Underwater Noise and Electromagnetic Fields

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Underwater Noise and
Electromagnetic Fields

9. UNDERWATER NOISE AND ELECTROMAGNETIC FIELDS ............................................... 9-1 
Introduction 9-1 
Data sources and guidance 9-1
Stakeholder consultation 9-1
Baseline data methodology 9-1
Baseline environment 9-1
Marine mammal response to sound 9-2
Fish response to sound 9-2
Latest underwater noise research 9-3
EMF generation and the sensitivity of marine biological receptors 9-3
EMF and the Irish Sea context 9-4
Key considerations and next steps 9-4
References 9-5 

This chapter provides an overview of the underwater noise environment of the Irish Sea and
discusses briefly the key issues facing the offshore wind farm industry, both in respect to noise and
Electromagnetic Fields (EMF). This chapter focuses on the research that has been undertaken and is
currently underway to better understand the impacts of noise and EMF on sensitive marine mammals
and fish. Underwater noise modelling has been undertaken at ZAP for marine mammals and is
presented in Chapter 12.

Further noise modelling will be undertaken as part of project specific EIAs and impacts associated
with the entire lifecycle of projects (construction, operation, decommissioning etc.).

9.1 Introduction
Underwater noise and electromagnetic fields (EMF) are two impact pathways associated with the
construction and operation of offshore wind farms for which the potential effects on sensitive marine
wildlife receptors is not fully understood. Indeed, there is sufficient concern over the potential effects of
excessive noise in the marine environment that ‘Good Environmental Status’ (GES) under the
European Union Marine Strategy Framework Directive (2008/56/EC) recognises the need to manage
underwater noise levels.

As a result of these concerns, both noise and EMF have been subject to priority research by the wind
industry through the Collaborative Offshore Wind Research Into the Environment (COWRIE) charity
established under the first and second licensing rounds for offshore wind by The Crown Estate.

This chapter provides an overview of the existing underwater noise and electromagnetic environment
of the Irish Sea Basin, from desk-based sources, the concerns associated with the potential impacts
and an account of the ‘latest research’.

9.2 Data sources and guidance
Data sources and guidance on underwater noise and electromagnetic fields (EMF) and the
implications these might have on potential projects within the ISZ have been reviewed and include:
• COWRIE Research projects (www.offshorewind.co.uk
• OSPAR Guidance Documents (OSPAR 2008a; 2008b & 2009);
• Selected Environmental Statements for offshore wind farms in UK and European waters; and
• Relevant regulatory documents and scientific papers.

9.3 Stakeholder consultation
Consultation with respect to potential noise impacts on natural fisheries and marine mammals has
been undertaken with the relevant statutory authority and reported in Chapters 11 and 12 respectively.

9.4 Baseline data methodology
No surveys have been undertaken as part of ZAP to establish ambient underwater noise levels. Noise
levels will be established as part of project specific EIAs and will be considered during other project
activities (e.g. construction of met mast). Information on ambient levels has therefore been collected
from existing data sources as identified in Section 9.2.

Although noise data has not been collected as part of ZAP, acoustic modelling has been undertaken
on a number of piling scenarios in relation to marine mammals. This is discussed in more detail in
Chapter 12.

Of the data sources identified in Section 9.2 the majority of the information contained in this chapter
has been obtained from the UK Government’s sixth Offshore Energy Strategic Environmental
Assessment (SEA) (DTI 2005) for the Irish Sea region and Offshore Energy SEA (DECC 2009). Other
sources of information have included the Gwynt y Môr Offshore Wind Farm Environmental Statement
(ES) (RWE Group, 2005) and Burbo Bank Offshore Wind Farm ES (Seascape Energy Ltd., 2002).

