GreenHighlandRenewables

LochEtiveHydroDevelopments

SubmarineCableMarineLicenceApplication

Appendix1–MethodStatementIncludingScheduleofWork

1.1 IntroductionThisMethodStatementdescribeshowGreenHighlandRenewableswouldinstallasubmarinecableacrossLochEtivetoconnectanewhydro-electricinstallationontheAlltEasachriver.Thedocumenthasbeenprepared in supportof amarine licenseapplication toMS-LOTS.Some additional information has also been provided on the operation, repair and de-commissioningofthecableshoulditnolongerberequiredatsomepointinfuture.1.2 TheProposedSubmarineCable/RouteLochEtiveisanaturalsealochonthewestcoastofScotlandwithrelativelylowsalinityduetotheconstrictionattheentrancecausedbytheFallsofLora.ConnectionoftheAlltEasachhydroschemewillrequiretheinstallationofa33,000VcableontheseabedofLochEtive.Inchoosingarouteforthecable,GHRhavelookedatanumberofoptionsbeforedecidingontheproposedroute.NavigationalchartsandsonarsurveyssuggestedasuitablerouteexistedbetweentheheadlandonthesouthsideofArdmaddyBayandthebeachimmediatelytothewestofRhubhaBharr,approximately19kmbyseafromConnelBridge,asshowninFigure1.TheScottishAssociationofMarineSciencewerecommissionedtocarryoutabathymetricandecologicalsurveyoftheseabedovertheproposedroute. Basedonthesesurveystheinitialdesignwasmodifiedslightlytoallowtheproposedcableroutetoavoidareasofcobblesandboulderswherepossible.Thisshouldallowthecabletosinkintothesoftmudseabedintimeovermuchoftheroutelength.

Fig1–LocationPlanforProposedCableRouteAcrossLochEtive

Figure2–ProposedCableRouteAcrossLochEtiveTheNorthShoreEndPosition(NSE)is56°30.260N05°08.183W.TheSouthShoreEndPosition(SSE)is56°29.372N05°08.193W.TheCableLayingVesselhastobepositionedbetween100mand250moffshoretoavoidgroundinginshallowwater.Thevesselsspudlegsaredeployedatthesepositionstoholdpositionwhilethecableisbeingpulledashore.ThetwopositionsareknownastheNorthTransitPositionandtheSouthTransitPosition.TheNorthTransitPosition(NTP)is56°30.140N05°08.190W.TheSouthTransitPosition(STP)is56°29.401N05°08.265W.

AllpositionsrelatetotheWGS84chartdatum.Thecentrelineoftheproposedroutecanbeprojectedbetweenthesefourpositions.Thecablewillbelaidwithina40mcorridorontheseabed,20moneithersideofthecentreline.1.3 CableDesignThetypeofcableproposedforuseinLochEtiveisastandardsubmarinecabledesignthathasbeenusedextensivelyaroundScotland.ThesamecablewasalsousedbyGHRwhentheyinstalledaprivatecableacrossLochTayduring2015toconnectahydroschemeatArdtalnaig.The cable is a 3 phase 33,000V cable with copper cores and crosslinked polyethyleneinsulation.Thethreecablecoresarebundledtogetherandheldinplacebypolypropyleneservingtape.Asmall3corecommunicationscableisalsoincludedwithinthecablebundleandthiscablewillbeusedtoopenandcloseacircuitbreakerat theAlltEasachsite.Thecompletecablehasaprotectivelayerofgalvanisedsteelwirearmourlaidovertheoutsidetoprotect the cable from abrasion during installation and operation. A further layer ofpolypropyleneiswoundoverthearmourtogiveablackandyellowstripedappearancewhichmakesthecableeasiertofindontheseabed.Thecompletedcableisapproximately95mmindiameter.Theapproximateweightofthecableis15.5kgpermetre.AcrosssectiondrawingoftheproposedcableisincludedasFigure3.

