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COMBINED IMPACTS OF TIDAL STREAM ENERGY ARRAYS FINAL VERSION 29/09/15 Gemma Keenan and Frank Fortune (Royal HaskoningDHV)

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Page 1: COMBINED IMPACTS OF TIDAL STREAM ENERGY ARRAYS · arrays of tidal stream energy devices, scaling up impact predictions based on data collected for single device installations. This

COMBINED IMPACTS OF TIDAL STREAM

ENERGY ARRAYS

FINAL VERSION

29/09/15

Gemma Keenan and Frank Fortune (Royal HaskoningDHV)

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CONTENTS

Contents ................................................................................................................ 3

1. Introduction ....................................................................................................... 2

1.1 Background ................................................................................................... 2

2. Potential Combined Array Level Impacts ................................................................ 5

2.1 Physical processes .......................................................................................... 5

2.2 Marine mammals ............................................................................................ 6

2.3 Ornithology ................................................................................................. 13

2.4 Fish ............................................................................................................ 14

2.5 Benthic ecology ............................................................................................ 17

2.6 Shipping and navigation ................................................................................ 17

2.6.7 Commercial fishing .................................................................................... 23

3 Conclusions ....................................................................................................... 24

4 References ........................................................................................................ 25

This project has been co-funded by ERDF under the INTERREG IVB NWE programme. The report

reflects the author’s views and the Programme Authorities are not liable for any use that may be

made of the information contained therein.

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1. INTRODUCTION

1.1 BACKGROUND

This report provides a review of the potential impacts associated with the deployment of

arrays of tidal stream energy devices, scaling up impact predictions based on data

collected for single device installations. This is done through a review of the

Environmental Statement (ES) documents for planned tidal arrays, as well as a review of

any available literature in relation to predicting array level effects. At the time of writing

no tidal arrays have been deployed and therefore there are no available field data in

relation to array level impacts.

There are currently a small number of planned tidal array projects, some of which have

been consented. This report focusses on European projects, with key tidal array

Environmental Impact Assessment (EIA) examples from the UK discussed further in

Section 2. These represent an important opportunity for the industry and regulators to

develop further understanding of the potential impacts of an array through strategic

monitoring.

1.2 CURRENT STATUS

Table 1 provides a list of key individual tidal devices that have been installed for varying

periods of time.

TABLE 1: EXAMPLES OF TIDAL ENERGY DEPLOYMENTS IN EUROPE

Company Device

Technology

Location Capacity

(MW)

Andritz Hydro Hammerfest HS1000 Fall of Warness, European

Marine Energy Centre

(EMEC)

Single

1MW

device

Alstom DeepGen Fall of Warness, EMEC Single

1MW

device

Marine Current Turbines

(now owned by Atlantis)

SeaGen S Strangford Lough, Northern

Ireland

Single

1.2MW

device

Minesto Deep Green Strangford Lough, Northern

Ireland

Single

0.5MW

device

OpenHydro Open Centre Fall of Warness, EMEC Single

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TABLE 1: EXAMPLES OF TIDAL ENERGY DEPLOYMENTS IN EUROPE

Company Device

Technology

Location Capacity

(MW)

Turbine (OCT) 0.25MW

device

Scotrenewables Tidal Power

Ltd

SR250 Fall of Warness, EMEC Single

0.25MW

device

Voith Hydro Ocean Current

Technologies

Hy Tide Fall of Warness, EMEC Single

1MW

device

Sustainable Marine Energy

(SME)

Plat-O Yarmouth, Isle of Wight Single

0.1MW

device

Nova Innovation Ltd Nova 30 Bluemull Sound, North Yell,

Shetland

Single

0.03MW

device

Nautricity CorMaT Sound of Islay, and

Falls of Warness, EMEC

Single

0.5MW

device

EDF/ OpenHydro OCT Paimpol-Bréhat, Brittany

France

4 x 2MW

devices

Andritz Hydro Hammerfest HS300 Kvalsund, Norway Single

0.3MW

device

Sabella D10 Ushant island, France. Single

1MW

device

1.3 PLANNED PROJECTS – SCALING UP TO ARRAYS

The following tidal arrays have been consented in the UK, but are not yet installed:

Scottish Power Renewables (SPR) Sound of Islay Tidal Demonstration Array

(10MW);

Atlantis Resource Ltd (ARL) MeyGen Phase 1 Tidal Array (36MW, on the condition of

installing Phase 1a (6MW) and undertaking environmental monitoring before full

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build out of the remaining Phase 1 capacity); and

Marine Current Turbines (MCT, now owned by ARL) Skerries Tidal Stream Array

(10MW).

In 2010, the Crown Estate (TCE) undertook the Pentland Firth and Orkney Waters (PFOW)

leasing round, aimed at the development of tidal arrays of 100MW to 400MW. However,

the ambitious scale of the projects invited through that leasing round did not match the

level of technology readiness within the tidal sector. It became apparent that a leap from

single devices or prototypes, to full scale commercial arrays, carried very high project

risk, particularly in the PFOW, which is an extreme environment to undertake installation,

operation and maintenance for any marine project.

In addition, Perpetuus Tidal Energy Centre (PTEC) Ltd, secured a lease for a 30MW

demonstration site to the south of the Isle of Wight in 2012. This project is in the consent

determination phase at the time of writing.

In 2014, TCE undertook another leasing round and agreed the following tidal stream lease areas, each with the potential to deliver an array of 10MW or greater:

EMEC - Stronsay Firth;

MCT (ARL) - the Mull of Galloway;

EMEC working with the Islay Energy Trust - Islay;

Wave Hub - North Devon;

MCT (ARL) - Portland Bill, Dorset;

MCT (ARL) - Strangford Lough (in addition to the existing SeaGen device in

Strangford Lough);

Menter Môn - West Anglesey, north Wales; and

Minesto - Holyhead Deep, north Wales.

These projects have yet to submit applications for consent, although some have been

through the scoping phase of EIA at the time of writing.

