Key partners in the extraction of groundwater to augment the City of Cape Town's water supply believe that the city's current 100-million litres per day target is impossible.
Speaking as an audience member at a Muizenberg Festival gathering on Tuesday, Umvoto earth sciences consultancy director John Holmes explained that the total yield from groundwater extraction remains largely unknown.
Umvoto is one of the city's main partners to develop the Table Mountain Group Aquifer and Cape Flats Aquifer for groundwater extraction.
"Theoretically, it's possible to extract 100-million litres per day from that aquifer. Is that going to happen by December this year? Absolutely not," Holmes said.
"If you are thinking about the target for the whole programme, including desalination, [it] is 500-million litres a day. Essentially, we are saying [with the targets] we are going to replace the water supply of the city in six months - it is just not possible."
Holmes, an engineer, echoed the statements of his colleague, hydrologist Chris Hartnady, who said water extraction from the Table Mountain Group Aquifer is a long-term project.
Hartnady was invited to address the intimate gathering in the African Institute for Mathematical Sciences (AIMS) centre in Muizenberg under the theme of discussing Cape Town's water future.
He joined Piotr Wolski from the Climate System Analysis Group (CSAG), Jasper Slingsby from the South African Environmental Observation Network (SAEON); Kevin Winter from the environmental and geographical science (EGS) department at the University of Cape Town (UCT) and Tom Sanya from UCT's built environment department.
'We've delayed for too long'
During his presentation, Hartnady said their current expectation is to extract up to 10-million cubic meters per annum from the Table Mountain Group Aquifer, roughly 27-million litres per day.
"But implementing that in a short space of time is not going to be easy. We are not committing to any definite figures by any definite dates," he said.
"We've delayed for too long. We had five years more or less of kicking our heels and that's been [a] very frustrating experience."
Meanwhile, climatologist and hydrologist Wolski explained that South Africa's brightest weather forecasters and climate scientists forecast in April that Cape Town would have a wetter-than-average winter.
"What happened in April this year we had a meeting of all the climate forecasting gurus in South Africa… And we couldn't agree, with all the models at hand and all the simulations, we couldn't agree [on] how will the winter develop," he said.
"And the only sort of faint agreement is that winter was going to be wetter than average. What happened is totally opposite."
'Isn't going to be enough'
Wolski said the meeting, the Winter Rainfall Outlook Forum, was attended by roughly 60 forecasters and climate scientists across South Africa.
At his turn, Slingsby, a trained ecologist, explained that up to three months of the city's water needs is lost through invasive species.
"At the moment, the existing invasive species in our primary catchments in Cape Town are using as much water as the entire Wemmershoek Dam," he said.
"So that's enough water for the city [for] roughly two to three months."
Slingsby said predictions indicate that in the next 30 years, invasive species will consume as much as the Berg River Dam, which is seven to nine months of the city's water needs.
"All the hope is on until next winter, in the hopes that it rains, but unfortunately raining next winter isn't going to be enough."
Slingsby said that research has proved that pine forestry, which is an invasive species, has only ever been an expense to the South African economy.
The costs to South Africa in terms of water is much worse, he said.
"In terms of clearing, I think it would be a hell of a lot cheaper than desalination or any of the alternatives the city is thinking of," Slingsby said.