solution, with scour protection is:

Monopile: 1,848m2

CGBF 2,828m2

From the scenarios presented above it is evident that CGBFs may not always have a greater seabed

habitat loss footprint than monopile foundations. This is contrary to widely held preconceptions that

CGBFs, due to the larger diameter than monopiles, steel jackets and tripods, will always have a

larger seabed footprint.

ArtificialReefEffectandHabitatandCommunityLoss/AlterationNot only is there direct habitat loss below the foundation and any scour protection (if required), but

there may also be indirect effects associated with the introduction of artificial geogenic / rocky

habitats into sediment ecosystems. Introduction of these artificial habitats can result in the so‐called

“reef effect” which can result in the greatest impact at the ecosystem level (Cripps and Aabel, 2002;

Hiscock et al., 2002; Zucco et al., 2006). The “reef effect” is expected to be confined to the close

vicinity of the CGBF structure and any scour protection that may be required. ‘Fringe’ or ‘halo’

effects can manifest due to organic nutrient enrichment from biotopes that establish on the

foundation structure and scour protection material if required (Zucco et al., 2006 and references

cited therein; Coates et al., 2010 and references cited therein). Coates et al. (2010) state that:

“The presence of hard substrate epifauna produces a depositional flow of faeces, (pseudofaeces) and

other organic material which could create organic enriched sediments and therefore alter the soft‐

sediment macrobenthic communities.”

Not only are there possible nutrient enrichment pathways but also mobile fauna attracted to the

artificial reef‐like structures can exert pressures on the surrounding sediment biotopes and benthos.

Predatory organisms such as crustaceans (shrimps, prawns, crabs and lobsters) and fish may not only

live and hunt on the hard substrata communities but show wider foraging ranges across nearby

sediment communities (Page et al., 1999; Bremner et al., 2006). Posey and Ambrose (1994)

conducted a study on a rocky reef off the North Carolina coast of the USA. Their research suggested

a trophic link between the reef and the surrounding sediment communities. The result of their study

indicated potentially important indirect effects of predator‐prey interaction among the reef‐

associated predators and the sediment habitat prey species. However, changes of surrounding


61

infaunal communities appear to be limited to a small area around reefs or structures, generally no

more than tens of metres distant (Zucco et al., 2006).

Fish predators are more mobile, or able to forage wider distances and return to the artificial reef

refugia more rapidly, than invertebrate predators. There are records of these predators foraging out

from the ‘reefs’ on some cases up to 200m away (references cited in Zucco et al., 2010; Bremner et

al., 2006).

Monitoring of the post‐installation of CGBFs at the Thornton Bank OWF in Belgian waters has shown

that changes to infaunal communities have occurred in association with the introduction of CGBF

structures into the marine environment (Coates et al., 2010; Coates and Vincx, 2010; Derweduwen

et al., 2010). Noticeable differences in the soft‐sediment macrobenthic communities were observed

with respect to distance from the CGBFs studied. Gradients existed with a strong relationship to the

tidal and cross‐tidal axes within the array area. The main observations recorded were:

In close vicinity to the foundation structure certain hard substrate species were found in

high densities in the soft sediment; and

A decrease in median grain size coincided with an increase in polychaete densities (such as

Lanice conchilega and Spiophanes bombyx) at short distance from the CGBF.

It was concluded that along tide the changes in hydrodynamics (from the concrete foundation) due

to decreased current speeds may have altered the median grain size of the sediment along with the

creation of some ‘stable’ sand pits as a relic of ground preparation dredging activities. This probably

caused the accumulation of organic matter and enhanced larval settlement. The cross‐tidal gradient

showed lower organic material concentrations and a slightly higher median grain size and a

dominance of the tube building amphipod Monocorophium acherusicum not observed at baseline

conditions. Though limited in scale and repetition this small‐scale study suggests that the

introduction of the hard substrate turbine induced a local shift in the soft‐sediment macrobenthic

community. The baseline homogenous sandy biotopes of the Thornton sandbank have undergone a

change to a slightly higher heterogeneity at a very local scale.

However, it is unclear what factor(s) alone or combined has resulted in the community / biotope

changes. The authors proposed that the community shift is likely linked to:

Changing hydrodynamics;

Organic enrichment;

Altered particle size distribution; and / or

Dredge pits not remediated to reference seabed levels.

An intensive monitoring programme was conducted in association with two Danish offshore

windfarms, Horns Rev and Nysted (DONG Energy et al., 2006). The monitoring demonstrated that

the main effect from establishing the windfarms was associated with the introduction of hard

bottom structures onto sandy sediment seabeds. The result was increased habitat heterogeneity

that changed the benthic communities at the foundation sites from infaunal biotopes to epifaunal

biotopes. Abundance and biomass of the benthic communities increased at the foundations

(including scour protection used) compared with the pre‐installation baselines: an increase in

biomass by 50‐150 times was recorded within the arrays i.e. at a local scale. It was hypothesised that


62

much of this increased biomass may be available as food for fish and seabirds. However, monitoring

data suggest that fish abundances and biomass have not increased significantly beyond baselines

and seabirds are generally exhibiting avoidance behaviour (due to above water effects) (DONG

Energy et al., 2006).

The artificial reef effect can also manifest in direct habitat removal at the base of the foundation

and / or scour protection (if utilised) through the biological detritus associated with the epifaunal

reef communities. Dead blue mussel Mytilus edulis shells fallen from reef communities on the

artificial hard substrate may accumulate around the base of the foundation structure and alter /

coarsen the sediment habitat (Hiscock et al., 2002). This will result in a loss of pre‐installation /

baseline habitat and will be most relevant for CGBFs with no scour protection. Whilst not restricted

to CGBFs alone, it is possible that the larger surface area of submerged structure (c.f. monopile and

floating platform) may result in a larger footprint of shell mulch, due to the fact that attachment

space for mussels in accordingly greater.

Table 1.1 shows that the submerged surface area of concrete available for colonisation is 3,338m2

(worst case scenario – 50m BCD). The similar area associated with a 7m diameter monopile is

1,924m2. There is considerable more habitat space for epifauna associated with CGBF than with

monopile installations. Zucco et al., (2006) proposed that steel jacket foundations may provide a

comparable hard habitat resource to CGBFs. The intricate nature of the lattice structure may provide

a more complex niche and crevice habitat that may result in increased biodiversity when compared

with flat surfaces. However this is expert opinion and not currently supported by data or evidence

from the field.

PhysicalDamagePhysical damage can manifest itself in many ways and is generally associated with indirect or

secondary effects. In association with ground preparation operations (where required) the main

pressures are abrasion (from the draghead) and changes (increases) to suspended sediment loads

(concentrations) (Tillin et al., 2011). High (increased) suspended sediment loads would be unlikely to

affect many of the communities found at locations using CGBFs as they are evolved to exist in high

turbidity waters. However, sediment plumes can elevate suspended sediment concentrations (SSC)

above natural background loads, especially those associated with calm weather periods. Also the

temporal scale of dredging or grabbing may have an additive effect e.g. SSC increase may only be in

order of tens mg/l elevation above background levels but if this occurs every week then effectively

the operation is mimicking a significant increase in effects similar to storm events. Therefore care is

needed when assessing plume effects as whilst SSC increase may be minimal, the ‘scale’ of

(cumulative) effect may reach an ecological tipping point i.e. communities may be adapted to

periodic storm events but repetitive exposure over a short period of time may have a detrimental

effect as recovery periods are reduced.

The specific effects associated with the potential ground preparation are not considered in detail in

this section as they are considered analogous to those associated with marine aggregate dredging

operations. Appendix E provides specific details regarding marine aggregate operations in the

context of ground preparation should it be required. The benthic receptors are likely to be the same

as, or similar to, those exposed to effects from marine aggregate operations. It is suggested that any


63

project‐specific EIA will address these issues using the wealth of marine aggregate extraction

environmental research identified in Appendix E.

However, there is a foreseeable pathway associated with CGBF‐specific ground preparation that will

require extra consideration for EIA if it is required; beyond that currently assigned to marine

aggregate operations or offshore renewables projects using monopiles. This is associated with the

possible fate of fines dredged from the ground preparation area. The Thornton Bank OWF, Belgium,

used trailer suction hopper dredgers to remove the surficial layers of the foundation pits (Peire et

al., 2009). This component of ground preparation (where required) would realise the same types of

environmental effects as for commercial marine aggregate extraction activity. Piere et al. (2009)

describe how the dredged fines were then ‘temporarily’ disposed of (stored) within the footprint of

the OWF area. The ‘temporarily’ disposed fines were then re‐dredged, following emplacement of a

CGBF in the foundation pit, to supply ballast material for the CGBFs. The re‐dredged fines were also

used as backfill material to restore the foundation pits to reference seabed levels.

This twin‐phase dredge increased the extent of the environmental effect footprint of the project.

Additional to impacts associated with seabed removal at the foundation pit, including impacts from

the sediment plume, there was cumulative seabed loss where the dredge fines were disposed.

During the deposition of the fines it is expected that a sediment plume would propagate.

Consideration of the secondary (indirect) effects associated with this second sediment plume will

have to be considered in any project‐specific EIA where this activity may be required.

It is assumed that any area of seabed habitats and communities receiving the ‘temporary’ deposition

of fines will be identified as having a high recovery rate / high tolerance to smothering impacts.

Assuming this factor and the temporary nature of the deposition / ‘storage’ then the magnitude of

effects are possibly low. Therefore the impact may have a low overall significant effect, but it is still

an impact greater than usually associated with monopile, steel jacket, tripod or suction caisson

installations. The exception will be where monopiles, steel jackets and tripods require drive‐drill‐

drive operations for installation; in English waters this is usually associated with specific chalk sub‐

seabed bedrock layers (Ian Reach, pers. comm.; Centrica Energy Ltd, 2008, 2010). But here the

footprint of disposition is likely to be much smaller than that associated with foundation pit dredge

fine deposition / storage (Centrica Energy Ltd, 2008, 2010; Piere et al., 2009). Suction caisson

foundations may require a degree of seabed levelling to ensure a negative pressure ‘seal’ at the

seabed surface. However, the footprint of any fines removed as part of the seabed preparation is

likely to be much smaller than those associated with CGBF foundation pits (where these are

required).

During the re‐dredging operation another sediment plume is likely to be generated, though it is

possible this may be more limited in volume and extent (than the initial dredge and deposition

plumes) due to active sorting and screening of fines from the previous dredge and deposition

events. Regardless, this component of operations is novel to the use of CGBFs and will require clear

consideration within any EIA.

The effects associated with deposition and re‐dredging of excavation fines will be mitigated if a

barge is used to hold / store the fines until use as ballast or back‐fill, or removal to a licensed dredge

disposal site.


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Habitat damage will occur in association with construction vessels attendant at the array site. The

benthic impact pathways are derived from the spud cans (weight spreading “feet”) and anchors used

by jack‐up barges and other construction vessels and tenders. These impacts would manifest as

abrasion effects and would be a short‐term in nature associated with the positioning of legs from the

jack‐up barge onto the substrate for the duration of the engineering works. An indirect impact

pathway will be associated with the depression areas from the spuds and anchors. Observations

suggest that in certain benthic habitats and environments then depressions from spuds and anchors

can remain for up to 18 months (Centrica Energy Ltd., 2009; EMU Ltd, 2009). Recovery through in‐

filling from natural processes such as tide, current and sediment transportation will restore the

seabed to its natural state so long as active transport systems exist. In areas of very low energy then

these effects may persist for years (Cooper et al., 2011; Hill et al., 2011). Assessment of total area of

seabed impacted by placement of the installation vessels will be assessed at the EIA stage.

It is important to note that benthic effects directly associated with installation vessels and tenders

for CGBF is not expected to be any greater than those associated with installation of alternative

foundations. RPS Energy and RWE NPower Renewable (2011) report that an average seabed

footprint associated with a jack‐up barge is approximately 416m2 per jack‐up (including leg profile

area, additional spud can and an additional 10% margin). Where spud can depressions may be less

due to fewer jack‐up barges used, foundation laying / spreader barges will require anchoring to the

seabed. The spreader barge, the Thornton 1, used at the Thornton Bank OWF required six 7‐12

tonne flipper delta anchors to maintain position whilst deploying infill and ballast materials

(Figure 7.3).

Figure 7.3: Multi‐purpose barge Thornton 1 depicted in backfill and infill mode (From Peire et al., 2009).

Elevated sediment loads may result due to altered near‐bed transportation associated with the base

of the foundation (see Section 6). In most cases these would be expected to be at lower levels than

those derived from seabed preparation / dredging activities if used. Increased suspended sediment

concentrations (SSC) and scouring were implied as a possible source for suppressing blue mussel


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Mytilus edulis colonisation at seabed level on the Nysted OWF scour protection (DONG Energy et al.,

2006). However, there was no detection of effects due to increased SSC to the local infaunal

communities within the array.

InvasiveNon‐NativeSpeciesInvasive non‐native species are a threat to native fauna and flora due to the rapid colonisation and

displacement effects that can ensue. A lack of environmental checks and balances (from the absence

of their natural predators) means that invasive non‐native species can effectively remove native

species from several environmental niches. Artificial hard substrata can allow the colonisation by

invasive epiphytes and epifaunal species that would not normally (in the absence of such structures)

have access to certain areas of seas, due to the prevalence of sediment habitats and lack of naturally

occurring bedrock and boulder reefs.

The monitoring programme at the Thornton Bank OWF reported the presence of non‐native

barnacle species Balanus perforatus and Megabalanus coccopoma in the barnacle zone (Degraer et

al., 2010). This illustrates points cited by Brabant and Jacques (2010) and Linley et al. (2007) about

the colonisation opportunity offered by artificial hard substrata to non‐native invasive species

spreading into new regional seas such as the North Sea. The ‘stepping stone’ effect of artificial hard

substrata (Hiscock et al., 2002), such as large wind turbine foundations may be even more critical for

species that have no dispersive planktonic larval stage.

It is critical that monitoring programmes for offshore windfarms are detailed enough to detect the

spread of any invasive species. However this is not a CGBF‐specific requirement, rather generic

across the sector for all foundation types.

7.3 FishFaunaandAssemblagesThis section is intended to provide an overview of the fish fauna likely to interact with CGBFs and

how the effect pathways and impacts may interact with the ecology. Information on the distribution

and representativity of fish species and assemblages present within the Round 3 zones can be drawn

from several sources at a regional and sub‐regional seas scale; along with project‐specific

information derived from site‐specific characterisation and baseline surveys conducted to support

EIA and Environmental Statements.

Section 5.2 has identified Benthos as a receptor to activities and effects associated with each phase

of the lifespan of a CGBF considered in this report. Benthos consists of many sub‐receptors that can

be described in various ways and for the purposes of this report fish species and community are

considered as part of the benthos. This section will consider the fish receptors under several broad

descriptors dependent upon life strategies and biological traits. Ostensibly fish receptors can be

identified as those living on or dependent upon seabed sediment habitats – sandeels, flatfish etc.;

those associated with reefs; and those species generally pelagic, but with key life stages associated

with sediment or rocky reef habitats. Each of these broad sub‐receptor groups may have different

sensitivities to impacts from a CGBF and are considered below.

In the case of Round 3 offshore windfarm developments, the most likely benthic habitats and fish

assemblages present are those associated with surficial sediments such as sands and gravels. The


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distribution and location of Round 3 areas predominately occupy sediment habitat types (Figure

7.1), although there are localised areas of bedrock, and bedrock with sediment veneers, in some of

the regions and associated areas (especially along the South Coast, Southwest Approaches and

Bristol Channel). The range of species and assemblages are generally represented by burrowing fish

such as sandeels, weaver fish and flatfish associated with mobile sediments such as sands and

gravelly sands. More stable sediments consisting of larger particle sizes such as sandy gravels,

gravels, pebbles and cobbles may support more diverse fish assemblages though there is still a

representation of flatfish species. Rocky / geogenic reefs can act as a natural fish aggregating device

(FAD). The FAD and ‘reef effect’ can result from the introduction of artificial hard substrata into the

marine environment such as foundation structures and scour protection (if used).

7.3.1 ImportantFishResources

SandyorMobileSedimentHabitatSandy sediment habitats attract a variety of fish species which are generally adapted to being able to

burrow into the top few centimetres of sand. In UK waters demersal (bottom‐living) fish species are

commonly represented by sandeels, weaver fish, flatfish, skates and rays (Wootton, 1992). These

fish are predators, preying upon infauna associated with the sediment habitats or predating

planktonic or free‐swimming prey close to the seabed surface (Nybakken and Bertness, 2004).

Nybakken and Bertness (2004) report that demersal fish assemblages associated with sediment

communities can have a forcing effect upon community size and structure due to predation

pressure. They are adapted to the mobile nature of the sandy sediments and are relatively tolerant

of high turbidity and elevated suspended sediments (MarLIN, 2012). Their key sensitivity is related to

habitat loss and / or impacts upon prey species.

Coarse/MixedSedimentandRockyHabitatsConsolidated coarse and mixed sediment habitats (gravels, pebbles and sandy muddy gravels) may

not be very mobile with a clast matrix and structure that excludes burrowing by fish species. These

habitats (as described in Section 7.2), along with hard substrata, tend to support complex and

possibly diverse epifaunal communities. The abundance of prey items and the structural

heterogeneity of these habitats attract many fish species (Wootten, 1992). Representatives of

demersal species such as flatfish, gobies, wrasses, dragonets, pipefish, sea scorpions, butterfish,

gurnards, skates and rays are commonly associated with epifaunal communities of mixed and coarse

sediment habitats (Pinnegar et al., 2010; Reiss et al., 2010).

PelagicSpeciesThere are many pelagic species associated with the water column and surface waters of the sea that

may interact with offshore windfarm installations. Some species, such as herring Clupea harengus,

use coarse sediments (gravel) as spawning habitat; laying their eggs onto seabed surface. Other

species, such as mackerel Scomber scombrus, may have annual migration routes which traverse

windfarm zones.

Reef features standing proud of the surrounding seabed add a level of structural complexity and

heterogeneity to the benthic environment. In effect they act as oases, attracting fish species which

come to forage and predate the epifaunal communities and other mobile species similarly attracted

to the reef (Nybakken and Bertness, 2004; Wootten, 1992). Some species seek refuge provided by


67

the reef whilst others may use the feature as a breeding site, shelter from prevailing physical

conditions and predator avoidance (Reubens et al., 2010). This attraction to the habitat is known as

the ‘reef effect’ and artificial structures act in a similar manner, either demonstrating artificial reef

effects or acting as a fish attraction device (FAD) (Linley et al., 2007).

Pelagic species known to exhibit response to FADs and / or recorded from OWF monitoring

programmes (DONG Energy, 2006; Zucco et al., 2006; Derweduwen et al., 2010; OSPAR Commission,

2006) are numerous but include: mackerel, cod, saithe whiting, pouting, pollack, bib, sprat, mullet,

sea bass and herring.

7.3.2 ImportantInteractionsbetweenFishSpeciesandAssemblageswithCGBFsSeveral possible interactions between offshore wind turbine foundations (including CGBFs) and fish

species have been identified (Linley et al., 2007; Zucco et al., 2006; DONG Energy et al., 2006;

Scottish Executive, 2007). These are listed in Section 5 of this report and described in this section

below.

None of the effects listed above are solely specific to CGBF solutions but scale of effects may be

different compared with other engineering solutions.

Impacts associated with electro‐magnetic frequency (EMF) emissions from power cables are not

considered within in this report as these effects are not a direct result of foundation superstructure

itself.

DirectImpactsandPhysicalLossofHabitatThe monitoring programmes at Horns Rev and Nysted OWFS (DONG Energy et al., 2006) have not

documented major changes in the fish fauna with regard to overall abundance or species

composition following the construction and operation of the windfarms. However, it is important to

note that at the time of publication of the monitoring programmes (DONG Energy et al., 2006) of the

results that colonisation of the foundations by epifauna was relatively new. Therefore it is

hypothesised that successional colonisation would continue to develop and a stable climax fish

fauna is yet to appear. Data indicate that many of the species mentioned in Section 7.3.1 have

colonised the foundations and scour protection. These include: pipefish, wrasse, gurnards, flatfish,

cod, whiting, saithe, gobies, dragonets and sea scorpions. Diversity was found to be greater at the

Horns Rev array in comparison with the Nysted farm. It is suggested that this may be an artefact of

the differences in epifaunal community composition. Nysted artificial substrata (CGBFs and scour

protection) are dominated by a near mono‐culture of blue mussel Mytilus edulis. This relative

homogeneity may be mitigating the favourable reef effects (due to diverse and heterogeneous

epifauna) that attract a diverse reef fish fauna (DONG Energy et al., 2006).

The sandy habitats studied at Horns Rev support an abundant sandeel population (DONG Energy et

al., 2006). Sandeels are an important component of the ecosystem acting as a food source for larger

fish and apex predators such as marine mammals and birds (Pinnegar et al., 2010). As cited above,

alteration and removal of the sediment habitats within an array may have negative impacts on fish

assemblages. If these impacts result in adverse effects to ecological keystone species such as

sandeels the effects can cascade through food webs (Frederiksen et al., 2006). Therefore specific

investigations into the possible effects of sediment habitat loss and sandeel population were

conducted. The results do not suggest that sediment habitat and community composition has been


68

affected and sandeel populations are consistent relative to baseline. It is noted that sandeel

abundance in the array itself may have increased due to links between organic nutrient enrichment

(as a result of the epifaunal communities on the foundations) and successful sandeel recruitment.

The monitoring concludes that short‐term, near‐field effects on the fish abundance and composition

in the windfarm areas are few and not easily separated from larger scale changes in the fish

communities.

DONG Energy et al. (2006) postulate that the conclusions of the monitoring may apply to both the

North Sea and the Baltic Sea studies, the colonisation of the new artificial hard substrata habitats

may be more rapid and more pronounced in other regional seas areas where natural reef structures

in the vicinity of the windfarm area may enhance the supply of fish e.g.in the case of the UK; the

English South Coast, Southwest Approaches, Bristol Channel, the North Welsh coast and North

Scotland.

ArtificialReefandFishAggregationEffectsReubens et al. (2010) specifically investigated the reef effects of the Thornton Bank CGBFs, Belgium.

Fish Aggregation Device (FAD) effects result from several mechanisms affecting fish behaviour:

increased foraging / predation efficiency; predator avoidance / refuge; recruitment / nursery

location; and shelter from prevailing physical environmental factors (waves, currents etc.) (Reubens

et al., 2010 and references cited therein).

It is important to note that the FAD qualities of CGBFs may not mean a direct increase in the

numbers of individual fish species within a region. The nature of the FAD or ‘reef effect’ is such that

the artificial structures attract and concentrate fish from other areas, near‐field and possibly far‐field

too (Reubens et al., 2010). A possible ecological positive impact is that this aggregation of fish

species may be afforded protection if fisheries exclusion zones are in place within the array footprint

(Linley et al., 2007). If no protection measures exist then overfishing may result due to increased

catch per unit effort (CPUE) (Reubens et al., 2010; Linley et al., 2007).

Reubens et al. (2010) observed that several species recorded from shipwrecks in the Belgian North

Sea appeared to take up residence at the Thornton Bank OWF CGBFs. These included pollack, cod,

pouting, and horse mackerel and mackerel in the warmer summer and early autumn months.

Flatfish are noted to be attracted to scour protection taking advantage of increased prey species

abundance (Zucco et al., 2006).

The mackerel species data (obtained in the Thornton Bank study) implied that larger mature

individuals were attracted to the CGBFs compared to individuals associated with the surrounding

sediment habitats. This same observation was made for pouting. Cod attracted to the foundation

were predominantly juveniles which may benefit more than adults from the artificial refugia habitat

provided by the CGBFs, though this is only conjecture.

Compared to the natural sediment habitat surrounding the CGBFs the density of cod, pouting and

horse mackerel was statistically significantly higher; supporting the hypothesis that the CGBFs are

acting as FADs. Stomach content analysis of sampled pouting indicated a diet consisting of the

crustaceans Jassa herdmani and Pisidia longicornis. These epifaunal crustaceans are high density


69

colonisers of the CGBFs at Thornton Bank. Reubens et al. (2010) hypothesise that the CGBFs area is a

positive attractant (FAD) due to the density of prey species not found in the surrounding sediment.

Unfortunately there are no directly comparable monopile, steel jacket or tripod versus CGBF

artificial reef effect studies. The comparison between Horns Rev (monopile) and Nysted (CGBF)

OWFs is skewed due to the influence of the dominating blue mussel community and the brackish

water conditions (of the Baltic Sea) for the Nysted OWF compared with the diverse epifaunal

communities and full marine environment at Horns Rev. It is unclear if there is a direct relationship

between increased surface area colonised, increased refuge habitat space and a parallel increase in

fish population density. However, Zucco et al. (2006) state that the greater the physical complexity

of foundation then the higher the likelihood of larger reef effect manifesting. This is based in part on

monitoring of oil and gas platforms. Therefore it is possible that CGBFs hold the potential for

increased reef effects when compared with monopiles and that steel jackets may provide the most

complex and attractive artificial habitat; due to the complexity of the lattice structure, being similar

to oil and gas platform foundations. Research conducted primarily in the U.S.A. and in small part in

the North Sea, UK, demonstrates that oil and gas platforms have large reef effects and are well

documented FADs (Minerals Management Service, 2000 and references cited therein; Cripps and

Aabel, 2002; Kolian and Sammarco, 2008; BoEMRE, 2012) and this is thought to be in part due to the

complexity of the structures.

The attractant or impact range of an artificial reef is in the order of 200‐300m for pelagic species and

1‐100m for demersal species (Zucco et al., 2006 and references cited therein). Flatfish species have

been recorded moving between reefs >900m apart and significant abundances of reef‐dwelling fish

species observed where inter‐reef distances are <400m apart (Zucco et al., 2006 and references

cited therein). Therefore intra‐array turbine spacing may become a factor in determining the inter‐

connection of artificial reef effects in OWFs. As turbines increase in size (rotor sweep diameter) the

greater the inter‐turbine (and thus foundation) spacing will be required to mitigate turbulence

contamination between neighbouring turbines. Moving toward 5MW turbines will result in

approximately 800m or greater intervals and these may isolate each foundation to act as a single

reef with some interactions restricted to flatfish species (Zucco et al., 2006).

PhysicalDamageIncreases in suspended sediment concentrations (SSC) and turbidity and resultant deposition

(smothering) resulting from seabed preparation (if required) may affect spawning grounds for

demersal spawners e.g. herring and sandeel. Zucco et al. (2206) suggest that some small demersal

fish species with limited swimming ranges may also be sensitive to smothering impacts. EIA practices

adopted for marine aggregate extraction operations are applicable when considering smothering

effects. Regional‐scale habitat mapping (such as Strategic Environmental Assessment (SEA), marine

aggregate REC and REA), resource identification from ICES and Cefas spawning data records etc. will

assist identification of any sensitive areas. The Scottish Executive’s offshore renewables SEA (Linley

et al., 2007) advises that:

“Potential effect significance (for smothering) is considered to be moderate for demersal fish species

which are sensitive to smothering and major for demersal spawning species (herring and sandeel). A

smothering episode on a herring gravel bank, for example, could potentially impact an entire year


70

class in the locality. Avoidance of sensitive sites and periods could be expected to reduce residual

effects to minor.”

Impacts upon benthic habitats and biotopes can also result in indirect effects to demersal fish

species. Reduced biotope quality through habitat removal or smothering events (described in

Section 7.2 above) will have direct effects on prey availability for fishes that forage in these habitats.

Zucco et al. (2006) details research that has shown a decline in flatfish populations and related

reproductive success linked to large‐scale removal of high infaunal abundance sand habitat.

Research from marine aggregate licence area off the Humber coast, UK, has suggested that between

40% and 90% of species diversity, population density and biomass may be lost as a result of direct

dredging effects (Newell et al., 1998). It is likely that suppression of prey species within the

foundation pits (where used) will have effects on foraging efficiency of demersal fish fauna. The

scale of these impacts will be dependent upon similar unimpacted communities accessible in

foraging range of the fish. Dependent upon sediment habitat type removed by seabed preparation

operations (if undertaken) and assuming that backfill material is of the same particle size as baseline

then recovery to pre‐dredge communities can be expected to take 6 months to 8 years dependent

upon sediment habitat type (Hill et al. 2011; Cooper et al., 2011; see Section 7.2.2).

Impacts from any foundation pit dredging required are specific to CGBF solutions (compared with

alternative solutions which do not require this seabed preparation).

NoiseCertain fish species are sensitive to noise and pressure impacts. These fish species and identification

of sound and pressure frequencies likely to cause death or damage are known to some degree in the

context of offshore windfarm construction (Hiscock et al., 2002; Zucco et al., 2006; DONG Energy et

al., 2006; Scottish Executive, 2007; OSPAR Commission, 2006). Modelling sound generation,

propagation and attenuation is a standard component of OWF EIA. Source recording and monitoring

is conducted and the understanding of impacts is being increased.

The major source of noise impacts associated with OWF construction and operation, likely to affect

fish fauna receptors, is associated with the installation of monopiles by pile driving using hydraulic

hammers. The repeated ‘hammering’ of the monopile foundation into the seabed results in sound

and pressure waves that impinge upon fish.

In contrast to the installation of monopile, steel jacket, tripod and possibly floating platforms, CGBFs

and suction caissons are placed onto the seabed. There is no requirement for pile driving or drill‐

drive‐drill techniques. This means that installation and emplacement works for CGBF (and suction

caisson) solutions have a significantly reduced impact pathway for noise impacts (in comparison with

monopile foundations). Due to a lack of percussive piling operations CGBFs are unlikely to source

damaging or behaviour changing levels of noise. Noise will be associated with emplacement but at

levels difficult to distinguish from background vessel generated levels (Haelters et al., 2009).

Noise effects of CGBFs on sensitive receptor groups are specifically discussed in Section 7.6 below.


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7.4 MegafaunaResources‐MarineMammals,TurtlesandBaskingSharksThis section is intended to provide an overview of the interactions likely to occur between CGBFs

and their induced effects and impact pathways with marine megafauna (large‐very large animals).

Information on the distribution and representativity of marine megafauna present in UK waters and

associated with the Round 3 zones can be drawn from several sources at a national, regional and

sub‐regional seas scale; along with project‐specific information derived from site‐specific

characterisation and baseline surveys conducted to support EIA and Environmental Statements.

