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Cefas contract report C5748
Position Paper
(Module Two: Provision of Environmental Studies: Final
report)
Authors: Daniel Wood1, Freya Goodsir1, Rebecca Walker1 Victoria
Bendall1, Ines Martin Grandes1, Sarah Watts1,
Cormac Booth2, Chris Thaxter3 and Paul White4
Issue date: 16 December 2013
Commercial in Confidence
1CentreforEnvironment,FisheriesandAquacultureScience(Cefas),PakefieldRoad,Lowestoft,SuffolkNR330HT2SMRUMarineLtd,NewTechnologyCentre,NorthHaugh,StAndrews,FifeKY169SR3BritishTrustforOrnithology,BTO,TheNunnery,Thetford,NorfolkIP242PU4UniversityofSouthampton,Highfield,SouthamptonSO171BJ
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ModuleTwo:ProvisionofEnvironmentalStudies:FinalReport
CefasDocumentControlTitle:PositionPaper
Submittedto: TheGlostenAssociatesDatesubmitted:
16December2013ProjectManager: CharlottePerksReportcompiledby:
FreyaGoodsir,DanielWood,VictoriaBendallQualitycontrolby:
DanielWoodApprovedby&date: AdrianJudd16 December2013
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PositionPaper
ModuleTwo:ProvisionofEnvironmentalStudies:FinalReport
Authors:Daniel Wood, Freya Goodsir, Rebecca Walker Victoria
Bendall, Ines Martin Grandes, Sarah Watts,
Cormac Booth, Chris Thaxter and Paul White
Issuedate:16December2013
Head office
Centre for Environment, Fisheries & Aquaculture Science
Pakefield Road, Lowestoft, Suffolk NR33 0HT, UK
Tel +44 (0) 1502 56 2244 Fax +44 (0) 1502 51 3865
www.cefas.defra.gov.uk
Cefas is an executive agency of Defra
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ModuleTwo:ProvisionofEnvironmentalStudies:FinalReport Pageiv
Executive Summary
Cefas,incollaborationwiththeSeaMammalResearchUnit(SMRUMarineLtd),theBritishTrustforOrnithology
(BTO), and University of Southampton Institute of Sound and
Vibration
Research(ISVR),hasbeencontractedbyTheGlostenAssociatestoprovideenvironmentalscientificevidenceontheenvironmentaleffectsassociatedwiththePelaStarfloatingtension
legplatform(TLP)beingusedaround theUKcoast.Thispaper specifically
focusesonenvironmental considerationsofTLPmoorings (anchoring
systems), and the environmental interactions of key UK protected
speciesincludingmarinemammals,baskingsharksandseabirds.The mooring
systems to be utilised in the PelaStar design are different from
those used fortraditional
fixedturbinessuchasmonopiles.ThePelaStar5armTLP
istetheredtotheseafloorbyhighperformancesyntheticropetendonsandhighverticalloadanchors(drivenpileanchorsand/ordrilledandgroutedanchors).Whileanchoring
systemsarenew to theoffshorewind sector,
theyhavebeenusedformanyyears intheoilandgas
industry.Themethodsusedtoplacetheanchors(piledrivenanddrilledandgrouted)arewellknownmethodologies
intheoilandgasandthecivilengineeringsectorsandaresimilartoinstallationmethodsalreadyusedinoffshorewindfarms.Twomainenvironmentalimpactshavebeenassessed;seabeddisturbanceandnoise,comparingtheTLPdesignwithmore
traditional fixed foundations.ForbothTLPsand traditional
foundations, thetype of impact (e.g. loss of habitat) are the same,
however the scale of impact differs
betweendifferentfoundationtypes.Seabedpreparationactivities
intermsoftemporaryhabitat
losshavealowtohighimpactintermsofgravitybases,amoderateimpactbysuctioncaissons,alowimpactbymonopiles,multilegand
jackets,andnegligibleto low
impactforotherfloatingwindturbinesandTLPs. The environmental
effects attributable to scour processes are high for monopiles, low
tomoderate for floatingwindturbines (otherthanTLPs)and low
forgravitybases,multileg, jackets,suction caisson foundations and
TLPs. Environmental impacts attributable to blockage effects
(ofphysicalprocesses) arehigh for jacketand suction
caissons,moderate tohigh,dependingon thediameterof thedesign,
forgravitybasesandmultileg foundations,moderate
formonopiles,andnegligibleforTLPsandotherfloatingwindturbines.Thetablebelowsummarisestheimpactsontheseabedanddifferentfoundationtypes.Foundationtype
Habitatloss Scour NoiseGravityBases Lowtohigh Low LowSuction
Moderate Low LowMonopile Low High HighMultileg Low Low
LowtoHighJacket Low Low ModerateFloating devices
(otherthanTLPs)
Negligibletolow Lowtomoderate Moderatetolow
TLPs Low Moderatetolow
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UnderwaterpilingforTLPanchoringislikelytobeofthesamemagnitudeasforthatexperiencedfortraditionalmonopile
foundations.Withpilediametersvarying from2.1m
to3.7m,TLPpilenoiseshouldfallsomewherebetweenthenoiseexperiencedfortraditionaljacketpinpilesandmonopiles.Drilling
and grouting is significantlyquieter thanpiledriving,butwould take
longer to
complete,meaningelevatednoiselevelsoveragreaterperiodoftime.Formarinemammals,thebiggestconcernisunderwaternoise.Thenoisegeneratedbydrillingandgrouting
may cause a smallscale disturbance around the installation site,
and a wide range ofspecies couldencounter thedevicewhere it is
likely tobedeployed commercially.However, thenoise levels
fromdrillingandgroutingare likely tobe lowand canbeapproximated to
thenoisegeneratedfromamediumsizedvessel. It
isconcludedthatdrillingnoise
ishighlyunlikelytocauseauditoryinjury.Thenoisegeneratedbypiledrivinginstallationwould,however,belikelytohaveanimpactonmarinemammalsinthevicinity.Theimpactranges(auditoryinjury,behaviouralresponse,masking)may
be as large as or even greater than those for fixed foundationwind
turbines andwould be able to be determined through an EIA. The
potential for noise to be generated
fromstrumming(causedbywatermovingpasttheundertensiontendonsofthePelaStar)alsoneedstobe
considered.During theoperationalphase, theremaybe issuesofwhales
interactingwith
thetendons,representingacollisionorentrapmentrisk.Aswithmarinemammals,entanglementandconstructionnoiseareconcernsforbaskingsharks,butthereisalsothequestionastohowabaskingsharkmightrespondtoelectromagneticfields(EMFs)from
suspendedpowercables.Basking sharkscertainlyhave thecapability
todetectand react toanthropogenic EMFs transmitted through
electrical cables associated with renewable energydevelopments,but
there is currently no literature availableonwhether they actively
respond
totheseartificialEMFs,norwhethertheremightbeanynegativeimpact.Offshorewind
farms have the potential to affect birds through
fourmainmechanisms;
collision,disturbance,habitatlossandbarriereffects.Theassessmentofcollisionriskisimportantnotjustforbreeding
seabirds originating from nearby breeding colonies, but also for
those that may passthrough during migration and during the
nonbreeding season. There is also a potential risk ofcollision
during construction and harbour testing of the turbine. The HVLA
tendons may
alsoconstituteanadditionalunderwatercollisionriskfordivingspecies.Themainquestionishowbirdsmightrespond/interacttoafloatingturbine(i.e.doseabirdsshowattraction/avoidancebehaviour,resulting
in increased or decreased collision risk? Would a heavily
biofouled/colonised floatingstructure provide a food source for
local diving seabirds, increasing their risk
ofcollision/entanglement?).
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Table of contents
1 Introduction
................................................................................................................................
11.1
Thepurposeofthisdocument................................................................................................31.2
Potentialdevelopmentareas..................................................................................................31.3
Design......................................................................................................................................6
2 Anchoring methods
....................................................................................................................
72.1
Anchoringmethods.................................................................................................................72.2
Examplesofsimilarmoorings.................................................................................................82.3
ComparisonbetweenfixedfoundationsandfloatingTLPanchoring.....................................92.3.1
Seabeddisturbance.......................................................................................................112.3.2
Underwatersound........................................................................................................12
3 Floating TLP turbines and UK protected species
..................................................................
143.1
MarineMammals..................................................................................................................143.1.1
Introduction..................................................................................................................143.1.2
Constructionnoise........................................................................................................153.1.3
Operationalnoise..........................................................................................................163.1.4
Entanglement................................................................................................................173.1.5
Datagaps.......................................................................................................................17
3.2
BaskingSharks.......................................................................................................................183.2.1
Introduction..................................................................................................................183.2.2
Electromagneticfields...................................................................................................193.2.3
Constructionnoise........................................................................................................203.2.4
Entanglement................................................................................................................21
3.3
Seabirds.................................................................................................................................213.3.1
Introduction..................................................................................................................213.3.2
CollisionRisk..................................................................................................................223.3.3
Disturbanceanddisplacement.....................................................................................24
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3.3.4
BarrierEffects................................................................................................................263.3.5..............................................................................................................................................27
3.4
HabitatLossorChange(Includingnoise,sedimentation,electromagneticfields)..............274
Conclusions
..............................................................................................................................
304.1
TLPsedimentdisturbanceandnoise....................................................................................304.2
TLPsandimpactsonmarinemammals................................................................................314.3
TLPsandimpactsonBaskingsharks.....................................................................................314.4
TLPsandimpactsonSeabirds...............................................................................................32
5 References
................................................................................................................................
336 Annexes
....................................................................................................................................
40
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1 Introduction
Inrecentyearstherehasbeenarapidexpansionoftherenewableenergysectortomeetdemandsfor
green energy.Offshorewind farms are viewedbymany, including the
Energy TechnologiesInstitute (ETI),as themajorsourceofenergy in
thissector for the foreseeable future.Todate,alloffshorewind farms
around theUK havehad fixed foundation turbines,
andmostusemonopilefoundations,althoughjacketstructuresandgravitybasestructureshavealsobeenusedonoccasion.There
is, however, a limited area of theUK continental shelfwhere fixed
foundations are costeffective.Theneed
forsuitablewindspeedsandshallowwaterhasmeant thatRound3sitesaremany
kilometresoffshore. This is particularly true for
theDoggerBank,Hornsea and EastAngliazones,
Figure1.Asdistanceoffshore increases, sodoes the cost,both in
termsof accessing
andtransportinghardwaretothesitesandintermsofcablingcosts.The ETI
believes that floating offshore wind farms would overcome many of
the practical
andfinancialchallengesofaccessinghighwindspeedsofftheUKcoast,statingWhilefloatingturbineshaveahighercapitalcost,theycanaccessneartoshore,higherwindsitesofftheWestcoastoftheUK.
The studies showed that this access to high winds close to shore
means they may be anattractive investment;especially compared to
some Round3 siteswhichare locateda longwayfromshore inareasof
lowerwind.Thesestudiesalso indicatedthattheglobalmarket for
floatingturbinesislikelytobeconsiderable.TheGlostenAssociateshavepartneredwiththeETItodemonstratetheutilityofafloatingoffshorewind
turbine termedPelaStar,withadeploymentdateof2016, looks set tobe
the first fullscalefloatingwindturbinedeployedofftheUK.
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Figure1UKRound3offshorewindfarmsites(Crowncopyright).