At the time of writing, in September 2015, a further leasing round for projects under 3MW

has been announced by TCE, which will open for bids from the 21/09/2015.

OpenHydro was selected in 2014 by EDF to install a 14MW array of OpenHydro’s OCT

device in Raz Blanchard in Normandy, France. Installation is planned for 2018.

Tidal Sails has a 4MW demonstration project in the Sami community of Kvalsund,

Northern Norway. The project has consent from the Norwegian Water Resources and

Energy Directorate (NVE), and a power purchase agreement with Hammerfest Energi,

Norway.

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2. POTENTIAL COMBINED ARRAY LEVEL IMPACTS

This section provides a desk based review of potential impacts from tidal arrays, based on

lessons learned from the impacts assessed for a number of tidal array project consent

applications. Available technical studies are also considered, as is the variation in

receptor sensitivity at different sites and associated variations in the significance of

impacts.

2.1 PHYSICAL PROCESSES Robins et al. (2014) provides modelling of sedimentary processes off north west Wales for

theoretic arrays of 10, 50, 100 and 300MW. The results show that arrays of 10 to 50 MW

in this location reduce velocities locally by only a few percent, and reduce bed shear

stress and bed load transport by only slightly more. Suspended load transport is relatively

unchanged, since arrays induce locally increased turbidity. These changes are small

compared to the range of predicted natural variability. The modelling shows arrays of

more than 50 MW may significantly affect sedimentary processes locally. Further afield

(e.g. 10 km from the modelled array location), it is unlikely that the impact of energy

extraction on bed shear stress will exceed natural levels of variability. Sedimentary

processes are highly site specific, based on waves, tides, sediment type, and morphology

and so should be assessed on device and site specific basis.

The PTEC EIA (Royal HaskoningDHV, 2014) considered a wide range of tidal device types.

To help define which devices represent the worst case scenario in respect of the physical

process environment, a series of wake assessments were undertaken for both individual

tidal devices and arrays of tidal devices up to 10MW arrays, based on the indicative

spacing rules defined in the Project Description. The modelling determined that the

greatest wake effect from an individual device (of the device types and parameters

included in the PTEC Rochdale Envelope) will be generated by a seabed mounted twin

rotor tower device type e.g. SeaGen S, with 24m diameter rotors and hub heights 20m off

the seabed (although it was noted that the envelope of wake effects from all

representative technology types was narrow). The greatest 10MW array scale wake

effects were also found to arise from an array of the device type with the greatest wake

(i.e. seabed mounted twin rotor device type e.g. SeaGen S). Other array scenarios were

shown to have either:

(i) the same capacity but different device types (and hence will cause lower array

scale wake effects);

(ii) lower capacity, with fewer tidal devices of the same type and rating (and hence

will cause lower array scale wake effects); or

(iii) the same capacity, with more tidal devices of lower ratings and smaller diameters

(and hence will cause lower array scale wake effects).

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2.2 MARINE MAMMALS Potential impacts on marine mammals are defined in a number of sources including Faber

Maunsell & Metoc (2007); Aquatera (2012); and Thompson et al. (2013). These outline

the following key impacts, which are discussed further in this section:

Collision risk (vessels and devices);

Underwater noise;

Entanglement with device moorings (if applicable);

Electromagnetic fields (EMF); and

Barrier effects/ habitat exclusion, including disturbance at haul out sites.

In addition, the following potential impacts may cause indirect impacts on marine

mammals. The primary impacts are discussed in other sections of this report:

Increased turbidity - which links primarily to potential changes in physical

processes (discussed previously)

Water quality – dependent primarily on risk of accidental contamination which can

link to shipping and navigation assessments (discussed further below) and potential

changes to physical processes (discussed previously)

Changes to prey resource – dependent on changes to fish and/or benthic ecology,

described below.

There are significant knowledge gaps in relation to how individual marine mammals may

respond to the potential impacts described above and what the population level

consequences may be. This is coupled, in some cases, with uncertainty in the baseline

characteristics as well as understanding of how marine mammals use tidal environments.

There are currently a number of strategic studies underway, for example in relation to

understanding how seals use highly tidal areas and how seals respond to the operational

noise of a tidal turbine.

EIAs are undertaken on the basis of the best available guidance and information, which is

progressing rapidly. This section provides a review of current information in relation to the

key potential impacts listed above.

2.2.1 COLLISION RISK

Uncertainty regarding the potential for marine mammal collision risk is potentially a key

constraint for tidal developments, where the location has high densities of marine

mammals or has unstable populations, vulnerable to potential loss of animals from death

or injury.

There is limited actual understanding of how marine mammals will interact with

operational turbines (single devices or an array) and what the consequence will be for an

individual if a collision occurs (i.e. what is the likelihood of injury, or death).

Telemetry data collected during three years of monitoring for the SeaGen device in

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Strangford Lough, Northern Ireland indicated some local avoidance of the device. Tagged

seals continued to transit past SeaGen but transited further away from the centre of

Strangford Narrows (where SeaGen is located) than they had during the baseline (pre-

installation) period. However individual seal behaviour variability among tagged seals

was high. During the same period, passive acoustic monitoring indicated that harbour

porpoise also continued to transit past SeaGen, moving between Strangford Lough and

the Irish Sea. (Marine Current Turbines, 2011)

Carcass studies during the SeaGen Environmental Monitoring Programme (EMP) showed

the device was highly unlikely to have been the cause of any marine mammal fatalities.

(Marine Current Turbines, 2011).

Similarly it should also be noted that there is no evidence to date of any interaction

between any marine mammal species and the turbines at the European Marine Energy

Centre (EMEC) since the first turbine was deployed in 2006 (EMEC, 2014).

Consent conditions for SeaGen required shutdown of the device if a marine mammal came

within 30m in order to minimise the risk of a fatal collision as part of an adaptive

management strategy. This level of mitigation is unviable in the commercialisation of tidal

arrays and better understanding of actual, rather than hypothesised, marine mammal

interactions is required. The consent conditions for SeaGen were altered in 2014 to allow

operation without the shutdown requirement for marine mammals, however, the

operation of the device has been constrained since then.