9.5 Baseline environment
9.5.1 Physics of sub-sea noise
Sound waves have two features that can be measured; sound pressure and particle velocity. Both
of these components tend to change sinusoidally in sound waves, although not necessarily for
explosive or impact sounds. Water is a relatively dense and incompressible material compared to
air, and this has important consequences for underwater sound. Underwater sound travels almost
five times faster than in air. Moreover, the pressure associated with sound tends to be higher than in

The usual unit of measurement for underwater sound is the decibel scale (dB re 1 μPa), which is a
logarithmic measure of the square of the sound pressure measured in relation to a reference
pressure of 1 micro-pascal (1 μPa; where 1 Pa is equal to 1 Newton per m

When quoting source levels of sound, it is usual to quote the sound pressure level at a nominal
distance of 1 metre from the source (normally back-calculated from a series of measurements at
increasing distances). This unit is expressed as the ‘dB re 1 μPa @ 1 m’.

9.5.2 Sources of noise in the marine environment
Noise in the marine environment derives from a number of processes, with background noise
generated by natural mechanisms such as wind, waves, rain, surf, biological activity including marine
mammal and fish vocalisations, and sediment transport processes. In addition, man-made marine
noise originating from activities such as shipping, fishing and offshore industries is superimposed onto
natural noise, so that background noise levels in many coastal waters are relatively high.

Sub-sea noise is generated by a variety of marine organisms including crustacea such as certain
shrimps that make ‘snapping’ noises, fish that produce a variety of noises, and marine mammals that
produce a range of clicks, pops and whistles. Source levels for low tonal sounds made by cetaceans
have been recorded around 170–180 dB re 1 μPa @ 1 m, while high-frequency echolocation clicks
range from a source level of 170 dB re 1 μPa @ 1 m for the harbour porpoise (Phocoena phocoena)
up to 226 dB re 1 μPa @ 1 m for the bottlenose dolphin (Tursiops truncatus) (DTI, 2005).

In comparison, anthropogenic noises can range from 150 to 160 dB re 1 μPa @ 1 m (tugs, barges
and fishing vessels) to up to 260 dB re 1 μPa @ 1 m for large seismic air gun arrays (Richardson et al.
1995). Anthropogenic noises tend to be broadband and low frequency in nature and may be
intermittent or continuous. Noise levels associated with the noisiest wind farm construction activities,

namely pile driving of monopile foundations, are similar in peak levels to the larger seismic air guns
and considered in more detail later in this chapter.

9.5.3 Background noise in the Irish Sea
Baseline surveys of ambient noise levels have not been collected at this stage in development of the
ISZ. However, data published by COWRIE (Nedwell et al. 2003, 2007) for baseline conditions at
Burbo Bank and Barrow provide a useful indication of baseline conditions for noise in the eastern Irish
Sea, in addition to the COWRIE reports, baseline information is available in the Gwynt y Môr Offshore
Wind Farm Environmental Statement (RWE Group, 2005).

The Gwynt y Môr ES describes the findings of a site specific survey to predetermine the existing
background noise levels of the area. The ES, which reported noise levels against third octave bands,
states that background noise levels for the area were highly variable between measured sites varying
from below 120 to 147 dB re 1 µPa per third band level. Such a variation of nearly 30 dB appears
typical up to a frequency around 20 kHz beyond which, the variation reduces to 10 dB or less.
Although considerable variation was seen from location to location, this was attributed to a number of
factors including wind noise, wave slap, flow noise, anthropogenic noise, such as shipping and the
noise from the nearby North Hoyle Offshore Wind Farm.

Nedwell et al. (2007) report a similar ambient noise range of 110 to 150 dB re. 1 μPa for frequencies
between 10 Hz to 150 kHz, whilst measurements at the Barrow and North Hoyle wind farms in the
eastern Irish Sea fall within this range at 122 and 120 dB re.1 μPa respectively.

The above examples are not an exhaustive list of data for the Irish Sea but it does provide an
indication of the anticipated ambient noise levels in the ISZ. As will be shown in the next section,
these levels are lower than the noise levels generated during the construction of wind farms.

9.5.4 Offshore wind farm construction noise levels
Noise monitoring of pile driving activities has been routinely undertaken at most UK wind farms. The
results, described in Table 9.1, show peak levels of approximately 250 dB re μPa @ 1m at low-
frequency levels (generally less that 1000 Hz) associated with pile driving of monopiles between 4 to
4.7m diameter.