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1.1
ThepurposeofthisdocumentCefashasbeencontractedbyTheGlostenAssociatestoprovideenvironmentalscientificadvicetoaid
inthedesignprocessofthenew
floatingwindturbinesystem.CefashassubcontractedSMRUMarine Ltd,
theBritishTrust forOrnithology (BTO), andUniversityof Southampton
InstituteofSoundandVibrationResearch(ISVR)tocomplement
inhouseknowledge,andtogethertheaimofthisphaseof theprocess is
tocarryoutadeskbasedstudy toexaminehow thePelaStar
floatingturbinemightinteractwithandperhapsimpactthemarineenvironmentaroundtheUKcoast.Thepurposeofthispositionpaperistoformanexternallyfacingscientificevidencebaseandissplitintotwoparts.ThefirstpartfocusesontheenvironmentalconsiderationsofthePelaStaranchoringsystems.ThePelaStarturbineisbasedonatensionlegplatform(TLP),andwhereasTLPshavebeenwidelyusedwithintheoilandgassector,theyremainlargelyunknownwithinthewindindustry.Assuch,
regulatorybodies that licenceoffshorewind activities
areunfamiliarwith TLP turbines
andtheiranchoringmethods.Thesecondpart
focusesonkeyUKprotectedmarine faunaandhowtheymight interactwith
thePelaStar turbine.Here, keymarine animals are defined
asmarinemammals, basking sharks
andseabirds,althoughtherearemanyothergroupsofprotectedanimalaroundtheUKcoast,includingfishsuchas
lampreys,shadsandeels,marineturtlesandevenbats.However,itisthe
larger,morevisibleanimalssuchasmarinemammals,seabirdsandbaskingsharks
thatattract
themostpublicinterest.Thereisgreaterscientificunderstandingofthelikelyeffectsofoffshoreactivitiesonmarinemammals,andseabirdsthanbaskingsharksandothergroupsofprotectedanimals.ThispaperdoesnotconstituteanEnvironmentalImpactAssessment(EIA),nordoesittaketheformofaScopingReportorEnvironmentalStatement.Inadditiontherehasbeennoconsiderationyetofanycumulativeeffectsofsuchdevices,asthesearedeemedtobeoutsidethescopeofthisreport.1.2
PotentialdevelopmentareasThe flexibilityof the PelaStar TLP
designmeans that it canbe deployed in a varietyof locationsaround
theUK coast, taking advantage ofwind resources that are currently
out of the range ofanchoredwind turbines.Forexample,areason
thewestcoastof theUK,
inwaterdepthsgreaterthan50m,wheretherearehigherwindspeedscouldpotentiallybeacheaperalternativetocurrentUKproposedRoundthreesites(ETI,2013).Deploymentofsuchdevicesasclosetoshoreaspossiblewouldreducecablingandmaintenancecosts,and
it isunderstoodthatseveralcriterianeedtobemet toensure
floatingwinddevices are competitivewith competingoffshorewind
technologies.Suchcriteria
includewindspeed,distancefromgridconnections,andwaterdepth.Ofthese,windspeed
(and the regularitywithwhich appropriatewind speeds are
encountered) is probably themostcrucial.Windneeds tobeconsistent
toensurea regularsupplyofpower.Windspeedsalsoneed to be great
enough to drive the turbine efficiently, but not too high to
trigger a
safetyshutdownoftheturbine.Cablingcostscanformalargecomponentoftheexpenditureofanyoffshorewindfarm.Inordertoremain
costeffective, theETIhas advised thatwind farmsneed
tobedeployedwithina150 kmradius of a grid connection. Water depth
is also key for TLPs; if the depth is too shallow,
TLPtechnologybecomes impractical in termsofbothengineeringandof
cost competition from
fixedwindturbines;howeverwaterdepthsgreaterthan200marenottypicaloftheUKscoastalwaters.BVGassociatesandETIhavedefinedasetofparametersforselectingpotentialsitesfordeployingfloatingwinddevicesaroundtheUK(BVGAssociates,2013).BasedontherecommendationsoftheETI,wehaveconsideredareasaroundtheUKcoastthatmeetthefollowingconditions:
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Meanwindspeedabovebetween9ms1 Within100kmofshore
Waterdepthsgreaterthan50m
Theseareasareshown inFigure2.
IthasalsobeenproposedtotesttheturbineattheWaveHubdemonstratorsiteoffthesouthwesterncoastoftheUK.
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Figure2PotentialareasaroundtheUKcoastlineforaPelaStardeployment.Theareaindicatedisa)within100kmofthecoastb)experiencesaveragewindspeedsofmorethan9ms1andc)isatwaterdepthsofgreaterthan50m.
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1.3
DesignThePelaStarturbineisastandardhorizontalaxisturbinemountedonatensionlegplatform(TLP).
Figure 3 PelaStar Tension LegPlatform (TLP)with standard tower,
nacelle and rotor.Note the fivearmed hull,
fiveanchorpointsandthesuspendedpowercable.
Abovethewaterline,thetower,nacelleandrotorsareessentiallythesameaswouldbeusedonafixed
turbine (Figure3).Thedifferencesbetween thePelaStarTLPand the
traditionallydeployedfixed turbine, however, are the floating
platform, the power export cable and the
anchoringmethods.ThemaincomponentsthatmakeupthePelaStarTLPdesignarethehull,tendonsandanchors.Thehulldesignhas
five arms constructedofhighstrength steel.Attached to these arms
are tendonsmadeupofhighperformancesyntheticropefibre.The
lowerpartofthetendon isconnectedtoahighverticalload anchoring
(HVLA) system. The anchors proposed for the majority of
futurecommercial PelaStar deployments around the UK would be
drivenpile anchors, and
thedemonstratorPelaStarturbineisexpectedtobedeployedattheWaveHubsiteoffCornwallin2016.The
substratum there is very different frommany areasof theUKs
continental shelf,
consistinglargelyofbedrock.Therefore,drilledandgroutedanchorswillbeusedattheWaveHubsiteandforsimilarrockyareasoncommercialdeploymentsinfuture.ThepowerexportcableofthePelaStarTLPissuspendedbelowtheplatforminanSshapebeforeitmeetstheseabed.Thereforeexposedinthewatercolumn,theexposedportionofthecableabovetheseabedwillbefairlyshort,arraycablesarethoughttobeburiedorheldtotheseabedtorestrictmovement.Thisdiffersfromfixedfoundationssuchasmonopilesandgravitybasestructureswherethecableisconcealedwithinthestructureuntilitenterstheseabed.ThePelaStarTLPisdesignedtobedeployedinwaterdeeperthan50m.Thefloatinghullremainsatthesameheightabovetheseabedasaconsequenceofthetension
inthetendons, i.e. itdoesnotfollow tidalchanges inwater level.The
turbinewould remain largely stationary,and the tendonsprovide a
very stable platform in heave, pitch and roll, keeping the tower in
a vertical
position.Thereforeforthepurposesofthispaper,weconsiderthePelaStartobeastationaryobject.
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2 Anchoring methods
ThemooringsystemstobeutilisedinthePelaStardesignareconsiderablydifferentfromthoseusedfor
traditional fixed turbines.Herewe aim to highlight themain
differences between anchoringproposed
forthePelaStarTLPsandthoseusedforthemoretraditional
fixedformofturbine.Twoanchoring methods have been proposed for the
PelaStar TLP: drilled and grouted anchors,
anddrivenpiles.Bothhavebeenusedto installoffshorewind farm
foundations
(monopiles),buthaverarelybeenusedforanchoringsystemssuchasTLPs.Thepurposeofthischapteristo:
Describethetwoanchoringmethodsproposed.
Considerthekeyenvironmentalpressures theseanchoringmethodsare
likely to raise, i.e.
seabeddisturbanceandunderwatersound.2.1
AnchoringmethodsAnanchoringsystemconsistsoftheanchor,themooringlinethattransmitsforcesfromthemooredplatform
to the anchor, and an attachment pointor tensioning system on
themoored vessel
orplatform.Thesesystemsneedtobedesignedgeotechnicallyfor
installationconditionsandholdingcapacityaswellasforstructuralstrengthand
installationandsitespecificconditions(Elaheretal.,2003). Anchoring
systems have been utilised extensively in the oil and gas industry
to facilitateexploitationofresources
indeeperwaters.TherenewableenergysectorisincreasinglyconsideringusinganchoringsystemsforfloatingTLPs,toanchortheirstructurestotheseafloor(seereviewsin(EWEA,
2013; Main(e) International Consulting LLC, 2013). However, to date
none have beendeployedwithintheUK.TheuseofTLPmooringsystems isnovel
foroffshorewind farms,so it iscrucial that the environmental
effects associatedwith thesenewdesigns (where theymaydifferfrom
those in the oil and gas industry) have been reviewed to provide an
evidence base forregulators.Thiswilldecreasethe
likelihoodofdelayduring the
licensingprocess.Theuseofhighverticalloadanchors
isappropriateforTLPsastheyareabletoholdhighvertical
loadsandkeepafloating turbine in position. Anchors, or a
combination of anchors, are selected on the basis
ofsubstratum.Drilledandgroutedanchorsaremoreappropriateforbedrock,whereasdrivenpilesareutilisedforsoftsubstratasuchassilts,claysandsand.ThePelaStarTLPistobeattachedtotheseabedbyhighverticalloadanchors(HVLA)andtensionedtendons.Twooptions
forHVLAshavebeenconsideredwithin this review.
TheproposedPelaStardrivenpileanchoringsystemtobeusedformostUKwaters
isexpectedtobedeployed
insandtogravellysandseabed,buttheseafloorofthedemonstrationlocationproposedinthesouthwesternUK,
at the Wave Hub experimental site, consists of bedrock formed by
slate and sandstone
ofDevonianCarboniferousform(BuscomeandScott,2008).Overall,thecharacteristicsoftheanchorsystem
to be used, e.g. size, shape and installation method, depend on the
seabed and
suchenvironmentalconditionsasseafloortype,wind,waterdepth,wavesandtidalcurrents.
Option1:DrilledandgroutedanchorsDrilled and grouted anchors are
more suitable for hard substratum seafloor conditions such
asbedrock.Heretherearetwooptionswiththedrillingmethods,thedrillbitcaneitherbeextractedorcanformapartoftheanchorfittedtothetendonconnectionpadeye.Drilledanchorswilltake~40hper
anchor to install, equating to ~8.5days in all, assuming a
fiveanchordesign. The groutingwould take ~4060hper anchor
(~813days), again assuming five anchors. The
anchorswillbegroutedintoplacewithtypicalgroutofPortlandcementgrout(Glosten,pers.comm.).
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Drilling will be carried out either from barges or subsea
equipment. It is assumed that
thedemonstratorwillutilisebargemounteddrilling equipment,but
commercial installation in
futuremayusesubseadrillingequipment.Option2:DrivenpipepileanchorsDrivenpileanchorsare
likelytobethemostcommonanchorusedwherethehabitat is
i.e.;softersandandgravel.Thepileanchorsaresteeltubeswithadiameterof2.13.7m(712ft)andare~2346m
(75150 ft) long.Thepilesaredriven
intotheseabedbyanunderwaterhydraulic(suchasaMENCK500or800orsimilar
instrument).Whenthepile isdriven,asection is leftprotrudingfromthe
substratum,which acts as a connection point to the tendons. For
driven pile anchor pointswould
likelyprotrudeapproximatelyonemetreabovetheseabed,drilledandgroutedanchorsarelikelytositflushwiththeseabed(subjecttoscour/depositionofsediment).Theinstallationtimeforthepilesisassumedtobe1.75pilesperday,equatingtoabout3daysforafivearmTLP.An
alternative to impactpiling is vibropiling. There arehowever,nodata
availableon
thenoiselevelsofvibropilinginwatersdeeperthanshallownearshorewaters.Therefore,vibropilinghasnotbeenconsideredwithinthispaper.