As mentioned previously, studies are underway (Thompson, 2013) to monitor the

behaviour of seals in a tidal stream in the presence of artificial operational noise, based on

available operational noise data. It is important to understand whether devices produce

sufficient noise to instigate an avoidance response or whether changes to the sound

characteristics of the device or use of Acoustic Deterrent Devices (ADD) may be required

to minimise collision risk.

Ambient noise levels in tidal areas are generally high, with natural sources including water

flow and turbulence as well as movement of substrata, such as boulders and cobbles. As

a result marine mammals in these areas may have some existing habituation to noise

levels which are beyond the thresholds of predicted avoidance used in conservative noise

modelling.

As available information and guidance on collision risk for marine mammals has

developed, Environmental Statements have used a range of approaches to assess collision

risk, including collision risk modelling. A number of models have been used, including

models created by the Scottish Association of Marine Science (SAMS) and models derived

from the Band model used in ornithology collision risk modelling for wind farms.

In 2015, guidance from Scottish Natural Heritage (Band, 2015) was produced in relation

to using the following models:

“Collision Risk Model” (CRM) based on the Band model used for bird collision with

wind farms; and

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“Encounter Rate Model” (ERM) based on the work by the Scottish Association for

Marine Science (SAMS) (Wilson et al., 2007).

In the EMEC environmental appraisal (EMEC, 2014), Band noted that, for small animals,

the ERM is likely to over-estimate encounter rate, as it does not take account of the

geometry of the blade and under-estimates the likelihood that a small animal moving

downstream may pass between blades, making use of the pitch of the blade to allow free

passage. While this may apply to smaller diving bird species; it is less likely to apply to

much larger marine mammal species.

Band also noted that for large animals like marine mammals, an encounter with more

than one successive blade is quite possible. As the ERM calculates the encounter rate

with individual blades, rather than with the turbine as a whole, it counts such events as

multiple encounters, which may be hard to interpret. In contrast, the CRM counts such

events as a single no-avoidance collision. This is an issue particularly for basking shark

and minke whale, because of their body length (EMEC, 2014).

Band suggested a modified CRM approach for annular devices, such as the OpenHydro

OCT (EMEC, 2014). Annular devices have a ring of blades, surrounding an open central

core. The open core is typically sufficiently large to allow clear passage through for small

animals. The approach to collision estimation is to take into account the area of the open

core as a proportion of the overall device cross-sectional area, though allowing for the

body-width of the animal to clear the annulus, either within the open core or outside the

turbine (EMEC, 2014).

Each model provides a predicted impact for a single rotor, based on the project/ device

specific parameters fed in to the model. For a device with multiple rotors and/or an array

of multiple devices, the total collision risk is scaled up by direct multiplication from the

risk for a single rotor. There is insufficient understanding of collision risk to be able to

incorporate layout into the modelling scenarios. However, using the ERM described above

to compare the collision risk for a greater number of smaller devices against the risk

associated with fewer, larger devices with the same overall swept area, the results

indicate that collision risk may potentially be slightly greater for a higher number of

smaller devices. This indication is based on comparison of the ERM for the following

examples:

5 x open rotors of 20m diameter

o Swept area = 5 x 314.159 = 1570.8

20 x open rotors of 10m diameter

o Swept area = 20 x 78.540 = 1570.8

with all other applicable parameters equal

The majority of device technologies in development have axial flow rotors, either open

(unshrouded) rotors or ducted (shrouded) rotors and these are captured by the CRM, ERM

or modified ERM modelling approaches described above. However, there are a number of

devices that fall outside these characteristics, some examples of which are provided in

Figure 1, below.

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Image source: www.keplerenergy.co.uk

Image source: http://tidalsails.com Image source: http://minesto.com

FIGURE 1: EXAMPLE DEVICE TYPES THAT DO NOT FIT WITHIN TYPICAL COLLISION RISK

MODELLING (LEFT – RIGHT: KEPLER ENERGY, TIDAL SAILS, MINESTO)

There is no available information or guidance on modelling the collision risk for devices

that do not have axial flow rotors. The PTEC ES considers a wide range of device types,

however, it was agreed with the MMO and their advisors that, given the low numbers of

marine mammals at that site, it was appropriate to discuss the collision risk qualitatively

rather than providing quantitative modelling. That assessment considers the maximum

swept areas and tip speeds and provides discussion of all device types as it is not possible

to define which would represent the worst case scenario for collision risk.

2.2.2 UNDERWATER NOISE

There are limited available data for operational tidal devices, with all available data to

date being for single devices and in many cases for devices on a smaller scale than those

proposed for scaling up to arrays. Noise output is not likely to be directly affected by the

size of a device, for example larger devices may have different characteristics in terms of

generators and rotor blades and so it can be difficult to scale up the predicted noise levels

from one device capacity to another. However the best available data is used in EIAs and

underwater noise monitoring may be a condition of consent to account for uncertainty in

the assessments.

In the Kyle Rhea ES (SeaGeneration (Kyle Rhea) Ltd, 2012) Subacoustech provided

calculations on scaling up to a 2MW device, based on the increase in noise output that

was measured in relation to the 1.2MW device in Strangford Lough (operational noise

data collected by Kongsberg (Needham, 2010)) compared with the operational noise of

the 350kW SeaFlow device (Parvin et al., 2005). However, this study is specific to the

MCT device and dependent on having collected previous operational data. Other

developers are also collecting underwater noise data, for example, during deployments at

EMEC.

The MeyGen ES (Xodus Group, 2012) states that an array of 36 Atlantis or Hammerfest

Strøm turbines of 2.4MW produces higher noise emissions than an array of 86 turbines of

1MW. Noise modelling by Kongsberg is provided in the MeyGen ES for two phases of array

deployments including:

12 x 2.4MW devices; and

36 x 2.4MW devices.