Cefas (2010) note that piling noise is significantly higher than background levels and can be detected
through instrumentation headphones at distances of up to 25km from source and likely to be audible
to noise sensitive receptors.

It should be noted that the pile driving sound pressure levels presented in Table 9.1 relate to monopile
foundations, which have been scoped out of the project envelope (Chapter 6) for the ISZ as
unsuitable for the range of water depths present. Of the remaining foundations options, gravity base
foundations are expected to generate significantly lower noise emissions due to the absence of piling.
Jacket foundations are also anticipated to generate lower noise emissions as the 2.5 m pin-piles that
secure the jacket foundation to the seabed require a significant less powerful piling hammer to drive
them into the seabed.

Table 9.1 Key findings from construction noise monitoring reports

Pile Diameter
Depth along
transect (m)
Ambiant Noise
(dB re. 1 μPa @
noise level
(dB re. 1 μPa @
1 4.7 10-20 (122)
2 252
4.7 7-24 140 249
North Hoyle1 4.0 10-15 (120)
2 249
Scroby Sands
1 4.2 3.5-30 (132)
2 257
Kentish Flats
1 4.3 5-8 (113)
Gunfleet Sands1 4.7 ~2-15 113 245
Lynn1 2.0 (test pile) 3-7 70.5-97.6 224-236
Thanet3 4.1 7-15 109-135 248
Greater Gabbard
4 6 28 60-120 248
1 Cefas (2010),
2 Nedwell et al. (2007),
Thanet Offshore Wind Ltd. (2010),
4 Fluor Ltd. (2009)

CERI intends to measure underwater noise levels generated by the installation of a meteorological
mast in the ISZ in 2013. The meteorological mast will be installed on a jacket foundation of similar size
and proportions to that used for wind turbines. The measured noise levels will, therefore, allow for
more accurate predictions of the likely risk to noise sensitive receptors.

9.6 Marine mammal response to sound
It is anticipated that underwater construction noise will represent the most significant potential impact
on marine mammals.

Chapter 12 of the ZAP document focuses on the effects of construction noise, and more specifically
noise resulting from the driven piling of wind turbine foundations on key marine mammal species.
Anthropogenic noise which falls within the audible range of a marine mammal and exceeds natural
background levels has the potential to disturb, and in extreme cases, severely injure individuals. In
recent years, the potential ecological impacts of underwater noise associated with the construction of
offshore wind farms has been a topic of substantial research and review (e.g. Nedwell et al. 2004;
2007; Thomsen et al. 2006; OSPAR 2009).

9.7 Fish response to sound
Underwater noise will impact certain fish species differently as the hearing sensitivity of different fish
species is diverse and generally linked to the presence or absence of a swim bladder and the intimacy
of connection between the swim bladder and inner ear. The swim bladder, which is found in most
bony fish, can convert the pressure waves of sound in water to vibrations which can then be detected
by the inner ear and thus allow fish to detect sound and vibrations. Those species with a close
coupling of the swim bladder to the inner ear are particularly sensitive to sound and are referred to as
hearing specialists.

Species within this category include the Clupeids such as herring (Clupea harengus) and sprat
(Sprattus sprattus), allis shad (Alosa alosa) and the twaite shad (Alosa fallax). Fish that possess swim
bladders but without the close coupling of the inner ear are referred to as hearing generalists and
include the species salmon (Salmo salar), and cod (Gadus morhua), bass (Dicentrarchus labrax) and
other gadoids, whiting (Merlangius merlangus), and poor cod (Trisopterus minutus). Of these species,
it is known that cod are, in fact, almost as sensitive to sound as herring in the range 40 - 400 Hz,
where much of the energy from piling noise is found.

As for marine mammals, pile-driving noise during construction is of particular concern as the very high
sound pressure levels could potentially prevent fish from reaching breeding or spawning sites, finding
food, and acoustically locating mates in addition to physiological effects in close proximity to the pile-
driving activity.

