Brian Ingpen’s column in Wednesday’s Cape Times refers.
Some 15 years ago, during one of the common lessor water crises which Cape Town has suffered over many decades, experts were sounding warnings that the rapidly increasing population of the city would soon overtake any possible source of fresh water from rivers as there were no further possible sites to build water supply dams in the Western Cape.
As a result, newspapers were full of iceberg and desalinisation proposals. Regretfully these both have problems apart from the towing dilemma given by Ingpen.
For example, wherever the iceberg is moored for harvesting, it will reduce the ambient temperature of the sea by some degrees and reduce the salinity.
Large-scale desalinisation, unless closely monitored and controlled, returns saline remaining after the process to the sea, thus increasing the salinity in that area.
Maritime flora and fauna are sensitive to permanent changes in temperature and salinity and could therefore be damaged.
Pierre Louw (at the time manager of the Institute for Maritime Technology in Simon’s Town) and I did a small private study to search for other options, mainly looking at the possibilities of harvesting fresh water off the mouths of large rivers where river water remains on the surface (being less dense than seawater) reaching as far as 30 nautical miles out to sea.
The two rivers we looked at were the Congo, which flows more strongly and with greater constancy, making it the better option, and the Orange, which has a not-so-regular and a much lower volume.
We thought it necessary to look at both a short- and a long-term solution. The quick-fix short-term solution was to use the ballast tanks of passing empty tankers (normally filled with sea water).
The long-term more durable solution would be to instead use a dedicated coastal tanker or alternatively large rubber or plastic pods, already in use for the purpose of transporting large quantities of liquids by sea.
These pods can be manufactured to hold very large quantities of liquids such as fresh water, and as fresh water is less dense than sea water, the filled pods would float when full.
When empty they collapse flat, making it possible to either carry them as deck cargo or partially fill them with air and tow them to the filling area.
Additionally, a number of them could be towed in tandem tows by a single tug both to the source and back again after filling.
Then, by adding appropriate chemicals as the water is taken in at source, partial purification could be done during the delivery voyage.
We then made a formal presentation to a small number of the appropriate officials of the City Council, suggesting that the concept was both a short- and a long-term solution deserving of a proper detailed study.
Regretfully we were told that our concept was not needed then, nor would it be needed in the future, as Cape Town would never reach the stage where it would actually run out of water and therefore they could not recommend a more detailed study.