Figure 2 (source: Xodus, 2012; Kongsberg, 2012) provides the predicted Sound Pressure

Levels (SPL) for arrays of 12 and 36 devices of 2.4MW capacity. Kongsberg (2012) states

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that an array of 36 devices may reach SPLs of 166dB re 1 μPa and an array of 12 devices

may reach 163dB re 1 μPa. This is an increase of 11dB and 8dB, respectively, over that

generated by the operation of a single 2.4MW device. Maximum background noise levels

in the area were measured at 139 dB re 1 μPa.

FIGURE 2: PREDICTED SOUND PRESSURE LEVELS FOR MEYGEN BASED ON ARRAYS OF 12

(LEFT) AND 36 (RIGHT) 2.4MW DEVICES (SOURCE: XODUS GROUP, 2012)

The predicted impacts on marine mammals are dependent on the noise characteristics of

each tidal turbine and the hearing sensitivities of each marine mammal species/ group.

The noise propagation is also highly dependent on the environmental characteristics of

each development site (e.g. substrate type and depth).

Table 2 provides an example of the impact ranges when scaling up to arrays, showing the

predicted ranges for strong avoidance behaviour (90dBht) for 12 or 36 devices, from the

MeyGen ES (Xodus Group, 2012).

TABLE 2: PREDICTED STRONG AVOIDANCE RANGES FOR MARINE MAMMALS IN THE

MEYGEN ES

Marine mammal group 12 x 2.4MW Range (m) 36 x 2.4MW Range (m)

Pinnipeds 8 38

Odontocetes 63 98

Mysticetes 266 588

2.2.3 ENTANGLEMENT

Benjamins et al. (2014) provides a review of the risk of entanglement with tidal device

mooring lines for different marine mammal groups. It is not currently possible to quantify

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the risk of entanglement and there are limited EIAs that have been undertaken for

floating or moored buoyant devices at the time of writing. The PTEC ES provides an

assessment for a wide range of devices including floating structures with catenary

mooring (slack to allow the support structure to stay on the surface with the change in

tides) or tension mooring (taught where the device is buoyant but submerged). The

assessment considers the maximum area taken up by the anchor spread of moored

devices and the maximum possible area taken up by an array, based on spacing rules

defined in the project description. The PTEC site is in an area of low density for marine

mammal species and therefore the risk was deemed to be negligible.

As discussed in the preceding Section 2.2.1 and 2.2.2 of this report, there is uncertainty

regarding the extent of avoidance behaviour likely to be instigated by the presence/ noise

of a tidal turbine and as some anchor spreads may extend to approximately 200m there

may be risks of entanglement beyond the range of avoidance. Benjamins et al. (2014)

state that moorings typically consist of large cables that are likely to be detectable at

considerable distances (tens of metres) for echolocating odontocete cetaceans, and are

likely to be far more detectable than nylon or monofilament fishing gears.

Risk of entanglement for an array may vary depending on whether mooring lines are

shared between multiple devices in the same array, or whether individual devices each

have their own independent mooring system. A number of device technologies e.g.

Scotrenewables and Sustainable Marine Energy (SME) devices are likely to share anchors

but have individual mooring lines, allowing each device to be removed for maintenance if

required. It is uncertain whether layout will affect potential entanglement risk, for

example whether the risk could be greater with a row or network of joined devices (most

likely perpendicular to the water flow and predominant marine mammal movement

direction) or with multiple separate devices with space in between but a larger overall

array area. The risk of entanglement is likely to be greater where an array is in a narrow

channel or inlet due to confined space. Not enough information is currently known on the

risk of entanglement with tidal device moorings to understand what space is required for

safe transit by marine mammals, however, this is likely to vary according to multiple

factors, including current speed and directionality, device/mooring type, and species

characteristics (e.g. size, detection capabilities and swimming speed).

Benjamins et al. (2014) compares the qualitative risk of entanglement with mooring lines

for different marine mammal groups. Small dolphins (e.g. common and bottlenose

dolphin), porpoise and pinnipeds (i.e. harbour seal and grey seal) are deemed to

generally have the lowest level of risk for most mooring types with moderate risk for

certain types of mooring line e.g. those containing nylon. The lower risk is a result of

their body size and flexibility, as well as their feeding mode, and ability to detect mooring

lines.

2.2.4 ELECTROMAGNETIC FIELDS (EMF)

The potential impacts from Electromagnetic Fields (EMF) for tidal arrays may be

comparable with offshore wind farms once tidal arrays scale up to a similar level of

generation. To date there is no evidence of significant effects due to EMF for offshore

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wind farms. Modelled and measured data from ten offshore wind farms, summarised in

Figure 3, shows magnetic field ranges and distances. It can be seen that EMF are highly

localised. There is no available EMF data for single tidal turbine devices.

FIGURE 3: AC MAGNETIC FIELD PROFILES ACROSS THE SURFACE OF THE SEABED FOR 10

SUBMARINE CABLE SYSTEMS FOR 10 OFFSHORE WIND FARMS (SOURCE: NORMANDEAU

ET AL., 2011).

There may be potential for marine mammals to exhibit behavioural changes, including

displacement due to the presence of electromagnetic fields (EMF) around subsea cables

(Gill et al. 2005). There is currently limited information on this effect but it is widely

believed that marine mammals use the geomagnetic field of the earth to navigate during

long distance migrations (Kirschvink et al. 1986; Klinowska 1985).

Although it is assumed that harbour porpoise are capable of detecting small differences in

magnetic field strength, this is unproven and is based on circumstantial information.

There is also presently no evidence to suggest that existing subsea cables have influenced

cetacean movements. Harbour porpoise move in and out of the Baltic Sea, with several

crossings over operating subsea high voltage direct current cables in the Skagerrak and

western Baltic Sea without any apparent effect on their migration pattern.

2.2.5 BARRIER EFFECTS/ HABITAT EXCLUSION/ HAUL OUT DISTURBANCE

The potential for barrier and exclusion effects are highly site specific. Barrier effects may

apply if the site is confined and represents an important transit route between important

areas, e.g. haul out sites and feeding grounds or a larger scale migratory route. Exclusion

effects may apply if the site is in, or close to, an important area e.g. feeding ground or

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haul out site.