The marine ecology chapter (Chapter 11) provides a description of the baseline environment from a
demersal fisheries and epibenthic perspective and provides an overview of the main demersal fish
species sampled during the demersal ZAP surveys. The ZAP impact assessment on the marine
ecological environment mainly focuses on benthic habitats, specifically potential Annex 1 habitats.
Impacts associated with underwater noise on fish, fish eggs and larvae will be dealt with at the project
EIA level. Justification for why certain marine ecological receptors were scoped in or out of ZAP are
provided in Chapters 3 and 11.

9.8 Latest underwater noise research
As previously mentioned studies initiated and funded by the COWRIE charity investigating the
reaction of marine mammals and fish to anthropogenic sound and the potential ecological impacts of
underwater noise associated with the construction of offshore wind farms has been a topic for
substantial research and has resulted in the following key outputs:
• Measurement and interpretation of underwater noise during construction and operation of
offshore wind farms in UK waters – several projects between 2003 and 2007;
• Assessment of the potential for acoustic deterrents to mitigate the impact on marine mammals
of underwater noise arising from the construction of offshore wind farms;
• Assessment and costs of potential engineering solutions for the mitigation of the impacts of
underwater noise arising from the construction of offshore wind farms;
• Measurement and assessment of background underwater noise and its comparison with noise
from pin pile drilling operations during installation of the SeaGen tidal turbine device,
Strangford Lough;
• Measurements of Underwater Noise Generated by Acoustic Mitigation Devices;
• Research into the behavioural response of harbour porpoise and harbour seals to acoustic
mitigation devices (AMDs) to deter marine mammals from pile-driving areas at sea; and
• Methodologies for measuring and assessing potential changes in marine mammal behaviour,
abundance or distribution arising from the construction, operation and decommissioning of
offshore wind farms July 2010.

These documents and the results of research into a number of priority research areas are available
from the COWRIE website (www.offshorewind.co.uk

The work undertaken by COWRIE and other groups has highlighted a need for further consideration
of these issues including the requirement for a better framework for establishing ‘risk’ and more
effective mitigation options.

Given the scale of Round 3, the Industry has established an Offshore Wind Underwater Noise
Working Group, of which CERI is a member, comprising wind farm developers, regulators and
statutory advisors to further tackle some of the issues that have been discussed above. The
objectives of the group are:
• To share knowledge on the rapidly emerging regulatory and policy landscape for underwater
• To share knowledge of individual developer/project actions relating to underwater noise;
• To identify key noise related risks to the development of offshore wind; and
• To identify developer led follow on actions.

9.9 EMF generation and the sensitivity of marine biological receptors
A preliminary investigation of the potential impacts of offshore wind farm power cables on electro-
sensitive fish was carried out by Gill and Taylor (2002) who demonstrated that electro-sensitive fish
species such as the Small-spotted catshark, (Scyliorhinus canicula) could detect the electrical field
from a power cable.

Given the apparent lack of information and the potential significance of impacts, COWRIE identified
electromagnetic fields as a priority research topic and recommended a two-phase approach to
investigating their potential ecological impacts:
• Phase 1 (CMACS, 2003; Gill et al. 2005): a study to calculate the electromagnetic field
generated by power cables at the seabed, assess the effects of burial and/or shielding and
carry out some preliminary in situ measurements of the electromagnetic field generated by an
existing sub-sea power cable; and
• Phase 2 (Gill et al. 2009): investigation of the actual impact of electromagnetic fields on the
behaviour and ecology of electro-sensitive and magnetically sensitive marine species through
in situ experiments and monitoring.
The results of the Phase 1 study demonstrated that whilst a correctly shielded alternating current (AC)
power cable did not leak an electric field, the alternating current in the cable generates a magnetic
field in the local environment. This in turn generates an induced electric field close to (within tens of
metres) the cable that is within the range detectable by electro-sensitive fish species such as
elasmobranchs (sharks, skates and rays).

