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Publication

THE WATER WHEEL

Page

32-34

Date

Thurs 01 Mar 2018

AVE (ZAR)

19908.91

Feature

Photosupplied

That icebergsattract thiskind ofattention isperhapsnotsurprising,given the enormoussizeof thepolar freshwaterresource- a singlelarge (in theorderof 10km long) bergcontainsenough water tosupplyCapeTownfora coupleofdecades

Towing icebergs isnot a new phenomenon, the idea crops uppretty much any time a majorcoastalcity isbesetby water-supply issues,asa seriesof feasibilitystudiesby both USandAustralian authorities (and most recently Abu Dhabi) in thesecondhalfof the twentieth century canattest.

That icebergsattract this kind of attention isperhaps notsurprising,given the enormous sizeof the polar freshwaterresource- a single large (in the order of 10km long) bergcontainsenough water to supply CapeTown for a couple ofdecades.So, is it assimple asgrabbing some free freshwater,or isthisjust the tip of ... er ... iceberg?

3 2 The Water Wheel March/April 2018

One can go pretty deeply into this topic, but some frequentlyaskedquestionsare summarisedbelow:

Can we get it there?

The short answer:Maybe... Probably.

Thelong answer:Icebergsare large, and heavy.Therefore, in order to get adecent-sized (say 20 km-long) iceberg it is estimated that sometwenty large oceangoing tugs would be needed to move the

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Water supply

iceberg the 6 000odd km from the Southern Ocean to CapeTown.Thiswould be done at a speed of approximately one knot,thus making ajourney of 250 daysto reachthe Cape and losingabout 40% ofits massalong the way.

With this classof tug being in limited supply, they cost around$250000-$500000adayto charter.Ifone includesthe needforeach tug to be refuelled three times during the tow, you get to acostof at least2.5 BillionUSD (to put this into perspective- thisexercise would burn around 100 000 tons of fuel).

Despite being mathematically and theoretically possible, it hasbeen these physicalconstraintswhich, in the some200-yearhistory of 'let's go get usan iceberg, haskept anyone fromactually trying it.Although possiblemethods have evolvedover the last50yearsand useof oceancurrentsor kitesforpropulsion, and shieldsto slow down the melting of the icehave been put forward, none of these are able to change thefundamental physicalscaleof the task.Small-scaleexperimentshave proved that the instabilityof icebergs,due to their ever-changing centre of gravity asthey melt, makesthe useofalternative propulsion methods very difficult.

It hasalsobeen proposed that the natural drift of the icebergwith ocean currents could be harnessed to direct it towardsits destination. However, while this looks easy on schematicdiagrams, in reality the ocean isa cauldron of turbulent currents(which we do not entirely understand at small scales)and inorder to get to CapeTown, the iceberg would have to crosstheAntarcticCircumpolar and Agulhas Currents, two of the mostenergetic ocean currents on the planet, aswell asan areaaptlyknown asthe 'Cape Cauldron.

Asa marine engineering exercisethis isa fascinatingproblem -how does one attach the tow cables, what do you do when theiceberg rollsover, how long will it take to get moving (severaldays actually), how does one steer it around othericebergs?Despite pitfalls,humans are creativewhen confronted with greatchallenges,and perhapswe do have the technological ability(given an unlimited budget) to transport an iceberg, but thebigger question remains,would we want to?

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How do we harvest it?

Theshort answer:Not aseasilyasyou might think...

Thelong answer:Once an iceberg hasarrived in CapeTown waters, it then hastobe melted and transported to land.Thiswould have to be doneeither by pipeline or tanker ship.The elephant in the room hereisdepth. An iceberg of the sizeneeded for water supply willhave a depth of at least200m.This depth requirement resultsin the iceberg having to be placed around 50 km offshore,andthus increasesthe costand difficulty of transporting the waterto shore. In addition to this isthe challenge of keeping thewater uncontaminated by saltand pollution during the meltingprocess.

What are the consequences?

Theshort answer:How long isa piece of string?

Thelong answer:One can divide the consequencesof iceberg harvesting into twomain categories- the practicaland the environmental (althoughsome overlap between these is inevitable). Environmentally, theeffecton localweather patterns and ocean currentswould haveto be quantified.

However, the presenceof sucha large, cold input of freshwaternearthe coastwould undoubtedly have an effecton the coastalwater circulation, which makes the ocean off Cape Town oneof the most biologically productive in the world's oceans.This biological productivity is reliant on the upwelling of cold,nutrient-rich water from deep, which supportsa staggering arrayof life, including mostof the country's large commercialfisheries.A cap of cold, fresh meltwater could reduce the efficiency ofthis system, causing a regime shift to an alternative, and far lessproductive, ecological state.

Of more immediate impact and interest to mostof CapeTown'scitizenswould be the effectof a large iceberg sitting offshoreofthe city on localweather patterns.One argument which couldbe made isthat the cold air descending above the icebergwould result in a localisedhigh pressure.The contrastof thiswith the warm land during the summer months could result inan acceleration of the South-Easter. An increase in these winds,even ifonly 10%or so,could have somefairlycatastrophicconsequenceson the buildings of the city and hasthe addeddownside of deflecting rainfall from cold fronts southwards,away fromthe city and itscatchmentareas.