The physical presence of turbines, noise (underwater and airborne in the case of haul out

site disturbance), and increased human activity may cause displacement or barriers.

Very little is known about this potential impact and it is likely that with sufficient

motivation (e.g. feeding or reproduction) marine mammals will habituate to the presence

of an array. Data collected during the Environmental Monitoring Programme (EMP) for the

single SeaGen turbine in Strangford Lough (Marine Current Turbines, 2011) has shown

that harbour porpoise (monitored through the use of MMOs and Passive Acoustic

Monitoring (PAM)) continued to use the tidal narrows as did harbour and grey seals

(monitored by MMOs and active sonar around the device). This was in keeping with the

predictions of the EIA (MCT, 2005) which predicted strong avoidance to 9m for harbour

porpoise and 1m for harbour seal, and mild avoidance at 108m for harbour porpoise and

15m for harbour seal. Kongsberg (2010) provides operational noise measurements for the

SeaGen device, as well as background noise and ferry noise, which are all below the levels

at which strong avoidance by marine mammals would be expected (with background

noise around the mouth of the lough, around 1-3km south of the SeaGen device providing

the highest noise measurements).

The potential for marine mammals to continue to transit through or around a tidal array

should be considered in relation to potential collision risk, along with the potential for

mitigation in terms of active discouragement or displacement of marine mammals as

mitigation (e.g. using Acoustic Deterrent Device (ADD)), in order to minimise collision

risk. Deployment of ADD would have to be carefully planned and monitored, so as to not

limit access to important areas (e.g. for feeding and reproduction) as a result of barrier

effects if it is uncertain that marine mammals will find an alternative resource in the

surrounding area.

Array spacing and layout may alter the potential for marine mammals to pass through an

array, however, not enough is known about this potential impact to determine what would

represent the best layout to mitigate such effects. There is insufficient information on the

impacts of individual tidal devices, as well as of tidal arrays, to understand what space is

required for transit by marine mammals within and/or around arrays and therefore the

potential for barrier effects. It is likely to be highly site specific, with variation dependent

on multiple factors, including current speed and directionality, device type, and species

characteristics (e.g. size, detection capabilities, swimming speed, site specific behaviour).

As discussed previously, motivation/habituation may greatly alter the nature, extent and

significance of impacts, compared with hypothetical assessment (e.g. underwater noise

modelling). The monitoring of operational tidal arrays in areas of high usage by marine

mammals will be highly valuable, providing better understanding of true nature of

potential barrier effects.

2.3 ORNITHOLOGY The key impact on birds which is of relevance in relation to scaling up to tidal arrays is

collision risk. Other impacts on birds relate to disturbance from vessels and increased

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activity which will be temporary although of increased duration with increasing array size.

As discussed in the marine mammals section, disturbance effects are likely to be highly

device/array specific as well as site specific. Tidal devices/arrays may also cause indirect

impacts as a result of changes to prey resource (which are discussed below in relation to

fish and benthic impacts).

2.3.1 COLLISION RISK

The moving rotors of tidal devices pose a theoretical risk to some diving bird species. To

date, there is no evidence of a bird collision with a tidal turbine.

The potential significance of collision risk will be dependent on the presence of diving birds

which dive to sufficient depth to encounter the rotors of the tidal device. This is therefore

also device and site specific, depending on the device parameters and water depth.

There is also uncertainty as to whether animals of relatively small size such as diving

seabirds would be struck by a rotor blade or would be swept past by hydrodynamic flow

and, if a collision were to occur, it is also unknown whether the force would be sufficient

to cause injury or death (Wilson et al., 2007).

For developments where collision risk may be relevant, collision risk modelling has been

undertaken in order to provide a conservative impact assessment. A further area of

uncertainty in relation to collision risk modelling is the likely avoidance rates for diving

birds whilst underwater. The PTEC ES (Royal HaskoningDHV, 2014) considers avoidance

rates of 95%, 98% and 99% in line with previous advice received by the authors from

Scottish Natural Heritage and JNCC, with respect to tidal array projects in Scotland,

acknowledging that there is no available data in relation to underwater avoidance rates.

The PTEC ES (Royal HaskoningDHV, 2014) states these avoidance values reflect the

general view of many biologists working in the field that the actual number of harmful

collisions will be substantially lower than the predicted number of encounters (Robbins, et

al, 2014).

Given the high levels of uncertainty in relation to the potential collision risk for diving

birds, it is not possible to determine if altered array configuration could have a potential

effect on the overall impact significance.

2.4 FISH Tidal energy developments may result in the follow key impacts on fish ecology:

Collision risk with operational tidal turbines;

Underwater noise impacts;

EMF;

Exclusion/ barrier effects; and

Habitat loss as a result of the seabed footprint – discussed in Benthic ecology

section.

2.4.1 COLLISION RISK

Further to the uncertainty discussed previously in relation to marine mammal and bird

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collision risk, there is additional uncertainty in relation to fish collision risk modelling due

to a lack of understanding of the baseline environment, particularly in terms of fish

density estimates in the marine environment.

Most assessments are therefore done on a qualitative basis, however, as with birds, there

is also little understanding regarding whether fish will pass around or through a tidal

device and if a collision occurs what the consequence on the individual and population will

be.

Direct observational research of interactions between fish and tidal devices is limited but

provides the best available insight into any potential risks or behavioural changes

associated with the presence of turbines (Copping et al., 2014).

Viehman, 2012 provides a study of fish behaviour around a barge-mounted tidal turbine

in Maine, U.S, using acoustic cameras either side of the turbine. The camera data showed

fish to regularly approach the area containing the barge and turbine, interactions were

highest when the turbine was stationary and during these periods fish commonly entered

the turbine. The study recorded no incidences of dead or dying fish to the lee side of the

turbine.