2.2
ExamplesofsimilarmooringsBothdrivenpileanddrilledandgroutedanchoringmethodshavebeenusedwithintheoilandgassectorandarecommonlyusedtoanchoroilandgasTLPs,alongwithmostotherfoundationtypes.TLPsareaproventechnology,havingbeenusedwithintheoilandgas
industryfor>30years,withthe firstoilandgasTLP
(theHuttonplatform) installed in theNorthSea in1984
(Randolphetal.,2005). TLPs are now used in deepwater in theNorth
Sea, theGulf ofMexico,WestAfrica andIndonesia
(Randolphetal.,2005;www.floatec.com/images/posters/Offshore2010TLPPoster)andtogether
with other floating and submerged systems have become the principle
platforms
forextractingoilandgasfromdeepwaterregions(JengandBrandes,2011).TLPsystemsrelyheavilyontheirmooringandanchoringsystems,sotheyhavebeentheobjectofmuch
researchand investmentover thepast30years, toensure that
thesystemsbeingusedarebothefficientandeffective(JengandBrandes,2011).DuggalandFontenot(2010)reviewedvarioustypesofpermanent
(anchor leg)mooringsystems for theoilandgassector,evaluating
longtermperformanceandmonitoringtechniques,andtheynoteddevelopmentsand
improvements
inboththesystemsusedandthemonitoringemployedovertime.Further,theyconcludedthatmostofthemooringsystemshadperformedwelloverthe30years.Drivenpileanchorsarecommonlyused
in theoilandgas industry,offering
reliableandpreciselylocatedpositioning
(Musialetal.,2003;OregonWaveEnergyTrust,2009).However,
inhardrock,drilling and grouting is the most effective method of
anchor installation (Musial et al.,
2003).Underwaterpiledrivingwasdeveloped
inthe1980s(Randolphetal.,2005)and
itdiffersfromthemoretraditionalvesselpiledriving,onlyintheadditionofamechanismtopileunderwater,e.g.theuseofapowerpackplaceddirectlyon
thehammer
(www.menck.com).Theuseofapowerpackeliminatestheneedforlonghydraulichosesthattraditionallylinkthehammerwiththepilingvessel.However,
the principle of underwater piledriving remains essentially the
same as for
moretraditionalvesselpiledriving,i.e.thesystemusedcurrentlywithintheoffshorewindfarmsector.Theuseofdrivenpileanddrillandgroutanchoringsystemsisnotlimitedtotheoilandgassector,but
isalsoused inotherpermanentmooring systems,e.g.mooringanoffshore
ironore shipping
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terminal(Gerwick,2007).Similartechnologiesexistwithinthecivilconstruction
industry,
insimilardepthstooffshorewinddevelopmentsites.Drillandgrouttechniquescanbeusedintheinstallationof
bridges, piers, breakwaters and tunnels
(www.pelastarwind.com/anchors). There are
varioussystemsthatcanbeused,e.g.groutedsockanchoranddrillhollowbarsystems,buttheprinciplesremainthesamewhenusedincivil/onshoreconstructionsandintheoilandgassector.In
termsof theoffshorewind industry,mostof the researchon
floatingwindplatformshasbeendirectedatplatformdesignandstabilityratherthantheanchoringsystemsthemselves(MusialandButterfield,2004;MusialandRam,2010;ORECCA,2011).Thismaybebecauseanchoringsystemshavebeenused
forsome time intheoilandgas industrysohaveaproven trackrecordwith
fewchanges/adaptationsbeingrequiredfor implementation.However, it
isalsopossiblethatthefocushasbeenplacedontheplatformsbecausemostoftheinnovativedevelopmentsarerequiredtheretoensurethattheturbinesremainafloatinallweatherconditions.Variousfloatingturbinesystemshavebeenproposedandare
instagesofconceptualandexperimentaldesign.Alternativetypesoffloating
platform (e.g. HyWind Spar design; www.statoil.com) can use
different mooring
andanchoringsystems(withanchortypedependingonwhethertherearemainlyhorizontalorverticalforcesoracombinationofthetwo).However,theGICONturbineproposestouseaTLP,andtankexperiments
have tested a range of anchoring options.Although not detailed,
those options
arelikelytoincludedpiledrivenanddrillandgroutedanchors(www.gicon.de).Overall,althoughunderwaterpiledrivinganddrillandgroutanchoringsystemshavenotbeenusedextensivelywithintheoffshorewind
farm industryyet,vesselbasedpiling
(principallythesameasunderwaterpiling)isalreadycommontothesectorandunderwaterpiledrivinganddrillandgroutanchoringsystemsarewidelyusedwithintheoilandgasandcivilengineeringsectors.Floatingwindfarm
research isheavily invested
inplatformdesignoveranchoringmethods,whichsuggests
thatdevelopersarecomfortablewiththetrackrecordoftheseanchoringsystems.
2.3 ComparisonbetweenfixedfoundationsandfloatingTLPanchoringThe
aimof this section is todescribe thepotential impacts attributable
to thedifferentoffshorewind turbine foundations and to compare them
with those likely to be caused by floating TLPanchoring systems. In
this section, we describe the major impacts of seabed disturbance
andunderwaternoise(otherimpactsaredescribedin(Bremneretal.,2013)).Currently,
floatingwind turbinesarestill in theexperimental stage
(Lambkinetal.,2009;SanjeevMalhotra,2011;Reachetal.,2012),althoughdevelopmentandtestinghasbeenongoingsincetheearly
1990s (Henderson et al., 2002). Information on the likely effects
of anchoring systems forfloatingwind turbineson the seabed
anddeepwater is still scarce,and the same applies toTLPmooring
systems. Therefore, the information reviewed here considers the
PelaStar engineeringdesign details provided by The Glosten
Associates (Moon III and Nordstrom, 2010; The
GlostenAssociates,v.00andv.01,2012),aswellascurrentguidanceusedtoinformEIAstudiesonpotentialimpactsonthephysicalenvironmentattributabletooffshorewindturbinefoundationsforRound1and
Round 2 developments (Lambkin et al., 2009), and relevant published
papers and
greyliterature.Ingeneral,theprincipaloffshorewindfarmfoundationtypesmaybegroupedasfollows(Lambkinetal.,2009;Reachetal.,2012):Monopilefoundations
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Amonopileconsistsofa largediametercylindricalsteel tube
(typicalpilediameter47m)withatransition piece connecting the pile
to the turbine tower. Depending on the soil
characteristics,monopilesarepredominatelydrivenintotheseabedandaresuitableforshallowwaterupto2535mdeep(relatedtoMeanSeaLevel,MSL).Theycanbeinstalledindeeperwater,butthatincreasesthe
cost of development. An existing variant of monopile foundations
for deep water is guyedmonopile towers, allowing the monopile to be
stabilized with tensioned guy wires (SanjeevMalhotra,2011).
Gravitybasefoundations(GBF)Gravitybasefoundationstypicallyconsistofaslendersteelorconcretesubstructuredesignedtobeheldinplacebygravity.Thedesigndependsontheapplication,hydrodynamicregime,waterdepth(normally
shallow todeepwater
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inthewatercolumnwillfalltotheseabed.Therefore,aseabedsedimentdisturbancezonewillbecreated
inahaloaroundthedevicebetweenthe
locationswherethecablesarerepeatedlyraisedfromtheseabed(Figure4).Thesizeandshapeofthedisturbancehalowilldependonthenumber/designof
thecatenarycablesusedand the frequency,magnitudeanddurationofwaveor
tidalevents.
Figure4Schematicpresentationofa catenarymooringdisplaced
(fromposition1 to2)bywaveor tidalaction
(redarrow).Resultantdisturbanceoftheseabedbyraisingor
loweringofcables/chainsystem
isshownasa"halo"withintheanchoringsystem.
Todate,monopileandgravitybasefoundationsarethemostcommonlyusedstructuresinoffshorewind
developments in the UK; multileg foundations and jacket foundations
have been usedextensivelyover thepast40years in theoilandgas
industry (Reachetal.,2012)and toa lesserextent
inoffshorewinddevelopments.Only the impactsof
seabeddisturbanceandnoisewillbereviewed in the following sectionsas
theseare themost relevant in the comparisonofTLPsandmore
traditional fixed turbines. For a wider evaluation of possible
impacts is contained within(Bremneretal.,2013).2.3.1
SeabeddisturbancePotentialimpactsontheseabedassociatedwithfixedfoundationsorfloatingmooringsystemsdifferforthestagesof
installation,operationanddecommissioning.Likelyeffectsontheseabedneedingto
be assessed during the installation phase are those caused by
seabed preparation
activities(temporaryhabitatloss),orthosecausedbythetechniquesusedforinstallation(i.e.drilling,suction,jetting
or hammering). Those activities, also depending on soil condition,
are likely to create
anincreaseinsuspendedsedimentconcentration(SSC),formationofsedimentplumesandchangesinseabed
level. Duringtheoperationalphase,offshorewindturbineswill
leadtoscouringcausedbythe foundations in
termsofseabeddisturbanceaswellaspotentialchanges
tothehydrodynamicregimeasaresultofblockageeffects.Consequently,potentialvariationsinwaveandtidalcurrentsmay
change the sediment transport regime and potentially, (for example)
impact the form and
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functionof anynearby sandbanks.Changes in the sediment transport
regime can impacton theconservation designation associated with
Natura 2000 sites and/or Marine Conservation
Zones(MCZs).Thepotentialeffectsduringdecommissioningofoffshorewind
turbinesmaybesimilar
tothosecausedduringinstallation,buttheywillberelatedtothetypeoffoundationusedbecauseoftheinherentdifficultyinremovingtheentirestructurefromtheseabed(i.e.thepiles).The
study conducted by Reach et al. (2012), based on a review of marine
environmentalconsiderations associated with concrete gravity base
foundations (CGBFs) in offshore winddevelopments, provides an
overview of the generic effects related to the different
foundationoptions.Insummary,seabedpreparationactivitiesintermsoftemporaryhabitatlosshavealowtohigh
impact intermsofGBFs,amoderate impactbysuctioncaissons,a low
impactbymonopiles,multileg and jacket, and negligible to low impact
for floating offshore wind platforms.
Theenvironmentaleffectsattributabletoscourprocessesarehighformonopiles,
lowtomoderate forfloating wind foundations and low for GBFs,
multileg, jacket and suction caisson foundations,because they have
the requirement to use scour protection as a mitigation measure.
Seabedfootprintassessed intermsofhabitat
losshasGBFs,multileg,jacketandsuctioncaissonshavingahighenvironmentalimpact,monopileshavingamoderateimpactandfloatingturbinesalowimpact.Finally,
environmental impacts attributable to blockage effects are high for
jacket and suctioncaissons, moderate to high, depending on the
diameter of the design, for GBFs and
multilegfoundations,moderateformonopiles,andnegligibletolowforfloatingwindturbines.With
regards to the PelaStar TLPdesign, the installationmethodsdescribed
(section 2.1) do
notrequireseabedpreparation.FurthermoreaTLPstructuresuchasthiswouldnotrequireacatenarymooring
system (eliminating the halo effect described in section 2.3
(Figure 4)), which wouldminimise thepotential impacts to
theseafloor.Temporary seabeddisturbance
isexpectedduringtheinstallationphaseastheanchorpenetratesthesedimenttotherequireddepth;whichislikelytocause
temporary habitat loss and sediment disturbance for sand, gravelly
sand, silt and clay
soilsubstratumconditions.A5mdiametermonopilehasa20m2footprintontheseabed,comparedto18m2forfive2.1mdiameterpiledanchorsand54m2forfive3.7mdiameteranchors.Assuchthepotential
environmental effect attributable to TLP installation are
comparable to
monopilefoundationsif2.1mdiameterpilesareused,butwillbesignificantlymoreiflargerdiameteranchorpiles
areused.During theoperationalphase, scour effects around the
anchoringpointsof a TLPwouldbe limited
inhardsubstrata;theseabedfootprint intermsofhabitat losswouldbe
low. Todate, blockage effects have not been identified. In soft
sediments scouring is possible. For
thesmallerdiameterpiles(2.1m)potentialscouringaroundthefiveanchorswouldbe
lessthana5mdiameter monopile (but higher levels would be expected
for five 3.7 m diameter piles).
