Water Shortage? Let's Lasso an Iceberg

Peter Johnston, a climate scientist at the University of Cape Town, reports that while city officials are not currently considering the plan, he thinks it could be worth a shot. As he says, an iceberg about 100 million tons (91 million metric tons) in size, could ideally be found within a thousand miles (1,610 kilometers) of Cape Town. The iceberg, according to the plan, would be harnessed with a big belt and slowly towed by tanker, aided by ocean current and, perhaps, kite sails. Once the iceberg was moored offshore, a lattice steel structure lined with plastic would capture fresh water, pumping it into pipes that would carry the water to shore. After filtering, it could be channeled into the parched city's water supply system at, according to Sloane, an overall expense that would be half the cost of desalinization.

"If we did get one of these medium-sized icebergs, we're looking at supplying about 20 percent of the city's water needs per day at a cost of about a dollar per each 100 gallons (378 liters)," Johnston says.

A similar proposal about a year ago by an Abu-Dhabi-based firm, suggested relieving water shortages in the United Arab Emirates by towing an iceberg holding 20 billion gallons (76 billion liters) of fresh water to the coast of Fujairah, on the east coast of the Gulf of Oman. According to the firm, once anchored here, the iceberg could meet the needs of a million people for five years, as well as offer a tourist attraction and change the local climate to spur more rainfall. Here's a video presentation outlining the proposal:

But run an iceberg-towing scheme by a glaciologist and you're likely to have some very cold water splashed on your face.

"The scale is just really daunting," says Ted Scambos, lead scientist at the National Snow and Ice Data Center at the University of Colorado at Boulder. "Even tiny little icebergs are huge and most of the mass is below the water. It dwarfs the ship, so the idea of dragging it seems unrealistic."

In fact, there are Canadian companies that specialize in moving icebergs away from offshore platforms where they might strike and damage facilities. But those efforts, which use massive cables that are then nearly eaten away by friction, involve smaller-sized icebergs and the distances they are towed are miniscule compared with the distance that icebergs would need to be hauled to relieve areas with water shortages.

The shape of the iceberg is another factor. As Grant Bigg, a professor of Earth systems at Sheffield University in the U.K. and author of the 2015 book, "Icebergs", points out, an irregularly shaped iceberg "might roll over or break up," so you'd be better off selecting a tabular-shaped iceberg, with vertical sides and a flat top, like the ones more commonly found in the Southern Ocean.

Tabular icebergs may be better shaped for towing, but they also present drainage issues, according to Scambos. A drainage system would need to be installed on the iceberg, he says, otherwise, as the ice is hauled to warmer climates, water pooling at the top of the giant ice mass could penetrate the ice mass, weaken it and cause it to fracture. That's what happened to the 1,250-square-mile (3,237-square-kilometer) Larson-B ice shelf when it collapsed in 2002.

So say you've found the ideal tabular-shaped iceberg and installed a drainage system. Then as Bigg puts it, "There's a scale issue to be solved."

A medium- to large-sized iceberg of about a hundred billion tons (90.7 billion metric tons) could certainly solve someone's freshwater problems for quite a while, but, as Scambos says, "all the navies in the world wouldn't have enough power to move the massive icebergs around." Some proposals have suggested ways around the melting issue when it comes to transporting smaller icebergs.

In 2009, for example, a French software firm called Dassault Systemes, created a simulation of an iceberg towing project that would wrap smaller icebergs with insulating skirts. The coverings could reduce melting and keep an iceberg intact during transport. But, according to Phys.org, their calculations showed that after traveling at a rate of about 1 knot, a small iceberg tugged from Newfoundland to the Canary Islands would lose 38 percent of its ice during the five-month journey. The cost: $10 million.

Since it may be difficult to get your money's worth from tugging smaller icebergs, Scambos suggests there could be another approach to transporting bigger icebergs. "I think the way to go would be kedging," he says. For the non-sailors among us, kedging is an 18th-century nautical concept that takes advantage of natural tidal forces.

As originally proposed by glaciologist Doug MacAyeal and his colleagues at the University of Chicago, engineers could anchor a massive iceberg using a base slab and cables. When the tide is pushing the iceberg away from its destination, the anchor would hold it in place. Then, when the tide shifts a half day or so later toward the desired direction, the anchor would be released and the berg would be pulled naturally toward its destination.

"This could move a large mass without nearly as much motor power as the more simplistic idea of going down there with a big ship," Scambos says. "You're not going to move the iceberg very fast, but it could work."

Currently there are no iceberg kedging plans in place and, for that matter, Cape Town officials have yet to sign onto any iceberg-towing plan. Johnston says he doesn't believe the city is seriously considering any iceberg plan at this point, but while he acknowledges it's a risky, controversial proposal, he argues iceberg towing could offer a viable short-term solution to Cape Town's pressing water needs. He also acknowledges there would be a significant carbon footprint involved in the project — mainly in the fuel required to transport the iceberg. There's also the question of what effect introducing a freshwater iceberg to oceans around Cape Town might have on local marine ecosystems.

So, while Cape Town residents are making strides in their water conservation efforts, Johnston believes any negative impacts of a freshwater iceberg may be less than those associated with other proposals and, he argues, it's critical to consider all options.

"We're basically on survival water rations now," Johnston says. "I don't think we can conserve any more water than we are already. If we don't see sufficient rainfall by September, we'll need a contingency plan."