Section 5.2 has identified ‘Marine Mammals’ as a receptor to activities and effects associated with

each phase of the lifespan of a CGBF considered in this report. For the purposes of this report the

receptor group ‘Marine Mammals’ should also be assumed to include pelagic sharks and sea turtles

as well as whales, dolphins, porpoises and seals. This section will consider the ‘Marine Mammal’

receptors under several broad descriptors dependent upon life strategies and biological traits of

marine megafauna. Each of the sub‐receptor groups may have different sensitivities to impacts from

a CGBF and these are considered below.

In the case of Round 3 offshore windfarm developments, the most likely megafaunal assemblages

present will vary dependent upon regional seas and distance from the coast. Some receptor species

such as Harbour porpoise Phocoena phocoena are relatively ubiquitous throughout UK waters, whilst

Basking sharks Cetorhinus maximus have a distribution generally restricted to the Southwest

Approaches and the Irish and Celtic Seas. Harbour seals Phoca vitulina tend to be coastally

distributed compared with Grey seals Halichoerus grypus which have a wider offshore foraging

range.

7.4.1 ImportantMegafaunalResourcesMarine megafauna in UK waters are typically represented by pelagic Elasmobranchs (sharks),

Pinnipeds (seals) and Cetaceans (whales, dolphins and porpoises) which are regularly recorded in all

UK regional seas (UKBAP, 1999).

Sea turtles also constitute a component of the UK marine megafauna but these are considered

transient or migratory visitors and are not resident species, being occasionally recorded mostly along

the western coasts of England, Wales and Ireland (UKBAP, 1999).

PelagicSharksThere are many species of medium‐large sized pelagic sharks that frequent UK waters. Some are

resident and others demonstrate migration across large distances. All the large species of sharks are

carnivorous with most having a diet consisting of fish and squid and carrion (Shark trust, 2010;

Compagno et al., 2005). The notable exception is the planktivorous Basking shark Cetorhinus

maximus which feeds primarily on zooplankton. The large sharks encountered within the UK belong

to the group Galeomorphii and include species such as: Basking shark Cetorhinus maximus;

Porbeagle Lamna nasus; Longfin Mako Isurus paucus; Shortfin mako Isurus oxyrhincus; Thresher

shark Alopias vulpinus; and Blue shark Prionace glauca.

Coastal species such as the Porbeagle and Basking shark are mostly likely to have the highest rates of

interaction with Round 3 zones (Bloomfield and Solandt, 2008), whilst pelagic species such as Blue,

Thresher and the Mako tend to be more restricted in distribution, associated with deeper waters

along the UK western offshore and nearshore (Compagno et al, 2005).


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SeaTurtlesAs previously mentioned, marine turtles in UK waters are considered migratory visitors with only the

large Leatherback turtle Dermochelys coriacea considered part of the native British fauna (JNCC,

2007).

The majority of records from recent years are distributed along the Southwest Approaches and

through the Irish Sea with the Leatherback the most common species recorded (TURTLE, 2012; MCS,

2012; UKBAP, 1999).

MarineMammalsMarine mammals in UK waters are represented by seals (Pinnipeds) and whales, dolphins and

porpoise (Cetaceans) with numerous species from a range of families and genera. 2 species of seal

are considered native to Britain, these are: the Harbour seal Phoca vitulina; and the Grey seal

Halichoerus grypus. Colonies of Harbour seals are strongly distributed within the North Sea and

Scottish waters with approximately 90% of the European population in British waters (Scottish

Executive, 2007). Britain holds about 39% of the world’s population of Grey seals with 90% of these

located in Scottish waters (Scottish Executive, 2007; JNCC 1995).

There are 15 species of cetacean (whales, dolphins and porpoise) known to inhabit UK waters

(http://www.seawatchfoundation.org.uk/speciesid.php); of these 10 have been recorded regularly

along the coasts or nearshore waters (within 60 km of the coast) since 1980 (JNCC, 1995; Reid et al.,

2003).

During June 2008 The National Whale and Dolphin Watch conducted a week of dedicated surveys

across the UK. The findings from these surveys indicated that maximum counts were recorded in

West Wales ‐ 83; and the minimum was southern England and Bristol Channel, both with 1 sighting;

N = 372. The survey only provides a snap shot of sightings but does highlight important regions for

cetaceans around the UK coast. The southwest coasts and through the Irish and Celtic seas to

Scottish waters maintaining the most diverse assemblages of cetaceans (Scottish Executive, 2007;

Reid et al., 2003).

7.4.2 ImportantInteractionsbetweenMarineMammalsandBaskingSharkswithCGBFsSeveral possible interactions between offshore wind turbine foundations (including CGBFs) and

marine mammals have been identified (Linley et al., 2007; Zucco et al., 2006; DONG Energy et al.,

2006; Scottish Executive, 2007). These are listed in Section 5.2 of this report and described in this

section below and for the purposes of this report are assumed to also be applicable to Basking

sharks and sea turtles.

Sensitivities for elasmobranchs (sharks) with windfarms are generally associated with

electromagnetic fields produced by electric current passing through the inter‐array and landfall

power cables (Zucco et al., 2006). This effect pathway is predominantly associated with demersal

elasmobranchs such as catfish, angel sharks, skates and rays and not necessarily galeomorphs. As

this impact pathway is not sourced directly from the foundation structure itself (not associated with

CGBF structures), then it is not considered within this report.


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CollisionRiskCollision risk with vessels associated with ground preparation (if used), CGBF installation and

servicing is one of the main pressure pathways for marine megafauna. For sea turtles this is deemed

negligible considering the very low abundance of turtles and general lack of exposure pathway. The

risk to turtles from CGBF installation and emplacement is assumed to be less than that for collisions

with other vessels in UK waters. This is due to the fact that transit to site with CGBF structures is low

speed (Peire et al., 2009) and during emplacement installation plant is relatively static (Scottish

Executive, 2007).

Marine mammals are most susceptible to collision where vessels display erratic behaviour and/or

operate at high speeds >14 knots. The expected typical speed of a dredger preparing a foundation

pit (if this is required and dredgers are used rather than grabs) will be no more than 2‐3 knots and

the vessel will transit along a predetermined route within defined seabed preparation areas. Both

factors are likely to mitigate against any potential collision risks. No recorded collision incidents

between aggregate dredgers and marine megafauna (including sea turtles) have been recorded in

UK waters during 50+ years of operation (Mark Russell, BMAPA, pers. comm.). In the context of

foundation pit excavation it is important to note that the areas will be much smaller (50 m by 80 m)

than marine aggregate areas and associated dredging lanes (Peire et al., 2009). This will further

mitigate collision due to the small area of dredging operations. Basking sharks show avoidance

behaviour to slow moving vessels (Ian Reach, pers. obs.) and can be expected to avoid CGBF‐related

vessel movements.

All species of marine mammals, turtles and Basking sharks are mobile species that can avoid areas of

active dredging and emplacement works and the resulting effects from vessel displacement, noise

and vibration, and suspended sediment plumes. They are able to return to the area once dredging

has ceased.

PhysicalDisturbance,DisplacementandHabitatExclusionSeals and Harbour porpoise have been observed to avoid construction zones for OWFs (Scottish

Executive, 2007; Zucco et al., 2006; DONG Energy et al., 2006) with noise described as the key factor

along with physical presence of vessels. Hauled out seals appear to be the most sensitive with a

‘flight reaction’ threshold of 900m in response to vessels reported by the Scottish Executive (2007).

Vessel presence is by no means CGBF‐specific and will be considered as part of any project‐specific

EIA. The industry forecast and this report assumes that the immediate UK market for CGBFs is

intended to be the Round 3 offshore windfarm installations (Lynch and Fulcher, 2012). Round 3

zones are generally located in the offshore marine environment with significant distances from

coastlines and nearshore banks that act as seal haul out areas. Therefore the lack of potential

exposure of vessel disturbance effects during the installation of CGBFs results in negligible effects.

This determination appears to be supported by monitoring conducted at Nysted OWF during

construction in 2003 (DONG Energy et al., 2006). Nysted foundations are CGBF so no piling

associated with foundation installation was anticipated. The distance between a Harbour and Grey

seal colony at Rødsand is greater than the 900m radius flight response threshold, as the Nysted

Windfarm is 4 km away from the seal sanctuary. No displacement or flight response was observed in

hauled out seals due to construction vessel traffic (DONG Energy et al., 2006). However there was a


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clear link to construction activities seen during sheet piling operations that were conducted out at a

single foundation located approximately 10 km distant from the haul out area. The operation

comprised piling of several individual sheet piles over a 3 month period. A significant decrease in the

number of seals hauled out during pile driving was seen. These observations support the position

that emplacement of CGBFs does not cause displacement to hauled out Harbour and Grey seals, or

affect their access and use of these habitats, so long as disturbance zones are not encroached.

Introduction of percussive sound into the marine environment however, does cause disturbance and

displacement impacts.

Satellite tracking of seals from the Rødsand colony has shown that there is no change in habitat use

or foraging behaviour post‐construction. Present studies do not suggest that operation at the either

Horns Rev or Nysted has resulted in negative impacts to the seal populations.

There are no known records of displacement of basking sharks due to windfarm construction or in

situ foundations and arrays.

Monitoring at the Nysted and Horns Rev OWFs has shown some interesting habitat use responses

from harbour porpoise Phocoena phocoena. Aside from effects associated with noise impacts

(discussed below and in Section 7.6) the behavioural responses to the physical presence of the

arrays have been studied. Strong negative impacts resulting in displacement of porpoise from the

Horns Rev site during construction (due to pile driving operations) was observed with a subsequent

return post‐construction (DONG Energy et al., 2006). The operation and presence of the array does

not appear to have displaced the porpoises. At Nysted the small population of Harbour porpoises did

not return to the array post‐construction (first 2 years of operation monitoring). Nysted used CGBFs

but there was a sheet piling construction phase for one foundation that caused noise displacement.

However, the porpoises appear to have remained displaced. The authors hypothesise that the

difference in displacement response may be associated with the quality of the habitat at baseline

conditions. Nysted had a small population and may not have been key (prime) habitat for that

population. In contrast Horn Rev occupies a high density population area and the habitat appears to

be important. Implications on populations cannot be estimated but are thought unlikely to be very

large (DONG Energy et al., 2006).

SmotheringofPreySpeciesSection 7.3.2 describes the effects of smothering on benthic habitats and communities and sensitive

(low mobility) fish fauna. Smothering impacts resulting in direct impacts to megafauna are unlikely

but there may be complex indirect effects due to cascades through trophic / food webs (Frederiksen

et al., 2006). Alteration of benthic productivity may affect fish predator populations which may

affect secondary predator condition or mortality; these effects may then knock‐on (cascade) to apex

predators such as cetaceans and seals (Nybakken and Bertness, 2004; Frederiksen et al., 2006).

However due to the large foraging ranges of marine mammals, and using Harbour seals as the

benchmark due to smallest range at 60 km (Tappin et al., 2011), then the significance of removal of

benthic communities and fish through smothering is deemed to have a negligible effect on marine

mammal condition (Scottish Executive, 2007).


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IncreasedTurbidityandChangesinSuspendedSedimentConcentrationsThe Scottish Executive’s Renewables SEA (2007) identifies that increased turbidity can have effects

on foraging, social and predator/prey interactions for marine mammals. Project‐specific variables

will have to be considered through the EIA process with the highest loadings associated with any

seabed preparation dredging operations where these are required. However considering the

location of the Round 3 zones and information presented in Section 6 it is likely the small amounts of

sediment released into the water column during CGBF emplacement will have a negligible impact on

background suspended sediment and turbidity levels. Grey and harbour seals have been identified

as having a high sensitivity to reductions in visibility, whilst the cetaceans in the study area have a

moderate sensitivity to this impact (Scottish Executive, 2007). Evidence from marine aggregate

Regional Environmental Assessments suggest that impacts from increased sediments and elevated

SSC are not significant at a regional scale (EMU Ltd, 2010b, 2011; ERM 2011) for marine mammals.

As these assess much larger scale dredging campaigns then any ground preparations works that may

be associated with CGBF installation then it is reasonable to assume that impacts from this activity

will be negligible in comparison.

IncreasedForagingOpportunitiesAs discussed in Section 7.3.2 CGBFs will likely function as artificial reefs or fish aggregating devices.

As a product of this habitat change they have the potential to alter the distribution of certain marine

mammal fauna through enhanced foraging opportunities (Scottish Executive, 2006). Harbour

porpoise, Harbour seals and Grey seals are the species most likely to interact / be attracted to the

proposed arrays. There is also video footage available on the social medium YouTube that shows

Porbeagle sharks recorded by remote operated video systems at North Sea submerged

superstructures (Ian Reach, pers. obs.). Whether the artificial reef effect present opportunities that

would enhance the foraging prospects for such species for the better is not yet clear.

NoiseMarine mammals along with certain fish species are sensitive receptors to sound and pressure wave

impacts. These species and identification of sound and pressure frequencies likely to cause death or

damage are known to some degree in the context of offshore windfarm construction (Hiscock et al.,

2002; Zucco et al., 2006; DONG Energy et al., 2006; Scottish Executive, 2007; OSPAR Commission,

2006). Modelling sound generation, propagation and attenuation is a standard component of OWF

EIA. Source recording and monitoring is conducted and the understanding of impacts is being

increased.

The major source of noise impacts associated with OWF construction and operation, likely to affect

megafauna receptors, is associated with the installation of monopiles, steel jackets and tripods by

pile driving. The repeated ‘hammering’ of the monopile foundation into the seabed results in sound

and pressure waves that interact with the receptor species. Currently all Round 1 and 2 OWF

foundations have been steel monopiles with very limited use of steel jackets (with small suction

caisson restricted to meteorological masts) incorporating piling or drive‐drill‐drive installation

techniques used.

In contrast to the installation of monopile, steel jacket and tripod foundations, CGBFs are placed

onto the seabed. There is no requirement for pile driving or drive‐drill‐drive techniques. This means

that installation and emplacement works for CGBF solutions have a significantly reduced impact


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pathway for noise impacts (in comparison with monopile, tripod and steel jacket foundations). Due

to a lack of percussive piling operations CGBFs are unlikely to source damaging or behaviour

changing levels of underwater noise and pressure waves. Noise will be associated with emplacement

but at levels difficult to distinguish from background vessel generated levels (Haelters et al., 2009).

Noise effects of CGBFs on sensitive receptor groups are specifically discussed in a Section 7.6 below.

7.5 Avifauna‐BirdsThis section is intended to provide an overview of the interactions likely to occur between CGBFs

and their induced effects and impact pathways with ornithological receptors (avifauna – birds)

present at UK coasts and waters. Information on the distribution and representativity of marine

megafauna present in UK waters and associated with the Round 3 zones can be drawn from several

sources at a national, regional and sub‐regional seas scale; along with project‐specific information

derived from site‐specific characterisation and baseline surveys conducted to support EIA and

Environmental Statements.

Section 3.2.7 and 5.2 has identified birds as a receptor to activities and effects associated with each

phase of the lifespan of a CGBF considered in this report. In the context of this report it is important

to note that effects associated with engineering and structures above the sea surface are not

considered. The focus of identifying any effect and impacts on avifauna will be primary effects /

pressures from CGBF structures related to:

Water quality (changes in turbidity) interfering with predation;

Alteration of habitat supporting birds species (roosting, nesting, loafing, prey species);

and / or

Disturbance / displacement.

The bird receptors can be categorised under several broad descriptors dependent upon life

strategies and biological traits. Ostensibly bird receptors can be identified as those passing through a

windfarm array as part of foraging behaviour – foragers; those passing through an array as part of

migration transits – passage migrants; and those species using the habitat for social behaviour e.g.

loafing – rafters. Of these groups foragers may be attracted to different benthic habitat types

dependent upon geomorphological features or prey habitat preference, or displaced if favoured

habitats are removed. Similarly if CGBFs result in changes to benthic habitats or geomorphology that

alters habitats then social behaviour may be impacted. The passage migrant receptor group are not

investigated in this report further as any impacts are not directly related to CGBF presence /

absence. The exposure pathways exist due to the proposed location of the OWF array and would be

present even if alternative foundation solutions (to CGBFs) were used.

7.5.1 ImportantBirdResourcesSeabirds including divers, grebes, seaducks, auks, gannets, gulls, terns, petrels and shearwaters are

numerous in UK waters with internationally important populations of many species recognised by

various designated nature conservation sites around the coastline and offshore.


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In the context of monitoring environmental effect associated with OWFs all seabird species should

be considered of significant importance as most will have some form of conservation status.

7.5.2 ImportantInteractionsbetweenBirdsAndCGBFsThe three main effects possibly affecting seabirds are: habitat loss due to disturbance, barrier

effects, and fatal collisions (Zucco et al., 2006). Of these the first effect group, habitat loss due to

disturbance (and /or alteration), accords with the analysis of critical effects in this report. Additional

are water quality impacts on prey availability and predation success. Barrier effects and collisions are

both related to above water pressures.

HabitatLossAccording to recent studies reviewed in Zucco et al. (2006):

“six out of the 35 seabird species regularly living in German waters strongly avoid offshore windfarms

(Red‐throated Diver, Black‐throated Diver, Gannet, Common Scoter, Guillemot, Razorbill), and one

other species (Long‐tailed Duck) was recorded which showed much lower numbers in windfarm areas

after construction than before. Seven species occur within windfarms which do not show any obvious

effects, and three gull species even increased in numbers compared to the preconstruction period.

For 18 seabird species, it is not known how and whether the windfarms affect their habitat use.”

It is also important to note that species which avoid the array areas are exposed to greater extent of

habitat loss than just the windfarm area itself, due to avoidance distances from the turbines

themselves (Scottish Executive, 2007; DONG Energy et al., 2006). DONG Energy et al. (2006) state

that behavioural avoidance of the vicinity of turbines could also potentially displace feeding birds

from windfarms. This would result in “effective” habitat loss as stated above. So, even if the habitat

and food resource remain intact, they are lost to the birds because of their reticence to approach

the turbines. However this habitat removal is predominantly associated with the visual presence of

the turbines and is not believed to be associated directly with the foundation structures.

Zucco et al. (2006) go on to say that physical habitat loss due to the introduction of a hard bottom

fauna on foundations and scour protections seems to be of minor importance. The overall

consideration should be judged on the net change of habitat i.e. baseline habitat loss considering

new habitat created. A key question still unanswered is to what extent, if at all, seabirds make use of

any new food supply associated with artificial hard substrata or if fish fauna attracted by reef effect

will be exploited.

To some degree any positive effects of additional food supply may be masked if the avoidance

behaviour due to turbine presence means that this resource is effectively beyond reach. Also if bird

fauna is attracted to new feeding habitat will this increase the possibility of collision with the

turbines / rotors resulting in a higher mortality rate?

DisturbanceandDisplacementDisplacement and disturbance during any ground preparation required and emplacement are

impacts that may manifest for CGBFs. Pathways exists due to the presence of dredgers, removal of

habitat and effects associated with the sediment plumes. Installation plant and vessels may displace

birds from areas of use.


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Research has been conducted through the Marine Aggregate Levy Sustainability Fund (MALSF) to

investigate potential impacts on seabirds from commercial marine aggregate activities. Cook and

Burton (2010) considered all the impacts and potential impact pathways associated with marine

aggregate operations by reviewing the existing research and the current state of knowledge up to

2010. Various receptor species and their sensitivities to habitat removal, sediment plume effects

including increases in turbidity and elevated suspended sediment concentrations and vessel

displacement effects are considered. Foraging ranges from coastal colonies are also presented per

species reviewed.

Cook and Burton (2010) determined, considering the scale of dredging areas in the context of overall

habitat availability, that habitat removal was likely to not be significant. Considering the scale of

marine aggregate dredging then it is reasonable to propose that habitat loss to any CGBF ground

preparation work required will have minimal effects on seabirds. However, this determination will

have to be made through project‐specific EIA to ensure that local conditions and environment,

including any ‘hot‐spots’ of local bird populations or aggregations, are accounted for.

Cook and Burton (2010) also determined displacement of seabirds due to dredger presence was

unlikely considering vessel traffic in English waters. For Round 3 projects specific navigation and

vessel traffic studies will have to be commissioned. These will inform EIA regarding displacement

effects. Critical to the assessment of vessel‐associated displacement impacts will be the density of

vessels already using the habitat where CGBFs will be installed. If these areas are outside of existing

navigation routes then additional displacement effects from any ground preparation required and

emplacement vessels may occur. These effects may manifest both onsite and also whilst vessels are

in transit to and from the site. Whilst these effects are not completely CGBF‐specific consideration of

any differences in payload and carrying capacity between various foundation solutions may equate

to variations in number of transits required. This may then result in different potential levels of

disturbance.

ChangesinWaterQualityCook and Burton (2010) determined that in association with marine aggregate operations that

changes to water clarity resulting from the re‐suspension of sediments would negatively affect the

foraging capabilities of some species. They report that in the case of the Sandwich tern, this has

resulted in negative impacts on populations elsewhere. However, the impact of increases in turbidity

is likely to be dependent (both in scale and spatial extent) on initial suspended sediment background

levels.

Considering any ground preparation activities that may be required for CGBFs in spatial and

temporal terms, in relation to existing and proposed marine aggregate extraction in English waters,

and considering the magnitude of these effects it is unlikely that the construction of OWFs using

CGBFs will have significant effects on overall seabird populations. However local and site‐specific

environmental conditions have to be considered and cumulative effects assessed. Loss of a foraging

for a small period of time may not be significant alone, but if other foraging areas area also receiving

plume impacts at the same time then this may have impacts on foraging efficiency. These

considerations will be made at an EIA‐level.


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7.6 NoiseThis section is intended to present an overview of CGBF‐source noise effect pathways and associated

impacts to biological receptors. Detailed information concerning noise frequencies, propagation and

attenuation and attendant pressure wave effects can be drawn from technical papers, peer‐

reviewed papers and guidance notes generated over the last decade or so and are beyond the scope

of this report to provide in detail. Information held by Subacoustech Ltd

(http://www.subacoustech.com/index.shtml) and that generated by COWRIE

(http://data.offshorewind.co.uk/) is particularly useful in setting the context and current knowledge

base for noise‐related impacts from OWFs. It is expected that this information will be drawn upon

and presented in any project‐specific EIA and Environmental Statement.

The Marine Strategy Framework Directive (EC Directive 2008/56) is a European Union Directive

which commits European Union member states to achieve ‘Good Environmental Status’ (GES) by

2020 across Europe’s marine environment. Good Environmental Status (GES) involves protecting the

marine environment, preventing its deterioration and restoring it where practical, while using

marine resources sustainably. This aligns with the UK Government’s and Devolved Administrations

vision of ‘clean, healthy, safe, productive and biologically diverse oceans and seas’.

The Directive sets out 11 high‐level Descriptors of Good Environmental Status which cover all the

key aspects of the marine ecosystem and all the main human pressures on them. Of significance for

the offshore windfarm sector are the qualitative descriptors for determining good environmental

status with particular reference to descriptor number 11:

Introduction of energy including underwater noise is at levels that do not adversely affect the marine environment.

HM Government is currently conducting a public consultation on the descriptors for GES and various

scenarios proposed to meet targets that may be set to achieve GES (HM Government, 2012). For

‘impulsive noise’, which includes hammer piling generated noise, one of the proposed targets is to:

“…establish and maintain a ‘noise registry’ which would record in space and time activities

generating noise… (allowing a determination of)…whether they may potentially compromise the

achievement of GES.”

Issues surrounding considerations of Habitats Directive Annex IV European protected species (EPS)

and compliance with Regulation 41(1)(b) of the Habitats Regulations and Regulation 39(1)(b) of the

Offshore Habitats Regulations are considered in Section 7.7 below.

Any compliance with legislation governing the production of underwater energy, including noise,

may have time and cost repercussions for Round 3 developments. Any foundation solution that will

not generate underwater noise at levels deemed to be significant may bring an advantage to the

pre‐application and application process for any Round 3 project using them.

As discussed within this review, and specifically within this section, it is apparent that CGBFs present

a notable positive effect considering the lack of significant underwater noise emissions during

emplacement. Alternative deeper water foundation solutions such as steel jackets and tripods will

require piling operations. Whilst the piles are generally smaller (2.5‐4m) in diameter than monopiles,


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the fact that 3‐4 piles per foundation are required, may negate any reduced noise emissions due to

possible smaller forces and durations of hammering required per pile i.e. the total period for

installation of a single foundation structure may be similar to that associated with a monopile.

Section 5.2 has identified noise as an effect with pathways associated with benthos (including

sensitive fish species) and marine mammals (pinnipeds and cetaceans). Noise impacts are identified

with various phases of the lifespan of a CGBF considered in this report. These are notably: ground

preparation (if required), emplacement of a CGBF, remedial activities (placement of scour materials

if deemed appropriate) and decommissioning.

Propagation of noise during operation is not considered within this report as the source of emissions

is not associated with the CGBF structure.

The context of noise emissions will focus on the known greatest point source of underwater noise

impacts; namely those associated with pile driving operations during installation of monopile, steel

jacket and tripod (and possibly floating platform) structures. This is considered appropriate as there

is a large evidence base for these effects (specifically monopiles and steel jackets) and all existing

Round 1 and 2 projects have used monopiles or to a much smaller degree steel jackets. This is also

significant given the lack of piling driving techniques required for the emplacement of CGBF

structures (and suction caisson) on the seafloor. Whilst hammer piling‐sourced noise impacts are not

derived from CGBF installation it is important to note that an additional noise source may be

associated with the use of CGBFs: this is noise associated with dredgers or grabs and excavation

operations as part of any ground preparation activities should they be required.

7.6.1 SensitiveNoiseReceptorsAs mentioned above there are several receptors that are considered sensitive to artificial

underwater noise emissions. Primarily these are:

Benthic invertebrates;

Certain fish species including larval stages; and

Marine mammals ‐ Pinnipeds (Seals) and Cetaceans.

The different receptor groups display different sensitivities and are likely to receive different

exposures dependent upon the activities considered e.g. dredging of foundation pits, scour

protection installation etc. if used, and their life strategies. A very brief overview of the various

sensitivities is presented below.

BenthicInvertebratesThere is a very weak evidence base considering noise impacts upon benthic invertebrates. The

literature review conducted by Zucco et al. (2006) cites a few examples of species‐specific

investigations that have been conducted. Research on effects of noise on growth and reproduction

in the brown shrimp Crangon crangon is cited. Reduction in growth and the reproduction rate,

increased aggression (cannibalism) and mortality rate, and decrease in food intake were observed in

the laboratory. It is postulated that responses in the wild may manifest as avoidance behaviour

resulting in displacement: it was not reported if this displacement was considered likely to be

temporary or permanent.


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It is apparent that vibration associated with noise propagation underwater and operation of offshore

windfarms may be more significant than the noise impacts alone (Zucco et al., 2006). The brittle star

Ophiura ophiura can detect both near‐field vibrations down to a few Hertz and far‐field pressure

waves (Moore and Cobb, 1986 cited in Zucco et al., 2006).

It is interesting to note that due to recorded colonisation of existing wind turbine towers and

foundations the effects of vibration is taken as an indication that noise and vibration have no

detrimental effects on the attached epifauna (Hiscock et al., 2002; Zucco et al., 2006; OSPAR

Commission, 2006). The Scottish Marine Renewables SEA did not even consider noise and vibration

as a valid pressure group for benthic ecology receptors (Scottish Executive, 2007).

Further studies are required to significantly add knowledge of the effects of noise and vibration on

marine invertebrates. Especially in the range of those effects associated with foundation installation

and operation of wind turbines.

FishSpeciesThe Scottish Marine Renewables SEA (Scottish Executive, 2007) reports that marine fish can produce

and hear noise which may be associated with alarm calls and social behaviour.

Hiscock et al. (2002) reviewed in detail considerations of fish fauna sensitivity to underwater noise.

In summary the sensitivity of fish species depends on their hearing thresholds, which have only been

studied in a few species such as cod, salmon, haddock, plaice, pollock and dab. Swim bladders may

resonate at low frequencies so that fish with swim bladders may be more sensitive to low frequency

sound than fish without swim bladders, e.g. flatfish, sharks and rays. Similarly, larger fish with larger

swim bladders may be more sensitive to noise impacts e.g. larger cod avoided areas subject to

seismic surveys more than small cod (references cited in Hiscock et al., 2002). Further it is suggested

that fish in which the swim bladder is physically coupled to the ear would be more sensitive still.

The current state of knowledge implies that fish responses to noise, pressure and vibration impacts

are not dissimilar for those recorded for marine mammals (see below). Primarily these are:

Alteration of schooling and social behaviour;

Avoidance resulting in displacement; and

Death or physical damage resulting from pressure wave damage to air spaces (swim

bladders).

Adverse effects are also possible to fish eggs and larvae / fry and primarily those that are demersal

(bottom) spawners (Hiscock et al., 2002; Perrow et al., 2011).

MarineMammals–PinnipedsandCetaceansIn overview marine mammals are considered highly sensitive to artificial underwater noise

generation and propagation. This is due in part to the ecology and life strategies that these fauna

have evolved and the way that they use sound to interact with the marine environment (Thomsen et

al., 2011). Cetaceans, in‐particular toothed whales (Odontocetes), use sound in nearly every aspect

of the lives including communication, socialisation, navigation and hunting (by echo‐location) (Evans,

1987). The baleen whales (Mysticetes) use sound to communicate and socialise over long distances,

and possibly for navigation (Evans, 1987).


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Pinnipeds (true seals) use sound to communicate and socialise and recent research work has

suggested that detection of sound or pressure changes may play an important role in assisting seals

to sense their environment and to hunt efficiently (Royal Haskoning, 2005 cited in Scottish Executive,

2007). Seals are also sensitive to noise impacts close to haul out sites which may cause displacement

effects (Skeate et al., 2011).

Within the zones listed by Hiscock et al. (Section 7.7.2 below) impacts on marine mammals can

manifest in several ways but can generally be grouped as:

Death – caused by damaging pressure waves disrupting internal organs and tissues;

Injury – causing auditory impairment;

o Permanent damage to hearing – Permanent Threshold Shift (PTS);

o Temporary hearing loss – Temporary Threshold Shift (TTS);

Displacement – causing receptor to vacate an area of sea;

o Temporary ‐ until noise effects is removed / ceases;

o Permanent – receptor does not return to area receiving the noise impact; and

Masking – noise is such that it interferes with ecology of receptor e.g. prevents successful

hunting.