Fish passage through another barge-mounted turbine was examined on the Mississippi

River by introducing two size classes of fish outfitted with radiofrequency and balloon tags

directly into the turbine. The fish were retrieved downstream and assessed for mortality

and injury immediately after retrieval, held and re-examined after 48 hours. Survival for

the small (115 to 235 mm length) and large (388 to 710 mm length) fish was greater

than 99% after 48 hours (Normandeau Associates, 2009).

Video footage at the face of the pile mounted open-centred ducted turbine at EMEC in

Scotland recorded fish, primarily pollock, visiting the lee side of the turbine to graze on

the vegetation attached to the structure. This occurred at times when tidal currents were

lower than the cut in speed of the turbine. As currents increased and the turbine began to

rotate the fish appeared to disperse. To date the video data has not recorded any fish

passing through the turbine when it is rotating and therefore no observations relating to

fish strike mortality have been made (Polagye et al., 2011).

Laboratory and flume experiments have also been undertaken by researchers, with fish

directed towards rotating turbine blades, with limited potential for avoidance. This

allowed assessment of injury, survival rates and behavioural changes as a result of

passage through such an aggressive turbine. Alden Laboratory (U.S) experiments found

only small numbers of fish passed through the turbine-swept area; the majority of fish

swam upstream and/or were swept around the turbine. For those fish passing directly

through the turbines, all trials produced survival rates greater than 98%, with these rates

similar between the experimental and control groups. Conte laboratory (U.S) recorded no

injuries to fish passing through the turbine or around it, and again, no significant

differences between survival and control mortalities were observed (Jacobson et al.,

2013).

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Given the high variability of factors affecting fish collision risk (e.g. fish parameters and

behaviour, site depth, tidal flows, and device parameters), it is not possible at this stage

to determine whether scaling up to tidal arrays and array configuration could significantly

alter the potential collision risk.

2.4.2 UNDERWATER NOISE

The potential changes in source level and propagated sound pressure levels associated

with tidal devices and arrays is discussed previously in the marine mammals section.

Disturbance impact ranges for fish during the operation of tidal arrays are highly localised,

with strong avoidance ranges generally around 10m or less (Royal HaskoningDHV, 2014,

SeaGeneration (Kyle Rhea) Ltd, 2012, Tidal Ventures, 2014). The MeyGen ES (Xodus

Group, 2012) states that hearing specialists (e.g. herring) could be expected to show

strong avoidance up to 18m from the tidal array, whereas hearing generalists would need

to be less than 1m from the source of the noise to exhibit a behavioural response.

These ranges are less than the likely spacing between tidal devices in an array and

therefore no additive weighted (in relation to the receptor hearing capability) received

level effects are likely. The impacts of the array are therefore likely to be the direct

displacement, locally, around each device.

2.4.3 EMF

As with marine mammals, the potential impacts from EMF for tidal arrays is likely to be

comparable with offshore wind farms once tidal arrays scale up to this level.

A range of marine species including elasmobranchs, salmon, trout and eel, have adapted

to detect naturally occurring electric and magnetic fields in order to locate prey, avoid

predation and navigate. While it is recognised that potential pathways for interactions

between EMF emitted from subsea cables and fish and shellfish exist, there is no

conclusive evidence to date of the nature of these interactions or whether they have

positive or negative effects on species. Studies to date have shown EMF to both repel and

attract individuals of different species under different conditions; consequently it is not

currently possible to infer the nature, nor significance, of these observed responses (Gill

et al., 2010, Marine Scotland, 2015)

2.4.3 EXCLUSION/ BARRIER EFFECTS

As with marine mammals, the potential for barrier and exclusion effects are highly site

specific. Barrier effects may apply if the site is confined and/or represents an important

route for migratory fish. However there remains significant uncertainty in the routes taken

by migratory fish whilst at sea.

Exclusion effects may apply if the site is in, or close to an important area, e.g. spawning

or nursery area where impacts such as noise may affect the success of the population. As

discussed previously the impacts of noise are highly localised for fish and the impact of an

array is likely to be localised around each device. This extent of the predicted array level

impacts can then be considered in the context of the surrounding area e.g. available

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habitat or space for transiting through or around the array.

2.5 BENTHIC ECOLOGY The key relevant impact on benthic ecology, when considering the potential effects of

scaling up from a single device to a tidal array, is habitat loss or disturbance. Indirect

impacts may also occur as a result of changes to physical processes (discussed

previously), but these are anticipated as being far less significant.

2.5.1 HABITAT LOSS/ DISTURBANCE

Habitat loss and disturbance is highly dependent on the device type to be installed. For

arrays of seabed mounted devices, the footprint on the seabed will be a direct

multiplication of the device parameters for a single device and the number of devices.

This can then be considered in the context of the available relevant habitat.

Some device types have established areas of efficiency in the number of rotors/generators

on each support structure and foundations/moorings. For example, MCT’s SeaGen and

Tidal Energy Ltd’s Delta Stream, mount two or three large rotors on a single foundation.

Similarly, platform structures, such as Tidal Stream’s Triton can hold multiple small rotors

on a single structure and foundation.

A number of device types can share components of the foundation structure or moorings

between individual devices within an array. In particular, floating or buoyant technologies

may share anchors between devices to minimise footprint and infrastructure. In a similar

way, transverse axis devices, such as those developed by Kepler Energy and Ocean

Renewable Power Company, can be deployed as a linear array or ‘fence’, with the

potential to share support structure and foundations between devices within the fence.

An indicative array layout is usually provided in the ES for tidal arrays, with some

parameters defined e.g. maximum and minimum spacing, in order to provide a

meaningful assessment. This flexibility allows the final array layout to be provided based

on detailed site investigation, generally undertaken post-consent. This may include micro-

siting the array around species of conservation importance where necessary.

2.6 SHIPPING AND NAVIGATION Constraints in relation to navigational risk associated with the deployment of a tidal array

depend on the importance of the site as a shipping route and the potential for an

alternative route around the proposed array. This section provides a review of key

available impact assessments for a number of tidal array sites with discussion of lessons

learned in relation to shipping and navigation.