Theenvironmentaleffectsduringdecommissioningwilldependontheanchoringsystemutilised,butwillbesimilartothosecausedduringinstallation.2.3.2
UnderwatersoundTheanchoringpilesoftheTLParenotverydifferenttomonopilesusedintheNorthSeawindfarms.Thesourcelevelassociatedwithdrivingthesepilesislikelytobeintheregionof250dBre1Pa@1mbutwilldependonthesizeofpileused.WithTLPpilediametersvaryingfrom2.1mto3.7m,TLPpilenoiseshouldfallsomewherebetweenthenoiseexperiencedfortraditionaljacketpinpiles(smallerthantheTLPpilesproposed)andmonopiles
(biggerthantheTLPpilesproposed).Gravitybase foundationdonot
requirepiledriving aspartof their installation,
thereforehavenotbeenconsidered but construction noise effects are
likely to be significantly lower than TLP, jacket
ormonopilefoundations.
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Two different methods are proposed for installing the TLP
anchoring systems, respectively
piledrivingordrillingandgrouting.Theevidence isthatdrilling
issignificantlyquieterthanpiledriving.However,whencomparingthetwoprocessescarehastobetakenthatthepilingnoiseisexpressedindifferentquantitiestothatofthedrillingnoise.Therearesomemoresubtleeffects,associatedwith
thedrillingprocess,which shouldbeconsidered.Specifically, the
tonalqualityof thedrillingnoise issuchthat
itmaybeaudibleoversignificantranges.The
levelsofsuchsoundswillfallwellbelowany thresholds forbehavioural
response currently inuseand sowouldnotbeexpected toelicit a strong
reaction. However the longer duration of the installation process
associatedwithdrillingwillrequireactivityatthesiteforagreaterperiodoftimeandthesupportvesselscouldwellproducenoise
thatexceeds thenoiseof thedrilling itselfacrossmostof the frequency
range.
Inaddition,thegreaternumberofpilingeventsrequiredforthePelaStardesignmeanthatthenoisemaybeemittedmoreoftenand/orforalongeroveralldurationthanforfixedarrays(fivepilesperturbine,comparedwithoneforamonopileandupto4forjackets).The
operational noise from a floating wind turbine is expected to be
reduced relative to aconventionalturbineasaconsequenceof
itnotbeingrigidlyattachedtotheseabed,soremovingone
couplingmechanism.However, there isapotential for strumming
(causedbywatermovingpast the undertension tendons of the PelaStar
design). Strumming noise is likely to be at a
lowfrequencyifatall,Strummingwillbeminimisedduetolowtidalcurrents.Thedecommissioningphaseforthetwoanchoringmethodsislikelytoinducesimilarlevelsofunderwaternoise.
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3 Floating TLP turbines and UK protected species
ManyUKmarineanimalsareprotectedbyUKandEuropeanlegislation,e.g.theEuropeanHabitatsDirective
(92/43/EEC) and European Birds Directive (2009/147/EC). Animals
include
marinemammals(whales,dolphinsandseals),seabirdsandseveralspeciesoffish(suchaslampreys,shadsand
salmon), sharks such as the basking shark, turtles and bats. Fish,
turtles and bats are
notconsideredhere.Theeffectsofoffshorewinddevelopmentsonprotectedfishspeciesarestilllargelyunknown(seeGill,etal.,2012,andMuellerBlenkleetal.,2010forfurtherdetail),andtheeffectsonturtles
and bats are emerging issueswith very little publishedmaterial.
Additionally, the
limitedinformationavailableonthepotentialeffectsofoffshorewindturbinesonturtlesandbatsdoesnotsuggest
thatanyeffectswouldbeunique to floating turbines
(seeAhlnetal.,2009;
Ingeretal.,2009).Marinemammals,seabirdsandbaskingsharksareofbothpublicandscientific
interest,andmanyquestionsstillremainabouttheirpotentialimpactswithoffshorewindfarms.Formarinemammalsthere
is a perceived (as opposed to a proven) concern that certain
species might be at risk
ofbecomingentangledwithinthetethersofafloatingplatform.Therefore,theavailableliteraturehasbeen
reviewed to determinewhether this is simply a perceived concern or
a risk supported
byevidence.However,formarinemammals,thebiggestconcernisunderwaternoise.Intermsofseabirdsthequestion
ishowbirdsmightrespond/interacttoafloatingturbine (i.e.dosea birds
show attraction or avoidance behaviour, therefore resulting in
increased or
decreasedcollisionrisk.Wouldaheavilybiofouled/colonisedfloatingstructureprovideafoodsourceforlocalseabirds?Thisquestionhasbeenconsidered,alongwiththepossibilitythatattractiontoafloatingturbinemightincreasetheriskofcollisionwiththeturbinerotors.Furthertothis,dothetethersoftheTLPposeanyotherthreattodivingbirds?Baskingsharksareahighlymigratorycoastalpelagicspeciesthatiswidelydistributed
inUKwatersandoffIrelandandnorthernFrance(Goreetal.,2008).CornishandScottishcoastalregionsarewellknownhotspotsforbaskingsharks,wheretheycanbeobservedatthesurfaceingroupsfeedinganddisplayingcourtship,mostnotablyaround
theLizard, the IsleofMan, theHebridesand
theClydeSea(Sims,2008;Speedieetal.,2009).Baskingsharkshavebeenincludedherebecausetheproposeddevelopmentareas,bothatWaveHubandatfuturePelaStarcommercialdeployments,arelikelytooverlapwithbaskingsharkmigrationroutes(seeFigure2andFigure5).Aswithmarinemammals,entanglementandconstructionnoiseareperceivedconcerns,but
there isalso thequestionas
tohowabaskingsharkmightrespondtoelectromagneticfields(EMFs)fromsuspendedpowercables.Inall
cases,wehaveonly consideredmarine animals thatare likely
tobepresent inornear
thepotentialdeploymentareasofaPelaStarturbine(Figure2).3.1
MarineMammals3.1.1
IntroductionAseriesofmappingprojectsdocumentthebroadspatial(and
insomecasestemporal)patternsofmarinemammaloccurrencearoundtheUK.(Baxter,etal.,2011;Reid,etal.,2003)Incontributingtotheassessmenthere,thefollowingdatasourceswereexplored:
General(Baxter,etal,2011)Cetaceans(Reid,etal,2003).
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Seals
SCOSReports:ScientificAdvice(www.smru.standrews.ac.uk/sealpopulations)
Greyandharboursealusagemaps
(www.scotland.gov.uk/Topics/marine/science/MSInteractive/Themes/sealdensity)BelowisatableofthekeyandmostcommonspeciesthatoccurconsistentlyaroundtheUK.
Speciesname LatinnameGreyseal
HalichoerusgrypusHarbour/commonseal PhocavitulinaHarbourporpoise
PhocoenaphocoenaShortbeakedcommondolphin
DelphinusdelphisBottlenosedolphin
TursiopstruncatesWhitebeakeddolphin
LagenorhynchusalbirostrisAtlanticwhitesideddolphin
LagenorhynchusacutusRissosdolphin GrampusgriseusKillerwhale
OrcinusorcaLongfinnedpilotwhale GlobicephalusmelasMinkewhale
BalaenopteraacutorostrataHumpbackwhale Megapteranovaengliae
3.1.2 ConstructionnoiseThe
issueofunderwaternoisefromconstructionhas
longbeenaconcernformarinemammals,sotheriskofunderwaternoiseassociatedwithmarinemammals
isrelativelywellstudied.
ThemostwidelyadoptedframeworkforassessingtheeffectofnoiseonmarinemammalsisthatproposedbySouthalletal.
(2007). Thisworkproposes theuseofweighting functions, in thesame
formasCweightingcurvesforhumans.Inparticularthegroupsare:highfrequencycetaceans(e.g.porpoises),midfrequencycetaceans(e.g.dolphins),lowfrequencycetaceans(baleenwhales)andpinnipeds(inairand
inwater). WaveHubsitethemostcommonlyencounteredspecieswillbe
included
inthehighfrequency(hf)cetaceangroupandmidfrequency(mf)cetaceans,alongwithpinnipeds(p).Theweightingcurvescanbeusedtocomputeweightedsoundlevels.Southalletal.
(2007)alsoproposedassociatedthresholdcriteria fortheweighted levels
for
injury(hearinglosspermanentthresholdshift(PTS))andforbehaviouralresponse.Thesethresholdsforexample,forinjuryweightedSELs(soundexposurelevel)of198dBhf,mf,alongwith186dBp,whereasforbehavioural
responses the183dBhf,mfand171dBp. Whilst
themethodologyofconstructingametrichasgeneralacceptance(althoughmostwouldprobablyacceptitisnotcomplete)thevaluesforthestatedthresholdsarelesswidelyaccepted.InparticularthresholdsforPTSarenotconsistentwith
subsequent observed findings that show the (Lucke et al. 2009)
temporary threshold
shifts(TTS)canoccuratlevelswhichareroughly20dBbelowthoseimpliedbySouthalletal.(2007).An
alternative approach is that adopted by the German Government where
a threshold for
anunweightedSELof160dBre1Pa2sisappliedat750m.Anotherapproachwhichhasbeenapplied,especially
within a UK setting, is the dBht. This uses the audiogram of a
species to compute aweightedthreshold. However,themethodsuffers
froma lackofstandardisationand
itsscientificfoundationisnotwidelyaccepted.Asdescribedinsection2.1,twopotentialinstallationmethodswillbeusedinanchoringthePelaStardevice,
one using a drilling/grouting technique and another utilising a
piledriving approach. Formarinemammals,
thenoisegeneratedbydrillingandgroutingmaycause
smallscaledisturbance
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aroundtheinstallationsite,andawiderangeofspeciescouldencounterthedevicewhereitislikelyto
be deployed commercially, ranging from lowfrequency specialists,
e.g.minke and humpbackwhales, to highfrequency specialists, e.g.
