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Groundwater to be prioritised over desalination plants – report

By Isabelle Coetzee

The City of Cape Town should prioritise groundwater extraction over desalination plants in order to diversify its water supply during the current drought.

This is according to Cape Town’s New Water Augmentation Programme (CTNWAP), which was released by the City in May.

It outlined the time it would take to implement the following alternative water sources:  

  • Groundwater Extraction: Pumping water out from below the earth’s surface.
  • Desalination Plant: Converting sea water into drinking water.
  • Wastewater Use (re-use): Purifying waste water into drinking water.
  • Surface Water: Collecting water in dams.  

The report confirmed: “Groundwater projects should be fastest to implement, then re-use and then desalination, based on project complexity and logistical requirements.”

Desalination plants require extensive marine works, such as tunnelling. However, the technology required to extract ground water is simpler and the energy requirements are lower.

The report included the below graph, illustrating the number of months it would take to implement each augmentation programme:

Besides the amount of time it would take to create these alternative water supplies, another key issue is how much it will cost.

Counsellor Xanthea Limberg, mayoral committee member for water and sanitation, explained that sustainable groundwater extraction is cheaper, specifically for large yields.

“Our approach remains to ensure we maximise the water yield sustainably at the lowest possible cost,” said Limberg.

“Temporary desalination and re-use should not be pursued further as emergency solutions as this is not affordable, and rarely provides the promised volumes of water,” she added.

“However, for future resilience, permanent desalination and water re-use are recommended as alternative sources of water to add to ground and surface water supply sources,” she explained.

Below is a graph from the report that compares the costs of different augmentation programmes:

The report concluded: “Desalinated water is the most expensive and is likely to take longer to implement than the alternatives… Ground water is faster to implement and is also much cheaper.”

The following table is an updated account of the deadlines of each augmentation programme currently in progress:

Project

Date of full production

Temporary Desalination

 

Monwabisi Temporary Desalination Plant (7 million litres/day)

End July 2018

Strandfontein Temporary Desalination Plant (7 million litres/day)

June/July 2018 - Treatment process is currently being optimised. Currently supplying 5,8Ml/day

Waterfront Temporary Desalination Plant (2 million litres/day)

June/July 2018 - Treatment process is currently being optimised. Currently supplying 0,4Ml/day

Groundwater Programme

 

Cape Flats and Table Mountain Group Aquifer

Under way. Timeframes are dependent on variables such as water quality and land access, as well as environmental factors.  

Atlantis Aquifer

Currently producing 6Ml/day

Water Transfers

 

Groenland

A total of 7,3 million cubic metres were released to Steenbras Upper Dam

Springs

 

Albion Spring

Currently abstracting 3,2Ml/day

Oranjezicht Main Springs Chamber

Currently abstracting 1,6Ml/day

Lourens River

Currently treating 3,8Ml/day at Helderberg Water Treatment Plant

Water Reuse Projects

Proceeding with planning and preliminary design for a permanent wastewater re-use facility

 

According to Limberg, the City’s augmentation programme has achieved in four months what would usually take two years in terms of project development and progress.

These programmes were set in motion in response to 3 years of consecutively low rainfall in Cape Town, resulting in a one in 400-year drought event.

Level 6B water restrictions were implemented in January and a national state of disaster was declared in March.

The most recent Water Dashboard showed optimistic results, with the combined level of the dams reaching 42.7% compared to 24.3% last year.

It was recently announced that the national state of disaster will not be renewed, and the day the taps run try – Day Zero – has been moved out to 2019. 

So, will Day Zero happen in 2019?

According to Limberg, assessments will be made nearer the end of the winter rainfall period and at the end of the hydrological year.  

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