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30 Apr 2018 11:58
The Southern Ice team hopes to capture icebergs that have drifted northward to Gough Island, about 2 700 km south west of Cape Town. (Reuters)
South African marine salvage expert Nick Sloane, who sprang to international fame when he refloated the massive Costa Concordia wreck in the Mediterranean in 2013, is hatching a plan to tow icebergs to Cape Town to ease the city’s water crisis.
It may sound off the wall, but Sloane says the iceberg proposal has generated enough interest among experts for him to hold a seminar on the project in Cape Town in mid-May.
Engineers and University of Cape Town academics have been assessing it.
Dr Chris von Holdt from Aurecon’s advisory practice, who has done a technical assessment and economic evaluation of the iceberg proposal, said: “I believe it has sufficient technical feasibility and economic merit to be considered seriously as a supply option for filling the supply gaps during periods of drought.”
Sloane, from Cape Town, with the two other members of his Southern Ice team, French engineer Georges Mougin and Norwegian glaciologist Dr Olav Orheim, will be joined by global experts at the seminar to decide: “Is the iceberg project a ‘Go’ or a ‘No-Go’?”
“I am driving the campaign - mainly due to our water crisis - and the fact that now these icebergs are tracked and found about a third of the distance to Antarctica, only around 1 200 nautical miles away,” Sloane said.
Although the City has projects underway to increase Cape Town’s water supply, Sloane says these will still leave a gap of around 100 million litres a day.
“With Saldanha Bay now facing a Day Zero, it does look like this water crisis is going to continue to haunt us into 2019,” Sloane said.
Estimates are that more than 2 000 billion tons of icebergs break off the Antarctic ice-shelf every year and drift with ocean currents until they melt in warmer water.
The Southern Ice team hopes to capture icebergs that have drifted northward to Gough Island, about 2 700 km south west of Cape Town.
Not just any iceberg will do. Orheim, who was the director or the Norwegian Polar Institute from 1993 to 2005, has analysed 271 000 icebergs, of which only 7% would be suitable.
The shape must be tabular, with a flat top and steep sides, and a thickness of 200m to 250m.
Once a suitable iceberg has been assessed, it will be “captured”.
Two tugs will encircle the iceberg, pulling an enormous piece of geotextile material around it as a “skirt” that reaches down the sides of the iceberg beneath the sea.
A third tug stands by as back up.
A tanker will then tow the iceberg, with the distance between the tanker and the iceberg about 1.5km.
The two tugs will steam alongside, ensuring the iceberg stays on its course.
The destination will be Cape Columbine north of Saldanha Bay.
Because of its big draught, the iceberg cannot go close inshore but will “anchor” itself on the seabed about 40km offshore.
It will then be moored using a system similar to that used by certain offshore oil rigs.
Orheim said getting the iceberg into a useable form of water was still “part of the unknowns”, but a number of ideas have been proposed.
“A significant part of the fresh water yield will be generated simply by natural melting at the surface of the berg, but there are challenges in harnessing this water, not least caused by the distance from land as the berg has a draught exceeding 150m,” Orheim said.
One proposal is for helicopters to lift machinery from a barge onto the iceberg, where it will be assembled and used to “mine” the ice similar to open cast mining.
The harvested ice would result in a pool of melted ice inside the saucer-like “mine”, which would be pumped into tankers and taken to a discharge point on shore.
The team says the iceberg would supply 55 million kilolitres a year, more than 150 million litres a day.
Orheim estimates about 30% of the iceberg would melt during the towing.
Orheim said an advantage of the iceberg scheme is that that it could be used when there was a need for water, and stopped when there was not.
“There is not a large capital investment.”
Sloane said the latest price for water from a permanent desalination plant in Cape Town was around R20 a kilolitre.
“We are looking to deliver pure Antarctic water for less than R30 a kilolitre.
“And this is without the high Eskom tariff risks, and the environmental damage caused by millions of litres of brine into the ocean every day,” Sloane said.
UCT academic Dr Kevin Winters of the Future Waters Institute said a range of scientists and engineers had become involved in the iceberg proposal.
“I love it. The narrative we have at the moment about icebergs as a water source is that they are too far away, it’s too expensive, too complicated - it’s all about the ‘can’ts’. So this proposal challenges that narrative and let’s find out more,” Winter said.
Asked to comment, the city council said it would not consider the iceberg proposal as a new water supply because of the “risks, complexities and expense involved in such operations”. — News 24
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