Figure3–ProposedSubmarineCableCrossSection

1.4 CableDelivery,LoadOutandTransittoSiteThesubmarinecabletypeusedbyGHRiscurrentlymanufacturedinJapan.ThecompletedcablewillbeshippedtotheUK inOctober2019anddeliveredbya low loadheavygoodsvehicletoCorpachBoatyard,FortWilliam.BriggsMarinewillbecontractedtoinstallthecableusingtheircableinstallationvessel“ForthGuardsman”.ThevesselwillbefittedouttoreceivethecabledrumatCorpachBoatyard,andoncecompletethecablewillbeloadedaboardusinga 300Tmobile crane. AMarineWarranty Surveywill inspect the loaded vessel and oncesatisfiedwillissueaCertificateofApproval,verifyingthattheinstallationmeetstheinsurersrequirements.TheGuardsmanwillthensaildownLochLinnieandtheLynneofLorneandpassbelowConnelBridgeintoLochEtive,arrivinglateonthefloodtidetoavoidtheworsteffectsoftheFallsofLora.ThevesselwillthensailupLochEtivetotheinstallationsite.ThetotaljourneyfromCorpachtositewilltakeapproximately8hours.OnceonsitethevesselwillmakeanumberoftransitsoverthecableroutebeforepositioningatthesouthernRhubanaStaingshoreend.1.5 CableInstallationTheGuardsmancanbefittedwithtworetractablepileswhichcanbeloweredtotheseabedinwaterlessthan10metresdeeptoholdthevesselinplace,withoutanyneedforsettingapatternofanchorsandmoorings.Thissavestimeduringthecableinstallationprocessandavoidstheneedforadditionalvesselstohandleanchors,minimisingthehazardsassociatedwiththistypeofwork.AtRubhanaStaingthevesselwillbepositionedapproximately100mfromtheshoreinwaterwithadepthofbetween5m–10m.The“spudlegs”willbedeployedtoholdherinposition.Oneendofthesubmarinecablewillbepulledashorebyasmallwinchpreviouslyinstalledonshore.Thecablewillhavefloatsattachedtopreventittouchingtheseabed.Thisoperation takesapproximately2hours.Havingcompleted theshoreend thevesselraisesthespudlegsandthentransitsacrossthelochpayingoutthecableasshegoes,totheothershoreendatRhubhaBhar.Thistransitcloselyfollowstheagreedcablerouteandthe actual “as laid” position of the cable is recorded. The maximum depth likely to beencounteredisapproximately70movertheproposedroute.ThetransitacrosstheLochwilltakeapproximately2hours.Oncethevesselisinpositionatthesecondshoreendthespudlegs are once again deployed. The vessel will be approximately 100m offshore. Ameasurement ismadebetweenthecabledrumonthevesselandasuitablepositionwellabovethehigh-watermarkashore.Thesamelengthofcableisthentakenoffthedrumandcoiledonthedeckbeforethecableiscut.Thiscableisthenwinchedashorewithfloatsjustliketheothershoreend. Thesecondshoreendwill takeapproximately2hoursto installgivingatotalof6hoursforthecompleteinstallation.

Fig4-ForthGuardsmanwithSpudLegsDeployed(yellowcappedpiles)1.6 CableProtectionOncethecablehasbeeninstalledtheshoreendswillbeburiedtobelowthelowwatermarkto hide it from view and remove any tripping hazard for shore users. A yellowdiamondbeaconwillbeinstalledonbothshorelinestomarkwherethecablecomesashore.TheaslaidpositionofthecablewillbenotifiedtotheUKHydrographicOfficewhomarkthepositiononAdmiraltyChartsandadviseothersuppliersofmarinemappingsoftwareofthenewcable.TheEuropeanSubseaCablesAssociationandTheCrownEstatewillalsobenotified.OverahundredsimilarsubmarinecableinstallationsexistinNWScotlandwhereelectricitycablescrosssealochsorprovideconnectionstotheScottishIslands.Thesecablesaresimplylaidontheseabedandtheirlocationsmarkedonchartstoavoiddamagefromotherusers.Where the cables are laid in harbours, or on rocky shorelines,wheredamage fromwaveaction is possible, additional protection is sometimes provided using cast steel cableprotectors.Theseinterlockingunitsarefittedaroundthecableonceitisinstalled,usuallyatlowtideintheinter-tidalzone,orbyusingdiverswhenthecableisinstalledbelowthelowwatermark.Inpreparingthecontractdocumentationfortheinstallation,anoptionhasbeenincludedforfittingsteelcableprotectorsatoneorbothshoreendsdowntoadepthof10mbelowchartdatum.Inrecentyearstherehasbeengrowinginterestinthepossibleimpactsthattheoperationofsubmarinecablesmighthaveonmarineorganismsasaresultofelectro-magneticfieldsorEMFs produced by cables. In preparing this applicationGreenHighland Renewables havetakenadvicefromafisheriesscientistwhohasproducedareportwhichisincludedaspartofAppendix7.4ofthisapplication.Electricfieldsareveryunlikelytobegeneratedoutsidethescreenedcable typebeingused for thisapplication. It is likely thatmagnetic fieldswillbepresentoutside thecablealthough it isnotclearwhether thesewouldhaveanynegativeeffectonmarineorganisms.Itispossibletoreducethemagneticfieldwhichsurroundsacable