2.6.1 KYLE RHEA TIDAL STREAM ARRAY

The Marine Current Turbines (MCT) Kyle Rhea Tidal Stream Array Environmental

Statement (SeaGeneration (Kyle Rhea) Ltd, 2012) showed that shipping and navigation

was one of the key constraints for the project. The project proposed an array of four

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SeaGen S devices with a surface piercing tower of up to 18m above Lowest Astronomical

Tide (LAT) in a narrow tidal strait (approximately 600m wide). The ES provided an

indicative layout for assessment which was highly constrained by resource (optimum

towards the centre of the channel) and space for navigation (requiring the array to be as

far to the western side of the channel as possible).

Consultation with key stakeholders confirmed that the strait was a commonly used

through route for a variety of sea users and that alternative routes passing around the

Isle of Skye which would add considerable time and cost as well as additional risk of

encountering extreme weather conditions. Figure 4 shows the summer survey tracks for

existing traffic as part of the baseline characterisation confirming the high use of the site.

FIGURE 4 SUMMER 2010 SURVEY DATA (20 DAYS) IN GENERAL AREA OF KYLE RHEA

(SOURCE: SEAGENERATION (KYLE RHEA) LTD, 2012)

The Navigation Risk Assessment (Appendix 17.1 of SeaGeneration (Kyle Rhea) LTD, 2012)

determined that without mitigation the risk of collision was potentially unacceptable. The

following mitigation measures were proposed with the aim of bringing the impacts to an

acceptable level:

The Project will be depicted on Admiralty Charts produced by United Kingdom

Hydrographic Office (UKHO) with an associated note on the available underwater

clearance;

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Information about the devices will be distributed, e.g. liaison with local harbours,

clubs and associations; Coastguard Maritime Safety Information broadcasts;

Notices to Mariners; inclusion in Clyde Cruising Club Sailing Directions and other

almanacs, etc.;

Marking and lighting of the Project will be decided by Northern Lighthouse Board

once they have reviewed the NRA and consulted on the appropriate scheme to

ensure devices are conspicuous and / or to mark a safe passage. The existing

leading light will need to be altered; and

Fendering of towers (if practical) - a bumper surrounding the device to absorb the

kinetic energy of a vessel in the event of a collision, could potentially mitigate the

impact if a small vessel collided with a device. This would be effective only in a

glancing collision with the device.

The project is currently on hold due to grid connection issues and consent determination

was not fully processed.

2.6.2 SKERRIES TIDAL STREAM ARRAY

The MCT Skerries Tidal Stream Array project proposes an array of the same device

technology (SeaGen S) as proposed for Kyle Rhea, but located in open water. The ES

provides minimum and maximum spacing parameters along with two indicative layouts,

one with the array in one row, with relatively close spacing, the other in two rows, taking

up a larger area overall, but with more spacing between the devices (Figure 5). The

shipping and navigation assessment assumes a larger overall array area represents the

worst case scenario for assessment.

Site characterisation surveys showed the key shipping route is further offshore than the

planned array. This means that navigation and space to manoeuvre is not constrained or

confined, unlike Kyle Rhea (Section 2.6.1) where navigation is within an already

constrained and relatively narrow strait.

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FIGURE 5 INDICATIVE ARRAY LAYOUTS IN THE MCT SKERRIES ES (SOURCE:

SEAGENERATION (WALES) LTD, 2011)

The assessment concludes that the devices should be avoidable, with traffic able to pass

through or around the array. The assessment indicated that all identified risks are

classified As Low As Reasonably Practicable (ALARP) or better.

2.6.3 TORR HEAD TIDAL ARRAY

As with the Skerries Tidal Array (Section 2.6.2) the Torr Head ES provides an indicative

layout of an array, with the devices located in a relatively open coast location. The array

includes up to 100 fully submerged devices with 8m clearance above LAT.

The assessment concludes that all impacts are tolerable or broadly acceptable, with the

exception of fishing interaction with subsea equipment (discussed further in the

commercial fisheries section below).

The Torr Head tidal array proposal is in the consent determination phase at the time of

writing.

2.6.4 MEYGEN PHASE 1 TIDAL ARRAY

The MeyGen ES states that due to the minimum surface clearance of 8m below LAT for

their proposed devices, and given the shallow draught of most local vessels; the risk of

collision is minimal. A collision would therefore only be possible given a combination of

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low tide and extreme wave conditions, a set of conditions during which local vessels are

unlikely to be out at sea.

Transiting of larger vessels through the development site is relatively low, however, any

vessels constrained by their draught will have to re-route to the south of the array, which

has reduced sea room (see Figure 6), or via the Outer Sound. This will lead to increased

encounters with other vessels and therefore increased collision risk but the overall change

from the baseline risk levels is assessed as low (Xodus Group, 2012).

MeyGen has received consent to deploy a first phase on four devices. This was restricted,

primarily due to uncertainties in relation to marine mammal impacts. Shipping risk will be

significantly reduced compared with the assessment of 100 devices.

FIGURE 6: MEYGEN INDICATIVE LAYOUT

2.6.4 SOUND OF ISLAY TIDAL ARRAY

The Sound of Islay Tidal Array is located in a narrow channel (approximately 1km width).

The sound provides a direct route for traffic and is preferential to the increased distance,

cost, travel time and risk of inclement weather encountered if travelling around Islay.

The Navigation Safety Risk Assessment concluded that the potential impacts are tolerable

with monitoring (Scottish Power Renewables, 2010). Key factors in this acceptable level

of risk were the available space to manoeuvre within the Sound of Islay, the general

absence of difficult tidal eddies and other navigation hazards, as well as the use of fully

submerged tidal technology, with substantial clearance above rotors to allow passage of

vessels.