Observed effects of noise on marine mammals include: changes in vocalizations, respiration, swim

speed, diving, and foraging behaviour; displacement, avoidance, shifts in migration path, stress,

hearing damage, and strandings (Thomsen et al., 2011). Responses of marine mammals to noise can

often be subtle and barely detectable, and there are many documented cases of apparent tolerance

of noise (Weilgart, 2007).

7.6.2 ImportantInteractionsbetweenNoiseSensitiveReceptorsandCGBFsHiscock et al. (2002) list the areas of noise effect on receptor species as:

Zone of audibility ‐ the widest area in which an organism can perceive or hear the noise;

Zone of responsiveness ‐ the area in which the organism reacts behaviourally or

physiologically;

Zone of masking ‐ the area in which the noise is intense (loud) enough to interfere with

communication;

Zone of physiological effect ‐ the area in which the sound level is great enough to cause

physiological; and

Damage such as hearing loss or injury to internal organs.

As such a hierarchy of impacts is likely to occur with noise from offshore windfarm construction and

operation, with minor effects such as masking of natural sounds at great distance to more serious

effects of avoidance and displacement to injury or fatality close to the noise source.

Different receptor species from the groups identified in Section 7.7.1 will have different sensitivities

to noise impacts as a product of the thresholds at which they are intolerant and the exposure to the

source of the noise – dependent upon complex physical environmental factors including; water

depth, bathymetry, haloclines, distance and strength (and sound wave range) of the emission.


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Modelling of noise impacts conducted as part of routine EIA for offshore windfarm projects but

currently there is little in‐field validation of these models conducted (Bailey et al., 2010).

Therefore it is important that consideration of noise impacts receives a suitable level of monitoring

and validation moving into the future. Especially as Round 3 zones are located in deeper water, are

more distant from coastal and inshore geomorphologically complex features and with possible

greater interaction with some sensitive receptors e.g. pelagic and less coastal species.

For CGBF projects the notable phases of activity likely to source noise impacts are:

Ground preparation (if required);

Emplacement of a CGBF;

Remedial activities (placement of scour materials if deemed necessary); and

Decommissioning (if required).

NoisefromDredgingFoundationPits(whererequired)Recent research has been conducted by Robinson et al. (2011) regarding noise generated by marine

aggregate dredgers, funded through the Marine Aggregate Levy Sustainability Fund. The sources of

noise associated with marine aggregate dredging are derived from: the vessel itself (propeller

cavitation etc.), noise associated with machinery and specifically the centrifugal pump and the intake

pipe, and possibly the draghead on the seabed. Noise emissions are also associated with grab bucket

dredging, which is an alternative method to trailer suction hopper dredging that could be used for

ground preparation on some projects.

It is likely that fish are able to avoid sites of intermittent noise (Tillin et al., 2011), but that they

habituate to regular noise of the frequency and level likely to be encountered close to shipping

activity (Hiscock et al., 2002; Zucco et al., 2006; Scottish Executive, 2007; OSPAR Commission, 2006).

This observation appears to be supported by the fact that commercially important inshore fisheries

resource areas are located in close proximity to major vessel transit and marine aggregate licence

areas.

The research undertaken by Robinson et al. (2011) determines that hearing damage is unlikely to

occur at the sound frequencies and intensities associated with aggregate dredging and that the main

effect that could be expected in the affected zone would be avoidance by mobile animals. Dredging

of sand cargoes was less noisy than dredging for gravel cargoes and it is proposed that this is due to

variations in mechanical noise in the uptake pipe and pump due to the difference in particle size of

the sediments. Therefore, if required, ground preparation of sandy seabeds will generate less noise

than for areas of mixed and coarse sediments.

Based on the Robinson et al. (2011) report, even though noise associated with any foundation pit

preparation required is likely to be heard some distance away (as it is analogous to marine aggregate

dredging with effects detected at distances of less than a kilometre), the effect of noise disturbance

on fish is likely to be negligible. At present there is insufficient scientific evidence to support firm

conclusions relating to the impacts of dredge‐related noise on fish communities particularly

regarding recovery from any displacement that occurs. However, the fact that successful commercial

fisheries coincide with marine aggregate licence areas implies that fish either acclimate to dredger

noise, or rapidly return areas from which they may be displaced.


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CEDA (2011) states that noise generated from the operation of grab buckets dredging is generally

relatively low frequency and these are not expected to elevate above background levels associated

with coastal vessel transits.

PilingOperationsAs previously stated the single largest source of anthropogenic‐sourced underwater noise is

recorded from pecussive piling activity associated with foundation installation (Hiscock et al., 2002;

Zucco et al., 2006; Scottish Executive, 2007; DONG Energy et al., 2006; OSPAR Commission, 2006;

Perrow et al., 2011a, 2012; Bailey et al., 2010; Thomsen et al., 2011). Pile driving generates very high

sound pressure levels that are relatively broad‐band (20 Hz ‐ > 20 kHz) and these interact with

auditory ranges of the sensitive receptors.

The construction monitoring programme at the Danish OWFs, Horns Rev and Nysted, observed the

effects of piling operation on sensitive receptors. In‐particular Harbour and Grey seals and Harbour

porpoise were monitored to look for any impacts or adverse effects associated with piling

operations (DONG Energy et al., 2006). A good comparison between piled and non‐piled installation

should have been achieved given that Nysted uses CGBFs and Horns Rev is built with monopiles.

However, the requirement for sheet metal piling at one of the foundations at Nysted negated this

comparison (DONG Energy et al., 2006; Zucco et al., 2006).

In overview the monitoring of Harbour porpoise at Horns Rev showed a statistically significant

displacement of Harbour porpoise from the location and vicinity of the installation site (DONG

Energy et al., 2006). This displacement was strong and occurred during the entirety of the

construction period but relatively short‐lived, as the population returned to the area in pre‐

construction numbers within the first 2 years post‐construction.

The data collected from Nysted was also useful in the context of piling noise impacts. During the 3

months that intermittent sheet metal piling occurred did there was a strong negative reaction with

total avoidance of the area at a population scale. Further, there is a prolonged effect as during the

first 2 years post‐construction the porpoise did not returned to the area. Some of the hypotheses for

this prolonged displacement are presented in Section 7.6.2 above. However this does highlight the

fact that site‐specific considerations are extremely important when determining project‐specific

impact scenarios.

For the Harbour and Grey seal populations in the vicinity of Horns Rev and Nysted no statistically

significant variations in population numbers or usage of the areas were observed, except for the

haul out site as Rødsand during the pile driving operations, when reduced numbers of seals were

observed hauled out. These numbers recovered to pre‐construction levels following cessation of

piling.

The noise monitoring recorded by Haelter et al. (2009) at the Thornton Bank OWF, Belgium, is

interesting because this assessed the emplacement of large CGBF structures into the southern North

Sea. The marine environment of the Thornton Bank may be similar to some Round 3 zones and

specifically noise effects during emplacement where recorded. The levels measured were 5 to 25 dB

higher than the background noise levels making them similar to increases caused by local ship traffic.


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To set the emplacement of the CGBFs in context, during this first phase of piling activity at the Bligh

Bank (Belwind) OWF, Belgium, the noise from pile driving was recorded at a maximum peak of

196dB re 1μPa at a distance of 520m, with a piling blow energy of 990kJ (Norro et al, 2010).

The monitoring studies conducted at the Belwind OWF, confirmed that the underwater noise level

associated with piling should be of concern, particularly for Harbour porpoise (Norro et al., 2010).

The authors further stated that it is very difficult to quantify and qualify the effects of the increased

underwater noise level on other components of the ecosystem and that further research is required

to model noise propagation in the bathymetrically complex southern North Sea region.

Skeate et al. (2011) observed that there was a significant displacement of Harbour seals from the

haul out sites at the Scroby Sands bank, UK, during the construction of the Scroby Sands OWF. This

appeared to be linked to the piling construction period. Similar to the case of Harbour porpoise at

Nysted, the seals did not return during the post‐construction period. Grey seals at the site appeared

less sensitive and have subsequently returned to the area. The continued absence of pre‐

construction population of Harbour seals may be related to inter‐specific competition between Grey

and Harbour seals with similar shifts in inter‐species populations observed at other East Anglian

coast colonies (Skeate et al., 2012). However it is suggested that the noise impacts may have

precipitated this population change at Scroby Sands.

Previous reported research at Scroby Sands may also help explain the decline in the Harbour seal

population there. This also is linked to piling impacts, but related to herring Clupea harengus egg

mortality due to noise, pressure and vibration induced impacts (Perrow et al., 2012). Herring are

important prey species for apex predators such as Harbour seals and Little tern Sternula albifrons.

Perrow et al. suggest that a significant reduction in herring abundance from 2004 (construction year)

onwards could not be explained by environmental factors. Intensely noisy monopile installation

during the winter spawning period was suggested to be responsible. Reduced prey abundance

corresponded with a significant decline in Little tern foraging success and also decline of the local

Harbour seal population (linked to displacement effect).

Bailey et al. (2010) conducted recording studies during the piling of two steel jacket foundations to

support 5 MW turbines offshore from the Moray Firth, Scotland. Each steel jacket required four piles

to secure the structure to the seabed at water depths of 42 m (BCD). Pile‐driving operations took

two hours per pile resulting in a total duration of 16 hours for both foundations. Hammer blow

forces of 200‐500 kJ per strike were measured and a mean average of just over 6000 blows was

required per pile. Strike rate was just under one minute per blow. Noise emissions at damaging

levels to bottlenose dolphin were recorded at a distance of 100 metres from the steel jacket.

However noise at levels likely to cause displacement ot otherwise interfere with normal behaviour

were detected at a distance of 50 km away. Noise levels above ambient were detectable at 70 km

but no longer distinguishable at a distance of 80 km.

Whilst there are locality specific issues regarding seabed topography it is clear that there are

significant effects associated with the installation of steel jacket (and likely tripod) structures, much

the same as for steel monopiles. Also a further likely significant factor is the number of piles per

foundation structure for steel jackets (3‐4) and tripods (3). Piling duration may be less per pile than a


86

5‐6 m diameter monopile, but Bailey et al. (2010) have shown that damaging noise emissions are

associated with installation of these foundations.

It is important to recognise the fact that for CGBFs piling is not required to emplace the structures

onto the seabed. Without the piling operations there is no effect / pressure pathway associated with

sensitive receptors. As such the adverse effects from piling do not exist. Perrow et al. (2011) suggest

that a precautionary approach may translate into greater restriction of the timing and duration of

pile‐driving activities or the adoption of alternative means of turbine installation. This view may also

align with the ‘noise register’ approach considered to deliver GES under the MSFD. Skeate et al.

(2012) go further to recommend that effective means of protecting marine mammals (seals) is to use

alternatives to pile‐driven monopiles such as gravity‐base designs (along with the development of

more effective means of mitigating noise).

A consortium of developers, sponsored by the German Federal Environment Ministry, as part of the

Evaluation of Pile Driving Noise Mitigation Systems (ESRa) program, has just published a report (July,

2012) detailing field trials in the German Baltic Sea to assess the use of piling noise mitigation

systems (ESRa, 2012). Protecting Harbour porpoises from harmful noises during pile driving

operations has undergone close scrutiny by the German authorities. During construction of the

Alpha Ventus and BARD Offshore 1 windfarms the noise emission limit of 160 dB at 750 m from the

source was often exceeded by 10 dB (a factor of 10). Five noise protection systems were compared:

a pipe with an internal bubble curtain; the fire hose method; a small, staged bubble curtain; noise

reduction shells with two bubble curtains and a Hydro Sound Damper (ESRa, 2012; Wilke et al.,

2012).

The pile‐driving operations were evaluated by the Institute for Technical and Applied Physics of

Oldenburg. It was found that within a 750 m radius from the sound source, and in the highest energy

range of 100‐300 Hertz, the sound damping effect was found to be between 0 and 10 dB (Wilke et

al., 2012). Wilke et al. (2012) also found that at the range up to around 5000 Hertz, to which sea

mammals are particularly sensitive, the highest reduction effect was 25 dB.

The authors of the study conclude that further research to improve the understanding of the factors

influencing sound during pile‐driving operations for offshore wind turbine foundations are required.

Also the cost of employing such mitigation, both in terms of capital and time, is still currently a

limiting factor in effectively deploying these mitigation systems (ESRa, 2012).

7.6.3 SummaryPossibly the single most important consideration for the use of CGBFs in the marine environment is

the fact that piling is not required to emplace the structures onto the seabed.

Monopiles, steel jackets and tripods (and possibly floating platforms) all require hammer piling to

secure them to the seabed. Steel jacket and tripod foundations can each have 3‐4 piles with piling

times of approximately 2 hours per pile. Cumulatively these noise emissions are very likely to be

significant. In the absence of piling operations associated with CGBF emplacement there is no high

impact noise pressure pathway linking CGBFs with noise sensitive receptors. As such the adverse

effects do not exist.


87

There is an increase in legislative requirements to demonstrate no impulsive noise‐related impacts

on sensitive and designated nature conservation species. The use of CGBFs can streamline Round 3

pre‐application and application phases when considering noise impacts – specifically as use of CGBFs

may not require the need to be added to a ‘noise register’ and should be secure under Regulation

41(1)(b) of the Habitats Regulations and Regulation 39(1)(b) of the Offshore Habitats Regulations (as

considered in Section 7.7 below).


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7.7 DesignatedSitesandotherNatureConservationInterestsThis section presents an overview of the current and proposed Marine Protected Areas (MPA)

network in UK waters. Detailed information can be drawn from several sources including: site

assessment dossiers; department briefings; (Habitats) Regulation 33(2) and 35(3) packages and

(Regulatory) Impact Assessments.

Section 5.2 has identified nature conservation habitats and species as a receptor to activities and

effects associated with each phase of the lifespan of a CGBF considered in this report. Many of the

considerations of sensitivity of conservation habitats and species have been described in the

preceding sub‐sections of Section 7 of this report. Benthic habitat and species, fish species, bird

fauna and megafauna all have representatives that are considered to be of conservation importance.

An overview of international and national marine nature conservation legislation is provided in

Appendix A. Lists of international and national marine habitats and species of conservation

significance and likely to interact with CGBFs are presented in Appendix F.

It is important to note that impacts associated with development of construction yards in terrestrial,

coastal and estuarine habitats are beyond the scope of the report; including any designated nature

conservation features restricted to association with these operations and not also found offshore.

Nature conservation sites at the coast may need to be considered by a project using CGBFs, though

for Round 3 developments it is believed unlikely that environmental effects will manifest at the coast

(see Sections 5.3, 6.2.1 and 6.2.3).

Projects that may use CGBFs are most likely to have to consider impacts upon:

Special Areas of Conservation (SAC) designated under the Habitats Directive;

Special Protection Areas (SPA) designated under the Birds Directive; and

Marine Conservation Zones (MCZ) to be designated under the Marine and Coastal Access Act

2009 (at the time of drafting this report MCZs are recommended to Defra, who are

reviewing them before designation).

7.7.1 NatureConservationFeaturesLists of habitats and species of significance at a Northeast Atlantic bio‐geographic regional scale are

presented in Appendix F. These include Annex I habitats, Annex II species and Annex IV European

protected species of the Habitats Directive and Annex I bird species listed under the Birds Directive.

Also included are broadscale habitats, habitat features of conservation interest and species of

conservation interest listed under the Marine and Coastal Access Act (2009). Links to other lists of

marine habitats and species of conservation importance, such UK biodiversity Action Plans and

OSPAR Convention lists, are also presented in Appendix F.

The focus of conserving marine habitats and species was derived from protecting rare, scarce and

threatened species. A shift in recent years has brought a focus onto areas of sea that are

representative of the range of marine wildlife in UK waters thus building resilience into the MPA

network.

As described below the focus for CGBFs should be consideration of the location of Round 3 zones,

the extent of likely direct and indirect impact footprints from the foundations and spatial or


89

temporal overlap with designated features within designated or recommended nature conservation

sites.

The main focus of assessing interactions of effects from CGBFs with nature conservation features will

be set by the conservation objectives for a site. These objectives detail the designated features and

parameters used to ensure that features are maintained or restored to favourable condition;

allowing contribution to overall favourable conservation status for that habitat or species at a

network scale.

MPA site‐specific information is provided (from the statutory nature conservation agencies) to

advise management of activities that interact, or may foreseeably interact, with each MPA. This

information e.g. Regulation 35(3) packages for SACs, will indicate: the boundary of the site; location

and extent of designated features; important biological components and attributes (with

thresholds); and sensitivities to effects. These allow assessment of impacts and judgement about

feature condition to be determined.

Assessing the impacts on any features from CGBF derived impacts will usually be conducted through

a Habitats Regulations Assessment within the EIA. If the statutory nature conservation agencies

(SNCAs) cannot determine that there will be no likely significant effects then an appropriate

assessment will be required. The most common mechanism for assessment is through the Habitats

Regulations or Offshore Habitats Regulations The appropriate assessment process is analogous to a

detailed, focussed EIA and must allow a determination of no adverse effect on site integrity, or not,

to be made.

Assessment of noise impacts from OWF installation and construction has recently received intense

scrutiny from the SNCAs. Case Law from the European Court of Justice has tightened the

considerations of deliberate disturbance of fauna listed under Annex IV ‐ European Protected Species

‐ of the Habitats Directive. It is now an offence (under Regulation 41(1)(b) of the Habitats

Regulations and Regulation 39(1)(b) of the Offshore Habitats Regulations) to deliberately disturb

wild animals of a European Protected Species:

“…in such a way as to be likely significantly to affect:

a) the ability of any significant group of animals of that species to survive, breed, or rear or

nurture their young; or

b) the local distribution or abundance of that species.”

The installation of driven piles in the marine environment without mitigation is likely to produce

noise levels capable of causing injury and disturbance to marine mammals. Such effects, although

incidental to consented activities, have the potential to conflict with the legislative provisions of The

Habitats and Offshore Habitats Regulations.

JNCC, NE and CCW have produced guidance on ‘the protection of marine European protected species

from injury and disturbance’ (JNCC, NE and CCW, 2010). The JNCC has also produced a specific ‘piling

protocol’ which forms part of that more general guidance and the recommendations should be

considered as ‘best practice’ for piling operations (JNCC, 2010b). The implications of this statutory

assessment are discussed in the section below.


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The Marine Strategy Framework Directive (MSFD) commits European Union member states to

achieve ‘Good Environmental Status’ (GES) by 2020 across Europe’s marine environment. Good

Environmental Status (GES) involves protecting the marine environment, preventing its deterioration

and restoring it where practical, while using marine resources sustainably.

The Directive sets out 11 high‐level Descriptors of Good Environmental Status which cover all the

key aspects of the marine ecosystem and all the main human pressures on them. Of significance for

the offshore windfarm sector are the qualitative descriptors for determining good environmental

status with particular reference to descriptor number 11:

Introduction of energy including underwater noise is at levels that do not

adversely affect the marine environment.

The issues from MSFD Descriptor Target number 11and the benefits from the potential use of CGBFs

in Round 3 projects are discussed above in Section 7.6.

7.7.2 ImportantInteractionsbetweenNatureConservationFeaturesandCGBFsThe potential impacts on designated nature conservation features from CGBFs are detailed in

Section 5.2 but may be summarised as:

• Impacts within the boundaries of the dredged site;

• Impacts outside the boundaries of the dredge site;

• The rate of recovery of seabed resources following emplacement and settlement

impacts and at decommissioning; and

• Impacts on non‐site protected mobile species.

As discussed in many of the sections above the extent of impacts will depend on a combination of

factors including: the operation occurring; the sediment and habitat type; the sensitivity of the

receptors to the impact; the physical conditions of the environment, the type of CGBF being used

along with orientation, spacing and possibly timing of operations. Therefore only generic statements

can be made about significant effects on nature conservation features outside of a project‐specific

EIA.

FeatureRemoval/LossEnvironmental effects associated with the lifespan of a CGBF on the seabed will result in physical

effects that may interact with and influence the health, function and quality of conservation sites,

features and species. The most significant impact from CGBFs will be the direct removal of habitats

and species. If the CGBFs are located on designated features then this will result in direct impacts of

physical loss of the feature. This may not exclude the co‐location of CGBFs with certain nature

conservation features e.g. Annex I sandbanks that are submerged by seawater at all times, but a

large amount of time and likely costs will have to be expended by the developer during the

application process to allow a determination of no adverse effect on the integrity of the site.

Feature removal or loss may be associated with: dredging of the foundation pits (if required); under

the physical footprint of the CGBF; below any surficial scour protection (if used); and from possible

reef effect halos. Consideration of any areas intended for disposal of the foundation pit fines (if

appropriate) will also have to be assessed.


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Physical loss may also result from smothering effects associated with settlement of fines dredged

from the foundation pits if undertaken. If disposal or storage of the dredged fines is proposed within

the boundary of the site then the location of features related to the smothering footprint will have

to be assessed. If the deposited fines are intended to be used for foundation pit backfill then further

smothering effects may result at both the ‘storage’ area when they are re‐dredged, and also at the

foundation pit when deposited for backfill (if needed). It is considered unlikely that any significant

sediment plumes or smothering impacts will be associated with CGBF ballasting operations (aside

from those mentioned previously from any re‐dredging operations).

During decommissioning the fate of ballast will also have to be considered. If the intention is to re‐

deposit ballast originally sourced from foundation pits within the designated site then toxic

contamination will have to be assessed for impact pathways. There will also be a smothering

footprint involved with the deposition, though this may be mitigated if associated with particle sizes

likely to allow fast colonisation e.g. sands. If crushed rock fines or non‐marine gravels are used for

ballast then there may be a requirement to either dispose of these (when pumped out of the CGBF)

at a licensed disposal site. If the developer intends to deposit these within the site and certainly onto

any designated feature then loss through smothering will have to be assessed along with any toxic

contamination pathways. SNCAs are likely to have a position that ballast and scour protection

material, along with any foundation layers will have to be removed from the seabed during

decommissioning. There is evidence to support a position that foundation layers may be left in situ

at decommissioning so long as the material is deeper than 1 m below the seabed surface and not

likely to be exposed through subsequent seabed bedform activity. This is supported by the use of the

upper 1 m of sediment layers by infaunal species (EMU Ltd, 2010a; Hiscock et al., 2002). So long as

the foundation layer is back‐filled to a depth greater than 1 m (below seabed surface) with a

sediment of the same grain size as occurred naturally pre‐installation, then recovery to baseline

conditions may be achievable. However this will likely require detailed project‐specific discussion

between the developer and the relevant SNCA(s).

FeatureDamageandDisplacementImpactsIndirect effects that overlap designated features will have to be assessed for impact. This may result

from alterations in sediment transport pathways and sediment flux from hydrological changes due

to CGBF structures. Changes in near seabed energy from altered wave climates and tidal streams

may affect sediment habitats, though at the water depths considered for Round 3 zones these are

unlikely to manifest (see Section 6.2). Impacts at the coastline are also unlikely to occur in

association with CGBFs at Round 3 zones (see Section 6.2) so impacts on habitats at coastal sites are

not expected.

Sediments plumes resulting from various dredging activities associated with ground preparation (if

required) will raise turbidity levels and increase suspended sediment concentrations. If these

footprints overlap designated features then an assessment of significance will be required. It is

expected that indirect impact halos for sediment plumes will be the same as those routinely

assessed for marine aggregate extraction operations in relation to MPAs; though of smaller volumes

and effectively time‐limited events unlike aggregate extraction (NE and JNCC, 2011).

The introduction of hard substrata into designated sites with sediment habitat features will alter the

habitat matrix. Reef effect halos may alter the infaunal communities. If these halos overlap the


92

extent of designated features then interactions may need consideration. Loss or damage of infaunal

communities may occur though this is generally restricted to predators foraging out from the ‘reefs’

up to no more than 200m away (reference cited in Zucco et al., 2010; Bremner et al., 2006).

Nature conservation benefits of artificial hard substrata acting as reefs or as fish aggregating devices

(FADs) and any increased biodiversity effects are generally not considered by the SNCAs as positive

effects if located within a designated site (Ian Reach, pers. obs.). These are not necessarily

considered as negative effects either, just that if the site is designated for sediment habitat features

then introduction of reef communities does not contribute to delivering conservation objectives for

those features and that site. This said there may be positive effects for certain fish species or apex

predators such as seals and Harbour porpoise; through increased foraging efficiency that may

contribute to favourable condition of a conservation species. These effects are difficult to

demonstrate but should not be discounted.

Displacement of sensitive species may result due to the presence of artificial structure on the

seabed. DONG Energy et al. (2006) reported that Harbour porpoise displaced from Nysted OWF,

Denmark, by piling operations had not returned to the habitat space up to two years post‐

construction. It is not determined if this continued displacement is due to the presence of the array

or that other ecological factors are contributing. Regardless it is unlikely that CGBFs themselves will

cause any greater displacement effects of mobile fauna than other foundation solutions.

Zucco et al. (2006), Scottish Executive (2007), and DONG Energy et al. (2006) have all noted that

habitat loss and subsequent displacement of sensitive bird fauna may become more critical under

cumulative conditions. For species with highly restricted marine habitats, habitat loss may have

population level effects, because displaced birds have poorer quality or little alternative habitat to

move to. However, it is clear that the habitat loss effect and displacement for bird fauna is related to

physical presence of the array itself and above waterline effects of towers and turbines. The area of

habitat loss is therefore much greater than the physical footprint of any foundation type. As turbine

sweep diameters increase then the required inter‐foundation spacing will also increase. This may

result in greater habitat loss for sensitive mobile species, however again this is independent of

foundation type.

PossiblePositiveEffectsCGBFs may provide pathways for nature conservation gains. The required consideration of

deliberate disturbance to European Protected Species is useful in the context of the use of CGBFs.

The fact that noise emissions from emplacement of these structures in no more noisy than that

sourced from shipping transits (Haelters et al., 2009) means that demonstrating compliance with

Regulation 41(1)(b) of the Habitats Regulations and Regulation 39(1)(b) of the Offshore Habitats

Regulations, should be much less onerous than for projects involving pile driving operations (e.g.

steel jackets and tripods). It is also possible that installation and emplacement of CGBFs may

mitigate the requirement for a project using them to be required to enrol on a ‘noise register’; if this

proposed legislative procedure is agreed necessary from responses to Defra’s MSFD consultation.

The significant lack of impact pathway may transfer into significant time and cost savings during the

application phase of a project proposing to use CGBFs.


93

The combination of reef effect and fish aggregating device effects and the possibility of fishery

exclusion zones around turbines mean that positive effects on local fish population may accrue.

Post‐construction monitoring of the Thornton Bank OWF, Belgium, showed that some fish species

attracted to the CGBFs were of conservation importance such as cod Gadus morhua (Reubens et al.,

2010). It has been proposed that the FAD effect may contribute to MPA‐like effects with safe refuge

for certain commercial species that may then ‘spill‐over’ into fishery accessible areas. The counter‐

point is that if no fishery exclusion zones exist then catch per unit effort (CPUE) may increase

resulting in increased population‐level pressures for certain species (Reubens et al., 2010).

DONG Energy et al., (2006) noted that the ross worm Sabellaria spinulosa may have the potential to

colonise the foundation structure at the Horns Rev OWF, Denmark. This species of tube‐building

polychaete worm can form biogenic reef structures which qualify as Annex I habitat (also listed

under the OSPAR Convention; UK BAP; and MCZ lists). It has been hypothesised that structural

complex artificial structures in the right environmental conditions may have a high potential for

colonisation or to have increased reef effects (Zucco et al., 2006). CGBFs certainly fall into this

category.

If CGBFs do act as sanctuaries for nature conservation important habitats and species it is

noteworthy to question the consequences that decommissioning these structures may have on this

nature conservation enhancement.

InvasiveNon‐NativesOrganismsArtificial hard substrata may act as ‘stepping stones’ for invasive non‐native epiphytic and epifaunal

species by providing habitat that elsewise would not be present in sediment habitats (Hiscock et al.,

2002). This may be even more critical for species that have no dispersive planktonic larval stage.

Most MPA conservation objectives have a statement about the introduction of invasive non‐natives

resulting in detrimental effects, possibly resulting in failure of maintaining favourable conservation

status.

The monitoring programme at the Thornton Bank OWF reported the presence of non‐native

barnacle species Balanus perforatus and Megabalanus coccopoma in the barnacle zone (Degraer et

al., 2010). Consideration of appropriate control methods may be required if invasive non‐native

species are detected. However, there are examples of SACs being designated in favourable condition

with a large community of invasive non‐native species present within the site e.g. The Solent

Maritime European marine site and the American slipper limpet Crepidula fornicata. So it is unclear

at this time of the significance that the presence of these species in relation to conservation

objectives.

The consideration of non‐native species colonisation is not CGBF‐specific though the increased

surface area of these structures may facilitate a higher potential for colonisation; though this

statement is not substantiated by evidence.