harbour porpoises. However, the noise levels fromdrilling/grouting
are likely tobe low (sowouldpropagate lessdistance in thewater) and
canbeapproximated to the noise generated from amedium sized vessel
(Robinson and Lepper, 2013).Moreover, the noise generated by
installation vessel thrustersmay bemore disturbing than
thedrillingitself.Also,itislikelythatanydisturbanceordisplacementwouldbeshortterm(installationtends
to be fairly swift, albeit longer than is estimated for piling) and
small scale (becauseinstallationnoise isnot great). It is
thereforequestionablewhether suchnoisewouldbe able
tocauseauditoryinjurytomarinemammalspeciesthatarelikelytoencountertheconstructionnoisefield.The
noise generated by piledriving installationwould, however, be
likely to have an impact
onmarinemammalsinthevicinity.BasedonthereportednoiselevelsprovidedbyMenck(e.g.>190dBpeakSPL750m
fromthepile),the impactranges (auditory
injury,behaviouralresponse,masking)may be as large as or even
greater than those for fixed foundation wind turbines. An
impactassessmentwouldprobablybeable topredictwithsomeaccuracy the
impact ranges forauditoryinjury foreach
species/speciesgroup,butbasedon currentunderstanding from fixed
installationoffshore wind farms, there is potential for them to be
significant. For marine mammals,
theinstallationscenariodescribedforPelaStarislikelytocausedisturbanceoversignificantranges.Thisisbecausemarinemammalshave
excellentunderwaterhearing and theunderwaternoise
levelsgeneratedaspartofthepiledrivinginstallationmethodwillbehigh.Behaviouralavoidanceofsiteswhere
piles are being driven has been observed for many species of marine
mammal
(e.g.Carstensenetal.,2006;Edrenetal.,2010;Brandtetal.,2011).Theextent
towhichanimalsaredisturbedorperhapsdisplacedwilldependon factors
including (butnot limited to)noise
sourcecharacteristics,watercolumnproperties,bottomsedimenttype,thediameterofthepilesandthedurationofpiledrivingoperations.3.1.3
OperationalnoiseThepotentialfornoisetobegeneratedfromstrumming(causedbywatermovingpasttheundertensiontendonsofthePelaStar)requiresconsideration.Asnotedabove,there
isthepotential
forseveralspeciesofmarinemammaltobefoundadjacenttoPelaStartypeinstallations,rangingfromlow
frequency tohigh frequencyspecialists.Strummingnoise is likely
tobeata low frequency ifatall,Strumming will be minimised due to
low tidal currents. The levels and temporal component of
suchsoundswillneedtobeassessedfurther.Thepotential
forunderwaternoisetobe introduced intothewatercolumn from fixed
foundationwind farms has been assessed before (e.g.Nedwell et al.,
2007;Marmo et al., 2013): themaintransmission route for
suchoperationalnoise is via the foundation into thewater column. If
thenoisetypesgeneratedbyPelaStararesimilar(i.e.fromthegearboxandotherhomologouselementsof
the technology), then itmaybepredicted that theoperational
turbinewillbeaudible
tomostmarinemammalsaboveambientnoise(dependingonthelocationoftheturbineandambientnoiselevels)andinsomecasestherecouldbepotentialforbehaviouralavoidance.Basedonsuchstudiesaroundfixedinstallationsites,itishighlyunlikely,however,thatmarinemammalswouldexperienceauditory
injury from the noise levels generated by PelaStar devices.
However, the
operationaloutputsofafloatingPelaStarunitwouldneedtobeassessedandmonitoredbeforeafullevaluationofthepotentialimpactscouldbeaddressed.
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3.1.4 EntanglementMany species of baleen whale have been
entangled in the subsea ropes of static fishing
gear(Northridgeetal.,2010), thiscauseofmortalityaccounts
forapproximately50%ofbaleenwhalemortalityoff Scotland (Northridge
et al., 2010). Fishing gear (e.g. lines and traps) tends
tobeoflighterconstructionthanthatusedfortetheringTLPs,thoughthe
interactionsofmarinemammalswith aquaculture and static fisheries
(e.g. creel fishing)may be analogous to thosewith
subseastructuresofTLPs.Thecables/tetheringitselfmaybetoolargetoposeanentanglementthreat,butthere
could be similar issuesofwhales interactingwith them, representing
a collision and/or anentrapmentrisk.3.1.5 DatagapsThe following
have been identified as data gaps in terms of what is known about
how marinemammalswillinteractwithPelaStardevices:
pollution increasedturbidity/suspendedsediments
impactsthedevicesmayhaveonmarinemammalpreyspecies
thepotentialforbarriereffects/habitatexclusion
whetherthedevicesmayactasFishAggregatingDevice(FADs)
sealmortalityfromductedpropellersusedonvesselsattheinstallationorservicingphases
There is the risk that construction activity might increase the
turbidity of the water
column.Increasedturbiditycanaffectsocialinteractionsandforagingefficiencyofmarinemammalsandmayalso
affect the prey species. The potential magnitude of such an impact
is, however,
currentlyunclearandwilldependonthecharacteristicsofthelocalenvironment(i.e.waterflow,seabedtype,etc)inthedevelopmentarea.However,itisbelievedthattheseimpactswillbeshortlivedandoverasmallspatialscaleonly.Once
theunitsare installed, it ispossible that,while smallandbenign,
thearraycouldpresentabarrier (either realorperceived) to animalsor
result inhabitatexclusion. It isnot clear towhatextent this
phenomenon exists at this scale orwhether the TLP technology could
cause such aneffect.Anassessmentof thenoisegeneratedby
thedevicesonce
installedandoperationalcouldinformfutureassessments.Thepotentialforafloatingstructuretoattractpelagicfishiswelldocumented(Castroetal.,2002),soTLPdevicesmaywellserveasaFAD.Thisprocesshasthepotentialtogenerateanenrichedornovel
foraginghabitat formarinemammals,and theenhanced
attractionofmarinemammals tothe devices may increase their risk by
increasing their exposure to collision,
entanglement,contamination,etc.ThepotentialbroadscaleimpactsofFADsdoneedtobefurtherconsidered.One
emerging issue identified is the interaction seals have with
vessels with cowled or ductedpropellers (SCNA,2012).Many
sealshavebeenkilledby corkscrew injuries (adescriptionof thewound
likely caused by animals being rotated past a propeller; Thompson
et al., 2010).Consequently, if the use of vessels with such
propellers is planned for the construction
andoperational(intermsofmaintenance)phases,thiswillbeanareaoffurtherconsiderationinfutureassessments.
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3.2 BaskingSharks3.2.1
IntroductionThebaskingshark(Cetorhinusmaximus)isthelargestfishspeciesinUKwaters,attaininglengthsupto
11m andweights of up to 7 t.During spring and summer, basking
sharks tend to aggregatearound the coastsof southwest
andnorthwestUK.Within such temperatewatersof continentalshelves,
theyareoftenseen baskingat theseasurfaceclose toshore,
typicallywith
theirsnout,dorsalfin,caudalfinandbackpartlyexposed(BerrowandHeardman1994;Simsetal.,1997).To
feed, basking sharks favour transitional waters between stratified
and mixed water columns(thermal tidal fronts),actively
selectingareas thatcontain thegreatestdensitiesof
largecalanoidzooplanktonprey (mainly
thecopepodCalanushelgolandicus;SimsandQuayle,1998;Simsetal.,2006).
Swimmingwith theirmouths open, they capture prey in thepassive flow
across their gillarches,a strategyknownas ram filterfeeding
(Sims,1999;Compagno,2001).Ram
filterfeedingallowsupto2000tofwatertobefilteredperhour(FAO,2005),socanbehighinpotentialenergycontent;basking
sharks thereforeneed toactively selectand remainwithinareasof
thegreatestzooplanktonconcentrationstopreventfeedingatanenergeticloss(Sims,1999).Basking
sharksarehighlymigratorycoastalpelagicspecies
thataredistributedallaround theUK,IrelandandnorthernFrance
(Goreetal.,2008).WithinBritishwaterstheyhaveastrongwesterlybiastotheirdistribution,withsightingdensitieshighestoffCornwallandScotland,bothwellknownhotspotswherebaskingsharkscanbeseenatthesurfaceingroupsfeedinganddisplayingcourtship(mostnotablyaroundtheLizardandtheHebridesandintheClydeSea;Simsetal.,2005;Sims,2008;Speedie
etal.,2009). Surface sightings areusually recordedbetweenApril
andOctober,peakingfrom June toAugust, periods that appear to be
correlated significantlywithwarmer sea surfacetemperatures (SST)
and the occurrence of theNorth AtlanticOscillation (NAO), an
atmosphereoceanclimatephasethoughttocauseanincreasetheabundanceofthepreferredzooplanktonpreyofbaskingsharks
(Wittetal.,2012).Literature
(Simsetal.,2005;Southalletal.,2005;BloomfieldandSolandt2008;Wittetal.,2012)andFigure5showthatbaskingsharksfavourtheareaaroundtheWaveHubdemonstrationsiteandwillcertainlymigratethroughanyofthepotentialareasforPelaStarcommercialdeploymentonthewesternsideoftheUK.
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Figure5a)Thedistributionof9,470individualbaskingsharksightingsaroundtheUKandIreland,plottedassinglereddots,b)samedata,plottedassightingdensityper10km2grid,tohighlightthegreatestdensitiesonthewestcoastofScotland,aroundtheIsleofManandoffsouthwesternEngland(fromBloomfieldandSolandt,2008).
3.2.2
ElectromagneticfieldsElectromagneticfields(EMFs)areproducedbyelectricallychargedobjects.Theyareacombinationofelectrical
fields (createdbyvoltageoranelectricalcharge)andamagnetic field
(createdbyanelectricalcurrent).EMFsarepresent throughout
themarineenvironmentandpresent inall
livingorganisms(Kalmijn,1982).SharkshavethegreatestelectricalsensitivityofanyanimalandaregenerallyassumedalsotousetheEarthsmagnetic
field
fornavigationandtobeabletodetectandrespondtootherbioelectricfieldsencounteredwithintheirmarineenvironment.Usingsmall,poreshapedcanals(theAmpullaeofLorenzini,
tinyelectrosensorypores), thatpepper
theirsnoutsandheads,sharkscansense
thetiniestEMFsemittedbypotentialpreyspecies(Kalmijn,1982).Forbaskingsharks,itisthoughtthatthe
spacing and orientation of these pores within their snout enables
them to use passiveelectroreception to guide them towards dense
zooplankton assemblages (Kempster and Collin,2011).Subsurface
marine electrical cables for offshore renewable installations
produce EMFs into themarine environment as electrical currents move
through the cable. These currents have beenestimatedtoemitEMFs
intothesurroundingwaterupto17mperpendicularfromtheaxisofthecable(Gilletal.,2005).TheseanthropogenicEMFscanbealteredbyshieldingthecables,whichwillhelp
to contain theelectrical field,butnot themagnetic field componentof
theEMF.Therefore,
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whenachargedparticle,suchasamarineorganismora
tidalmovement,crosses thepathof
theresultingmagneticfield,afurthermomentaryelectricfieldcanbegenerated.ForallUKmarinespecies
thataresensitive toEMFs, it isevident thatcurrentknowledgeof
theirinteractionwith anthropogenic EMFs is limited and highly
speculative; knowledge of the use orsensitivity toEMFsofbasking
sharks remains largelyunknown.Basking sharks certainlyhave
thecapability to detect and react to anthropogenic EMFs transmitted
through electrical cablesassociated with new TLP or other renewable
energy developments, but there is currently noliterature
availableonwhether they actively respond to these artificial
EMFs,norwhether theremightbeanynegativeimpact.3.2.3
ConstructionnoisePilingoperationsforTLPsarelikelytobetheprincipalsourcesofnoiseanddisruptionthatmayhaveanimpactonbaskingsharkswithinandadjacenttoconstructionareas.Thisstatementisparticularlyimportantbecause
the anticipated installationwindow forTLPs is likely
tobebetweenApril andOctober,when
theweatherconditionsarebestandbaskingsharksaremostabundantat
theseasurfaceoffsouthwesternEnglandforaginganddisplayingcourtship.Few
studies have considered the potential impact of piling activities
on sharks, and hearingcharacteristics of basking and other shark
species remain largely unknown. However, sharks areknown to have
welldeveloped hearing and there is evidence that they can and do
detect andrespond to sound, with sound playing a major role in
their lives (Myrberg 1978, 1990, 2001).Moreover, Casper and Mann
(2009) and Casper et al. (2012) recently determined the
hearingbandwidths of four species of shark; Atlantic sharpnose
(Rhizoprionodon terraenovae),
horn(Heterodontusfrancisci),lemon(Negaprionbrevirostris)andnurseshark(Ginglymostomacirratum).Hearing
rangesweremeasured from 20 Hz to 1 kHz, despite sharks not having
an internal
gaschambersuchasaswimbladderorothergasbubbleassociatedwiththeirhearing(commonlyfoundin
other fish species). Suchmeasurements give an indication of
thepotential hearing range
thatbaskingsharksmayexhibit,butcautionneedstobeappliedsincesuchdataarecurrentlytheonlysource
for future environmental assessments of TLP construction
activities.Note, however, thatgiven the lack of a swimbladder or
gas chamber in basking sharks, and other shark species,
thepotentialforsignificantphysiologicaleffectsassociatedwithconstructionnoisesuchasbarotrauma(physicaldamagetobodytissuescausedbyadifferenceinpressurebetweenagasspaceinternally)shouldbesubstantiallylessthanforotherfishspecies.Themostimportantconcernforbaskingsharksishowpilingandanchoringoperationscanaltertheirnatural
behavioural response or mask other natural marine noise on which
they may rely.Constructionnoisecanmasknaturalmarinenoise involved
in zooplanktonpreycapture,
seasonalcourtshipandeffectivesafenavigationaroundTLPandotherdevelopments.Also,withinthevicinityofTLPs,suchnoisemaydisruptbaskingsharks
fromseekingoutand
feedinghighdensityareasofzooplanktonwithinthevicinity,forcingthemtofeedinlessproductiveareasatanenergeticlossandultimatelyinfluencingpopulationsurvival.Giventheargumentsabove,carefulconsiderationneedstobegiventotheproposedpositioningofTLPs,toprecludetheirdeploymentinimportanthotspottidalfrontareaswithhighseasonalsurfaceabundanceofbaskingsharkaggregationsaroundtheUKcoasts(notablyaroundtheLizard,thewestcoastoftheIsleofMan,theHebridesandtheClydeSea).