Given the conservation and commercial importance of a number of the priority species identified in the
Phase 1 review and concern over the continuing paucity of data regarding this potential impact,
COWRIE decided to proceed with Phase 2. The aim was to make use of live fish in controlled
conditions that simulated the natural environment as fully as possible so that behavioural responses in
the wild could be investigated.

Two aquaculture sea pens of 40 metres diameter and 5 metres deep were constructed off the shore at
Ardtoe, Scotland. Ultrasonic positioning tags were used to study the behaviour of three benthic
elasmobranch species; Thornback ray (Raja clavata), Spurdog (Squalus acanthias) and S. canicula to
the EMF generated by subsea power cables dissecting each sea pen.

The study found that that the species studied did respond to the presence of EMF that is of the type
and intensity associated with sub-sea cables. However, the authors reported that a response was
not always predictable and did not always occur. Furthermore, when it did occur, it appeared to be
species dependent and individual specific, meaning that some species and their individuals are
more likely to respond by moving more or less within the zone of EMF. The Small-spotted catshark
(S. Canicula) were more commonly found closer proximity to the cable when energised and
displayed reduced movements consistent with feeding behaviour. In contrast, the responses of
some Thornback Ray individuals suggested a greater searching effort.

Whilst the COWRIE research has demonstrated that some species can detect and react to the EMFs
generated by AC power cables in close proximity to those cables, the biological and population-level
consequences remain unknown.

Finally, EMF research carried out to date has concentrated on the use of AC power cables. Changing
market conditions now means that the use of High Voltage Direct Current (HVDC) technology is
commercially viable for shorter transmission distances. Manufacturers state that, due to their bipolar
design, electric fields are not detectable outside the cable and magnetic fields are negligible (a cable
with a current of 1,000 amps gives a magnetic field of less than 0.2 μT within 10 m). Indeed, several
HVDC power cables have been operating in the ISZ and wider Irish Sea for a number of years.
Furthermore, modern HVDC cables do not contain oil or other toxic components. Based on the
information available, the environmental impacts of HVDC are likely to be less than for AC. However
despite the presence of existing cables in the ISZ 7 species of Elasmobranchs were recorded during
the site specific demersal trawl surveys

9.10 EMF and the Irish Sea context
Chapter 11 reports that more than 30 species of elasmobranch have been recorded in the region with
seven species recorded from site specific trawls of the ISZ. From these surveys the Small-spotted
catshark (S. canicula) was found to be the most abundant followed by spotted ray (Raja montagui),
cuckoo ray (Raja naevus), nursehound (Scyliorhinus stellaris), thornback ray (Raja clavata), blonde
ray (Raja brachyuran) and smoothhound (Mustelus asterias), all of which have been demonstrated to
be able to detect or are likely to be able to detect EMFs generated by wind farm AC power cables.

The Environmental Statements for the North Hoyle and Burbo Bank wind farms also recognised a
number of pelagic shark species such as tope as being present within the wider Irish Sea. The ability
of pelagic species to detect the EMF found locally around AC power cables is less well understood.

Despite the presence of sensitive receptors within the ISZ, potential impacts associated with EMFs on
these receptors was scoped out of the ZAP on the following basis (see also Chapter 3 and Chapter
11); electro-sensitive fish populations do not show an especially strong association with the ISZ, but
are generally widespread through much of the Northern Irish Sea, with local fisheries for skates and
ray (principally thornbacks) within a few miles of the North Wales coast, for example. Referring to
Chapter 11, section 11.5.3 on spawning and information on the spatial records for the usage of areas
as nursery and spawning grounds by CEFAS (2011) the ISZ appears to be of very limited importance
as elasmobranch nursery grounds and there is an absence of detailed information on important
spawning areas for elasmobranchs.

9.11 Key considerations and next steps
Development of wind farms within the ISZ could potentially impact marine mammals and fish species.
One of the key considerations for ZAP will be the sensitivity of marine mammals to underwater noise
and the effects of noise on European Protected Sites. The key considerations for marine mammals
will be discussed further in Chapter 12. The impact associated with noise and Natural fisheries has
been scoped out of this report and will be considered in more detail at the project EIA stages.