by encasing it in a ferromagnetic material like steel or cast iron. The steel wire armourcoveringoftheproposedcablewillthereforereducethemagneticfield,butbyanunknownamount.Itwouldbereasonabletoassumethataddingsteelcableprotectorstocompletelysurroundthecablewillfurtherreducethemagneticfield.Onthisproject,theplanistoretrofitsteelcableprotectorsusingdiversdowntoadepthof10mtoprovideadditionalprotectioninthenearshorearea.Asaresult,anymagneticfieldproducedbythecable is likelytobereducedintheshallowwater.ManyofthemarineorganismsfoundinLochEtivetendtoswimclosetothesurface,andthisadditionalprotectionintheshallowwatershouldeliminateanyimpact to theseorganisms. Retrofittingcableprotectors indepthsexceeding10mcanbechallengingfordiversduetothelimitationsonproductiveseabedtimecausedbytheneedtode-compress.Itisnotpracticaltofittheprotectorstothecableaboardthevesselduringthecablelayprocesswithoutriskingdamagetothecable.

Figure5–SteelSubmarineCableProtectorsbeforeburialontheforeshore.Anyadditionalactivityassociatedwiththecablelaywillextendthetimetakentoconducttheoperation.Thismeansthesizeofweatherwindowrequiredincreaseswhichcouldresultinthevesselhavingtospendlongeronsitewaitingonweather.Thesedelaysarefactoredintothecontractor’scostswhichwillriseasaresult.Buryingthecablehasafurtherimpactoncosts,largelydependentontheburialmethodemployedandthedepthatwhichburialtakesplace.Thefollowingtablesgivedetailsoffourburialtechniquesandgivesanestimateofthelikelyadditional costsandanyother consideration.Allof thesemethodswill increase theenvironmentalimpactoftheproject.

Mass Flow Excavation - This technique would be themostsuitableasthereisnocontactbetweentheburialequipment and the cable, so the risk of damage isreduced.Largeimpellorsfittedonthedeviceareusedtoforce sea-water downwards into the seabed whichfluidises, allowing the cables or pipelines to sink. Theexcavatedtrenchisapproximately4mwidebutitcanbedifficult to control the depth of the excavation. Thismethodcanalsobequitedestructivetotheseabedwitharelativelylargedisturbedareaaroundthetrench

This burial method would require a separatemulti-catvesselwithalargecranetodeploytherig.ThevesselshouldbeabletopassbelowtheConnel Bridge. This type of burial would addapproximately £190k to the projected cableinstallationcostsof£470k,atotalof£660k,a40%increase.

Table1–MassFlowExcavationDetailsTrencher-Thistechniqueismorehi-techandinstallsthecablemorepreciselythanMFEusingwaterjetsateachend of the rig Cable trench is approx. 0.5mwidewithmuch less environmental impact as a result. There iscontact between the device and the cable using thismethodhowever,whichincreasestheriskofdamage.

A larger DP2 vessel is required and a smallervessel may be also required for burial in theshallowerwater.ItisunlikelythevesselwouldbeabletopassbelowtheConnelbridge.Thistypeofburial would add approximately £476k to theprojectedcableinstallationcostsof£470k,atotalof£946k,a101%increase.

Table2–TrencherDetails

Jetting by Divers - This technique is a very focussedmethodofburyingcableusingairlancestofluidisetheseabed and allowing the cable to sink in. Practicalsolutiondown for shorter lengthsofcabledowntoadepthof20m.There isnocontactwiththecablebutthemethoddoestendtoputalotofsedimentintothewatercolumn.