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Baskingsharksare,however,highlymobileandadaptiveandhavebeenpreviouslyobservedtoshifttheirhabitatsinresponsetochangesinrelationtootherenvironmentalchangesinzooplanktonpreyabundance(SimsandReid,2002).3.2.4
EntanglementBasking sharks are thought to be particularly
susceptible to collision with vessels and
marineconstructions.Surfacefeedingsharksrarelyshowareactiontoapproachingvessels,oftenappearingunawareofthepresenceofpotentialsurfaceobstacles
(Speedieetal.,2009).Baskingsharkshaverelativelypoorvisionandhavebecomeentangled
infishinggear(Valeirasetal.,2001).Theeffectscanrangefromminorscarringtodeath.Entanglementinsetnets(suchasgillnets)iscommon(Doyleetal.,2005),andwithintheCelticSeaalone
isthoughttoresult in77120baskingsharksannuallybeingkilled
(BerrowandHeardman,1994).However,other static fishinggear suchas
lobsterpotheadropeshavealsoentangledandkilledbaskingsharks(BloomfieldandSolandt,2008).Entanglement
in TLP anchoring tendons and electrical cables might well increase
the levels ofphysical injuryoraccidentalmortality
inbaskingsharks.It is importanttostressherethatTLPswillpresent a
new obstacle for basking sharks and othermarine species unlike
anything theymightpreviouslyhaveencountered.Basking
sharksaregenerally slowmovingandbecauseof their
sizeandseasonalbaskingbehaviouratthesurface,haverelativelylimitedmanoeuvrability,puttingthemat
high risk of collision and entanglement. The potential risk of
collision for basking sharks
willdependlargelyonthevisibilityandthelevelofnoiseemittedbyTLPs,thebodysizeoftheindividualfish,
its levelof social interactionand foragingactivity,and
thequantityandqualityof tidal
frontconditionspresentatorwithincloseproximitytotheproposedsites.3.3
Seabirds3.3.1
IntroductionOffshorewindfarmshavethepotentialtoaffectbirdsthroughfourmainmechanisms(LangstonandPullan2003;DrewittandLangston2004;Petersonetal.,2006),althoughtheydonotallnecessarilyapplyateachofthephasesofconstruction,operationanddecommissioning:
Collision risk (assumed mortality) with abovesurface structures,
especially wind
turbineblades(traditionallyonlyduringoperation,butpossiblyalso
iftestingofturbines iscarriedoutduringconstruction);
Disturbance and the displacement of birds from favoured
habitats,which could result
inincreasedmortalityorreducedproductivityofseabirdpopulations(allphases);
Effectsassociatedwithhabitatlossandchange,e.g.changes
intheseabedthatwhichmayaffectbirdsthroughchangestopopulationsoftheirpreyorpreyavailability(allphases).
Barriereffectstomigratorybirdsorthosecommutingbetweenbreedingsitesandoffshorefeedingareas,whichcouldpotentiallyresult
inelevatedenergycostsandhence
increasedmortalityorreducedproductivity.
Keyissuesforconsiderationofeffectsassociatedwitheither(a)or(b)areseabirdspeciessensitivitytotheeffectconsidered(Furnessetal.,2013,TableA1inappendix),thespeciesassemblagespresentatsea,andtheseabirdpopulationsnearbythatarewithinforagingrangeatthetime(s)ofyearthatthevariousphasesof
construction,operationanddecommissioning takeplace
(Skovetal.,1995;JNCC,2012,2013;Thaxteretal.,2012).
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3.3.2
CollisionRiskCollisionriskisthelikelihoodofseabirdscollidingwithabovesurfacestructuressuchaswindturbineblades,withtheoutcomeassumedtobemortality.Calculationofthecollisionriskusesinformationonthenumberofbirds
inthesurveyarea,followingthestandardmethodologyof(Camphuysenetal.2004),minusthoseexpectedtoavoidthewindfarm,togetherwithspeciesbiometricdataandturbinespecificdataforawindfarm,toestimatetheprobabilityandhencethenumberofbirdsthatmight
be killed through collidingwith a structure. This calculation is
traditionally done using
theacceptedBandmodel,updatedfortheoffshoreenvironment(Band,2012).Theassessmentofcollisionrisk
is importantnot
justforbreedingseabirdsoriginatingfromnearbybreedingcolonies,butalso
forthosethatmaypassthroughduringmigrationandduring thenonbreeding
season.Formigrants, collision risk isbest informed through
considering
likelymigrationroutes,usingrecentlydevelopedtoolsthatcangeneralisethe
likelyareasthroughwhichbirdsofaparticularspeciesmightmigrate(Wrightetal.,2012seeFigure6asanexample)andthenmodelthenumberslikelytopassthroughthewindfarm.
Figure6MigrationzonesofBewicksswansvisitingBritainandIreland(darkblue)andIrelandonly(lightblue)fromWrightetal.(2012).BluedotsshowSpecialProtectedAreas(SPAs)forBewicksswans.
TheTLPturbineissimilarinabovewaterdesigntothatofatraditionalmonopiledesign.Hence,theoverallriskposedtoindividualspeciesislikelytobesimilartothatreportedelsewhereformonopileturbines,andthestandardBandmodel(2000),modifiedforuseintheoffshoreenvironment(Band,2012;Cook
etal.,2012), is applicable, assuming thatotherparametersof the TLP
andmonopiledesignsaresimilar,forinstancerotationspeed(e.g.upto8.8rpm)andapitchof10degrees.
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Thedemonstratorturbinewill likelybetested
intheharbourbeforebeing loweredtoahorizontalposition and loaded
onto a transporter vessel to be deployed in place at the Wave Hub
site.However, the rotation speed of the rotor during testing will
be minimised to avoid powergeneration. Despite the rotation speeds
being lower, any test undertaken in a harbour
wouldconstituteanadditionalcollisionriskforseabirds.Duringthetestingphase(althoughitisnotedthatthisphasewouldbeshortterm),considerationwouldneedtobegiventopopulationsofseabirdsinthevicinityoftheharbour,includinganyprotectedpopulations(includinglocationoftheircoloniesandforagingranges;Figure7).Collisionriskalsoappliestootherwaterbirds(Cooketal.,2012),ofwhich
theUK holds internationally important numbers,mainly during their
nonbreeding
season(Holtetal.,2012).Asaconsequence,informationonimportantwinteringsitesofwaterbirdsnearbyandthepassageofsuchbirdsthroughorovertheharbourwouldneedtobeconsidered.Figure7Exampleoflesserblackbackedgulldistributionfromprotected(SPA,SSSI,Ramsar)breedingsites(seeTableA1inappendixfornumberperspecies),duringthebreedingseason,basedonknowledgeoftheirforagingrange(Thaxteretal.,2012,meanmaximum
foraging range=141km) (note thisdoesnotaccount
forwintering/migration
range).AlsoshownareallrecordsofthespeciesatseafromEuropeanSeabirdsatSeasurveys(conductedusingvariousmethodsindifferentseasons)absenceofadotdoesnotnecessarilymeanthebirdsdidnotusethearea.
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Collision risk will also depend on the sensitivity of the
species considered at the Wave
Hubdemonstratorsite(seeTableA1inAppendix).ThePelaStardevice is
likelytohave
littlebiofoulingprotection;antifoulingcoatingwillpotentiallybeusedatthetendonconnectionpoints,mainlytoaideasyremovaloftendons
inthefuture,andhoweverthismeansthatsomebenthiccolonisationmayoccuronnoncoatedpartsofthetendons.Seabirdsseekingtoaccessthisadditionalpreysourceclosetotheseasurface,maybeattractedtosuch
benthic colonisations (see below for more detailed discussion under
habitat loss/change),whichmay raise their collision risk as a
consequence. Hence this potential impact needs to
befactoredintothecalculationofcollisionrisk.The cable carrying
thepower to the grid is able tomove
aroundunderwater,perhapsbecominganotherhazardfordivingseabirds,butsuchaneffectislikelytobelocalised.ForthedemonstratorTLP,
five individualtendonsofthicknessca.200mmextenddown from
thePelaStarandareanchored to the seafloor.The fixed tendons
thatkeep the turbine
inplacemayconstituteanadditionalunderwatercollisionriskfordivingspeciessuchasscoters,divers,auksandcormorants/shags,allofwhich
forage forpreyvisuallyunderwater,divingdown fromthesurface.However,
plungedivers such as gannets should not be impacted by deployment
of the
PelaStardevicebecausetheywouldbeunlikelytodiveinthevicinityoftheturbine.With
the increased number of turbines at a commercial level of
deployment, the potential forunderwater collision risk increases.