94

7.9 SummaryofBiologicalReceptors

A comparison of the relative magnitude of effects, between a CGBF and alternative solutions, is

presented considering the evidence reviewed in this section. Note that the effects of a large number

of small foundations, compared with a smaller number of larger foundations, is not yet well


Key


Receptor Sub‐receptors Description Phase effect

detected

Relative effect

Scale Significance

Biological ‐ Benthos

Infauna Epifauna Mobile species

Direct loss of habitat from placement of foundation only

I / O / D CGBF similar to other Round 3 solutions in most cases

May be moderately significant across a large array

" Direct loss of habitat from placement of foundation plus surficial scour protection (if used)

I /O / D CGBF similar to or greater than other Round 3 solutions in most cases


" Alteration of the sediment habitat and communities through changes to particle size or sediment matrix due to changes in local hydrodynamic caused by the foundation

I / O CGBF similar to or less than other Round 3 solutions in most cases


" Habitat loss from excavation of sediment from ground preparation for CGBF (if required) and removal



" Smothering from sediment plumes by ground preparation for

I / D CGBF similar to or greater than other

May be moderately significant


95

CGBF (if required) or drilling of pile or removal

Round 3 solutions where used

across a large array

Infauna Epifauna Mobile species

Impact from increased turbidity or raised suspended sediment concentrations from sediment plumes by ground preparation for CGBF (if required) or drilling of pile or removal



" Alteration of sediment habitat from changes to sediment transport pathways

O CGBF similar to other Round 3 solutions in most cases


" Reef effects

O / D CGBF similar to or greater than other Round 3 solutions in most cases


" Foundation acting as a ‘steeping stone’ for colonisation by non‐native invasive species

O / D CGBF similar to other Round 3 solutions in most cases


" Noise impacts to fauna from emplacement / installation activity or removal

I / D CGBF less than other Round 3 solutions

Likely to be insignificant for CGBFs

Biological ‐ Fish

Demersal Pelagic Reef‐dwellers


I /O / D CGBF similar to other Round 3 solutions in most cases


" Direct loss of habitat from placement of foundation plus surficial scour protection (if used)

I / O / D CGBF similar to or greater than other Round 3 solutions in most cases



96


Alteration of the sediment habitat supporting fish fauna and assemblages through changes to particle size or sediment matrix due to changes in local hydrodynamics caused by the foundation



" Habitat loss from excavation of sediment from ground preparation for CGBF (if required)



" Smothering from sediment plumes by ground preparation for CGBF (if required) or drilling of pile or removal



" Impact from increased turbidity or raised suspended sediment concentrations from sediment plumes by ground preparation for CGBF (if required) or drilling of pile or removal


May be of minor significance across a large array

" Alteration of sediment habitat from changes to sediment transport pathways



" Fish Aggregation Device potential




97


Potential for increased prey species and foraging halos over surrounding sediment habitats



" Displacement from existing habitat due to presence of foundations – negative fish aggregation through avoidance behaviour



" Noise impacts to fauna from emplacement / installation activity or removal



Biological ‐ Megafauna

Marine mammals Sea turtles Pelagic sharks incl. Basking shark


I / O CGBF similar to other Round 3 solutions in most cases


" Direct loss of habitat from placement of foundation plus surficial scour

protection (if used)



Marine mammals Pelagic sharks (Not applicable to sea turtles or Basking shark)

Direct loss of habitat supporting prey species from

foundation only



" Direct loss of habitat supporting prey species from

foundation plus scour protection (if used)

O / D CGBF similar to or greater than other Round 3 solutions in most cases


" Alteration of the sediment habitat supporting prey species through

changes to particle size or sediment

matrix due to changes

O CGBF similar to or less than other Round 3 solutions in most cases

May be low to moderately significant across a large array


98

in local hydrodynamic caused by the foundation


Prey species loss from excavation of

sediment from ground preparation for CGBF

(if required)



" Prey species smothering from

sediment plumes by ground preparation for CGBF or drilling (if required) of pile or

removal




Impact from increased turbidity or raised

suspended sediment concentrations from sediment plumes by ground preparation for CGBF (if required) or drilling of pile or

removal




Alteration of sediment habitat and prey

species from changes to sediment transport

pathways



" Structure blocks the normal passage of

tidal currents altering distribution of planktonic prey




Collision risk from presence of ground preparation and

installation vessels should they be

required

I / D CGBF similar to other Round 3 solutions in most cases

May be moderately significant in certain areas across a large array


99


Potential for increased prey species due to Fish Aggregation Device effects

O CGBF similar to or greater than other Round 3 solutions in most cases (Positive effect)



Displacement from existing habitat due to

presence of foundations and

avoidance behaviour



" Noise impacts to fauna from

emplacement / installation activity



Biological ‐ Birds

Grebes, divers, Seaducks, gulls, terns, auks, gannets, petrels and shearwaters



Likely to be insignificant across a large array

"

"

"

"

Direct loss of habitat from placement of foundation plus surficial scour





foundation only




foundation plus scour protection (if used)



Alteration of the sediment habitat supporting prey species through

changes to particle size or sediment




100

Grebes, divers, Seaducks, gulls, terns, auks, gannets, petrels and shearwaters "

" " " " "

matrix due to changes in local hydrodynamic

caused by the foundation

Prey species loss from excavation of

sediment from ground preparation for CGBF

(if required)



Prey species smothering from

sediment plumes by ground preparation for CGBF (if required) or drilling of pile or

removal

I / D CGBF similar to or less than other Round 3 solutions in most cases


Impact from increased turbidity or raised

suspended sediment concentrations from sediment plumes by ground preparation for CGBF (if required) or drilling of pile or

removal



Alteration of sediment habitat and prey

species from changes to sediment transport

pathways



Structure blocks the normal passage of

tidal currents altering distribution of

plankton‐fish prey trophic link



Displacement from presence of ground preparation (if used)

and installation vessels




101

Grebes, divers, Seaducks, gulls, terns, auks, gannets, petrels and shearwaters

"

Potential for increased prey species due to Fish Aggregation Device effects



Noise impacts to fauna from

emplacement / installation activity (if

required)



Biological – Nature Conservation

Habitats and benthic species features

Direct loss of habitat or species features from placement of foundation only



" Direct loss of habitat

or species features from placement of foundation plus surficial scour




Mobile species features

Direct loss of habitat supporting a feature’s prey from foundation

only



" Direct loss of habitat supporting feature’s prey from foundation plus scour protection

(if used)



Habitat and benthic species features

Alteration of the sediment habitat through changes to particle size or

sediment matrix due to changes in local

hydrodynamic caused by the foundation




102


Alteration of the sediment habitat supporting prey species through

changes to particle size or sediment matrix due to changes in local

hydrodynamic caused by the foundation




Loss or removal from excavation of sediment from

ground preparation for CGBF(if required)




Loss of feature’s prey species from excavation of sediment from

ground preparation for CGBF (if required)




Smothering from sediment plumes by ground preparation for CGBF (if required) or drilling of pile or

removal




Smothering of feature’s prey species

from sediment plumes by ground

preparation for CGBF (if required) or drilling of pile or removal



Habitat, benthic and mobile species features

Impact from increased turbidity or raised suspended

sediment concentrations from sediment plumes by ground preparation for CGBF (if required) or drilling of pile or

removal




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Habitat, benthic and mobile species features

Alteration of sediment habitat and prey species from

changes to sediment transport pathways




Structure blocks the normal passage of

tidal currents altering distribution of

plankton‐fish prey trophic link



" Displacement of mobile species features from

presence of ground preparation and

installation vessels if used



" Barrier effects to migration or transits of mobile designated

species



" Potential for increased prey

species due to Fish Aggregation Device effects and cascade up trophic chain



" Potential for Fish Aggregation Device resulting in increase of fish populations of

conservation or commercial importance



Habitat and benthic features

Potential for enhancement of habitat or species

features

O CGBF similar to or greater than other Round 3 solutions in



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most cases (Positive effect)

Habitats and benthic species

Foundation acting as a ‘steeping stone’ for colonisation by non‐

native invasive species



" Noise impacts to fauna from

emplacement / installation activity

CGBF less than other Round 3 solutions




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8 HumanReceptorsThere are a number of potential interactions that could occur with CGBFs and the Human

environment. The majority of these issues arise from the physical presence of the CGBF on site, and

the associated displacement activities associated with their emplacement and subsequent removal.

In addition, there is also the potential during emplacement works to impact the pre‐history of the

seabed and wreckage which might exist at the emplacement site. The following section therefore

highlights the effects and issues identified within Section 5.2 but does not provide an exhaustive list

of potential human receptors to CGBFs in the marine environment, but may highlight some of the

more important which should be considered universally across all CGBF EIA documents. The effects

on Archaeology are split into a separate sub‐heading as the effects are independent from all other

human receptors.

8.1 VesselPresenceduringEmplacement,GroundPreparation,RemediationandRemovaloftheCGBF

Vessel presence during ground preparation if undertaken, emplacement and remedial work (if used)

will displace activities that usually occur within the region unimpeded. The presence of the vessel

that are utilised if ground preparation work is undertaken may prohibit activities such as fishing

(both commercial and recreational), navigation, recreation craft transiting the area and other

activities such as diving. Therefore the ES should review available literature and data sources or

commission appropriate site specific studies in order to ascertain the exact use of the site prior to

construction. The ES should also make a judgement on the level of impact given the proposed

construction methodology set out by the developer.

Vessels displaced from the windfarm zone may result in increased noise in another part of the region

which may contain receptors that are sensitive to it. Therefore the ES should identify all features

within the vicinity of a proposed windfarm that could potentially be impacted from the displacement

of these activities.

The plume and turbidity generated during ground preparation, foundation and remediation

placement on the seabed if used, visibility can be significantly reduced. This can have impacts upon

recreational activities such as diving which may be precluded from operations as a result of the

decreased visibility in the region. As above, the ES should consider the effects in light of the

construction plan proposed by the developer.

8.1.1 SecondaryEffectsIn addition to the direct effects as a result of displacement, there are also indirect effects associated

with the displacement of activities into other areas that would not normally be targeted by the

displaced activity. This can have knock‐on effects as a result of increased pressure on the receptors

now being targeted by the displaced activities. This can potentially have significant effects upon

fishing, as the resources are potentially targeted by multiple vessels putting pressure on the fish

stocks targeted.

The potential preparation of the ground surrounding the CGBF and remedial action if utilised can

potentially impact infrastructure already in place in the areas affected. It is therefore important to

map out the position of all infrastructure prior to the selection of emplacement sites to minimise the

potential impacts upon these structures.


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Further secondary impacts result from the effects received on the benthos from any preparation,

remediation, emplacement and removal activities undertaken. Changes to the benthic community

can affect a variety of human receptors such as fishing and diving.

Effects may also arise as a result of decommissioning of the CGBF structures is the fill and scour

protection material (if used) is disposed of outside of the existing footprint of effects. If this is the

case, then human receptors operating at the proposed disposal site could potentially be impacted.

Therefore it is pertinent to check the location of the disposal site once a methodology and timetable

have been established for decommissioning.

8.2 CGBFPresenceduringSettlementandOperationOnce emplaced the presence of the CGBF also has a displacement effect on activities that would

have historically had access to the site. However, in addition to this displacement, the “reef effects”

associated with the CGBFs may attract activities such as fishing and diving to the CGBFs. This

potential interaction could be dangerous if the fishing gear gets caught in the structure of the CGBF,

or if vessels operating close to the CGBFs loose power and strike the CGBFs potentially causing

damage to the CGBF or the vessel itself.

8.2.1 SecondaryEffects

In addition to the direct effects as a result of displacement, there are also indirect effects associated

with the displacement of activities into other areas as discussed above in Section 8.1.1.

Furthermore, as a result of the physical effects resulting from the structures, it is possible that

erosion resulting from hydrodynamic changes around the CGBF could potentially impact upon

infrastructure within the scour footprint. Therefore all infrastructure should be mapped out in

advance to ensure that any overlap of the scour and existing infrastructure can be avoided.

8.3 EffectsasaResultofBiologicalImpactsFurthermore, as a result of some of the other effects identified in Sections 6 and 7, the indirect

effect of changes to the benthos could potentially affect fisheries in the region. Fisheries are

transient and tend to be mobile and are often able to adapt to changes in the populations and

spatial changes that may be associated with the receptors.

In addition, effects of the CGBFs on habitats and features of conservation significance could also

impact upon human receptors as a result of the decreased availability of benthic species –

particularly those of commercial interest.

8.4 FisheriesIn order to fully understand the fishing activity occurring within a given region, it is important to map

the fishing effort from recent landings, VMS and observation data to ensure that the current status

of the fishery is captured. Historical data can also help to analyse trends and may help to identify

areas that are consistently fished. Liaison with local fishermen is also advised as this can help to

understand their concerns and current practices, as well as identifying important areas currently

fished.

Details of the scope and nature of such an assessment are detailed in the 2004 windfarm guidance

note written by Cefas (2004).


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8.5 NavigationNavigational impacts should be fully considered within the ES. Guidance for this element has been

written by the Maritime and Coastguard Agency (MCA) in conjunction with the Department for

Trade and Industry (Dti) and the Department for Transport (DfT) and is available from the MCA’s

website. This document details the potential issues, provides a methodology for assessment of

impacts and shows the process for decision makers.

8.6 ArchaeologyandotherHistoricalUsesoftheSeabedArchaeology has become a key concern for marine development, including for the development of

offshore windfarms. There is express provision in wider UK policy on marine planning and licensing,

and in EIA regulations, for considering the effects of marine development on the archaeological

heritage (see Appendix A). These provisions are supported by commitments in international law and

they are accompanied by measures for designating important sites, together with other legal

requirements. Archaeology also enjoys widespread popular interest, which can enable

archaeological work in connection with windfarm development to be disseminated as a benefit to

the local and wider community. A good track‐record of engagement by marine developers and their

teams with archaeological concerns on a pro‐active basis has enabled the introduction of a variety of

‘best practice’ mechanisms, including agreed methodological standards and a Protocol for

Archaeological Discoveries introduced by The Crown Estate across the offshore windfarm sector.

Although there is a potentially wide range of archaeological effects arising from offshore windfarms,

most direct effects arise from impacts on the seabed attributable to foundations. Deposits of

archaeological interest can be found many metres below the seabed, and these deposits may be at

risk from piled foundations. Although gravity base foundations are unlikely to have such effects on

deeper deposits of archaeological interest, they are likely to require intentional disturbance of a

larger area on the seabed than piled solutions. Where preparation of the seabed is required,

dredging in advance of installation is a potentially significant concern. The full range of potential

archaeological impacts from concrete gravity based foundations is considered below.

TheScopeofArchaeologicalHeritageArchaeological material comprises artefacts, structural remains, the deposits in which they are

situated, and their wider context. Artefacts found at sea sometimes prove to be ‘isolated’, that is to

say they are no longer associated with other artefacts, structures or deposits that warrants

examination as a ‘site’. Isolated artefacts can sometimes be very important, as they can provide new

insights into the past simply by themselves. However, in general terms, greater significance arises

from assemblages of artefacts, and artefacts that can be shown to be more or less in their original

location (‘in situ’) with associated structures or deposits.

Archaeologists commonly use the term ‘historic environment’ to encompass the totality of the

physical remains of heritage material in the environment, underlining the need to consider the role

and value of past human actions alongside natural processes in the development of the environment

we experience today. The term ‘heritage asset’ is used to refer to discrete features within the

historic environment, such as identifiable sites or monuments. In international and European

frameworks, the terms ‘archaeological heritage’ and ‘cultural heritage’ are often used, including

‘underwater cultural heritage’ for elements of the historic environment situated under the sea.


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The archaeological concerns raised by offshore windfarms generally fall into five categories, as

follows:

PrehistoryPrehistoric archaeology is concerned with artefacts and deposits dating from the earliest human

inhabitation of the British Isles through to the Roman period, when sea‐level approached its current

height. Sea‐level has fallen and risen repeatedly over the past million years so changes in sea‐level

are of paramount importance to understanding early human activity. At times of lower sea level,

very large areas of land that are now submerged as part of the UK Continental Shelf were available

for humans to inhabit. The most striking recent illustration of the potential for prehistoric material

to be present on the UKCS has been the discovery of large numbers of flint tools that were made

over 200,000 years ago. These tools appear to be in situ and are associated with an extensive gravel

deposit in about 30m of water off East Anglia.

MaritimeMaritime remains comprise artefacts, structures and wrecks that have arisen from various forms of

seafaring from the prehistoric period onwards, encompassing all manner of vessels from logboats to

20th Century warships. Although generally small in overall extent, shipwrecks can include very dense

concentrations of significant archaeological material. Recent examples of previously‐unknown

wrecks discovered in the course of marine development include substantially‐intact remains of

vessels from the Sixteenth and Seventeenth Centuries. In addition, a wide range of maritime

material – sometimes isolated, sometimes as assemblages – has been found in the course of

dredging in UK waters.

AviationAircraft crash sites at sea have become a particular concern in recent years because of the frequency

with which they have come to light as a result of marine development, and the importance of the

material that has been uncovered. Even though aircraft were mass produced, surprisingly few

examples of some types have survived in museums; some types and versions are effectively extinct.

Recent examples of aircraft discoveries that have arisen from development‐led archaeology include

substantial fragments and entire airframes of a variety of British, American and German bombers

and fighters. Military aircraft crash sites are automatically protected under the protection of Military

Remains Act 1986, and there are particular concerns about the presence of human remains and

ordnance.

CoastalThere is an enormous range of archaeological material found at the coast. Some of it was intended

to have a coastal location, such as landing sites, ship‐building sites, fishing infrastructure, defensive

installations and a range of industrial sites for the production of salt and pottery, for example. Some

archaeological material just happens to be present at today’s shoreline as a result of coastal change.

The widest range of periods may be represented, from early prehistory to the Modern period.

Coastal archaeology ranges from important prehistoric deposits buried under beaches through to

historic buildings and standing ruins, including designated sites such as Listed Buildings and

Scheduled Monuments.


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LandscapeLandscape is a broad term for a variety of circumstances where archaeological significance arises

from remains that are extensive or are influenced by a large area, and where part of the character of

a place arises from the interest generated by the landscape as a whole, rather than each separate

structure or deposit. On land, it can include ‘designed landscapes’ such as parks and gardens, but

also historic landscapes whose character has arisen gradually from small incremental changes over

very long periods. Landscape is also used as a term that draws together evidence of prehistoric

inhabitation in now‐submerged areas of the UK Continental Shelf, and also to identify wider patterns

of ship‐ or aircraft‐based activity offshore. Landscape can encompass elements of the other

categories above, but is distinguished here as an additional category because it introduces particular

perspectives on dealing with the historic environment at large scales.

ImpactsandEffectsThe impacts caused by offshore windfarms can have a variety of effects on archaeological heritage.

The choice of foundation solution, however, is only going to be of incidental relevance to the

assessment of some archaeological effects. Specifically, the choice of concrete gravity bases is

unlikely to have any distinct effect, as compared to other foundation solutions, on the following:

Visual effects on historic landscapes and seascapes, as perceived by people either on shore

or offshore.

Effects from inter‐array and export cabling, which are not affected by choice of foundations.

Although these impacts will have to be assessed in respect of any particular offshore windfarm

development, they are unlikely to be altered by choosing CGBF instead of other methods.

It is also likely that the following potential archaeological effects can be scoped out with respect to

CGBF:

Effects on coastal archaeology prompted by changes to wave energy reaching the shore, to

sediment transport etc., as any such changes are likely to be minor or indiscernible in terms

of, for example, archaeological material being newly washed out of adjacent foreshores.

Effects attributable to smothering / plume. The effects of deposition of fine‐grained material

over artefacts, sites and deposits are unlikely to be distinguishable from cycles of naturally‐

occurring deposition. In any case – and in general terms – deposition of fine‐grained

material is likely to be beneficial to the future survival of archaeological material, though it

may result in some masking to visual or geophysical survey.

Effects attributable to off‐site dredging of sand and gravel. It is assumed that any such

external material will be acquired from sources that are subject to archaeological

assessment, mitigation and monitoring in the course of their own consenting processes.

From the above it will be apparent that the effects of the use of CGBF on the categories ‘Coastal’ and

‘Landscapes’ (above) are indistinguishable from the effects of other foundation solutions.

Consequently, the remainder of this section will focus on impacts and effects relating to Prehistory,

Maritime and Aviation archaeology.

It should be noted that whilst impacts on landscapes as a whole from CGBF may be indistinguishable

from other solutions, impacts on landscape elements – e.g. specific horizons of prehistoric


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archaeological interest, or individual wrecks that might be interpreted within a broader setting –

may be greater as a consequence of the use of CGBF, steel jacket, tripods or suction caissons. Hence

although ‘landscape’ impacts might not be relevant in choosing CGBF, this is not to suggest that they

do not have impacts that are relevant to landscapes. These impacts can, however, be addressed in

terms of Prehistory – Maritime – Aviation, as below.

Archaeological material of prehistoric, maritime or aviation interest is generally fragile and non‐

renewable. Although archaeological material may have survived in its location for thousands of

years, disturbance is likely to destroy the all‐important relationships between artefacts, structures

and their surrounding matrix directly, or as a consequence of physical, biological and/or chemical

processes triggered by the disturbance. In consequence, archaeological material should be regarded

as having a low tolerance to being disturbed, low (no) adaptability to disturbance, and low (no)

recoverability. Where disturbance is unavoidable and the site is to be extinguished, mitigation must

focus on seeking to conserve the significance of the archaeological material and its relationships by

investigation, recording, recovery and analysis, coupled with material conservation of artefacts and

structures that are recovered.

EffectsonArchaeologicalHeritageAssociatedwithCGBFThe effects where the decision to adopt CGBF is likely to significantly alter the conduct of EIA and

associated licensing and management are set out below:

Direct:SeabedPreparation(ifrequired)Archaeological material of prehistoric, maritime or aviation interest is most likely to occur in the

upper few metres of seabed, especially in areas where the seabed is sufficiently consolidated to be

suitable for CGBF. As noted above, archaeological material is highly susceptible to physical impacts.

Consequently, the greatest potential archaeological effects arise where the seabed is subject to

direct impacts of the sort associated with ground preparation.

Impacts will vary according to the geology and morphology of the foundation site, the details of

ground preparation, and the presence and character of any archaeological material present.

If geological strata are present that predate the inhabitation of the British Isles, either at the surface

or just below, then any archaeological material will be present at or above bed‐level, or within the

veneer of overlying material. However, it should not be assumed that the presence of exposed rock

will mean that no archaeological material is present. Such material can survive extraordinarily well

even in small niches of shallow sediment or in fissures. In some cases, the highly localised

hydrodynamic influence in the past of a structure such as a wreck can cause scouring, such that

archaeological material can bury itself within even relatively hard seabed materials.

If the seabed comprises recent (i.e. post‐transgression Holocene) mobile sand then there is potential

for very substantial remains to survive buried within and beneath the sand itself. Sand may also

overlie features that have provided a suitable niche for archaeological material, such as in‐filled

channels. Large sandwaves, or even relatively thin mobile sand that overlies softer fine‐grained

deposits, can hide entire shipwrecks.

Where the seabed is comprised of generally stable gravels and sands of pre‐transgression origin,

there is also the possibility that structures such as wrecks may bury themselves through the action of


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localised scouring processes. The sands and gravels also have archaeological potential too, as they

may contain or comprise artefacts and deposits from very early prehistory.

CGBF has the advantage over pile‐based and suction caisson approaches in that it will not have a

direct impact on deeper horizons of archaeological interest. However, the area and depth of seabed

preparation for CGBF is likely to be greater within the important top few metres than is typically the

case for piled foundations. Effects will be minimised where seabed preparation can be reduced, e.g.

by reducing the margin of over‐dredging around and below the foundation, and through the use of

designs that require less excavation because they can adapt to non‐level ground.

The scope for mitigating impacts will be greatest where detailed site investigations become available

at an early stage, to help establish the presence and character of any archaeological material at the

foundation location. Where site investigation data has been acquired in a way that optimises its

archaeological use, such data may also provide contribute to mitigation where impacts are

unavoidable.

Direct impacts attributable to ground preparation are largely confined to the construction phase.

Subsequent seabed works during operation and maintenance, and decommissioning, might be

expected to be restricted to the horizontal and vertical extents of construction. Heritage assets do

not recover; impacts during construction are likely to be such that impacts in subsequent phases will

be of minor concern. The key exception to this is if groundworks in the operational phase or during

decommissioning cut into areas that have not previously been affected, then archaeological effects

could certainly arise. The potential for operational and/or decommissioning impacts on the

archaeological heritage will be greatest where archaeological material is close to – or continues from

– the footprint of the original seabed preparation. This scenario might arise, for example, where a

CGBF has been micro‐sited to avoid a heritage asset in order that construction‐phase effects are

minimised; but this constraint is not taken into account when managing operational activities on the

seabed, or during decommissioning.

Direct:ScourProtection(ifused)Scour protection will extend the seabed footprint of direct impacts on material of archaeological

interest, especially if the installation of scour protection requires prior preparation of ground that

has previously been undisturbed. It may be possible to install scour protection on top of buried

archaeological material without prompting a direct impact. However, assessment will need to take

into account secondary impacts on the underlying archaeological horizons from the imposition of

extensive, weighty material.

The installation of scour protection over material of archaeological interest will have the effect of

precluding access to that material in future, either for research purposes or by the public.

Obstructing access may be regarded as a significant effect, even if the material itself is not subject to

direct impacts.

As above, installation of scour protection is predominantly a construction‐phase impact. Impacts

from scour protection during operation and decommissioning will be limited to circumstances where

the original footprint of works relating to scour protection extend – vertically or horizontally –

beyond the seabed that has already been affected.


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Direct:VesselActivityImpacts on archaeological material can arise from construction vessels where those vessels have

contact with the seabed, either through anchoring or from jack‐up footings etc. Depending on the

detail of anticipated vessel activities, CGBF may have a lower archaeological impact attributable to

vessel activities than installation of pile‐based foundations. Archaeological concerns can be

alleviated by careful management of vessel activity with respect to seabed impacts.

Impacts from vessel activity could occur in each main phase: construction; operation; and

decommissioning.

Secondary:ScourScour may affect archaeological material in the same way as seabed preparation, except that the

process is not under the immediate control of construction and environmental management

personnel. Archaeological material of prehistoric, maritime or aviation interest may be displaced,

disrupted, removed from its surrounding context or subjected to renewed physical, chemical or

biological processes as a result of scour. The horizontal and vertical extents of scour, and its

archaeological implications, will depend on the geological/ geomorphological character of the site

and the presence and character of archaeological material. The comments above on seabed

preparation are generally relevant to scour also.

Impacts attributable to scour are most likely to become apparent in the later stages of the

construction phase and in the operational phase.

Secondary:ChangestoBedformsandSedimentFluxesAny change in the seabed attributable to hydrodynamic and sedimentological processes could have

implications for the survival of archaeological material. The greatest concern arises where

archaeological material that was buried becomes exposed, as it may collapse and / or suffer from

renewed physical, chemical or biological processes that result in its decay.

As with scour, impacts attributable to scour are most likely to become apparent in the later stages of

the construction phase and in the operational phase.

Secondary:AccessibilityAs noted above, any process that results in access to archaeological material being prevented or

constrained may be regarded as an impact, because the scope to research the material or to enable

visits by the public are curtailed, compromising the capacity to realise the material’s significance.

Accessibility may be curtailed where archaeological material is overlain by the foundation and any

scour protection. Insofar as CGBF and any scour protection are likely to be more extensive than pile‐

based foundations, then the possible impact from CGBF may be greater than piling. Nonetheless, it

may be more likely that in the event that archaeological material is identified below a proposed

CGBF and any scour protection, if required, then the impact is mitigated by avoidance (re‐siting the

CGBF) or by investigation in advance of construction if there are concerns about the effects of

placing a foundation above archaeological material.

The wider impacts of offshore windfarms on archaeological material as a result of reduced

accessibility – acting at larger scales where, for example, access for research or public appreciation is


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curtailed by the presence of safety zones – is unlikely to be greater for CGBF than for other forms of

foundation.

Accessibility may be an effect throughout the construction, operational and decommissioning

phases.

CumulativeEffectsCGBF are not distinguishable from other forms of foundation in terms of cumulative effects on

archaeology, except in relation to cumulative inter‐array impacts from seabed preparation and scour

protection / scour on horizons of prehistoric interest. Where there are horizons of prehistoric

interest within the vertical and horizontal footprint of CGBF seabed preparation, then the overall

extent of seabed preparation might be regarded as having a substantial cumulative effect.

This matter is unlikely to arise in respect of material of maritime and aviation interest because such

sites are usually not closely associated with each other at windfarm scales.

8.7 Summary A comparison of the relative magnitude of effects, between a single monopile and single CGBF, is

presented considering the evidence reviewed in this section. Note that the effects of a large number

of small foundations, compared with a smaller number of larger foundations, is not yet well


Key


Receptor Sub‐receptor Description Effect occurrence

Relative effect

Scale Significance

Human Fishing activity Displacement of fishing activity from the vicinity of the foundation



Other vessel activity

Displacement of other vessel activity from the vicinity of the foundation




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Navigation Displacement of shipping from established navigation routes



Infrastructure Impact on renewable energy, oil and gas, cables, pipelines, disposal sites, tourism, recreation



Archaeology Potential impact on palaeo‐landscape surfaces

I CGBF similar to other Round 3 solutions in most cases


" Potential impact of placement and/or scour on known wrecks and aircraft remains



" Potential impact of placement and/or scour on unknown wrecks and aircraft remains




115

9 CumulativeandIn‐combinationEffectsThe EIA Directive (see Section 2.1) requires consideration of the direct impacts and of any indirect,

secondary and cumulative effects of a project.

Therefore cumulative impact assessment (CIA) forms part of the EIA process. It considers the effects

of the construction, operation and decommissioning of the project, both intra‐array and with other

offshore windfarm projects as well as other seabed user activities in the area that have the potential

to impact on the same receptors. The nature of potential cumulative effects and their resulting

impacts will depend on the density of CGBFs within a single windfarm, the proximity of other

windfarms and the proximity and nature of other anthropogenic activities.

Under the Habitats and Birds Directives there is also a statutory requirement to consider cumulative

impacts as part of an appropriate assessment if it cannot be determined that a plan or project will

not have a likely significant effect. Article 6(3) states that:

“Any plan or project not directly connected with or necessary to the management of the site but

likely to have a significant effect thereon, either individually or in combination with other plans or

projects, shall be subject to appropriate assessment of its implications for the site in view of the site's

conservation objectives.”

It is generally accepted that in‐combination (under Article 6(3)) is interpreted to have the same

meaning as cumulative as described in the EIA Directive (under Article 4(2)). Article 6(3) is

transposed into national legislation under Regulation 61 of the Habitats Regulations (see

Appendix A) and Regulation 25 of the Offshore Habitats Regulations.

Cumulative Impacts:

Impacts that result from incremental changes caused by other past, present or reasonably

foreseeable actions together with the project under consideration. For example:

Incremental habitat loss from a number of separate windfarms;

Combined effect of individual impacts from CGBFs, e.g. removal, from a single windfarm

on a particular receptor (e.g. habitat); and / or

Several windfarms with insignificant impacts individually but which together have a

cumulative effect, e.g. development of an offshore windfarm may have an insignificant

impact, but when considered with several nearby windfarms there could be a significant

cumulative impact on local, regional or national ecology and landscape.


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Figure 9.1: Flow diagram for assessing cumulative impacts (adapted from Walker and Johnson, 1999).