A more detailed review of the sensitivity and assessment of EMF effects on marine biological
receptors will be undertaken at the project EIA stage when further information is available on the
electrical infrastructure of projects in particular.

9.12 References
Cefas (2010), Strategic Review of Offshore Wind Farm Monitoring Data Associated with FEPA
Licence Condition. Project ME117. Annex 4: FEPA offshore Wind Farm Monitoring review:
Underwater Noise Strategic.

Cefas (2011). Estimating spawning stock biomass using egg surveys. Website information, accessed
on 19/10/2011 at; http://cefas.defra.gov.uk/our-science/fisheries-information/surveys/estimating-
CMACS (2003) A baseline assessment of electromagnetic fields generated by offshore windfarm

DECC (2009) UK Offshore Energy Strategic Environmental Assessment. Future Leasing for
Offshore Wind Farms and Licensing for Offshore Oil & Gas and Gas Storage. Environmental Report
DTI (2005) Strategic Environmental Assessment 6 Technical Report: underwater ambient noise.

Flour Ltd. (2009) Greater Gabbard Offshore Wind Farm. Underwater noise monitoring during marine
piling. July 2009.

Gill, A.B. and Taylor, H. (2002). The potential effects of electromagnetic fields generated by cabling
between offshore wind turbines upon elasmobranch fishes. Report to the Countryside Council for
Wales (CCW Contract Science Report No. 488).

Gill, A.B., Gloyne-Phillips, I., Neal, K.J. & Kimber, J.A., The potential effects of electromagnetic fields
generated by sub-sea power cables associated with offshore wind farm developments on electrically
and magnetically sensitive marine organisms – a review. COWRIE (1.5) 2005.

Gill, A.B., Huang, Y., Gloyne-Phillips, I., Metcalfe, J,. Quayle, V., Spencer, J., Wearmouth, V. (2009),
Electromagnetic Fields (EMF), Phase 2 Final report, EMF-sensitive fish response to EM emissions
from subsea electricity cables of the type used by the offshore renewable energy industry.

Nedwell J R and Howell D A (2004) review of offshore wind farm related underwater noise sources
Subacoustech Report for COWRIE Ltd, October 2004.

Nedwell J R, Langworthy and Howell D (2003) An assessment of sub-sea acoustic noise and
vibration from offshore wind turbines and its impact on marine wildlife; initial measurements of
underwater noise during construction of offshore wind farms, and comparison with background noise
Subacoustech Report for COWRIE Ltd, May 2003.

Nedwell J R, Parvin S J, Edwards B, Workman R , Brooker A G and Kynoch J E (2007) Measurement
and interpretation of underwater noise during construction and operation of offshore windfarms in UK
waters. Subacoustech Report for COWRIE Ltd, December 2007.

OSPAR (2008a) Assessment of the Environmental Impact of Offshore Wind Farms.

OSPAR (2008b) Guidance on Environmental Considerations for Offshore Wind Farm Development.

OSPAR (2009) Assessment of the environmental impact of underwater noise.

Richardson, W.J., Greene, C.R. Jr., Malme, C.I., & Thomson, D.H. (1995) Marine Mammals and
Noise. Academic Press, San Diego, CA, USA. 576p.
RWE Group (2005) Gwynt y Môr Offshore Wind Farm Environmental Statement.

Seascape Energy Ltd (2002) Burbo Bank Offshore Wind Farm Environmental Statement.

Thanet Offshore Wind Ltd. (2010) Thanet Offshore Wind Farm. Measurement and assessment of
underwater noise during impact piling operations to install monopile foundations: additional
monitoring report.

Thomsen, F., Lüdemann, K., Kafemann, R. and Piper, W. (2006). Effects of offshore wind farm noise
on marine mammals and fish, biola, Hamburg, Germany on behalf of COWRIE Ltd.