Moreover, the use of a threearm rather than a fivearmstructure
increases thenumberof tendonsper arm to two rather thanone. Such a
change at acommercial
levelmayposeanincreasedriskofentanglement/collisionofseabirdsbetweendoubletendons,whichwillnotapplytothedemonstrator.Speciesmostatriskintermsofthiseffectarethedivingspeciesnotedpreviously.Giventhelittlepublishedinformationavailabletodeterminetheriskofunderwatercollisionandthefactthatcompetingpressuresmaybeacting
indifferentways(e.g.theabsenceofbiofoulingallowing reef
constructionand theattractionof foraging seabirds), it
isdifficulttosaymorethanthatthethreatposedbyTLPstoseabirdsintermsofcollisionriskishighlyuncertain,butmaywellbegreaterthanfortraditionalmonopileturbines.3.3.3
DisturbanceanddisplacementDisturbanceanddisplacementareinterlinkedand,inessence,reflectdifferentlevelsofseverity.Theeffect
of disturbance refers to an effect that causes a direct behavioural
reaction of a bird,
e.g.increasedvigilanceoraflight/diveresponse.However,prolongeddisturbancecouldresult
inmorelongtermdisplacementfromapreviouslyfavouredhabitat,whichmaybecomepermanent
ifbirdsareunabletohabituate.Thesensitivityofseabirdstotheseeffectsvariesbetweenspecies(Macleanetal.,2009seeTableA1).Duringtheoperationofawind
farm,there ispotential for longtermdisplacement merely because of
the longterm presence of moving turbines and the
associatedmaintenanceboat
traffic.Suchdisplacementconstitutesaneffective lossofhabitat
(DesholmandKalhert2005;Langston2010).Behaviouraldisplacementiscommonlyequatedtomacroavoidance,althoughinthecontextofcollisionriskmodellingitreferstofarfieldevasiveactiontakenbyaflyingbird
toavoid thewind farm totally (Band,2012).Displacement, incontrast,
reflects the
longtermlossofallbirdsfromanareaofhabitat.Althoughdifferent,themacroavoidanceratesrecorded
instudiesofbird flightpathshasbeen used to
informonpotentialdisplacement ratesofdifferentspecies in
recentenvironmental impactassessments.Atpresent, there isonlya
relatively limitedevidence base on the effects of displacement from
offshore wind farms, and it is also unclearwhether
therewouldbeanyhabituationover time tonewstructures
(LangstonandPullan2003).LongtermhabituationhasbeenrecordedforcommonscoteratHornsRevwindfarmbyLindeboom
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etal. (2011),butsuchdataare lacking
formostspecies.Theevidencecurrentlyavailablesuggeststhatdifferencesexistintheratesofdisplacement,orattraction,betweendifferentspecies(Zuccoetal.2006Petersenetal.,2006and2011;PetersenandFox,2007;Krijgsveldetal.,2010and2011;APEM,
2011; Rexstad andBuckland, 2012).A classificationdetermined
byMaclean et al. (2009),incorporates informationon
speciesspecificbehavioural responsesusing indicationsof
sensitivitysuggested by Garthe and Hppop (2004), Petersen et al.
(2004) and Petersen and Fox
(2007).Furnessetal.(2013)usedascoringsystemsimilartothatofMacleanetal.(2009)toestablishthesensitivityofseabirdstodisplacementcausingfactors:1=verylow,2=low,3=medium,4=high,and5=veryhigh(Table1Speciessensitivitytodisturbancefromboats(derivedfromFurnessetal.,2013)).Theworstcaseassumptionofdisplacementoverthelongtermisthatapopulationwilldecreaseasaconsequence
of mortality (e.g. direct mortality of the adults because they are
unable to findalternative habitat) or suffer reduced breeding
success (e.g. McDonald et al., 2012).
Longtermfitnessconsequencesofdisplacementneedtobemeasured,buttheycannotbecondensed
intoasinglenumber(RexstadandBuckland,2012).Moreover,speciesresponsesarelikelytobevariablydependentonhabitatlossflexibility(Table2Speciessensitivitytohabitatloss(derivedfromFurnessetal.,2013))anddiet(seeBirdlifeInternational,2012),aswellasonthecarryingcapacityofanareaandtheabilityofaspeciestohabituatetoanotherarea(LangstonandPullan,2003).Table1Speciessensitivitytodisturbancefromboats(derivedfromFurnessetal.,2013)
Sensitivity todisturbance
Species/speciesgroup
VeryHigh Common scoter, velvet scoter, redthroated diver, great
northern diver, blackthroateddiver
High Commongoldeneye,greatcormorant,greaterscaup
Medium Common eider, longtailed duck, greatcrested grebe,
Slavonian grebe, shag,razorbill,blackguillemot,commonguillemot
Low
Northerngannet,herringgull,greatblackbackedgull,littletern,littleauk,blackheaded
gull, common gull, lesser blackbacked gull, blacklegged
kittiwake,Sandwichtern,commontern,roseatetern,Arctictern,Atlanticpuffin
VeryLow Great skua, northern fulmar, sooty shearwater, Manx
shearwater,
Europeanstormpetrel,Leachsstormpetrel,Arcticskua,littlegull
Table2Speciessensitivitytohabitatloss(derivedfromFurnessetal.,2013)
Sensitivityduetohabitatloss
Species/speciesgroup
VeryHigh RedneckedgrebeHigh Greater scaup, common eider,
longtailed duck, common scoter, common
goldeneye, redthroated diver, blackthroated diver, greatcrested
grebe,Slavoniangrebe,littletern,blackguillemot
Medium Velvet scoter, great northern diver, great cormorant,
shag, Sandwich tern,
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common tern, roseate tern, Arctic tern, common guillemot,
razorbill, Atlanticpuffin
Low
Arcticskua,greatskua,blackheadedgull,commongull,greatblackbackedgull,blackleggedkittiwake,littleauk
VeryLow Northern fulmar, sooty shearwater,Manx shearwater,
European
stormpetrel,Leachsstormpetrel,northerngannet,lesserblackbackedgull,herringgull
Vesselswillbeusedtotowtheturbine (onaplatform)
intoplace.Forboththedemonstratorandthecommercialdeployment,constructionwouldtakeplaceovera24hourperiodandtakebetween3
to 13days. Such towing anddeployment activitymay cause disturbance
tobirds preferring toavoidboatsandanyother
infrastructure.UnderwateractivitiesassociatedwithdeploymentofthePelaStar
(e.g.tendonsbeingdroppedandanchoredtotheseabed,usingdrillingandgrouting)willaffectspeciessuchasdivers,scoters,auksandotherseaducksthataresensitivetothepresenceofboats(Furnessetal.,2013,TableA1inappendix)andmayhavecoloniesnearby(JNCC,2012),withinforagingrangeof
thesite (Thaxteretal.,2012).Underwater
foragerssuchascommonguillemots,razorbills, and Atlantic puffins are
seen at the Wave Hub site (JNCC, 2013) and may show anunderwater
disturbance reaction to structures being deployed (see also the
section above
onunderwatercollision).Therewillbeaneedtocollectfurther
informationonprotectedpopulationsnear the area of
deployment.However, disturbance should benoworse than the
installation
oftraditionalmonopilefoundations.Thepresenceofasinglewindturbineisunlikelytocauseconsiderableeffectivehabitatloss,andthepotentialfordisturbance/displacementissimilartothatofatraditionalturbine.Widerscalehabitatlosswouldbeseenatacommercial
leveldeploymentoffloatingturbines,however,andtheeffectonseabirdswillbespeciesspecificanddependonthelocationchosenfordevelopments(Skovetal.,1995;
JNCC 2012, 2013; Thaxter et al., 2012). Again, the impact will be
similar to that from
atraditionalmonopileturbinewindfarm.Theeffectofdisturbance/displacementduringdecommissioningislikelytobesimilartothatduringconstructionforbothdemonstratorandlargerscalecommercialdeployment.Theprocessshouldberelativelyquickforfloatingturbinesandlikelymorefavourablethanforthedecommissioningphasesof
fixedmonopile turbines, requiring less vessel time at
sea.Nevertheless, the activitywill
causesomedisturbanceandconsequentlydisplacementofbirdsthroughtheirnegativereactiontoboattraffic,dependingagainonthespeciessensitivity(Furnessetal.,2013)andtheassemblagespresentatseaatthetimeofyearthatdecommissioningisundertaken.Thismayincludeaneffectonspeciesthatmightovertimehavehabituatedtotheeffectofthewindfarm.However,habitatwouldthenbegained
from the removalof the turbine.Although it ishard togeneralise
theeffectsgiven thevariability inspeciessensitivities, it
isanticipatedthatthedurationandextentofdecommissioningactivities
forfloatingturbineswillbenoworsethanforexisting fixedwind
farms,andagainshortterminnature.3.3.4
BarrierEffectsTraditionalwindfarmsmayposeabarriertomigratorybirdsorthosecommutingbetweenbreedingsitesandoffshorefeedingareas,whichcouldthenresultinelevatedenergyneeds(Speakmanetal.,2009)andevenpotentiallyincreasedmortalityorimpactsonproductivityatthecolonies.Increasesin
theenergycostsofdailymovementsof seabirdsorof
themovementsofmigratorybirdshavebeenshown inanumberofstudies
(Tulpetal.,1999;PetterssonandStalin,2003;Masdenetal.,2009, 2010),
although Masden et al (2009), reported changes in the migratory
trajectories ofcommon eiders at a Danish offshore wind farm
postconstruction, they suggested that this
hadminimallikelyeffectonthespeciesenergetics.However,itwasnotedthatcumulativeeffectscould
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besignificant,for instance,
ifotherwindfarmsorhumandevelopmentsworked
incombinationtodisrupttheroutesofbirds.DesholmandKalhert(2005)alsoreportedthatmigrantwildfowldivertedaroundtheNystedwindfarm,andTulpetal.(1999)foundthatcommoneidersdidnotflybetweenwindturbinesplaced200mapartintheKattegat.Duringconstruction,aprogressiveincreaseinthenumberof
turbines ata commercial scalewould increasinglypose a
greaterbarriereffect.Upondecommissioning, removal of the entire
wind farm would remove any barrier to
movementpreviouslyimposed,thenconstitutingapositiveeffect.Whilenotanissueforthedemonstratorturbine,atacommercialscaleofdeployment,theextentofthis
effectwill depend on the number of turbines eventually installed,
the area covered by
thedevelopment,andimportantlytheseabirdspeciescompositionsandnumberspresentseasonallyintheareabeingdeveloped.Differentspeciesare
lesssensitive toagreateror lesserdegree to
thiseffect(seeTableA1inappendix).Theassessmentofbarriereffectsistypicallybestassessedthroughdirectlymonitoring
individualbirdsmovingthroughthewindfarmzone,for
instanceusingtrackingtelemetryor radar (e.g. Krijgsveldt et al.,
2011).However, formany species,particularlymigrantspecies, a lackof
informationon trackedbirdsmeans that it is impossible
todeterminewhetherindividualstraverseanarea,nor is
itpossibletoassessthealtitudeatwhichtheyflyandthereforewhatroutesmightbebeingaffectedbythepresenceofawindfarm(althoughseeKrijgsveldetal.,2011).Analternativemethod
is togeneraliseonthe
likelyareasthroughwhichbirdsofparticularspeciesmightmigrate
(Wrightetal.,2012seeFigure6asanexample, in thiscase
forBewicksswans)andthentomodelthenumbersthatarelikelytopassthroughthewindfarm.TherearenodifferencesbetweentraditionalturbinesandfloatingTLPturbinesinthiseffect.3.4
HabitatLossorChange(Includingnoise,sedimentation,electromagneticfields)Duringallphasesofawindfarmsexistence,therearemanywaysbywhichbirdsmaybeimpactedeitherdirectly
throughalteringtheirhabitat,or indirectlythroughchangestotheirprey,
thatmayimpact the seabirds themselves.Sucheffects includehabitat
lossattributable to theexport cablecorridorandwind
farm,habitatchangesaffecting theavailabilityofprey speciesby, for
instance,duechangingthelevelofsuspendedsediments(whichcanaffectabirdsabilitytodetectandcatchprey
aswell as influencing the absolutenumbersofprey),underwaternoise
fromdrilling,piling,hammering or other construction activities,
electromagnetic frequencies (EMFs), and changes
tofishingactivityasaresultofthepresenceofawindfarm(longterm,throughouttheoperationallifeofthefarm).Evidencefromotheroffshoreactivitiessuchasaggregatedredging(CookandBurton,2010)suggeststhoseseabedhabitatsandthebenthic
invertebratesandfishfaunaassociatedwiththemmightbealteredbyallwindturbine
installationandcablelayingactivities,potentiallyhavingsome impact
on bird assemblages, although this is likely to be short term, with
recoverycommencingafterconstructionhasbeencompletedTheattractionoffloraandfaunatomanmadestructures,suchasoilplatforms,piersandwrecksiswelldocumented,
and includes positive effects on benthic flora and fauna,
zooplankton and fish(Wolfson etal.,1979;Baird1990;Wiese
etal.,2001;Wilhelmssonetal.,2006b; Langhamer
andWilhelmsson,2009;Langhameretal.,2009).Suchchangestofloraandfaunamaythenattracttheprey
species of seabirds (Wiese et al., 2001; Wilhelmsson, 2012). For
example, species such ascommoneiderand scoters forageon
themusselsandshellfish thatestablish
themselvesonmanmadestructures,althoughtheseabirdspeciesdotendtoavoidwindturbinesspecifically(Furnessetal.,2013,TableA1inappendix).ThePelaStarfivearmstructurehasindividualarmradiiof31.18m,awidthof3m,andapotentialdepthperarmofuptoca.9m.Fromthis,
justacrudecalculation(whichcannotbeexactbecauseof thecomplexityof
thecentral structurewhere
thearmsmeet)yieldsasurfaceareaperarmof744m2,or3,720m2forfivearms.Hence,evenforasinglePelaStar
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turbine, theamountofhabitatcreatedwillbe large,becauseof the
largehull.However,seabirdsmayalsobenegatively impactedbychanges
inthedistributionsoftheirprey.Attractioncausedbyhabitatbecomingmoresuitablemayalsomeananincreaseintheriskofcollisionforsomespecies,or
itmay lessenor reverse the impactofdisplacement
causedbydisturbance. Impactsmay
alsoeventuateonseabirdsbreedingnearawindfarm.Forexample,Perrowetal.(2011)examinedpreyabundancebeforeandafterassessmentofa30turbinedevelopmentatScrobySands,SEEngland,toassessthe
likely impactsonanearbycolonyofbreeding littleterns.Themost
importantprey inthe chickdiet,youngoftheyear (0group)herring,
showeda significant reduction from2004on,unexplainedbyenvironmental
factors, so turbine installationwas suggested tohaveaffected
fishreproductionlocally(Perrowetal.,2011).Availabilityofthesepreyspeciesinthetop45cmofwatercausedchangesinlittleternforagingbehaviour,andinturnmayhavecontributedtoincreasedeggabandonment
and low hatching success in subsequent years (Perrow et al., 2011).