While there are manyof thistype of environmentalconsequences,which would have to be thoroughly exploredthrough computer modelling simulations,there isa moreimmediate practicalconsideration to consider. Icebergsmelt,and will do soat some speed in the mid-latitude climate ofthe Cape. In addition, they do not melt quietly and calmly.Asthey melt and are eroded by the wind and waves,their weightdistribution changes, until such a point asthey are off balance.What happens then isthat the iceberg will turn over - which,

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Water supply

with the amount of weight involved, is not a trivial event. Thinkof the largestship you can imagine capsizing,then add a fewordersof magnitude.

These turnover events could alsoresult in 'mini-tsunami' waveeventswhich could prove a hazardto both shipping andcoastal structures. However, the real danger here is that whenan iceberg meltsand turns over, it alsosplinters, resulting inthe production of smaller icebergsand their pint-sized cousins,growlers and berg bits.These may sound cute, but each of themhasthe power to send a ship to the bottom. Hence, in mooringan iceberg off the coastof CapeTown, one of the world's busiestshipping laneswill become litteredwith floating hazards(mostpeople have seenTitanic and can deduce what happenswhenship collides with ice).

Is it legal?

The short answer:No.

Response to article - Iceberg harvesting IS a possibilityDr Olav Orheim, initiator of the ship-bore icebergobservation programme under SCAR, Georges Mougin,Director ofWater and Powerfrom Iceberg, and Capt NicholasSloane, Director of the ResolveMarine Group disagreewithNeilMalan'sview. In a letter to SAEONthey write:"we believethat the question of 'Ice to the Cape' ispossibleand shallbecomea reality ifthisconcept receivesseriousevaluation."

They disagreewith Malan'sview of a 'decent-sized' iceberg.According to the letter writers, a realistictowable icebergis 1.0x 0.5 km in above-water dimensions."Thissizecouldprovide CapeTown with 200 000 m?of freshwaterdaily, forabout ayear.

They alsopoint to the particular nature of the largeAntarcticicebergsascompared to Arctic icebergs."TheseAntarcticicebergsareflat 'tabular' slabsof ice, and although manyhave internalflawsand therefore may breakup, they do notroll over until their horizontal dimensions are reduced toabout the same as the vertical dimension, which isgenerallyaround 250m.

According to the authors, a 'small'tubular iceberg wouldnot affectocean circulation and localweather as it willbe strandedmany kilometresoffshore.Thus its impactonlocalair and water temperatureswould only be discernibleimmediately around the iceberg, with minor impactson thelocalecosystem.

"The article assertswrongly that it will be illegal to towicebergs from the Southern Ocean, and refers to theAntarcticTreaty.TheTreatydoes not discussice harvesting,which mostlikely isnot covered by the EnvironmentalProtocolunder the Treaty. In any case,any towed icebergwould be picked up far north of 6075,i.e.north of and

Thelong answer:Under the AntarcticTreaty (the body which essentiallygovernshow we treat Antarctica and its resources), activities related tothe removal of mineral resourcesare not allowed.The loopholehere isthat icebergsare difficult to categorise (e.g.is it a solidmineral or a liquid water resource).However even if one wrigglesthrough that loophole, the useof icebergs under the lawof theseawould be subject to an environmental impact assessment.

Basedon the key rolewhich Antarcticaand its ice play in drivingthe global overturning circulation, this would be difficult.Whilstwater supply to populations in dry areasof the world can beseen as important, preserving the mechanismswhich maintainour entire climatesystem(yes,the samesystemthat allowshuman existence on earth at all) must surely be seen asa greaterpriority. Itwould therefore be difficult to seethe decisiontoallow the harvesting of icebergsto be a moral one.

This article was first published by SAEON (www.saeon.ac.za).

outside the boundary of theTreaty. Itwould be an objectfloating in the High Seas,slowly melting on itseastwardpassagearound the southern oceans,or awaiting to beharnessedby the firstwho could do so."

There are at any time around 200000 icebergsfloating inthe Southern Ocean.While 20 km-long bergs are very rare,approximately 20 000 of the icebergshave lengths of over0.5 km.Of course,a very small proportion of these will havethe suitable position, sizeand strength for towing towardsCape Town.

The authors alsocaution the estimated cost of towing aniceberg to CapeTown."The article statesthat the cost oftowing a huge iceberg near to the Cape would run intobillionsof US Dollars.We estimate that towing, or guiding,realisticicebergs into the Benguela Current and makinga landfall north of Cape Town offshore of St Helena Bay,would be lessthan the cost per cubic metre of desalinatedwater schemespresently approved by the Western CapeGovernment. We believe that with venture capital, theconcept of 'Ice to the Cape'will become a reality in the nearfuture, and certainlywithin the next five to ten years!"

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