The introduction of a single CGBF structure has been identified as resulting in a series of

environmental effects (see Sections 5, 6, 7 and 8 of this report). As described in Section 5 and 6

there is limited real world evidence from introduction at a larger discrete spatial scale of concrete

structures into the offshore marine environment; certainly in UK waters. The scientific

understanding of the non‐linear interactions between the marine environment and a larger number

of CGBFs, which are potentially also complex shapes, also remains poor for certain physical

receptors and parameters. It is likely that differing profiles from the various CGBF engineering

solutions will result in variations of effects, alone and combined, and therefore foundation type‐

specific modelling will be required.

Deployment of CGBFs at a scale associated with the Round 3 programme will result in cumulative

effects, at intra‐ and inter‐array levels and with other seabed user activities, which will need

consideration to allow effective EIAs. However this is not restricted to the specific use of CGBFs and

will be required for any Round 3 project, regardless of the foundation structure deployed.

Intra‐Array(Inter‐FoundationandwithinaSingleWindfarm)CumulativeEffectsThe most obvious inter‐foundation cumulative effect will be direct habitat removal and loss of

benthic habitat. This will impact benthic fauna and possibly fish and bird fauna, megafauna and

nature conservation and / or archaeological features and fisheries resources. Consideration of the

extent of the array and location of foundations and the variety of different biotopes affected will set

the initial value of impact. This can then be related to known receptor resource at an appropriate

scale, e.g. within a sediment plume footprint or at regional or sub‐regional sea for mobile receptors,

and considerations of impacts from other activities on the same receptor can then be assessed.

Considering the possibility of a positive correlation between the extent of surface area of artificial

submerged structure and increased reef effects (see Section 7.2.2) then CGBFs (at a cumulative

scale) may result in greater reef effects (including ‘halo’ or ‘fringe’ effects) than foundations with a

smaller surface area. This may result in increased negative effects (damage) to the surrounding

natural sediment habitat and associated infaunal biotopes e.g. increased predation from mobile

macrofauna attracted to the reef habitat. This may also be increased if the inter‐foundation

distances are less than the attractant or impact range of artificial reefs (200‐300m for pelagic fish


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fauna and 1‐100m for demersal fishes, Zucco et al., 2006). However this is extremely unlikely due to

the engineering constraints as discussed below. In effect the CGBFs will act as many isolated reefs

with connectivity only established for more mobile species such as flatfish and marine mammals

(Zucco et al., 2006 and references cited therein).There is also a possible cumulative positive effect

for fish fauna from the potential for increased reef effect, if fishing exclusion zones are implemented

i.e. the foundations act as a refuge attracting fish from areas where they may be exposed to fishery

pressures to a location where they are protected from fishing pressures.

Inter‐foundation distances are likely to play a critical role in the scale of cumulative effects, for

physical, biological and human receptors. Rotor sweep diameter of a 5MW turbine will result in

approximately 800m or greater intervals between turbines and thus foundation structures (Zucco et

al., 2006). These distances and the number of foundations used, along with the shape of the

structures (profile), will dictate the cumulative effects and associated footprint for physical

environmental considerations. As described in Sections 5.3, 6.2.1 and 6.2.2, the complexities of

these interactions will result in blockage effects that will require detailed modelling.

The cumulative effects of the CGBF structures on the physical environment will force biological and

certain human activity receptors to respond to indirect effects such as scouring, changes to sediment

particle size, sediment flux etc. The scale of these physical indirect effects will influence the scale of

biological response e.g. larger areas of scouring or changes to sediment supply will alter the

sediment habitat resulting in habitat loss for certain infaunal species and communities. Similarly,

alterations to tidal streams or sediment flux can result in exposure or burial of palaeolandscape

features or wrecks. These effects will be delivered to a greater extent due to the cumulative scale

but will still need to be considered within the context of the overall extent of any receptor at an

appropriate spatial scale e.g. local, regional, national and international.

Some of the displacement effects associated with the presence of multitudes of CGBFs on the

seafloor may actually not be foundation type‐specific. The presence of anthropogenic structures

regardless of type may prevent a displaced organism from returning to the array footprint, be it due

to direct niche habitat removal, alteration of ecosystems resulting in unfavourable environmental

conditions (e.g. attraction of predators due to reef effect) or behavioural responses. This may

certainly be the case for certain seabirds which exhibit continued displacement due to the above

sea‐surface towers and turbines (see Section 7.5.2 and associated references cited). This latter effect

is independent of foundation type used.

Extra‐ArrayCumulativeEffectsofCGBFswithotherWindfarmsandPlansorProjectsCumulative effects with other windfarms and seabed user activities related to the deployment of

CGBFs at windfarm array scales may include:

Increased area of substratum loss due to CGBF footprints – affecting benthic habitats;

Increased risk of habitat exclusion (fish fauna, seabirds and marine mammals);

Increased long‐term displacement of fishing grounds due to CGBFs;

Increased changes in tidal flow and wave energy regimes;

Increased displacement of fishing activities; and

Increased displacement of shipping.


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Dredging footprint from any ground preparation activity that may be undertaken may be far‐field

and has the potential to interact with neighbouring windfarms and plans or projects. The habitat

removal associated with the foundation pit excavation will have to be assessed at an appropriate

(regional) scale, including habitat loss due to dredge disposal / holding areas.

Cumulative habitat loss and displacement effects are cited as the greatest concern for many

biological receptors (Hiscock et al., 2002; DONG Energy et al., 2006; Zucco et al., 2006; OSPAR

Commission, 2006; Scottish Executive, 2007). The installation of a single OWF using CGBFs may only

result in a negligible loss of benthic habitat (at a sub‐regional scale), but if several OWFs are

constructed on the same habitats within the sub‐region then the scale of extent increases. It may be

foreseeable where cumulative losses of a particular habitat to a series of OWFs using CGBFs, when

combined with loss due to marine aggregate extraction for example, may reach a significant level.

Zucco et al. (2006), DONG Energy et al. (2006) and the OSPAR Commission all note that cumulative

habitat loss and displacement may be the greatest impact regarding certain seabird fauna such as

divers and seaducks and also Harbour porpoise. However it is likely that these cumulative effects are

not CGBF‐specific i.e. it is not expected that CGBFs will result in any greater displacement effects for

these mobile receptors than from the use of other foundation types.

There is some research assessing the cumulative seabed footprint of anthropogenic activities in UK

waters. Eastwood et al. (2007) conducted an assessment of direct physical pressure on the seabed in

UK offshore waters. They concluded that the largest pressure footprint was in relation to selective

extraction effects from demersal and benthic fishery activity; accounting for 5.4‐21.4% of the total

seabed area. In context marine aggregate dredging‐related pressures of extraction and smothering

(from plumes) totalled 1.3% of the UK offshore seabed area. Oil and gas infrastructure related to

<0.1% (assuming averaged foundation footprint of 180m2) with offshore windfarm turbines (based

on 4m diameter monopiles with average 100m diameter scour effects) also accounting for <0.1% of

the offshore seabed area.

More recently Foden has reviewed the Eastwood et al. (2007) data and revised the extent of

anthropogenic pressures in UK waters (Foden, 2011; Foden et al., 2011). She estimated that 52.2%

of the UK seabed (134,400km2) has been exposed to demersal and benthic fishery activity related to

abrasion pressure. Using data from the period 2001‐2007 the abrasion pressure (from scouring)

related to offshore wind turbine foundations was evaluated at <0.01% of the total UK seabed

(assuming circular buffers of 100m diameter equalling an area of approximately 7850 m2 per

turbine, minus area of scour protection). Obstruction (direct habitat removal) from foundation

footprint equated to <0.01% of the seabed area (assuming the status of Round 1 and 2 OWFs built

up to 2007; and using a circular buffer of 30m diameter equalling an area of approximately 700m2

per turbine). Obstruction related to submarine cables and wrecks was <0.01% each and smothering

pressure from licensed dredge fines disposal covered 0.14% of the UK seabed. Extraction (removal)

pressure due to marine aggregate dredging activity resulted in removal of 0.05% of the seabed area.

Whilst these figures (at 2007) do not directly account for pressure footprints from large‐scale

deployment of deepwater foundations, such as CGBFs or steel jackets, it can be seen that offshore

wind turbine foundation‐related pressures sit well within or are comparable with other sector‐

related seabed pressure footprints. In this context it is worth considering that for certain CGBF


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solutions the foundation seabed footprint is approximately 0.7% of the total windfarm area, and can

be 0.06% after filling and scour protection is complete (Robert Foyle, STRABAG, pers. comm.).

Foden et al. (2011) also evaluated the cumulative footprint where more than one pressure from one

or more activities overlapped on benthic habitats and biotopes. In 2007 only 166km2 or 0.07% of the

UK seabed was estimated to be receiving combined pressure (from demersal trawling and marine

aggregate extraction). Approximately 0.2%, an area of 513.4km2 was receiving a cumulative pressure

from obstruction, extraction and smothering. Effectively >99.9% of anthropogenic pressure, based

on spatial area of effect between the period 2001‐2007, was due to demersal and benthic fishery

activity.

It is important to note that the above spatial footprint analysis is only meaningful for seabed

pressures and cannot be used to draw conclusions regarding far‐field effects such as noise‐related

disturbance or displacement effects. Further, the work conducted by Eastwood and Foden and

colleagues assesses the footprint at a national scale. At a regional and sub‐regional scale there will

be areas of seabed and associated features that have a high representativity of the entire national

resource e.g. an archaeologically important hand‐axe site or a major herring spawning site. It is for

these reasons that project‐specific EIA are required to assess cumulative effects at a site‐scale.

It is worth stating that considering anthropogenic noise impacts, there is a route for positive

cumulative effects if all Round 3 projects were to use CGBFs, in place of pile‐driven foundation

solutions. This would result in a significant reduction in high significance noise impacts associated

with piling. Any projects that use large‐scale deployment of CGBFs should certainly not be

considered as a significant addition to cumulative assessments of underwater noise impacts

associated with OWF construction / installation.

Human receptors often interact and as such are prone to cumulative and in‐combination effects.

Displacement of activities from the proposed windfarm area can potentially result in increased

activity elsewhere. This may occur within the same or similar sea‐space for certain activities resulting

in a significant in‐combination effect on certain receptors. For example, navigational shipping routes

could be transferred around the windfarm area, to a location where fishing activity has traditionally

been high. The increased vessel movements in the region may make the area difficult to work for the

fishermen and dangerous for shipping to transit through. Again these effects are not necessarily

CGBF‐specific.

In addition, if several windfarms are located in relative close proximity, the displacement effects of

the windfarm sites could concentrate human activities / receptors into the same or similar sea areas.

This could not only potentially increase the risk of collisions, but may also increase the pressure on

sensitive receptors such as commercial fish.

Displacement of fishing activity can also result in increased fishing effort elsewhere. As a result,

increased pressure can be placed on specific receptors which could result in a significant effect

occurring outside the boundaries of the windfarm site. While it is difficult to predict the exact

location, nature and consequences of such displacement and increased effort, the ES should

consider these effects in the context of existing fishing activity, landings data and historical trends.


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Plumes arising from other activities may also cause an in‐combination effect on Diving. For example,

if a windfarm and aggregate extraction site are located within a single tidal extent, during the ground

preparation (if undertaken) and emplacement stage of the CGBF, plumes could potentially be

present over a larger area, precluding diving from some sites.

As a result of the reef effect from the CGBFs and their remediation, it is possible that a ‘halo’ is

produced around the foundations in an array as a result of the cumulative effect of many CGBF

reefs. As a result, fishing activity may increase close to the boundaries of the windfarm site (due to

‘spill‐over’ effects) where it is deemed safe to fish, but where traditionally fishing has not been a

core use of the sea‐space.

SignificanceIt is not possible to quantify the cumulative effects in terms of effect significance. This is due to the

levels of uncertainty associated with project‐specific envelopes, inter‐foundation distances,

clustering / spacing of OWFs and combined effects with other sectoral activities. In fact the latter of

the three may currently be the easiest to consider through realistic worst case scenarios, certainly at

the more generic pre‐application phase and with the Round 3 zones already identified.

The potential for cumulative effects may be identified within an REA or SEA, prior to EIA. In the UK it

is envisioned that the current round of marine (spatial) planning, by the MMO to meet the

requirements of the Marine and Coastal Access Act 2009, may identify regional sea‐scale constraints

from cumulative effects and partition sea use accordingly. However the efficacies of these marine

plans are yet to be seen.

SummaryAs identified in this report, effects on alterations to wave climate, sediment transports pathways,

habitat removal or loss through exclusion and displacement effects will certainly need to be

considered cumulatively for CGBFs. Also the combined effects of artificial structures resulting in reef

effects will have to be considered and it may be that CGBFs will have a greater contribution to these

effects (both negative and positive) than some other foundation structures e.g. monopiles.

The profiles of some CGBF solutions mean that blockage effects are likely to be complex. When

considered cumulatively at an array scale, then these blockage effects may reach a significant

threshold. However until inter‐foundation distances can be confirmed and known profiles

(dependent upon the engineering of specific CGBF solutions) input, non‐linear modelling will remain

challenging.

Cumulative displacement effects from CGBFs on mobile fauna such as fish, seabirds and marine

mammals will be variable when compared with monopile foundations. It is envisaged that there may

be a greater benthic habitat loss that associated with CGBF cumulative effects but alteration at an

ecosystem scale e.g. reef effect may be greater and result in positive, attractant effects. The lack of

significant noise during emplacement will result in lower cumulative effects that installation of

foundations requiring piling. This may be significant for fish and marine mammal fauna. Considering

bird fauna specifically, it may be the case that CGBF cumulative effects on direct habitat loss may be

masked by greater displacement impacts associated with the above water presence of transition

pieces (towers) and turbines.


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10 DecommissioningConcrete is extremely durable and does not corrode to the same extent as steel structures placed in

the marine environment. Therefore, CGBFs will have a minimum design life of 50 years (the life

expectancy of the wind turbine is 20‐25 years), with the foundation able to be used to re‐power for

the next generation of 10MW wind turbines with a small amount of work (Alan Bromage, TCC,

pers. com.).

However, there may come a time when the CGBF needs to be removed and / or replaced. The

methodology for undertaking these works is likely to be the opposite of those utilised during

emplacement works. If used the fill and / or scour protection surrounding the structure may need to

be removed to allow the CGBF to be freed from its emplacement position and removed from the

site. The methods utilised for removing this material is not currently known and will vary from site to

site, but it is likely to be similar methodologies utilised to place the scour protection and fill material

during emplacement works. Once removed, the CGBF could be taken to an onshore site where the

structure could be broken up, reinforcing metal bars could be removed and recycled, and the

concrete itself could be recycled for use as aggregate.

In addition, further mitigating actions may need to be undertaken to restore the seabed to its pre‐

emplacement condition. This may require the removal or burial of any ballast and / or foundation

material and scour protection and replacement of the seabed sediments that existed prior to the

emplacement of the structure. All materials removed will need to be disposed in a suitable location

e.g. licensed disposal site, or reused as aggregate for other projects if the material is deemed

appropriate.

Alternatively, as a result of the additional habitats that may have been established during the

lifetime of the CGBF, there may be a requirement to leave the structures in place. The increased

biodiversity and “reef effects” associated with the structure may require the structure and any scour

protection measures to be left in place following decommissioning of the wind turbines. In this case,

some minor mitigation may be required to ensure that the CGBF is not a hazard to shipping and

other users of the sea, but the structure and scour protection measures would be required to be left

as they were when the windfarm was operational. Over time, without the maintenance required to

keep the CGBF operational, it is likely that the structure would eventually degrade and result in a

smaller, less prominent reef structure being present on the site.

The potential effects of decommissioning on the marine environment have be summarised in

Section 5.2.6, with the potential effects on the physical, biological and human environment

described in Sections 6, 7 and 8 respectively.


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11 DiscussionOffshore wind is a rapidly developing industry which is evolving towards bigger projects, further

offshore and in deeper and more exposed areas of the sea. In the UK the primary achievements to

date remain in constructing smaller scale projects generally using steel monopile foundations. At this

time, in UK waters, monitoring evidence of windfarms at construction and the initial periods of

operation is mainly related to the monopile option only. However, evidence is available from a

limited number of deployments in the North Sea environment, predominantly from Denmark and

Belgium for CGBFs and also Germany for steel jacket and tripod foundations.

Windturbinefoundations–AUKperspective,Round1and2andmovingtowardsRound3UK Round 1 and 2 offshore windfarms are predominantly restricted to nearshore waters and are

located in water depths generally less than 20 m deep. These water depths, and the suitability of the

substrate, has resulted in UK developers implementing near exclusive use of steel monopile

foundations for construction of the arrays (notable exceptions are Beatrice Demonstration Site and

Ormonde Offshore Windfarm having used steel jacket foundations). Most projects since Round 1

have been consented with regard to understanding their potential environmental effects using a

conservative approach often profiled around a gravity base option i.e. as part of the Rochdale

Envelope approach.

The next round of offshore windfarm development zones are identified primarily for deeper waters,

with a mixture of seabed types, which are typically further offshore than the previous Round 1 and 2

arrays (Rampion and Navitas Bay are notable exceptions at only 13km offshore). The different

physical environment will require the consideration of alternative foundation solutions to those that

the UK market has used to date. It is apparent that these offshore locations and the associated

physical environments for Round 3 zones means that those involved in the consenting process will

have to consider the different environmental impacts of these alternative designs as a standard for

the deeper water sites.

Water depth and seabed geology have an influence on the engineering parameters required to

provide a stable foundation for turbines – particularly regarding turbines of a 5 MW capacity and

above. Monopile structures are less suited to deep water depths as they can become unstable due

to hydrodynamic stresses including susceptibility to wave action (Seidel, 2010) and the possibility of

larger storm wave loadings means more resilient grouting at the foundation / transition / tower

connection. Taller monopiles are also less stable when considering the effects of rotor sweep and

transmission of rotational forces / cyclic loading through the tower and foundation making it difficult

to meet the requirements for turbine operation. Increased water depth will require greater

penetration depths for monopile solutions and structural resilience results in increased diameter of

monopiles and thicker pile walls meaning more steel required to build each foundation. Given

today’s market forces and the cost of steel, this alters the cost / benefit balance for the use of this

solution. Should monopiles still prove financially viable, for the deeper penetration and larger

diameter monopiles, a significantly larger hammer will be required to drive the piles into the seabed.

Therefore, noise effects are likely to increase, and will propagate further in the deep water locations

where the Round 3 sites are typically located.


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Alternative, deep water foundation solutions such as suction caisson, steel jacket, tripod and

concrete gravity base will by necessity have to be considered part of the ‘standard toolkit’ for Round

3 installations.

EffectsAssociatedwithDeeperWaterFoundationsHistorically the non‐monopile solutions have been considered as providing the realistic worst case

scenario threshold (under the Rochdale Envelope principle) regarding direct seabed habitat loss and

interruption of hydrological and sediment transport processes – blockage effects for Round 1 and 2

developments. Whilst these assessments are appropriate when comparisons are made with steel

monopiles in shallow water environments, they will require a shift in emphasis for Round 3. The

direct physical effect footprints will have to be considered by drawing comparisons between steel

jacket, tripod, concrete gravity bases and suction caisson foundations and not necessarily monopiles.

All these structures will be larger than has been the case in consented Round 1 and 2 projects. These

solutions have an increased direct physical footprint but there is variation between the different

solution types.

The spatial footprint analysis of the foundations shows that CGBFs can have a comparable physical

footprint for seabed habitat removal (during the life cycle at sea) when compared to steel jacket,

tripod and suction bucket foundations. This relates to a direct loss and alteration of seabed habitats

and associated communities, both individually per foundation and cumulatively; either within an

array or between windfarms. This footprint also considers ‘halo’ or ‘fringe’ effects associated with

seabed shadowing e.g. seabed located beneath the lattice of a steel jacket but not under one of the

feet, which may also be applicable to tripods.

It is also worth noting that CGBFs and suction caissons have a distinct advantage considering the

complete removal of the structure at the time of decommissioning. No piles are used to secure the

foundations to the seabed unlike steel jackets and tripods (and possibly floating platforms) where

the complete removal of piles from the seabed at decommissioning is currently unproven.

Alterations to, or effects on, the physical environment will be more complex to model for deeper

water foundation types when compared to monopiles. This is in part due to the more complex

profiles of the foundations and part due to increased water depth and the variations this brings to

wave energy transfer to the seabed. This in turn may affect tidal currents and surface and near

seabed sediment transport systems in different ways than for shallow water environments. The

number of foundations used within an array and the inter‐turbine spacing will also add complexity to

the non‐linear models. These models and scenarios have yet to be tested in a UK context, but there

are developments in other European countries that may provide an insight into this area of EIA work.

Test bed projects and pilot studies are envisaged in the near future in Germany and the UK. Careful

consideration of environmental monitoring programmes associated with the deployment of these

test‐bed studies is advised. This may enable solution‐specific data, relevant to physical and biological

environmental issues. to be collected to better describe the likely specific environmental footprint of

each solution type. These opportunities should be seized to assist in ‘filling’ the UK‐specific

knowledge gap regarding large‐scale deployments of CGBFs.

The general location of most Round 3 zones means that less of a focus may be required on coastal

impacts studies than has been the case for Round 1 and 2 arrays. Deeper water means that an


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alteration to the local wave climate and subsequent wave‐induced effects are much less likely to

impinge upon the seabed or reach the coast. Any local changes to tidal currents or surface sediment

transport pathways are similarly less likely to interface with coastal systems. Modelling will be

required at a project‐specific level to inform an EIA, but overall this could be of less concern than for

Round 1 and 2 projects. It is noteworthy that Rampion and Navitas Bay sites are located only 13km

from the South Coast and it is expected that detailed coastal impact studies will be required for

these arrays.

The water column profile of the deeper water foundations will be greater and more complex than

monopile profiles. This is in part due to the size of 5 MW (and greater) turbines and partly due to the

larger footprint required to provide a stable foundation. The profiles are likely to provide more

complex blockage effects and localised changes to the physical environments when considered alone

and also at an array scale. Steel jacket foundations may have a similar or greater blockage effect

than CGBFs due to their complex structure profile and surface area. The magnitude of these effects

has to be considered within the context of the known extent of environmental resources at a

regional sea scale and as part of appropriate marine planning and management i.e. even though

there may be a larger footprint per foundation (and array) this can be acceptable in suitable

locations given the entirety of the extent of receptors within a region.

The introduction of all foundation structures onto the seabed will result in a diversification of habitat

type which may have several effects on the natural environment by colonisation of rocky reef

communities on seabed areas previously unavailable to them. The ‘reef effect’ will result in local

changes to biodiversity and possible shifts at trophic or ecosystem scales through: changes to

sediment communities from nutrification by organic material deposited from the ‘reef’; the spread

of some invasive non‐native species through a ‘stepping stone’ effect from habitat provision;

predators attracted to the reef may alter sediment communities for a short distance around each

foundation ‐ ‘halo’ or ‘fringe’ ‐ through predation effects; local fish population dynamics may change

as the structures are likely to act as Fish Aggregation Devices (FADs), attracting fish from surrounding

areas to safety and opportunities that a ‘reef’ provides; and some mobile predatory megafauna such

as seals may be attracted to the relative abundance of prey species.

Reef and Fish Aggregation Device effects, either negative or positive, are not believed to be any

greater for CGBFs than other deeper water foundation solutions, especially when considering

seabed ‘shadowing’ effects beneath steel jackets and tripods.

In UK waters to date, possibly the greatest marine underwater impact associated with the

construction of offshore windfarms is the creation of very high levels of underwater energy, noise

and sound pressure waves, from the piling, drilling and hammering of monopile foundations into the

seabed: which produce underwater sound and pressure waves at high enough levels to cause death,

damage and displacement of marine mammals, sensitive fish species and some fish eggs and larvae.

The significance of such impacts is relatively poorly understood at population or ecosystem scales

and domestic and international legislation now reflects the serious consideration of these possible

effects.

Most importantly, from an environmental perspective, is the consideration of increased water depth

and the attendant forces required to install monopiles. Thicker larger piles require longer piling


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periods with greater sustained hammering using heavier hammers in comparison to shallow water

installation. There is already a level of evidence‐based concern regarding the sound and pressure

wave impacts from the piling operations associated with UK Round 1 and 2 arrays and German

projects and sensitive marine species. Offshore environments may also provide larger potential for

sound wave propagation over greater distances with less potential for attenuation (than in

nearshore environments).

Any CGBFs that require ground preparation works will generate noise associated with the dredging

activity. Evidence from marine aggregate extraction operations demonstrates that dredging noise

levels are barely detected above those associated with general dredger navigation and is no noisier

than merchant shipping vessel transits in the local area. Also the magnitude of effects from seabed

preparation will be very much lower in comparison with marine aggregate extraction areas; due to

the small area of seabed dredged and the time‐limited window of dredging. Not all ground

preparation works may be conducted via trailer suction hopper dredgers, as grab dredging may also

be employed. Noise generated by this activity again falls within the envelope of background coastal

vessel traffic.

Underwater noise impact pathways are still evident for some deeper water solutions such as steel

jackets and tripods, even if monopiles are not used in Round 3 developments. Both steel jacket and

tripod foundations require piling to secure each of the ‘feet’ to the seabed. This will result in

multiple noise emissions per foundation. Therefore increased noise impacts are a reality that,

moving into the future, will require closer scrutiny than previously.

More rigorous consenting procedures are now in place due to the implementation of marine

environmental legislation such as the Habitats Directive and the Marine Strategy Framework

Directive. Demonstration that installation and emplacement of CGBFs is ‘noise‐neutral’ or positive

may mean that the solution type does not have to be on any ‘noise register’, should Defra deem

such a register is required for ‘noisy’ activities as a suitable response to implementing the MSFD.

In this context it is likely that CGBF installation and emplacement will provide a very positive

foundation solution for Round 3 arrays due to the fact that no piling is required. This means that one

of the major environmental impacts associated with offshore windfarm developments can easily be

mitigated.

Deep water foundations also impact upon the human environment in a number of ways. The

changes to the physical and biological environment can affect the livelihood of fishermen operating

within the region. Reef effects may attract fish to the foundations away from ‘traditional’ habitat

areas and fishing grounds. However, fish aggregations may also allow fisheries to develop in areas

alongside windfarms. Archaeology is also a major consideration for the human environment.

Archaeological receptors tend to be located within the first few metres of the geological units on the

seabed, which may be impacted by the deep water foundation itself, or through any seabed

preparation required, scour and secondary impacts. However these possible effects are not CGBF‐

specific in their nature.

Overall, evidence from the examples identified to date suggests that the impacts from GCBFs are

broadly comparable to other foundation types likely to be used throughout Round 3 developments

in the UK. Furthermore, the significant advantage over other foundation types is the lack of


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significant levels of underwater noise emissions generated during installation, which many of the

other foundation types require to secure them to the seabed. This presents a very significant

advantage to developers should they choose to use CGBFs for Round 3 projects.


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12 ConclusionsGiven the environmental constraints associated with Round 3 zones it is unlikely that monopile

foundations will be a viable solution in a large number of cases for the next generation of UK

offshore windfarms. Of the deeper water engineering solutions steel jackets, tripods, suction

caissons, floating platforms and concrete gravity base foundations are suitable for Round 3

installations.

Through review of recent offshore windfarm construction case studies and environmental

monitoring programmes, and in the context of the known use of concrete in the marine

environment, the report is able to make some evidence‐based statements about the use of CGBFs

for Round 3.

BlockageEffectsCGBFs at a generic level have similar physical blockage effects to other deeper water foundation

solutions. The intricacy of a steel jacket structure is likely to have a greater effect on the water

column, but this may be mitigated by the reduced surface area interacting with the water column

when comparing effects from CGBFs. It is reasonable to expect similar levels of effects between

CGBFs and suction caissons where design parameters are similar: the two solutions in some cases

present similar profiles to the water column.

As already identified by solution providers, complex non‐linear modelling will have to be conducted

to evaluate environmental responses to each solution’s size, shape and profile. Water depth and

exposure to storm wave events will have to be factored as part of the process. In most cases for

Round 3 zones (notable exceptions being Rampion and Navitas Bay) it is anticipated that CGBF‐

related effects on physical receptors may be mitigated by distance from shore and water depth.

CGBFs, at a generic level, have similar physical blockage effects to other deeper water foundation

solutions. However, their different frontal and surface areas will result in localised effects on waves,

tidal currents and sediment transport mechanisms that may differ from steel jacket and tripod

foundations.

SeabedFootprintofFoundationRound 3 projects are likely to result in greater direct seabed footprints per foundation in comparison

with the majority of Round 1 and 2 arrays. This is related to the deeper water offshore environment

and technical and cost constraints associated with wide‐scale use of steel monopiles in these

offshore environments. Therefore there will be a shift to the use of alternative foundation solutions.

The direct physical effect footprints will have to be considered by drawing comparisons between

steel jacket, tripod, concrete gravity bases and suction caisson foundations and not monopiles.

These solutions have an increased direct physical footprint (in comparison to shallow water

monopiles) but there are variations between the different solution types and CGBFs can have a

comparable seabed footprint.


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SeabedPreparationandScourProtectionIt is important to note that preparation of foundation pits and the deposition of foundation layers

are not required for all CGBF designs and depends on the construction and installation methodology

selected by each solution provider.

Where preparation of the seabed is required then CGBFs and suction caissons are likely to result in

larger footprints of effects than steel jackets or tripods and certainly floating platforms (though it is

unlikely that this solution will be marketable in time for Round 3 developments). Foundation pit

excavation will result in a temporary direct habitat loss with an associated sediment plume and

resultant indirect effects from smothering and seabed bedform alteration. These footprints may

significantly increase the overall impact zones, but may not result in permanent damage to benthic

communities. However permanent effects on sub‐surface geology and archaeology may occur. The

scale of biological impact will, to a large degree, be based upon the sediment habitats affected and

benthic community recovery periods and tolerances to dredging impacts e.g. mobile sand habitats

may recover within 6‐24 months to extraction and within days or weeks to smothering, whilst low

energy environment consolidated gravel communities may take greater than 8 years to recover from

extraction and smothering.

Scour protection, if required, will result in direct loss of seabed habitats, biological communities and

possibly archaeological features (if the latter are present). All foundation types may require scour

protection so the magnitude of effect relates to the total additional area per foundation and is

generally site‐specific.

