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Icebergs can supply Cape Town with extra water in drought years at a far cheaper rate than a big desalination plant.
It will cost R3.8bn to use Antarctic iceberg water to bolster Cape Town's water supply for any three dry years that are likely to occur over the next 20 years – compared to R10.2bn for the same amount of water from a large-scale desalination plant for the same period.
This would be the cost for each source to produce 100 million litres of fresh water a day for any three dry years over the next 20 years.
These facts emerged from a seminar at UCT on Wednesday given by engineer Dr Chris von Holdt, who did a technical assessment and economic evaluation of the iceberg proposal.
He says towing icebergs to Cape Town for extra fresh water during droughts is more viable than he had expected.
"We believe it is worthy of a deeper look. It is not a short-term silver bullet that can solve the drought, but it can fit in as an option for Cape Town's long-term supply," he said.
Read: Water Research Commission to investigate tow-an-iceberg proposal
Von Holdt, from Aurecon's asset management, is one of several volunteers from a variety of disciplines who formed the Southern Ice Forum to help work on a plan to tow icebergs to drought-stricken Cape Town.
Speaking at UCT's Geological Sciences Seminar, Von Holdt said the idea of towing icebergs to South Africa had first been suggested by the former Department of Water Affairs in the 1990s. However, it was not pursued as there had been other conventional options for increasing water supplies in the 90s.
"But now we've run out of places to build dams. There are no more catchments we can dam up. The potential impact of Cape Town running out of water is devastating."
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Droughts were part of the past and of the future of the city because rainfall was highly variable. There would be times when the city would need extra water supplies on a big scale.
"How often will Cape Town need an additional large-scale water supply? There is a 61% chance that we will need extra supply for two years in the next 20 years, and a 25% chance we will need it for between three to five years in this time."
There was only a one percent chance that we would need extra large-scale water supplies for 10 years out of the next 20 years.
There were economic risks with building large-scale desalination plants. Several cities in Australia had built large-scale desalination plants at great expense during their long drought, but only Perth was still using it. Adelaide had used the desalination plant for only two years.
"We want a high level of assurance of water supply, but having a permanent back-up is starting to get really expensive. A 'top-up' like an iceberg could help us get through the periodic droughts," Von Holdt said.
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While there were risks with the iceberg-to-Cape Town proposal, which was technically complex with several unknowns, Von Holdt said the advantage was that private Swiss funders had undertaken to fund the operation, provided there was a guaranteed buyer of the iceberg water.
"The Swiss funders are willing to take the delivery risk as long as someone is willing to buy the water, cash on delivery. So the residents of Cape Town don't have to take that risk."
Read more: Iceberg proposal as new water source for Cape Town
The benefits of iceberg water were the short lead time, low capital expenditure, it could be ordered only when it was needed – and the order could be scaled up or down – and it was an effective economic model.
Cape Town was ideally placed for capturing icebergs as the currents carried some of the 140 000 that broke off the Antarctic ice shelf every year north towards Gough Island, only 2 700km from Cape Town.
Once an iceberg had been captured, the trip back would take two tankers, travelling at 1.5 knots, about 42 days.
"We asked the guy who ran the SA Agulhas for 10 years about the time to sail, and he said the first time to go south would be at the end of September, beginning of October. We could get the iceberg back to the mooring at Cape Columbine by the end of November, and get water from it in January."
* The Water Research Commission is expected to hold a seminar with the Southern Ice Forum in September to gain an understanding of the details of the iceberg proposal.
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