The exampledemonstrates the importance of adopting sensible
precautionary approaches to the timing
anddurationofpiledrivingactivity(Perrowetal.,2011).Indirecthabitatchangeforseabirdsmayalsoarisethroughreducingthe
impactoffisheriesonthehabitats of prey species underwater. Changes
to fishing practice may affect fish and shellfishpopulations and
hence the seabirds. However, as fishing may cause damage to seabed
habitat,disturb sediments, directly removes plants and other
organisms and alter habitat structure, areduction in
fishingcouldhaveapositiveeffect
formarinecommunitiesandseabirdpreyspecies.TheplannedconstructionactivitiesatthedemonstratorWaveHubsitehavethepotentialtocausedirecthabitatlossthroughexportcableconstructionandtheareaaroundthatcableontheseafloor.For
seabird prey, the area of seabed potentially affected is likely to
be small and unlikely to begreater than for a traditional fixed
wind turbine. For all commercial wind farms, changes
tocommercialfishingactivityasaresultoftheirestablishmentarelikelyandmaywellhaveanimpactonseabirds,generallythroughforaginghabitatandpreyavailabilitybeingaltered.Wind
turbinesmayalsohavepositiveeffects,attractingbirds
(increasinghabitat),providing themwithplatforms forperchingand
roosting
(Petersenetal.,2006;Krijgsveldetal.,2011).Birdsmayalsobeattractedtolightingaroundoffshorestructures,whichmayhelpthemlocatenocturnalprey(Sage,1979;HopeJones,1980;Taskeretal.,1986;Wieseetal.,2001).Agradual
increase in
thenumberofturbinesinasingleareawillofferincreasedopportunitiesforsomespeciestoperchandroost.Underwaternoisemayaffect
theprey speciesof seabirds (see
sectionsonmarinemammalsandbaskingsharks
formoredetail).Theeffectmaybeseen through lethal/injury toprey for
instancefrom auditory system damage, and behavioural changes in
swimming and schooling behaviouraffecting spawning which may in
turn affect nursery grounds, migration and feeding
patterns.Sedimentationhas thepotential toaffectdivingbirds
suchasdivers, scoters,
seaducks,auksandshags/cormorantsthrougheitherdirectdisruptionofnavigationinthewatercolumnandlocationofprey,orthroughaffectsonthepreythemselves,
indirectly impactingtheseabirds.Alossofhabitatmay impact
lessmobilespeciesmore,but inparticular itmay
impactshellfish,sandeelsandotherfish species
thathavehabitatpreferences, aswell as their eggs and larvae, for
instance throughreducing the likelihoodof theeggshatching, reduced
feedingand survivalpossibilities for larvae,adult suffocation (e.g.
of sandeels buried in the seabed), and the temporary loss of
spawninggrounds. It
isalsopossiblethatchangestothehydrographyduringoperationofthewindfarmcaninfluencethedistributionsofpreyspeciesofseabirds.DuringtheoperationalphaseofaTLP,noisemaybeproducedfromtheunderwatertendons(e.g.bystrumming)andexportcable,howeverthisisthoughtobeverylowifatall.Currently,thepotentialextentofthisdisturbanceanditseffectonseabirdsand/or
theirprey isunclear.Thegeneratorwouldbeexpected toproduce justa
regularnonintermittentlowdecibellevelofnoise,however,andthatwillnothavemucheffectonseabirds.
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Prey distributionsmay also be disrupted as a consequence of the
electromagnetic fields (EMFs)around installations throughout all
phases of a wind farms life, resulting in changes in
seabirdbehaviour (e.g.migrationpatterns and feeding
activity).However, thepotential impactsof
EMFsfromcablesonfishandseabirdsareveryuncertain(Gilletal.,2005,2009;GillandBartlett,2010).OneissuetonoteisthepotentialforalienhabitatsandnewspeciestobeintroducedwhenaTLP,orlateranextendednumberofTLPs,isdeployed.That,aswithanyothernewdevelopmentinthesea,isakintocolonisation,whichmighthaveknockonandpossiblypositiveconsequencesforseabirds.Thedietsof
speciessuchasgullsarediverse (seeBirdlife International,2012),so
introducinganyalienspeciesmayactuallyintroduceanewpreysourceforseabirds.Attheconstructionphase,sedimentmaybemobilisedbythedrillingandgroutingprocessapplied,andscouringcanarisearound
theanchors.Theknockoneffects toseabirdsand theirprey
isstillconsidered tobe localised,
intermittent,andshortterm.Finally,changes to the
localhydrographyduring operation of a commercial floating turbine
wind farm may conceivably influence
bothseabirdsandtheirpreybyalteringthemicrohabitat.HoweverthenatureofsuchchangesfromaTLPdesignareunknownatpresent.Table3Summary
comparisonofTLP floating turbinesandmonopile turbines
fordifferenteffects for seabirdsat thecommercial
level,andwhicheffectsarepredicted (basedon information received)
tobebetter (+),worse
(),ornodifferent(.)fortherespectivedesigns.
Stage Construction Operation DecommissioningTLP Monopile TLP
Monopile TLP Monopile
Abovewatercollisionrisk + . . . .Entanglement /
underwatercollision
+ Disturbance anddisplacement
+ . . + Barriereffects . . Habitatlossorchange . . + .
.Underwaternoise + . . + EMF . . Sedimentation + + Smothering
Ballast water issues /pollution
. . . .Scour . . . .
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4 Conclusions
The PelaStar floating turbine is a TLP designwith two possible
anchoring options dependant onsediment characteristics. This report
has shown that TLPs and their anchoring options are wellknownwithin
other offshore and onshore sectors, having been used successfully
for the last
30years.Floatingwindturbinesareanemergingtechnology,howeverthemajorityoftheresearchtodatehasfocussedontheplatformdesignandstability,possiblybecausedevelopersarecomfortablewiththetrackrecordoftheproposedanchoringsystems.Themajor
impacts reviewedwhen comparing TLPs andmore traditional foundations
are seabeddisturbance and underwater noise.Overall, the type of
impacts for all foundation types are thesame,however,theextentofthe
impactchangesdependingonfoundationtype(Error!Referencesourcenotfound.).4.1
TLPsedimentdisturbanceandnoiseThePelaStar
installationmethodsdonotrequireseabedpreparation,minimisingpotential
impactson the seafloor. Temporary seabed disturbance is expected
during the installation/constructionphaseowing to thepenetrationof
theanchor into thesediment; this is likely tocause temporaryhabitat
loss and sediment disturbancewhere sand, gravelly sand, silt and
clay are the dominantsubstrata, (compared with rock at the Wave Hub
site). Potential impacts from the installationmethods likely for
the anchoring systems are comparable with those caused by
monopilefoundations;however,becauseTLPinstallationutilisesfive(albeitsmallerdiameter)anchorpilestheeffectswillatbestbeequivalent
toamonopile foundation,but incertaincircumstancescouldbegreater.
Scoureffects shouldbe limitedand the seabed footprint in
termsofhabitat losswillbelowest for the smallest (2.1 m diameter)
anchor piles. Environmental effects
duringdecommissioningwilldependontheanchoringsystemutilisedasthepilesaredifficulttoremove.Two
different methods are proposed for installing the TLP anchoring
systems, respectively piledriving or drilling and grouting. The
noise generated by piledriving the anchors are not verydifferent to
that generated bymonopiles used inmostNorth Seawind farms. The
source levelassociatedwithdriving thesepiles is likely tobe in the
regionof250dB
re1Pa@1mbutwilldependonthesizeofpileused.Theevidenceisthatdrillingissignificantlyquieterthanpiledriving.The
operational noise from a floating wind turbine is expected to be
reduced relative to
aconventionalturbineasaconsequenceofitnotbeingrigidlyattachedtotheseabed.However,thereis
a potential for strumming (caused by water moving past the
undertension tendons of thePelaStar). Thedecommissioningphase for
the two anchoringmethods is likely to induce
similarlevelsofunderwaternoise.Table4Comparisonoffoundationtypewithseabeddisturbanceandnoiseimpacts(adaptedfromReachetal.,2012).
Foundationtype Habitatloss Scour NoiseGravityBases Lowtohigh Low
LowSuction Moderate Low LowMonopile Low High High
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Multileg Low Low LowtoHighJacket Low Low ModerateFloating
devices (otherthanTLPs)
Negligibletolow Lowtomoderate Moderatetolow
TLPs Low Moderatetolow
4.2
TLPsandimpactsonmarinemammalsDuringconstruction,underwaternoise is
likelytobethekeymechanism indisturbingtherangeofmarinemammal
species likely to encounter the device. Themethod of installation
chosen
(piledrivingvs.drillingandgrouting)willhaveasignificanteffectontheextentofdisturbanceandcouldcauseauditory
injuryout to largedistances from the site.Drillingandgrouting is
likely
tohaveamorebenigneffectonmarinemammals.Duringtheoperationalphase,themainimpactonmarinemammalsofthePelaStarTLPwillbeaheightenedriskofcollision,entanglementandentrapment,especiallyforlargebaleenwhales.Dependingonthenoisecharacteristicsofanystrumming,theremaybepotentialfordisturbingmarinemammals.There
are data gaps in scientific knowledge. Increased turbidity may
impact foraging, but thepotentialmagnitude
isunknown.Acommercialarraycouldpresentabarrier
tomarinemammals,butthereisnoevidencetosuggestwhetherfloatingturbinescouldcausesuchanimpact,andiftheycould,at