It is anticipated that ground preparation for suction caisson foundations will result in smaller scales

of effect to CGBFs. Both of which, where required, will have a greater effect footprint than for Steel

Jacket and Tripod foundations which generally do not require extensive seabed preparation.

Where preparation of the seabed is required then CGBFs and suction caissons will initially result in

larger footprints of effects than steel jackets or tripods, which are less likely to require sea bed

preparation. But recovery from these effects is expected within the lifespan of the windfarm project.

Steel jacket and tripod foundations may require scour protection which will add to the overall

seabed footprint of the structures; similar to the cases for some monopile foundations associated

with Round 1 and 2 installations.

ReefEffectsReef effects due to the presence of artificial hard substrata deposited on the seabed will apply to all

foundation types (though not anticipated to be great for floating platforms), regardless of water

depth or distance from shore. The evidence base demonstrates that more complex shapes providing

crevice and niche‐like spaces are likely to result in higher biodiversity of colonising rocky reef species

than smooth or simple surface relief structures e.g. the complex structure of steel jackets may

provide greater niche habitats for reef species and result in increased biodiversity than large

concrete surfaces. ‘Reef halo’ predation effects are not shape related but larger structures at the

seabed surface will have larger halos than smaller structures due to larger predator populations they

support. Changes to sediment communities and recruitment of different species have been recorded

in association with foundation structures.


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The area of seabed directly below a tripod or steel jacket structure can be expected to be altered

due to a high incidence of reef effects. These will manifest through altered hydrodynamics,

nutrification and predation and result in a larger area of natural habitat loss than that buried

beneath a CGBF (when also considering direct habitat loss to tripod and steel jacket footprint).

Artificial reefs are also known to act as Fish Aggregation Devices (FADs). FADs attract mobile species

of fish to the structures and the size and complexity of artificial structure may bear a relationship to

the size of fish populations attracted to and supported by a foundation structure, though the

evidence base is inconclusive to a large degree. From the evidence reviewed it is difficult to state

that any one foundation solution will have a greater or lesser effectiveness as a FAD.

FAD effects can also have an effect on local fishing activity. It is possible that some fish species may

leave areas of seabed which they have historically favoured in preference for the foundation

structures. However the review of evidence has not shown any quantitative differences between

foundation structure types.

Reef effects due to the presence of artificial hard substrata deposited on the seabed will apply to all

foundation types, regardless of water depth or distance from shore.

Reef and Fish Aggregation Device effects, either negative or positive, are not believed to definitively

be any greater for CGBFs than other deeper water foundation solutions, especially when considering

‘shadowing’ effects beneath steel jackets and tripods.

UnderwaterNoiseImpactsThe review of the current evidence base shows that CGBFs have a large positive noise‐related effect

associated with their installation on the seabed. There are very low underwater noise emissions

when placing the concrete foundations onto the seabed. No piling, hammering or drive‐drill‐drive is

required for CGBFs and this mitigates one of the potentially greatest impact pathways, namely

underwater noise and sound pressure wave impacts on sensitive marine species.

Deeper water environments will require longer piling periods with greater sustained hammering

using heavier hammers in comparison to previous UK monopile installation. Offshore environments

may also provide larger potential for sound wave propagation over greater distances with less

potential for attenuation (than in nearshore environments). Both steel jacket and tripod foundations

require piling to secure each of the ‘feet’ to the seabed. This will result in multiple noise emissions

per foundation.

The concern about underwater noise‐related impacts is growing and domestic and international

legislation now reflects the serious consideration of these possible effects. The use of CGBFs may

mitigate some of this legislative burden for developers.

It is clear that the use of CGBFs and suction caissons will mitigate significant environmental impacts

associated with noise emissions on mobile, wide‐ranging sensitive species such as marine mammals.

As such (due to the unproven nature of suction caissons for use with large turbines – 5MW and

greater) CGBFs are currently the only deeper water, Round 3 foundation solution that can be

deployed that will mitigate noise impacts.


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Evidence shows that emplacement of CGBFs, including seabed preparation (if required) is no noisier

than merchant shipping vessel transits in the local area.

CGBF solutions present a large positive effect when considering near and far‐field noise impacts as

no piling or hammering is required for installation.

One of the major environmental impacts associated with offshore windfarm developments can

easily be mitigated significantly by use of CGBFs.

Overall, in comparison with other currently commercially viable offshore deepwater turbine foundation types, CGBFs will:

Present similar blockage effects;

Have a similar direct seabed footprint (when also considering shading effects and habitat alteration);

Result in a larger, though likely temporary, impact footprint, where seabed preparation is required;

Result in similar reef and Fish Aggregation Device effects;

Provide no greater opportunity for spread of non‐native invasive species;

Have the smallest decommissioning footprint; and

Provide a major environmental and consenting advantage due to mitigation of significant underwater noise impacts associated with installation and emplacement.


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13 ObservationsandRecommendationsReview of evidence used in this report highlights areas of uncertainty regarding some interactions

between the marine environment and CGBF structures. To provide resolution to some of these

issues the following observations are made and recommendations suggested:

Observations

Non‐linear modelling of physical environmental and blockage effects is dependent upon

foundation solution‐specific engineering design and emplacement criteria;

o The engineering solutions have different dimensions and profiles which will result in

variations in effects – the physical environment will react differently to each design;

o The numbers and orientation of foundations and their spacing will affect the

responses from the physical environment;

The requirement for ground preparation and foundation pits will vary between solution

types. Clarity of solution‐specific requirements will assist environmental consultants,

regulators and their advisors to better understand impact scenarios;

The lack of significant underwater noise impacts associated with CGBFs is a major positive

effect from the use of this foundation type;

At the decommissioning phase the fate of ballast material and scour protection is unclear.

Consideration by the solution providers and developers should be provided to identify

feasible disposal options and unacceptable ones; and

Some environmental effects and impacts, whilst associated with CGBFs, are not restricted to

this foundation type alone.

Recommendations

Non‐linear modelling of physical environmental effects is dependent upon foundation

solution‐specific engineering design. The various solutions have different dimensions and

profiles. Clarity on these dimensions and any ‘real world’ data acquired by engineers will

assist in running these models for EIA;

Early and clear engagement between the engineers and the regulators and their technical

and statutory advisors (specifically The Concrete Centre, the Gravity Foundation Interest

Group, the MMO and the Offshore Renewable Energy Licensing Group) is advised. Case

history from other seabed user sectors demonstrates that early and continued engagement

can mitigate misunderstandings and result in cost‐effective application s and timely delivery

of projects;

Regulators and their advisors, along with solution providers and developers, need to ensure

that any monitoring requirements are fit‐for‐purpose and CGBF‐specific. Clear hypotheses to

be tested should be expected;

Strategic research to assess generic effects should be considered by regulators, their

advisors and industry. Reef effects associated with artificial hard substrata are common to

many sectors and foundation types, not just the offshore wind sector using CGBFs;

The findings and determinations within this report should be used to inform any ‘realistic


132

worst case scenario’ modelling that the regulators and their advisors conduct to better

inform all involved in delivering Round 3 developments; and

Any opportunity to gather ‘real world’ data should be considered and acted upon pro‐

actively. Deployment of solution types at test bed facilities will enable Pilot Studies to be

conducted. Best practice dictates that early consideration of beneficial monitoring of

environmental effects from the testing of techniques or structures will provide invaluable

data. Consideration to monitoring deployment of multiple structures will start to address

some of the current modelling constraints that can be monitored. Although extra cost will be

involved upfront there are likely to be cost benefits through the pre‐application and

application stages.


133

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Appendices


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A Review of Marine Environmental Considerations Associated with Concrete Gravity Base Foundations in Offshore Wind Developments:

Appendix A

A-1

AppendixA‐RegulatoryFrameworkThere are two routes for the licensing of CGBFs within the marine environment:

1 Through the Marine Management Organisation; and

2 Through the Planning Inspectorate (formally the Infrastructure Planning Commission).

Marine Licences are obtained through application to the Marine Management Organisation (MMO)

under the Marine and Coastal Access Act 2009 (MCAA). The MMO are responsible for licensing of

offshore energy installations where the project is between 1 and 100MW. Guidance for applications

made under the MCAA is provided by the MMO in their guidance notes which is available from their

website http://www.marinemanagement.org.uk/licensing/how/guidance.htm, Marine Management

Organisation, 2011.

A simplified description and overview of the process is outlined in Figure A.1 and can be broken

down into 5 stages, described below.

Stage 1: Screening Determination ‐ The Applicant contacts the Regulator to request their opinion as

to whether the application constitutes a relevant or habitat project, and whether the application

requires an Environmental Statement (ES). The regulator will then contact the applicant with their

decision.

Stage 2: Scoping Determination ‐ Where the application is deemed to require an Environmental

Statement, the Applicant, or their agent, will provide information to relevant consultees that

describe the nature of the development and requests their opinion, regarding the scope of the EIA

and ES. A Scoping Report is then compiled, based on the responses, which describes the results of

the consultation and outlines the scope of the ES. This report is then sent to the regulator to ensure

that their scoping opinion is also captured within the document.

Stage 3: Investigation and Preparation of the Environmental Statement ‐ The Applicant initiates

production of the ES based on the scope agreed in the preceding stages. At the outset of this

process, all consultees are contacted to request that relevant information is made available to the

Applicant, to enable completion of the ES. Data gaps identified are filled with specially

commissioned studies, or other relevant data or studies identified by the Applicant. The Applicant

will also prepare a draft schedule of conditions that will manage or mitigate the significant effects

identified through the production of the ES.

Stage 3b: Informal Consultation ‐ Following completion of the ES, the Applicant may wish to seek

the opinion of consultees regarding its findings and recommendations. Changes may be made to the

application, ES or supporting evidence before finalising the ES for submission (Stage 4).

Stage 4: Submission of the Application ‐ Once the Applicant is content that the evidence presented

within the application addresses the issues raised in the stages above then the Applicant submits the

application to the Regulator for decision.

Stage 5: Follows after Figure A.1.


Appendix A

A-2

Figure A.1: The Application process under the terms of the Marine and Coastal Access Act © Marine Management Organisation


Appendix A

A-3

Stage 5: Final Consultation and Decision ‐ Following receipt of the application, the Regulator will

advertise the application and contact consultees to seek confirmation that they are content with the

application. Following this process the Regulator will make a decision on the application and write to

all parties to notify them of their decision, which may take the form of an approval, refusal or a

public enquiry.

Stage 5a: Appeal ‐ The Applicant may, at the end of this process appeal the decision made.

Applications made to the Planning Inspectorate are made through the Planning Act 2008, which was

amended by the MCAA 2009 and the Localism Act 2011. The 2008 Act was introduced to streamline

the process for decision‐making of nationally significant infrastructure projects, allowing a fairer and

faster process for both communities and developers. The process was administered by the

Infrastructure and Planning Commission (IPC) until April 2012 when it was dissolved and the decision

making powers transferred to the Planning Inspectorate.

The process can be summarised by the following description of the stages of application involved.

Pre‐application – The application is initiated by a developer notifying the Planning Inspectorate that

they intend to submit an application. The applicant is required to consult extensively on the

application prior to submission to prevent issues arising later in the project. This pre‐application

consultation is a process which will vary in scale and length, depending upon the site under

consultation.

Acceptance – Following the formal application of the development, the Planning Inspectorate will

examine the documents submitted for up to 28 days to assess whether the application meets the

legislative requirements.

Pre‐examination – Pre‐examination allows members of the general public to register with the

Planning Inspectorate and submit written representations on the application. This stage takes

around 3 months and includes an informal meeting where everyone that has registered and

submitted their view is invited to attend.

Examination – The examination stage of the process lasts six months. People who have made

relevant representations are asked to provide further details in writing. The Examining Authority

takes account of all the information they have been presented with to consider all relevant

representations, evidence and questions and answers received during the hearing.

Planning Inspectorate recommendation / Secretary of State’s decision – The Planning Inspectorate

is required to submit a report within 3 months of the start of the examination period with a

recommendation to the relevant Secretary of State. The Secretary of State must then make their

decision on the application within the following 3 months of the examination period.

Post decision – Decision may be challenged in the High Court through a process known as Judicial

Review for 6 weeks following the decision from the Secretary of State.


Appendix A

A-4

NatureConservationLegislation

The nature conservation legislation considered most pertinent to the use of CGBFs in the deeper

offshore marine environment is mostly international in nature such as the Habitats Directive EC

Directive 92/43 on the Conservation of Natural Habitats and of Wild Fauna and Flora and the Birds

Directive EC directive 79/409 on the conservation of wild birds. Other international legislation that

may have a bearing upon CGBF installations includes:

The Convention for the Protection of the Marine Environment of the North‐East Atlantic

known as the OSPAR Convention is an intergovernmental treaty encourages International

cooperation to protect the marine environment of the Northeast Atlantic;

The Convention on Wetlands of International Importance called the Ramsar Convention

and is an intergovernmental treaty that provides the framework for national action and

international cooperation for the conservation and wise use of wetlands and their resources.

Ramsar;

The Water Framework Directive (EC Directive 2000/60) is a European Union directive which

commits European Union member states to achieve good qualitative and quantitative status

of all water bodies (including marine waters up to one nautical mile from shore) by 2015;

and

The Marine Strategy Framework Directive (EC Directive 2008/56) is a European Union

Directive which commits European Union member states to achieve ‘Good Environmental

Status’ (GES) by 2020 across Europe’s marine environment.

The most notable domestic legislation pertinent to nature conservation in the marine environment is

the recently enacted Marine and Coastal Access Act 2009. This legislation empowers the delivery of

an ecologically coherent network of well managed marine protected areas by 20102 discussed

below.

National legislation for the designation of conservation sites under the Wildlife and Countryside Act

(1981) as amended and the Natural Environment and Rural Communities Act 2006 is not

considered within this report. Most of the sites, known as Sites of Special Scientific Interest (SSSI)

and Areas of Scientific Interest (ASSI) in Northern Ireland, notified under this legislation are for

terrestrial and coastal features and are unlikely to interact with the effects from CGBFs (see Section

6.2).

The UK Government and the Devolved Administrations are aiming to achieve ‘clean, healthy, safe,

productive, and biologically diverse oceans and seas’. The UK Marine Policy Statement developed

under the Marine and Coastal Access Act 2009 sets out the objectives and priorities to enable that

aim to be realised. Further, the UK Government and the Devolved Administrations have certain

commitments and obligations directing policies regarding marine nature conservation to develop an

ecologically coherent network of well managed MPAs under the OSPAR12 Convention (Defra, 2010).

These are to:

Establish a representative network of MPAs by 2012 under the World Summit for

Sustainable Development (WSSD);


Appendix A

A-5

Establish a network of well managed MPAs by 2012 to enable delivery of WSSD targets

under the Convention on Biological Diversity;

Establish Special Protection Areas under the Wild Birds Directive and Special Areas of

Conservation under the Habitats Directive;

Support the achievement of Good Environmental Status under the Marine Strategy

Framework Directive;

Ensure the continuing delivery of favourable condition on marine and intertidal Sites of

Special Scientific Interest in line with the public service agreement target; and

Support the achievement of Good Ecological Status for estuarine and coastal waters under

the Water Framework Directive.

Projects that may use CGBFs are most likely to have to consider impacts upon:

Special Areas of Conservation (SAC) designated under the Habitats Directive;

Special Protection Areas (SPA) designated under the Birds Directive; and

Marine Conservation Zones (MCZ) to be designated under the Marine and Coastal Access Act

2009 (at the time of drafting this report MCZs are recommended to Defra, who are

reviewing them before designation).

ArchaeologicalLegalandPolicyFrameworks

ResponsibilityThe management of marine archaeology is subject to devolution. Separate administrative

arrangements apply in each home country, and there are separate policies and – in some cases –

legal provisions.

Home Country Organisation Overarching Policy England English Heritage Conservation Principles Wales Cadw The Welsh Historic Environment Strategic Statement:

Headline Action Plan Cadw Priorities 2011‐16 Scotland Historic Scotland Scottish Historic Environment Policy (SHEP) The Marine Historic Environment: strategy for the

protection, management and promotion of marine heritage 2012‐15

Northern Ireland NI Environment Agency

The immediate remit of each agency is territorial waters, but in practice, advice is offered to relevant

regulators in respect of the offshore zones of each home country to the limit of the UK Continental

Shelf.

PolicyThe UK’s overarching policy with respect to marine archaeology is set out in Our Seas ‐ A Shared

Resource: High Level Marine Objectives and in the UK Marine Policy Statement.

HM Government’s aspiration for the next 20 years, as set out in Our Seas – A Shared Resource,

envisages that the marine environment’s ‘rich natural and cultural heritage are better protected’,


Appendix A

A-6

‘the integrity of marine and coastal ecosystems and marine cultural heritage is conserved’, and

‘there will be appropriate protection for, and access to, our marine heritage assets’.

Further detail is provided by the UK Marine Policy Statement, which includes the following passage:

2.6.6.3 The view shared by the UK Administrations is that heritage assets should be enjoyed for

the quality of life they bring to this and future generations, and that they should be conserved

through marine planning in a manner appropriate and proportionate to their significance.

Opportunities should be taken to contribute to our knowledge and understanding of our past

by capturing evidence from the historic environment and making this publicly available,

particularly if a heritage asset is to be lost.

2.6.6.7 In considering the significance of heritage assets and their setting, the marine plan

authority should take into account the particular nature of the interest in the assets and the

value they hold for this and future generations. This understanding should be applied to avoid

or minimise conflict between conservation of that significance and any proposals for

development.

2.6.6.9 Where the loss of the whole or a material part of a heritage asset’s significance is

justified, the marine plan authority should identify and require suitable mitigating actions to

record and advance understanding of the significance of the heritage asset before it is lost.

There is a relatively small number of designated heritage assets that are subject to additional

statutory protection and are also accorded special attention in the UK MPS. However, the UK MPS

also makes the following important statement about undesignated heritage assets:

2.6.6.5 Many heritage assets with archaeological interest in these areas are not currently

designated as scheduled monuments or protected wreck sites but are demonstrably of

equivalent significance. The absence of designation for such assets does not necessarily

indicate lower significance and the marine plan authority should consider them subject to the

same policy principles as designated heritage assets.

In England, further detail on the consideration of archaeology in marine licensing is expected to

emerge in the detail of the regionally‐based marine plans that are either anticipated or in

preparation. The updated Draft Vision and Objectives for the East marine plans (East Inshore and

East Offshore) includes the following objective:

Objective 6: To conserve all heritage assets and ensure that marine development and use is in

keeping with the character of the local area.

In Scotland, the pre consultation draft of Scotland’s National Marine Plan included a section on the

Marine Historic Environment that identified the following ‘key challenge’:

To realise the full potential of the marine historic environment as a resource – cultural,

educational, economic and social.

The following objectives are set out:


Appendix A

A-7

To enhance and promote knowledge and understanding of the marine historic environment

through research, cross‐sector mapping initiatives and dissemination of evidence about coastal

and marine heritage assets

To protect key marine heritage assets through effective marine planning, supported by

statutory designation where desirable

To ensure development within the marine context respects the setting of key heritage assets

on land

To secure greater enjoyment and economic benefit from, key coastal and marine heritage

tourism resources

More specific policies to elaborate the UK MPS are yet to be developed in Wales and Northern

Ireland.

DesignatedHistoricAssetsA relatively small number of heritage assets are designated under a variety of pieces of legislation.

The Protection of Wrecks Act 1973 (PWA 1973) and the Ancient Monuments and Archaeological

Areas Act 1979 (AMAA 1979) have both been used to designate the remains of wrecks on the

grounds of their archaeological importance. The AMAA 1979 can be used to designate a wider range

of heritage asset types in addition to wrecks, though it has not been used extensively in this respect.

The PWA 1973 is used throughout territorial waters across each of the four home countries, but

administered separately by the four national heritage agencies. The AMAA 1979 applies in England,

Scotland and Wales. In Northern Ireland, the Historic Monuments and Archaeological Objects

(Northern Ireland) Order 1995 applies, and includes some generally applicable rules on searching for

and reporting archaeological objects, in addition to provisions on the designation of monuments. In

parallel, the Protection of Military Remains Act 1986 (PMRA 1986) has been used to designation a

variety of vessels in military service lost in UK waters or further afield. The PMRA 1986 also provides

that all military aircraft crash sites are automatically protected. The provisions of the PMRA 1986 are

administered by the Ministry of Defence.

Designated sites at sea are clearly identified in a variety of public sources. Marine planning will take

into account their particular importance, but such sites are also subject to specific legal restrictions –

often requiring a licence for any potentially damaging activities. If a wind farm site is to be

developed in an area that includes designated heritage assets, then it is important that account is

taken of the need for licences – even to carry‐out investigations,

Although the AMAA 1979 and the PWA 1973 remain in force in Scotland, the PWA 1973 is in the

course of being replaced by provisions on Historic Marine Protected Areas (HMPAs) contained in the

Marine (Scotland) Act 2010. Historic Scotland published guidance in March 2012 on how it intends

to select, designate and manage HMPAs.

As well as having a bearing on offshore wind farm proposals where there are already designated

heritage assets present, it should be borne in mind that the same legislation generally makes

provision for the designation of additional sites. This is especially important if an important site


Appendix A

A-8

comes to light in the course of marine development, and where a heritage agency wants a secure

mechanism over and above planning‐based requirements to ensure that the developer takes proper

account of the discovery. The Protection of Wrecks Act 1973, in particular, has been used to

introduce protection very rapidly in cases where sites have been brought to light by development

activities.

OtherStatutoryRequirementsAll archaeological material that meets the legal definition of ‘wreck’ that is found or taken

possession of in UK waters – or brought within those waters – must be notified to the Receiver of

Wreck by virtue of the Merchant Shipping Act 1995 (MSA 1995). The subsequent treatment of such

wreck, including ownership and salvage awards, is governed by the MSA 1995. For wreck that comes

to light in the course of offshore renewable development, adherence to the Offshore Renewables

Protocol for Archaeological Discoveries (ORPAD) will satisfy the requirements of the Merchant

Shipping Act 1995.

GuidanceAs indicated above, pro‐active collaboration between marine industries and archaeologists has

helped establish a range of ‘best practice’ frameworks set out in guidance documents.

JointNauticalArchaeologyPolicyCommittee(JNAPC)The JNAPC Code of Practice for Seabed Development (JNAPC 2006) sets out a general framework for

all forms of seabed development, providing generic guidance on the key steps that marine industries

should consider in safeguarding the marine historic environment in the course of developing and

implementing their proposals.

COWRIECowrie produced three sets of detailed guidance relating to offshore renewables and the historic

environment, as follows:

Wessex Archaeology, 2007. Historic Environment Guidance for the Offshore Renewable Sector

Oxford Archaeology and Lambrick G., 2008. Archaeology and Heritage 2008 Guidance for

Assessment of Cumulative Impacts on the Historic Environment from Offshore Renewable

Energy.

Gribble, J. and Leather, S., 2011. Offshore Geotechnical Investigations and Historic

Environment Analysis: Guidance for the Renewable Energy Sector.

TheCrownEstateThe Crown Estate has published two documents for industry‐wide adoption that are intended to

facilitate the agreement and implementation of specific mitigation measures for historic

environment effects arising from offshore renewables projects:

Wessex Archaeology, 2010a. Clauses for Archaeological Written Schemes of Investigation:

Offshore Renewables Projects.


Appendix A

A-9

Wessex Archaeology, 2010b. Protocol for Archaeological Discoveries: Offshore Renewables

Projects.

EnglishHeritageThe general policy of English Heritage towards wind farms is set out in Wind Energy and the Historic

Environment. The following detailed guidance is also relevant:

English Heritage, March 2012. Ships and Boats: Prehistory to 1840. Introductions to Heritage

Assets.

English Heritage, May 2012. Ships and Boats: Prehistory to Present. Designation Selection

Guide.

AggregateLevySustainabilityFundThe Aggregate Levy Sustainability Fund supported a large amount of highly relevant work on the

range, character, importance and optimum methodologies for addressing the marine historic

environment of the UK Continental Shelf. Although the principal focus was on the potential effects

of marine aggregate dredging, many of the results are applicable to offshore renewable

development. A wide range of detailed reports was made available as a result of the ALSF. The best

guide to these results is to be found in the following summaries:

Bicket, A., 2011. Submerged Prehistory: research in context.

Hamel, A.T., 2011. Wrecks at Sea: research in context.

BibliographyBicket, A., 2011. Submerged Prehistory: Research in Context. Marine Aggregate Levy Sustainability

Fund (MALSF) Science Monograph Series No. 5. Marine Aggregate Levy Sustainability Fund.

Cadw, 2011. “Cadw Priorities 2011‐16.”

http://cadw.wales.gov.uk/docs/cadw/publications/Cadw_priorities_2011_to_2016_EN.pdf .

Department for Environment, Food and Rural Affairs (Defra), 2010. The Government’s strategy for

contributing to the delivery of a UK network of marine protected areas.

English Heritage, 2008. “Conservation Principles, Policies and Guidance for the Sustainable

Management of the Historic Environment”. English Heritage. http://www.english‐

heritage.org.uk/publications/conservation‐principles‐sustainable‐management‐historic‐

environment/ .

English Heritage, 2012a. Ships and Boats: Prehistory to 1840. Introductions to Heritage Assets.

English Heritage.

English Heritage, 2012b. “Ships and Boats: Prehistory to Present. Designation Selection Guide”.

English Heritage.


Appendix A

A-10

Hamel, A., 2011. Wrecks at Sea: Research in Context. Marine Aggregate Levy Sustainability Fund

(MALSF) Science Monograph Series No. 6. Marine Aggregate Levy Sustainability Fund.

Historic Scotland, 2011. “Scottish Historic Environment Policy”. Historic Scotland.

http://www.historic‐scotland.gov.uk/shep‐dec2011.pdf .

Historic Scotland, 2012a. “The Marine Historic Environment: Strategy for the Protection,

Management and Promotion of Marine Heritage 2012‐15”. Historic Scotland. http://www.historic‐

scotland.gov.uk/marine‐strategy‐2012‐15.pdf .

Historic Scotland, 2012b. “Marine Protected Areas in the Seas Around Scotland: Guidelines on the

Selection, Designation and Management of Historic Marine Protected Areas.” http://www.historic‐

scotland.gov.uk/historic‐mpa‐guidelines.pdf .

HM Government, 2009. “Our Seas ‐ A Shared Resource: High Level Marine Objectives”. Department

for Environment, Food and Rural Affairs.

HM Government, 2011. “UK Marine Policy Statement”. The Stationary Office.

http://archive.defra.gov.uk/environment/marine/documents/interim2/marine‐policy‐

statement.pdf.

Joint Nautical Archaeology Policy Committee, 2006. “Code of Practice for Seabed Development”.

JNAPC.

Marine management Organisation (MMO), 2012. “Draft Vision and Objectives for East Marine Plans:

Update.”

Oxford Archaeology, and George Lambrick Archaeology and Heritage, 2008. Guidance for

Assessment of Cumulative Impacts on the Historic Environment from Offshore Renewable Energy.

COWRIE project reference CIARCH‐11‐2006. COWRIE Ltd.

Scottish Government, 2011. “Scotland’s National Marine Plan: Pre‐Consultation Draft.”

http://www.scotland.gov.uk/Resource/Doc/346796/0115349.pdf .

Welsh Assembly Government, Cadw. 2009. “The Welsh Historic Environment Strategic Statement:

Headline Action Plan.” http://www.rcahmw.gov.uk/media/123.pdf .

Wessex Archaeology, 2007. Historic Environment Guidance for the Offshore Renewable Energy

Sector. COWRIE Project ARCH‐11‐05. Newbury: COWRIE Ltd.

Wessex Archaeology, 2010a. Protocol for Archaeological Discoveries: Offshore Renewables Projects.

London: The Crown Estate.

Wessex Archaeology, 2010b. Model Clauses for Archaeological Written Schemes of Investigation:

Offshore Renewables Projects. London: The Crown Estate.


Appendix B

B-1

AppendixB–RequirementforEnvironmentalImpactAssessment

1.1 StatutoryRequirementsThe Environmental Impact Assessment Directive (97/11/EC) (the EIA Directive) requires an

assessment of the impacts that may potentially arise from the development of certain public and

private projects. Offshore windfarms (and consequently their GBFs) require an EIA because the

generation of electricity from wind installations are listed in Annex II of the EIA Directive. The EIA

Directive is transposed into UK law through the Planning Act 2008 and the Marine Works (EIA)

Regulations and enacted through the Planning Inspectorate and Marine Licensing system

respectively.

1.2 ScreeningOpinionThe EIA Directive allows for an applicant to request a Screening Opinion from the relevant authority.

This opinion assesses whether the development requires an EIA to be carried out. However, given

the size, nature and location of offshore windfarm sites (that may or may not utilise CGBFs), it is

unlikely that the requirement for EIA will be screened out at any site.

1.3 ScopingOpinionAs described in Section Error! Reference source not found. above, the scoping opinion can be

sought by the applicant from the relevant authority to ascertain the information and studies

required to be included within the EIA. It is recommended that a scoping report detailing the scope

and content of the proposed EIA is circulated to the relevant authorities for sign off.

1.4 HabitatsDirectiveandBirdsDirectiveEC Directive 92/43 on the Conservation of Natural Habitats and of Wild Fauna and Flora (Habitats

Directive)

The Habitats Directive was introduced to promote biodiversity by establishing measures to prevent

the further decline in biodiversity experienced by habitats or species. Furthermore, it established a

mechanism for the robust protection for those habitats and species of European importance listed in

the annexes of the document – Annex I habitats, Annex II species and Annex IV European protected

species.

Under the Habitats Directive, a list of sites is proposed to form a network of Sites of Community

Importance (SCIs). Once approved on a European scale, the sites become designated as Special

Areas of Conservation (SACs), and together with Special Protection Areas (SPAs) classified under the

Birds Directive, form a network of protected areas known as Natura 2000.

The Habitats Directive is implemented through The Conservation of Habitats and Species Regulations

2010 – The Habitats Regulations ‐ and the Offshore Marine Conservation (Natural Habitats, &c.)

(Amendment) Regulations 2010 – The Offshore Habitats Regulations. Within English territorial

waters, the legislation is administered by Natural England (NE), whilst the Joint Nature Conservation

Committee (JNCC) is responsible for the administration of the legislation for UK’s waters beyond 12

nautical miles.