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2.6.5 PERPETUUS TIDAL ENERGY CENTRE (PTEC)

The PTEC ES (Royal HaskoningDHV,2014) includes a range of options for the potential

tidal devices that may be deployed. The minimum and maximum likely device spacing is

used in the impact assessment and to consider the maximum overall space the array

could take up within the wider redline boundary as well as the potential space to navigate

through arrays. The PTEC site will provide berths for different developers and therefore

within berth and between berth spacing was considered.

The site could include surface piercing or fully submerged devices with clearance from a

minimum of 3m above LAT to much deeper/ increased clearance. The devices (submerged

or surface piercing) could include an anchor spread and/or may also move around on their

anchors or foundations.

Site characterisation for PTEC, through consultation and data collection, including

commissioned surveys, showed that the study area has relatively high levels of vessel

traffic, with the majority passing around development site. A particular constraint is the

use of the site by recreational yachting, in particular the attraction of the Round the

Island Race (RIR) which attracts yachting competitors internationally and is of high socio-

economic value to the Isle of Wight.

The Navigation Risk Assessment concludes that the impacts predicted are broadly

acceptable. However, a commitment is made to providing array layout and navigation

information to the MMO prior to the deployment of any devices. This will allow

confirmation of how well any particular layout and navigation risk fits within the impacts

assessed in the ES, as well as providing any information on device/array specific

mitigation and residual risk.

The PTEC proposal is in the consent determination phase at the time of writing.

2.6.6 SHIPPING AND NAVIGATION SUMMARY

The review of various ESs for tidal arrays shows that shipping and navigation impacts

vary, particularly in relation to the following key factors:

Site characteristics (e.g. open sea or narrow channel, shallow or deep water);

Alternative route options;

Existing levels and types of traffic; and

Device type characteristics (e.g. submerged or surface piercing and extent of

surface clearance).

Minimising the impacts on shipping and navigation falls primarily at the site selection and

device selection (e.g. feasibility) stage of the project. For example, if the site is narrow,

with high levels of existing traffic, and limited alternative options, a submerged device

technology with sufficient clearance (based on the latest available guidance) may be

advisable.

The potential impacts on different users may also differ, for example depending on the

size of the vessels, powered or non-powered, likely skill of the skippers (e.g. recreational

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or professional). Recreational vessel users, in particular, yachts may be additionally

affected due to largely being under sail and therefore have less manoeuvrability on a

small scale and involve amateur skippers who may have more potential to misjudge the

situation.

The detailed layout of each of the tidal array examples discussed in this section will be

defined post consent. This is likely to be on the basis of additional site investigation in

terms of seabed/ geological characterisation and tidal resource characterisation. In

addition, some flexibility in the array layout post-consent may also allow some micro-

siting of devices in an array to incorporate mitigation for shipping impacts.

Lessons learned from offshore wind farms are also likely to be valuable, particularly when

tidal array sizes increase. For example arrangement of devices in straight lines and with

sufficient spacing to allow navigation through the array may reduce the impact.

2.6.7 COMMERCIAL FISHING Impacts on commercial fishing are related to shipping and navigation impacts affecting

the potential to use and access to fishing areas, as well as any impacts on fish and

benthic ecology, discussed previously. In addition, a key potential hazard of tidal arrays in

relation to commercial fishing is that of potential snagging or entanglement hazard

through the deployment of fishing gear. The consequence could be serious if the snagged

/ entangled gear causes the vessel to capsize. This significant of these impacts will be

highly dependent on the level of use of the development site for fishing, as well as the

type of fishing activity.

There is no available information at present as to whether the potential snagging risk may

vary with device technology.

Spacing of devices within an array may be sufficient to allow vessels to move through the

array (see Section 2.6.6), but may be insufficient for the safe deployment and recovery of

fishing gear. This is particularly the case in highly tidal environments where a vessel may

drift considerable distances whilst gear is deployed or being recovered. Array layouts

with minimum spacing and therefore taking up a smaller area overall may be preferable in

some areas, however, this would be assessed on a site specific basis, and will be highly

dependent on the types of fishing gear used and the presence of available alternative

fishing areas nearby.

The PTEC proposal includes a number of potential berths, suitable for various developers,

and so there will be between three and six arrays within the site. The spacing between

arrays is likely to be greater than the spacing between devices of a single array. PTEC has

committed to ongoing discussions with fishermen, to include discussing the potential for

fishermen to continue to use the site.

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3 CONCLUSIONS

Due to the evolving nature of the tidal industry there is still uncertainty regarding the

nature and significance of the potential impacts of single tidal turbines and consequently

for tidal arrays. For this reason conservative approaches are taken through any tidal

array EIA to carefully assess the combined impacts.

This report reviews available literature and ES documents to demonstrate that the

potential impacts of any tidal array are uncertain, highly site specific and also technology

specific. The deployment of tidal arrays which are currently in planning or consented

(generally around 10MW or less) will provide an excellent opportunity for ecological and

physical monitoring, as well as providing data on actual commercial fisheries, socio-

economic, shipping, and recreational impacts. The lessons learned can be taken forward

in the further commercialisation of the tidal industry and the deployment of arrays in the

order of 100MW or greater.

The layout of an array is likely to be defined, primarily, by ground conditions, water depth

and tidal resource. This will usually be informed by detailed site investigation works, post-

consent and therefore EIAs generally assess an indicative layout with a range of spacing

parameters. Where there is sufficient physical space as well as other suitable conditions,

there may be an opportunity for micro-siting to minimise and mitigate risks and impacts.

This approach would be applied using a balanced approach to appraisal and prioritisation,

considering the key constraints of each site, particularly if receptors have conflicting

mitigation requirements. Not enough is currently known about the potential combined

impacts of arrays to fully understand the effect (if any) that micro-siting the array layout

could have on receptors.

Strategic industry level monitoring is underway to improve understanding of key issues, in

particular in relation to marine mammal collision risk, including activity around tidal

devices and behavioural response of seals to artificial operational noise of tidal devices.

Monitoring to verify key assumptions made during the impact assessments for various

receptors, once tidal arrays are deployed and operational, will be valuable in better

understanding the true impacts and the differences associated with differing device

technologies and site variations.

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