TheoperationcouldbeconductedfromaDPMulti-catvesselequippedforusebydivers.TherewouldbenoissuewithgettingundertheCoonelBridge.Thistypeofburialwouldaddapproximately£100ktotheprojectedcableinstallationcostsof£470k,atotal of £570k, a 21% increase. The cable wouldonlybepartiallyburiedhowever.

Table3–JettingbyDiversConcreteMats–Thistechniqueusesavesselmountedcrane to lower concretemats on top of the cable toprotectit.Matsareusuallyonlyusedtoprotectshortsections of cable for pipeline crossing etc. To protecttheentireroutewouldmeanlayingapprox.2506mx3matsweighing 8 tonnes each onto the cable. placingthisamountofnewmaterialontheseabedwouldbeintrusiveanddifficulttojustify.

ThismethodwoulduseadeliverybargeandaDPMulti-cat vessel with a drum crane and liftingframetoplaceupto3matsatatimeontheseabed.ThevesselsshouldbeabletopassbelowtheConnelBridge.This typeofprotectionwouldaddapproximately £430k to the projected cableinstallationcostsof£470k,atotalof£906k,a92%increase.

Table4–ConcreteCableProtectionMats

1.7 CableRepairorReplacementSubmarinecablesdooccasionallybecomefaultywithmostdamageactuallycausedduringinstallationorattemptedburial.Thetypeofrepaircarriedoutonafaultedcabledependsontheageandconditionofthecableandwhereaboutsonthecableroutethefaulthasoccurred.Ifacablehasfaultedrelativelyclosetoshorethenitwouldbenormalpracticetorenewthesectionofcablefromthefaultbacktotheshore.Werethecabletofaultnearthemiddleoftherouteandthepointoffaultcanbeclearlyidentified,thenitmaybepossibletocutthecableontheseabedandbringthefaultedendtothesurface.Thefaultysectionofcableisremovedandapieceofnewcablejointedon.Theotherendisthenretrievedfromtheseabedandjointedontothenew“piecedin”section.Thecompletecableisthenreturnedtotheseabedandre-energised.Wherethecableisinverydeepwaterorcannotbecutforwhateverreasonthentheonlyoptionistoabandonthecableandlayanewoneonasimilarroute.ThisisobviouslyexpensiveandwouldmeantheoutputfromtheAlltEasachschemecouldnotbeexporteduntilthecircuitwasrestored.Thedeliveryandinstallationtimeforanewcablefromwhenanorderisplacedwouldbeapproximately1year.1.8 DecommissioningSubmarinecableshavebeeninusearoundtheUKfor150yearsandsomecablesownedbySSEarestilloperationalafter60years.GHRcannotimaginecircumstanceswhichwouldresultinahydroschemebeingcloseddown.Normallyaschemeisrefurbishedafter40yearsorso,givingitanewleaseoflife.Ifforsomereasonthecabledidbecomesurplustorequirementsthen the cable couldbe removed in a similarway tohow itwas installed. Itmayalsobeacceptabletoleavethecabledisconnectedbutstill inpositionontheseabedandthishasuntilnowbeenthegenerallyacceptedpractice.DiscussionswithMarineScotlandandTheCrownEstatewouldoccuratthetimetoagreeonasolutionbuttheschemesaroundLochEtiveareexpectedtodeliverrenewableenergytothegridindefinitely.1.9 ProjectScheduleThismarinelicenceapplicationwassubmittedduringJuly2018.TheplanningapplicationsforthethreehydroschemesweresubmittedduringMay2018,withconstructionworkplannedtocommenceinDecember2018.ThesubmarinecablewillbeorderedduringDecember2018andwillbedeliveredtotheUKinOctober2019.ThecableinstallationwilltakeplaceduringOctober2019.Thehigh-levelprojectscheduleisshowninFigure6. 2018 2019 J F M A M J J A S O N D J F M A M J J A S O N D

Marinelicenceapplicationprocess Order/manufacturesubseacable Subseacabledelivery/installation Hydroschemeconsentingprocess Hydroschemeconstructing Gridconnection

Figure6–HighLevelProjectSchedule

1.10 LocationPhotographs

Figure7–SouthShoreEndandIndicativeCableRoute

Figure8–NorthShoreEndandIndicativeCableRoute