Appendix B

B-2

EC directive 79/409 on the conservation of wild birds (Birds Directive)

The Birds Directive provides the framework for the conservation, management and human

interactions with wild birds in Europe. The main provisions of the Birds Directive include:

• The maintenance of the populations of all wild bird species across their natural range (Article

2) with the encouragement of various activities to that end (Article 3).

• The identification and classification of Special Protection Areas (SPAs) for rare or vulnerable

species listed in Annex I of the Directive, as well as for all regularly occurring migratory species

(Article 4).

• The establishment of a general scheme of protection for all wild birds (Article 5).

• Restrictions on the sale and keeping of wild birds (Article 6).

• Specification of the conditions under which hunting and falconry can be undertaken (Article

7).

• Prohibition of large‐scale non‐selective means of bird killing (Article 8).

• Procedures under which Member States may derogate from the provisions of Articles 5‐8

(Article 9)

• Encouragement of certain forms of relevant research (Article 10 and Annex V).

• Requirements to ensure that introduction of non‐native birds do not threatened other

biodiversity (Article 11).

Together with Special Areas of Conservation (SACs) designated under the Habitats Directive, SPAs

form a network of European protected areas known as Natura 2000.

The Birds Directive is implemented through the Wildlife & Countryside Act 1981 (as amended), The

Conservation of Habitats and Species Regulations 2010; the Wildlife (Northern Ireland) Order 1985;

the Nature Conservation and Amenity Lands (Northern Ireland) Order 1985; the Conservation

(Natural Habitats, & c.) (Northern Ireland) Regulations 1995 (as amended); the Offshore Marine

Conservation (Natural Habitats & c.) Regulations 2007 (as amended 2010) as well as other legislation

related to the uses of land and sea. The Directive is administered by the statutory nature

conservation agencies including Natural England (NE) and the Joint Nature Conservation Committee

(JNCC).

1.5 TheMarineandCoastalAct2009The Marine and Coastal Access Act 2009 created a new type of Marine Protected Area (MPA), called

a Marine Conservation Zone (MCZ).

MCZs will protect nationally important marine wildlife, habitats, geology and geomorphology. The

Marine Conservation Zone Project concerns the selection of MCZs in English inshore waters and

offshore waters next to England, Wales and Northern Ireland. Sites will be selected to protect not

just the rare and threatened, but the range of marine wildlife.

MCZs, together with other types of MPA, will deliver the Government's aim for an 'ecologically

coherent network of Marine Protected Areas'. This means the MPA network will be a collection of

areas that work together to provide more benefits than an individual area could on its own.


Appendix B

B-3

Currently there is no statutory obligation to consider the series of recommended MCZs submitted by

the regional projects to Defra for designation.

1.6 DataforinclusionintheEnvironmentalStatementThe details of exactly what is required to be included within the Environmental Statement will be

bespoke to the individual site where GBFs are due to be placed. However, there are several guidance

documents that provide details of the generic information that may be applicable, and show

methodologies for undertaking the Environmental Statement.

The MMO suggest using the Essex Guide for EIA, whilst the Windfarm guidance document suggest

use of the ‘Environmental Impact Assessment – A Guide to Procedures’, produced by the

Department of Transport, Local Government and the Regions (DTLR) (Department of Transport,

Local Government and the Regions 2000), and in guidance on assessments under Section 36 and

Section 37 of The Electricity Act 1989.

Atmospheric emissions must also be taken into account during the EIA process, particularly CO2 and

NOx. These must include the costs associated with the construction of the CGBF, the emissions

relating to the transport and emplacement of the CGBFs and their decommissioning. The carbon

costs for aggregates are well documented and Aumônier et al. (2010) provides detail on the carbon

costs associated with marine aggregate dredging, which can be used as a proxy for the ground

preparation works and backfill operations. As the CGBFs are recyclable (see Section 10 for more

details) the carbon costs associated with construction are essentially a one‐off cost. In addition, the

ES should include details of the likely carbon savings arising as a result of the wind turbines

supported by the CGBF.

BibliographyAumônier, S. H., 2010. Carbon footprint of marine aggregate extraction. The Crown Estate.


Appendix B

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Appendix C

C-1

AppendixC–AMethodologyforAssessmentofEnvironmentalRiskPosedbyConcreteGravityBaseFoundationStructures

1.1 OverviewIn order for a plan, project or proposal to be assessed in a robust manner with necessary levels of

transparency a clear risk assessment methodology is required. There are a number of ways that this

can be achieved but in the simplest sense the assessment process must attempt to quantify the

following in order to determine the significance of the risk posed by the proposals:

1. The nature of the environment in which the plan, project or proposal will be undertaken;

2. The likely physical effects of the proposals in terms of how they alter the environment

around them;

3. The nature of the impacts that may result from the physical effects of the proposals;

4. The environmental, social and economic features (known as receptors) in the vicinity of the

works that may be susceptible to the impacts;

5. The level of susceptibility of the receptors to the impacts and their ability to recover from

impacts (known as sensitivity);

6. The spatial and temporal extent over which impacts may be felt by the receptors (known as

exposure); and

7. The severity of the impacts with reference to the baseline conditions of the site and the

natural variability of the environment (known as magnitude).

Items 1‐3 above are determined through analysis and reporting of available data and literature

review. Where data/knowledge gaps are evident, there may be the need for specific technical or

field studies to obtain, a) the most robust baseline description of the development site and b) the

nature of impacts likely to result from the proposals.

Once items 1‐3 have been satisfactorily completed, the risk assessment can be undertaken. This

process begins with identification of all the potential receptors that may be affected by the impacts

of the proposals. Once this has been completed, the sensitivity of the receptors is determined

through review of technical/scientific literature. Then, using the description of the physical effects

of the proposals, the level of exposure of the receptors to the impacts can be determined. At this

stage, if it can be shown that there is no exposure pathway between the project and the receptor

then the impact assessment can conclude that there is negligible risk to that receptor. If exposure is

proven for a specific receptor and impact, the magnitude of the impact is then determined. In this

way, by applying a staged approach, only those receptors that are shown to be sensitive to impacts

and exposed to impacts will need to be subjected to the entire process.

More detail regarding the process for items 1‐3 is presented in Sections 5, 6, 7, 8 and 9. Further

detail regarding the risk assessment methodology, items 4‐7, is presented below. An overview of

the rationale and assessment process that can be used to determine the environmental risk of a

proposed activity, operation, plan or project is provided. It has been developed by MarineSpace

Limited and allows the delivery of a standardised, repeatable and transparent methodology. The


Appendix C

C-2

risk assessment process flow is illustrated in FigureC.1 and an illustration of the risk assessment

matrix is presented in FigureC.2.

The Marine Works Regulations (2011) provide the most relevant overview of the process for

completing an Environmental Statement (ES) for marine developments. The basic elements of this

process have been incorporated into the methodology that has been applied to developing the risk

assessment. In essence, the methods applied to developing the risk assessment, should utilise the

best available evidence of environmental/impact receptor sensitivity and the best available evidence

of the nature, scale, extent and magnitude of impacts resulting from the proposed construction,

operation and decommissioning, to determine the severity of the risk posed by the proposals.

Obviously, the results of process are open to debate insofar as the determination of the level of risk

posed will require, in some cases, application of expert judgement. However, provided that the

evidence base used in the risk assessment is relevant and scientifically robust, then the

determination of level of risk should be suitable for purposes of determining whether a licence to

construct or operate may be granted.


Appendix C

C-3

Figure C.1: Process flow for completion of an environmental risk assessment.

Project Design

Site Description Impact Description

Identification of Receptors and Determination of Sensitivity

Index of Sensitive Receptors Determination Impact Extent

Determination of Impact Magnitude

Determination of Receptor Exposure to Impacts

Index of Sensitive Receptors with Risk of Exposure

Determination of Risk

Options for Risk Mitigation

Risk Management Plan

ES / EIA / Risk Assessment Scoping Study


Appendix C

C-4

1.2 RiskAssessmentMethodologyTo assess the level of risk from impacts resulting from a particular plan or project to a range of

receptors, a methodology has been developed that takes account of the sensitivity of the receptor,

the exposure of the receptor to effects / impacts and the magnitude of the effects / impacts over

and above the baseline condition and inherent natural variability. More guidance on the criteria to

be considered when determining levels of sensitivity, exposure and magnitude is provided below. It

should be borne in mind that the rationale for this assessment requires an understanding of the

baseline environmental conditions at the location of the proposed activity. This will usually be

provided from a desktop study reviewing all suitable available environmental data, published

research reports, grey literature and peer review publications. In most cases it is appropriate that a

dedicated environmental characterisation survey will also be required to provide the suitable

resolution of site‐specific environmental information. This baseline sets the context for the

environmental risk assessments.

1.2.1 CriteriaEmployedtoDetermineLevelsofSensitivity,ExposureandMagnitudeWhen conducting the risk assessment process, detailed in this section, determinations should be

supported by receptor‐specific risk matrices. The risk matrices provide details of the limits

employed when determining the scores for the individual elements of receptor sensitivity, receptor

exposure to impact and impact magnitude. An illustrative example is provided in Appendix C Section

1.7 below.

1.2.2 SensitivityThe risk assessment process presented in this document facilitates the identification of notable

seabed features that may be sensitive to the proposed activities. Such features are usually

associated with nature conservation habitats and / or species and / or archaeology and heritage;

though important features supporting fisheries resources or key life stage areas may also be

identified. Anthropogenic structures such as gas pipelines and high use areas such as Traffic

Separation Scheme lanes and approaches may also be identified as sensitive to CGBF construction

and operation.

Where specific sensitive receptors have been identified during the EIA scoping phase of a project,

these are assessed as discrete entities. Sensitivity thresholds are determined for each receptor and

presented individually within the risk matrices to ensure a clear single‐receptor assessment. This

helps clarify exposure and magnitude assessments to allow appropriate mitigation or management

advice to be identified.

Notable features/receptors should also be specifically identified, described and the assessment

presented within the final ES. For example, in the case of heritage features and Sabellaria spinulosa

reefs (where identified within the impact footprint of the proposals) specific investigation of

sensitivity will be required.

Prior to completion, the context of the risk assessment should always be clearly stated in terms of

scale of the proposals, the nature of the works to be carried out, a clear overview of the types of

effect/impact that may occur during different phases of the works and the timescales for

construction and operation phases of the project. This will ensure that a clearly defined ‘effect


Appendix C

C-5

envelope’ is established that will assist in determining if receptors will be affected (exposure) and

the frequency, longevity and magnitude of any effect.

1.2.3 SensitivityofSpecificReceptorstoImpactsfromCGBFsSensitivity information should be drawn from relevant scientific sources, as applicable. An overview

of the basic process required to develop understanding of sensitivity for a range of broad receptor

groups is presented below.

Similarly, information presented in relevant Natura 2000 site designation and assessment dossiers

and Regulation 33(2) and 35(3) conservation objective packages should be used to determine

sensitivity of designated nature conservation features.

1.2.4 CoastlinesandNearshoreBanksIt is well understood that the foundations of offshore wind turbines have the potential to impact

hydrodynamic processes and sediment transport patterns. Generally, effects are localised although

there is the potential for effects from a number of foundation structures to combine and create

effects over a greater extent (see Section 9). The sensitivity criteria for the geomorphological

receptors of coastlines and nearshore sandbanks are related to the stability and erosional potential

of these features. Risk assessment must therefore identify areas of the coast or nearshore banks

that may be particularly vulnerable to erosion and/or high‐energy (storm) events, and determine

where there are potential interactions between the predicted future physical effects of CGBFs and

the receptors.

The physical effects deemed to have the greatest potential impact on coastlines and nearshore

banks are altered wave climate and tidal currents caused by refraction effects, bathymetric change,

near bed sediment transport, and sediment flux. These effects may lead to potential impacts on

protective banks, which may in turn lead to increased coastline erosion; disruption/alteration of

sediment supply; and changes in wave‐ and tidal‐driven processes if structures are placed close to

the shore.

Both coastlines and nearshore banks may have a range of geomorphological characteristics and a

natural potential for change i.e. they are not equally vulnerable to the effects of installation of

gravity base foundation structures. Those coastlines characterised by unconsolidated easily erodible

sediments, with a low occurrence of hard coastal engineering structures, are deemed to be the most

sensitive to the effects. Nearshore banks composed of unconsolidated sand will have the greatest

potential to be affected by hydrodynamic changes, and the associated sediment transport effects. It

is also recognised that nearshore sand banks are often persistent features, despite the natural

effects of erosive, high energy, storm events. They therefore have a moderate to high tolerance,

adaptability and recoverability to the effects of waves and changes in sediment flux.

1.2.5 BenthicEcologyandFishSpeciesDetails of the intolerance to effects for specific benthic habitats, species and biotopes (also fish

species) are described in great detail on the MarLIN website. Use of the MarLIN sensitivity indices

and thresholds is standard practice within UK benthic ecology EIA determinations (Tyler‐Walters and

Hiscock, 2005; MarLIN, 2012).


Appendix C

C-6

Where possible individual biotopes must be identified within the environmental footprint

(application area and SIZ) of the proposed activity described in the ES and then assessed according

to the various effects / pressures arising from gravity base construction activity and during their

operational lifetime. In many cases due to the limited resolution of benthic data and habitat maps

then an amalgamation of biotopes / biotope complexes will need to be assessed. In these cases,

where it is not possible to assign an effect pathway to one single benthic receptor group,

consideration should been given to the sensitivity of habitats or species known to be constituents of

the amalgamated group receptor. To ensure a conservative or precautionary assessment in the

absence of higher resolution data the sensitivity assessment should be conducted using the most

sensitive representative species or biotope.

1.2.6 FishandShellfishSpeciesPossible fish and shellfish receptor species should be identified and the most sensitive of these used

to inform the risk assessment. The process should consider that highest sensitivity receptors are

likely to be those associated with habitats supporting key life stages of species, such as spawning

grounds and nursery areas.

Information located on the MarLIN website, both species‐specific and that associated with habitats /

biotopes, should be used along with that contained in relevant reference material cited in the

baseline description of fish and shellfish communities.

1.2.7 BirdspeciesSpecific references related to sensitivity of bird species should be reviewed and summarised in the

baseline description of the development site. The primary effects / pressures assessed are related

to water quality (changes in turbidity) interfering with predation, alteration of habitat supporting

birds species (roosting, nesting, loafing, prey species) or disturbance / displacement. NB Effects

considered in this document are related to the foundations structures and not the turbine blades.

Sensitivity associated with habitats or prey species should be drawn from the risk assessments for

coasts, nearshore banks, benthic ecology and fish/shellfish ecology (as described above). Species‐

specific sensitivity should be informed by references cited in the baseline site description.

Additionally for bird species the risk assessment as a whole will need to draw from the baseline

description and assessment associated with nature conservation. Relevant references from Natural

England, Countryside Council for Wales, Scottish Natural Heritage and the Joint Nature Conservation

Committee will need to be reviewed in respect of Special Protection Areas and Ramsar sites

supporting bird species listed in the related section of the environmental baseline description.

1.2.8 NatureConservationHabitats,SpeciesandSitesSensitivities for nature conservation receptors are associated with benthic habitats and species, fish

species, bird species, and marine mammal species. The sensitivities should be drawn from the

information used to assess these receptors as described above. The nature conservation sensitivity

must also draw on information published by the Countryside Council for Wales, Natural England,

Scottish Natural Heritage and the Joint Nature Conservation Committee regarding designated

habitats, species and sites. For example, Regulation 33(2) and 35(3) conservation objective packages

describe in detail the sensitivities of designated features and these should be used accordingly.


Appendix C

C-7

1.2.9 HeritageandArchaeologicalFeaturesThe sensitivity criteria and thresholds for in situ archaeological / prehistoric finds, isolated

prehistoric finds, aviation, and maritime heritage resources must be determined in the assessment.

Each of these broad receptor / resource categories will need to be assigned sensitivity categories

(value, adaptability, tolerance and recoverability) based upon peer‐review literature, research

reports and expert judgement.

It should be noted that in most cases historic/archaeological receptors in the marine environment

have high national value, low adaptability, low tolerance and low recoverability values. The risk of

impact can (generally) be considered medium to high, yet appropriate mitigation measures for

known resources can result in impact significance being low. This reduced impact significance is

possible through restriction of exposure (most obviously through avoidance), by clearly determining

the magnitude of effects and applying relevant management measures during project planning and

construction.

1.2.10 OtherSeaUsersandSeabedInfrastructureSensitivities associated with other sectors operating in the vicinity of the application area should be

drawn from relevant literature and authorities. In the case of the commercial fishing, recreational

sailing and shipping industries, focused consultation and/or technical studies is likely to be required

to determine the nature of use of an area. To determine the presence or absence of infrastructure

on the seabed, relevant authorities should be consulted (e.g. DECC – oil and gas, Kingfisher – cables

and pipelines).

The sensitivity of other users will need to be determined and will primarily be based on their ability

to withstand the displacement effects of construction activities and CGBF operation. Longer‐term

displacement during turbine operation is more likely to be considered during EIA for the wind farm

development rather than the construction of the foundations.

1.3 ExposureExposure is determined by the overlap of effects temporally and spatially with receptors. Exposure

pathways can be determined through strategic of regional cumulative assessments as a worst case

scenario. These assessments are useful for regulators, planners, managers and their advisors.

However final quantitative assessments can only be determined at the application stage when a

project specific Environmental Statement and EIA have been produced.

Spatial analysis through the use of GIS software and known or modelled effect footprints and the

mapped extent, distribution and occurrence of receptors is a standard tool used to allow exposure

determinations.

1.4 MagnitudeofImpactsfromCGBFsThe magnitude of impacts resulting from CGBFs must be considered in both the context of the

baseline condition of the environment at the time of the assessment and the natural variability in

physical conditions at the site, which may exert similar pressures as those resulting from site

preparation and emplacement activity. All consideration of impact magnitude should be made in

the context of these basic considerations of baseline condition and natural variability.


Appendix C

C-8

1.5 MagnitudeintheContextofNaturalVariabilityThe natural variability of physical and hydrodynamic conditions at a site will have an effect on the

significance of impacts occurring as a result of emplacement of a gravity base structure. The

magnitude of impacts resulting from the GBF structures should be considered in the context of the

variability of the natural environmental conditions at the site. This consideration is only possible for

receptors that are influenced by the environmental conditions of the site e.g. benthic species, fish,

birds etc. Consideration of the magnitude of impacts in the context of natural variability cannot be

given to receptors that are unaffected by natural variability e.g. fishing, shipping etc.

The evidence used regarding the physical and biological characteristics of the site and its regional

setting will provide the basis for the consideration of the natural variability of the environment. This

evidence should then been considered in the context of the magnitude of impacts resulting from the

construction and operation of the CGBFs.

To assess the magnitude of impacts in the context of natural variability some expert judgement will

need to be applied utilising the description of the physical and biological conditions and the nature,

scale and extent of impacts likely to result from GBF emplacement.

1.6 MagnitudeabovethePresentBaselineIn any environmental impact assessment, the present baseline of the site will have been described in

terms of the physical, biological and socio‐economic characteristics of the site, including;

Oceanographic conditions, seabed character, sediments, sediment transport

Benthic communities, fish, shellfish, birds and marine mammals

Conservation sites, habitats and species

Other users of the seabed and marine space

The primary method of determining the magnitude of impacts is by expert judgement, informed by

the best available descriptions of physical and biological conditions, and a description of the

historical activities at the site.

The magnitude of impact above current baseline conditions is best determined through reference to

the type and level of historical activity at the site and the type and level of activity likely to result

from the CGBF emplacement proposals. The magnitude of impacts will also be controlled by the

period over which seabed preparation and construction will occur.

1.7 WorkedExampleFor the purposes of the risk assessment undertaken in this document, sensitivity is defined in terms

of a receptor’s value (in terms of importance, quality and rarity), tolerance, adaptability and

recoverability. For each receptor, consideration is given to each of these component parts of the

sensitivity assessment with overall sensitivity being governed by the combined scores for each part.

The scores for each element range from 0‐3 and are determined based on consideration of the

available evidence.

In practice, to determine the sensitivity of a receptor each characteristic (value, adaptability,

tolerance and recoverability) is scored from 0‐3. In most cases 0 represents a negligible score


Appendix C

C-9

whereas 3 indicates a high value for the characteristic. In the case of recoverability, adaptability and

tolerance a low score indicates that the receptor is capable of withstanding the impact pressure and

should reduce the sensitivity score, whereas a high score for these characteristics will lead to a high

sensitivity.

As an example, a receptor is considered to have the following scores for the different elements of

sensitivity:

Sensitivity Element Score

Value (importance, quality, rarity) 2

Tolerance 2

Adaptability 1

Recoverability 2

Combined score (sum) 7

The following limits have subsequently been used to determine whether the sensitivity of the

receptor is negligible, low, medium or high.

Combined score Sensitivity

0‐3 Negligible (0)

4‐6 Low (1)

7‐9 Medium (2)

10‐12 High (3)

In this example the additive result indicates that the sensitivity of the receptor is considered medium

as it falls in the 7‐9 combined score range (7). A sensitivity score of 2 is therefore carried forward to

the final risk assessment (see below).

1.7.1 ExposureFor this methodology, exposure is defined in terms of how the impacts affect a receptor including

the spatial extent of the impact, its longevity above baseline levels and the frequency at which the

impact occurs.

In practice, to determine the exposure of a receptor to a particular impact, each characteristic

(spatial extent, longevity and frequency) is scored from 0‐3. The combined scores are then used to

determine the level of exposure that a receptor will experience. As an example, a receptor is shown

to have the following exposure scores:

Exposure Element Score

Spatial extent 2

Longevity 2

Frequency 1



Appendix C

C-10

The following limits have subsequently been used to determine whether the exposure to the impact

is negligible, low, medium or high.

Combined score Exposure

0 Negligible (0)

1‐4 Low (1)

5‐7 Medium (2)

8‐9 High (3)

Therefore in this example, the additive result indicates that the exposure level of a receptor to a

specific impact is medium as it falls in the 5‐7 combined score range. An exposure score of 2 is

therefore carried forward to the risk assessment (see below).

1.7.2 MagnitudeMagnitude is defined in terms of the level of the impact above background conditions and natural

variability by whatever parameters are measurable.

In practice, to determine the magnitude of an impact, each characteristic (level above background,

level in the context of natural variability) is scored from 0‐3. The combined scores are then used to

determine the level of exposure that a receptor will experience. As an example, a receptor has been

scored as follows:

Magnitude Element Score

Impact level above background 1

Impact level in the context of natural variability 2


The following limits have subsequently been used to determine whether the magnitude of the

impact is negligible, low, medium or high.

Combined score Magnitude

0 Negligible (0)

1‐2 Low (1)

3‐4 Medium (2)

5‐6 High (3)

Therefore in this example, the additive result indicates that the magnitude level of the impact is

medium as it falls in the 3‐4 combined score range. A magnitude score of 2 is therefore carried

forward to the risk assessment (see below).

As noted, the methodology adopted for this assessment utilises three elements; receptor sensitivity,

exposure to impact and the magnitude of impact. As described, limits will be defined to assist in

ascribing relevant values to these elements for all the receptors and potential impacts considered.


Appendix C

C-11

The parameters adopted to ascribe values to the level of sensitivity, exposure and risk will be

adjusted according to the nature of the receptor and the impact.

1.7.3 OverviewoftheEnvironmentalRiskAssessmentMatrixA risk assessment matrix has been developed to determine the risk posed by a range of impacts to a

range of receptors. The matrix is illustrated in Figure. In practice, to determine the level of risk

posed by an impact to a receptor, the scores resulting from the assessment outlined above are

multiplied to determine the level of risk. Using the scores in the example above (sensitivity – 2,

exposure – 2, magnitude – 2) a medium level of risk has been ascribed (see Figure C.2).

In the example shown in Figure C.2, the receptor and impact considered has resulted in a medium

level of risk. By applying this method to assessment of all receptors and impacts, a clearly defined

result can be achieved which will be based on available evidence regarding the issues discussed.

It should be noted that broad receptor groups e.g. the coast, marine ecology, infrastructure etc., are

made up of a range of individual receptors e.g. fish and shellfish, pipelines, benthic habitats etc. As

such, a risk assessment would be conducted to account for the individual elements of the broad

receptor groups with an overall risk summary for each broad group also presented.

Figure C.2: Risk assessment matrix.

Magnitude

Sensitivity

Exposure0

1

2

3

0

1

2

30 1 2 3

Risk = 2 x 2 x 2 = 8

Score Risk Value

0 = Negligible 1‐5 = Low 6‐15 = Medium 16‐30 = High


Appendix C

C-12

For the purposes of this assessment, risk scores of <6 (Negligible and Low values) are considered

insignificant and mitigation is unnecessary. Risk scores of 6‐15 (Medium values) are considered

significant but impacts are capable of being suitably mitigated through application of appropriate

management or monitoring measures. Risk scores >15 (High values) are considered significant and

impacts are likely to be mitigated only through application of specifically targeted measures and/or

acquisition of further environmental information to better determine impact severity and

significance.

BibliographyCIRIA, 1998. Regional seabed sediment studies and assessment of marine aggregate dredging.

Construction Industry Research and Information Association, London, Report C505.

Genus Traits Handbook: http://www.genustraithandbook.org.uk/

Jones, L.A., Hiscock, K. and Connor, D.W., 2000. Marine Habitat Reviews. A summary of ecological

requirements and sensitivity characteristics for the conservation and management of marine SACs.

Peterborough: Joint Nature Conservation Committee.

MarLIN website: http://www.marlin.ac.uk/sensitivityrationale.php

Tyler‐Walters, H. and Hiscock, K., 2005. Impact of human activities on benthic biotopes and species.

Report to Department for Environment, Food and Rural Affairs from the Marine Life Information

Network (MarLIN). Plymouth: Marine Biological Association of the UK. [Contract no. CDEP 84/5/244].


Appendix D

D-1

AppendixD–ProductionofCGBFsHaskoning (2011) provide details of the likely space required to establish a CGBF production plant of

around 100 units per year. The space calculated was a maximum of 50 Ha. There is also significant

available wharf space available at the major port around the UK as shown in the figure below:

Figure D.0: Major UK Port availability for CGBF construction (from Haskoning, 2011)

The key components required to produce CGBFs are:

1. Cement

2. Fine aggregate (e.g. sand)

3. Coarse aggregate (e.g. gravel or crushed rock)

These elements can be supplied from different sources, but are restricted through the location of

the geological deposits from which the elements are sourced.

CementCement for example is located in regions where limestone is readily available. The figure below is

taken from the MPA website and shows the cement plants operated by its members which are

concentrated in the midlands.


Appendix D

D-2

Figure D.2: MPA Cement Plants in UK (from MPA website)

CrushedRockCrushed rock production occurs within the geologically older parts of the UK. The 2009 quarries

utilised in the BGS minerals survey are shown in the figure below (Mankelow et al. 2011). Whilst

crushed rock produces the coarse elements of aggregate required for concrete, it also produces

significant fines which although not presently utilised in concrete production, may in future be

utilised for this purpose. Alternatively, as a result of the significant volumes of crushed rock fines

produced, the fines may be used as backfill for the CGBFs.


Appendix D

D-3

Figure D.3: UK Quarries Producing Crushed Rock Fines in 2009 (from Mankelow et al., 2011)

SandandGravelSand and gravel can be obtained from either land based or marine based sources. The current land

based sources as recorded by BGS (Mankelow et al. 2011) are shown in the figure below:


Appendix D

D-4

Figure D.4: UK Quarries Producing Sand and Gravel in 2009 (from Mankelow et al., 2011)

It is also important to note the location of marine aggregate dredging sites around the UK, as whist

some marine ports are included within the Sand and gravel section, marine fill may be utilised to

backfill the CGBFs. Therefore the following map shows the current location of UK marine aggregate

extraction areas:


Appendix D

D-5

Figure D.5: Marine Aggregate Licence Areas in English and Welsh Waters in 2009 (adapted Licence Area data from The Crown Estate)

MarineAggregateEmissionsAumônier et al. (2010) provide an assessment of the carbon cost of the production of a tonne of

marine aggregate. They calculate the emissions occurring as a result of transit to a dredging site, the

dredging of a cargo, the transit to the wharf and the discharge and processing of the cargo. The


Appendix D

D-6

carbon cost of producing this material on a long‐range cycle (which may be required for CGBF

backfill) was calculated to be 11.73 kg CO2‐eq per tonne of aggregate delivered.

This is likely to be an overestimation of the carbon cost as the British Marine Aggregate Producers

Association (BMAPA) have produced a sustainable development report that has calculated the CO2

emissions released through the production and transportation of marine aggregates from 2006 to

2009 (BMAPA 2010). The results of this report are shown in Error! Reference source not found., and

the average of the values presented is 7.58kg/t.

Table D.1: CO2 Emissions Arising from Marine Aggregate Extraction during the Period 2006‐2009 UK Quarries Producing Crushed Rock Fines in 2009 (from BMAPA, 2010)

2009 2008 2007 2006

Total CO2 emissions (tonnes) 120.81t 134,64t 157,15t 158,20t

Marine aggregate production 14.94mt 19.75mt 20.64mt 20.29mt

CO2 emissions per tonne landed 8.09kg/t 6.82kg/t 7.61kg/t 7.80kg/t

Excluding transportation from the calculation and comparing the energy use to land based

production, the following comparison can be established (Kemp, 2008):

Figure D.6: Energy Use in Material Extraction (from Kemp, 2008)

Whilst long haul marine aggregate production appears to consume a similar amount of energy when

compared to land based production, the differences are very small. The differences become smaller

still when the costs of transportation are added to the production costs illustrated above.

BibliographyAumônier, S. H., 2010. Carbon footprint of marine aggregate extraction. The Crown Estate.

BMAPA., 2010. Strength from the depths ‐ fourth annual sustainable development report.

Kemp, R., 2008. Energy Consumption of Marine Aggregate Extraction. The Crown Estate.

Mankelow, J.M., Sen, M.A., Wrighton,C.E. & Idoine D., 2011. Collation of the results of the 2009

aggregate minerals survey for England and Wales. HMSO.


Appendix E

E-1

AppendixE‐OverviewoftheDredgingProcessanditsPotentialEnvironmentalEffects This section presents the range of potential environmental impacts associated with dredging of the seabed. As the dredging process required for preparation of the seabed prior to emplacement of GBFs is identical to that undertaken when extracting marine aggregate, technical reports related to the effect of marine aggregate dredging have been used to provide the basis for this section.

TheDredgingProcess Dredging of the seabed is undertaken using either of two main methods; trailer dredging or static dredging. A description of the two methods is provided below.

Trailerdredging During trailer dredging, the vessel dredges whilst traversing over the area of seabed from where removal of sediment is required. Upon reaching the dredging area, the crew of the vessel deploys the dredge pipe which is lowered to the seabed. Powerful pumps are used to draw sediment and water up to the vessel where the mixture is discharged into the dredger’s hopper. Following discharge into the hopper, the coarse sediment settles out of the sediment/water mixture and is retained in the hopper. Water and unwanted fine sediment leaves the hopper via spillways and is returned to the sea. During the loading process the hopper gradually fills with sediment until the vessel’s hopper reaches capacity. At this point the dredge pipe is retrieved and the vessel transits to its discharge location. Discharge of the load to land is achieved by a variety of methods including grabs, drag‐buckets and bucket wheels, or some vessels have the facility to discharge the load at sea through doors in the hull.

Staticdredging During static dredging, the vessel loads whilst anchored over the dredging location. Upon reaching the dredging area, the vessel anchors and lowers its dredge pipe to the seabed. As with trailer dredging, powerful pumps are then used to suck sediment and water up from the seabed. The sediment/water mixture is discharged into the hopper of the vessel following which retention of coarse sediment and rejection of unwanted material is achieved as described for trailer dredging. Following loading, discharge occurs in the same way as for trailer dredging.

ThePhysicalEffectsofSeabedDredging In preparing this overview the following technical studies and resources have been used: ALSF monograph series (http://CEFAS.defra.gov.uk/alsf/downloads/monograph‐series‐

2011.aspx) Thames Estuary Marine Aggregate Regional Environmental Assessment (MAREA) (ERM Ltd,

2010)


Appendix E

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The MAREA report highlighted nine effects of seabed dredging, which have the potential to impact the marine environment. The physical effects of seabed dredging activities are summarised as: Seabed removal Vessel displacement Noise and vibration Suspended sediments Fine sand dispersion Bathymetric changes Waves changes Tidal current changes Sediment flux (proxy for sediment erosion and accretion)

The physical effects of dredging listed above may subsequently cause a range of impacts on physical, biological and socio‐economic receptors. More detail regarding the potential impact of dredging are provided below. ThePotentialImpactsofSeabedDredgingDredging causes direct, indirect and cumulative impacts in the marine environment. An overview of the potential direct, indirect and cumulative impacts of dredging is presented below. ImpactsonthephysicalenvironmentSeabed dredging can potentially cause changes in the physical environment, directly through the removal of seabed sediments, and indirectly, through changes in waves, tidal currents and suspended sediment concentrations. DirectphysicalimpactsRemoval of surface layers of sediment from the seabed is the primary direct impact on the physical environment resulting from dredging. The physical characteristics of the seabed (topography and sediment particle size) and the bathymetry (water depth) are altered. The dredging method determines the extent of topographical and bathymetrical changes: • Static dredging creates deeper (5‐10m) depressions in the seabed, over time these depressions may coalesce to form an irregular seabed topography; • Trailer hopper suction dredging creates shallow furrows that can extend for several kilometres in length. Generally these depressions are 2‐3 m wide and initially only around 0.5m deep potentially up to approximately 3m. Such impacts are confined to the area from which sediment is removed by the drag head. IndirectphysicalimpactsSeabed dredging has the potential to indirectly impact the physical environment in a variety of ways including: • changing of local wave conditions • reduction of the sheltering effects of offshore sandbanks • exacerbation of beach drawdown processes • changes to tidal currents • alteration of sediment transport pathways


Appendix E

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The removal of sediment from the seabed has the potential to affect the hydrodynamic and sedimentary regimes both within and surrounding the dredge site and further afield e.g. at adjacent coastlines.

Effectstomarineecologyfrommarineaggregateextractionontheseabed Dredging will result in impacts on seabed habitats and the animal communities that use them. Seabed fauna can be affected by direct impacts, when sediment is removed from the dredge site, and also by indirect impacts related to sediment deposition and transport around the dredge site. PhysicallossMarine aggregate extraction directly removes the surface layer of the seabed, which has a direct impact on the benthic communities within the dredging area, including the removal of infauna and epifauna. Physical loss of habitat during extraction operations could also result from the settlement of suspended particles mobilised during dredging, including fine sediments released during screening. The deposition of these fine sediments can locally change the nature of the surface substratum, making it finer and potentially altering the benthic communities where these changes occur. Also, fine sediments settling onto the seabed can (subject to prevailing environmental conditions) be transported on or near the seabed further away from the dredging area by tidal currents and waves, extending the potential area of seabed/community changes and potential smothering of sessile benthic communities beyond the boundaries of a dredging area.

PhysicaldamagePhysical damage can manifest itself in many ways. In association with marine aggregate extraction operations the main pressures are abrasion (from the draghead) and changes (increases) to suspended sediment loads (concentrations). High (increased) suspended sediment loads would be unlikely to affect the communities in the (assessment) area as they are evolved to exist in high turbidity waters. However, sediment plumes can elevate suspended sediment concentrations (SSC) above natural background loads, especially those associated with calm weather periods. There are variables that may result in impacts, e.g. cumulative effects of several plumes adding together. Also the temporal scale of dredging may have an additive effect e.g. SSC increase may only be in order of tens mg/l elevation above background levels but if this occurs every week then effectively the operation is mimicking a significant increase in effects similar to storm events. Therefore care is needed when assessing plume effects as whilst SSC increase may be minimal the ‘scale’ of (cumulative) effect may reach an ecological tipping point. ImpactsonMarineEcologyThe seabed supports a highly diverse range of animals including invertebrates such as sponges, anemones, crabs, shellfish, molluscs and burrowing worms and larger species such as fish, birds and marine mammals (whales, dolphins and seals). Aggregate dredging has the potential to impact the marine ecology directly via:

Removal of material from the seabed

The creation of sediment plumes The removal of seabed deposits has impacts on seabed habitats, benthic organisms and fish species through the removal of habitats and changes in seabed topography. Research by Newell et al., (1998) identified that there is a 30‐70% reduction in species diversity, a 40‐95% reduction in the


Appendix E

E-4

number of individuals and a similar reduction in biomass of benthic communities under the path of the draghead in dredge areas as benthic species are unable to escape entrainment. The removal of seabed deposits can also entrain fish and fish eggs and larvae and entrain eggs from fish that use the seabed for spawning (e.g. herring, sand eels and black bream). Sand and gravel habitats are important spawning grounds for several fish species. Sediment plumes in the water column created by outwash and screening can directly impact the marine ecology in two ways:

reduced water clarity (turbidity) research has shown can lead to short term avoidance of the working area by some animals.

increased sediment concentration can lead to a reduction in the respiration and feeding efficiency of benthic organisms. Increased sediment can block organs as animals have to filter a much greater proportion of organic from inorganic particles, potentially reducing feeding efficiency

Sediment plumes can also indirectly impact animals through the deposition of sediment. Deposition of suspended sediments has two impacts on the seabed. Animals living in or on the seabed can be immediately smothered and buried; while the habitat change from coarse sediments to finer sands alters the character of the associated benthic community.

ImpactsontheHistoricenvironment The marine environment contains a huge wealth of historic and culturally important assets. Dredging of the seabed has led to the recovery of numerous important archaeological remains that may otherwise have not been discovered. This has expanded the available knowledge base of the marine historic resource. DirectImpactsontheHistoricenvironmentDirect damage to heritage resources from the draghead and the loss of artefacts and heritage resources through entrainment alongside the removed sediment are the main impacts from dredging to the historic environment. IndirectImpactsontheHistoricenvironmentChanges in the physical environment, through bathymetric and sediment transport pathways alteration can lead to sediment scour and deposition around an historic artefact or site. This can alter the degradation rates, and potentially remove or relocate archaeological remains. However, deposition of sediment over a site or artefact may offer protection to the remains, which could be considered a positive effect of dredging.

Impactstoothermarineusers The main impact arising from seabed dredging on other marine users is temporary exclusion from the area being dredged. This could impact commercial fisheries, shipping and recreational users.


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TheExtentofthePhysicalEffectsofMarineAggregateExtraction For the purposes of this document, available literature regarding the nature and extent of impacts arising from marine aggregate extraction has been reviewed. In addition to the direct effects on the seabed that result from the passage of the dredge gear (drag‐head), several distinct secondary impact zones are detectable around a dredging location. The effects of dredging are summarised in Figure E.1. Figure E.1: Direct and indirect impacts of dredging on the marine environment (from Tillin et al, 2011)

Several studies of marine aggregate dredging activities (EMU Ltd, 2010; ERM Ltd, 2010; Hill et al., 2011; HR Wallingford, 2010a, 2010b, 2010c, 2010d; Tillin et al., 2011) indicate that zones of secondary impact are detectable around the direct impact area where removal of sediment has occurred. The literature cited indicates that immediately surrounding the direct impact zone, a zone of smothering exists resulting from deposition of plume sediment discharged from the vessel. Around this smothering zone, a zone of sediment bedforms may develop if sediment deposition occurs in large enough volumes (e.g. if dredging occurs for extended periods or if large volumes of sediment are dredged). Beyond the bedform zone, a zone of dispersed sediment may develop as fine sediment is transported by tidal currents away from the dredging area.

Bibliography EMU Ltd, 2010. South Coast Marine Aggregate Regional Environmental Assessment Volume 1 & 2. Report No. J/1/06/1165. ERM Ltd, 2010. Marine Aggregate Regional Environmental Assessment of The Outer Thames Estuary (MAREA). Prepared for the Thames Estuary Dredging Association (TEDA). 347pp. Hill, J.M, Marzialetti, S and Pearce, B., 2011. Recovery of Seabed Resources Following Marine Aggregate Extraction. Marine ALSF Science Monograph Series No. 2. MEPF 10/P148. (Edited by R. C. Newell & J. Measures). 44pp. ISBN: 978 0 907545 45 3. HR Wallingford., 2010a. South Coast Dredging Association MAREA: Wave Study Technical Note DDR4323‐04. HR Wallingford., 2010b. South Coast Dredging Association MAREA: Tidal Flows and Sediment Transport Study Technical Note DDR4323‐05.


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HR Wallingford., 2010d. A Review of Waves, Tides, Sediment Transport and Plume Dispersion Impacts from Aggregate Dredging to 2013, South Coast Region. Report for Haskoning UK Ltd. Report No. EX6301. 88pp. Newell, R.C, Seiderer, L.J and Hitchcock, D.R., 1998. The impact of dredging works in coastal waters: a review of the sensitivity to disturbance and subsequent recovery of biological resources on the sea bed. Oceanography and Marine Biology: an Annual Review, 36: 127‐178. Tillin, H. M, Houghton, A. J, Saunders, J. E and Hull, S. C., 2011. Direct and Indirect Impacts of Marine Aggregate Dredging. Marine ALSF Science Monograph Series No. 1. MEPF 10/P144. (Edited by R. C. Newell & J. Measures). 41pp. ISBN: 978 0 907545 43 9.


Appendix F

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AppendixF–NatureConservationHabitatsandSpeciesThere are several lists of marine habitats and species of nature conservation importance. This

appendix lists the habitats and species that the life cycle of a Concrete Gravity Base Foundations in

the marine environment is likely to interact with.

No statements regarding sensitivity of receptor habitats or species or the likely significance of any

exposures or vulnerabilities is made. Sensitivity information can be sourced from the standard EIA

toolkit, such as the Marine Life Information Network (MarLIN, www.marlin.ac.uk) and the Genus

Trait Handbook (http://www.genustraithandbook.org.uk/). Reference should also be made to site‐

specific designation, classification and management advice published by the Statutory Nature

Conservation Agencies (SNCAs) such as Site Assessment Documents and Regulation 33(2) and

Regulation 35(3) Conservation Objectives and Advice on Operations packages.

The relevant SNCAs are:

The Environment Agency for Northern Ireland (EANI) – with remit for Northern Irish waters

out to 12 nautical miles;

The Countryside Council for Wales (CCW) – with remit for Welsh waters out to 12 nm;

Natural England (NE) – with remit for English waters out to 12 nm;

Scottish Natural Heritage (SNH) – with remit for Scottish waters out to 12 nm; and

The Joint Nature Conservation Committee (JNCC) – with remit for all UK waters beyond 12

nm out to the Continental Shelf.

As cited in Section 7.7 of the main report, there are numerous domestic and international legislation

that details conservation and protection measures for marine habitats and species. The following are

sub‐divided by the most relevant legislation for Concrete Gravity Base Foundations associated with

deployment as part of Round 3 in UK waters. Only habitats and species likely to interact with CGBFs

or works associated with their lifecycle in the marine environment are listed i.e. these are not

complete lists of all marine habitats and species listed under the relevant legislation.

HabitatsDirective

AnnexIHabitats(From http://jncc.defra.gov.uk/page‐1523; http://www.ukmarinesac.org.uk/ms1_2.htm)

UK marine habitats listed in Annex I of the Habitats Directive whose conservation requires the designation of Special Areas of Conservation

EU Code

1110 Sandbanks which are slightly covered by seawater all the time

1130 Estuaries


Appendix F

F-2

1140 Mudflats and sandflats not covered by seawater at low tide

1160 Large shallow inlets and bays

1170 Reefs

1180 Submarine structures made by leaking gases

1180 Submarine structures made by leaking gases

AnnexIISpecies(From http://jncc.defra.gov.uk/page‐1523)

UK marine species listed in Annex II of the Habitats Directive whose conservation requires the designation of Special Areas of Conservation

EU Code

1095 Petromyzon marinus Sea lamprey

1099 Lampetra fluviatilis River lamprey

1102 Alosa alosa Allis shad

1103 Alosa fallax Twaite shad

1106 Salmo salar Atlantic salmon

1349 Tursiops truncatus Bottlenose dolphin

1351 Phocoena phocoena Harbour porpoise

1364 Halichoerus grypus Grey seal

1365 Phoca vitulina Common seal

AnnexIVSpecies(From http://www.legislation.gov.uk/uksi/2010/490/schedule/2/made)


Appendix F

F-3

Note: there are no marine flora (sea grasses) or seaweeds listed on Annex IV of the Habitats

Directive only marine fauna.

UK marine European protected species listed in Annex IV of the Habitats Directive whose conservation requires the protection of species from injury and disturbance

Cetacea Dolphins, porpoises and whales (all species)

Caretta caretta Marine turtles Loggerhead turtle

Chelonia mydas Marine turtles Green turtle

Lepidochelys kempii Marine turtles Kemp’s Ridley turtle

Eretmochelys imbricata Marine turtles Hawksbill sea turtle

Dermochelys coriacea Marine turtles Leatherback turtle

BirdsDirective

AnnexIspeciesThere are numerous bird species listed for conservation under the Birds Directive. Seabirds and

estuarine/coastal bird species fall into two lists:

Annex 1 species of the Birds Directive; and

Regularly occurring migratory birds around the UK not on Annex 1 of the Birds Directive.

Specifically for interactions with CGBFs then seabirds including grebes, divers, gulls, sea ducks, auks,

cormorants and shags, shearwaters and petrels, gannets and skuas will need to be considered where

their ranges overlap the wind array.

Given the limited likelihood of effects from Round 3 deployed CGBFs reaching the coast, then it is

unlikely that species of duck, geese, swans and waders will need to be considered as interacting with

these foundation structures.

Full lists of bird species protected under the Birds Directive can be found at

http://www.ukmarinesac.org.uk/ms1_2.htm and http://eur‐

lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2010:020:0007:0025:EN:PDF

Ramsarsites

The Convention on Wetlands of International Importance is called the Ramsar Convention and is an

intergovernmental treaty that provides the framework for national action and international

cooperation for the conservation and wise use of wetlands and their resources. Ramsar sites support


Appendix F

F-4

bird species and in the UK are usually underpinned by Sites of Special Scientific Interest and

designated with SPAs. All Ramsar sites with seabird features are designated at the coast. Considering

the limited likelihood of CGBF‐related effects from Round 3 interacting with the coast then the sites

are not examined in detail in this report. Qualifying species that may be offshore foraging and which

can interact with the foundations are generally considered through the auspices of the Birds and

Habitats Directive in the UK.

MarineandCoastalAccessAct2009

The provisions under the Marine and Coastal Act 2009 for the implementation of Marine

Conservation Zones (MCZs) cites lists of habitats and species that are regarded rare, scarce or

representative and for which protection through a national Marine Protected Area (MPA) network is

appropriate. The suite of recommended MCZs in English waters has been submitted to Defra for

review with a requirement to designate by the end of 2012.

Whilst Round 3 zones and recommended MCZs are not coincidental it is prudent to consider the

qualifying features as potentially part of CGBFs installation until such time that the MPA network is

deemed sufficient and ecologically coherent.

There are two lists of habitats and one of species that are nationally important and for MCZs may be

designated. There are:

Broadscale habitats;

Habitat Features of Conservation Importance; and

Species Features of Conservation Importance.

The full lists of habitats and species are listed in the Ecological Network Guidance which is located at:

(http://www.naturalengland.org.uk/Images/100608_ENG_v10_tcm6‐17607.pdf).

Broadscale habitats and Habitat FOCI (those coloured orange are unlikely to interact with CGBFs as

part of Round 3 projects).

Blue mussel beds

Cold‐water coral reefs

Coral gardens

Deep‐sea sponge aggregations

Estuarine rocky habitats

File shell beds

Fragile sponge and anthozoan communities on subtidal rocky habitats

Honeycomb worm reefs

Horse mussel beds

Intertidal underboulder communities

Littoral chalk communities

Maerl beds

Mud habitats in deep water

Native oyster beds

Peat and clay exposures


Appendix F

F-5

Ross worm reefs

Sea pen and burrowing megafauna communities

Seagrass beds

Sheltered muddy gravels

Subtidal chalk

Subtidal sands and gravels

Tide‐swept channels

Species FOCI (those coloured orange are unlikely to interact with CGBFs as part of Round 3 projects).

Scientific Name Common name

Gitanopsis bispinosa Amphipod shrimp

Cruoria cruoriaeformis Burgundy maerl paint weed

Phymatolithon calcareum Common maerl

Lithothamnion corallioides Coral maerl

Gobius couchi Couch's goby

Caecum armoricum Defolin’s lagoon snail

Anguilla anguilla European eel

Atrina pectinata Fan mussel

Gobius cobitis Giant goby

Pollicipes pollicipes Gooseneck barnacle

Grateloupia montagnei Grateloup's little‐lobed weed

Haliclystus auricula Kaleidoscope jellyfish

Gammarus insensibilis Lagoon sand shrimp

Armandia cirrhosa Lagoon sand worm

Tenellia adspersa Lagoon sea slug

Hippocampus guttulatus Long snouted seahorse

Lucernariopsis campanulata Stalked jellyfish

Lucernariopsis cruxmelitensis St John’s jellyfish

Ostrea edulis Native oyster

Arctica islandica Ocean quahog

Padina pavonica Peacock's tail

Eunicella verrucosa Pink sea‐fan

Amphianthus dohrnii Sea‐fan anemone

Paludinella littorina Sea snail

Hippocampus hippocampus Short snouted seahorse

Osmerus eperlanus Smelt

Palinurus elephas Spiny lobster

Nematostella vectensis Starlet sea anemone

Leptopsammia pruvoti Sunset Cup Coral

Alkmaria romijni Tentacled lagoon‐worm

Victorella pavida Trembling sea mat

Raja undulata Undulate ray


Appendix F

F-6

TheConventionfortheProtectionoftheMarineEnvironmentoftheNorth‐EastAtlantic known as the OSPAR Convention.

OSPAR has established a list of threatened and/or declining species and habitats in the North‐East

Atlantic. The list provides an overview of the biodiversity in need of protection in the North‐East

Atlantic and is being used by the OSPAR Commission to guide the setting priorities for further work

on the conservation and protection of marine biodiversity under Annex V of the OSPAR Convention.

Some of the habitats and species of the list have the potential to interact with CGBFs in Round 3

installations and will warrant consideration in any project‐specific EIA.

MarineStrategyFrameworkDirectiveThe Marine Strategy Framework Directive (EC Directive 2008/56) is a European Union Directive

which commits European Union member states to achieve ‘Good Environmental Status’ (GES) by

2020 across Europe’s marine environment.

UK Government is currently conducted a public consultation on the various delivery scenarios and

costs for the 11 descriptors of Good Environmental Status (GES). The most relevant information

including lists of notable habitats and indicator species can be found at:

http://www.defra.gov.uk/environment/marine/msfd/

TheUKBiodiversityActionPlanInformation regarding UKB BAP marine habitats and species can be found at:

http://jncc.defra.gov.uk/default.aspx?page=5155

The following habitats and species are on the marine list. Those colour‐coded in orange are unlikely

to inhabit areas where CGBFs may be emplaced as part of Round 3 projects.

Taxon Scientific Name Common name

alga

Anotrichium barbatum Bearded Red Seaweed

Ascophyllum nodosum ecad mackaii Wig Wrack or Sea‐loch Egg Wrack

Cruoria cruoriaeformis Burgundy maerl paint weed

Dermocorynus montagnei

Lithothamnion corallioides Coral Maërl

Padina pavonica Peacock’s tail

Phymatolithon calcareum Common Maërl

bird

Aythya marila Greater Scaup

Gavia arctica Black‐throated Diver

Larus argentatus subsp. argenteus Herring Gull

Melanitta nigra Common Scoter

Puffinus mauretanicus Balearic Shearwater

Sterna dougallii Roseate Tern


Appendix F

F-7

bony fish

Ammodytes marinus Lesser Sandeel

Aphanopus carbo Black Scabbardfish

Clupea harengus Herring

Coryphaenoides rupestris Roundnose Grenadier

Gadus morhua Cod

Hippocampus guttulatus Long‐snouted Seahorse

Hippocampus hippocampus Short‐snouted Seahorse

Hippoglossus hippoglossus Atlantic Halibut

Hoplostethus atlanticus Orange Roughy

Lophius piscatorius Sea Monkfish

Merlangius merlangus Whiting

Merluccius merluccius European Hake

Micromesistius poutassou Blue Whiting

Molva dypterygia Blue Ling

Molva molva Ling

Pleuronectes platessa Plaice

Reinhardtius hippoglossoides Greenland Halibut

Scomber scombrus Mackerel

Solea solea Sole

Thunnus thynnus Blue‐fin Tuna

Trachurus trachurus Horse Mackerel

cnidarian

Amphianthus dohrnii Sea‐fan Anemone

Arachnanthus sarsi Scarce Tube‐dwelling Anemone

Edwardsia timida Timid Burrowing Anemone

Eunicella verrucosa Pink Sea‐fan

Funiculina quadrangularis Tall Sea Pen

Haliclystus auricula Kaleidoscope jellyfish

Leptopsammia pruvoti Sunset Cup Coral

Lucernariopsis campanulata Stalked jellyfish

Lucernariopsis cruxmelitensis St John’s jellyfish

Pachycerianthus multiplicatus Fireworks Anemone

Pachycordyle navis Brackish Hydroid

Swiftia pallida Northern Sea Fan


crustacean

Arrhis phyllonyx

Mitella pollicipes Gooseneck Barnacle

Palinurus elephas Crayfish, Crawfish or Spiny Lobster

mollusc

Atrina fragilis Fan Mussel

Ostrea edulis Native Oyster

Tenellia adspersa Lagoon Sea Slug

cetacean Balaenoptera acutorostrata Minke Whale


Appendix F

F-8

Balaenoptera borealis Sei Whale

Balaenoptera musculus Blue Whale

Balaenoptera physalus Fin Whale

Delphinus delphis Common Dolphin

Eubalaena glacialis Northern Right Whale

Globicephala melas Long‐finned Pilot Whale

Grampus griseus Risso's Dolphin

Lagenorhynchus acutus Atlantic White‐sided Dolphin

Lagenorhynchus albirostris White‐beaked Dolphin

Megaptera novaeangliae Humpback Whale

Mesoplodon bidens Sowerby's Beaked Whale

Mesoplodon mirus True's Beaked Whale

Orcinus orca Killer Whale

Phoca vitulina Common Seal

Phocoena phocoena Harbour Porpoise

Physeter catodon Sperm Whale

Stenella coeruleoalba Striped Dolphin

Tursiops truncatus Bottle‐nosed Dolphin

Ziphius cavirostris Cuvier's Beaked Whale

shark/skate/ray

Centrophorus granulosus Gulper Shark

Centrophorus squamosus Leafscraper Shark

Centroscymnus coelolepsis Portuguese Dogfish

Cetorhinus maximus Basking Shark

Dalatias licha Kitefin Shark

Dipturus batis Common Skate

Galeorhinus galeus Tope Shark

Isurus oxyrinchus Shortfin Mako

Lamna nasus Porbeagle Shark

Leucoraja circularis Sandy Ray

Prionace glauca Blue Shark

Raja undulata Undulate Ray

Rostroraja alba White or Bottlenosed Skate

Squalus acanthias Spiny Dogfish

Squatina squatina Angel Shark


tunicate Styela gelatinosa Loch Goil Sea Squirt

turtle Caretta caretta Loggerhead Turtle

Dermochelys coriacea Leatherback Turtle

UK BAP Broad Habitat UK BAP Priority Habitat


Appendix F

F-9

Supralittoral Rock Maritime Cliff and Slopes

Supralittoral Sediment Coastal Vegetated Shingle

Coastal Sand Dunes

Littoral Rock

Intertidal Chalk

Intertidal Underboulder Communities

Sabellaria alveolata reefs

Littoral Sediment

Coastal Saltmarsh

Intertidal Mudflats

Seagrass Beds

Sheltered Muddy Gravels

Peat and Clay Exposures

Sublittoral Rock

Subtidal Chalk

Tide‐Swept Channels

Fragile Sponge and Anthozoan Communities on Subtidal Rocky Habitats

Estuarine Rocky Habitats

Seamount Communities

Carbonate Mounds

Cold‐water Coral Reefs

Deep‐Sea Sponge Communities

Sabellaria spinulosa Reefs

Sublittoral Sediment

Subtidal Sands and Gravels

Horse Mussel Beds

Mud Habitats in Deep Water

File Shell Beds

Maerl Beds

Serpulid Reefs

Blue Mussel Beds on Sediment

Saline Lagoons


Appendix F

F-10

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Appendix G

G-1

AppendixG–Contacts

Keycontacts

MarineManagementOrganisationMarine Management Organisation Lancaster House Hampshire Court Newcastle upon Tyne NE4 7YH Tel: 0300 123 1032 Fax: 0191 376 2681 Email: [email protected]

ThePlanningInspectorateThe Planning Inspectorate Temple Quay House Temple Quay Bristol BS1 6PN Tel: 0303 444 5000 E‐mail: [email protected]

RegulatoryAdvisorsGroup

CadwCadw Welsh Government Plas Carew Unit 5/7 Cefn Coed Parc Nantgarw Cardiff CF15 7QQ Tel: 01443 336000 Fax: 01443 336001 E‐mail: [email protected]


Appendix G

G-2

CentreforEnvironment,Fisheries&AquacultureScience(Cefas)Regulatory Assessment Team Centre for Environment, Fisheries & Aquaculture Science Pakefield Road Lowestoft Suffolk NR33 0HT Tel: 01502 562244 Fax: 01502 513865

CountrysideCouncilforWalesThe Countryside Council for Wales Maes y Ffynnon Ffordd Penrhos Bangor Gwynnedd LL57 2DW Tel: 01248 385500

EnglishHeritageEnglish Heritage Eastgate Court 195‐205 High Street Guildford GU1 3EH Tel: 01483 252000

HistoricScotlandHistoric Scotland Longmore House Salisbury Place Edinburgh EH9 1SH Tel: 0131 668 8600


Appendix G

G-3

JointNatureConservationCommitteeJoint Nature Conservation Committee Dunnet House 7 Thistle Place Aberdeen AB10 1UZ Tel: 01224 655704

NaturalEnglandNatural England 3rd Floor Touthill Close City Road Peterborough PE1 1UA Tel: 0845 600 3078 Email: [email protected]

NorthernIrelandEnvironmentAgencyNorthern Ireland Environment Agency Klondyke Building Cromac Avenue Gasworks Business Park Lower Ormeau Road Belfast BT7 2JA Tel: 0845 302 0008 Fax: 028 9056 9264 Email: [email protected]

ScottishNationalHeritageScottish National Heritage Battleby Redgorton Perth PH1 3EW Tel: 01738 444177 Fax: 01738 458611 Email: [email protected]


Appendix G

G-4

FisheriesFor enquiries regarding commercial fisheries please contact the main MMO office in the first instance. For enquiries regarding dispensation for fisheries surveys please contact the main MMO office in the first instance.

LocalMMOOffices:See http://www.marinemanagement.org.uk/contacts/local.htm for contact details.

AssociationofSeaFisheriesCommitteesAssociation of Sea Fisheries Committees 6 Ashmeadow Rd Arnside Via Carnforth Lancashire LA5 0AE Tel: 01524 761 616

NationalFederationofFishermensOrganisationsNational Federation of Fishermens Organisations Marsden Road Fish Docks Grimsby South Humberside DN31 3SG Tel: 01472 352141 e‐mail: [email protected]

Navigation

EnglishHeritageArchive(formallytheNationalMonumentsRecordCentre)English Heritage Archive The Engine House Fire Fly Avenue Swindon SN2 2EH Tel: 01793 414700 Fax: 01793 414444 Email: archive@english‐heritage.org.uk


Appendix G

G-5

MaritimeandCoastguardAgencyMaritime and Coastguard Agency Hydrography, Meteorology and Ports Branch Spring Place 105 Commercial Road Southampton SO15 1EG Tel: 023 80329138 Fax: 023 80329204

NERCSeaMammalResearchUnit(SMRU)NERC Sea Mammal Research Unit (SMRU) University of St Andrews Fife KY16 8LB Tel: 01334 462630

RSPBRSPB The Lodge Sandy Bedfordshire SG19 2DL Tel: 01767 683355

UKCableProtectionCommitteeUK Cable Protection Committee Level 3 Communications Limited Level 3 House Prescot Street London E1 8HG Tel: 020 7954 2575


Appendix G

G-6

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07/09/2012

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